Thermal resistance transmitter capable of switching measuring range and outputting signal

Abstract

The utility model relates to a thermal resistance transmitter capable of switching measuring ranges and outputting signals, which comprises an outer shell formed by buckling an upper shell and a lower shell up and down, and a circuit board is arranged in the upper shell. A first thermal resistance signal input terminal, a second thermal resistance signal input terminal, a third thermal resistance signal input terminal and a fourth thermal resistance signal input terminal are arranged at the left end of the circuit board; the right end of the circuit board is provided with a first analog quantity signal output terminal, a second analog quantity signal output terminal, a first signal input terminal and a second signal input terminal, the rear end of the circuit board is provided with a communication interface, a first indicating lamp and a second indicating lamp, and the circuit board is also provided with a first dial switch and a second dial switch. According to the utility model, the temperature can be measured by connecting two-wire system, three-wire system and four-wire system thermal resistors, and meanwhile, the input signal measuring range and the output signal can be changed through the dial switch or the communication interface.

Description

Technical Field

[0001] The utility model relates to the technical field of temperature measurement, in particular to a thermal resistance transmitter capable of switching measuring ranges and outputting signals. Background Art

[0002] A thermal resistor transmitter typically consists of a reference unit, an R / U conversion unit, a linear circuit, reverse polarity protection, current limiting protection, and a U / I conversion unit. After the thermal resistor's temperature measurement signal is converted and amplified, a linear circuit compensates for the nonlinear relationship between temperature and resistance. Ultimately, the U / I conversion circuit outputs a current signal that is linearly related to the measured temperature. This signal is used in industrial processes as an indicator, recorder, and regulator, and can also serve as a computer input signal for computer-controlled production processes. Currently, most thermal resistor transmitters have the following drawbacks:

[0003] (1) Most thermal resistance transmitters have only fixed ranges, and users cannot change the range according to the actual measured temperature.

[0004] (2) Most RTD transmitters only support two-wire and three-wire RTDs, but not four-wire RTDs, and cannot achieve higher-precision temperature measurement.

[0005] (3) Most thermal resistance transmitters have fixed output signals, and users cannot adjust the transmitter's output signal according to the subsequent receiving device. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a thermal resistance transmitter with switchable measuring range and output signal to solve the above-mentioned problems.

[0007] The purpose of this utility model is achieved in this way:

[0008] A thermal resistance transmitter with switchable measuring range and output signal, comprising an outer shell composed of an upper shell and a lower shell with upper and lower buckles, a circuit board disposed within the upper shell, a first thermal resistance signal input terminal, a second thermal resistance signal input terminal, a third thermal resistance signal input terminal, and a fourth thermal resistance signal input terminal disposed at the left end of the circuit board, a first analog signal output terminal, a second analog signal output terminal, a first signal input terminal, and a second signal input terminal disposed at the right end of the circuit board, a communication interface, a first indicator light, and a second indicator light disposed at the rear end of the circuit board, and a first dip switch and a second dip switch disposed on the circuit board;

[0009] The rear end of the lower housing is provided with a flip cover, which corresponds to the position of the communication interface. The flip cover is opened to set different ranges and analog signal outputs of the thermal resistance transmitter through the communication interface;

[0010] The circuit board is also provided with a power input circuit, a power isolation conversion circuit, a thermal resistor signal sampling circuit, a dip switch circuit, an analog signal output circuit and a single-chip microcomputer circuit. The single-chip microcomputer circuit is respectively connected to the power input circuit, the analog signal output circuit, the communication interface and the dip switch circuit. The power input circuit is connected to the power isolation conversion circuit, and the thermal resistor signal is connected to the single-chip microcomputer circuit through the thermal resistor signal sampling circuit; the power input circuit steps down the input power and stabilizes it into the voltage required by the thermal resistor transmitter. The analog output circuit converts the thermal resistor signal into an analog output signal of corresponding size according to the size of the thermal resistor signal, and finally transmits it to the outside through the first analog signal output terminal 12 and the second analog signal output terminal;

[0011] The thermal resistance signal is converted into a voltage signal through the thermal resistance acquisition signal on the circuit board, and is transmitted to the single-chip microcomputer circuit; the single-chip microcomputer circuit on the circuit board detects the status of the first dial switch and the second dial switch or opens the flip cover to set different ranges and analog signal outputs of the thermal resistance transmitter through the communication interface.

