A constant current powered pressure sensor temperature compensation circuit and compensation method

Abstract

The present invention provides a temperature compensation circuit and method for a constant-current-powered pressure sensor. The compensation circuit comprises: a PTC shunt resistor network, connected in parallel to the exterior of a pressure core, for shunting the constant-current excitation power supply and fitting the required shunt resistor network temperature characteristic curve to compensate for the pressure core's sensitivity temperature drift; and an NTC zeroing resistor network, connected in series and parallel to the arms of the Wheatstone bridge, for fitting the resistance-temperature characteristic curve required for zero-point compensation and compensating the pressure core's zero-point output and temperature drift to within acceptable ranges. The present invention employs thermistors instead of fixed resistors to compensate for pressure sensors with large zero-point output temperature drift within acceptable ranges.

Description

Technical field

[0001] The present invention relates to a constant current powered pressure sensor, in particular to a temperature compensation circuit and compensation method for a constant current powered pressure sensor. [Background Technology]

[0002] At present, the existing temperature compensation methods for pressure sensors on the market are mainly divided into analog compensation and digital compensation. Digital compensation is calibrated through a signal conditioning chip, and the output voltage is usually in the volt level (V); analog compensation mainly uses a resistor network or amplifier circuit outside the pressure core to achieve temperature compensation of the pressure sensor, and its output voltage is usually in the volt level (V) or millivolt level (mV).

[0003] like Figure 1 As shown, the internal circuit of the pressure core in the pressure sensor can be equivalent to a Wheatstone bridge, which has four bridge arm resistors R1, R2, R3, and R4. The resistance values of the four bridge arm resistors are positively correlated with the temperature. The bridge arm resistance temperature characteristics are as follows: Figure 2 shown.

[0004] The sensitivity of the pressure core is positively correlated with the excitation power supply of the core and negatively correlated with temperature changes. That is, when the excitation voltage is constant, the sensitivity of the core decreases with increasing temperature; when the temperature is constant, the sensitivity of the core increases with increasing excitation voltage.

[0005] Therefore, the temperature characteristic of the pressure core with constant current excitation is: if the pressure core adopts constant current excitation, since the resistance of the bridge arm increases with temperature, the power supply of the core also increases with temperature, while the sensitivity decreases with temperature. Therefore, when constant current power supply is adopted, the pressure core has a self-compensation effect. The sensitivity temperature characteristic curve of the pressure core with constant current power supply is as follows: Figure 3 shown.

[0006] Since most pressure sensors are powered by a constant voltage excitation power supply, the above two compensation methods are not fully applicable to pressure sensors with constant current excitation. The main reasons are:

[0007] 1. Since the sensitivity and resistance of the pressure core of the constant current excitation pressure sensor are positively correlated with the temperature, the sensitivity temperature drift can be compensated by connecting a parallel resistor network outside the sensor. However, the temperature drift cannot be compensated by connecting a series resistor network outside the sensor.

[0008] 2. Constant current excitation pressure sensors will cause large zero output temperature drift due to the use of constant current excitation. For pressure sensors with large zero output temperature drift, the solution of connecting fixed resistors in series and parallel on the core body cannot fully compensate for the temperature drift.

[0009] Therefore, this application proposes a constant current excitation pressure sensor temperature compensation method, which uses a thermistor instead of a fixed resistor to compensate the pressure sensor with a large zero-position output temperature drift to an acceptable range. It is mainly used to compensate for the temperature drift of the pressure sensor with a small signal output in the millivolt (mV) level to meet the technical index requirements. [Summary of the invention]

[0010] In view of this, the technical problem to be solved by the present invention is to provide a temperature compensation circuit and compensation method for a constant current-powered pressure sensor, which uses a thermistor instead of a fixed resistor to compensate a pressure sensor with a large zero-position output temperature drift to an acceptable range.

