A fluid processing apparatus, a capacitance sensor and a method of sensing a substance

Abstract

A fluid processing apparatus comprising: a first piece of equipment, the equipment being selected from vessels for holding chemical substances and conduits for allowing flow of fluids; and a capacitance sensor, wherein the capacitance sensor comprises: an electrode assembly provided on a surface of the equipment; and a measurement unit electrically connected to the electrode assembly, the measurement unit being configured to: measure a signal representing a change in a capacitance associated with the first electrode and the substance; and determine, based on the measured signal a change in the substance in the first piece of equipment.

Description

[0001] A Fluid Processing Apparatus, a Capacitance Sensor and a Method of Sensing a Substance

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to GB 2410289.9, filed on July 15, 2024, which is hereby incorporated by reference in its entirety.

[0004] FIELD

[0005] Embodiments described herein relate to a fluid processing apparatus, a capacitance sensor and a method of sensing a substance.

[0006] BACKGROUND

[0007] The monitoring of substances, including fluids (liquids and gases) and solid materials, in various settings is advantageous. This can assist in determining the presence of undesirable or desirable substances, fluid levels, the condition of vessels used to store or carry fluids or solid materials, and whether deposits have been formed on the surfaces of equipment such as vessels and tubes.

[0008] BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0010] Fig. 1a illustrates a fluid processing system in accordance with an embodiment;

[0011] Fig. 1b illustrates a substance sensor system according to an embodiment;

[0012] Fig. 1c illustrates a substance sensor system according to an embodiment;

[0013] Fig. 1d illustrates a substance sensor system according to an embodiment;

[0014] Fig. 2a illustrates a substance sensor system according to an embodiment;

[0015] Fig. 2b illustrates a substance sensor system according to an embodiment;

[0016] Fig. 2c illustrates a substance sensor system according to an embodiment;

[0017] Fig. 3a illustrates a measurement unit according to an embodiment;

[0018] Fig. 3b illustrates a measurement unit according to an embodiment;

[0019] Fig. 4a illustrates a substance level sensor system according to an embodiment;

[0020] Fig. 4b illustrates a substance level sensor system according to an embodiment; Fig. 5 details method steps performed by the system of Fig. 4a or Fig. 4b according to an embodiment;

[0021] Fig. 6a illustrates a phase separation sensor system according to an embodiment;

[0022] Fig. 6b illustrates a dead volume of the vessel according to an embodiment;

[0023] Fig. 6c shows an example of a transition from air to water passing through a vessel according to an embodiment;

[0024] Fig. 7a details method steps performed by the system of Fig. 6a according to an embodiment;

[0025] Fig. 7b details method steps performed by the system of Fig. 7c according to an embodiment;

[0026] Fig. 7c illustrates a chemical processing system in accordance with an embodiment;

[0027] Fig. 8a illustrates a vessel contamination sensor system according to an embodiment;

[0028] Fig. 8b illustrates a vessel contamination sensor system according to an embodiment;

[0029] Fig. 9 details method steps performed by the system of Fig. 8a and Fig. 8b according to an embodiment;

[0030] Fig. 10a illustrates a suspended particle sensor system according to an embodiment;

[0031] Fig. 10b illustrates a suspended particle sensor system according to an embodiment;

[0032] Fig. 10c illustrates an example signal obtained from the system of Fig. 10a or 10b;

[0033] Fig. 11 details method steps performed by the system of Fig. 10a and Fig. 10b according to an embodiment;

[0034] Fig. 12a is a schematic of a sensor for detecting a substance in a tube;

[0035] Fig. 12b is a cross section of the sensor of Fig. 12a;

[0036] Fig. 13 illustrates a perspective of a support part of the sensor of Figs. 12a and 12b;

[0037] Fig. 14a is a variation on the sensor of Fig, 12a; and

[0038] Fig. 14b is a cross section through the sensor of Fig. 14a.

[0039] DETAILED DESCRIPTION OF EMBODIMENTS

[0040] In a first embodiment, a fluid processing apparatus is provided comprising: a first piece of equipment, the equipment being selected from vessels for holding chemical substances and conduits for allowing flow of fluids; and a capacitance sensor, wherein the capacitance sensor comprises: an electrode assembly provided on a surface of the equipment; and a measurement unit electrically connected to the electrode assembly, the measurement unit being configured to: measure a signal representing a change in a capacitance associated with the first electrode and the substance; and determine, based on the measured signal a change in the substance in the first piece of equipment.

[0041] The above apparatus is provided with a sensor which allows the first piece of equipment to be monitored to determine its status. For example, the sensor may be configured as a fluid level sensor; a phase separation sensor; a contamination sensor; or a suspended particle sensor. From this status monitoring, it is possible to determine problems in the system, but also provide automated control for the system since the detection of a fluid level and / or a phase boundary allow a control signal to be output which can be used to move a chemical or fluid process to the next stage.

[0042] The fluid processing apparatus may be configured as a chemical processing system for use in chemical synthesis and / or other chemical processes such as purification, distillation, agitation etc. However, the fluid processing apparatus may be apparatus used for medical apparatus, for example IV drips, dialysis etc.

[0043] The signal representing a change in capacitance may be any signal used to measure capacitance, for example an output of an analogue digital converter that measures a voltage where the change of the voltage is caused by a change in capacitance. In other embodiments, it may be a frequency shift in the FFT of an ADC signal for oscillating circuits that undergo that change due to a change in capacitance.

[0044] The electrode assembly may comprise: a pair of electrodes configured located on either side of the equipment or a pair of electrodes configured located on the same side of the equipment. In a further embodiment, the electrode assembly consists of a single electrode. In the single electrode arrangement, the chemical substance itself acts as a second electrode.

[0045] In an embodiment, the determined change in the substance comprises a change in volume of the substance in the equipment or a change in the substance from a first substance to a second substance. The measurement unit may be further configured to: based on the determined change, send a control signal to a controller, to actuate or inhibit movement of the substance to or from the first piece of equipment. To determine, based on the measured signal, the change in the substance or mixture of substances, the measurement unit may be configured to: compare the measured signal with a reference signal, wherein the reference signal indicates a desired amount of the substance to be held in the equipment.

[0046] In an embodiment, based on the determined change, the measurement unit may be configured to send a control signal to a controller, to actuate or inhibit movement of a cleaning fluid to or from the vessel.

[0047] In an embodiment, determining based on the measured signal, the change in the substance or mixture of substances may comprise: comparing the measured signal with a reference signal, wherein the reference signal is a baseline signal, the baseline signal obtained by the measurement unit when the vessel does not comprise the substance.

[0048] In a further embodiment, determining, based on the measured signal, the change in the substance may comprises: determining a change in the substance from a first substance to a second substance based on a change in the measured signal.

[0049] For example, the change in the measured signal comprises a magnitude of the measured signal changing from a first magnitude to a second magnitude.

[0050] In an embodiment, the first equipment is a tube configured to be fluidly connected between a mixture vessel and a sample vessel, the mixture vessel comprising an outlet valve connected to the tube, the mixture vessel configured to contain at least two immiscible liquids comprising the first substance and the second substance, the first substance, the vessel configured to move the first substance from the mixture vessel to the sample vessel, the measurement unit further configured to: based on determining the change from the first substance to the second substance, send the control signal to a valve controller to close the valve and inhibit movement of the second substance through the tube into the sample vessel.

[0051] The above controller may be a pump controller or a valve controller. In a further embodiment, determining, based on the measured signal, the change in the substance may comprise: identifying a suspended particle or bubble in the substance based on a change in the measured signal, wherein the change in the measured signal comprises a spike in the measured signal that exceeds or falls below a given threshold.

[0052] In a further embodiment, the measurement unit may be further configured to, based on the determined change, send an alert signal to a user. For example, the alert signal may indicate the equipment needs to be replaced or cleaned, that the equipment is contaminated, that the equipment does not comprise a desired volume of the substance, or that the substance comprises a suspended particle or bubble.

[0053] In a further embodiment, the measurement unit may comprise: a microprocessor comprising a first input / output (IO) pin, a second input / output (IO) pin and a ground pin; a resistor coupled between the first IO pin and the first electrode, the second electrode coupled to the ground pin; and a reference capacitor coupled between the first IO pin and the second IO pin; the microprocessor configured to: at a first time, cause the reference capacitor and the capacitor formed between the first electrode and the second electrode to discharge; at a second time, cause the capacitor formed between the first electrode and the second electrode to charge; at a third time, cause the capacitor formed between the first electrode and the second electrode to discharge into the reference capacitor; and at a fourth time, measure a voltage across the reference capacitor.

[0054] In further embodiments, variations on the above measurement are possible, for example, if the circuit is oscillating, either by having a frequency applied via similar pin state switching or by being constructed as an oscillating circuit, a change in substance will cause a change in oscillation frequency and this can also be used to determine changes in the resistance. A direct voltage level measurement is possible where the voltage level of one pin is measured while holding the other pin at a fixed level. In a yet further embodiment, the first piece of equipment is a tube and the electrode assembly is provided as a clip for the tube. The measurement unit may be located in a box and the electrode assembly is provided on a surface on said box. This allows the sensor to be easily installed in a chemical processing apparatus as a standalone unit. In further embodiments, the electrodes can be provided directly inside a vessel or tube.