[0012] Furthermore, the power input circuit includes a power chip IC4, which is connected to a varistor RV1, a TVS tube TVS1, a capacitor C20, and a capacitor C21 in parallel. One end of the varistor RV1 and the TVS tube TVS1 are connected through an inductor L3, and the other end is connected through an inductor L5. One end of the TVS tube TVS1 is connected to a diode D7, and the diode D7 is connected to the capacitor C20 through a fuse F1.

[0013] Furthermore, the power isolation conversion circuit includes a chip U6 and a transformer T1. The chip U6 is connected to a resistor R31 and a resistor R31 respectively. The resistor R31 is connected to a MOS transistor Q4 through a capacitor C24. The resistor R32 is connected to a MOS transistor Q6 through a capacitor C27. The MOS transistor Q4 is connected to a MOS transistor Q5. The MOS transistor Q6 is connected to a MOS transistor Q7. The MOS transistors Q4, Q5, Q6 and Q7 invert the DC power supply into an AC power supply and perform isolation conversion through the transformer T1. The transformer T1 is connected to diodes D10, D12, D13 and D15 respectively. The diodes D10 and D12 are connected to capacitors C25 and C26 and a voltage regulator D11 respectively. The diodes D13 and D15 are connected to capacitors C29, C30 and a voltage regulator D14 respectively.

[0014] Furthermore, the thermal resistor signal sampling circuit includes chip IC6, chip IC7 and TVS tubes TVS2, TVS3, TVS4 and TVS5. Chip IC6 converts the thermal resistor signal into a voltage signal, and chip IC7 transmits the collected voltage signal to the single-chip microcomputer circuit; the TVS tubes TVS2, TVS3, TVS4 and TVS5 are connected in parallel.

[0015] Furthermore, the TVS tube TVS2 is connected in parallel with the capacitor C53, and the two ends of the TVS tube TVS2 are respectively connected to the resistors R66 and R70, the resistor R66 is connected to the capacitor C49, the resistor R70 is connected to the capacitor C54, and a capacitor C50 is provided between the resistors R66 and R70; the TVS tube TVS3 is connected in parallel with the capacitor C55; the TVS tube TVS4 is connected in parallel with the capacitor C58, and the two ends of the TVS tube TVS4 are respectively connected to the resistors R78 and R85, the resistor R78 is connected to the capacitor C56, the resistor R85 is connected to the capacitor C59, and a capacitor C57 is provided between the resistors R78 and R85; the TVS tube TVS5 is connected in parallel with the capacitor C60.

[0016] Furthermore, the dip switch circuit includes a dip switch SW1 and a dip switch SW2, the dip switch SW1 and the dip switch SW2 are used to detect the input state, the pins 1 to 8 of the dip switch SW1 are respectively connected to the pull-up resistors R44, R47, R49, R51, R53, R55, R57 and R59, and the pins 1 to 10 of the dip switch SW2 are respectively connected to the pull-up resistors R44, R46, R48, R50, R52, R54, R56, R58, R60 and R61.

[0017] Furthermore, the analog signal output circuit includes a photocoupler U5, a chip U4, a chip IC2A, a chip IC2B, a chip IC3A, a chip IC3B, and optocoupler relays U1 and U3. The photocoupler U5 is connected to the chip U4 via a resistor R11. The resistor R11 is connected to the resistor R8 and the voltage regulator D4 respectively. The chip U4 is connected to the resistors R13, R14 and R15 in series. A capacitor C12 is connected between the resistors R13 and R14. The capacitor C12 is connected to the capacitor C1. 4. Capacitor C14 is connected to resistor R15, the resistor R15 is connected to chip IC2B, the chip IC2B is connected to capacitor C7 in parallel, the chip IC2B is connected to chip IC3A via resistor R18, the chip IC3A is connected to transistor Q3 via resistor R19, transistor Q3 is connected to resistor R12 and resistor R22 respectively, resistor R12 is also connected to chip IC3B and resistor R66, the chip IC3B is connected to transistor Q2 via resistor R7, and the transistor Q2 is connected to transistor Q1.