[0011] To achieve one of the aforementioned objectives of the invention, the technical solution adopted in an embodiment of the present invention is: a temperature compensation circuit for a constant current-powered pressure sensor, wherein the internal circuit of the pressure core in the pressure sensor is equivalent to a Wheatstone bridge, characterized in that the compensation circuit includes:

[0012] The PTC shunt resistor network is connected in parallel to the outside of the pressure core to shunt the constant current excitation power supply and fit the required shunt resistor network temperature characteristic curve to compensate for the sensitivity temperature drift of the pressure core;

[0013] The NTC zero adjustment resistor network is connected in series and in parallel to the arms of the Wheatstone bridge and is used to fit the resistance temperature characteristic curve required for zero point compensation, thereby compensating the zero point output and temperature drift of the pressure core to a qualified range.

[0014] To achieve the second object of the aforementioned invention, the technical solution adopted by the embodiment of the present invention is: a method for compensating the temperature of a constant current powered pressure sensor, including a constant current excited pressure sensor sensitivity compensation process and a zero adjustment resistance and temperature drift compensation process;

[0015] The constant current excitation pressure sensor sensitivity compensation process includes:

[0016] S11, connecting a shunt resistor network in parallel outside the pressure core to shunt the constant current excitation power supply, so that the supply current of the Wheatstone bridge increases first and then decreases;

[0017] S12. Calculate the supply current of the Wheatstone bridge according to the following formula (1):

[0018]

[0019] In formula (1):

[0020] U out —Full-scale output target value;

[0021] U FS —Supply current IT The full-scale output of the pressure core is obtained through actual measurement;

[0022] I T —Total supply current;

[0023] I B — Supply current of the Wheatstone bridge;

[0024] S13, according to the supply current I of the Wheatstone bridge B Calculate the resistance R of the shunt resistor network at each temperature P , obtaining a temperature variation trend of the resistance of the shunt resistor network;

[0025] First calculate the resistance R of the shunt resistor according to Ohm's law P ;

[0026] U B =I B ×R B (4)

[0027] I p =I T -I B (5)

[0028]

[0029] in:

[0030] U B —The supply voltage of the Wheatstone bridge is equal to the voltage across the shunt resistor network;

[0031] R B —The total resistance of the bridge arms of the Wheatstone bridge is obtained by actual measurement;

[0032] I P — shunt current;

[0033] R P —Resistance of the shunt resistor network;

[0034] Then, the resistance of the shunt resistor network at each temperature is calculated to obtain a resistance variation curve of the shunt resistor network over temperature;

[0035] S13, forming a PTC shunt resistor network with a PTC thermistor and a fixed resistor, and fitting a required shunt resistor network temperature characteristic curve through the PTC shunt resistor network according to a shunt resistance temperature variation curve;

[0036] The compensation process of the zero adjustment resistance and temperature drift is:

[0037] An NTC thermistor and a fixed resistor are connected in series and in parallel on the arms of the Wheatstone bridge to form an NTC zero adjustment resistor network, which is used to fit the resistance-temperature characteristic curve required for zero-point compensation. According to the temperature characteristics of the NTC thermistor, the zero-point output can output the same voltage value at different temperatures.

[0038] The advantages of the present invention are: the temperature compensation circuit and compensation method of the constant current powered pressure sensor of the present invention can shunt the constant current excitation power supply by connecting a parallel resistor network outside the core body, thereby reducing the current flowing into the pressure core body, and thus compensating for the sensitivity temperature drift by controlling the current flowing into the pressure core body. Since the required shunt resistance increases with temperature, a PTC thermistor and a fixed value resistor can be used to fit the required resistance curve. In terms of compensation for zero adjustment resistance and temperature drift, since the use of a fixed resistor cannot compensate the zero point output and temperature drift to a qualified range, an NTC thermistor solution is used to compensate for the zero point temperature drift. According to the temperature characteristics of the NTC, the zero point output can achieve the same voltage value at different temperatures. It can be mainly used to compensate for the temperature drift of pressure sensors with small signal output in the millivolt level (mV) to meet the technical index requirements.

Brief Description of the Drawings

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Figure 1 It is a schematic diagram of the equivalent circuit structure of the pressure core of the pressure sensor of the present invention.

[0041] Figure 2 This is a numerical table of the temperature characteristics of the bridge arm resistance of an example of the present invention.

[0042] Figure 3 FIG. 4 is a temperature characteristic curve of the pressure core sensitivity of an embodiment of the present invention.

