Signal transmission circuit and pressure transmitter

Abstract

The present invention relates to a signal transmission circuit and a pressure transmitter. The signal transmission circuit includes a signal amplification adjustment subcircuit and a signal conversion subcircuit. The signal amplification adjustment subcircuit mainly includes operational amplifiers U1.1, U1.2, U1.3, adjustable resistors P1, P2, resistors R6, R7, R10, R11, R12; the signal conversion subcircuit includes an operational amplifier U1.4, a transistor Q1 and resistors R1, R2, R3, R4, R5, R15. The present invention can amplify the weak differential signal of the sensor through the first-stage differential amplification unit composed of U1.2, P2, R6, R7, and U1.3, and provide a reliable and effective signal for the post-stage processing; the zero adjustment unit composed of R11, R10, P1, and R12 can maintain the compensation characteristics of the sensor itself. The signal conversion subcircuit delicately completes the conversion of the differential voltage signal into a 4-20mA current.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure transmission, in particular to a signal transmission circuit and a pressure transmitter. Background Art

[0002] A pressure transmitter is a device that converts pressure into a pneumatic signal or an electric signal for control and remote transmission. Pressure transmitters usually use strain resistors as sensors to detect pressure. A diffused silicon pressure sensor is a strain resistor that works on the principle of piezoresistive effect. A diffused silicon pressure sensor is usually made using integrated process technology, which contains a Wheatstone bridge composed of multiple basic resistors. The pressure of the diffused silicon pressure sensor acts directly on the diaphragm of the sensor, causing the diaphragm to produce a micro-displacement proportional to the medium pressure, and the resistance value of the sensor changes. When the designed electronic circuit detects this change and converts and outputs a standard measurement signal corresponding to this pressure, a pressure transmitter can be obtained.

[0003] In existing pressure transmitters using diffused silicon pressure sensors, the Wheatstone bridge is zeroed to stabilize the sensor signal. The currently widely used zeroing circuit is to connect the adjustment resistor in parallel to the bridge of the sensor itself, such as Figure 1 As shown, this can easily destroy the circuit balance of the sensor itself, resulting in a poor temperature coefficient of the final output signal. The traditional method uses high-end precision devices to convert weak differential signals into two-wire current output signals. High-end precision devices are expensive and difficult to obtain, which increases the cost and difficulty of V / I signal conversion. Summary of the invention

[0004] Based on this, it is necessary to provide a signal transmission circuit and a pressure transmitter to address the problems of high cost and difficulty in V / I signal conversion.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A signal transmission circuit includes a signal amplification adjustment subcircuit and a signal conversion subcircuit; the signal amplification adjustment subcircuit includes three operational amplifiers U1.1, U1.2, and U1.3, two adjustable resistors P1 and P2, five resistors R6, R7, R10, R11, and R12, and five capacitors C1, C2, C3, C6, and C8. The signal conversion subcircuit includes an operational amplifier U1.4, a transistor Q1, and six resistors R1, R2, R3, R4, R5, and R15.

[0007] The specific connection method of the signal transmission circuit is as follows: the non-inverting input terminal of U1.2 is connected to one end of C2 and C3, and serves as the input terminal +S of the signal transmission. The other end of C2 is grounded. The inverting input terminal of U1.2 is connected to the output terminal, and is connected to one of the fixed pins of P2 and one end of R10. The inverting input terminal of U1.3 is connected to one end of R6 and R7, and the other end of R7 is connected to the output terminal of U1.3 and one end of C6 and R1. The other fixed pin and the moving pin of P2 are connected to the other end of R6. The non-inverting input terminal of U1.3 is connected to one end of C8 and the other end of C3, and serves as the input terminal -S of the signal transmission circuit. The other end of C8 is grounded and serves as the input terminal -I of the signal transmission circuit. The non-inverting input terminal of U1.1 is connected to the other end of C6, R10 and the moving pin of P1. One of the stator pins of P1 is connected to one end of R12, and the other end of R12 is grounded; the other stator pin of P1 is connected to one end of R11, and the other end of R11 is connected to one end of C1, and serves as the input terminal +I of the signal transmission circuit, and the other end of C1 is grounded. The inverting input terminal and output terminal of U1.1 are connected, and connected to one end of resistor R3. The voltage input terminal of U1.1 serves as the voltage-stabilizing input terminal of the signal transmission circuit, and the ground terminal of U1.1 is grounded. The non-inverting input terminal of U1.4 is connected to the other end of R3 and one end of R4, and the other end of R4 is connected to one end of R5, and serves as the output terminal OUT1 of the signal transmission circuit. The inverting input terminal of U1.4 is connected to the other end of R1 and one end of R2. The other end of R2 and the other end of R5 are grounded and connected to the emitter of Q1. The output terminal of U1.4 is connected to one end of R15, and the other end of R15 is connected to the base of Q1.