[0055] In a further embodiment, a capacitance sensor for a chemical processing apparatus is provided, the chemical processing apparatus comprising at least one tube, the capacitance sensor comprising an electrode assembly; and a measurement unit electrically connected to the electrode assembly the measurement unit being configured to: measure a signal representing a change in a capacitance associated with the electrode assembly, wherein the measurement unit is provided in a casing connected to the electrode assembly and the electrode assembly is provided as a clip to receive a tube of the chemical processing apparatus.

[0056] In a yet further embodiment, a method, is provided, of sensing a substance in a first piece of equipment comprising: measuring, by a measurement unit, a measurement signal representing a change in a capacitance associated with an electrode assembly, the electrode assembly configured to be placed in proximity to at least one surface of the first piece of equipment; and determining a change in the substance in the first piece of equipment based on the measured signal.

[0057] Fig. 1a is a schematic of an apparatus configured as a chemical processing system. In this example, the processing system comprises a first reaction vessel 1 and a second reaction vessel 3. In this simplified example there are two vessels. However, in further examples, there may just be tubes through which fluids can flow.

[0058] A pump and valve unit 4a, 4b is provided. Four ports are shown on the valve 4a, but this is just purely for example. The valve 4a operates under the control of computer system 6, the control signals of which are represented by dotted lines. The control signals may be wired signals, wireless signals or a combination of both. In the example, first tube 5a is connected to a first port, a second tube 5b is connected to a second port, a third tube 5c is connected to a third port and a fourth tube 5d is connected to a fourth port of valve 4a. Control of the valve 4a allows a port to be selected for the input and a port to be selected for the output, or put another way, to allow fluid to be communicated through the valve between the two ports. In this example, the first tube 5a is connected to the drain of the first reaction vessel 1 , the second tube 5b is connected to the top of the second vessel 3, the third tube 5c is connected to a cleaning solution vessel 10 which holds a cleaning solution and the fourth tube 5d is connected to the top of the first reaction vessel 1. Thus, through the valve 4a, the drain of the first reaction vessel 1 can be connected to the top of the second reaction vessel 3. Thus tubes 5a and 5b allow fluid to be transferred between reaction vessel 1 and reaction vessel 3.

[0059] The valve pump unit also comprises a pump 4b, for example a syringe pump which allows the fluid to move through the system. In some embodiments, the speed at which the pump 4b operates can be controlled such that the speed can be reduced to allow the fluid to move more slowly through the system at some points. For example, the pump is controlled via a control signal from the computer system 6. The speed of the pump 4b may be controlled in accordance with the status of the system determined by a measurement system 11 which will be described later.

[0060] In this example, a chemical substance, which in this case will be referred to as a liquid, needs to be transferred between the first reaction vessel 1 and the second reaction vessel 3. Although the chemical substance will be discussed in terms of a liquid, the chemical substance could be a gas or a solid, for example a particulate mixture.

[0061] The liquid exits the first reaction vessel 1 via exit port 7 (or drain) which is coupled to first tube 5a. The fluid is pumped via a pump 4b. The valve 4a is set to allow fluid from tube 5a to exit the valve 4a via tube 5b and the to the inlet 9 of second reaction vessel 3. The first tube 5a passes through measurement system 11 which has a capacitive sensor which, in this case, is shown as a pair of electrodes 13. The measurement system 11 allows for the flow of liquid through the tube and the status of the tube 5 to be determined. For example, the system 11 may operate as one or more of: a fluid level sensor; a phase separation sensor; a contamination sensor; sensor to detect bubbles; or a suspended particle sensor. Configurations of the sensor 11 , methods of operation of the sensor 11 will be described below. The signals from the measurement system 11 are sent to computer system 6 which is used to control at least one or more of the pump 4b, the valve 4a and the inlet and outlets of the vessels. In this simplified example, there is just one combined valve 4a / pump 4b unit. However, these units may be separate units and only one of them may be present or operate under the control of computer system 6. In further embodiments, a plurality of valves and / or pumps may be provided.

[0062] In Fig. 1a, the sensor 11 is shown attached to first tube 5a. However, it is possible for the sensor to be incorporated onto one of the reaction vessels. For example, reaction vessel 1 or reaction vessel 3. It is also possible for the sensor to be provided at the inlet port or outlet port of one or more of the reaction vessels 1 , 3. It is also possible for the sensor 11 to be provided in any vessel or conduit in the system.

[0063] A very basic system is shown in Fig. 1a. However, the system may just comprise a single reaction vessel, a plurality of reaction vessels or even just a plurality of tubes without reaction vessels. One or more sensors 11 may be provided within the system.

[0064] In further embodiments, the sensors 11 are used to provide an output signal in order to control equipment via the computer system 6. For example, if the sensor indicates that there is a problem, an alarm can be sounded and or the system can be shutdown. If a pump 4b is provided, the pump can be shut off and / or the inlet / outlet of any of the vessels be closed following an output indicated by the sensor. In other embodiments, the sensor 11 might indicate that a certain operation is complete, for example, if a phase separation boundary is detected or a particular amount of fluid is detected in a vessel, then the sensor can output control signal that indicates an endpoint or that initiates the start of the next stage of the processing. The next stage of the processing, may, for example, comprise, opening a further inlet of a reaction vessel, indicating to a controller, such as computer system 6, that a further reagent is now to enter the system for processing etc. This may be provided via valve 4a or a further valve. Valve 4a is shown with just 4 ports, but it is possible for valve 4a or other valves to have more ports, for example at least 7.

[0065] Tube 5c connects valve 4a to vessel 10 which comprises a cleaning fluid. As will be described later with reference to Figs. 8a, 8b and 9, if contamination is determined within a vessel, the computer system can start a cleaning process. In this cleaning process, the pump and valve can be set to allow all reactants to be pumped out of the system, then valve 4a is set to allow tube 5c to be in fluid connection with tube 5d which is connected to an inlet of reaction vessel 1. The pump 4b is then used to pump cleaning fluid from vessel 10 through the system to allow contaminants to be removed. Further operations may be performed on the vessel when it contains cleaning fluid, for example it might be heated or stirring, agitation and / or scrubbing might be used. For example, agitation may be applied using repeated mechanical shocks or high frequency vibration, for example, ultrasound. A mechanical bush scrubber may be used for scrubbing.

[0066] The operation of the sensor 11 will now be described with reference to Figs. 1 b to 3. Applications for of the sensor will be described with reference to Figs. 4a to 11 . In the description relating to Figs. 4a to 11 , as an example, the sensor is applied to a vessel. Figs 12a to 14b describe embodiments of the sensor which are configured for connecting to a tube or conduit.

[0067] A capacitor comprises two electrodes (or plates) separated by a dielectric. A dielectric is an insulating medium capable of sustaining an electric field. A dielectric can be a solid, liquid or gas. Capacitance, C, is given by: where Q is the charge on each electrodes and V is the voltage between the electrodes. The capacitance, C, depends on the geometry of the electrodes and the dielectric between them.

[0068] In the case of a simple parallel plate conductor, comprising two parallel plates (or electrodes) with an area of overlap A, separation distance d, the capacitance can be given by

[0069] C = - -A Eq. 2 a. where s0is the permittivity of free space (vacuum) (8.85pF / m), and sris the relative permittivity or dielectric constant of the insulating material.

[0070] By changing sr, d or A, the capacitance can be changed.

[0071] To detect the presence of a substance, such as a fluid, the substance may be used as the dielectric between the electrodes. If all other configuration parameters of the sensor, such as electrode separation d and area of overlap A are static (unchanging) and known, then any change in the substance causes the change in capacitance. Fig. 1b to Fig. 1d illustrate a substance sensor system 100 according to an embodiment. The substance sensor system 100 comprises a first electrode 101 , a second electrode

[0072] 102, and a measurement unit 104 electrically coupled to the first electrode 101 and the second electrode 102.

[0073] In Fig. 1b, the electrodes 101 and 102 are arranged so as to be separated by a vessel

[0074] 103, such as a bottle, tube or other vessel suitable for holding a substance. The substance may be a fluid, such as a gas or a liquid, or solid material, such as a powder. Vessel 103 may be fabricated from glass, Perspex, plastic, or another material including both insulating and non-insulating materials. The vessel 103 has a width d.

[0075] The electrodes 101 , 102 are conductive. They can be made from metal or other conductive material. While in Fig. 1b and Fig. 1c, the electrodes 101 , 102 are shown as being rectangular in shape, the electrodes can be any shape. The electrodes 101 , 102 can also be curved or flat.

[0076] In an embodiment where the vessel 103 is fabricated from a non-insulating material, the electrodes 101 , 102 may comprise an insulating coating on the side proximate to the vessel 103 to prevent short-circuiting of the electrodes 101 , 102 via the vessel 103.

