Moisture sensors and their respective measurement methods

Abstract

The present invention relates to a moisture sensor (10) for measuring the moisture of materials in the form of dry, liquid, or gaseous granules or powders in at least one conduit partially disposed along the axis (XX) of the moisture sensor (10) through which the materials to be measured for moisture flow. The moisture sensor (10) comprises at least one capacitor through which the materials to be measured for moisture flow, and the capacitor comprises rings (20) made of a dielectric material interposed between metal rings (30) mounted coaxially with respect to the axis (XX) between receiving flanges. At least one non-contact optical temperature sensor (40, 50) configured to measure the temperature of the capacitor is associated with the moisture sensor (10), which is for calculating a correction to be applied to the capacitance (CX) of the empty moisture sensor (10) due to the thermal expansion of the capacitor due to the flow of the materials to be measured for moisture.

Description

Technology Field

[0001] The present invention relates to a moisture sensor for industrial applications and a method for measuring each. In particular, the present invention relates to a sensor for measuring the moisture of products undergoing industrial processing, such as, for example, materials in the form of dry, liquid, or gaseous granules, or materials in the form of powders. Background Technology

[0002] As previously announced, devices exist for measuring moisture present in many material samples, and these devices have many applications, particularly in the food, chemical, and pharmaceutical industries.

[0003] In some disclosed devices, moisture measurement does not occur in-line during the production process, but is generated by sampling and subsequent measurement.

[0004] This approach is very complex and requires a long time, and since many factors can lead to improper sampling, the measurements are unreliable.

[0005] In addition, sampling is not very representative of production in progress, as laboratory systems can only sample a few grams, and in some production processes, such as silos or dryers in nitrogen environments, it is not possible to collect samples at specific points of interest.

[0006] Systems in which measurements are performed inline are also disclosed.

[0007] For example, the document WO 2012 / 004621 discloses an apparatus for measuring the moisture of materials flowing in the form of dry, liquid, or gaseous granules or powders within at least one conduit through which the material to be measured flows. The conduit is positioned at least partially along the axis through which the material flows. The apparatus comprises at least one capacitor through which the material to be measured flows. Again, the capacitor comprises at least two metal rings mounted coaxially with respect to the axis and adjacent to the inner wall of the conduit through which the material to be measured flows, and at least one dielectric element having a dielectric constant substantially linear with respect to temperature change.

[0008] For the installation of certain types of industrial machinery, such as injection molding machines, extruders, and dryers, periodic calibration procedures for the equipment configured to allow for measurement repeatability and accuracy are required.

[0009] In some industrial contexts, calibration also provides short production downtime because calibration operations are performed only within specific ambient temperature and humidity values.

[0010] Another problem that is highlighted is that when the measurement system is exposed to temperatures exceeding 50°C, measurement errors are inevitable due to dimensional changes and dielectric constant changes that affect the appropriate value of the measurement, mainly due to thermal expansion and dielectric constant changes of the dielectric material on which the sensor is composed.

[0011] The total capacitance measurement is the result of the capacitance value of the empty sensor (Capacitor CX) + the permittivity value of the material passing through it (CM) + the permittivity attributable to the relative humidity of the air (HRU). In other words, the total capacitance (Ctot) is given by the following equation: Ctot = CX + CM + HRU.

[0012] From the above equation, it is evident that the capacitance value of the empty sensor CX is essential for proper measurement, especially for the repeatability of the measurement. The capacitance drift caused by changes in dielectric capacitance is neither constant nor linear, as it depends on many factors such as the thermal expansion of all constituent materials and the peculiarities of some installations where mechanical devices can thermally and mechanically affect the structure of the CX sensor, thereby generating drift or often hysteresis of the CX capacitance value and consequently forming a problem that is much more complex to correct mathematically.

[0013] Due to its structure, the sensor is also exposed to electromagnetic disturbances arising from interactions with other machines, which can further alter the value of the signal originating from the sensor. While a metal shield eliminates this problem, it introduces another issue by causing an additional temperature rise within the system, resulting in increased drift in the capacitive signal due to the thermal expansion of the sensor's components.