[0008] In one embodiment, the signal conversion sub-circuit further includes a current limiting protection unit composed of a linear regulator U3 and a resistor R13, and the maximum conduction current I of the current limiting protection unit is m =1.25V / R13≈22mA, 1.25V is the inherent reference voltage of U3, and the current limiting protection unit is connected in series to the collector of Q1. The collector of Q1 is connected to the adjustable end of U3 and one end of R13, the output end of U3 is connected to the other end of R13, and the input end of U3 is connected to the supply voltage VCC.

[0009] In one embodiment, the signal conversion subcircuit further includes a stabilizing unit composed of a resistor R17 and a capacitor C9. The existence of the stabilizing unit can effectively eliminate the self-excitation inside the circuit. One end of R17 is connected to the base of Q1, the other end of R17 is connected to one end of C9, and the other end of C9 is connected to the emitter of Q1.

[0010] In one embodiment, the signal conversion subcircuit further includes capacitors C5 and C7. One end of C5 and C7 is connected to the input end of U3, the other end of C5 is grounded, and the other end of C7 is connected to one end of R5 as the output end of the signal transmission circuit. The output current I OUT1 For: I OUT1 =(+Vi~-Vi) / R5, where +Vi~-Vi is the differential pressure signal entering the signal conversion subcircuit

[0011] Furthermore, operational amplifiers U1.2, U1.3, variable resistor P2, resistor R6, and resistor R7 constitute a first-stage differential amplifier unit for amplifying the detection signal of the sensor.

[0012] Furthermore, the gain A1 of the first-stage differential amplifier unit is: A1=R7 / (R6+R P2 ), where R P2 is the resistance value of the adjustable resistor P2.

[0013] The present invention also includes a pressure transmitter, including a sensor, a power supply circuit and a signal processing circuit. The power supply circuit is used to provide the required power supply. The sensor is used to generate a corresponding detection signal during the detection process. The signal processing circuit is used to convert the detection signal into a corresponding current signal; the signal processing circuit adopts the above-mentioned signal transmission circuit.

[0014] Furthermore, the power supply circuit includes a constant current voltage regulation subcircuit and a power input signal output subcircuit. The constant current voltage regulation subcircuit includes a linear voltage regulator U2, two resistors R9, R16 and a capacitor C4. The constant current voltage regulation subcircuit outputs a constant current of 1.5mA for the sensor and a constant voltage output of 5V for the op amp. The power input signal output subcircuit includes a self-recovery fuse F1 and diodes D1 and D2.

[0015] The specific connection method of the power supply circuit is as follows: the input pin of U2 is connected to the negative poles of D1 and D2, and the output pin of U2 is connected to one end of R9 and R16, and serves as the voltage-stabilized output end of the power supply circuit. The other end of R16 is grounded, C4 is connected in parallel with R16, and the adjustable pin of U2 is connected to the other end of R9, and serves as the constant current output end of the power supply circuit. The output current +I = 1.25V / R9, where 1.25V is the inherent reference voltage of U2. The positive pole of D2 is connected to the output end OUT1 of the signal transmitter circuit, and serves as the signal output end of the pressure transmitter. The positive pole of D1 is connected to one end of F1, and the other end of F1 serves as the power input end of the pressure transmitter.

[0016] In one embodiment, the power input signal output subcircuit further includes magnetic beads L1 and L2. The input pin of the linear regulator U2 is connected to one end of L1, and the other end of L1 is connected to the negative electrodes of D1 and D2; one end of L2 is connected to the output end OUT1 of the signal transmission circuit, and the other end is connected to the positive electrode of D2.