[0018] Furthermore, the voltage input terminal Vin is connected to the chip IC2A, the chip IC2A is connected to the resistors R16 and R20 connected in parallel, and is also connected to the resistor R17. The resistors R16, R17, R20 and the chip IC2A constitute a voltage output circuit.

[0019] Furthermore, the signal input terminal S21 is connected to a diode D3, the diode D3 is connected to the parallel inductors L1 and L2, a capacitor C10 is connected between one end of the inductors L1 and L2, and a capacitor C9 is connected between the other ends, and the capacitor C9 is connected in parallel with the diode D5 and the TVS tube D6.

[0020] Furthermore, the single-chip microcomputer circuit includes chip IC5, chip U7, voltage transformer PT1, indicator light LED1 and interface J1. Chip IC5 calculates the thermal resistor signal into the corresponding temperature value and transmits it to the analog output circuit through a PWM signal. Chip IC5 also receives the state of the dial switch to set different temperature ranges and output signals. Chip U7 stores the temperature table corresponding to the thermal resistor; the voltage transformer PT1 is connected to the resistor R40 and is responsible for measuring the temperature on the board; the indicator light LED1 is connected to the resistors R42 and R43 respectively, which is an indicator circuit for indicating the operating status and alarm status of the transmitter; the interface J1 is the program burning port of the chip IC5.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] The utility model provides a thermal resistance transmitter with switchable measuring range and output signal, comprising a thermal resistance signal acquisition circuit, a single-chip computer circuit, an analog output circuit and a power supply circuit. The temperature can be measured by connecting to two-wire, three-wire and four-wire thermal resistances, and the input signal range and output signal can be changed by a dip switch or a communication interface.

[0023] The utility model supports measuring different temperature ranges, and the user can change the input signal range through a dial switch or a communication interface.

[0024] The utility model can realize the access of two-wire, three-wire and four-wire thermal resistors through different wiring terminals, and the user can adjust the output signal of the transmitter according to the subsequent acquisition equipment through the dial switch or communication interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural diagram of the present utility model.

[0026] Figure 2 This is a principle block diagram of the utility model.

[0027] Figure 3 This is a circuit diagram of the power input circuit of the utility model.

[0028] Figure 4 This is a circuit schematic diagram of the power isolation conversion circuit of the present utility model.

[0029] Figure 5 This is a circuit schematic diagram of the thermal resistance signal sampling circuit of the present utility model.

[0030] Figure 6 This is a circuit principle diagram of the DIP switch circuit of the present utility model.

[0031] Figure 7 This is a circuit principle diagram of the analog signal output circuit of the present utility model.

[0032] Figure 8 This is a circuit principle diagram of the single chip microcomputer circuit of the present utility model.

[0033] in:

[0034] Upper housing 1, circuit board 2, communication interface 3, first indicator light 4, second indicator light 5, first thermal resistor signal input terminal 6, second thermal resistor signal input terminal 7, third thermal resistor signal input terminal 8, fourth thermal resistor signal input terminal 9, flip cover 10, lower housing 11, first analog signal output terminal 12, second analog signal output terminal 13, first signal input terminal 14, second signal input terminal 15, first dip switch 16, second dip switch 17. DETAILED DESCRIPTION

[0035] To better understand the technical solution of the present invention, the following detailed description is provided with reference to the relevant illustrations. It should be understood that the following specific embodiments are not intended to limit the specific implementation of the technical solution of the present invention; they are merely examples of possible implementations of the technical solution of the present invention. It should be noted that the description herein of the positional relationships of the various components, such as component A being located above component B, is based on the relative positions of the components in the illustrations and is not intended to limit the actual positional relationships of the components. Example 1

