Disposable plastic pressure sensor

Abstract

The present invention discloses a polymer fluid sensor, which includes an inlet configured to receive a fluid and an outlet. A polymer tube is disposed between the inlet and the outlet in fluid communication, and has a first sensing location and a second sensing location spaced apart from the first sensing location. The first sensing location has a first sidewall thickness, and the second sensing location has a second sidewall thickness. A sleeve surrounds the polymer tube. The first sidewall thickness is less than the second sidewall thickness, and a first sensing element is disposed at the first sensing location, while a second sensing element is disposed at the second sensing location. In another example, the first sidewall thickness and the second sidewall thickness are the same, and a fluid restrictor is disposed within the polymer tube between the first sensing location and the second sensing location.

Description

Background Art

[0001] The present invention relates to a disposable plastic pressure sensor. Background Art

[0003] Many processes require the use of sensors to control the process. In some industries, these processes may involve biological or hygienic processes and must therefore remain contamination-free. Examples of sensors for such processes include pressure sensors, temperature sensors, flow sensors, pH sensors, conductivity sensors, etc.

[0004] Biopharmaceutical manufacturers are increasingly using disposable equipment to enhance efficiency, make the equipment more versatile, and reduce the risk of cross-contamination. Similarly, in the hygiene and food processing industries, due to the high cost of cleaning or the problem of maintaining hygienic conditions, there is an increasing expectation to use disposable or discardable measuring equipment. In many of these applications, high precision is not required, which favors the use of the most cost-effective and easier-to-manufacture materials other than metals. Further, in some cases, it may be mandatory to design without a filling fluid to avoid potential contamination of the process stream. Summary of the Invention

[0005] The polymeric fluid sensor includes an inlet configured to receive a fluid and an outlet. A polymeric tube is disposed between the inlet and the outlet in fluid communication and has a first sensing location with a first sidewall thickness and a second sensing location spaced apart from the first sensing location with a second sidewall thickness. A sleeve surrounds the polymeric tube. The first sidewall thickness is less than the second sidewall thickness, and a first sensing element is disposed at the first sensing location while a second sensing element is disposed at the second sensing location. In another example, the first sidewall thickness and the second sidewall thickness are the same, and a fluid restrictor is disposed within the polymeric tube between the first sensing location and the second sensing location. Brief Description of the Drawings

[0006] Figure 1 is a schematic diagram of a disposable plastic pressure sensor according to an embodiment of the present invention;

[0007] Figure 2 is a schematic cross-sectional view of a non-invasive and non-intrusive pressure sensor according to an embodiment of the present invention;

[0008] Figure 3 is a graph showing stress versus cycles at different temperatures, showing the curves of polycarbonate and ABS at different temperatures;

[0009] Figure 4 is a chart depicting the fatigue limits of polycarbonate and ABS at different temperatures;

[0010] Figure 5 Schematic diagram of a disposable plastic mass flow sensor according to an embodiment of the present invention;

[0011] Figure 6 Schematic diagram of a disposable plastic fluid sensor according to another embodiment of the present invention;

[0012] Figure 7 Schematic diagram of a disposable plastic fluid sensor according to another embodiment of the present invention;

[0013] Figure 8 Schematic diagram of a system for measuring fluid properties according to an embodiment of the present invention; and

[0014] Figure 9 Flowchart of a method for providing fluid properties in a biopharmaceutical or sanitary fluid handling system according to an embodiment of the present invention. Detailed Description

[0015] In sanitary applications, there is generally a problem of process batch contamination from sensors used to monitor processes. Using organic filled fluids (sometimes required for pressure sensing) in sensors can solve some toxicity problems, but does not eliminate the potential for contamination, resulting in the loss of an entire process batch. An oil-free design for pressure sensors can solve this problem to some extent, but still requires expensive cleaning. Disposable and throwaway sensors eliminate the cleaning cost, but must be offset by a competitive throwaway cost and ease of use.

