Circuit for measuring multiple composite signals

Abstract

The utility model relates to the technical field of single crystal furnace step ladders, in particular to a circuit for measuring multiple composite signals, which comprises a TC input detection circuit, an RTD input detection circuit, a voltage input detection circuit, a current input detection circuit and an AD circuit, the TC input detection circuit, the RTD input detection circuit, the voltage input detection circuit and the current input detection circuit are connected with the AD circuit through the switching circuit, a voltage signal generated by the TC is input through the TC input detection circuit, a resistance signal generated by the RTD is input through the RTD input detection circuit, the voltage signal is input through the voltage input detection circuit, and the current input detection circuit is connected with the AD circuit. A current signal is input through the current input detection circuit. According to the utility model, the universality of the product is improved, and the overall cost is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of signal measurement in automated industrial control, in particular to a circuit for compounding multiple signal measurements. Background Art

[0002] In industrial automation applications, different sensor types may correspond to different signal types. Commonly used sensors include 0-20mA current, 0-5V voltage, TC (mV voltage), and RTD (PT100 resistance). The control room's PLC or DCS collects these signals through card components and converts them into corresponding process quantities, such as temperature, pressure, and flow. This requires a wide variety of signal isolation and transmission instruments to isolate and convert sensor signals into standard measurement signals, such as the standard 4-20mA signal. Failure to use the wrong instrumentation can damage the sensor at best, or even hinder project progress. Furthermore, during subsequent maintenance, the wide variety of stockpiles can lead to inventory backlogs and waste resources.

[0003] A single signal isolation and transmission instrument can no longer meet actual needs, which is mainly manifested in its narrow applicability, the need to purchase many varieties, high costs, and long cycles. Utility Model Content

[0004] The utility model provides a circuit for compounding multiple signal measurements, which improves the versatility of the product and reduces the overall cost.

[0005] In order to achieve the purpose of the present utility model, the technical solution adopted is: a circuit for composite multiple signal measurement, including a TC input detection circuit, an RTD input detection circuit, a voltage input detection circuit, a current input detection circuit and an AD circuit. The TC input detection circuit, the RTD input detection circuit, the voltage input detection circuit and the current input detection circuit are connected to the AD circuit through a switching circuit. The voltage signal generated by the TC is input through the TC input detection circuit, the resistance signal generated by the RTD is input through the RTD input detection circuit, the voltage signal is input through the voltage input detection circuit, and the current signal is input through the current input detection circuit.

[0006] As an optimized solution of the present utility model, the TC input detection circuit includes an RTD temperature sensor, a first excitation circuit, a first filtering circuit, a first amplifying circuit, a first protection circuit, a second filtering circuit and a second amplifying circuit. The TC signal is input through ports 1 and 2, passes through the first protection circuit, the second filtering circuit and the second amplifying circuit in sequence, and then enters the switching circuit. The RTD temperature sensor measures the temperature of the TC cold end compensation. The first excitation circuit provides a constant current to generate a voltage signal on the RTD, which is sent to the AD measurement inside the MCU through the first filtering circuit and the first amplifying circuit.

[0007] As an optimized solution of the present utility model, the first excitation circuit includes an operational amplifier U23, a PMOS tube Q1, a resistor R3, a resistor R21, a resistor R4, a resistor R18, a capacitor C6 and a capacitor C26, the first amplification circuit includes a resistor R8, a resistor R68, a resistor R71, a capacitor C87, a resistor R35 and a capacitor C86, the first protection circuit is a transient voltage suppression diode D6, the second filter circuit includes a capacitor C16, an inductor L2, a resistor R44, a capacitor C35, a resistor R45 and a capacitor C38, the second amplification circuit includes a U1B operational amplifier, a transient voltage suppression diode D6 is connected between ports 1 and 2, the capacitor C16 is connected between port 2 and ground, the inductor L2 and the resistor R44 are connected in series between terminal 2 and one end of the resistor R45, the capacitor C35 is connected between one end of the resistor R45 and ground, and the other end of the resistor R45 is connected to the positive input of the U1B operational amplifier. Ends are connected, capacitor C38 is connected between the other end of resistor R45 and ground, resistor R8 and resistor R68 are connected in series between the power supply 2.5V and ground, resistor R68 is connected between the 2nd pin of the operational amplifier U23 and ground, resistor R71 and capacitor C87 are connected in parallel between the 2nd pin of the operational amplifier U23 and ground 1 pin, resistor R35 and capacitor C86 are connected between the 1st pin of the operational amplifier U23 and ground, resistor R4 is connected between the power supply 2.5V and the 5th pin of the operational amplifier U23, resistor R18 is connected between the 5th pin of the operational amplifier U23 and ground, capacitor C26 is connected between the output end of inductor L2 and ground, resistor R3 is connected between the power supply 2.5V and the source of PMOS tube Q1, resistor R21 is connected between the output end of inductor L2 and the drain of PMOS tube Q1, and capacitor C6 is connected between the gate and source of PMOS tube Q1.