[0017] In one embodiment, the sensor includes a Wheatstone bridge composed of four voltage-variable resistors, and the four bridge arms of the Wheatstone bridge serve as four wiring terminals of the sensor, which are respectively connected to the input terminals +I, -I, +S and -S of the signal transmission circuit.

[0018] The technical solution provided by the present invention has the following beneficial effects:

[0019] 1. The signal transmission circuit provided in the present invention can transform the weak differential signal of the sensor into a corresponding constant current output signal, and the constant current output signal is linearly related to the pressure sensed by the sensor; the first-stage differential amplifier unit composed of U1.2, P2, R6, R7, and U1.3 can amplify the weak differential signal of the sensor; the zero adjustment unit composed of R11, R10, P1, and R12 is located in the circuit at the rear end of the first-stage differential amplifier unit, thereby maintaining the compensation characteristics of the sensor itself, so that the signal output by the signal transmission circuit has higher accuracy.

[0020] 2 The pressure transmitter provided in the present invention utilizes a common and inexpensive quad operational amplifier to complete the process of converting the differential signal of the sensor into a standard current signal; the power supply circuit can not only provide a constant current source for the sensor, but also provide a voltage stabilizing source for the operational amplifier, thereby realizing two functions.

[0021] 3. The present invention sets R17 and C9 to stabilize the circuit to prevent the circuit from self-excitation; sets U3 and R13 to limit the current so that the maximum current does not exceed the preset value of 22mA, thereby protecting the circuit; and sets magnetic beads L1 and L2 to improve the anti-electromagnetic interference capability of the pressure transmitter when it is connected to the outside. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a circuit connection diagram of a conventional zero adjustment circuit and a sensor in the prior art;

[0023] Figure 2 A circuit diagram of a signal transmission circuit of the present invention;

[0024] Figure 3 Based on Figure 2 A circuit diagram of a signal amplification and adjustment sub-circuit;

[0025] Figure 4 Based on Figure 2 A circuit diagram of a signal conversion subcircuit;

[0026] Figure 5 is a circuit diagram of the pressure transmitter in Example 2;

[0027] Figure 6 Based on Figure 5 Circuit diagram of the constant current and voltage stabilizing subcircuit;

[0028] Figure 7 Based on Figure 5 A circuit diagram of a power input and signal output sub-circuit;

[0029] Figure 8 Based on Figure 5 Signal flow diagram of the pressure transmitter;

[0030] Fig. 9 Based on Figure 5 The overall connection circuit diagram of the pressure transmitter. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] This embodiment solves the problem in the prior art that the differential voltage signal cannot be accurately converted into the corresponding output signal due to circuit imbalance when using an amplifier to amplify the weak differential signal, and the cost and difficulty of V / I signal conversion are high. This embodiment can amplify the weak differential signal of the sensor through the first-stage differential amplifier unit composed of U1.2, P2, R6, R7, and U1.3. The first-stage differential amplifier unit A1: A1 = R7 / (R6+R P2 ), where R P2 is the resistance value of the adjustable resistor P2. The zero adjustment unit composed of R11, R10, P1, and R12 is located in the circuit at the rear end of the first-stage differential amplifier unit and is not directly connected in parallel to the bridge of the sensor, thereby maintaining the compensation characteristics of the sensor itself, making the signal output by the signal transmission circuit more accurate.

[0034] like Figure 2As shown, the signal transmission circuit of this embodiment includes a signal amplification adjustment subcircuit and a signal conversion subcircuit. The signal amplification adjustment subcircuit includes three operational amplifiers U1.1, U1.2, and U1.3, two adjustable resistors P1 and P2, five resistors R6, R7, R10, R11, and R12, and five capacitors C1, C2, C3, C6, and C8. The signal conversion subcircuit includes an operational amplifier U1.4, a transistor Q1, a linear regulator U3, eight resistors R1, R2, R3, R4, R5, R13, R15, and R17, and three capacitors C5, C7, and C9.

[0035] like Figure 3 As shown, the signal amplification and adjustment subcircuit includes a first-stage differential amplification unit composed of U1.2, P2, R6, R7, and U1.3, and a zero adjustment unit composed of R11, R10, P1, and R12. The function of U1.1 is to perform impedance transformation on the signal after zero adjustment. Capacitors C5, C7, and C9 play a signal filtering role to eliminate clutter and increase anti-interference capability.