[0016] Some designs employ a plastic film interface between the process fluid and the metal isolation diaphragm of the pressure sensing system. However, even these designs are still vulnerable to damage, as well as the possibility of contamination from the isolation fluid generated by the pressure sensing system in the presence of the sensor, and sacrificing performance.

[0017] The embodiments described below generally provide a non-invasive and non-intrusive pressure sensor constructed from a polymer (preferably plastic) tube that utilizes multiple conductive coated regions on its outer diameter to provide capacitive measurements for a disposable sensing solution with no contamination possibility. The sensor is designed such that it allows a section of the tube to deflect under pressure, which deflection reduces the gap between the tube and the contacts on the outer sleeve. This gap can be monitored using capacitive measurements and is referenced to a pseudo-fixed gap capacitor that is set in a region of the tube that is more rigid and does not deform significantly with changes in internal pressure. Since the sensor is developed from a polymer tube, the sensor can be simply coupled to a conduit to direct process flow through the sensor and then through an outlet of the sensor that is coupled to an additional process conduit that returns the process flow to the process. Further, it will be noted that the designs provided in the following embodiments generally do not include any electronics. Thus, the sensor provided herein can withstand sterilization cycles using steam and / or gamma radiation that are commonly used in pharmaceutical and hygienic processing applications.

[0018] Figure 1 is a schematic diagram of a disposable plastic pressure sensor in accordance with an embodiment of the present invention. The pressure sensor 100 generally includes a pair of tubular portions 102, 104 that are configured to be coupled to a conduit or pipeline of a biopharmaceutical or hygienic process. In the example shown, a conduit 106 is coupled to the conduit portion 102 such that process fluid flowing through the conduit 106 generally does not include any obstructions or intrusions within the flow path of the fluid. Similarly, a conduit 108 is coupled to the conduit portion 104 such that process fluid flows through the conduit section and the sensor in a substantially unobstructed and non-intrusive manner. As will be shown in more detail below, the sensor 100 includes a plurality of electrical structures that are arranged such that deflections of the tube wall can be measured and characterized in order to provide the associated process fluid pressure. Since it is the deflection of the wall itself that is measured, no pressure sensors or other structures are inserted into the flow stream. Further, a measurement circuit 110 is coupled to the various electrical structures within the sensor 100 by means of one or more conductors 112 such that the measurement circuit 110 can identify or otherwise detect changes in the electrical characteristics of the structures that indicate the process fluid pressure.

[0019] Figure 2Schematic cross-sectional view of a non-invasive and non-intrusive pressure sensor according to an embodiment of the present invention, the pressure sensor using a polymer tube to provide a capacitive measurement for a disposable sensing solution, wherein the polymer tube includes a conductive coating or deposition area on its outer surface. The sensor 100 is designed such that a section of the tube (schematically shown by reference numeral 120) is allowed to deflect under pressure, which deflection will reduce the gap G01 between the tube contact 122 and the sleeve contact 124. This gap G01 can be measured using capacitive measurements or otherwise monitored (such as using the measurement circuit 110 ( Figure 1 shown in)), and is referenced to a pseudo-fixed gap capacitor schematically shown by reference numeral 126, which pseudo-fixed gap capacitor can be formed in a region 127 of the tube that is more rigid and does not deform significantly with changes in internal pressure.

[0020] As Figure 2 shown, the sensor 100 includes a pair of polymer tubular portions 102, 104, which pair of polymer tubular portions assist in coupling the sensor to a plastic pipe or conduit. The portions 102, 104 can be formed from any suitable polymeric material and are coupled to the polymer tube 134. As can be appreciated, the shape and structure of the tubular portions 102, 104 can vary significantly in order to accommodate various different techniques for coupling the sensor to a pipe or conduit. Further, each of the tubular portions 102, 104 can be sealingly coupled to the tube 134 in any suitable manner. However, preferably, the tube 134 is formed from the same material as the tubular portions 102, 104. Further, preferably, the tube 134 and the tubular portions 102, 104 are formed as a single integral piece from the same material. For example, the tubular portions 102, 104 and the tube 134 can be formed as a single piece from 3D printed plastic or injection molded plastic.

