Monitoring a flow of a powder suspended in a fluid

Abstract

A method (100) of monitoring a flow of a powder (3) suspended in a fluid (7) through a section of pipe (5), the method (100) comprising: emitting a light signal (102) across the flow of powder (3); detecting the light signal (104) on an opposing side of the flow of powder (3), and generating an electrical signal (106) representative of the detected light signal as a function of time; dividing the electrical signal (108) into a plurality of windows (43); for at least some of the windows (43): converting the signal data to the frequency domain (110); determining one or more characteristics of the signal data (112) in the frequency domain; and determining flow properties of the powder (114) from the one or more characteristics of the signal data in the frequency domain.

Description

[0001] MONITORING A FLOW OF A POWDER SUSPENDED IN A FLUID

[0002] The present disclosure relates to a method of monitoring a flow of a powder suspended in a fluid through a section of pipe, a device for measuring flow of a powder suspended in a fluid and pipe arrangements and sections in which such measurements can take place.

[0003] Powdered substances are used in a wide variety of different processes including, but not limited to, production of substances in the healthcare, food and pharmaceutical industries. In such processes, it is often necessary to verify that powder is flowing as expected and required. It is also desirable to determine various features of the flow of powder and the powder itself, along with identifying if faults occur.

[0004] The accurate measurement of mass flow rate or distributions of powder in a pipe is a technically challenging area. To avoid any measurement interfering with the flow of powder, and to avoid contamination of the powder, inferential or non-contact sensing is often used to measure the mass or volume of powder being moved. Together with knowledge of the particle velocity, this can provide information on the flow rate.

[0005] Furthermore, there can be a number of different types of flow in a conveying system. Typically, powders are considered to be in either the dilute phase or dense phase. The dilute phase occurs when the materials are conveyed at relatively high velocities, and the particles are suspended in a carrier fluid / gas. The dense phase occurs at relatively low velocities, in which the material moves through the pipe in “slugs” of accumulated material at bulk density, with pockets of carrier gas between the slugs. Powders moved by pneumatic transfer or under gravity are typically in the dilute phase.

[0006] The type of powder can also affect the flow characteristic. Microcrystalline cellulose (MCC) powder is generally free flowing, whilst powder such as milk protein concentrate (MPC) is more cohesive, resulting in agglomeration of powder in the flow.

[0007] Examples of non-contact inferential sensing methods used include electrostatic sensors, capacitive sensors, acoustic sensors (active or passive), electromagnetic sensors, laser doppler anemometry and particle image velocimetry. In all of these examples, fouling of the measurement probes (or the windows through which the measurement probes measure the powder) frequently occurs which is problematic for the measurement. Fouling is a commonly occurring and an expected occurrence in powder conveying systems.

[0008] Low signal-to-noise ratios in electrostatic and electrical capacitance sensors make them difficult to implement for dilute phase flows. Electrical and capacitance sensors are also sensitive to ambient factors such as moisture content, particle size and the chemical composition of the solid phase.

[0009] Noisy processing environments, such as manufacturing plants, can make the use of acoustic sensors difficult. In addition, active ultrasonic sensors (that send and then receive a corresponding attenuated acoustic signal) require fine tuning to achieve efficient operation for the particular particle sizes being measured, and several transducers are also needed to interrogate the cross section of a pipe.

[0010] The measurement of attenuated or scattered incident light intensity in the visible region can be used to determine the average solids concentration and does not have all of the drawbacks discussed for the techniques discussed above. However, such sensors typically require extensive calibration against known mass flow rates. Furthermore, fouling of the sensors is also still a problem.

[0011] According to a first aspect of the invention, there is provided a method of monitoring a flow of a powder suspended in a fluid through a section of pipe, the method comprising: emitting a light signal across the flow of powder; detecting the light signal on an opposing side of the flow of powder, and generating an electrical signal representative of the detected light signal as a function of time; dividing the electrical signal into a plurality of windows; for at least some of the windows: converting the signal data to the frequency domain; determining one or more characteristics of the signal data in the frequency domain; and determining flow properties of the powder from the one or more characteristics of the signal data in the frequency domain.

[0012] The one or more characteristics of the frequency domain signal may include one or more of: the root mean square or average signal level; average frequency of the signal; magnitude and / or frequency of peaks; frequency at which the largest peak occurs; ratio of the power of the signal to the power of the noise; and integral of the signal.

[0013] Flow properties relate to the behaviour of the powder suspended in the fluid as a collective or bulk, as opposed to properties of individual particles.

[0014] The flow properties may include one or more of: the presence or absence of a flow; mass flow rate of the powder; flow stability; a fault in a powder distribution system including the pipe; moisture content; flow index; particle size distribution; bulk density changes; and powder accumulation in a powder distribution system including the pipe.

[0015] The one or more characteristics of the signal may include the root mean square or average signal level. Mass flow rate of the powder may be determined based on the root mean square or average signal level.

[0016] The one or more characteristics of the signal may include the average frequency of the signal or frequency of the maximum peak in the signal. Flow stability may be determined based on the average frequency of the signal or the frequency of the maximum peak. Changes of the average frequency or the frequency of the maximum peak may indicate unstable flow.

[0017] The one or more characteristics may include an amplitude and / or frequency at which peaks of the signal frequency domain signal occur. Variation in the amplitude and / or frequency of the peaks may be indicative of a fault in a powder distribution system including the pipe.

[0018] The method may comprise: for at least some of the windows analysing the time domain signal. The flow properties of the powder may be determined from the combination of the one or more characteristics of the signal data in the frequency domain and the analysis in the time domain.

[0019] An absence of flow may be determined based on the combination of a low magnitude or no magnitude at which peaks of the frequency domain signal occur and low variance of the signal in the time domain. The light signal may be generated by a light source having a variable intensity. The method may comprise: at a first time, determining a threshold detected signal associated with a first light intensity of the light source; at a second time, determining a second light intensity of the light source required to measure the threshold detected signal; and determining a change in the accumulation of powder on an interior of the pipe based on a variation between the first light intensity and the second light intensity.

[0020] The threshold detected signal associated with a first light intensity of the light source may be determined when the pipe is clean of any accumulation.

[0021] The method may comprise: determining information about the powder based on the variation between the first light intensity and the second light intensity.

[0022] The method may comprise: monitoring the one or more flow properties of the powder; and if at least one of the one or more flow properties crosses a predetermined threshold, triggering an alarm.

