Pressure transmitter with multi-range pressure sensor

Abstract

A pressure transmitter for sensing a pressure of a process fluid in an industrial process includes a pressure sensor body fluidly coupled to the process fluid, the pressure sensor body configured to receive a applied pressure related to the pressure of the process fluid. The pressure sensor body has a high pressure region configured to deform in response to the applied pressure and a low pressure region configured to deform in response to the applied pressure. A high-range resistance bridge circuit is mounted in the high-voltage region, the high-range resistance bridge circuit having a power supply node, a common node, and an output node, and having a resistance that varies in response to a pressure applied to the high-voltage region. A low-range resistance bridge circuit is mounted in the low-voltage region, the low-range resistance bridge circuit having a power supply node, a common node, and an output node, and having a resistance that varies in response to a pressure applied to the low-voltage region. A pressure output circuit is coupled to the output node of the high range resistance bridge and the output node of the low range resistance bridge, and provides an output related to applied pressure based on a voltage difference between the output node of the high range resistance bridge and the output node of the low range resistance bridge.

Description

Background Art

[0001] The present invention relates to a pressure transmitter of the type used to measure the pressure of a process fluid in an industrial process. More particularly, the present invention relates to a pressure transmitter including a pressure sensor configured to sense pressure within a plurality of pressure ranges.

[0002] Process instrumentation is used to monitor process variables such as pressure, temperature, flow, and level of process fluids used in industrial processes. For example, process transmitters are commonly used in industrial manufacturing facilities at multiple locations to monitor various process variables along various production lines. Process transmitters include sensors that generate electrical signals in response to physical changes in the process. For example, a pressure transmitter includes a pressure transducer that generates an electrical signal based on the pressure of a process fluid (such as in a water line, a chemical tank, etc.). Process transmitters also typically include transmitter electronics for receiving and processing sensor signals so that the transmitter and process can be remotely monitored. Remotely monitored transmitters include electronics that transmit electrical outputs to a central monitoring location (such as a control room) via a control loop or network. So configured, the process can be regulated from the control room by including automatic switches, valves, pumps, and other similar components in the process control system and control loop.

[0003] The process control industry has also developed sensors, such as pressure sensors, that provide highly accurate output signals over different ranges. For example, one such sensor has an upper range of 4,000 psi and provides a high level of performance over a calibration range of about 30 to 1 (or about 150 psia to 4,000 psia). However, when the 4,000 psia sensor range drops below 150 psia, the total error (percentage of reading) in the output signal increases and may provide a lower than desired level of performance. Other sensors are used to measure pressures from 0 psia to 200 psia and are designed to provide a high level of performance over this entire operating range. There may be multiple different pressure sensors in a pressure transmitter, each of which is designed to accurately measure pressure over a different pressure range. However, this requires significant changes to the design of a typical transmitter configured for use with a single pressure sensor. Summary of the invention

[0004] A pressure transmitter for sensing the pressure of a process fluid in an industrial process, the pressure transmitter comprising a pressure sensor body fluidically coupled to the process fluid, the pressure sensor body being configured to receive an applied pressure associated with the pressure of the process fluid. The pressure sensor body has a high pressure region configured to deform in response to the applied pressure and a low pressure region configured to deform in response to the applied pressure. A high range resistance bridge circuit is installed in the high pressure region, the high range resistance bridge circuit having a power supply node, a common node, and an output node, and having a resistance that changes in response to the pressure applied to the high pressure region. A low range resistance bridge circuit is installed in the low pressure region, the low range resistance bridge circuit having a power supply node, a common node, and an output node, and having a resistance that changes in response to the pressure applied to the low pressure region. A pressure output circuit is coupled to the output node of the high range resistance bridge and the output node of the low range resistance bridge, and provides an output associated with the applied pressure based on a voltage difference between the output node of the high range resistance bridge and the output node of the low range resistance bridge.