[0043] Figure 4 This is a schematic diagram of a temperature compensation circuit for a constant current powered pressure sensor according to an embodiment of the present invention.

[0044] Figure 5 1 is a flow chart of a method for compensating temperature of a constant current powered pressure sensor according to a second embodiment of the present invention.

[0045] Figure 6 Schematic diagram of a temperature characteristic curve of a shunt resistor network according to an embodiment of the present invention.

[0046] Figure 7 FIG. 1 is a schematic diagram of a resistance-temperature characteristic curve required for zero-point compensation according to an embodiment of the present invention.

[0047] Figure 8 FIG. 1 is a schematic diagram of a shunt resistance curve varying with temperature according to an embodiment of the present invention.

[0048] Figure 9 Schematic diagram of a temperature drift curve of a PTC thermistor according to an embodiment of the present invention.

[0049] Figure 10 1 is a schematic diagram comparing a curve fitted by a PTC thermistor and a shunt resistor curve according to an embodiment of the present invention. [Specific implementation method]

[0050] The embodiment of the present invention provides a temperature compensation circuit and compensation method for a constant current-powered pressure sensor, which uses a thermistor instead of a fixed resistor to compensate a pressure sensor with a large zero-position output temperature drift to an acceptable range.

[0051] The technical solution in the embodiment of the present invention is to solve the above problems. The overall idea is as follows: a constant current powered pressure sensor cannot be temperature compensated by connecting a resistor network in series outside the core. Therefore, it is necessary to use a parallel connection outside the core. By connecting a resistor network in parallel outside the pressure core, the constant current excitation power supply can be shunted to reduce the current flowing into the pressure core, so that the sensitivity temperature drift can be compensated by controlling the current flowing into the pressure core. Since the required shunt resistance increases with temperature, a PTC thermistor and a fixed resistor can be used to fit the required resistance curve. In terms of compensation for zero resistance and temperature drift, since the use of a fixed resistor cannot compensate the zero-point output and temperature drift to the qualified range, the NTC thermistor solution is used to compensate for the zero-point temperature drift. According to the temperature characteristics of the NTC, the zero-point output can output the same voltage value at different temperatures.

[0052] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0053] Example 1

[0054] See also Figure 4 As shown, the temperature compensation circuit of the constant current powered pressure sensor of this embodiment includes a PTC shunt resistor network and an NTC zero adjustment resistor network.

[0055] The PTC shunt resistor network is connected in parallel to the outside of the pressure core to shunt the constant current excitation power supply, reduce the current flowing into the pressure core, and fit the required shunt resistor network temperature characteristic curve. By controlling the current flowing into the pressure core, the sensitivity temperature drift of the pressure core is compensated.

[0056] The PTC shunt resistor network includes a PTC thermistor RP and two fixed resistors R5 and R6. The PTC thermistor RP is connected in parallel with R5 and then in series with R6.

[0057] The NTC zero adjustment resistor network is connected in series and in parallel to the arms of the Wheatstone bridge and is used to fit the resistance temperature characteristic curve required for zero point compensation, thereby compensating the zero point output and temperature drift of the pressure core to a qualified range.

[0058] The NTC zeroing resistor network includes an NTC thermistor RN and three fixed resistors R7, R8, and R9; the bridge arm R3 of the Wheatstone bridge is connected in parallel with the fixed resistor R7 and then connected in series with the fixed resistor R8; that is, one end of the fixed resistor R8 is connected to the bridge arm R3 and the other end is grounded, and the fixed resistor R7 has one end connected to the voltage output terminal Vout+ of the Wheatstone bridge and the other end connected to the fixed resistor R8; the fixed resistor R9 is connected in parallel with the NTC thermistor and then connected in series with the bridge arm R4 of the Wheatstone bridge; that is, after the NTC thermistor is connected in parallel with R9, one end is connected to the bridge arm R4 and the other end is grounded.