[0036] See also Figures 1-8 , Figure 1 A schematic diagram of the structure of the present invention is drawn. As shown in the figure, the present invention relates to a thermal resistor transmitter with switchable measuring range and output signal, which includes an outer shell composed of an upper shell 1 and a lower shell 11 with upper and lower snaps. The upper shell 1 is provided with a circuit board 2. The left end of the circuit board 2 is provided with a first thermal resistor signal input terminal 6, a second thermal resistor signal input terminal 7, a third thermal resistor signal input terminal 8, and a fourth thermal resistor signal input terminal 9. The right end of the circuit board 2 is provided with a first analog signal output terminal 12, a second analog signal output terminal 13, a first signal input terminal 14, and a second signal input terminal 15. The rear end of the circuit board 2 is provided with a communication interface 3, a first indicator light 4, and a second indicator light 5. The circuit board 2 also has a first dip switch 16 and a second dip switch 17.

[0037] A flip cover 10 is provided at the rear end of the lower housing 11 . The flip cover 10 corresponds to the position of the communication interface 3 . When the flip cover 10 is opened, different measuring ranges and analog signal outputs of the thermal resistance transmitter can be set through the communication interface 3 .

[0038] join Figure 2 , Figure 2 This is a block diagram of the principle of the present invention. As shown in the figure, the circuit board 2 is also equipped with a power input circuit, a power isolation conversion circuit, a thermal resistor signal sampling circuit, a DIP switch circuit, an analog signal output circuit, and a single-chip microcomputer circuit. The single-chip microcomputer circuit is respectively connected to the power input circuit, the analog signal output circuit, the communication interface, and the DIP switch circuit. The power input circuit is connected to the power isolation conversion circuit, and the thermal resistor signal is connected to the single-chip microcomputer circuit via the thermal resistor signal sampling circuit. The power input circuit steps down the input power and stabilizes it to the voltage required by the thermal resistor transmitter. The analog output circuit converts the thermal resistor signal into an analog output signal of corresponding size, which is ultimately transmitted externally through the first analog signal output terminal 12 and the second analog signal output terminal 13.

[0039] The thermal resistance signal is converted into a voltage signal by the thermal resistance signal collected by the circuit board 2 and transmitted to the single-chip microcomputer circuit; the single-chip microcomputer circuit on the circuit board 2 detects the status of the first dial switch 16 and the second dial switch 17, or opens the flip cover 10 to set different ranges and analog signal outputs of the thermal resistance transmitter through the communication interface 3.

[0040] join Figure 3 , Figure 3 This is a schematic diagram of the power input circuit of the present invention. As shown, the power input circuit, which is a DC20-35V input power supply circuit, includes a power supply chip IC4. This chip is connected to a varistor RV1, a TVS diode TVS1, capacitors C20, and C21 connected in parallel. The varistor RV1 and TVS diode TVS1 are connected at one end via an inductor L3 and at the other end via an inductor L5. One end of the TVS diode TVS1 is connected to a diode D7, which is connected to capacitor C20 via a fuse F1. The varistor RV1, TVS diode TVS1, inductor L3, and inductor L5 provide EMC protection for the power input. Diode D7 provides reverse polarity protection, fuse F1 provides current limiting protection, and capacitors C20 and C21 provide filtering. The power supply chip IC4 converts the output voltage.

[0041] join Figure 4 , Figure 4This is a circuit diagram of the power isolation conversion circuit of the present utility model. As shown in the figure, the power isolation conversion circuit includes a chip U6 and a transformer T1. The chip U6 is connected to a resistor R31 and a resistor R32 respectively. The resistor R31 is connected to a MOS transistor Q4 through a capacitor C24. The resistor R32 is connected to a MOS transistor Q6 through a capacitor C27. The MOS transistor Q4 is connected to a MOS transistor Q5. The MOS transistor Q6 is connected to a MOS transistor Q7. The MOS transistors Q4, Q5, Q6 and Q7 invert the DC power supply into an AC power supply and perform isolation conversion through the transformer T1. The transformer T1 is connected to diodes D10, D12, D13 and D15 respectively. The diodes D10 and D12 are connected to capacitors C25 and C26 and a voltage regulator D11 respectively. The diodes D13 and D15 are connected to capacitors C29 and C30 and a voltage regulator D14 respectively. Diodes D10 and D12 act as rectifying diodes, Zener diode D11 acts as clamping diode, capacitors C25 and C26 act as filtering diodes, diodes D13 and D15 act as rectifying diodes, Zener diode D14 acts as clamping diode, capacitors C29 and C30 act as filtering diodes.