[0077] The electrodes 101 and 102 are configured to be proximate to an outer surface of the vessel 103. The electrodes 101 , 102 can be fabricated, for example, on a flexible pcb, from metal tape or solid metal.

[0078] The electrodes 101 , 102 can be mounted directly onto an outer surface of the vessel 103 so that surfaces of the electrodes 101 , 102 are in contact with the outer surface of the vessel 103. The electrodes 101 , 102 may be placed on the outer surface of the vessel 103 by adhesive, by clamping, or by inserting the electrodes 101 , 102 in a holder configured to be placed around the vessel 103 so that the electrodes 101 and 102 are in contact with the outer surface of the vessel 103.

[0079] In an embodiment, the electrodes 101 , 102 are fabricated from aluminium tape. The aluminum tape may have an adhesive layer on one side. The aluminium tape is cut to the desired size of each electrode 101 , 102, and attached to the outer surface of the vessel 103 using the adhesive layer. Aluminium tape has the advantage that it can be easily cut to the desired size. In an embodiment, a wire is then soldered on to the side of each electrode 101 , 102 distal to the outer surface of the vessel 103 to facilitate electrical connection to the measurement unit 104. In further variations, thevessel is provided in a holder, for example a clamp, and the electrodes are provided connected to the holder. For example, the electrodes may be adhered to the holder via adhesive tape. Electrical contact may then be provided to the electrodes via the holder, for example a screw or other conductor provided through the holder.

[0080] In an alternate embodiment, the electrodes are fabricated from solid metal. The electrodes 101 , 102 may be semi cylindrical solid metal electrodes configured to be placed on the outside of the vessel or rectangular with a flat surface. The solid metal electrodes 101 , 102 may then be used with a clip, clamp or other holding device to place the electrodes in contact with an outer surface of the vessel 103.

[0081] In a further embodiment, the electrodes 101 , 102 can be placed within a fixed distance of the outer surface of the vessel 103 so that the surfaces of the electrodes 101 , 102 are not in contact with the outer surface of the vessel 103. This may be achieved by clamping, by inserting the electrodes 101 , 102 in a holder configured to be placed around the vessel 103 so that the electrodes 101 and 102 are within a fixed distance, and proximate to, the outer surface of the vessel 103, or another suitable means.

[0082] In theory, there is no limit to the distance between the electrodes 101 , 102 and the outer surface of the vessel 103. However, the distance between the electrodes 101 , 102 and the outer surface of the vessel 103 affects the signal quality of the signal measured by the measurement unit. As the distance between the electrodes 101 , 102 and the outer surface of the vessel 103 is increased, the signal quality decreases. In an embodiment, the distance between the electrodes 101 , 102 and the outer surface of the vessel 103 is in the range from 0cm to 5cm.

[0083] The electrodes 101 , 102 that are to be placed within a fixed distance of the outer surface of the vessel 103 can be fabricated from aluminium tape or solid metal or any other conductive material. In Fig.1 b, the first electrode 101 is configured to be placed on a first surface of the vessel 103. The second electrode 102 is configured to be placed on a second surface of the vessel 103.

[0084] In Fig. 1b, the electrodes 101 and 102 are placed on opposing sides of the vessel 103. In this arrangement, more of the substance within the vessel 103 is contributing to the capacitive field. In an embodiment, the electrodes 101 102 are fabricated from aluminium tape and placed on opposing sides of the vessel so that each electrode 101 102 covers approximately 1 / 3 of the circumference of the vessel 103.

[0085] In other embodiments, the electrodes 101 and 102 may be placed on a same side of the vessel 103, as discussed below.

[0086] Fig. 1c illustrates a perspective view of the electrodes 101 , 102 and vessel 103 of Fig. 1 b.

[0087] In the embodiment of Fig.1b to Fig. 1d, the vessel 103 may be cuboid in shape so that the electrodes 101 and 102 are flush with respective sides of the vessel 103. In another embodiment, the vessel 103 may be cylindrical, conical or another shape, and the electrodes 101 and 102 may be curved so as to be flush with the outer surface of the vessel 103.

[0088] In the embodiment of Fig. 1c, the electrodes 101 and 102 have the same width w, the same length I, and hence, the same area A. In another embodiment, the electrodes 101 and 102 have different areas, and it is the area of the area of overlap between both electrodes 101 and 102 that contributes to the capacitance.

[0089] When the substance within the vessel 103 between the electrodes 101 and 102 changes, the dielectric material between the electrodes 101 , 102 changes, and, hence, the capacitance measured by the measurement unit 104 changes.

[0090] Fig. 1d illustrates the arrangement of Fig. 1b where the vessel 103 comprises two fluids or substances. This results in two different dielectric materials between the plates - a first dielectric 105, such as water, with a relative permittivity Eltand a second dielectric 106, such as air, with a relative permittivity s2. If the walls of the vessel 103 are assumed not to contribute to the dielectric material, this results in two capacitors in parallel. The first capacitor comprises the first dielectric 105 £ and a first area Ai of the electrodes 101 and 102. The capacitor comprises the second dielectric 106 and a second area A2 of the electrodes 101 and 102.

[0091] The total capacitance of the sensor formed by electrodes 101 and 102 is the sum of the capacitances:

[0092] From Fig. 1b and Fig. 1c, A1= wx and 42= w(l - x), where w is the width of the electrodes, I is the length of the electrodes, and x is the length of the first dielectric material 105 between the electrodes 101 and 102 .

[0093] Therefore, by monitoring the capacitance C, for fixed electrodes with a known separation distance and known geometry, and if the vessel 103 geometry and properties are unchanging, then it can be determined if the dielectric material, or substance, within the vessel 103 has changed.

[0094] If the vessel 103 is a tube for carrying fluids, a change in a type of fluid flowing through the tube can be detected. This can be particularly useful in liquid-liquid separation, where two immiscible liquids, such as oil and water need to be separated.

[0095] In addition, if all other parameters are known in Equation 4 above, then it is possible to determine x. For example, if the vessel 103 of Fig. 1d is to be used to hold water, it can be possible to measure a level of fluid, or substance, in the vessel 103.

[0096] In another embodiment, the sensor electrodes 101 and 102 may be co-planar. Fig. 2a shows an embodiment where electrodes 101 and 102 are in a co-planar arrangement, with both electrodes on the same side of the vessel 103. Fig. 2b shows a top view of the electrode 102 103 and vessel 103 arrangement of Fig. 2a. As shown in Fig. 2b, the fringing electric fields 200 between the coplanar electrodes 101 102 bend and penetrate into the vessel 103 and the dielectric.

[0097] The capacitance of the coplanar electrode arrangement will depend on the electric field in the dielectric and can be solved by techniques such as conformal mapping. However, for this disclosure, it is sufficient to represent the capacitance of the capacitor of the electrodes 102 103 of Fig. 2a due to the dielectric material on one of its sides as:

[0098] C = l£0£rf(d, w, t) Eq. 5 where I is the length of the electrodes, d is the separation between the electrodes 102 103, w is the width of the electrodes 102 103 and t is the thickness of the dielectric.

[0099] In Fig.2c, the vessel 103 comprises two fluids, or substances. This results in two different dielectric materials between the plates - a first dielectric 105, such as water, with a relative permittivity £ltand a second dielectric 106, such as air, with a relative permittivity£2 -

[0100] If the walls of the vessel 103 are assumed not to contribute to the dielectric material, this results in two capacitors in parallel. The first capacitor comprises the first dielectric 105 £±and electrodes with a height x. The second capacitor comprises the second dielectric 106 and electrodes with a height l-x.

[0101] The total capacitance of the sensor formed by electrodes 101 and 102 is the sum of the capacitances:

[0102] C = X£a£1f d, w, t) — (Z — x)£0£rf(d, w, t) Eq. 6

[0103] In Figs.1 a-1c and 2a-2c, the electrodes 101 102 are in contact with the outer surface of the vessel 103. In an alternate embodiment, the electrodes 101 102 are maintained at a fixed distance from the outer surface of the vessel 103. The air space between each electrode and the outer surface of the vessel 103 also contributes to the overall capacitance measured by the measurement unit 104. However, as the distance between the electrodes 101 102 and the outer surface of the vessel 103 does not change, then this does not affect the measurement, as the contribution of the air space can be included as part of the baseline measurement.

[0104] For the above the wall of the vessel 103 in contributing to the dielectric material has not been considered. In practice, the vessel 103 also contributes to the overall capacitance measured by the measurement unit 104. However, as the properties of the vessel 103 does not change, then this does not affect the measurement as the contribution of the vessel wall can be included as part of the baseline measurement.

[0105] However, if one were to model this from a physical standpoint, then the space between each electrode 101 102 and the outer surface contributes a capacitance Cspace, the vessel walls contributes a capacitance Cwa / / , and then, according to the equations above, the substance within the vessel contributes a capacitance Csubstance. The measured capacitance would be these capacitances in series so that = - - - 1-

[0106] ^Total ^substance wall

[0107] To measure variations in the capacitance, electrical energy flowing into and out of the electrodes 101 102 is measured as the voltage or potential is varied between the electrodes is changed.