[0036] For the selection of capacitors and resistors, this embodiment provides a specific method: the five capacitors C1, C2, C3, C6, and C8 are all selected as chip capacitors 104, that is, 0.1 μF capacitors. R6 selects chip resistor 201, that is, 200Ω resistor; R7 and R10 select chip resistor 202, that is, 2KΩ resistor; R11 selects chip resistor 203, that is, 20KΩ resistor; R12 selects chip resistor 514, that is, 51KΩ resistor.

[0037] like Figure 4 As shown, U1.4, R1, R2, R3, R4, R15, Q1, and R5 in the signal conversion subcircuit can convert the differential signal into a corresponding single-ended signal to achieve the purpose of linear signal conversion. The stabilization unit composed of resistor R17 and capacitor C9 can prevent the circuit from self-excitation. The current limiting protection unit composed of linear regulator U3 and resistor R13 makes the maximum current not exceed the preset value (22mA), thereby protecting the circuit. The calculation method of the preset value, that is, the maximum on-state current I m :I m =1.25V / R13≈22mA, 1.25V is the inherent reference voltage of U3.

[0038] For the signal conversion subcircuit output current I OUT1 Calculation method: I OUT1 =(+Vi~-Vi) / R5, where +Vi~-Vi is the differential pressure signal entering the signal conversion sub-circuit.

[0039] The electronic components of the signal conversion subcircuit are selected as follows: Q1 uses an NPN transistor, and the model BD237 can be selected, which has a high collector-emitter breakdown voltage characteristic, the collector-emitter breakdown voltage (Vceo) is 80V, and the collector current (Ic) is 2A. U1.4 can choose the same operational amplifier as U1.1, U1.2, and U1.3. It has the characteristics of being cheap and universal.

[0040] The linear regulator U3 uses an adjustable three-terminal positive voltage LDO regulator, which is composed of a three-terminal adjustable voltage regulator integrated circuit LM317. It cleverly uses the special structure of LM317 to simultaneously output a 1.5mA constant current to power the sensor, and output a 5V regulated power supply to provide a stable power supply for the operational amplifier. Specifically, it is an LM317LBDR2G adjustable regulator. It can provide a current greater than 1.5mA in the output voltage range of 1.2V to 37V. It is easy to use and only requires 2 external resistors to set the output voltage. In addition, it also uses internal current limiting, overheating shutdown and safe area compensation to greatly reduce the possibility of damage. It is basically not damaged.

[0041] For the selection of capacitors and resistors, this embodiment provides a specific method: R1, R2, R3, R4, and R5 select chip resistor 203, i.e., a 20KΩ resistor; R13 selects a 56Ω resistor; R15 selects chip resistor 103, i.e., a 10KΩ resistor; R17 selects chip resistor 101, i.e., a 100Ω resistor. C5 and C7 select chip capacitor 104, i.e., a 0.1μF capacitor; and C9 selects chip capacitor 105, i.e., a 1μF capacitor.

[0042] The operational amplifiers U1.1, U1.2, U1.3, and U1.4 in the signal transmitter circuit use cheap general-purpose operational amplifiers. For example, the precision operational amplifier GS8594 has the characteristics of low power consumption, and its performance meets the requirements of a single power supply circuit, and can work with the sensor in a single power supply. In addition, the GS8594 also has the characteristics of zero drift, and the drift is close to zero within the entire tolerable temperature range. At the same time, the operational amplifier is inexpensive and common, and can completely replace the precise and expensive imported integrated circuits to complete the functions required by the pressure transmitter. Other operational amplifiers can also be selected, as long as the rated operating voltage is greater than 7.5V and the static operating current is less than 1.5mA.