[0042] join Figure 5 , Figure 5 This is a circuit diagram of the thermal resistor signal sampling circuit of the present invention. As shown in the figure, the thermal resistor signal sampling circuit includes chips IC6, IC7, and TVS tubes TVS2, TVS3, TVS4, and TVS5. Chip IC6 converts the thermal resistor signal into a voltage signal, and chip IC7 transmits the collected voltage signal to the single-chip microcomputer circuit; the TVS tubes TVS2, TVS3, TVS4, and TVS5 are connected in parallel, the TVS tube TVS2 is connected in parallel with the capacitor C53, and the two ends of the TVS tube TVS2 are connected to resistors R66 and R70 respectively. Resistor R66 is connected to capacitor C49, resistor R70 is connected to capacitor C54, and capacitor C50 is provided between resistors R66 and R70; the TVS tube TVS3 is connected to capacitor C55 in parallel; the TVS tube TVS4 is connected to capacitor C58 in parallel, and the two ends of the TVS tube TVS4 are respectively connected to resistors R78 and R85, resistor R78 is connected to capacitor C56, resistor R85 is connected to capacitor C59, and capacitor C57 is provided between resistors R78 and R85; the TVS tube TVS5 is connected to capacitor C60 in parallel.

[0043] TVS tubes TVS2, TVS3, TVS4 and TVS5 act as thermal resistor signal clamps, capacitors C53, C55, C58 and C60 act as high-frequency absorbers, resistors R66, R70, R78, R85 and capacitors C49, C50, C54, C56, C57, C59 act as filters.

[0044] join Figure 6 , Figure 6This is a schematic diagram of the DIP switch circuit of the present invention. As shown, the DIP switch circuit includes a DIP switch SW1 and a DIP switch SW2. The DIP switches SW1 and SW2 are used to detect input states. Pins 1 through 8 of the DIP switch SW1 are connected to pull-up resistors R44, R47, R49, R51, R53, R55, R57, and R59, respectively. Pins 1 through 10 of the DIP switch SW2 are connected to pull-up resistors R44, R46, R48, R50, R52, R54, R56, R58, R60, and R61, respectively.

[0045] join Figure 7 , Figure 7 This is a schematic diagram of the analog signal output circuit of the present invention. As shown in the figure, the analog signal output circuit includes a photocoupler U5, a chip U4, a chip IC2A, a chip IC2B, a chip IC3A, a chip IC3B, and optocoupler relays U1 and U3. The photocoupler U5 is connected to the chip U4 via a resistor R11. The resistor R11 is respectively connected to the resistor R8 and the voltage regulator D4. The chip U4 is connected to the series resistors R13, R14, and R15. The capacitor C12 is connected between the resistors R13 and R14. The capacitor C12 is connected to the capacitor C1. 4. Capacitor C14 is connected to resistor R15, the resistor R15 is connected to chip IC2B, the chip IC2B is connected to capacitor C7 in parallel, the chip IC2B is connected to chip IC3A via resistor R18, the chip IC3A is connected to transistor Q3 via resistor R19, transistor Q3 is connected to resistor R12 and resistor R22 respectively, resistor R12 is also connected to chip IC3B and resistor R66, the chip IC3B is connected to transistor Q2 via resistor R7, and the transistor Q2 is connected to transistor Q1. U5 isolates and transmits the PWM wave signal. Resistors R8, R11 and Zener diode D4 stabilize the amplitude of the isolated PWM wave signal. Chip U4 performs waveform shaping on the PWM wave signal. The circuit composed of resistors R13, R14, R15, capacitors C12, C14, C7 and chip IC2B outputs a voltage signal of corresponding size according to the duty cycle of the PWM wave. Chips IC3A, IC3B, resistors R19, R22, R66, transistors Q1, Q2 and diode D2 form a current output circuit. Optocoupler relays U1 and U3 switch the current and voltage output circuits.