[0023] The light signal may be in the visible range of wavelengths.

[0024] The fluid may be selected from: air; inert gas; non-inert gas; a liquid.

[0025] According to a second aspect of the invention, there is provided a measurement system for measuring flow of a powder suspended in a fluid, the measurement system comprising: a pipe section arranged to carry a powder suspended in a fluid along a length of the pipe; a light source arranged to emit a light signal into the pipe section across a flow of the powder; a detector arranged to detect light from the light source across the pipe section, arranged to detect the light signal emitted by the light source and generate an electrical signal representative of the detected light signal as a function of time; and a controller configured to: divide the electrical signal into a plurality of windows; for at least some of the windows: convert the signal data to the frequency domain; determine one or more characteristics of the signal data in the frequency domain; and determine flow properties of the powder from the one or more characteristics of the signal data in the frequency domain.

[0026] The controller may be configured to perform the method of the first aspect. The light signal may be in the visible range of wavelengths.

[0027] The fluid may be selected from: air; inert gas; non-inert gas; a liquid.

[0028] The pipe section may comprise: a housing defining a passage extending along a from a first end to a second end; a first pipe section extending along the same direction as the passage, a portion of the first pipe section received in the first end of the passage; a second pipe section extending along the same direction as the passage, a portion of the second pipe section received in the second end of the passage; a transparent section received in the passage, between the first pipe section and the second pipe section, the first pipe section, second pipe section and transparent section forming a continuous passage through the housing; wherein the light source and detector are received in the housing, between the housing and the transparent sleeve, aligned with the transparent section along the length of the passage.

[0029] The pipe section may include clamping means to secure the housing to the first and second pipe sections, such that the transparent section is held in place between the first and second pipe sections.

[0030] The clamping means may comprise flanges formed on an exterior of the first and second pipe sections. The housing may extend between the flanges, such that the flanges are outside the passage formed in the housing and the housing is clamped to the flanges.

[0031] The continuous passage may have a constant diameter along its length.

[0032] The measurement system may comprise sealing means provided between the first and second pipe sections and the transparent section.

[0033] According to a third aspect of the invention, there is provided a pipe arrangement comprising: a housing defining a passage extending along a length from a first end to a second end; a first pipe section extending along the same direction as the passage, a portion of the first pipe section received in the first end of the passage; a second pipe section extending along the same direction as the passage, a portion of the second pipe section received in the second end of the passage; a transparent section received in the passage, between the first pipe section and the second pipe section, the first pipe section, second pipe section and transparent section forming a continuous passage through the housing; a light source received in the housing, aligned with the transparent section along the length of the passage; and a detector received in the housing, aligned with the transparent section along the length of the passage, the detector arranged to detect light from the light source, and monitor attenuation of the light source to detect flow of powder.

[0034] The passage defined by the housing may be colinear with the continuous passage.

[0035] The continuous passage may have a constant diameter along its length. Alternatively, the continuous passage may have a varying diameter along its length.

[0036] The continuous passage may be circular in cross section.

[0037] The pipe section may include clamping means to secure the housing to the first and second pipe sections, such that the transparent section is held in place between the first and second pipe sections. The clamping means may comprise flanges formed on an exterior of the first and second pipe sections. The housing may extend between the flanges, such that the flanges are outside the passage formed in the housing and the housing is clamped to the flanges.

[0038] The first and second pipe sections may connect to the transparent section at respective first and second ends, wherein the first and second flanges are spaced from the respective first and second ends.

[0039] At least one of the clamping means may be a tri-clamp.

[0040] Sealing means may be provided between the first and second pipe sections and the transparent section. The first and second pipe sections and / or the transparent section may comprise seats for locating the sealing means. The sealing means may be at least one of: i) an O-ring; or ii) a gasket. The housing may comprise one or more connectors configured to provide power and / or data communication between the light source and the light detector to components external to the pipe arrangement.

[0041] The transparent section may be formed of or comprise glass.

[0042] The light source may be configured to produce a light signal having a variable intensity.

[0043] The light source may be configured to produce a light signal in the visible range of wavelengths.

[0044] The pipe arrangement of the third aspect may be used to measure flow properties of powder passing through the pipe according to the method of the first aspect. The pipe arrangement may form the pipe section used in the second aspect.

[0045] The inventors of the current application have realised that the frequency characteristics of the measured signal are not affected by window fouling. Therefore, the use of signal characteristics in the frequency domain allows for a robust signal to be captured, even with the sensor window is fouled, and provides reliable measurements over long periods.

[0046] The method and device provide a simple system using visible light that is easy and low cost to set up and maintain, requires minimal calibration, and does not require any regular cleaning of the window. The method and device are suitable for any type of powder flow, without requiring complicated and expensive equipment.

[0047] The pipe arrangement of the third aspect provides an apparatus in which the measurement and device in the first and second aspect can be provided, and which helps provide a reliable measurement over a long period of time whilst protecting the sensor and light source from the powder flow itself. Since the internal surface of the passage is constant diameter and uninterrupted along the length of the pipe arrangement, there is minimal disruption caused to the powder during measurement.

[0048] According to a fourth aspect of the invention, there is provided a pipe section formed of a boundary wall defining a passage extending along a first axial direction, the pipe section having: an inlet arranged to couple to an upstream pipe section, the inlet having a first cross-sectional shape and a first cross-sectional area; an expanded portion having a second cross-sectional shape different to the first cross-sectional shape, and a second cross-sectional area larger than the first cross-sectional area; an outlet arranged to couple to a downstream pipe section, the outlet having a third cross-sectional shape and a third cross-sectional area; a first connecting portion coupling the inlet to the expanded portion, wherein along an axial length of the first connecting portion the cross-sectional area of the pipe expands from the first cross-sectional area to the second cross-sectional area; and a second connecting portion coupling the expanded portion to the outlet, wherein the expanded portion includes: a first planar surface extending parallel to the axial direction on a first side of the passage, the first planar surface including a first aperture; a light source positioned in the first aperture such that a front surface of the light source is flush with the first planar surface; a second planar surface spaced from and parallel to the first planar surface, on an second side of the passage, opposite the first side, the second planar surface including a second aperture; and a light detector positioned in the second aperture such that a front surface of the light detector is flush with the second planar surface, the light detector arranged to detect signals emitted by the light source.

[0049] The pipe section of the fourth aspect may be used to measure flow properties of powder passing through the pipe according to the method of the first aspect. The pipe section may form the pipe section used in the second aspect.