[0021] The tube 134 includes a pair of collars 136, 138 having an outer diameter 140 sized to receive a sleeve 142. The sleeve 142 can be attached to the outer diameter 140 of the collars 136, 138 in any suitable manner (including ultrasonic welding). Alternatively, it will be clearly envisioned that the sensor can be constructed using additive manufacturing techniques (such as 3D printing), and the tube and the sleeve can be formed as a single integral component. When the sleeve 140 is coupled to the collars 136, 138, a pair of gaps G 0 1, G 0 2 are formed between the inner surface 144 of the sleeve 142 and the outer surface 146 of the tube 134. Further, the first gap G 0 1 is formed between the relatively thin section 148 and the inner surface 144 of the sleeve 142. The second gap G 02 is formed between the relatively thick portion 127 of the tube 134 and the inner surface 144 of the sleeve 142. Conductive electrodes or conductive plates 122, 150 are attached to the outer surface of the tube 134 at positions 148, 127 respectively. Similarly, conductive electrodes or conductive plates are attached to the inner surface 144 of the sleeve 142 at positions 152, 154.

[0022] The conductive electrodes or conductive plates 122, 150 can be considered sensing elements in that the conductive electrodes or conductive plates 122, 150 form part of a variable capacitor having a gap-based capacitance. The conductive electrodes or conductive plates can take any suitable form including but not limited to circular pads, oval pads and annular bands extending a selected amount (such as 270 degrees) around the surface. Thus, a first variable capacitor is formed between the plate or conductive electrode 122 at position 148 and the plate 152. A reference capacitance is formed between the plates 150 and 154. Due to the relatively thick portion of the conduit at position 127, the reference capacitor does not deflect significantly with changes in pressure within the tube 134. In a preferred embodiment, when the sensor is unpressurized (i.e., zero pressure), the gaps G 0 1 and G 0 2 are equal. This feature is provided by using different sidewall thicknesses for the sleeve. However, other factors affecting capacitance (such as changes in temperature and thermal expansion and contraction of the sensor 100) are generally relatively common to both capacitors. Thus, comparing the responses of the sensing capacitor C1 and the reference capacitor C2 provides a direct indication of pressure that is substantially independent of other factors.

[0023] To quantify how the outer diameter of a thick-walled pipeline changes (denoted as ΔD o ), some assumptions are helpful when introducing a pressure P inside the pipeline. The first assumption is that the external environment of the pipeline is at ambient pressure, so the pressure is applied as gauge pressure. Under such an assumption, the change in outer diameter (ΔD0) can be calculated according to Equation 1 below:

[0024]

[0025] where E is the Young's modulus of the pipeline, and D i and D o are the inner tube diameter and the outer tube diameter respectively. Since plastics and plastic-like materials have a large thermal expansion, it is desirable to passively correct for temperature changes through a ratio or differential scheme. Figure 2 The example depicted in

[0026] is a sensor that can passively correct for temperature effects (especially at zero pressure). Figure 2As shown. The gap surfaces are the plates of a parallel capacitor, which decrease as the pressure inside the tube increases. Note that the tubes at positions C1 and C2 have different thicknesses 159, 161 at positions 148, 127 respectively. Each of the plates is connected to an electrical wire, which is operably connected to a measurement circuit ( Figure 8 shown in), to allow the controller to determine the capacitance (and thus the pressure). The expansion of the tube due to temperature is the same at these two positions, but the amount of change in the gap due to pressure is different because the wall thicknesses of the tube are not equal. Therefore, although the pressure signal is insensitive to changes in steady-state temperature, the pressure signal can be extracted by subtracting the signals from the two positions.