[0005] This summary is provided to introduce selected concepts in a simplified form, which are further described in the following specific embodiments. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an auxiliary tool to determine the scope of the claimed subject matter. The claimed subject matter is not limited to specific implementations that solve any or all of the shortcomings pointed out in the background technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a simplified block diagram of a pressure transmitter including a multi-range pressure sensor.

[0007] Figure 2 is a cross-sectional view of an example of a dual range pressure sensor.

[0008] Figure 3 is an electrical schematic of the two resistor bridges in a dual range pressure sensor connected to two differential amplifiers.

[0009] Figure 4 is an electrical schematic of the two resistor bridges in a dual range pressure sensor connected to a single differential amplifier.

[0010] Figure 5 yes Figure 4 V of different amplifiers 输出 Graph of relationship with pressure.

[0011] Figure 6 is an electrical schematic of two resistor bridges in a dual range pressure sensor coupled to a differential amplifier, where each resistor bridge is formed using only two resistors. DETAILED DESCRIPTION

[0012] As discussed in the Background section, in order to measure pressures within more than one pressure range, a pressure transmitter may use different pressure sensors to measure process pressures within different pressure ranges. In another configuration, a pressure transmitter may include a single pressure sensor configuration capable of sensing pressures within multiple ranges. For example, a single sensor body may include multiple pressure sensing regions and associated sensors, each of which is configured to sense pressures within different or overlapping pressure ranges. In such a configuration, electrical connections must be provided to the individual sensors within each of the pressure sensing regions so that the measurement circuitry in the pressure transmitter can receive output signals from the sensors.

[0013] The present invention provides a multi-range pressure sensor in which individual pressure sensors are formed using resistor bridges. The resistance of these resistor bridges is arranged to vary based on the pressure applied to the pressure sensing area of ​​the pressure sensor body. Each of the resistor bridges includes a power supply node and a common or ground node connected to the power supply. The output node from each of the resistor bridges is connected to a pressure output circuit that detects a voltage difference between the output nodes. The voltage difference varies based on the applied pressure and can be characterized to accurately associate the voltage difference with a specific applied pressure.

[0014] A multi-range pressure sensor is provided that combines both a low-range pressure sensing region and a high-range pressure sensing region in one silicon die, each pressure sensing region having its own sensor configured to sense deformation. For example, a piezoresistive strain gauge can be configured as two resistive bridge circuits arranged in a push-pull configuration. Specifically, the two bridge circuits can have a common voltage and ground, but the voltage output of each sensor is separate. This requires two additional electrical connections to the pressure sensor and requires a new header design. In addition, the two outputs require modifications to the existing measurement circuitry and software. The configuration described herein eliminates these changes by utilizing existing sensor board measurement electronics and software.

[0015] Figure 1 1 is a block diagram of a multi-sensor pressure transmitter 10 according to the present invention. The transmitter 10 includes a multi-range pressure sensor 4, a plurality of sensors 12 and 14. The outputs from the sensors 12 to 14 are provided to a differential amplifier 6, which has an output digitized by an optional analog-to-digital (A / D) converter 16. The transmitter 10 also includes a control electronics 18 and a transmitter electronics 20 coupled to a process control loop 22. The control electronics may include, for example, a microprocessor including a memory. In addition, it should be understood that the present invention may be implemented using analog or digital techniques. If analog processing techniques are used, the A / D converter 16 may be eliminated.