[0108] Fig. 3a illustrates a measurement unit 104 according to an embodiment. Ctube represents the capacitor formed by electrodes 101 and 102. One electrode 101 102 is connected to ground, while the other electrode 101 102 is connected to one leg of a 1kOhm resistor. The other leg of the 1 kOhm resistor is connected to a first leg of a reference capacitor Cref and a measurement terminal Vmeas. In Fig. 3a, Cref is 22pF. However, Cref could be 5pF to 50pF. The first leg of Cref is connected to a first terminal of switch SW1 and the second leg of Cref is connected to a first terminal of switch SW2. The second terminal of SW1 is connected to a power supply V2. The second terminal of SW2 is grounded.

[0109] When SW1 is closed, and SW2 is open, the capacitor Ctube charges.

[0110] When SW1 is opened and SW2 is closed, the charge from Ctube will discharge into Cref.

[0111] The measurement unit 104 then measured the voltage across the capacitor Cret at Vmeas. In an embodiment, the circuit of Fig. 3a is implemented using a microprocessor which, may be for example, an Atmel Mega 2560 micro controller, with R1 , Ctube and Cref. This is illustrated in Fig. 3b.

[0112] Three pins of the Atmel Mega 2560 are used. AO and A1 are analog output / inputs. GND is a ground pin. The Atmel Mega 2560 effectively replaces the switches SW1 and SW2, the power supply V2 and any measurement terminal at Vmeas.

[0113] The text below illustrates example code used to program the Atmel Mega 2560 microcontroller.

[0114] / / defining circular buffer

[0115] #define BUFFER_SIZE 1024 int circBuf[BUFFER_SIZE] = {0}; int bufferPointer = 0; float cumulativeRead = 0; int currRead = 0;

[0116] / / pin setup

[0117] #define PIN_A A0

[0118] #define PIN_B A1 void setup() {

[0119] / / setting up serial connection

[0120] Serial. begin(115200);

[0121] Serial. flush();

[0122] } void loop() {

[0123] 11 Discharge the Cref and Ctube pinMode(PIN_A, OUTPUT); analogWrite(PIN_A, 0); pinMode(PIN_B, OUTPUT); analogWrite(PIN_B, 0); delayMicroseconds(5); / / setting pins to charge the Ctube pinMode(PIN_B, INPUT);

[0124] / / charging cap for 5 microseconds analogWrite(PIN_A, 1023); delayMicroseconds(5);

[0125] / / setting pins to dis-charge the Ctube into Cref pinMode(PIN_A, INPUT);

[0126] / / setting PinB to ground to discharge into known capacitor for 5 microseconds pinMode(PIN_B, OUTPUT); analogWrite(PIN_B, 0); delayMicroseconds(5);

[0127] The above code uses a purpose built circular buffer to reduce signal noise by averaging over 1024 measurements. However, the signal can be averaged over a different number of measurements. In an embodiment, the Atmel Mega 2560 microcontroller can be configured to receive input from the user to allow the user to adjust the number of measurements to average over.

[0128] The serial is connection is set up. Serialbegin (115200) opens serial port and sets the data rate to 115200 bps. Serial. flush() waits for the transmission of outgoing serial data to complete.

[0129] Next the capacitors Cref and Ctube are discharged as follows: pin A0 (defined as being PIN_A) and pin A1 (defined as being PIN_B) are defined as outputs using pinMode().

[0130] Next using analogWrite (pin, value), an analog value PWM (pulse width modulation) wave) is written to each pin. The “pin” parameter specifies the Atmel Mega 2560 pin to write to. The ‘value’ parameter specifies the duty cycle of the PWM wave is the duty cycle. By setting the ‘value’ parameter to 0, the PWM wave is always off resulted in a 0V output on both pin A0 and pin A1. Next the pins are set to charge Ctube. By setting pin A1 (PIN_B) to be an input, it causes pin A1 (PIN_B) to be in a high-impedance state. Pin AO (PIN_A) is set to be always on (analogWrite(PIN_A, 255)) and output a 5V signal. Because of the high impedance connection between pin A1 (PIN_B) and Cref, the output of pin AO (PIN_A) will charge the Ctube only. This is done for 5 microseconds.

[0131] Next the pins are set to discharge charge from Ctube into Cref. Pin AO (PIN_A) is set to be an input resulting in a high impedance connection between Pin AO (PIN_A) and the resistor R1. Pin A1 (PIN_B) is set to ground by setting Pin A1 (PIN_B) to be an output and output OV. As Ctube and Cref are now in series (along with R1), charge from Ctube discharges into Cref until they both have the same voltage across their electrodes.

[0132] After a delay of 5 microseconds, the voltage at PIN_A (AO) is read using analogRead(). This converts the voltage signal to a digital signal using Analog to Digital Conversion. This digital measurement is then averaged with other measurements using the circular buffer.

[0133] In a further embodiment, the controller is configured to calculate a variance of the measurements. The variance is calculated in real time (on the fly). This allows the sample rate to be lowered since the variance provides a secondary indicator on a change in the capacitance.

[0134] The voltage across Cref is the same as the voltage across Ctube. As the value of Cref is known along with the initial voltage applied to Ctube when charging (5V), a value of Cref may be determined. Alternatively, as the measured voltage is linearly proportional to the capacitance Ctube, and an increase in the measured voltage corresponds to an increase in the capacitance Ctube, the measured voltage signal may be used as a direct indication of a change in capacitance of Ctube. Alternative measurement circuits can be used, including an oscillator circuit, or a Wheatstone bridge.

[0135] The requirement for calibration of the sensor is dependent on the application. When monitoring fast, relative changes in the vessel (rather than absolute values or drift over hours or days), the sensor system need not be calibrated. For the application of assessing contamination of the vessel, a baseline may be established for the sensor. This may be achieved by either having a controlled environment (humidity, temperature, no external influence) outside the vessel as well as a clean (e.g. purging with dry nitrogen gas) inside such that the signal only consists of the tube itself. In an embodiment, the baseline measurement may be saved on the senor system itself (e.g. in EEPROM) and the baseline may be subtracted digitally from any measurements. Alternatively, a Wheatstone bridge with capacitors may be used. One arm of the Wheatstone bridge may comprise a reference capacitor that is subject to the same environment as the capacitor formed by electrodes 101 and 102. In this way any environmental drift can be compensated for and will not affect the measured signal.

[0136] In an embodiment, the electrodes 101 102 and a portion of the vessel 103 in proximity to the electrodes 101 102 are surrounded by a grounded metallic housing to reduce electrical interference.

[0137] In embodiments, the electrodes 101 102 fabricated from aluminium tape with an adhesive layer are also used with clips, clamps or holders that are configured to attach to the vessel 103. These clamps can be used to stabilize the tape on the vessel 103 and stabilize the solder connection of the wire onto the tape to prevent any damage to the solder connection due to pulling etc.

[0138] The microprocessor outputs data to a computer for further analysis. Sending data from the microprocessor requires processing power and this can be a bottleneck as the controller expends too much time sending data and this reduces the availability of the processor for analysing data.

[0139] In an embodiment, the system is configured to minimise delay between a phase boundary moving through the sensor and the detection of the movement of the phase boundary. In an embodiment, using a microprocessor that can only perform one task at a time, there is a balance between:

[0140] (i) Frequency of sending data from the microprocessor to the computer (every time the microprocessor sends data to the computer, the sensor is not collecting data since everything is executed linearly on the microprocessor). Further, the more data that is sent, the shorter the time between measurement and the computer being aware of the measurement. (ii) Speed between consecutive measurements on the micro controller. Any time the controller is doing any mathematical operations or sending data it is not collecting the next measurement.

[0141] The extreme cases here would be:

[0142] (i) Send every single datapoint up to the computer after it is measured. This would, minimise delay between measurement and computer being aware of the measurement since there are no mathematical calculations being performed on the micro controller. However, this essentially maximises delay between consecutive measurements since the entire send cycle has to be conducted.

[0143] (ii) Collect an arbitrarily large number n of consecutive measurements before sending them in bulk to the computer. This minimises delay between measurements, but maximises time delay until the computer becomes aware of the measurement. Additionally, this eventually runs into memory issues (one cannot save an infinite number of measurements on the chip) or increases time between measurements by adding up the measurements or conducting more complex math on the measurements collected (average, deviation, etc.).

[0144] In an embodiment, the microprocessor is configured to balance these competing requirements. In an embodiment, n consecutive measurements are collected and these are averaged and this single number, which is the average is sent up to the computer for evaluation.

[0145] The memory vs processing time on the microcontroller is a trade-off between:

[0146] (i) Just adding all consecutive measurements together (add is fast in micro controller terms), but the number grows arbitrarily large as n increases.

[0147] (ii) Adding all numbers and immediately averaging them (thereby the upper bound of memory usage is known since it will never exceed the maximum value the ADC can return)

[0148] In an embodiment, the number of added values is kept low enough such that the upper bound remains in a common data type size (e.g. 32 bits) and then averaging once before sending the data to the computer. Alternatively, the sum and the sample rate can be sent to the computer for it to perform the averaging. Therefore, in an embodiment, the system is configured to add n consecutive values and average the n-consecutive values prior to sending to the computer. In an embodiment, n is set so that the added values do not exceed a common data type size, for example, 32 bits, n may be set to be 64.