[0008] As an optimized solution of the present utility model, the RTD input detection circuit includes a second excitation circuit, a third filtering circuit, a third amplifying circuit, a second protection circuit, a fourth filtering circuit and a fourth amplifying circuit. The resistance signal generated by the RTD is input through ports 1, 2 and 3. Terminal 3 provides a constant current excitation source through the second excitation circuit to generate a voltage signal on the RTD, which is sent to the analog switch after passing through the third filtering circuit and the third amplifying circuit; terminal 2 collects the line resistance signal, which is sent to the analog switch after passing through the second protection circuit, the fourth filtering circuit and the fourth amplifying circuit in sequence. The line resistance compensation operation is performed based on the two collected signals to obtain the final measured resistance value.

[0009] As an optimization solution of the present invention, the fourth filtering circuit includes a resistor R33, a resistor R34, a capacitor C27, a capacitor C28 and a capacitor C30. ，The fourth amplifier circuit includes an operational amplifier U1, a resistor R38, a resistor R40, a resistor R41 and a capacitor C29, wherein the resistor R33 is connected between the output pin of the inductor L2 and one end of the capacitor C27, the other end of the capacitor C27 is grounded, the resistor R34 is connected between one end of the capacitor C27 and the third pin of the operational amplifier U1, the capacitor C28 is connected between the third pin of the operational amplifier U1 and ground, and the capacitor C30 is connected between one end of the capacitor C27 and one end of the resistor R45; the capacitor C29 and the resistor R38 are connected in parallel between the second pin and the first pin of the operational amplifier U1, and the resistor R40 and the resistor R41C are connected in series between the second pin and the seventh pin of the operational amplifier U1.

[0010] As an optimized solution of the present invention, the voltage input detection circuit includes a third protection circuit, a voltage divider circuit and a fifth filter circuit. The voltage signal is input through ports 1 and 4, and is sent to the switching circuit in sequence through the third protection circuit, the voltage divider circuit and the fifth filter circuit.

[0011] As an optimized solution of the present utility model, the voltage signal is input through ports 1 and 4, the third protection circuit includes a transient voltage suppressor diode D8, the voltage divider circuit includes a resistor R37 and a resistor R47, the fifth filter circuit includes a resistor R6, a capacitor C25, a capacitor C34, a resistor R5 and a capacitor C24, the transient voltage suppressor diode D8 is connected between the 4th port and the ground, the resistor R6 is connected between the 4th port and one end of the capacitor C25, the other end of the capacitor C25 is grounded, the resistor R37 is connected between one end of the capacitor C25 and one end of the resistor R47, the capacitor C34 is connected between one end of the resistor R47 and the ground, and the resistor R5 and the capacitor C24 are connected in series between one end of the resistor R47 and the ground.

[0012] As an optimized solution of the present invention, the current input detection circuit includes a fourth protection circuit, an anti-reverse circuit, a current limiting circuit, a sampling circuit and a sixth filtering circuit. The current signal is input through ports 1 and 5, and enters the sampling circuit after passing through the fourth protection circuit, the anti-reverse circuit and the current limiting circuit in sequence. The sampling circuit converts the input current into a voltage signal and then filters it by the sixth filtering circuit.