[0050] By making the sensors flush with the interior surface of the passage, and by using planar walls rather than curved walls, scattering of the light signal is reduced.

[0051] The first and third cross-sectional areas may be the same or different The first and third cross-sectional shapes may be the same or different.

[0052] The expanded portion may comprise a plurality of planar surfaces, such that the second cross-section is polygonal. Preferably, the second cross-section is square.

[0053] The cross-section of the connecting portions may be the same as the expanded portion. The connecting portions may be made of planar surfaces angled towards / away from the axial direction. The ends of the planar surfaces at the inlet and / or outlet may be shaped to mate with the first / third cross-sectional shapes.

[0054] The light source and detector in the pipe section may be used to implement the flow measurement system.

[0055] It will be appreciated that any feature discussed in relation to a particular aspect may be applied to any other aspect, unless mutually exclusive.

[0056] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0057] Figure 1 schematically illustrates a measurement system according to a first embodiment, for measuring powder flow;

[0058] Figure 2 illustrates a flow chart for a method of measuring powder flow using the system of Figure 1;

[0059] Figure 3 illustrates the electric signals generated by the detector of the system of Figure 1, as a function of time, for different types of powder in the absence of light intensity adjustment;

[0060] Figure 4 schematically illustrates a signal generated by the detector of the system of Figure 1, as a function of time;

[0061] Figure 5A illustrates the frequency domain signals for a single window, for different types of powder;

[0062] Figure 5B illustrates the frequency domain signal for different types of powder, for a series of windows;

[0063] Figure 5C illustrates the ASL of a frequency domain signal, overlaid on the mass flow rate;

[0064] Figure 5D illustrates the Av Freq of a frequency domain signal, overlaid on the mass flow rate;

[0065] Figure 6 illustrates the signal in the time domain and frequency domain, and the mass flow rate, when the flow rate is changed between flow and no flow;

[0066] Figure 7 schematically illustrates a method for determine the amount of powder accumulation, using the system of Figure 1;

[0067] Figure 8 illustrates a pipe arrangement for implementing the flow measurement system of Figure 1, in sectional view; Figure 9 illustrates an alternative pipe section for implementing the flow measurement system of Figure 1, in sectional view; and

[0068] Figures 10A to 10E illustrate the signals measured for different powder over time, using the system of Figure 1.

[0069] Figure 1 schematically illustrates a measurement system 1 for measuring the flow rate and other properties of the flow of a powder 3 in a powder distribution system. Typically, powder is fed through a powder distribution system from a hopper, having a feeder screw used to expel powder from the hopper. An agitator may also be used to break up powder in the hopper. Both the feeder screw and agitator rotate or are operated at characteristic frequencies.

[0070] The powder distribution system makes use of hygienic stainless-steel pipes, with long or short radius bends to convey powders 3. The powders 3 are typically fluidised in a fluid 7 such as air, and conveyed under, for example, pneumatic pressure.

[0071] Figure 1 shows a short straight section of pipe 5, in which powder 3 is conveyed in the direction shown by the arrows. The pipe 5 can be connected into a powder conveying system using any suitable connecting means.

[0072] The pipe 5 is formed by an outer wall 9. To measure and characterise the flow of powder 3 through the pipe section 5, the outer wall 9 is provided with apertures 11, 13 arranged at diametrically opposed positions around the circumference of the pipe 5. At a first aperture I l a visible light source 15 is provided, and a corresponding detector 17 is provided at the second aperture 13.

[0073] To avoid contamination of the powder 3 and / or the light source 13 and detector 15, the apertures 11, 13 may be closed by a material 19 that is transparent to the light emitted by the light source. This may be formed as part of the pipe 5, or part of the light source 15 and detector 17. Various arrangements for implementing the measurement system 1 will be discussed in more detail below.

[0074] Generally, light is emitted from the source 15 and detected by the detector 17. On receiving a light signal, the detector 17 generates an electrical signal with voltage or current proportional to the magnitude of the detected signal. As will be discussed in more detail below, the attenuation of the light from the light source 15 is analysed to derive various properties of the flow of powder 5.

[0075] A controller 21 is provided to control operation of the light source 15 and detector 17 and process the output from the detector 17.

[0076] The controller 21 includes drivers 23a, b for communicating with, controlling and reading the light source 13 and detector 17. A processor 25 is also provided, along with a memory 27.

[0077] The memory 27 includes a programme storage portion 29 and a data storage portion 31. The programme storage portion 29 includes instructions 33 which, when performed by the processor 25, implement the methods discussed below. The data storage portion 31 includes calibration data 35 and other stored data such as threshold, and previously measured data.

[0078] A user interface 37 is also provided to allow a user to monitor the operation of the system 1, and control / programme various aspects of the system 1. The user interface may be accessible remotely, for example via the internet.

[0079] The drivers 23a, b, processor 25, memory 27 and user interface 37 are all in communication via a bus 39. Any suitable communication protocol(s) can be used within the controller 21 and between the controller 21 and the light source 15 and detector 17.

[0080] A method 100 of detecting the flow rate and other properties of the flow through the pipe 5 will now be discussed with reference to Figure 2.

[0081] In a first step 102, a light signal is emitted by the light source 15. It will be appreciated that to allow continual monitoring of the flow rate and other properties, the light signal is emitted continually. This may be a constant output, or a pulsed output or any other suitable output. In a second step 104, the light signal is detected at the detector 17. This is then converted into an electrical signal in a third step 106. The electrical signal is provided to the controller 21 for processing.

[0082] The detected signal is recorded at a chosen sampling rate, resulting in a time series of voltage values. In one example, the voltage may be measured every 0.002 (sampling frequency 500Hz), however, any suitable frequency may be used.

[0083] Figure 3 illustrates an example of the raw voltage signal 41a detected for MCC powder in the upper panel, and an example of the raw voltage signal 41b detected for MPC powder in the lower panel. It will be appreciated that these signals are provided for illustrative purposes only, and the shape of the signal is not limiting.

[0084] As can be seen, in both signals 41a, 41b there is a general trend in the voltage reducing. This is due to a reduction in the signal over time due to accumulation of powder on the wall 9 of the pipe section 5. This accumulation partially obscures the light source 15 and / or detector 17.

[0085] Figure 4 schematically illustrates an example of the time series of the measured voltage values Vi-n.