[0149] Thus, in an embodiment, the samples are grouped into batches and a mean is determined for each batch.

[0150] In further embodiments, the microprocessor calculates and approximates of the standard deviation (see firmware above) on the fly to be able to pick a lower sample rate.

[0151] In this embodiment, the averages will be received by the computer or the average will be calculated from the sum received at the computer, these averages will be referred to as the received samples. In a further embodiment, the received samples which are sent to the computer are further grouped into blocks at the computer. For example, the microprocessor collects n samples and sends their sum or their average to the computer. The computer then keeps a rolling average of m of the received samples (since computer and micro controller can do calculations in parallel). For example, if a batch comprises 64 samples (the received sample will be the average of the 64 samples), then m may be 8, so that the computer keeps a rolling average of 8 received samples. With these figures, this essentially makes the sample averaging 512, thereby improving the signal-to-noise ratio while updating the measurements roughly at the sample rate speed of 64 samples.

[0152] The computer then looks at a measure of the difference or variance between the blocks of the received samples. For example, each block can be averaged and the value compared with the next block received by the computer. This allows the signal difference to be more pronounced. In reality the rate of change of the signal might be slow compared to the sample rate (e.g. 1 sample every 10 ps, but the signal changes over 100 ps). Thus, if neighbouring blocks of 8 samples, that each comprise of n ADC readings, are compared the signal-to-noise is very poor. By keeping a block of 8 measurements in between the difference in the averages over the 8 measurements will be greater and thus easier to detect. This of comes at a cost of detection speed (since it is necessary to wait for a total of 24 received samples before being able to act on the signal). The above embodiment has been designed to allow the system to operate with a simple microprocessor which requires operations to be performed in a linear manner. However, in further embodiments, other microprocessor designs may allow more processing to be performed on the microprocessor and possibly operations to be performed in parallel.

[0153] If the difference between these two blocks is greater than a threshold, e.g. 5%, then this suggests that something interesting has happened in the gap between these two blocks and it is possible to slow down and reverse the flow of fluid and then advance the fluid slowly through the sensor to be able to determine the exact position of the phase boundary. In some embodiments, the fluid may be run backwards and forwards through the sensor for a plurality of times to determine the exact position of the phase boundary. This arrangement where the flow of fluid is slowed to provide better data supports a simplified processor design as the rate at which data is collected is kept constant and the size of the batches which are sent to the computer remain constant. This allows fast and simplified data processing.

[0154] The length of the connections between the vessels is known and therefore, if the exact time when the phase boundary passes through a sensor is known, the control of vessels downstream from the sensor can be coordinated with the expected arrival time of the phase boundary. For example, if is desired for the next downstream vessel to only receive the liquid before the phase boundary, then the valves on that vessel can be controlled to shut just as the phase boundary arrives.

[0155] In some embodiments, valves are provided with multiple ports and a controller is provided to change the output from one port to another port as the phase boundary arrives to allow one phase to be directed towards one vessel and the second phase to be directed towards a different vessel.

[0156] The above has primarily discussed the measurement of the capacitance by comparing the capacitance of the capacitor formed by the electrodes and the substance and with a reference capacitor and looking at the change is capacitance due to the movement of the substance. However, in further embodiments the absolute value of the capacitance may be measured instead or as well as changes in the capacitance. In some embodiments an oscillating circuit can be used. This may receive an AC input or have a switched (square wave) input signal. In one embodiment a Wheatstone bridge or related circuit is used as an oscillating circuit. In a Wheatstone bridge, variations in the resistance (due to capacitance variations) between the arms of the bridge allow a capacitance in one arm of the bridge to be compared to a known capacitance in another arm of the bridge. In this arrangement, changes in the substance will cause a change in oscillation frequency. Variations in the capacitance can be determined by phase shifts and / or changes in the oscillation frequency.

[0157] In further embodiments, capacitance of the sensor is measured via a direct voltage level measurement, for example, by directly measuring the voltage level of one pin while holding the other pin at a fixed level.

[0158] Applications

[0159] Fig. 4a illustrates a substance level sensor system 400 for determining if a vessel 103 comprises a desired amount of a substance. In an embodiment, the substance is a fluid.

[0160] In Fig. 4a, the vessel 103 stores a substance for use, for example, in an automated system. The capacity of the vessel may be 10mL to 50 litres.

[0161] Electrodes 101 102 of the sensor system 100 are placed on an outer surface of the vessel 103. While in Fig. 4a, the electrodes 101 , 102 are in a co-planar arrangement, they may alternatively be placed on opposite sides of the vessel 103, as indicated in Figs. 1a to 1c. The measurement unit 104 measures a voltage signal proportional to the capacitance between the electrodes 101, 102. The measured voltage signal may be used to determine a level of a substance in the vessel 103.

[0162] In an embodiment, the measurement unit 104 compares the measured voltage or capacitance to a predetermined voltage or capacitance value. Alternatively, the measurement unit 104, compares the determined level to a predetermined level using, for example Eq. 4. Based at least in part on the comparison, the measurement unit 104 may determine that there is not sufficient substance to execute a given task.

[0163] For example, it may be known that 200mL of water is required for a given task, such as a recipe. If it is determined that there is less than 200mL of water in the vessel 103 then the measurement unit 104 may prevent an action from taking place, or alert a user that there is not sufficient water in the vessel 103. For example, if the determined substance level is less than the predetermined substance level, a message may be displayed on a user interface, an alarm may be activated, or a light, LED, may be switched on.

[0164] In an embodiment, the vessel 103 may be fluidly coupled to a tube 401 or other means of extracting fluid from the vessel 103. In an embodiment, the tube 401 is coupled to a pump (see Fig. 1a) to allow for fluid from the vessel 103 to be drawn along the tube 401 and out of the vessel 103.

[0165] Before withdrawing the fluid, or substance, from the vessel 103, it is known what amount of fluid is needed to execute a given task. For example, it may be desired to move 200m L of water from the vessel 103 to another vessel. Before executing the task, the level sensor system 400 may monitor the level of fluid in the vessel 103. If the fluid level is less that the desired level of 200ml, then the measurement unit 104 cause an action of the pump to move fluid to be inhibited. In an example, the measurement unit 104 may cause a signal to be sent to the pump, or a pump controller, to inhibit the pump from pumping fluid from the vessel 103. If the fluid level then changes to be equal to or greater than the desired level of 200ml, the measurement unit 104 may cause a signal to be sent to the pump, or a pump controller, to enable the pump to pump fluid from the vessel 103.

[0166] In an embodiment, the vessel 103 may be fluidly coupled to a tube 401 or other means of inserting fluid into the vessel 103. In an embodiment, the tube 401 is coupled to a pump to allow for fluid to be moved along the tube from a fluid reservoir into the vessel 103.

[0167] Before inserting the fluid into the vessel 103, it is known what amount of fluid is needed. For example, it may be desired to move 200mL of water into the vessel 103 from another vessel. The level sensor system 400 may monitor the level of fluid in the vessel 103. Once the fluid level is equal to the desired level of 200ml, then the measurement unit 104 may cause a signal to be sent to the pump or pump controller to inhibit an action of the pump to move the water through the tube 401.

[0168] Fig. 4b illustrates a substance level sensor system 400 for determining if a vessel 103 comprises a desired amount of a substance. In an embodiment, the substance is a fluid. In Fig. 4b the vessel 103 comprises a valve 402 at an outlet of the vessel 103. When the valve 402 is open the fluid or substance (powder) in the vessel 103 may drain out of the vessel 103 under gravity. The measurement unit 104 may determine, based on the change in capacitance, when the level of the substance in vessel 103 has reached the desired level, and send a control signal to a valve controller to close the valve 402.

[0169] Fig. 5 details method steps performed by the system of Fig. 4a or Fig. 4b according to an embodiment.

[0170] In Step S501 , the measurement unit 104 measures a signal representing a change in a capacitance associated with a first electrode 101 in proximity to a first surface of a vessel 103, a second electrode 102 in proximity to a second surface of the vessel 103 and a substance within the vessel 103.

[0171] In Step S502, the measurement unit 104 compares the measured signal with a reference signal, wherein the reference signal indicates a desired amount of the substance to be held in the vessel 103.

[0172] In Step S503, the measurement unit 104 send a signal to a controller to actuate or inhibit movement of the substance to or from the vessel 103.

[0173] Fig. 6a illustrates a phase separation sensor system 600 according to an embodiment.

[0174] Vessel 103 is fluidly coupled to an outlet of a mixture vessel 601. Mixture vessel 601 comprises a mixture of immiscible fluids - first immiscible fluid 602 and second immiscible fluid 603. Vessel 103 is a tube to allow flow of fluid to another vessel or container. The outlet of the mixture vessel 601 may be coupled to a valve 604. When the valve 604 is open, it allows substances in the mixture vessel 601 to move (for example under gravity) into the vessel 103. When the valve 604 is closed, it stops substances in the mixture vessel 601 moving into the vessel 103. The opening and closing of the valve 604 may be controller by a valve controller (not shown).