[0013] As an optimized solution of the present utility model, the fourth protection circuit includes a transient voltage suppression diode D5, the anti-reverse circuit includes an anti-reverse polarity diode D7, the current limiting circuit includes a fuse F2, the sampling circuit includes a resistor R48, and the sixth filter includes a capacitor C82, a capacitor C13, a capacitor C22, a resistor R1 and a resistor R2. The transient voltage suppression diode D5 is connected between the 5th port and the ground, the anti-reverse polarity diode D7 and the fuse F2 are connected in series between the 5th port and one end of the resistor R48, the other end of the resistor R48 is grounded, the capacitor C82 is connected between one end of the resistor R48 and the ground, the resistor R1 is connected between one end of R48 and one end of the capacitor C13, and the resistor R2 and the capacitor C22 are connected in series between one end of the capacitor C13 and the ground.

[0014] The utility model has positive effects: 1) The utility model provides a TC (mV voltage, compatible with common thermocouple signals such as K, S, B and linear 0-100mv signals), RTD (PT100, CU50, BA1, 0-400Ω resistance, etc.), 0 / 4-20mA (active, passive), 0 / 1-5 / 10V voltage signal multi-input detection circuit technology through composite circuit design, adaptive to multiple input signal input, to meet the needs of more industrial sensors;

[0015] 2) The utility model greatly expands the application scope of a single device, reduces the demand for different types of signal processing equipment in industrial sites, simplifies the system structure, reduces costs, and improves the reliability and maintainability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0017] Figure 1 This is the principle block diagram of the TC input detection circuit of the utility model;

[0018] Figure 2 This is the circuit principle diagram of the TC input detection circuit and the RTD input detection circuit of the utility model;

[0019] Figure 3 This is the circuit principle block diagram of the RTD input detection circuit of the utility model;

[0020] Figure 4 This is a circuit diagram of the switch circuit of the utility model;

[0021] Figure 5 This is a principle block diagram of the voltage input detection circuit of the utility model;

[0022] Figure 6 This is a circuit schematic diagram of the voltage input detection circuit of the utility model;

[0023] Figure 7 This is a principle block diagram of the current input detection circuit of the utility model;

[0024] Figure 8 This is a circuit principle diagram of the current input detection circuit of the utility model. DETAILED DESCRIPTION

[0025] The utility model discloses a circuit for measuring multiple composite signals, including a TC input detection circuit, an RTD input detection circuit, a voltage input detection circuit, a current input detection circuit, and an AD circuit. The TC input detection circuit, the RTD input detection circuit, the voltage input detection circuit, and the current input detection circuit are connected to the AD circuit via a switch circuit. The voltage signal generated by the TC is input via the TC input detection circuit, the resistance signal generated by the RTD is input via the RTD input detection circuit, the voltage signal is input via the voltage input detection circuit, and the current signal is input via the current input detection circuit. The four input circuits operate independently without interfering with each other, and different input signal types can be matched by inputting through different ports.

[0026] like Figure 1 As shown, the TC input detection circuit includes an RTD temperature sensor, a first excitation circuit, a first filtering circuit, a first amplifying circuit, a first protection circuit, a second filtering circuit, and a second amplifying circuit. The TC signal is input through ports 1 and 2, passes through the first protection circuit, the second filtering circuit, and the second amplifying circuit in sequence, and then enters the switching circuit. The RTD temperature sensor measures the temperature of the TC cold junction compensation. The first excitation circuit provides a constant current to generate a voltage signal on the RTD, which is sent to the AD measurement inside the MCU through the first filtering circuit and the first amplifying circuit.

[0027] During implementation, the Tc / mV signal is input through ports 1 and 2, passes through the first port protection circuit, enters the second filtering circuit, and then enters the second amplification circuit before being fed into the switching circuit. The first port protection circuit prevents high voltage from damaging the backend circuitry. The second filtering circuit removes interference from the line, and the second amplification circuit amplifies the signal to facilitate backend measurement. The RTD is a temperature sensor that measures the temperature of the thermocouple's cold junction compensation. The first excitation circuit provides a constant current to generate a voltage signal across the RTD, which is then filtered and amplified before being fed into the ADC within the MCU for measurement.