[0086] In a next step 108 of the method 100, the voltage signal is divided into separate windows 43, each window 43 comprising a plurality of voltage values. Each window may have any suitable duration. In the example shown, each window comprises four measurements, but this is only for illustration purposes. For example, each window may be between 5 and 60 seconds in length. In this case (with sampling frequency of 500Hz), the window may contain between 2,500 and 30,000 voltage values.

[0087] In the example shown, the windows 43 overlap. Again, this is by way of example only, and the windows 43 may not overlap, or may have any suitable overlap.

[0088] In the following steps, each window 43 of the signal is processed separately. The processing may proceed down two branches, in the first branch, the signal is converted to the frequency domain. In the second branch, the signal is analysed in the time domain. In the first branch, the time domain signal in each window 43 is converted to the frequency domain at step 110. This is done by a Discrete Fourier transform (DFT) given by equation 1 :

[0089] Where x(k) is the signal in the frequency domain, x(n) are the voltage values of the signal in the time domain for a window (where a window has n values), and j is the root of -1. The result of the transform is a data series of amplitudes at a series of frequency values.

[0090] Figure 5A illustrates an example of the frequency domain signal 45a derived from a single window for MCC powder (upper window) and the frequency domain signal 45b derived from a single window for MPC powder (lower window).

[0091] In addition, Figure 5A shows markers at the operation frequency of screw and its harmonics 47a and also at harmonic frequency 49 of the agitator as reference values (the agitator operates at very low frequency, so only the harmonic is shown).

[0092] As can be seen from Figure 5A, both types of powder have peaks aligned with the operational frequency of the screw and its harmonics. The MCC powder also shows a frequency signature that is aligned with the harmonic of the agitator frequency.

[0093] The feeder screws are directly responsible for dosing the powder into the powder distribution system and across the detector 17. The presence of a frequency signal aligned with the agitator harmonic when feeding MCC but not MPC, means that the agitator has an influence on how the screws are fille for MCC but not for MPC.

[0094] Figure 5B illustrates the frequency domain signal plotted for a series of windows (i.e. as a function of time) for MCC (upper panel) and MPC (lower panel) for consistent feeding into the system.

[0095] The data in the frequency domain shows the presence of mostly stable peaks for both MCC and MPC powder despite the time domain data indicating a trending or moving baseline (see Figure 3). This shows that the frequency domain data is unaffected by the accumulation of powder, which causes drift in the time domain data. At a next step 112 of the method 100, various characteristics of the frequency domain signal are determined and then at step 114, properties of the powder flow are determined from the characteristics of the frequency domain signal.

[0096] In the second branch the signal in the time domain is characterised at step 116, and then flow state indicators are derived from the characteristics in the time domain at step 118. In a further step 120, further information on the flow is derived from the combination of the time domain and frequency domain statistics.

[0097] A first characteristic determined from the frequency domain signal 45 is the average signal level (ASL), also referred to as the root means square of the signal. This is given by: n is the number of frequency values in the data series forming the frequency domain signal. Xi is the magnitude of the frequency for each of the n frequency values.

[0098] On assembly, servicing or refitting of the powder distribution system, the ASL can be calibrated to provide a measure of the mass-flow rate assuming that the frequency at which powder passes the detector does so with a consistent mass. By way of example only, Figure 5C illustrate the ASL overlaid on the same plot as the mass flow rate determined by other means. This shows the two overlie each other and thus the ASL can be used to determine the mass flow rate.

[0099] A second characteristic determined from the frequency domain signal 45 is the average frequency (Av Freq). This is given by:

[0100] As discussed above, n is the number of frequency values in the data series forming the frequency domain signal. Where f is the frequency of each data point in the series, and Pi is the corresponding magnitude at that frequency.

[0101] Monitoring changes in Av Freq provides information on flow stability. By way of example only, Figure 5D illustrate the Av Freq overlaid on the same plot as the mass flow rate. As can be seen, even though the mass flow rate changes, the Av Freq remains constant, indicating a stable flow. In general, where Av Freq does not vary, the flow is stable, whilst changes in Av Freq indicates unstable in flow. The integral of the signal in the frequency domain can also be used to provide information on flow stability.

[0102] By combining statistical analysis across both the time and frequency domains, it is possible to detect instances when powder is flowing and when it is not flowing.

[0103] Figure 6 shows the feeding of a free-flowing grade of lactose powder into a pipe 5. The flow rate is deliberately varied. The top panel shows the electric signal 51 generated by the sensor as a function of time. The middle panel shows the known mass flow rate 53 and also artefacts 47b resulting from the screw moving from closed loop control of mass flow rate to open loop control. The lower panel shows the frequency domain signal 55 measured at different frequencies as a function of time.

[0104] At times where there is zero mass flow, the signal measured in the time domain has low variance (less noisy), and a low magnitude is measured in the frequency domain signal 55. Therefore, where flow frequency magnitude is very low or the flow frequency is not detected AND a reduced variance of the time signal persists, zero mass flow is detected.

[0105] As discussed above, powder can accumulate in the pipe 5, resulting in the light source 15 and / or detector 17 being partially obscured and causing drift in the time domain signal. Figure 7 illustrates a method 200 of using the measurement system 1 discussed above to determine a relative level of accumulation. With calibration of the system, this can be converted into an absolute measurement.

[0106] In a first step 202, a measurement of an output intensity of the light source 15 required to achieve a reference signal level at the detector 17 is measured. In one example, this may be measured when the pipe 5 is clean, with no accumulation.

[0107] At a next step 204, the process of determining the intensity required to achieve the reference signal level at the detector 17 is repeated. This second step 204 is performed at a different time to the first step 202. By taking the difference between the intensity at the first step 202 and the intensity at the second step 204, a relative degree of powder accumulation can be determined at step 206. The higher the intensity required to obtain the reference signal level at the detector 17, the more likely it is that powder 3 is accumulating mass at the light source 15 and / or detector 17, or in the system overall.

[0108] This step 204 of redetermining the intensity required to achieve the reference signal level at the detector 17 is repeated at a desired frequency. The change in intensity required to achieve the reference signal level at the detector 17 is referred to as the Powder Accumulation Offset (PAO).

[0109] Stable values for the PAO represent stable steady state conditions of the powder flowing in the pipe 5. Where the PAO trend upwards over time this is expected to result in greater fouling at the light source 15 or detector 17. This in turn provides indirect information about the properties of the powder being processed, e.g. moisture content or ‘stickiness’, static charge on the powder.