[0016] exist Figure 1 In the illustrated embodiment, the sensors 12 and 14 preferably provide output signals indicative of the sensed pressure to the differential amplifier 6. The A / D converter 16 converts the voltage difference signal to a digital value and provides the digital value to the control electronics 18. The control electronics 18 typically includes signal conditioning and correction circuits that correct various errors and nonlinearities of the sensor signals (such as those caused by static pressure, differential pressure, and temperature changes). The control electronics 18 then provides an output signal to the transmitter electronics 20 based on two or more input signals received from the sensors 12 and 14. The transmitter electronics 20 provides an output signal to the loop 22 based on the sensed pressure. In one embodiment, the loop 22 is a 4mA to 20mA current loop modeled by a battery and a resistive load connected in series. The transmitter 10 can be powered entirely by the current loop 22. The transmitter electronics 20 provides an output signal on the loop 22 according to a standardized two-wire 4mA to 20mA current loop transmitter communication protocol. The loop 22 can be a completely analog loop, in which there is no digital communication, and the current represents the sensed pressure. Other standardized transmitter communication protocols may be used. A digital signal may also be output on a 4mA to 20mA current loop, such as loop 22. Alternatively, the transmitter 10 may output a digital signal in FIELDBUS, and all information output by the transmitter 10 (and information present on the loop 22) is represented by the digital signal. The loop 22 may also be based on (IEC 62591) or ISA 100.11a (IEC62734) or another wireless communication protocol (such as WiFi, LoRa, Sigfox, BLE or any other suitable protocol including custom communication protocols) is implemented as a wireless loop.

[0017] exist Figure 1 In the illustrated embodiment, sensor 12 is calibrated for a lower operating pressure range and provides a highly accurate output signal indicative of pressure in the lower range. Sensor 14 is calibrated for a higher operating pressure range and provides a highly accurate output signal indicative of pressure in the higher range.

[0018] Figure 1 Also illustrated is a manifold 26 in a housing 28 of transmitter 10. Manifold 26 provides a sealed barrier that is typically capable of withstanding high pressures. If a process fluid leak occurs at sensors 12, 14, manifold 26 prevents process fluid from entering the portion of housing 28 that includes the transmitter electronics. However, manifold 26 must also allow electrical connections to be made between the transmitter circuitry and sensors 12, 14.

[0019] In one embodiment, the sensor 4 is implemented as Figure 2 The illustrated dual range inline strain gauge pressure sensor. This sensor configuration combines both a low range pressure sensor and a high range pressure sensor in one silicon die, each having its own piezoresistive strain gauge configured in a push-pull bridge configuration. The sensor 4 is made of a lower silicon substrate 30 bonded to an upper silicon substrate 32 by a glass frit 34. The substrate 12 includes a low pressure diaphragm 40 and a high pressure diaphragm 42. An instrument vent 50 is provided in the lower substrate 30 to allow the gauge pressure to be coupled to the cavities 56, 58 formed by the diaphragms 40 and 42 within the sensor 4. A channel 52 is formed in the glass frit 34 to connect the cavities 56 and 58.

[0020] The low-pressure diaphragm 40 is larger than the high-pressure diaphragm 42 and is more easily deflected in response to an applied pressure P in the low-pressure range. An overpressure stopper 44 on the low-pressure diaphragm 40 prevents the low-pressure diaphragm 40 from deforming beyond its operating range in response to an applied high pressure, which may result in failure of the low-pressure diaphragm 40. Piezoresistive strain gauges are mounted on the diaphragms 40 and 42 and have a change in response to the deformation of the diaphragms 40 and 42 to the applied pressure P.

[0021] To sense deformation, the piezoresistive strain gauges may be arranged as a high-pressure range Wheatstone bridge 60 and a low-pressure range Wheatstone bridge 62, as shown in FIG. Figure 3 As illustrated. Each bridge 60, 62 includes four resistive strain gauges R1, R2, R3 and R4. These provide a supply node 70 between resistor R1 and resistor R2, a common node 72 between resistor R2 and resistor R3, a first output node 74 between resistor R3 and resistor R4, and a second output node 76 between resistor R1 and resistor R2. A voltage source 78 provides a voltage between the supply node 70 and the common node 72. A differential amplifier 80 provides an output signal VH related to the voltage difference between node 74 and node 76 of the high voltage range bridge 60, and a differential amplifier 82 provides an output signal VL related to the voltage difference between node 74 and node 76 of the high voltage range bridge 62.

[0022] Bridge 60 and bridge 62 are configured with a push-pull topology whereby under applied pressure, two of the resistors go into tension and two of the resistors go into compression as indicated by the arrows. The two states are represented by the up and down arrows. In this push-pull arrangement, the voltage difference is doubled from one side of the bridge, causing the voltage to increase while the other side decreases. The net effect is a doubling of the differential voltage.