[0043] The specific connection method of the electronic components of the signal transmission circuit is as follows: the non-inverting input terminal of U1.2 is connected to one end of C2 and C3, and serves as the input terminal +S of the signal transmission, and the other end of C2 is grounded. The inverting input terminal of U1.2 is connected to the output terminal, and is connected to one of the stator pins of P2 and one end of R10. The inverting input terminal of U1.3 is connected to one end of R6 and R7, and the other end of R7 is connected to the output terminal of U1.3 and one end of C6 and R1, and the other stator pin and the moving pin of P2 are connected to the other end of R6. The non-inverting input terminal of U1.3 is connected to one end of C8 and the other end of C3, and serves as the input terminal -S of the signal transmission circuit. The other end of C8 is grounded and serves as the input terminal -I of the signal transmission circuit. The non-inverting input terminal of U1.1 is connected to the other end of C6, R10 and the moving pin of P1. One of the stator pins of P1 is connected to one end of R12, and the other end of R12 is grounded. The other fixed pin of P1 is connected to one end of R11, the other end of R11 is connected to one end of C1, and serves as the input end +I of the signal transmission circuit, and the other end of C1 is grounded. The inverting input end and output end of U1.1 are connected, and connected to one end of resistor R3. The voltage input end of U1.1 serves as the voltage-stabilizing input end of the signal transmission circuit, and the ground end of U1.1 is grounded. The non-inverting input end of U1.4 is connected to the other end of R3 and one end of R4, the other end of R4 is connected to one end of R5 and C7, and serves as the output end OUT1 of the signal transmission circuit. The inverting input end of U1.4 is connected to the other end of R1 and one end of R2. The other end of R2 and the other end of R5 are grounded, and connected to the emitter of Q1. The output end of U1.4 is connected to one end of R15, and the other end of R15 is connected to the base of Q1. The collector of Q1 is connected to the adjustable end of U3 and one end of R13, the output end of U3 is connected to the other end of R13, and the input end of U3 is connected to the supply voltage VCC. One end of R17 is connected to the base of Q1, the other end of R17 is connected to one end of C9, and the other end of C9 is connected to the emitter of Q1. The other end of C7 is connected to the input end of U3, and the other end of C5 is grounded.

[0044] The signal amplification and adjustment subcircuit of this embodiment amplifies the weak differential signal of the sensor, and the signal conversion subcircuit then performs the conversion process of converting the differential pressure signal into a current signal. The zero adjustment unit is located behind the first-stage differential amplification unit, and does not destroy the circuit balance of the sensor itself. The signal conversion subcircuit can convert the differential voltage signal into a corresponding constant current output signal, and the signal is linearly related to the pressure value sensed by the pressure sensor.

[0045] Example 2

[0046] like Figure 5As shown, this embodiment introduces a pressure sensor, including a sensor, a power supply circuit and a signal processing circuit. The power supply circuit is used to provide the required power. The sensor is used to generate a corresponding detection signal during the detection process. The signal processing circuit is used to convert the detection signal into a corresponding current signal. The signal processing circuit adopts the signal transmission circuit in Example 1.

[0047] The sensor is composed of a Wheatstone bridge composed of four voltage-variable resistors. The four bridge arms of the Wheatstone bridge serve as four wiring terminals of the sensor and are respectively connected to the input terminals +I, -I, +S and -S of the signal transmission circuit.

[0048] The power supply circuit includes a constant current and voltage stabilization subcircuit and a power input signal output subcircuit. Figure 6 As shown, the constant current and voltage stabilization subcircuit includes a linear voltage regulator U2, two resistors R9 and R16, and a capacitor C4. The constant current and voltage stabilization subcircuit outputs a constant current of 1.5mA for the sensor and a constant voltage of 5V for the op amp. Figure 7 As shown, the power input signal output subcircuit includes a self-recovery fuse F1, diodes D1, D2 and magnetic beads L1, L2, which are used to protect the circuit.

[0049] The electronic components of the power supply circuit are selected as follows: Linear regulator U2 is the same model as U3, namely LM317, which cleverly achieves two functions: one is to provide a 1.5mA constant current source for the sensor, and the other is to provide a 5V constant voltage source for the op amp. F1 is used to prevent damage caused by current surges and overheating, and to limit the flow of large currents. Since it can be reset after the circuit fault is cleared and the power is disconnected, the number of maintenance times can be reduced. The model of F1 can be ASMD1206-005, which maintains a current of 0.05A.