[0175] Electrodes 101 , 102 of the sensor system 600 are placed on an outer surface of the fluid vessel 103. While in Fig. 6a, the electrodes 101 , 102 are in a co-planar arrangement, they may alternatively be placed on opposite sides of the vessel 103, as indicated in Figs. 1b to 1d. While in Fig. 6a, the electrodes 101 , 102 are in contact with an outer surface of the vessel 103, they may alternatively be maintained at a fixed distance from the outer surface of the vessel 102. The capacitance between the electrodes 101 , 102 is measured by the measurement unit 104 to determine a change in the type of fluid in the vessel 103.

[0176] As fluid 602 drains from the mixture vessel 601 through the vessel 103, the capacitance measured will not change. However, once the fluid 603 (above the meniscus) enters the vessel 103, it will alter the capacitance by causing a change in the dielectric. On detecting this change in capacitance, or that the capacitance has changed by a predetermined amount, the measurement unit 104 may send a signal to cause the valve 604 at the outlet of the mixture vessel 601 to close and prevent liquid 603 from exiting the mixture vessel 601.

[0177] Alternatively, instead of sending a signal to a valve controller, the measurement unit 104 may send a signal to inhibit a pump from moving the liquid 603 through the vessel 103.

[0178] In an embodiment, the vessel 103 is fluidly coupled to a pump which enables movement of the substance 103 from the mixture vessel 601 through the vessel 103 to sample vessels. In the case where it is desired to keep the liquid 602 (the one that drains first because the outlet of the vessel is at the bottom, also referred to as the bottom phase), the valve 604 is first opened to allow the liquid 602 to move into vessel 103. The pump causes the liquid 602 to move through the vessel 103 to a first sample vessel.

[0179] When the measurement unit 104 detects a change from liquid 602 to liquid 603, a control signal will be sent to the valve controller to cause the valve 604 to close and prevent the liquid 603 from moving along the vessel 103 to the first sample vessel. However, the pump will continue to cause liquid to move through the vessel for the remaining “dead volume” of the tube. Fig. 6b illustrates the dead volume of a vessel according to this embodiment. The length I and diameter d of the vessel 103, and hence a volume of the tube, are known. The distance x between the valve 604 and the distal end of electrodes 101 102 is known. Hence, a volume of the tube from the valve 604 to the end of the electrodes can be determined. When a change is measured, then the substance within the volume of the tube from the valve 604 to the end of the electrodes now comprises a mixture of liquid 602 and 603. This should not be included in the first sample vessel. However, the volume associated with the remaining length of the tube (l-x) comprises only the liquid 602 and should be included in the first sample vessel. The volume associated with the length l-x of the tube is the dead volume. A control signal can be sent to the pump to pump the dead volume into the first sample vessel. The vessel 103 can then be coupled to a second sample vessel. The valve may then be opened and the pump operated to allow for the volume of the tube from the valve 604 to the end of the electrodes to be drained into the second sample vessel along with the liquid 603 remaining in the mixture vessel 601.

[0180] If it is desired to keep the liquid 603 (the top phase), the system will continue to drain the liquid 602 until the signal measured by the measurement unit 104 has stabilized (or reached a steady voltage state). The vessel 103 is then coupled to a second sample vessel instead of the first sample vessel, to allow the liquid 603 to drain into.

[0181] Phase boundaries tend to not be perfectly well formed and by making the above adjustment the 'ambiguous' part gets lumped in with the phase the user does not wish to retain.

[0182] Fig. 6c shows an example of a transition from air to water passing through a vessel 103, such as a tube. From time t1 to time t2 air is passing through the tube resulting in a stable voltage signal. At t2, water is introduced into the tube until at time t3 the tube is full with water and the air has been moved out. As can be seen in Fig. 6c, there is a rapid increase in the voltage signal measured by the measurement unit 104 between time t2 and t3 which corresponds to the change in capacitance as the dielectric between the electrodes 101 102 changes from air, to air and water, to just water.

[0183] Fig. 7a details method steps performed by the system of Fig. 6a according to an embodiment.

[0184] In Step S701 , the measurement unit 104 measures a signal representing a change in a capacitance associated with a first electrode 101 in proximity to a first surface of a vessel 103, a second electrode 102 in proximity to a second surface of the vessel 103 and a substance within the vessel 103.

[0185] In Step S702, the measurement unit 104 determines, based on the measured signal, a change in the substance from a first substance to a second substance. In Step S703, the measurement unit 104 sends a signal to a valve controller to inhibit movement of the second substance to or from the vessel 103.

[0186] Fig. 7b shows a variation on the method of Fig. 7a. In Fig. 7b, the system is configured to separate two phases into two separate vessels. The fluid can be thought of as having three phase boundaries, a first phase boundary between the air and the first phase, a second phase boundary between the first and second phases and a third phase boundary between the second phase and air.

[0187] The flow chart of Fig. 7b can be used for the type of system of Fig. 7c. Fig. 7c is based on Fig. 1a and where appropriate, like reference numerals have been used to denote like features. For simplicity, a vessel holding cleaning fluid has been removed from the system of Fig. 7c. However, such a vessel may be present. In the system of Fig. 7c, there is a first reaction vessel 1 , a second reaction vessel 3a and third reaction vessel 3b. Reaction vessel 1 holds a liquid which comprises 2 phases. It is desired to separate the first phase into the second reaction vessel 3a and the second phase into the third reaction vessel 3b.

[0188] In step S751 , the first phase boundary which is the first air / liquid interface causes a variation in the capacitance as it enters the sensor 11 . Once this is detected, the valve 4a can be set to direct liquid leaving the first reaction vessel 1 into the second reaction vessel 3a (first receiving vessel) via tube 75 in step S753. As the liquid flows through the sensor 11 , eventually, a capacitance change between the first liquid phase and the second liquid phase is determined signifying the second phase boundary in S755.

[0189] Once this is determined, the volume of the first liquid phase is known. As the dimensions of the tube 5a are known, it is possible for computer system 6 to switch the valve 4a at the exact time to ensure that just the first liquid phase is transferred to the second reaction vessel 3a since the volume of the first phase can be determined from the capacitance measurements. The volume of the first phase may also be determined from the flow speed of the liquid and the time taken. For this, the position of the sensor along the tube is immaterial as the pump can be instructed by the controller to perform a liquid movement that will cause the exact volume of the tube to be drawn into the pump and by measuring the time between the start of the movement and the detection of the phase boundary a delay is known that can be repeated for further phase boundary detections. For example, given a total tube volume of 10 mL, a phase sensor positioned such that 1 mL of the tube is before the sensor (as seen from the direction of travel of the liquid) and 9 mL are behind the sensor and a liquid travel speed of 1 mL / s as provided by the pump: If the pump is instructed to move 10 mL and the liquid travels for 5 seconds before a signal is detected (indicating the phase boundary to be 5 mL before the pump) this volume (5 mL from detection of signal) can be used for subsequent phase detections. E.g. if the second phase boundary is detected move the liquid a further 5 mL to bring the phase boundary exactly to the valve on top of the pump, thus making knowledge of the position of the sensor along the tube not required for the phase separation to work.

[0190] In an embodiment, the position of the phase boundary can be accurately determined by slowing down the pump when the position of the phase boundary is expected in step S757. In some embodiments, the liquid is reversed back and forth slowly through the sensor to determine the exact position of the second phase boundary. For example, the speed of the pump may be halved each time as the phase boundary is moved through the sensor to determine its exact position.

[0191] In an embodiment, the change in capacitance is denoted by a sigmoid type response, by slowing down the passage of the liquid through the sensor, it is possible to obtain a sharp profile to accurately determine the exact position of the phase boundary. This allows the exact volume of the first phase to be determined in S759.

[0192] Once the exact position of the second phase boundary is determined, the speed of the pump can be increased. Since the volume of the first phase is accurately known in, the valve 4a is controlled to switch to tube 76 which is connected to the third reaction vessel when the second phase boundary reaches valve 4a in step S781. This then allows the second phase to be directed to the third reaction vessel 3b (second receiving vessel).

[0193] The third phase boundary may be of less importance. However, similar to the first phase boundary, this third phase boundary can be used to measure the volume of the phase quite accurately. This can be useful if the volume of the top phase is needed for some later stage or if the partition coefficient is to be determined. In the system of Fig. 7c, there are two valves, the first closes off the first reaction vessel right at the bottom to allow reactions to take place in a defined space. The second valve, 4a sits atop the pump 4b, which means that the sensor 11 is located on the tube between two valves. The first valve is opened at the beginning of the separation and the second valve 4a is set to point at the first receiving vessel (bottom phase vessel) 3a. When a change is detected the pump 4b is stopped immediately and then instructed to move exactly the remaining volume of the tube between the sensor 11 and the second valve 4a (bringing the phase boundary to that valve). The valve 4b is then switched to the second receiving container (top phase bottle) 3b and the remaining volume of the vessel originally containing the biphasic mixture is drained into the top phase bottle.