[0023] exist Figure 3In the embodiment of the present invention, bridges 60, 62 have a common voltage and ground, but the voltage output of each sensor is separate. This requires two additional electrical connections through the manifold 26 compared to a single pressure sensor using only a single bridge circuit. Therefore, this configuration requires a new manifold design. In addition, the two outputs VH and VL require changes to the measurement circuit as well as modifications to the software to accept the two outputs. Therefore, this arrangement requires the manifold body to include two additional pins to accommodate the second output. In addition, the two outputs must be processed separately using electronics that include two ASICs that read the two outputs or a multiplexer that multiplexes the two outputs into a single ASIC. This requires a major redesign of the transmitter circuitry and software.

[0024] Figure 2 The dual range pressure sensor 4 combines two sensors into a single piece and provides a cost-effective technology for providing a device with a low pressure range and a high pressure range. Figure 3 These issues discussed, Figure 4 Another configuration is illustrated. Figure 4 In the configuration shown, only half of the bridge 60, 62 output from each sensor 12, 14 is used, with one sensor using the push side of the bridge 60 and the other sensor using the pull side of the other sensor bridge 62. Figure 4 As shown, this configuration does not require additional electrical connections through the header 26 and can further be used with Figure 1 The single differential amplifier 6 shown in FIG.

[0025] When Figure 4 When configured as shown, the output V from the differential amplifier 6 输出 In response to changing pressure, it behaves as Figure 5 As shown in Figure 1. In this configuration, the voltage output of the low-range sensor and the high-range sensor is essentially reduced by 50%. Therefore, the range of the sensor is effectively reduced to 2:1. If the sensor provides a large enough voltage swing, this can be considered an acceptable trade-off considering the simplicity of the specific implementation.

[0026] like Figure 5 As shown, the output is very sensitive to pressure changes in the low pressure range. However, once the overpressure stopper 44 (such as Figure 2As the diaphragm 40 is prevented from further deflecting by the pressure sensor 20 (shown), the output becomes less sensitive to pressure changes in the high pressure range. This is because the high pressure diaphragm 42 has a smaller area and deflects less in response to changes in applied pressure. The output may be calibrated for applied pressure using any suitable technique. The calibration may also include the temperature of the pressure sensor to account for changes in how the diaphragms 40, 42 deflect in response to applied pressure at different temperatures. In one example calibration technique, a very high order polynomial fit is implemented in the control electronics 18 and is used to accommodate the pressure changes in the output. Figure 5 The sharp discontinuity between the low pressure transition region and the high pressure transition region is shown. In another configuration, a polynomial with a weighted fit is used, where the weights are lower in the low and high regions where the linearity is good, and higher weights are used around the knee region. In another example, a piecewise polynomial fit is used, which consists of three separate polynomials, each independently for the low pressure range, the high pressure range, and the transition between the two ranges.

[0027] Figure 6 Another example embodiment is shown. Figure 6 In the configuration of , two resistors in each bridge circuit 60, 62 are removed. Figure 6 The configuration provides a differential voltage with the Figure 4 However, by eliminating the resistor pair on each bridge 60, 62, Figure 6 The current used in the configuration is Figure 4 This is useful in current limited systems. However, it should be noted that the voltage output V 输出 will have Figure 5 The discontinuity shown. In addition, a resistance bridge can be used to sense temperature. In this configuration, the current through the bridges 60, 62 can be measured, for example, by the voltage source 78, and the current can be related to the temperature by the control electronics 18. However, compared to sensors with a single bridge circuit, Figure 4 The resistance provided by the bridge configuration shown will present an uncalibrated current temperature distribution to the control electronics 18. However, Figure 6 The configuration shown provides a current temperature distribution similar to that provided by a single bridge sensor and can be appropriately calibrated for temperature.

[0028] The embodiments of the present disclosure will be described more fully below with reference to the accompanying drawings. Elements identified with the same or similar reference symbols refer to the same or similar elements. In order to simplify the illustration, some elements may not be shown in each figure in the figure.