[0014] Another issue to be highlighted is the heating of electronic components, which often exceeds 100°C. The sensor's PCB (electronic board) must be mounted as close as possible to the sensor's electrodes, primarily to avoid parasitic capacitances caused by contact impedance. The terminal capacitance must be within a narrow window between 130 fF (femtofarads) and 170 fF, and, where possible, have a very weak temperature dependence that is negligible. The problem to be solved

[0015] Therefore, the objective of the present invention is to manufacture a system capable of compensating for changes in the capacitance of a moisture sensor caused by thermal expansion.

[0016] An additional objective of the present invention is to manufacture a system capable of compensating for changes in the dielectric constant of a dielectric material interposed between electrodes.

[0017] Finally, but importantly, the objective of the present invention is to achieve the above-described results in a practical and economical manner. means of solving the problem

[0018] These and other objectives are achieved by a method for measuring the moisture of materials in the form of dry, liquid, or gaseous granules or powders within at least one conduit partially disposed along the axis of the moisture sensor through which the moisture sensor and the materials to be measured flow.

[0019] A moisture sensor comprises at least one capacitor through which a material to be measured for moisture flows, wherein the capacitor comprises rings made of a dielectric material interposed between metal rings mounted coaxially with respect to the axis between receiving flanges, and the moisture sensor is characterized by being associated with at least one non-contact optical temperature sensor configured to measure the temperature of the capacitor in order to calculate a correction to be applied to the capacitance of the empty moisture sensor due to the thermal expansion of the capacitor due to the flow of the materials to be measured for moisture.

[0020] The method for measuring moisture includes the following steps:

[0021] - A step of pre-positioning a moisture sensor inside a conduit, wherein the moisture sensor comprises at least one capacitor including dielectric material rings interposed between metal rings mounted coaxially with respect to the axis of the sensor between receiving flanges, and at least one non-contact sensor associated with the moisture sensor (10);

[0022] - A step of measuring the temperature of the capacitor through a moisture sensor; and

[0023] - A step of calculating a correction to be applied to the capacitance of an empty moisture sensor due to the thermal expansion of the capacitor caused by the flow of the materials to be measured for moisture. Effects of the invention

[0024] The advantage of the present invention is that it enables automatic correction of the capacitance of a bin sensor caused by both thermal expansion and dielectric constant change of the dielectric material interposed between the electrodes.

[0025] The use of non-contact sensors offers several advantages, including non-invasiveness, resistance to electromagnetic interference, the ability to operate in harsh environments, and the possibility of performing measurements remotely.

[0026] Further features of the present invention can be derived from dependent claims.

[0027] In the remainder of this description and in the appended claims, the expression “capacitance of the empty moisture sensor” refers to the capacitance of the sensor when no material passes through it. Brief explanation of the drawing

[0028] Further features and advantages of the present invention will become more apparent from reading the following description, provided by example and without limitation, with the help of the drawings illustrated in the attached tables, and in said drawings: - FIG. 1 illustrates a plan view of a moisture sensor according to one embodiment of the present invention; - FIG. 2 illustrates a drawing according to the AA cross-section of FIG. 1 of a moisture sensor; and - Figure 3 shows the axial view of the sensors in Figures 1 and 2. Specific details for implementing the invention

[0029] Now, the present invention will be described with reference first to FIG. 1, which illustrates a moisture sensor according to one embodiment of the present invention, and the moisture sensor is generally denoted by reference numeral 10.

[0030] Moisture sensors of this type are known and generally consist of some metal rings (30) and some rings made of dielectric material (20), each metal ring (30) is interposed between two rings made of dielectric material (20) to form the structure of a ring-shaped electric capacitor having a substantially cylindrical extension along axis XX (Fig. 2).

[0031] According to one embodiment of the present invention, the dielectric material on which the rings (20) are manufactured is PEEK (polyether ether ketone), that is, a high-performance semicrystalline thermoplastic material.

[0032] As previously announced, PEEK is a good electrical insulator with low thermal expansion and high resistance to heat and chemical agents.

[0033] In the moisture sensor (10) of the present invention, metal rings (30) and rings made of dielectric material (20) are assembled between two ring-shaped receiving flanges using assembly screws. The receiving flanges are not shown for simplification.

[0034] The moisture sensor (10) of the present invention measures moisture in-line in processes in which materials flowing in the form of dry, liquid, or gaseous granules or powders are processed.

[0035] The flow of these materials occurs within the substantially cylindrical structure of the moisture sensor (10) in the direction of the axis of Fig. 2.