[0194] Fig. 8a and Fig. 8b illustrate a vessel contamination sensor system 800 according to an embodiment. During use, buildup of fluid residue, or other contaminates, may occur on the inside of a vessel, such as tubes for transporting fluid in an automated system. In such cases, this residue may not be visible to the human eye, or may be located such that inspection by a user is not possible. A means of monitoring the condition of the inside of vessels is desirable.

[0195] In Fig. 8a and Fig. 8b, the sensor system 100 may be used to determine a contamination of the vessel 103. In Fig. 8a, a baseline capacitance measurement of the empty vessel 103 when not in use is taken. In Figs. 8a and 8b, an electrode arrangement is shown with the electrodes on the same side of the vessel. However, the electrode arrangements of Figs. 1 b, 12a or 12b could also be used. Here empty means that the vessel 103 has a well-defined state, for example the vessel contains a vacuum, air, pure N2 or a pure solvent.

[0196] The capacitance of the sensor is then monitored at times when the vessel 103 is not in use and should only be holding air. Fig. 8b shows residue 801 that has built up on an inside surface of the vessel 103. The residue will contribute to the dielectric and cause a change in the capacitance measured by the measuring unit 104.

[0197] If the measured capacitance reaches a threshold value above or below the baseline measurement, the measurement unit 104 identifies that there is a buildup or residue in the fluid vessel 103, or that the vessel 103 is otherwise contaminated. An alert may be sent to a user to indicate that the vessel 103 needs to be cleaned or replaced.

[0198] The sensor may be used to detect a change in the capacitance due to contamination which builds up over weeks.

[0199] Fig. 9 details method steps performed by the system of Fig. 8a and Fig. 8b according to an embodiment.

[0200] In Step S901 , the measurement unit 104 measures a signal representing a change in a capacitance associated with a first electrode 101 in proximity to a first surface of a vessel 103, a second electrode 102 in proximity to a second surface of the vessel 103 and a substance within the vessel 103.

[0201] In Step S902, the measurement unit 104 determines, based on the measured signal, a contamination of the vessel.

[0202] In Step S903, the measurement unit 104 sends a signal to a controller to actuate or inhibit movement of a cleaning fluid (see Fig. 1a) to or from the vessel.

[0203] Fig. 10a and Fig. 10b illustrate a suspended particle sensor system 800 according to an embodiment. The sensor system 100 may be used to determine if there are air bubbles or other undesirable components, such as dirt particles, suspended within the fluid in the vessel 103, or any undesired droplets or particles passing through an empty vessel 103. In Fig. 10a, the vessel 103 is full with a single fluid with no suspended particles. A baseline measurement may be taken.

[0204] In Fig. 10b, the vessel 103 holds the single fluid of Fig. 10a, and suspended particles 1001 , such as air bubbles, are within the single fluid. The presence of the suspended particles 1001 alters the dielectric between the electrodes 101 102 and the capacitance of the sensor formed by the electrodes 101 102 and the dielectric. This causes a change in the voltage signal measured by the measurement unit 104. When suspended particles are present in the single fluid, the signal measured by the measurement unit 104 will show rapid changes from the baseline voltage due to the capacitance of the single fluid before returning to the baseline voltage. These rapid changes may take the form of positive or negative spikes.

[0205] In the case where the suspended particles are due to a non-homogenous mixture of substances, a continued voltage drift may be evident in the measured voltage.

[0206] When it is determined that the vessel 103 comprises undesirable particles (i.e drops of fluid in an empty vessel, air bubbles or unwanted particles in the substance), the measurement unit may send a control signal to a controller to cause a valve to open or a pump to operate and remove a volume of substance from the vessel until the measured signal returns to a stable level with no spikes.

[0207] The embodiment of Figs. 10a and 10b are additionally of use in medical equipment where the presence of contamination and / or bubbles can be used to sound an alarm or shut off the equipment.

[0208] Fig. 10c shows an example of a water droplet running down an empty (air containing) vessel (in this case a tube). From t1 to t2 there is a baseline voltage representing the capacitance of an air filled tube. At t2 the voltage rapidly increases over short time before returning to baseline at t3. The period t2-t3 corresponds to the water droplet moving through the tube where the electrodes are placed. Hence, a measurable change in the voltage signal indicative of the change in capacitance caused by the water droplet can be obtained.

[0209] Fig. 11 details method steps performed by the system of Fig. 10a and Fig. 10b according to an embodiment.

[0210] In Step S1101 , the measurement unit 104 measures a signal representing a change in a capacitance associated with a first electrode 101 in proximity to a first surface of a vessel 103, a second electrode 102 in proximity to a second surface of the vessel 103 and a substance within the vessel 103.

[0211] In Step S1102, the measurement unit 104 determines, based on the measured signal, a contamination of the vessel. In Step S1103, the measurement unit 104 sends a signal to a controller to actuate or inhibit movement of the undesirable particles from the vessel, by draining the vessel 103.

[0212] Fig. 12(a) is a schematic of a further sensor in accordance with an embodiment. Here, the equipment is tube 1201. Tube 1201 is a flexible tube which is used to transfer fluids, gases or the like in a chemical processing apparatus. The sensor 1203 comprises a support (which will be described in more detail with reference to fig. 12b. Support 1203 has a lid. A first electrode 1205 and a second electrode 1207 are provided on the lid. The first electrode 1205 and the second electrode 1207 positioned in such a way that the tube 1201 can be clipped between the two electrodes. In an embodiment, the two electrodes are shaped and spaced apart to hold the tube 1201 without any other clip or holder required, in other words, the profiles of the two electrodes are shaped to receive the tube 1201.

[0213] Fig. 12b shows a cross-section through the dotted line of Fig. 12a. Here, it can be seen that the tube 1201 is held between first electrode 1205 and second electrode 1207. A 1stcontact 1209 is made to first contact 1205. A second contact 1211 is made to second electrode 1207. The capacitance measurement is made using the first contact 1209 and the second contact 1211. The electrical signal is carried away from the first contact 1209 via first wire 1213 and from the second contact 1211 via the second wire 1215.

[0214] The above arrangement with the electrodes also serve to clip the tube into place means that there is not a need for a separate mechanism for holding the tube 1201 .

[0215] Fig. 12b shows a cross-section through support 1203 at the dotted line of fig 12a. The support comprises a base 1221 and a lid 1223 that fits on top of the base 1221 and cooperates with the base 1221 such that the box 1221 and lid 1223 are fixed to one another and can be installed in a chemical processing apparatus such that they do not come apart. The base 1221 is box -shaped and the lid 1223 forms the lid for the box. The base is split into 2 sections via tray 1225. Tray 1225 slots into the box into a first groove 1227 provided in the box. The tray 1225 divides the box into an upper section and a lower section. In this embodiment, a circuit board 1235, for example an Arduino, is provided in the lower section of the box whereas measurement electronics 1237 which allow the capacitive signal to be read provided above the tray 1225 in the upper section. The lid 1223 fits onto the base 1221. As the base is provided with a groove 1229 and the lid is provided with a lug, ridge or projection 1231 which fits into the groove 1229.

[0216] The two (pair of) electrodes 1205 and 1207 may be of any shape. As noted above, in an embodiment, the pair of electrodes are configured to hold the tube. Any arrangement may be provided which allows the tube to be held, for example, the pair of electrodes are shaped to form a gap therebetween which receives the tube 1201 . The entrance to the gap is narrower than the tube 1201 such that the tube is flexed to be fitted into the gap, but is then prevented from detaching from the electrode due to the narrower entrance gap.

[0217] In an embodiment, a holder is provided to receive the tube 1201 and the electrodes are provided as a tape on the surface of the holder which receives the tube 1201. An electrical connection can be made to the electrodes via a screw or other conductive material which extends through the holder.

[0218] Fig. 13 shows a perspective of the support 1203. The support is again shown as a box 1221 with a lid 1223. The box 1221 houses an integrated circuit 1235 at its base. On the right-hand side of the box openings 1251 can be seen to allow power to be provided to the circuit 1235 and signals to be provided to and from the circuit 1235. (Although not shown, electrical contact may also be provided to the measurement electronics 1237 via openings 1251). Groove 1227 is shown extending along an elongate edge of the box 1221 . Tray 1225 is inserted into groove 1227 at the far end of the box and located within the groove 1227. This allows the tray to be provided above the integrated circuit 1235 to support further electronics, for example, the measurement readouts for the capacitor electrodes (not shown). In this embodiment, the tray extends partially along the length of box 1221 , but in some embodiments, it might extend the entire length of the box 1221 . Second groove 1229 is provided parallel to first groove 1227 and further away from the lower section of box 1221. The second groove 1229 is provided to receive lug, projection or ridge 1231 which is provided on a lower edge of the lid 1223. Lug 1231 is configured to couple to second groove 1229 which allows the lid to be slideably coupled with box 1221.