[0029] The various embodiments of the present disclosure may be embodied in many different forms and should not be construed as limited to the specific embodiments described herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete and will fully convey the scope of the present disclosure to those skilled in the art. Although the present invention has been described with reference to 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. Although two sensing ranges are illustrated, the present invention may be implemented with more than two sensing areas and resistive bridge circuits. However, each additional bridge will result in an overall reduction in the sensitivity of the pressure sensor. As used herein, the pressure output circuit includes a differential amplifier, an analog-to-digital converter, and / or transmitter electronics. Although Figure 6 The configuration shown in does not show a conventional bridge circuit, but the configuration of circuits 60, 62 as used herein is considered a bridge circuit.

Claims

1. A pressure transmitter for sensing the pressure of a process fluid in an industrial process, the pressure transmitter comprising: a pressure sensor body fluidly coupled to the process fluid, the pressure sensor body configured to receive an applied pressure related to a pressure of the process fluid, the pressure sensor body having a high pressure region configured to deform in response to the applied pressure and a low pressure region configured to deform in response to the applied force; a high range resistance bridge circuit mounted in the high voltage region, the high range resistance bridge circuit having a supply node, a common node, and an output node, and having a resistance that varies in response to a pressure applied to the high voltage region; a low-range resistance bridge circuit mounted in the low-voltage region, the low-range resistance bridge circuit having a power supply node, a common node, and an output node, and having a resistance that varies in response to a pressure applied to the low-voltage region; and A pressure output circuit is connected to the output node of the high-range resistor bridge and the output node of the low-range resistor bridge, and the pressure output circuit is configured to provide an output related to the applied pressure based on a voltage difference between the output node of the high-range resistor bridge and the output node of the low-range resistor bridge. 2 . The pressure transmitter of claim 1 , wherein the high range resistance bridge and the low range resistance bridge have a supply voltage and a ground.

3. The pressure transmitter of claim 1 wherein the output is measured on one side of the low range resistance bridge.

4. The pressure transmitter of claim 1 wherein the output is measured on one side of the high range resistance bridge.

5. The pressure transmitter of claim 1, wherein the pressure sensor output is calibrated for temperature and pressure.

6. The pressure transmitter of claim 1, wherein the pressure sensor output is calibrated using a high order polynomial.

7. The pressure transmitter of claim 1, wherein the pressure sensor output is calibrated using a weighted polynomial.

8. The pressure transmitter of claim 1, wherein the pressure sensor output is calibrated using a piecewise fit of a plurality of polynomials.

9. The pressure transmitter of claim 1 wherein the high pressure region and the low pressure region include diaphragms that deflect in response to the applied pressure.

10. The pressure transmitter of claim 9, comprising an overpressure stop associated with the low pressure diaphragm.

11. The pressure transmitter of claim 1 comprising a passage between the high pressure region and the low pressure region.

12. The pressure transmitter of claim 1, wherein the sensor body comprises two substrates bonded together.

13. The pressure transmitter of claim 12, wherein the two substrates are bonded using glass frit.

14. The pressure transmitter of claim 1, wherein the pressure sensor body comprises silicon.

15. The pressure transmitter of claim 1 wherein the pressure output circuit comprises a differential amplifier connected to the output node of the high range resistor bridge and the output node of the low range resistor bridge.

16. The pressure transmitter of claim 1, comprising a header separating the pressure sensor body from the pressure output circuit. 17 . The pressure transmitter of claim 16 , wherein the output node of the high range resistance bridge and the output node of the low range resistance bridge are electrically connected to the pressure output circuit through the header.

18. The pressure transmitter of claim 1, wherein the high range resistance bridge circuit is formed of four resistance elements and includes a second output node, and the low range resistance bridge circuit is formed of four resistance elements and includes a second output node.

19. The pressure transmitter of claim 1, wherein the pressure output circuit is further configured to measure temperature based on current flowing through the high range resistance bridge circuit and the low range resistance bridge circuit.

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