[0036] These moisture sensors (10) are configured to be located within an unillustrated conduit, and moisture can be measured in-line in the conduit, that is, along the axis XX through which the material to be measured for moisture flows.

[0037] In particular, thanks to the structure of the sensor described above, the capacitance of the capacitor is influenced by the dielectric constant of the material between the plates, and said dielectric constant changes depending on the moisture content of the material to be measured, because water has a much higher dielectric constant than solid materials or air, and this phenomenon enables the moisture measurement of the material passing through the sensor to be obtained.

[0038] As previously mentioned, the total capacitance measurement is the result of the capacitance value of the empty sensor (capacitor CX) + the permittivity value of the material passing through it (CM) + the permittivity due to the relative humidity of the air (HRU), i.e., total capacitance (Ctot) = CX + CM + HRU.

[0039] From the above equation, it is evident that the capacitance value of the empty sensor CX is essential for proper measurement, especially for the repeatability of the measurement.

[0040] According to one embodiment of the present invention, a holder made of a mica-based material is designed, said holder is capable of channeling airflow through a fan to maintain a uniform heat distribution along the entire length of the sensor. said holder is not illustrated for simplification.

[0041] According to one embodiment of the present invention, the use of a pair of temperature sensors (40, 50) is provided to measure the temperature of a moisture sensor (10).

[0042] Temperature sensors (40, 50) applied to the moisture sensor (10) can be seen in FIGS. 1 to 3.

[0043] The temperature sensors (40, 50) are non-contact optical temperature sensors, that is, sensors capable of measuring temperature by detecting the optical properties of materials as known, and said properties change predictably according to temperature.

[0044] According to one embodiment of the present invention, at least one first non-contact sensor (40) is provided to be placed in close proximity to a moisture sensor (10) to accurately measure the temperature of a dielectric (30) placed between metal rings (30) and to measure temperature changes of 0.1°C.

[0045] Information obtained from the sensor (40) enables the calculation of a correction to be applied to the measurement value of the moisture sensor (10) through a control algorithm, due to both thermal expansion and a change in dielectric constant over a temperature range of 10°C to 200°C, said change being less than 2.8 fF / °C.

[0046] At least one second non-contact sensor is additionally provided, positioned in close proximity to the moisture sensor (10) to measure temperature changes of 0.1℃ and to accurately calculate the thermal expansion of the metal rings (30).

[0047] The information obtained from the sensor (50) enables the calculation of a change in capacitance caused by thermal movement of the metal part of the sensor and appropriate compensation through a control algorithm, that is, the calculation of a correction to be applied to the measurement value of the moisture sensor (10) due to thermal expansion.

[0048] In this way, in a temperature range of 20°C to 200°C, the change in capacitance from the capacitance value of the empty sensor is maintained so as not to exceed + / - 200 fF (femtofarad) over time.

[0049] The use of two very accurate (0.1°C) non-contact sensors (40, 50) for measuring electrode and dielectric temperatures enables automatic correction of the capacitance of the empty sensor caused by both thermal expansion of the dielectric material interposed between the electrodes and changes in the dielectric constant, thanks to appropriate adjustment algorithms.

[0050] Additionally, according to one embodiment of the present invention, a holder made of a mica-based material is designed, said holder is capable of channeling airflow through a fan to maintain a uniform heat distribution along the entire length of the sensor. said holder is not illustrated for simplification.

[0051] The operation of a moisture sensor for measuring the moisture of materials in the form of dry, liquid, or gaseous granules or powders within at least one conduit according to the present invention is clear to a person skilled in the art thanks to the description above, and is particularly as follows.

[0052] First, a moisture sensor (10) is positioned inside a conduit. Then, the temperature of the capacitor through which the material flows is measured via the moisture sensor (10). Finally, a correction is calculated to be applied to the CX capacitance of the empty moisture sensor (10), that is, when no material passes through the moisture sensor (10), and this correction takes into account the thermal expansion of the capacitor due to the flow of the materials to be measured.

[0053] In particular, the measurement step includes measuring the temperature of rings made of dielectric material (20), and the calculation step includes calculating a correction to be applied to the measurement value of the moisture sensor (10) due to both thermal expansion and change in dielectric constant over a temperature range of 10°C to 200°C, said change being less than 2.8 fF / °C.