[0027] Since the gap is proportional to the reciprocal of the capacitance, taking the difference between the reciprocals of each capacitance is effectively taking the difference between the two gaps G1 and G2, as shown in Equation 2 below:

[0028]

[0029] where K is a constant. By design, G1 = G2 = G0, i.e., the gaps at zero gauge pressure are the same, but the variation of the gaps with pressure is not the same because the wall thicknesses are different. Since the gaps are the same at zero gauge pressure, the variation with temperature is also the same. Therefore, at zero gauge pressure, there will be no variation with temperature. It can also be seen from Equation 3 (below) that ΔG has the following approximate pressure-dependent form:

[0030]

[0031] where t1 and t2 are the respective wall thicknesses of the two diameters at positions C1 and C2. Therefore, the pressure P can be obtained from the measured output values using Equations 2 and 3. That is,

[0032]

[0033] The sensor design described herein preferably uses non-toxic rigid plastics such as polycarbonate or acrylonitrile-butadiene-styrene (ABS) as the main components. Before discussing the exothermic details of the design, it is necessary to address the issue of plastic creep. To control this limitation, the maximum stress encountered during the use of the sensor should be kept below an upper level so that it can still withstand when exceeding the so-called fatigue limit. Figure 3 and Figure 4 Data on the fatigue limits of polycarbonate and ABS plastics are provided.

[0034] Figure 3 is a graph of stress in megapascals versus the number of cycles at different temperatures, which shows the stress-life or Curve. Additionally, Figure 4 Various fatigue limits (expressed in megapascals) of polycarbonate and ABS at various temperatures are provided. As can be seen, the data indicate that a design using polycarbonate plastic, which maintains the stress level below 10.3 megapascals (about 1500 PSI), should be able to withstand long-term cyclic stress operation without creep. Thus, if the stress is kept below the fatigue limit level, it should be possible to construct a pressure sensor that can withstand long-term use using 3D printing or injection molding methods with plastic structures.

[0035] Providing a plastic sensor offers many benefits. First, the entire sensor body generally has no internal dead zones or step changes or material transitions. Further, at least in the case of polycarbonate, the plastic has a Young's modulus that is 50x lower than that of 304 stainless steel. This difference provides significantly more deflection per PSI. Additionally, polycarbonate is electrically insulating, having a dielectric constant of approximately 3. Further, the plastic sensor facilitates the incorporation of an overpressure stop and a mounting bracket. Finally, another benefit of the plastic sensor is that the plastic sensor is generally non-toxic.

[0036] So far, the embodiments have described a plastic pressure sensor that provides an electrical response indicative of the pressure of a fluid flowing through a tube. However, similar techniques can also be used to sense or otherwise determine additional properties of the fluid.

[0037] Figure 5 is a schematic diagram of a disposable plastic mass flow sensor according to an embodiment of the present invention. Sensor 200 has many similarities to sensor 100, and similar components are numbered similarly. However, the main difference between sensor 200 and sensor 100 is that the tube portion 234 of sensor 200 includes a plastic orifice plate 236 inside the tube 234 that separates two capacitance regions C1 and C2. Additionally, unlike sensor 100, the wall thicknesses at positions C1 and C2 of the tube are the same on both sides of the sensor. When there is flow, a pressure difference appears across the orifice plate 236, and the mass flow is proportional to the square root of the pressure difference. Thus, the square root of the output scaled with an appropriate constant as defined in Equation 2 (above) is proportional to the mass flow through tube 234. Additionally, since both capacitances formed at positions C1 and C2 are affected by temperature in the same way, sensor 200 will still be substantially unaffected by temperature changes.

[0038] Another fluid property that can be measured using the techniques described herein is the conductivity of the fluid itself. Using an alternating current (AC) excitation of the capacitor electrodes, the reactive and dissipative properties of the dielectric and conductivity properties of the fluid can be determined. Specifically, the conductivity of the fluid can be determined from the measured value of the capacitance ESR or equivalent series resistance. The bulk conductivity, denoted as σ, will be related to the measured value of the ESR by the following Equation 5:

[0039] σ = ∈(2πf) 2 C·ESR Equation 5

[0040] where ∈ is the dielectric constant, C is the capacitance, and f is the excitation frequency. Note that the measurement assumes knowledge of the dielectric constant, frequency, and capacitance.