[0028] Specific circuits such as Figure 2As shown, the first excitation circuit includes an operational amplifier U23, a PMOS tube Q1, a resistor R3, a resistor R21, a resistor R4, a resistor R18, a capacitor C6 and a capacitor C26, the first amplification circuit includes a resistor R8, a resistor R68, a resistor R71, a capacitor C87, a resistor R35 and a capacitor C86, the first protection circuit is a transient voltage suppressor diode D6, the second filtering circuit includes a capacitor C16, an inductor L2, a resistor R44, a capacitor C35, a resistor R45 and a capacitor C38, the second amplification circuit includes a U1B operational amplifier, a transient voltage suppressor diode D6 is connected between ports 1 and 2, the capacitor C16 is connected between port 2 and ground, the inductor L2 and the resistor R44 are connected in series between terminal 2 and one end of the resistor R45, the capacitor C35 is connected between one end of the resistor R45 and ground, the other end of the resistor R45 is connected to the positive input terminal of the U1B operational amplifier, and the capacitor C16 is connected between port 2 and ground. Capacitor C38 is connected between the other end of resistor R45 and ground, resistor R8 and resistor R68 are connected in series between the power supply 2.5V and ground, resistor R68 is connected between the second pin of the operational amplifier U23 and ground, resistor R71 and capacitor C87 are connected in parallel between the second pin of the operational amplifier U23 and ground pin 1, resistor R35 and capacitor C86 are connected between the first pin of the operational amplifier U23 and ground, resistor R4 is connected between the power supply 2.5V and the fifth pin of the operational amplifier U23, resistor R18 is connected between the fifth pin of the operational amplifier U23 and ground, capacitor C26 is connected between the output end of inductor L2 and ground, resistor R3 is connected between the power supply 2.5V and the source of PMOS tube Q1, resistor R21 is connected between the output end of inductor L2 and the drain of PMOS tube Q1, and capacitor C6 is connected between the gate and source of PMOS tube Q1.

[0029] The Tc / mV signal is input through ports 1 and 2. Transient voltage suppressor diode D6 prevents high voltage damage to downstream components. Capacitor C16, inductor L2, resistor R44, capacitor C35, resistor R45, and capacitor C38 form a filtering circuit. U1B is an operational amplifier that amplifies the filtered mV signal. When measuring Tc, an RTD temperature measuring resistor is connected between pins 3 and 1. U23B, Q1, resistors R3, R21, R4, R18, capacitors C6, and C26 form a constant current source circuit to generate an excitation current. This voltage flows through the temperature measuring resistor and is input to the non-inverting input of the operational amplifier through resistor R82. Resistors R8, R68, R71, capacitors C87, R35, and C36, along with the op amp, form a differential amplifier circuit, amplifying the temperature measuring resistor signal to an appropriate value for measurement within the MCU's internal AD.

[0030] like Figure 3As shown, the RTD input detection circuit includes a second excitation circuit, a third filtering circuit, a third amplifying circuit, a second protection circuit, a fourth filtering circuit, and a fourth amplifying circuit. The resistance signal generated by the RTD is input through ports 1, 2, and 3. Terminal 3 provides a constant current excitation source through the second excitation circuit, generating a voltage signal on the RTD, which is sent to the analog switch after passing through the third filtering circuit and the third amplifying circuit; Terminal 2 collects the line resistance signal, which is sequentially sent to the analog switch after passing through the second protection circuit, the fourth filtering circuit, and the fourth amplifying circuit. A line resistance compensation operation is performed based on the two collected signals to obtain the final measured resistance value.

[0031] During implementation, the resistance signal is input through ports 1, 2, and 3. Three-wire balanced compensation is used to compensate for measurement errors caused by lead resistance. Terminal 3 provides a constant current excitation source, generating a voltage signal across the RTD. This signal is filtered, amplified, and then fed into the analog switch. Terminal 2 acquires the line resistance signal, which is filtered, amplified, and then fed into the analog switch. The MCU performs line resistance compensation calculations based on these two acquired signals to determine the final measured resistance value.