[0046] The voltage input terminal Vin is connected to the chip IC2A, the chip IC2A is connected to the resistors R16 and R20 connected in parallel, and is also connected to the resistor R17. The resistors R16, R17, R20 and the chip IC2A constitute a voltage output circuit.

[0047] Signal input terminal S21 is connected to diode D3, which is connected to parallel inductors L1 and L2. Capacitor C10 is connected between one end of inductors L1 and L2, and capacitor C9 is connected between the other ends. Capacitor C9 is connected in parallel with diode D5 and TVS diode D6. Diode D3 provides reverse polarity protection, while capacitors C10, C9, inductors L1 and L2 filter out high-frequency interference signals. Diode D5 and TVS diode D6 provide clamping.

[0048] join Figure 8 , Figure 8 This is a schematic diagram of the single-chip microcomputer circuit of the present invention. As shown, the single-chip microcomputer circuit includes chip IC5, chip U7, voltage transformer PT1, indicator LED1, and interface J1. Chip IC5 calculates the RTD signal into a corresponding temperature value and transmits it to the analog output circuit via a PWM signal. Chip IC5 also receives the status of a DIP switch to set different temperature ranges and output signals. Chip U7 stores a temperature table corresponding to the RTD. Voltage transformer PT1 is connected to resistor R40, which is responsible for measuring the on-board temperature. Indicator LED1 is connected to resistors R42 and R43, forming an indicator circuit for indicating the transmitter's operating status and alarm status. Interface J1 is the program burning port for chip IC5.

[0049] Working principle:

[0050] The utility model relates to a thermal resistance transmitter with switchable measuring range and output signal, which comprises a thermal resistance signal acquisition circuit, a single-chip computer circuit, an analog output circuit and a power supply circuit which are centrally installed in two housings. The device can measure temperature by connecting to two-wire, three-wire and four-wire thermal resistances, and can change the input signal range and output signal by means of a dial switch or a communication interface.

[0051] The installation method is as follows:

[0052] Solder the communication interface 3, first indicator light 4, second indicator light 5, first thermal resistor signal input terminal 6, second thermal resistor signal input terminal 7, third thermal resistor signal input terminal 8, fourth thermal resistor signal input terminal 9, first analog signal output terminal 12, second analog signal output terminal 13, first signal input terminal 14, second signal input terminal 15, first DIP switch 16, and second DIP switch 17 to the circuit board 2. Install the circuit board 2 into the lower housing 11. Install the flip cover 10 into the lower housing 11, and then connect the upper housing 1 and lower housing 11 with a snap fit. The two DIP switches on the circuit board 2 can be exposed through the opening in the upper housing 1.

[0053] First signal input terminals 14 and second signal input terminals 15 serve as the signal input terminals for the RTD transmitter. The power supply circuit on circuit board 2 steps down the input power and stabilizes it to the voltage required by the RTD transmitter. First analog signal output terminals 12 and second analog signal output terminals 13 serve as analog signal output terminals. The analog output circuit on circuit board 2 converts the RTD signal into an analog output signal of corresponding magnitude, which is ultimately transmitted externally through first analog signal output terminals 12 and second analog signal output terminals 13. First RTD signal input terminals 6, second RTD signal input terminals 7, third RTD signal input terminals 8, and fourth RTD signal input terminals 9 serve as RTD signal input terminals. The RTD signal is collected by the RTD on circuit board 2, converted into a voltage signal, and transmitted to the microcontroller circuit. The microcontroller circuit on circuit board 2 can set the RTD transmitter's different ranges and analog signal outputs by detecting the status of first and second DIP switches 16 and 17, or by opening flip cover 10 and using communication interface 3.

[0054] The above are only specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. Any technical solution formed by equivalent transformation or equivalent replacement shall fall within the scope of protection of the present invention.