[0041] Another fluid property that can be determined using the embodiments and techniques described herein is the fluid flow rate. It has been observed that the dielectric properties of a fluid vary with the flow rate. For example, the phenomenon was demonstrated in the paper "Dynamic Dielectric Effect in Liquids at Low Flow Rates" by A.A. Potapov in Zh.Eksp.Teor.Fiz 101, 895 - 900 (March 1992), Irkutsk Scientific Center, Siberian Department, Academy of Sciences USSR (submitted April 18, 1991), and it was proposed that the dielectric flow effect depends on the partial orientation of the liquid molecules such that the long axes of the liquid molecules tend to be aligned with the direction of liquid flow. This in turn will affect the dielectric properties of the fluid, which can be measured. This effect (referred to as the dynamic dielectric effect in the paper) has been observed in both polar and nonpolar liquids. Thus, in a fluid with a substantially constant conductivity, using the above effect, a change in the dielectric constant can be considered to indicate a change in the fluid flow rate.

[0042] Figure 6 is a schematic diagram of a disposable plastic fluid sensor 250 according to another embodiment of the present invention. Although the embodiments have thus far generally utilized capacitor plates to sense tube deformation (i.e., gap change), embodiments can be practiced that sense tube deformation in other ways in response to fluid pressure. Figure 6Shows a pair of strain gauges 252, 254, which are connected to the pipe wall 256 at positions 258, 260 respectively. A strain gauge is a device with a resistance that changes with strain. Generally, a strain gauge is formed of a long, thin conductive strip with a zigzag pattern of parallel lines. The strain gauges 252, 254 can be applied to the pipe wall 256 or fabricated into the pipe wall 256. Additionally, the strain gauges 252, 254 can be arranged to partially surround the pipe wall 256, or the strain gauges 252, 254 can substantially completely surround the pipe wall 256. However, preferably, the strain gauges 252, 254 extend the same amount around the pipe wall. Since strain gauges can be vulnerable to changes in temperature, Figure 6 the embodiment shown in Figure 6 uses the strain gauge 254 as a reference sensor at the thicker position 260. This is because the position 260 does not strain with fluid pressure (at least to the extent of position 258). Thus, changes in the signal from the strain gauge 254 will indicate non-pressure-related factors, such as temperature. Then, this signal can be subtracted from or otherwise removed from the signal from the strain gauge 252 to provide a compensated strain-related output.

[0043] Figure 7 is a schematic diagram of a disposable plastic fluid sensor according to another embodiment of the present invention. The sensor 300 has some similarities with the above-described sensors 100 and 200, and similar components are numbered in a similar manner. Notably, the sensor 300 includes a pair of temperature sensors that are disposed on the outer surface of the tube 334 at positions T1 and T2. These temperature sensors can also be considered sensing elements. Additionally, the thickness of the tube at positions T1 and T2 is different. This is similar to the embodiment described above with respect to Figure 2 and the sensor 100. However, integrating two thickness dimensions into a disposable pressure sensor allows for the measurement of heat flow between two conductive plates. A simple steady-state heat flow calculation can be used to provide information about the actual internal temperature of the fluid flowing through the sensor tube. Due to the presence of stray thermal paths within the sensor, a simple geometric relationship for thermal impedance is not described. However, it can be shown that, to a good approximation, the process fluid follows the following relationship, as shown in Equation 6.

[0044] T process = T1 + (T1 - T2) * N Equation 6

[0045] where, T process equals the temperature of the internal process fluid flowing through the tube, and N is a constant that can be determined experimentally.

[0046] Polycarbonate or other plastics have relatively poor thermal conductivity, but there are some materials that can provide better thermal conductivity to improve the time response of measurements. An example of such a material is sold by Covestro AG of Germany under the trademark Makrolon, which is a polycarbonate material with some use as a heat sink because it provides improved thermal conductivity compared to other plastics.