[0110] The analysis of the raw sensor signal over time (e.g. the PAO) combined with analysis in the frequency domain can also enable the detection of process anomalies.

[0111] One anomaly that can be detected is unexpected changes in feeder screw speed. As discussed above, the signal in the frequency domain shows peaks at the rotation frequency of the screw (and its harmonics). Therefore, monitoring the frequency of the strongest peak in the frequency domain can provide information on the screw speed.

[0112] As powder from a source is consumed, the screw speed may vary. For example, as powder is used, the powered becomes less compacted, therefore the screw has less resistance, and so the speed may increase. Alternatively, if powder becomes more compacted, the screw speed may slow.

[0113] A relatively constant PAO compared to changes in the frequency of the strongest peak in the frequency domain may indicate changes in the screw speed.

[0114] On the other hand, the PAO value is increasing and the frequency of the strongest peak in the frequency domain changing (or is non-existent), assuming constant mass flow, may represent an instant where powder is accumulating in the line and pipe and hence is trending towards blockage. Using similar methods, the performance of the agitator can also be monitored in MCC powder flow, by monitoring the frequency of the peak associated with the agitator.

[0115] The monitoring of the screw and agitator is by way of example only. In general, when a powder distribution system is commissioned, the signal in the frequency domain can be analysed to identify peaks associated with different equipment used in the system. Any equipment which may control the flow of powder through the system will cause a peak in the frequency domain. Tracking the frequency where these peaks occur can track the operation of the equipment.

[0116] Intermittent blockages can also be detected by the measurement system 1 discussed above. As powder 3 is conveyed around pipes and bends, powder that is cohesive or which has high moisture content may adhere significantly to pipe walls 9 rather than lightly coat or dust the wall 9. As this powder adheres it may further restrict powder flow, leading to short lived plugging or intermittent blocking of the pipe 5. Release of this plug as powder build up cleaves off the inside of the pipe results in a distinct signal.

[0117] The dislodging of such intermittent blockages is identified by a step change in the sensor signal in the time domain. Therefore, monitoring the derivative of the sensor signal over time allows intermittent blockages to be identified (as peaks in the derivative). The frequency of such blockages forming and being cleared can thus also be monitored.

[0118] Monitoring of the attenuation of the signal can also provide information on the solids volume fraction of the powder. The maximum solids volume fraction, SVFmax is given by:

[0119] Where Pbuik is the poured bulk density (i.e. the density of solid transferred from the solid store) and ptrUe is the true density of the solid (the density of the solid without any air space between molecules).

[0120] The solids volume fraction can be measured by: Where I is the signal intensity (voltage), Io is signal intensity when the pipe is empty and Imin is when the pipe is filled.

[0121] Statistical analysis of the SVFmeas with time can be used as a direct means to quantify differences in the powder dispersion (or distribution). For example, MCC is characterised by a consistent volume fraction (pipe) occupancy whereas MPC is characterised by rapid intermittent interruption of the light. Therefore, the type of powder can be checked and anomalies spotted. For example, for MCC, which expects a consistent MVF, rapid intermittent interruption of the light (MVF oscillating with time) would indicate anomalous flow.

[0122] In a powder distribution system, the particle size distribution (PSD) is a measure of the different particle sizes in a powder. A narrow distribution indicates all the particles are of similar size, whilst a wide distribution indicates particles of lots of different sizes. In some cases, a PSD may even be bimodal (the PSD clearly has a large particle size fraction and a smaller or “fine” particle size fraction. The fine fraction is usually of a size < 50 pm).

[0123] The particle distribution can effect how the particle is conveyed and processed. For example, smaller particles can have significant impact on powder material properties such as moisture uptake, wettability, compressibility and the like.

[0124] Analysis of the measured signals can also provide detection of changes in the powder fine fraction content. For example, fine particle content in powders tend to scatter light more than larger particles.

[0125] The measurement system 1 can be calibrated to the fine powder content of the powder. This may correlate the mean or variance of the time domain signal to the fine fraction.

[0126] The controller 21 may monitor any of the parameters determined, and trigger an alarm or other notification if the pass a defined level or threshold.

[0127] In the example discussed above, the flow measurement system 1 is implemented in a pipe section 5 having apertures 11, 13 for the light source and light detector. The flow measurement system 1 may be implemented in any suitable pipe, and may be oriented vertically, horizontally, or at any other angle.

[0128] Figures 10A to 10E illustrate the signals measured for different powder over time, using a flow measurement system as discussed above. Over the period shown in Figures 10A to 10E, the flow rate is varied to show the change in signal, demonstrating that the signal can provide measurement of various flow characteristics.

[0129] Figure 10A shows the signal 501a from a sensor measuring the flow of a first free flowing lactose powder. The dashed line 503a shows the controlled flow rate of powder.

[0130] Figure 10B shows the signal 501b from a sensor measuring the flow of a second free flowing lactose powder. The dashed line 503b again shows the controlled flow rate of powder.

[0131] Figure 10C shows the signal 501c from a sensor measuring the flow of a cohesive lactose powder. The dashed line 503c shows the controlled flow rate of powder.

[0132] In each of Figures 10A to 10C, the x-axis is time, the left-hand y-axis is the voltage of the signal, and the right-hand y-axis is the mass flow rate of the powder.

[0133] As can be seen from Figures 10A to 10C, the variation on the signal increase with increasing flow rate.

[0134] By way of example, Figure 10D shows the cumulative mass flow throughput of powder 507 (left hand y-axis) through the pipe and the accumulate signal variance 509 (right hand y-axis). This shows the signal variance tracks with the mass flow rate.

[0135] Figure 10E shows the cumulative signal variance as a function of the total mass throughput for the first free flowing powder 511, the second free flowing powder 513 and the cohesive powder 515. This also shows the relationship between signal variance and mass flow.

[0136] Figures 10C also illustrates the effect of powder build up, even over a short period of 30 minutes, for the cohesive lactose powder, this is clearly demonstrated by the gradual decline of the baseline value of the signal, starting at the inflexion point 505 at around 20 minutes. The inflexion 404 is also visible in the plot of Figure 10E.

[0137] Figure 8 illustrates a first example of an alternative pipe arrangement 300 for implementing the measurement system 1 discussed above.

[0138] In this example, a feed-in pipe section 302 is provided to receive powder and a feed-out pipe section 304 is provided to couple to the downstream portion of the powder distribution system. The feed-in and feed-out pipe sections are coupled into the powder distribution system by standard means.