[0054] Alternatively or additionally, the measurement step includes measuring the temperature of the metal rings (30), and the calculation step includes calculating a correction to be applied to the measurement of the moisture sensor (10) due to thermal expansion, so that the change in capacitance from the capacitance value of the empty sensor does not exceed + / - 200 fF in the temperature range of 20°C to 200°C.

[0055] Clearly, a person skilled in the art may make additional modifications and variations to the present invention, all of which are included within the scope of protection of the present invention as defined by the following claims, for the purpose of satisfying incidental and specific needs.

Claims

Claim 1 A moisture sensor (10) for measuring the moisture of materials in the form of dry, liquid, or gaseous granules or powders, wherein the moisture sensor (10) is for measuring the moisture of the materials in at least one conduit partially disposed along the axis (XX) of the moisture sensor (10) through which the materials to be measured flow, and the moisture sensor (10) comprises at least one capacitor through which the materials to be measured flow, wherein the capacitor comprises rings (20) made of a dielectric material interposed between metal rings (30) mounted coaxially with respect to the axis (XX) between receiving flanges, and the moisture sensor (10) is associated with at least one non-contact optical temperature sensor (40, 50) configured to measure the temperature of the capacitor in order to calculate a correction to be applied to the capacitance (CX) of the empty moisture sensor (10) due to the thermal expansion of the capacitor through which the materials to be measured flow. Claim 2 In claim 1, the at least one non-contact optical temperature sensor (40) is a sensor positioned in close proximity to the capacitor to accurately measure the temperature of the rings (20) made of a dielectric material. Claim 3 In claim 2, the temperature measurement obtained from the non-contact optical temperature sensor (40) enables the calculation of a correction to be applied to the measurement of the moisture sensor (10) due to both thermal expansion and a change in dielectric constant over a temperature range of 10°C to 200°C, wherein the change is less than 2.8 fF / °C. Claim 4 In claims 1 to 3, the at least one non-contact optical temperature sensor (50) is a sensor positioned in close proximity to the capacitor to accurately measure the temperature of the metal rings (30). Claim 5 In claim 4, the temperature measurement obtained from the temperature sensor (50) enables the calculation of a correction to be applied to the measurement of the moisture sensor (10) due to thermal expansion, thereby maintaining the capacitance change from the capacitance value of the empty sensor in a temperature range of 20°C to 200°C so as not to exceed + / - 200 fF. Claim 6 In any one of claims 1 to 5, the non-contact optical temperature sensor (40, 50) is configured to measure temperature changes with an accuracy of at least 0.1°C. Claim 7 In any one of claims 1 to 6, the moisture sensor (10) comprises a holder made of a mica-based material, and the holder is coupled with a fan to promote uniform heat distribution along the entire length of the sensor. Claim 8 In any one of claims 1 to 7, the rings (20) made of a dielectric material are made of PEEK (polyether ether ketone), thereby imparting to the moisture sensor (10) high resistance to thermal and chemical agents as well as good electrical insulation properties. Claim 9 A method for measuring the moisture of materials in the form of dry, liquid, or gaseous granules or powders within at least one conduit, comprising: a step of pre-positioning a moisture sensor (10) within the conduit, wherein the moisture sensor (10) comprises at least one capacitor including rings (20) made of a dielectric material interposed between metal rings (30) mounted coaxially with respect to the axis (XX) of the sensor between receiving flanges, and at least one non-contact sensor (40, 50) associated with the moisture sensor (10); a step of measuring the temperature of the capacitor through the moisture sensor (10); and a step of calculating a correction to be applied to the capacitance (CX) of the empty moisture sensor (10) due to the thermal expansion of the capacitor due to the flow of the materials to be measured. Claim 10 The method of claim 9, wherein the measuring step comprises measuring the temperature of the rings (20) made of a dielectric material, and the calculating step comprises calculating a correction to be applied to the measurement of the moisture sensor (10) due to both thermal expansion and a change in dielectric constant over a temperature range of 10°C to 200°C, wherein the change is less than 2.8 fF / °C. Claim 11 A method according to claim 9 or claim 10, wherein the measuring step comprises measuring the temperature of the metal rings (30), and the calculating step comprises calculating a correction to be applied to the measurement value of the moisture sensor (10) due to thermal expansion, so as to maintain the change in capacitance from the capacitance value of the empty sensor not exceeding + / - 200 fF in a temperature range of 20°C to 200°C.

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