Claims

1. A thermal resistance transmitter with switchable measuring range and output signal, characterized in that: The invention comprises an outer shell composed of an upper shell (1) and a lower shell (11) with upper and lower buckles, wherein a circuit board (2) is provided in the upper shell (1), a first thermal resistor signal input terminal (6), a second thermal resistor signal input terminal (7), a third thermal resistor signal input terminal (8) and a fourth thermal resistor signal input terminal (9) are provided at the left end of the circuit board (2), a first analog signal output terminal (12), a second analog signal output terminal (13), a first signal input terminal (14) and a second signal input terminal (15) are provided at the right end of the circuit board (2), a communication interface (3), a first indicator light (4) and a second indicator light (5) are provided at the rear end of the circuit board (2), and a first dial switch (16) and a second dial switch (17) are also provided on the circuit board (2); The rear end of the lower housing (11) is provided with a flip cover (10), and the flip cover (10) corresponds to the position of the communication interface (3). When the flip cover (10) is opened, different measuring ranges and analog signal outputs of the thermal resistance transmitter can be set through the communication interface (3); The circuit board (2) is further provided with a power input circuit, a power isolation conversion circuit, a thermal resistor signal sampling circuit, a dial switch circuit, an analog signal output circuit and a single-chip microcomputer circuit. The single-chip microcomputer circuit is respectively connected to the power input circuit, the analog signal output circuit, the communication interface and the dial switch circuit. The power input circuit is connected to the power isolation conversion circuit. The thermal resistor signal is connected to the single-chip microcomputer circuit via the thermal resistor signal sampling circuit. The power input circuit steps down the input power and stabilizes the voltage into the voltage required by the thermal resistor transmitter. The analog output circuit converts the thermal resistor signal into an analog output signal of corresponding size according to the size of the thermal resistor signal, and finally transmits the signal to the outside through the first analog signal output terminal (12) and the second analog signal output terminal (13). The thermal resistance signal is converted into a voltage signal by the thermal resistance signal collected by the circuit board (2), and is transmitted to the single-chip microcomputer circuit; the single-chip microcomputer circuit on the circuit board (2) sets different ranges and analog signal outputs of the thermal resistance transmitter through the communication interface (3) by detecting the states of the first dial switch (16) and the second dial switch (17) or opening the flip cover (10).

2. A thermal resistance transmitter with switchable measuring range and output signal according to claim 1, characterized in that: The power input circuit includes a power chip IC4, which is connected to a varistor RV1, a TVS tube TVS1, a capacitor C20, and a capacitor C21 in parallel. One end of the varistor RV1 and the TVS tube TVS1 are connected through an inductor L3, and the other end is connected through an inductor L5. One end of the TVS tube TVS1 is connected to a diode D7, and the diode D7 is connected to the capacitor C20 through a fuse F1.

3. The thermal resistance transmitter capable of switching measuring ranges and output signals according to claim 1, characterized in that: The power isolation conversion circuit includes a chip U6 and a transformer T1. The chip U6 is connected to a resistor R31 and a resistor R32, respectively. The resistor R31 is connected to a MOS transistor Q4 through a capacitor C24. The resistor R32 is connected to a MOS transistor Q6 through a capacitor C27. The MOS transistor Q4 is connected to a MOS transistor Q5. The MOS transistor Q6 is connected to a MOS transistor Q7. The MOS transistors Q4, Q5, Q6 and Q7 invert the DC power supply into an AC power supply and perform isolation conversion through the transformer T1. The transformer T1 is connected to diodes D10, D12, D13 and D15, respectively. The diodes D10 and D12 are connected to capacitors C25 and C26 and a voltage regulator D11, respectively. The diodes D13 and D15 are connected to capacitors C29, C30 and a voltage regulator D14, respectively.

4. The thermal resistance transmitter capable of switching measuring ranges and output signals according to claim 1, characterized in that: The thermal resistor signal sampling circuit includes chips IC6, IC7 and TVS tubes TVS2, TVS3, TVS4 and TVS5. Chip IC6 converts the thermal resistor signal into a voltage signal, and chip IC7 transmits the collected voltage signal to the single-chip microcomputer circuit; the TVS tubes TVS2, TVS3, TVS4 and TVS5 are connected in parallel.