[0139] A transparent section 306 is provided between the feed-in pipe section 302 and the feed- out pipe section 304. The feed-in pipe section 302, transparent section 306 and feed-out pipe section 304 form a continuous passage 308 with circular cross section and constant internal diameter, through which powder flows.

[0140] A housing 310 with an internal passage 312 formed therein is also provided. The passage 312 extends along the length of the housing 310, and receives the transparent section 306, along with the ends 314, 316 of the feed-in pipe section 302 and feed-out pipe section 304 adjacent the transparent section 306. Therefore, the passage 312 in the housing 312 is colinear with the passage 308 formed by the feed-in pipe section 302, transparent section 306 and feed-out pipe section 304.

[0141] The light source 15 and detector 17 are received in the housing 310, aligned with the transparent section 306 along the length of the passage. The rest of the flow measurement system 1 may also be provided in housing 310, or some or all of the flow measurement system 1 may be outside the housing 310.

[0142] Where necessary, the housing 310 may include suitable connectors for power and / or data communication between the light source 15 and light detector 17 (and any portion of the flow measurement system 1 in the housing 308) to external components.

[0143] The feed-in pipe section 302 and feed-out pipe section 304 both have an annular flange 318, 320 spaced from the ends 314, 316 of the sections 302, 304, and the transparent section 306. The housing 310 extends along a length from the flange 318 on the feed-in pipe section 302 to the flange 320 on the feed-out pipe section 304.

[0144] In use, the pipe arrangement 300 is assembled by aligning the pipe sections 302, 304, transparent section 306 and housing 310. The housing 310 is then secured to the flanges 318, 320 by any suitable clamping means, such as tri-clamps (not shown). This holds the arrangement 300 together.

[0145] Optionally, seals 322 such as O-rings or other gaskets may be provided between the ends 314, 316 of the pipe sections 302, 304 and the transparent section 306, to ensure the passage 308 is fully enclosed. The pipe sections 302, 304 and / or the transparent section 306 may be provided with seats to locate the seals 322.

[0146] The pipe sections 302, 304 and housing 310 may be made of any suitable material for the environment they are to be used in. The transparent section 306 is made of glass or other transparent material.

[0147] In the example shown, the passage 308 through which powder passes is circular in cross section along its length, and has constant diameter. This is by way of example only. The passage 308 may have any suitable shape and the shape may be consistent along the length of the passage or may vary.

[0148] Likewise, the diameter of the passage 308 may vary along its length or be consistent.

[0149] Where the shape and / or size of the passage varies, this may be a step change within one of the pipe sections 302, 304 or transparent section 306, or between any two of the pipe sections 302, 304, or transparent section 306. Alternatively, the change may be gradual or tapered along one or more of the sections 302, 304, 306.

[0150] The housing 310 may have any suitable shape and size.

[0151] An alternative pipe section 400, which may be used to implement the flow measurement system is shown in Figure 9. Unlike the arrangement in Figure 8, this is a single section of pipe for coupling into a powder distribution system. The pipe section 400 comprises a boundary wall 402 that defines an enclosed passage 404 extending along an axial direction 406 from an inlet 408 to an outlet 410.

[0152] The inlet 408 and outlet 410 are circular in cross-section and shaped and sized for fitting into the powder distribution system in the normal manner pipes are connected together.

[0153] Between the inlet 408 outlet 410, an expanded portion 412 is formed. The expanded portion is square or rectangular in shape, having planar sides 414a-d extending parallel to the axial direction 406, forming the sides of the passage 404.

[0154] The expanded portion 412 has a large cross-sectional area than the inlet 408 and outlet 412, such that the inlet 408 and outlet 410 could be fitted within the expanded portion.

[0155] Connection portions 416, 418 are formed between the inlet 408 and outlet 410 and the expanded portion 412. The connecting portions 416, 418 taper outwards from the inlet 408 or outlet 410 to the expanded portion 412.

[0156] In the example shown, the connecting portions 416, 418 are the same cross section shape as the expanded portion, when viewed at a cross-section along the length of the passage. Therefore, the connecting portions 416 418 are formed by four planar walls 420a-d, 422a-d, arranged in square based pyramid shape, with the top truncated by the inlet 408 or outlet 410.

[0157] At the axial positions 424, 426 where the connecting portions 416, 418 meet the inlet 408 or outlet 410, the walls 420a-d, 422a-d forming the sides of the connecting portions 416, 418 are curved in a convex shape in the plane of the wall 420a-d, 422a-d to meet the inlet 408 and outlet 410.

[0158] In the expanded portion 412, a pair of apertures 428, 430 are formed an opposite sides 410a, 410c of passage 404. The two apertures 428, 430 are formed at the same axial position along the length of the passage 404.

[0159] The light source 15 is provided at the first aperture 428 and the detector 17 is provided at the second aperture 430. Side housing portions 432, 434 extend radially out from the pipe section 5, enclosing the electronics for the light source 15 and detector 17. The side housings 432, 434 may include additional electronic for the flow measurement system 1, or suitable connectors for coupling to external components, as with the example shown in Figure 8.

[0160] In one example, the front faces (not shown) of the light source 15 and detector 17 are arranged flush with the inner surface of the passage 404. Seals may be provided around the light source 15 and detector 17 to ensure the passage 404 is fully closed.

[0161] The pipe section shown in Figure 9 is given by way of example only. The pipe section may have any suitable size and shapes in the different sections.

[0162] For example, the inlet 408 and outlet 410 may be of different shape and / or size to each other.

[0163] The expanded section 412 may also have any suitable shape. For example, the expanded section may have any polygonal arrangement, with the apertures 428, 430 arranged on opposing planar sides.

[0164] Alternatively, the expanded sections may comprise first and second planar sides 414a,c arranged opposite each other with curved sides or any other shape joining the planar sides 414a, c.

[0165] In the example discussed above, the connecting portion 416, 418 have the same shape as the expanded portion. However, this is by way of example only. The connecting portions may have any suitable shape, and the inlet 408, outlet 410 and sides 414 of the expanded portion 412 may be shaped to mate with the connecting portions 416, 418.

[0166] In the examples shown in Figures 8 and 9 and discussed above, the pipe section / arrangement is arranged vertically. However, it will be appreciated that these pipe sections can be vertical, horizontal, or at any other angle.