[0050] D1 is a reverse protection diode, which plays a role in circuit protection. The model of D1 can be 1N4148, which is easy to obtain, low-priced and widely used. D2 is an overvoltage protection TVS diode with a protection voltage of 26V. You can choose the model SMBJ26AQ, whose reverse cut-off voltage (Vrwm) is 26V. D2 can choose other models of overvoltage protection TVS diodes, but the protection voltage must meet 26V. The DC impedance of the magnetic beads L1 and L2 is zero, and they have a certain inductive reactance to high frequencies. You can choose MMZ1608Q601, whose operating temperature is between -20-90℃, which meets the daily use environment.

[0051] For the selection of resistors and capacitors, this embodiment provides a specific method: R9 selects the chip resistor 821, that is, the 820Ω resistor; R16 selects the chip resistor 103, that is, the 10KΩ resistor; C4 selects the chip capacitor 225, that is, the 2.2μF capacitor.

[0052] The specific connection method of each electronic component in the power supply circuit is as follows: the input pin of U2 is connected to the negative poles of D1 and D2, and the output pin of U2 is connected to one end of R9 and R16, and serves as the voltage-stabilized output end of the power supply circuit. The other end of R16 is grounded, C4 is connected in parallel with R16, and the adjustable pin of U2 is connected to the other end of R9, and serves as the constant current output end of the power supply circuit, and the output current +I = 1.25V / R9, where 1.25V is the inherent reference voltage of U2. The positive pole of D2 is connected to the output end OUT1 of the signal transmission circuit and serves as the signal output end of the pressure transmitter. The positive pole of D1 is connected to one end of F1, and the other end of F1 serves as the power input end of the pressure transmitter. The input pin of U2 is connected to one end of L1, and the other end of L1 is connected to the negative poles of D1 and D2. One end of L2 is connected to the output end OUT1 of the signal transmission circuit, and the other end is connected to the positive pole of D2.

[0053] like Figure 8 As shown, the power supply circuit can provide a 1.5mA constant current source for the sensor and a 5V regulated voltage source for the signal transmission circuit. The signal transmission circuit first amplifies and processes the differential voltage signal (detection signal) of the sensor, then adjusts the zero position, and finally linearly transforms it into a single-ended current signal, and outputs a standard 4-20mA current signal through the power supply circuit.

[0054] This embodiment uses a general-purpose and inexpensive quad op amp to perfectly convert the differential signal of the sensor into a 4-20mA standard signal, and makes this current signal linearly related to the pressure value sensed by the pressure sensor, thereby improving the accuracy of the output current signal.

[0055] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A signal transmission circuit, which is used to collect a detection signal of a sensor and generate a current signal corresponding to the detection amount according to the detection signal of the sensor, characterized in that: The signal transmission circuit includes a signal amplification adjustment subcircuit and a signal conversion subcircuit; the signal amplification adjustment subcircuit includes three operational amplifiers U1.1, U1.2, U1.3, two adjustable resistors P1, P2, five resistors R6, R7, R10, R11, R12, and five capacitors C1, C2, C3, C6, C8; the signal conversion subcircuit includes an operational amplifier U1.4, a transistor Q1 and six resistors R1, R2, R3, R4, R5, R15; Among them, the in-phase input terminal of U1.2 is connected to one end of C2 and C3, and serves as the input terminal +S of the signal transmission, and the other end of C2 is grounded; the inverting input terminal of U1.2 is connected to the output terminal, and is connected to one of the stator pins of P2 and one end of R10; the inverting input terminal of U1.3 is connected to one end of R6 and R7, the other end of R7 is connected to the output terminal of U1.3 and one end of C6 and R1, and the other stator pin and the moving pin of P2 are connected to the other end of R6; the in-phase input terminal of U1.3 is connected to one end of C8 and the other end of C3, and serves as the input terminal -S of the signal transmission circuit; the other end of C8 is grounded, and serves as the input terminal -I of the signal transmission circuit; the in-phase input terminal of U1.1 is connected to the other end of C6, R10 and the moving pin of P1; one of the stator pins of P1 is connected to one end of R12, and R1 2 is grounded; the other fixed pin of P1 is connected to one end of R11, the other end of R11 is connected to one end of C1, and serves as the input end +I of the signal transmission circuit, and the other end of C1 is grounded; the inverting input end and the output end of U1.1 are connected, and are connected to one end of R3; the voltage input end of U1.1 serves as the voltage-stabilizing input end of the signal transmission circuit, and the ground end of U1.1 is grounded; the in-phase input end of U1.4 is connected to the other end of R3 and one end of R4, the other end of R4 is connected to one end of R5, and serves as the output end OUT1 of the signal transmission circuit; the inverting input end of U1.4 is connected to the other end of R1 and one end of R2; the other end of R2 and the other end of R5 are grounded, and connected to the emitter of Q1; the output end of U1.4 is connected to one end of R15, and the other end of R15 is connected to the base of Q1.