[0059] Example 2

[0060] See also Figure 5 As shown, the temperature compensation method of the constant current powered pressure sensor of this embodiment includes a constant current excited pressure sensor sensitivity compensation process and a zero adjustment resistance and temperature drift compensation process;

[0061] The parallel resistor network outside the core can shunt the constant current excitation power supply, reduce the current flowing into the pressure core, and compensate for the sensitivity temperature drift by controlling the current flowing into the pressure core. The change trend of the resistance value of the shunt resistor network with temperature is obtained by calculation. Figure 6 As shown by Figure 6 It can be seen that the required shunt resistance increases with temperature, and a PTC thermistor and a fixed resistor can be used to fit the required resistance curve.

[0062] Zero adjustment resistance and temperature drift are usually compensated by connecting fixed resistors in series and parallel on the bridge arms of the pressure core. For pressure sensors with large zero temperature drift, the resistor temperature characteristics required to compensate for its zero temperature drift are as follows: Figure 7 As shown. Figure 7 It can be seen that the use of fixed resistors cannot compensate the zero-point output and temperature drift to the qualified range. This solution proposes to use NTC thermistor to compensate for the zero-point temperature drift. According to the temperature characteristics of NTC, the zero-point output can achieve the same voltage value at different temperatures.

[0063] The specific compensation methods are as follows:

[0064] The full-scale output voltage of the pressure core is proportional to the supply current. To keep the full-scale output voltage constant at different temperatures, it is only necessary to make the supply current of the Wheatstone bridge (i.e., the current flowing through the Wheatstone bridge) increase first and then decrease. To achieve this, the supply current needs to be shunted to change the trend of the bridge supply current. Therefore, the sensitivity compensation process of the constant current excitation pressure sensor specifically includes:

[0065] S11, connecting a shunt resistor network in parallel outside the pressure core to shunt the constant current excitation power supply, so that the supply current of the Wheatstone bridge increases first and then decreases;

[0066] S12. Calculate the supply current of the Wheatstone bridge according to the following formula (1):

[0067]

[0068] In formula (1):

[0069] U out —Full-scale output target value;

[0070] U FS —Supply current I T The full-scale output of the pressure core is obtained through actual measurement;

[0071] I T —Total supply current, which is composed of the current in the shunt resistor network and the supply current of the Wheatstone bridge;

[0072] I B — Supply current of the Wheatstone bridge;

[0073] S13, according to the supply current I of the Wheatstone bridge B Calculate the resistance R of the shunt resistor network at each temperature P , obtaining a temperature variation trend of the resistance of the shunt resistor network;

[0074] If the current in the shunt resistor network I P Known, we can first calculate the resistance value R of the shunt resistor according to Ohm's law. P ;

[0075] U B =I B ×R B (4)

[0076] I P =I T -I B (5)

[0077]

[0078] in:

[0079] U B —The supply voltage of the Wheatstone bridge is equal to the voltage across the shunt resistor network;

[0080] R B —The total resistance of the bridge arms of the Wheatstone bridge is obtained by actual measurement;

[0081] I P —Shunt current, i.e. the current in the shunt resistor network, can be calculated according to formula (5);

[0082] R P —Resistance of the shunt resistor network;

[0083] Then the resistance of the shunt resistor network at each temperature is calculated to obtain the resistance variation curve of the shunt resistor network with temperature, such as Figure 8 As shown;

[0084] S13, and then Figure 9 As shown in FIG, the temperature drift curve of the PTC thermistor, therefore, the PTC thermistor and the fixed value resistor can be combined into a PTC shunt resistor network, and the required shunt resistor network temperature characteristic curve can be fitted through the PTC shunt resistor network according to the shunt resistance temperature variation curve;

[0085] The PTC shunt resistor network includes a PTC thermistor and two fixed-value resistors, R5 and R6. The PTC thermistor is connected in parallel with R5 and then in series with R6. The temperature curve fitted by the PTC shunt resistor network is compared with the desired shunt resistor curve, and they are basically consistent, indicating a good fitting effect.

[0086] There are usually three types of curves for the zero-position output voltage to change with temperature: 1. Monotonically increasing curve; 2. Monotonically decreasing curve; 3. Broken line type (increases first and then decreases or decreases first and then increases). By setting the resistor R7 on the Wheatstone bridge, the temperature drift curve can be unified into a monotonically decreasing type. Figure 2 As shown in the figure, the principle is that the resistance of the bridge arm of the Wheatstone bridge increases monotonically with temperature.