[0032] like Figure 2 As shown, the fourth filter circuit includes a resistor R33, a resistor R34, a capacitor C27, a capacitor C28 and a capacitor C30 ， The fourth amplifier circuit includes an operational amplifier U1, a resistor R38, a resistor R40, a resistor R41 and a capacitor C29, wherein the resistor R33 is connected between the output pin of the inductor L2 and one end of the capacitor C27, the other end of the capacitor C27 is grounded, the resistor R34 is connected between one end of the capacitor C27 and the third pin of the operational amplifier U1, the capacitor C28 is connected between the third pin of the operational amplifier U1 and ground, and the capacitor C30 is connected between one end of the capacitor C27 and one end of the resistor R45; the capacitor C29 and the resistor R38 are connected in parallel between the second pin and the first pin of the operational amplifier U1, and the resistor R40 and the resistor R41C are connected in series between the second pin and the seventh pin of the operational amplifier U1.

[0033] In specific implementation, when measuring the RTD, pins 1 and 2 are connected to the AA end of the thermistor, and pin 3 is connected to the B end of the thermistor. Pin 2 measures the resistance on the compensation wire. Pin 3 measures the thermistor plus the wire resistance. By subtracting these two, the RTD resistance value minus the compensation wire resistance is obtained. This achieves wire compensation. Resistor R31 is a pull-up resistor that provides a bias voltage when the input resistor is disconnected, facilitating disconnection detection. Resistor R33, resistor R34, capacitor C27, capacitor C28, and capacitor C30 form a filtering circuit. U1A, resistor R38, resistor R40, resistor R41, capacitor C29, and U1B form a hardware subtraction circuit that directly outputs the resistance value minus the compensation wire resistance.

[0034] like Figure 4As shown, the switch circuit U3 is an analog switch. The signals input from different ports are measured by switching the analog switch.

[0035] like Figure 5 As shown, the voltage input detection circuit includes a third protection circuit, a voltage divider circuit and a fifth filter circuit. The voltage signal is input through ports 1 and 4, and is sequentially sent to the switch circuit through the third protection circuit, the voltage divider circuit and the fifth filter circuit.

[0036] The voltage signal is input through ports 1 and 4. The third protection circuit prevents the port from overvoltage and damages the back-end circuit. The voltage divider circuit reduces the input voltage to a voltage that can be measured by the back-end AD. The fifth filter circuit filters out interference on the signal and then sends it to the switching circuit for the back-end AD to collect.

[0037] like Figure 6 As shown, the voltage signal is input through ports 1 and 4, the third protection circuit includes a transient voltage suppressor diode D8, the voltage divider circuit includes a resistor R37 and a resistor R47, and the fifth filtering circuit includes a resistor R6, a capacitor C25, a capacitor C34, a resistor R5, and a capacitor C24. The transient voltage suppressor diode D8 is connected between the fourth port and ground, the resistor R6 is connected between the fourth port and one end of the capacitor C25, the other end of the capacitor C25 is grounded, the resistor R37 is connected between one end of the capacitor C25 and one end of the resistor R47, the capacitor C34 is connected between one end of the resistor R47 and ground, and the resistor R5 and the capacitor C24 are connected in series between one end of the resistor R47 and ground.

[0038] The voltage signal is input through ports 1 and 4, pin 1 is the input common ground, transient voltage suppression diode D8 prevents high voltage from damaging the back-end devices, resistor R6 and capacitor C25 are a first-order filter circuit, resistor R37 and resistor R47 form a voltage divider circuit, which reduces the input voltage to a value suitable for AD measurement, capacitor C34, resistor R5, and capacitor C24 are a second-order filter circuit, which filters out the interference signal and then sends it to the input end of the switching circuit.

[0039] like Figure 7 As shown, the current input detection circuit includes a fourth protection circuit, an anti-reverse circuit, a current limiting circuit, a sampling circuit and a sixth filtering circuit. The current signal is input through ports 1 and 5, passes through the fourth protection circuit, the anti-reverse circuit and the current limiting circuit in sequence, and then enters the sampling circuit. The sampling circuit converts the input current into a voltage signal, which is then filtered by the sixth filtering circuit.

[0040] like Figure 8As shown, the fourth protection circuit includes a transient voltage suppressor diode D5, the anti-reverse polarity circuit includes an anti-reverse polarity diode D7, the current limiting circuit includes a fuse F2, the sampling circuit includes a resistor R48, and the sixth filter includes a capacitor C82, a capacitor C13, a capacitor C22, a resistor R1 and a resistor R2. The transient voltage suppressor diode D5 is connected between the fifth port and ground, the anti-reverse polarity diode D7 and the fuse F2 are connected in series between the fifth port and one end of the resistor R48, the other end of the resistor R48 is grounded, the capacitor C82 is connected between one end of the resistor R48 and ground, the resistor R1 is connected between one end of R48 and one end of the capacitor C13, and the resistor R2 and the capacitor C22 are connected in series between one end of the capacitor C13 and ground.