[0219] A gap 2143 is provided in groove 1229 and also a gap 1241 is provided in the centre of lug 1231 along the edge of the lid. This arrangement allows the lid 1223 to be slid onto and coupled to the box 1221 by engaging a first part of the lug 1245 in gap 1243 and then sliding it along once the lug starts to cooperate groove 1229.

[0220] Thus, in order to remove the lid 1223 are from the box 1221 , it is only necessary to slide the lid 1223 part of the way along box 1221 as opposed to fully along the length of the box 1221 . In other embodiments, the lid 1223 and the box 1221 could be a hinged or a clip connection.

[0221] This allows the box 1221 to be installed in tight spaces while still allowing removal of the lid 1223 in order to allow maintenance with the box in-situ. In the arrangement of Fig. 13, the gap 1241 allows the lid 1223 to be installed halfway along the box 1221. However, other arrangements are possible. For example, there may be multiple gaps in the lug 1231 and the groove 1229 which allow the lid 1223 to be affixed to box 1221 requiring only a minimal gap around the box to allow removal and reattachment of the lid 1223. In this arrangement, the lid would only need to slide a fraction of the length of the box 1221 in order to be removed.

[0222] The above arrangements, there are 2 electrodes. However, a further embodiment is shown in Figs. 14a and 14b. To avoid any unnecessary repetition, like references will be used to denote like features. In the arrangement of Fig. 14a, there is a single electrode 1206 which holds tube 1201. The single electrode partially extends around tube 1201. Single electrode 1206 is shown in more detail in Fig. 14b. Here, it can be seen that there is a single electrode with a gap which is capable of receiving and holding the tube 1201. For example, as shown in Fig. 14b, the cross-section of the gap in electrode 1206 is circular and extends beyond the midpoint of the tube to allow the tube 1201 to be firmly held. As there is a single electrode, only a single contact 1212 is required to the single electrode 1206.

[0223] In this example, the liquid in tube 1201 acts as the second electrode. Thus, the liquid in the tube 1201 acts like an electrode that permanently replenishes itself and discharges. In the example of Fig. 12a, the two electrodes 1205 and 1207 are two plates of a capacitor which charge up. This can be thought of as a static assembly. In the arrangement of Fig. 14a, there is a single electrode 1206 which attempts to charge any liquid in the tube 1201. Any charge in the liquid dissipates with the physical movement of the liquid. When the liquid acts as an electrode it forms a dipole moment arrangement that disappears physically as the liquid flows through the tube.

[0224] The arrangement of Fig. 14a where there is a single fixed electrode can be used in all of the cases explained above for two electrodes, i.e. a substance level sensor; a phase separation sensor; a contamination sensor; or a suspended particle sensor. The single fixed electrode may be of any shape. As noted above, in an embodiment, the single fixed electrode is configured to hold the tube. Any arrangement may be provided which allows the tube to be held, for example, the electrode is shaped to form a gap which receives the tube 1201. The entrance to the gap is narrower than the tube such that the tube is flexed to be fitted into the gap, but is then prevented from detaching from the electrode due to the narrower entrance gap.

[0225] The arrangement of Figs. 12a to 14b provides a measurement unit which can be connected to a tube anywhere within a system by fixing a tube between the two electrodes or inserting the tube into a single electrode which is shaped to receive a tube. The box can be connected to an external power source or be provided with a battery so that it can be located without the need to accommodate cabling from an external power source.

[0226] The above discussion has considered the sensor applied to a vessel which contains a chemical substance or a conduit for a chemical substance such as a tube. Throughout the embodiments, a vessel 103 may be an entire vessel or part thereof. For example, the vessel 103 may be an entire length of tube, or only a section thereof. The arrangement of Fig. 14a and b can be used with larger vessels as well as for a tube.

[0227] Any measurements indicated throughout the description or in the figures are for only example purposes, and other dimensions may be used.

Claims

1. CLAIMS:1 . A fluid processing apparatus comprising: a first piece of equipment, the equipment being selected from vessels for holding chemical substances and conduits for allowing flow of fluids; and a capacitance sensor, wherein the capacitance sensor comprises: an electrode assembly provided on a surface of the equipment; and a measurement unit electrically connected to the electrode assembly, the measurement unit being configured to: measure a signal representing a change in a capacitance associated with the first electrode and the substance; and determine, based on the measured signal a change in the substance in the first piece of equipment.

2. A fluid processing apparatus according to claim 1 , wherein the electrode assembly comprises a pair of electrodes configured located on either side of the equipment.

3. A fluid processing apparatus according to claim 1 , wherein the electrode assembly comprises a pair of electrodes configured located on the same side of the equipment.

4. A fluid processing apparatus according to claim 1 , wherein the electrode assembly consists of a single electrode.

5. A fluid processing apparatus according to any preceding claim, wherein the determined change in the substance comprises a change in volume of the substance in the equipment or a change in the substance from a first substance to a second substance.

6. A fluid processing apparatus according to any preceding claim, the measurement unit further configured to: based on the determined change, send a control signal to a controller, to actuate or inhibit movement of the substance to or from the first piece of equipment.

7. A fluid processing apparatus according to any preceding claim, wherein to determine, based on the measured signal, the change in the substance or mixture of substances, the measurement unit is configured to: compare the measured signal with a reference signal, wherein the reference signal indicates a desired amount of the substance to be held in the equipment.

8. A fluid processing apparatus according to any preceding claim, the measurement unit further configured to: based on the determined change, send a control signal to a controller, to actuate or inhibit movement of a cleaning fluid to or from the vessel.

9. A fluid processing apparatus according to claim 8, wherein to determine, based on the measured signal, the change in the substance or mixture of substances comprises: comparing the measured signal with a reference signal, wherein the reference signal is a baseline signal, the baseline signal obtained by the measurement unit when the vessel does not comprise the substance.

10. A fluid processing apparatus according to any one of claims 1 to 6, wherein to determine, based on the measured signal, the change in the substance comprises: determining a change in the substance from a first substance to a second substance based on a change in the measured signal.

11. A fluid processing apparatus according to claim 10, wherein the change in the measured signal comprises a magnitude of the measured signal changing from a first magnitude to a second magnitude.

12. A fluid processing apparatus according to claim 10 or claim 11 , wherein the piece first equipment is a tube configured to be fluidly connected between a mixture vessel and a sample vessel, the mixture vessel comprising an outlet valve connected to the tube, the mixture vessel configured to contain at least two immiscible liquids comprising the first substance and the second substance, the first substance, the vessel configured to move the first substance from the mixture vessel to the sample vessel, the measurement unit further configured to:based on determining the change from the first substance to the second substance, send the control signal to a valve controller to close the valve and inhibit movement of the second substance through the tube into the sample vessel.

13. A fluid processing apparatus according to any one of claims 1 to 6, wherein to determine, based on the measured signal, the change in the substance comprises: identifying a suspended particle or bubble in the substance based on a change in the measured signal, wherein the change in the measured signal comprises a spike in the measured signal that exceeds or falls below a given threshold.

14. A fluid processing apparatus according to any one of claims 6 to 13, wherein the controller is a pump controller or a valve controller.

15. A fluid processing apparatus according to any preceding claim, the measurement unit further configured to: based on the determined change, send an alert signal to a user.

16. A fluid processing apparatus according to claim 15, wherein the alert signal indicates the equipment needs to be replaced or cleaned, that the equipment is contaminated, that the equipment does not comprise a desired volume of the substance, or that the substance comprises a suspended particle or bubble.

17. A fluid processing apparatus according to any preceding claim, the measurement unit comprising: a microprocessor comprising a first input / output (IO) pin, a second input / output (IO) pin and a ground pin; a resistor coupled between the first IO pin and the first electrode, the second electrode coupled to the ground pin; and a reference capacitor coupled between the first IO pin and the second IO pin; the microprocessor configured to: at a first time, cause the reference capacitor and the capacitor formed between the first electrode and the second electrode to discharge; at a second time, cause the capacitor formed between the first electrode and the second electrode to charge;at a third time, cause the capacitor formed between the first electrode and the second electrode to discharge into the reference capacitor; and at a fourth time, measure a voltage across the reference capacitor.

18. A fluid processing apparatus according to any preceding claim, wherein the first piece of equipment is a tube and the electrode assembly is provided as a clip for the tube.

19. A fluid processing apparatus according to any preceding claim, wherein the measurement unit is located in a box and the electrode assembly is provided in a surface on said box.

20. A capacitance sensor for a fluid processing apparatus, the chemical processing apparatus comprising at least one tube, the capacitance sensor comprising an electrode assembly; and a measurement unit electrically connected to the electrode assembly the measurement unit being configured to: measure a signal representing a change in a capacitance associated with the electrode assembly, wherein the measurement unit is provided in a casing connected to the electrode assembly and the electrode assembly is provided as a clip to receive a tube of the chemical processing apparatus.21 . A method of sensing a substance in a first piece of equipment comprising: measuring, by a measurement unit, a measurement signal representing a change in a capacitance associated with an electrode assembly, the electrode assembly configured to be placed in proximity to at least one surface of the first piece of equipment; and determining a change in the substance in the first piece of equipment based on the measured signal.

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