[0087] The compensation process of the zero adjustment resistance and temperature drift is:

[0088] like Figure 4 As shown, first connect a fixed resistor R7 in parallel to the bridge arm R3 to reduce the resistance of the bridge arm R3, and the reduction at high temperature is greater than the reduction at low temperature. The following formula is used to calculate

[0089] R3 (-55℃) <R3 (25℃) <R3 (125℃)

[0090] After R3 is connected in parallel with the fixed resistor R7, the changes at -55℃, 25℃, and 125℃ are:

[0091] △R3 (-55℃) =R3 (-55℃) -R3 (-55℃) ×R7 / (R3 (-55℃) +R7)

[0092] △R3 (25℃) =R3 (25℃) -R3 (25℃) ×R7 / (R3 (25℃) +R7)

[0093] △R3 (125℃) =R3 (125℃) -R3 (125℃) ×R7 / (R3 (125℃) +R7)

[0094] The selected R7 is a low temperature drift resistor, and the effect of temperature on the resistance of R7 can be ignored, so

[0095] △R3 (-55℃) <△R3 (25℃) <△R3 (125℃)

[0096] The output mode of the Wheatstone bridge circuit is differential output, where the zero-position output voltage can be expressed as:

[0097]

[0098]

[0099]

[0100] Where:

[0101] U in is the supply voltage of the Wheatstone bridge;

[0102] R1, R2, R3 and R4 are the four arm resistors of the bridge;

[0103] V out+ is the voltage between bridge arms R2 and R3;

[0104] V out- is the voltage between bridge arms R1 and R4;

[0105] V out is the differential output voltage of the bridge;

[0106] Since the resistor R7 is connected in parallel to the bridge arm R3 first, it has no effect on the resistance values of the bridge arms R1, R2 and R4, so V out-unchanged, V out+ Decrease. According to △R3 (-55℃) <△R3 (25℃) <△R3 (125℃) ,so

[0107] △V out+(-55℃) <△V out+(25℃) <△V out+(125℃)

[0108] The Wheatstone bridge output voltage Vout decreases, with the change at high temperatures greater than at low temperatures. Through iterative calculations, we can select an appropriate resistor R7, unifying the temperature drift curve into a monotonically decreasing pattern. This allows us to calculate the zero-adjustment resistor specifications required to compensate for the zero-position output voltage at different temperatures.

[0109] After the temperature drift curves are unified, the series resistor R8 on the bridge arm R3 is increased so that Vout+>Vout- at all temperatures, that is, the output voltage of the Wheatstone bridge is positive. From formula (8), it can be seen that increasing the resistance of the bridge arm R4 can increase Vout-, that is, increasing the series resistor R9 and RN on R4 so that Vout+=Vout- and the output voltage is 0.

[0110] Bridge arms R1, R2, R3, and R4 can all be directly measured. The fixed-value resistor R7 is a known value, allowing the calculation of the required zero-adjustment resistor value when Vout+ = Vout-. This is the value obtained by connecting R9 and the NTC thermistor in parallel. The zero-adjustment resistor has different values at different temperatures, showing a monotonically decreasing trend. The NTC thermistor has a temperature drift characteristic that decreases monotonically with temperature. By connecting the NTC thermistor in parallel with the fixed-value resistor R9, a temperature-dependent resistor can be constructed, connected in series with R4, ensuring that the zero-position output voltage is 0 at all temperatures.

[0111] The NTC zero adjustment resistance network includes an NTC thermistor and three fixed resistors R7, R8, and R9; the bridge arm R3 of the Wheatstone bridge is connected in parallel with the fixed resistor R7 and then connected in series with the fixed resistor R8; the fixed resistor R9 is connected in parallel with the NTC thermistor and then connected in series with the bridge arm R4 of the Wheatstone bridge.