[0041] The current signal is input through ports 1 and 5, with pin 1 serving as the input common ground. D5 is an overvoltage protection (TVS) to prevent high voltage damage to downstream components. D7 is a diode to prevent reverse current. F2 is a resettable fuse to prevent excessive current from damaging downstream circuitry. Resistor R48 is a current sampling resistor, converting the current signal into a voltage signal. Capacitors C82, C13, C22, R1, and R2 form a second-order filter circuit, filtering out interference signals before feeding them into the downstream switching circuit.

[0042] The switching circuit is an analog switch, which is fed to the AD circuit through the analog switch. The AD circuit converts the analog signal into a digital signal and feeds it to the back-end controller, thereby measuring the four input signals.

[0043] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A circuit for composite multi-signal measurement, characterized in that: It includes a TC input detection circuit, an RTD input detection circuit, a voltage input detection circuit, a current input detection circuit and an AD circuit. The TC input detection circuit, the RTD input detection circuit, the voltage input detection circuit and the current input detection circuit are connected to the AD circuit through a switching circuit. The voltage signal generated by the TC is input through the TC input detection circuit, the resistance signal generated by the RTD is input through the RTD input detection circuit, the voltage signal is input through the voltage input detection circuit, and the current signal is input through the current input detection circuit.

2. The circuit for composite multi-signal measurement according to claim 1, characterized in that: The TC input detection circuit includes an RTD temperature sensor, a first excitation circuit, a first filtering circuit, a first amplifying circuit, a first protection circuit, a second filtering circuit, and a second amplifying circuit. The TC signal is input through ports 1 and 2, passes through the first protection circuit, the second filtering circuit, and the second amplifying circuit in sequence, and then enters the switching circuit. The RTD temperature sensor measures the temperature of the TC cold-end compensation. The first excitation circuit provides a constant current to generate a voltage signal on the RTD, which is sent to the AD measurement inside the MCU through the first filtering circuit and the first amplifying circuit.

3. The circuit for composite multi-signal measurement according to claim 2, characterized in that: The first excitation circuit includes an operational amplifier U23, a PMOS tube Q1, a resistor R3, a resistor R21, a resistor R4, a resistor R18, a capacitor C6 and a capacitor C26. The first amplification circuit includes a resistor R8, a resistor R68, a resistor R71, a capacitor C87, a resistor R35 and a capacitor C86. The first protection circuit is a transient voltage suppressor diode D6. The second filtering circuit includes a capacitor C16, an inductor L2, a resistor R44, a capacitor C35, a resistor R45 and a capacitor C38. The second amplification circuit includes an operational amplifier U1B, a transient voltage suppressor diode D6 is connected between ports 1 and 2, a capacitor C16 is connected between port 2 and ground, an inductor L2 and a resistor R44 are connected in series between terminal 2 and one end of resistor R45, a capacitor C35 is connected between one end of resistor R45 and ground, the other end of resistor R45 is connected to the positive input terminal of the U1B operational amplifier, and a capacitor C 38 is connected between the other end of resistor R45 and ground, resistor R8 and resistor R68 are connected in series between the power supply 2.5V and ground, resistor R68 is connected between the second pin of the operational amplifier U23 and ground, resistor R71 and capacitor C87 are connected in parallel between the second pin of the operational amplifier U23 and ground pin 1, resistor R35 and capacitor C86 are connected between the first pin of the operational amplifier U23 and ground, resistor R4 is connected between the power supply 2.5V and the fifth pin of the operational amplifier U23, resistor R18 is connected between the fifth pin of the operational amplifier U23 and ground, capacitor C26 is connected between the output end of the inductor L2 and ground, resistor R3 is connected between the power supply 2.5V and the source of the PMOS tube Q1, resistor R21 is connected between the output end of the inductor L2 and the drain of the PMOS tube Q1, and capacitor C6 is connected between the gate and source of the PMOS tube Q1.