[0167] In the examples shown in Figures 8 and 9 and discussed above, the flow measurement system is partially or wholly collocated with the pipe, or provided externally. As discussed above, connectors may be provided for connecting to external components. In other examples, wireless communications may be used to communicate to any part of the controller located externally.

[0168] In all the above examples, reference is made to a controller 21 having memory 27. It will be appreciated that the controller 21 and memory 27 may be provided in any suitable way, and may use distributed processing and / or memory. The software instructions may be stored in non-transient memory.

[0169] The above methods and systems can be used in any type of powder distribution environment. The systems and methods may work with any different type of powder, moved in any fluid. The powder may be moved pneumatically, under gravity or by any other means.

[0170] Various examples of characteristics of the signal in the time domain and frequency domain are given above, and various characteristics about the flow are also discussed, These are given by way of example only, and any suitable characteristics may be determined.

[0171] In the frequency domain, signal characteristics determined may include the root mean square or average signal level; average frequency of the signal; magnitude and / or frequency of peaks; frequency at which the largest peak occurs; ratio of the power of the signal to the power of the noise (the mean or median of the signal to the variance); and the integral of the signal.

[0172] In the time domain, signal characteristics determined may include mean, median, mode, standard deviation, interquartile range.

[0173] Characteristics of the flow that can be determined include: the presence or absence of a flow; mass flow rate of the powder; flow stability; and a fault in a powder distribution system including the pipe.

[0174] Further characteristics that can be determined indirectly are moisture content; flow index; particle size distribution; and bulk density changes. These changes are determined by detecting changes indicative of these characteristics. Any suitable light source 15 and detector 17 may be used. In one example, the light source 15 may emit light in the range between 400nm and HOOnm, but this is by way of example only. The light source 15 and detector 17 may be chosen together to ensure that the detector is sensitive to at least part of the range of frequencies emitted by the light source. The detector 17 may be a photodiode or any other type of light detector.

Claims

Claims1. A method of monitoring a flow of a powder suspended in a fluid through a section of pipe, the method comprising: emitting a light signal across the flow of powder; detecting the light signal on an opposing side of the flow of powder, and generating an electrical signal representative of the detected light signal as a function of time; dividing the electrical signal into a plurality of windows; for at least some of the windows: converting the signal data to the frequency domain; determining one or more characteristics of the signal data in the frequency domain; and determining flow properties of the powder from the one or more characteristics of the signal data in the frequency domain.

2. The method of claim 1, wherein the one or more characteristics of the frequency domain signal includes one or more of: the root mean square or average signal level; average frequency of the signal; magnitude and / or frequency of peaks; frequency at which the largest peak occurs; ratio of the power of the signal to the power of the noise; and integral of the signal.

3. The method of claim 1 or claim 2, wherein the flow properties include one or more of: the presence or absence of a flow; mass flow rate of the powder; flow stability; a fault in a powder distribution system including the pipe; moisture content; flow index; particle size distribution; bulk density changes; andpowder accumulation in a powder distribution system including the pipe.

4. The method of any preceding claim, wherein the one or more characteristics of the signal includes the root mean square or average signal level and wherein mass flow rate of the powder is determined based on the root mean square or average signal level.

5. The method of any preceding claim, wherein the one or more characteristics of the signal includes the average frequency of the signal or frequency of the maximum peak in the signal and wherein flow stability is determined based on the average frequency of the signal or the frequency of the maximum peak.

6. The method of claim 5, wherein changes of the average frequency or the frequency of the maximum peak indicate unstable flow.

7. The method of any preceding claim wherein the one or more characteristics includes an amplitude and / or frequency at which peaks of the signal frequency domain signal occur and wherein variation in the amplitude and / or frequency of the peaks is indicative of a fault in a powder distribution system including the pipe-8. The method of any preceding claim, comprising: for at least some of the windows analysing the time domain signal, wherein the flow properties of the powder are determined from the combination of the one or more characteristics of the signal data in the frequency domain and the analysis in the time domain.

9. The method of claim 8, wherein an absence of flow is determined based on the combination of a low magnitude or no magnitude at which peaks of the frequency domain signal occur and low variance of the signal in the time domain.

10. The method of any preceding claim, wherein the light signal is generated by a light source having a variable intensity, the method comprising: at a first time, determining a threshold detected signal associated with a first light intensity of the light source;at a second time, determining a second light intensity of the light source required to measure the same threshold detected signal; and determining a change in the accumulation of powder on an interior of the pipe based on a variation between the first light intensity and the second light intensity.

11. The method of claim 10, wherein the threshold detected signal associated with a first light intensity of the light source is determined when the pipe is clean of any accumulation.

12. The method of claim 10 or claim 11, comprising: determining information about the powder based on the variation between the first light intensity and the second light intensity.

13. The method of any preceding claim, comprising: monitoring the one or more flow properties of the powder; and if at least one of the one or more flow properties crosses a predetermined threshold, triggering an alarm.

14. The method of any preceding claim, wherein the light signal is in the visible range of wavelengths.

15. The method of any preceding claim, wherein the fluid is select from: air; inert gas; non-inert gas; a liquid.

16. A measurement system for measuring flow of a powder suspended in a fluid, the measurement system comprising: a pipe section arranged to carry a powder suspended in a fluid along a length of the pipe; a light source arranged to emit a light signal into the pipe section across a flow of the powder; a detector arranged to detect light from the light source across the pipe section, arranged to detect the light signal emitted by the light source and generate an electrical signal representative of the detected light signal as a function of time; anda controller configured to: divide the electrical signal into a plurality of windows; for at least some of the windows: convert the signal data to the frequency domain; determine one or more characteristics of the signal data in the frequency domain; and determine flow properties of the powder from the one or more characteristics of the signal data in the frequency domain.

17. The measurement system of claim 16, wherein the controller is configured to perform the method of any one or more of claims 2 to 13.

18. The measurement system of claim 16 or claim 17, wherein the light signal is in the visible range of wavelengths.

19. The measurement system of any of claims 16 to 18, wherein the fluid is select from: air; inert gas; non-inert gas; a liquid.

20. The measurement system of any of claims 16 to 19, wherein the pipe section comprises: a housing defining a passage extending along a from a first end to a second end; a first pipe section extending along the same direction as the passage, a portion of the first pipe section received in the first end of the passage; a second pipe section extending along the same direction as the passage, a portion of the second pipe section received in the second end of the passage; a transparent section received in the passage, between the first pipe section and the second pipe section, the first pipe section, second pipe section and transparent section forming a continuous passage through the housing; wherein the light source and detector are received in the housing, between the housing and the transparent sleeve, aligned with the transparent section along the length of the passage.