2. The signal transmission circuit according to claim 1, characterized in that: The signal conversion subcircuit also includes a current limiting protection unit composed of a linear regulator U3 and a resistor R13, and the current limiting protection unit is connected in series to the collector of Q1; the collector of Q1 is connected to the adjustable end of U3 and one end of R13, the output end of U3 is connected to the other end of R13, and the input end of U3 is connected to the power supply voltage VCC.

3. The signal transmission circuit according to claim 2, characterized in that: The signal conversion subcircuit also includes a stabilization unit consisting of a resistor R17 and a capacitor C9; one end of R17 is connected to the base of Q1, the other end of R17 is connected to one end of C9, and the other end of C9 is connected to the emitter of Q1.

4. The signal transmission circuit according to claim 3, characterized in that: The signal conversion subcircuit also includes capacitors C5 and C7; one end of C5 and C7 is connected to the input end of U3, the other end of C5 is grounded, and the other end of C7 is connected to one end of R5 as the output end of the signal transmission circuit.

5. The signal transmission circuit according to claim 1, characterized in that: The operational amplifiers U1.2, U1.3, variable resistor P2, resistor R6, and resistor R7 constitute a first-stage differential amplifier unit for amplifying the detection signal of the sensor; the amplification factor A1 of the first-stage differential amplifier unit is: A1=R7 / (R6+R P2 ), where R P2 is the resistance value of the adjustable resistor P2.

6. The signal transmission circuit according to claim 5, characterized in that: The amplification factor A1 of the first-stage differential amplifier unit is: A1=R7 / (R6+R P2 ), where R P2 is the resistance value of the adjustable resistor P2.

7. A pressure transmitter, comprising a sensor, a power supply circuit and a signal processing circuit; the power supply circuit is used to provide the required power; the sensor is used to generate a corresponding detection signal during the detection process; the signal processing circuit is used to convert the detection signal into a corresponding current signal; characterized in that: The signal processing circuit adopts the signal transmission circuit as described in any one of claims 1-6.

8. The pressure transmitter according to claim 7, characterized in that: The power supply circuit includes a constant current voltage stabilization subcircuit and a power input signal output subcircuit; the constant current voltage stabilization subcircuit includes a linear voltage stabilizer U2, two resistors R9, R16 and a capacitor C4; the power input signal output subcircuit includes a self-recovery fuse F1 and diodes D1, D2; Among them, the input pin of U2 is connected to the negative poles of D1 and D2, the output pin of U2 is connected to one end of R9 and R16, and serves as the voltage-stabilized output end of the power supply circuit; the other end of R16 is grounded, C4 is connected in parallel with R16, the adjustable pin of U2 is connected to the other end of R9, and serves as the constant current output end of the power supply circuit; the positive pole of D2 is connected to the output end OUT1 of the signal transmission circuit, and serves as the signal output end of the pressure transmitter; the positive pole of D1 is connected to one end of F1, and the other end of F1 serves as the power input end of the pressure transmitter.

9. The pressure transmitter according to claim 8, characterized in that: The power input signal output subcircuit also includes magnetic beads L1 and L2; the input pin of the linear regulator U2 is connected to one end of L1, and the other end of L1 is connected to the negative poles of D1 and D2; one end of L2 is connected to the output end OUT1 of the signal transmission circuit, and the other end is connected to the positive pole of D2.

10. The pressure transmitter according to claim 7, characterized in that: The sensor comprises a Wheatstone bridge composed of four voltage-variable resistors, and the four bridge arms of the Wheatstone bridge serve as four wiring terminals of the sensor and are respectively connected to the input terminals +I, -I, +S and -S of the signal transmission circuit.

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