[0047] Although the temperature sensors disposed at positions T1 and T2 in the sensor 300 can take any form, such as thermocouples, thermistors, and RTDs, it is clearly conceivable that the temperature sensor elements themselves can be embedded within the capacitor plates. For example, the capacitor plates can be formed of a temperature-sensitive metal (e.g., copper or nickel) and etched or patterned such that the capacitor plates provide a measurable resistance that varies with temperature.

[0048] Figure 8 is a schematic diagram of a system for measuring fluid properties according to an embodiment of the present invention. The system 400 generally includes a disposable process fluid sensor 402 that surrounds capacitors 404, 406 and temperature sensors 408, 410 schematically shown as dashed boxes. As shown, each capacitor 404, 406 is operatively coupled to a switch or other suitable multiplexing circuit 412 controlled by a controller 414. The controller 414 can be any suitable electronic device that is capable of operating the switch 412 and interacting with a measurement circuit 416 to detect the electrical parameters of the capacitors 404, 406 and the temperature sensors 408 and 410. For example, the controller 414 can be a microprocessor coupled to or including an analog-to-digital converter that is capable of determining the voltage or other electrical response of the attached electrical devices. By controlling the switch 412, the controller 414 can interact with and measure the capacitance or capacitors 404 and 406 respectively. Additionally, the controller 414 can include appropriate processing capabilities (such as arithmetic processing) such that the various properties described above with respect to formulas 1 to 6 can be calculated to provide a calculated process fluid parameter output, e.g., fluid pressure, mass flow, flow rate, conductivity, and / or temperature.

[0049] Figure 9 is a flowchart of a method for providing fluid properties in a biopharmaceutical or sanitary fluid handling system according to an embodiment of the present invention. The method 500 begins at block 502, where a measurement value is obtained at a first position within a plastic tube through which the fluid flows. For example, the first measurement value can be a first resistance measurement indicating the strain of the plastic tube through which the process fluid flows, as indicated by reference numeral 503. Alternatively, the first measurement value can be an indication at, such as C1( Figure 2The first capacitance measurement of the gap between a pair of capacitor plates at the location (shown in Figure 2 ). This is shown at block 504. Additionally or alternatively, the first position measurement can be a temperature measurement, as shown at block 506. Next, at block 508, a second measurement is obtained at a second position of the plastic fluid sensor. As shown at block 509, this second measurement can be a resistance measurement of a second strain gauge. Alternatively, as shown at block 510, this second measurement can be a capacitance-based measurement at a location (such as location C2 ( Figure 2 shown)), and / or this second measurement can be a temperature measurement 512 at the same location. Next, at block 514, the fluid property is calculated based on the measurements obtained at blocks 502 and 508. As set forth above, the embodiments described herein can provide measurements that can be used to calculate various fluid properties. Moreover, a combination of fluid properties can provide a higher-order indication. For example, knowing the temperature of a known fluid can allow for compensating for fluid density to determine or even calculate the Reynolds number (Re). In any case, the calculated fluid properties can include pressure (as shown at block 516), mass flow (as shown at block 518), fluid flow rate (as shown at block 520), and temperature (as shown at block 522). Finally, at block 524, the calculated fluid properties are provided as an output, which can be in the form of a local output or can be communicated to a remote device as needed.

[0050] Although the invention has been described with reference to the preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

1. A polymer fluid sensor, comprising: An inlet configured to receive a fluid; An outlet; A polymer tube disposed between the inlet and the outlet in fluid communication, the tube having a first sensing location and a second sensing location spaced apart from the first sensing location, the first sensing location having a first sidewall thickness and the second sensing location having a second sidewall thickness; A sleeve disposed around the polymer tube, and Wherein the first sidewall thickness is less than the second sidewall thickness, and a first sensing element is disposed at the first sensing location and a second sensing element is disposed at the second sensing location.