21. The measurement system of claim 20, wherein the pipe section includes clamping means to secure the housing to the first and second pipe sections, such that the transparent section is held in place between the first and second pipe sections.

22. The measurement system of claim 21 wherein the clamping means comprises flanges formed on an exterior of the first and second pipe sections.

23. The measurement system of claim 22, wherein the housing extends between the flanges, such that the flanges are outside the passage formed in the housing and the housing is clamped to the flanges.

24. The measurement system of any of claims 20 to 23, wherein the continuous passage has a constant diameter along its length.

25. The measurement system of any of claims 20 to 24, comprising sealing means provided between the first and second pipe sections and the transparent section.

26. A pipe arrangement comprising: a housing defining a passage extending along a length from a first end to a second end; a first pipe section extending along the same direction as the passage, a portion of the first pipe section received in the first end of the passage; a second pipe section extending along the same direction as the passage, a portion of the second pipe section received in the second end of the passage; a transparent section received in the passage, between the first pipe section and the second pipe section, the first pipe section, second pipe section and transparent section forming a continuous passage through the housing; a light source received in the housing, aligned with the transparent section along the length of the passage; and a detector received in the housing, aligned with the transparent section along the length of the passage, the detector arranged to detect light fromthe light source, and monitor attenuation of the light source to detect flow of powder.

27. The pipe arrangement of claim 26, wherein the passage defined by the housing is colinear with the continuous passage.

28. The pipe arrangement of any of claim 26 or claim 27, wherein the continuous passage has a constant diameter along its length.

29. The pipe arrangement of any of claim 26 or claim 27, wherein the continuous passage has a varying diameter along its length.

30. The pipe arrangement of any of claim 26 to claim 29, wherein the continuous passage is circular in cross section.

31. The pipe arrangement of any of claim 26 to claim 30, wherein the pipe section includes clamping means to secure the housing to the first and second pipe sections, such that the transparent section is held in place between the first and second pipe sections.

32. The pipe arrangement of claim 31, wherein the clamping means comprises flanges formed on an exterior of the first and second pipe sections.

33. The pipe arrangement of claim 32, wherein the housing extends between the flanges, such that the flanges are outside the passage formed in the housing and the housing is clamped to the flanges.

34. The pipe arrangement of any of claim 32 or claim 33, wherein the first and second pipe sections connect to the transparent section at respective first and second ends, wherein the first and second flanges are spaced from the respective first and second ends35. The pipe arrangement of any of claims 31-34, wherein at least one of the clamping means is a tri-clamp.

36. The pipe arrangement of any of claims 26 to 35, comprising sealing means provided between the first and second pipe sections and the transparent section.

37. The pipe arrangement of claim 36, wherein the first and second pipe sections and / or the transparent section comprise seats for locating the sealing means.

38. The pipe arrangement of any of claim 36 or claim 37, wherein the sealing means is at least one of: i) an O-ring; or ii) a gasket39. The pipe arrangement of any of claim 26 to claim 38, wherein the housing comprises one or more connectors configured to provide power and / or data communication between the light source and the light detector to components external to the pipe arrangement.

40. The pipe arrangement of any of claim 26 to claim 39, wherein the transparent section is formed of or comprises glass.

41. The pipe arrangement of any of claim 26 to claim 40, wherein the light source is configured to produce a light signal having a variable intensity.

42. The pipe arrangement of any of claim 26 to claim 41, wherein the light source is configured to produce a light signal in the visible range of wavelengths.

43. The pipe arrangement of any of claim 26 to claim 42, wherein the pipe arrangement is configured to measure flow properties of powder passing through the pipe arrangement according to the method of any of claim 1 to claim 15.

44. A pipe section formed of a boundary wall defining a passage extending along a first axial direction, the pipe section comprising: an inlet arranged to couple to an upstream pipe section, the inlet having a first cross-sectional shape and a first cross-sectional area;an expanded portion having a second cross-sectional shape different to the first cross-sectional shape, and a second cross-sectional area larger than the first cross- sectional area; an outlet arranged to couple to a downstream pipe section, the outlet having a third cross-sectional shape and a third cross-sectional area; a first connecting portion coupling the inlet to the expanded portion, wherein along an axial length of the first connecting portion the cross-sectional area of the pipe expands from the first cross- sectional area to the second cross-sectional area; and a second connecting portion coupling the expanded portion to the outlet, wherein the expanded portion includes: a first planar surface extending parallel to the axial direction on a first side of the passage, the first planar surface including a first aperture; a light source positioned in the first aperture such that a front surface of the light source is flush with the first planar surface; a second planar surface spaced from and parallel to the first planar surface, on a second side of the passage, opposite the first side, the second planar surface including a second aperture; and a light detector positioned in the second aperture such that a front surface of the light detector is flush with the second planar surface, the light detector arranged to detect signals emitted by the light source.

45. The pipe section of claim 44, wherein the first and third cross-sectional areas are the same.

46. The pipe section of claim 44, wherein the first and third cross-sectional areas are different.

47. The pipe section of any one of claim 44 to claim 46, wherein the first and third cross sectional shapes are the same.

48. The pipe section of any one of claim 44 to claim 46, wherein the first and third cross sectional shapes are different.

49. The pipe section of any one of claim 44 to claim 48, wherein the expanded portion comprises a plurality of planar surfaces such that the second cross section is polygonal.

50. The pipe section of claim 49, wherein the second cross section is square.

51. The pipe section of any one of claim 44 to claim 50, wherein the cross section of the connecting portion is the same as the cross section of the expanded portion.

52. The pipe section of any one of claim 44 to claim 51, wherein the connecting portions are composed of planar surfaces angled towards or away from the axial direction.

53. The pipe section of any one of claim 44 to claim 52, wherein the ends of the planar surfaces at the inlet and / or the outlet are shaped to mate with the first / third cross sectional shapes.

54. The pipe section of any one of claim 44 to claim 53, wherein the pipe section is configured to measure flow properties of powder passing through the pipe arrangement according to the method of any of claim 1 to claim 15.

55. The measurement system of any one of claim 16 to claim 19, wherein the measurement system comprises the pipe section of any one of claim 44 to claim 53.

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