4. The circuit for composite multi-signal measurement according to claim 3, characterized in that: The RTD input detection circuit includes a second excitation circuit, a third filtering circuit, a third amplifying circuit, a second protection circuit, a fourth filtering circuit, and a fourth amplifying circuit. The resistance signal generated by the RTD is input through ports 1, 2, and 3. Terminal 3 provides a constant current excitation source through the second excitation circuit, generating a voltage signal on the RTD. The voltage signal is sent to the analog switch after passing through the third filtering circuit and the third amplifying circuit. Terminal 2 collects the line resistance signal, which is sent to the analog switch after passing through the second protection circuit, the fourth filtering circuit, and the fourth amplifying circuit in sequence. A line resistance compensation operation is performed based on the two collected signals to obtain the final measured resistance value.

5. The circuit for composite multi-signal measurement according to claim 4, characterized in that: The fourth filter circuit includes a resistor R33, a resistor R34, a capacitor C27, a capacitor C28 and a capacitor C30. ， The fourth amplifier circuit includes an operational amplifier U1, a resistor R38, a resistor R40, a resistor R41 and a capacitor C29, wherein the resistor R33 is connected between the output pin of the inductor L2 and one end of the capacitor C27, the other end of the capacitor C27 is grounded, the resistor R34 is connected between one end of the capacitor C27 and the third pin of the operational amplifier U1, the capacitor C28 is connected between the third pin of the operational amplifier U1 and ground, and the capacitor C30 is connected between one end of the capacitor C27 and one end of the resistor R45; the capacitor C29 and the resistor R38 are connected in parallel between the second pin and the first pin of the operational amplifier U1, and the resistor R40 and the resistor R41C are connected in series between the second pin and the seventh pin of the operational amplifier U1.

6. The circuit for composite multi-signal measurement according to claim 1, characterized in that: The voltage input detection circuit includes a third protection circuit, a voltage divider circuit and a fifth filter circuit. The voltage signal is input through ports 1 and 4 and is sent to the switch circuit in sequence through the third protection circuit, the voltage divider circuit and the fifth filter circuit.

7. The circuit for composite multi-signal measurement according to claim 6, characterized in that: The voltage signal is input through ports 1 and 4. The third protection circuit includes a transient voltage suppressor diode D8, a voltage divider circuit includes resistors R37 and R47, and a fifth filter circuit includes resistor R6, capacitor C25, capacitor C34, resistor R5, and capacitor C24. The transient voltage suppressor diode D8 is connected between the fourth port and ground, the resistor R6 is connected between the fourth port and one end of the capacitor C25, the other end of the capacitor C25 is grounded, the resistor R37 is connected between one end of the capacitor C25 and one end of the resistor R47, the capacitor C34 is connected between one end of the resistor R47 and ground, and the resistor R5 and capacitor C24 are connected in series between one end of the resistor R47 and ground.

8. The circuit for composite multi-signal measurement according to claim 1, characterized in that: The current input detection circuit includes a fourth protection circuit, an anti-reverse circuit, a current limiting circuit, a sampling circuit and a sixth filtering circuit. The current signal is input through ports 1 and 5, passes through the fourth protection circuit, the anti-reverse circuit and the current limiting circuit in sequence, and then enters the sampling circuit. The sampling circuit converts the input current into a voltage signal, which is then filtered by the sixth filtering circuit.

9. The circuit for composite multi-signal measurement according to claim 8, characterized in that: The fourth protection circuit includes a transient voltage suppressor diode D5, the anti-reverse polarity circuit includes an anti-reverse polarity diode D7, the current limiting circuit includes a fuse F2, the sampling circuit includes a resistor R48, and the sixth filter includes a capacitor C82, a capacitor C13, a capacitor C22, a resistor R1, and a resistor R2. The transient voltage suppressor diode D5 is connected between the fifth port and ground, the anti-reverse polarity diode D7 and the fuse F2 are connected in series between the fifth port and one end of the resistor R48, the other end of the resistor R48 is grounded, the capacitor C82 is connected between one end of the resistor R48 and ground, the resistor R1 is connected between one end of R48 and one end of the capacitor C13, and the resistor R2 and the capacitor C22 are connected in series between one end of the capacitor C13 and ground.

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