2. The polymer fluid sensor according to claim 1, wherein The first sensing element is a capacitor plate that together with an opposed capacitor plate disposed on the inner surface of the sleeve forms a first variable capacitor having a capacitance that varies as the polymer tube deflects at the first sensing location.

3. The polymer fluid sensor according to claim 2, wherein, The second sensing element is a capacitor plate that together with an opposed capacitor plate disposed on the inner surface of the sleeve forms a second variable capacitor having a capacitance that varies as the polymer tube deflects at the second sensing location.

4. The polymer fluid sensor according to claim 3, wherein, The first variable capacitor and the second variable capacitor have the same capacitance at zero pressure.

5. The polymer fluid sensor according to claim 3, wherein, The distance between the opposed capacitor plates of the first variable capacitor and the second variable capacitor is equal at zero pressure.

6. The polymer fluid sensor according to claim 1, wherein, The first sensing element and the second sensing element are temperature sensors.

7. The polymer fluid sensor according to claim 6, wherein, The temperature sensor is incorporated into the capacitor plate.

8. The polymer fluid sensor according to claim 1, wherein, The tube is constructed of polycarbonate.

9. The polymer fluid sensor according to claim 1, wherein, The tube is constructed of ABS.

10. The polymer fluid sensor according to claim 1, wherein, The first sensing element and the second sensing element are strain gauges.

11. A polymer fluid sensor, comprising: An inlet configured to receive a fluid; An outlet; A tube disposed between the inlet and the outlet in fluid communication, the tube having a first sensing location and a second sensing location spaced apart from the first sensing location, the first sensing location having a first sidewall thickness and the second sensing location having a second sidewall thickness the same as the first sidewall thickness, the tube having a flow restrictor disposed between the first sensing location and the second sensing location; A sleeve disposed around the tube; A first sensing element disposed at the first sensing location; And A second sensing element disposed at the second sensing location.

12. The polymer fluid sensor according to claim 11, wherein, The sleeve includes a plurality of capacitor plates that together with the first sensing element and the second sensing element form a capacitor.

13. The polymer fluid sensor according to claim 11, wherein, The tube is constructed of polycarbonate.

14. The polymer fluid sensor according to claim 11, wherein, The tube is constructed of ABS.

15. The polymer fluid sensor according to claim 11, wherein, The first sensing element and the second sensing element are strain gauges.

16. A method of sensing fluid properties, the method comprising: Guiding a fluid through a polymer tube having a plurality of sensing locations; Sensing an electrical property of a first sensing element located at a first sensing location among the plurality of sensing locations; Sense the electrical characteristics of a second sensing element located at a second sensing position among the multiple sensing positions; Calculate a fluid parameter based on the sensed electrical characteristics of the first sensing element and the sensed electrical characteristics of the second sensing element; Provide the calculated fluid parameter as an output; And Drive the first sensing element and the second sensing element with an alternating current excitation signal and determine the fluid conductivity.

17. The method according to claim 16, wherein The polymer tube has a first sidewall thickness at the first sensing position and a second sidewall thickness at the second sensing position, and the second sidewall thickness is greater than the first sidewall thickness.

18. The method according to claim 16, wherein, The calculated fluid parameter is fluid pressure.

19. The method according to claim 16, wherein The calculated fluid parameter is temperature.

20. The method according to claim 19, wherein, The sensed electrical characteristics are provided for heat flow calculation.

21. The method according to claim 16, wherein, The calculated fluid parameter is fluid flow rate.

22. The method according to claim 16, wherein The polymer tube has a first sidewall thickness at the first sensing position and a second sidewall thickness at the second sensing position, and the second sidewall thickness is the same as the first sidewall thickness. The polymer tube has a flow restrictor between the first sensing position and the second sensing position, and wherein the calculated fluid parameter is mass flow rate.

23. The method according to claim 22, wherein, The calculated fluid parameter is a combination of multiple calculated fluid parameters.

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