[0112] The present invention's temperature compensation circuit and method for a constant-current-powered pressure sensor shunts the constant-current excitation power supply through a parallel resistor network connected externally to the core, reducing the current flowing into the pressure core. This reduces the current flowing into the pressure core, thereby compensating for sensitivity temperature drift. Since the required shunt resistance increases with temperature, a PTC thermistor and a fixed-value resistor can be used to fit the required resistance curve. Regarding zero-adjustment resistance and temperature drift compensation, since fixed resistors cannot compensate for zero-point output and temperature drift within acceptable ranges, an NTC thermistor is used instead. Due to the temperature characteristics of the NTC, the zero-point output maintains the same voltage value at different temperatures. This is primarily used to compensate for temperature drift in pressure sensors with small millivolt (mV) output signals, ensuring they meet technical specifications. Our company's JCYYZ343V-2 pressure sensor uses this compensation scheme. After compensation, the accuracy is ±1% at room temperature, and both zero-point and sensitivity temperature drift are ±0.06% FS / °C.

[0113] Although the specific embodiments of the present invention are described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A temperature compensation circuit for a constant current-powered pressure sensor, wherein the internal circuit of the pressure core in the pressure sensor is equivalent to a Wheatstone bridge, characterized in that: The compensation circuit comprises: The PTC shunt resistor network is connected in parallel to the outside of the pressure core to shunt the constant current excitation power supply and fit the required shunt resistor network temperature characteristic curve to compensate for the sensitivity temperature drift of the pressure core; The NTC zero adjustment resistor network is connected in series and in parallel to the arms of the Wheatstone bridge, and is used to fit the resistance temperature characteristic curve required for zero point compensation, and compensate the zero point output and temperature drift of the pressure core to a qualified range; The PTC shunt resistor network includes a PTC thermistor and two fixed resistors R5 and R6. The PTC thermistor is connected in parallel with R5 and then in series with R6. The NTC zero adjustment resistor network includes an NTC thermistor and three fixed resistors R7, R8, and R9; the bridge arm R3 of the Wheatstone bridge is connected in parallel with the fixed resistor R7 and then in parallel with R8; the fixed resistor R9 is connected in parallel with the NTC thermistor and then in series with the bridge arm R4 of the Wheatstone bridge.

2. A method for compensating temperature of a constant current powered pressure sensor, characterized in that: The temperature compensation circuit of a pressure sensor powered by a constant current as claimed in claim 1 includes a pressure sensor sensitivity compensation process with constant current excitation and a zero resistance and temperature drift compensation process; The constant current excitation pressure sensor sensitivity compensation process includes: S11, connecting a shunt resistor network in parallel outside the pressure core to shunt the constant current excitation power supply, so that the supply current of the Wheatstone bridge increases first and then decreases; S12. Calculate the supply current of the Wheatstone bridge according to the following formula (1): In formula (1): U out —Full-scale output target value; U FS —Supply current I T The full-scale output of the pressure core is obtained through actual measurement; I T —Total supply current, which is the constant current value provided by the power supply system; I B — Supply current of the Wheatstone bridge; S13, according to the supply current I of the Wheatstone bridge B Calculate the resistance R of the shunt resistor network at each temperature P , obtaining a temperature variation trend of the resistance of the shunt resistor network; First calculate the resistance R of the shunt resistor according to Ohm's law P ; IN B =I B ×R B (4) I p =I T -I B (5) in: U B —The supply voltage of the Wheatstone bridge is equal to the voltage across the shunt resistor network; R B —The total resistance of the bridge arms of the Wheatstone bridge is obtained by actual measurement; I P — shunt current; R P —Resistance of the shunt resistor network; Then, the resistance of the shunt resistor network at each temperature is calculated to obtain a resistance variation curve of the shunt resistor network over temperature; S13, forming a PTC shunt resistor network with a PTC thermistor and a fixed resistor, and fitting a required shunt resistor network temperature characteristic curve through the PTC shunt resistor network according to a shunt resistance temperature variation curve; The compensation process of the zero adjustment resistance and temperature drift is: An NTC thermistor and a fixed resistor are connected in series and in parallel on the arms of the Wheatstone bridge to form an NTC zero adjustment resistor network, which is used to fit the resistance-temperature characteristic curve required for zero-point compensation. According to the temperature characteristics of the NTC thermistor, the zero-point output can output the same voltage value at different temperatures.

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