5. The thermal resistance transmitter capable of switching measuring ranges and output signals according to claim 4, characterized in that: The TVS tube TVS2 is connected in parallel with the capacitor C53, and the two ends of the TVS tube TVS2 are respectively connected to the resistors R66 and R70, the resistor R66 is connected to the capacitor C49, the resistor R70 is connected to the capacitor C54, and a capacitor C50 is provided between the resistors R66 and R70; the TVS tube TVS3 is connected in parallel with the capacitor C55; the TVS tube TVS4 is connected in parallel with the capacitor C58, and the two ends of the TVS tube TVS4 are respectively connected to the resistors R78 and R85, the resistor R78 is connected to the capacitor C56, the resistor R85 is connected to the capacitor C59, and a capacitor C57 is provided between the resistors R78 and R85; the TVS tube TVS5 is connected in parallel with the capacitor C60.

6. The thermal resistance transmitter capable of switching measuring ranges and output signals according to claim 1, characterized in that: The dip switch circuit includes a dip switch SW1 and a dip switch SW2, and the dip switch SW1 and the dip switch SW2 are used to detect the input state. Pins 1 to 8 of the dip switch SW1 are respectively connected to pull-up resistors R44, R47, R49, R51, R53, R55, R57 and R59, and pins 1 to 10 of the dip switch SW2 are respectively connected to pull-up resistors R44, R46, R48, R50, R52, R54, R56, R58, R60 and R61.

7. The thermal resistance transmitter capable of switching measuring ranges and output signals according to claim 1, characterized in that: The analog signal output circuit includes a photocoupler U5, a chip U4, a chip IC2A, a chip IC2B, a chip IC3A, a chip IC3B, and photocoupler relays U1 and U3. The photocoupler U5 is connected to the chip U4 via a resistor R11. The resistor R11 is respectively connected to the resistor R8 and the voltage regulator D4. The chip U4 is connected to the series resistors R13, R14 and R15. A capacitor C12 is connected between the resistors R13 and R14. The capacitor C12 is connected to the capacitor C14. Capacitor C14 is connected to resistor R15, the resistor R15 is connected to chip IC2B, the chip IC2B is connected to capacitor C7 in parallel, the chip IC2B is connected to chip IC3A via resistor R18, the chip IC3A is connected to transistor Q3 via resistor R19, the transistor Q3 is connected to resistor R12 and resistor R22 respectively, the resistor R12 is also connected to chip IC3B and resistor R66, the chip IC3B is connected to transistor Q2 via resistor R7, and the transistor Q2 is connected to transistor Q1.

8. The thermal resistance transmitter capable of switching measuring ranges and output signals according to claim 1, characterized in that: The voltage input terminal Vin is connected to the chip IC2A, the chip IC2A is connected to the resistors R16 and R20 connected in parallel, and is also connected to the resistor R17. The resistors R16, R17, R20 and the chip IC2A constitute a voltage output circuit.

9. The thermal resistance transmitter capable of switching measuring ranges and output signals according to claim 1, characterized in that: The signal input terminal S21 is connected to the diode D3, the diode D3 is connected to the parallel inductors L1 and L2, the capacitor C10 is connected between one end of the inductors L1 and L2, and the capacitor C9 is connected between the other ends. The capacitor C9 is connected in parallel with the diode D5 and the TVS tube D6.

10. The thermal resistance transmitter capable of switching measuring ranges and output signals according to claim 1, characterized in that: The single-chip microcomputer circuit includes chip IC5, chip U7, voltage transformer PT1, indicator light LED1 and interface J1. Chip IC5 calculates the thermal resistor signal into the corresponding temperature value and transmits it to the analog output circuit through PWM signal. Chip IC5 also receives the state of the dip switch to set different temperature ranges and output signals. Chip U7 stores the temperature table corresponding to the thermal resistor; voltage transformer PT1 is connected to resistor R40 and is responsible for measuring the temperature on the board; indicator light LED1 is connected to resistors R42 and R43 respectively, which is an indicator circuit for indicating the operating status and alarm status of the transmitter; interface J1 is the program burning port of chip IC5.

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