Temperature sampling circuit of platinum resistor and temperature sampling device of platinum resistor
By dynamically adjusting the equivalent resistance value of the bridge arm resistors in the bridge sampling circuit, the problem of poor compatibility between different types of platinum resistance thermometers on the same hardware circuit is solved, and high-precision temperature sampling is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-21
- Publication Date
- 2026-04-07
AI Technical Summary
Existing technologies struggle to be compatible with sampling of different types of platinum resistance thermometers (such as PT100 and PT1000) on the same hardware circuit, resulting in high hardware costs, large footprint, and low sampling accuracy.
Design a platinum resistance temperature sampling circuit. The controller sends a mode selection signal and uses a drive circuit to control the parallel switching circuit of the three bridge arm resistors in the bridge sampling circuit, dynamically adjusting their equivalent resistance values so that the same bridge sampling circuit can be adapted to different types of platinum resistances.
It enables sampling of different types of platinum resistance thermometers on the same hardware circuit, reduces hardware costs and PCB footprint, improves sampling accuracy, and avoids errors caused by software compensation.
Smart Images
Figure CN121804686A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of temperature detection technology, and in particular to a temperature sampling circuit and a temperature sampling device for a platinum resistance thermometer. Background Technology
[0002] Temperature is one of the most critical parameters in industrial process control, environmental monitoring, and equipment management. Platinum resistance temperature sensors, especially PT100 and PT1000, are widely used in high-precision temperature measurement due to their excellent accuracy, stability, and linearity.
[0003] Currently, the industry mainly uses the following two technical solutions to achieve compatible sampling between PT100 and PT1000: The first type is the independent hardware circuit solution. This solution designs two independent sampling circuits for the PT100 and PT1000 respectively, and switches are made via hardware jumpers, DIP switches, or physical plug-and-play modules in practical applications. The main drawbacks of this solution are: First, it requires twice the number of components (such as operational amplifiers, precision resistors, reference power supplies, etc.), significantly increasing hardware costs and the footprint of printed circuit boards (PCBs), which is not conducive to equipment miniaturization and cost control; Second, manual hardware adjustments are required during field maintenance or sensor type replacement, which is cumbersome and inefficient, and is highly susceptible to circuit damage or poor contact due to operational errors, affecting system reliability.
[0004] The second type is the analog switch-based sensor channel switching solution. This solution uses a common sampling circuit to switch the physical channel connected to the PT100 or PT1000 via an analog switch (such as a multiplexer). The microcontroller (MCU) identifies the sensor type by detecting the resistance value of the connected sensor, and then adjusts parameters such as the gain of the back-end operational amplifier via software to adapt to different signal amplitudes. While this solution reduces hardware redundancy, its core flaw lies in the fact that it only adjusts the operational amplifier gain at the software level, without addressing the impedance matching problem of the sensor itself at the hardware front end. Since the source impedances of the PT100 and PT1000 differ by a factor of ten, using the same front-end sampling network can lead to problems such as excitation current mismatch, poor signal level range, and decreased common-mode rejection ratio. The on-resistance of the analog switch itself also introduces additional measurement errors. Therefore, this solution struggles to achieve high-precision temperature sampling, especially in demanding industrial applications where its sampling accuracy often falls short of requirements. Summary of the Invention
[0005] This invention proposes a temperature sampling circuit and a temperature sampling device for platinum resistance thermometers, aiming to solve the technical problem that different types of platinum resistance thermometers cannot achieve compatible sampling on the same hardware circuit due to large impedance differences.
[0006] To achieve the above objectives, the present invention provides a temperature sampling circuit for a platinum resistance thermometer, comprising: A bridge sampling circuit includes a first bridge arm resistor, a second bridge arm resistor, a third bridge arm resistor, and an operational amplifier circuit. The first bridge arm resistor and the second bridge arm resistor are connected in series between a first reference power supply and ground. The common terminal of the first bridge arm resistor and the second bridge arm resistor is connected to the inverting input terminal of the operational amplifier circuit. The third bridge arm resistor and the platinum resistance thermometer are connected in series between the first reference power supply and ground. The common terminal of the third bridge arm resistor and the platinum resistance thermometer is connected to the non-inverting input terminal of the operational amplifier circuit. The first resistor switching circuit is connected in parallel with the first bridge arm resistor; The second resistor switching circuit is connected in parallel with the second bridge arm resistor; The third resistor switching circuit is connected in parallel with the third bridge arm resistor; Controller, used to output mode selection signal; The driving circuit has its input terminal connected to the output terminal of the controller, and its output terminal connected to the controlled terminals of the first resistor switching circuit, the second resistor switching circuit, and the third resistor switching circuit. When the mode selection signal is at the first level, the driving circuit drives the first resistor switching circuit, the second resistor switching circuit and the third resistor switching circuit to disconnect, and the bridge sampling circuit is adapted to the first type of platinum resistance. When the mode selection signal is at the second level, the driving circuit drives the first resistor switching circuit, the second resistor switching circuit and the third resistor switching circuit to conduct, thereby adjusting the equivalent resistance values of the first bridge arm resistor, the second bridge arm resistor and the third bridge arm resistor respectively. The bridge sampling circuit is adapted to the second type of platinum resistance.
[0007] Furthermore, the output terminals of the driving circuit include a first output terminal and a second output terminal; The first output terminal is connected to the controlled terminal of the first resistor switching circuit and the controlled terminal of the third resistor switching circuit, and the second output terminal is connected to the controlled terminal of the second resistor switching circuit. When the mode selection signal is high, the first output terminal outputs a high level, the second output terminal outputs a low level, the first resistor switching circuit, the third resistor switching circuit and the second resistor switching circuit are disconnected, and the bridge sampling circuit is adapted to PT1000 platinum resistance. When the mode selection signal is low, the first output terminal outputs a low level, the second output terminal outputs a high level, and the first resistor switching circuit, the third resistor switching circuit, and the second resistor switching circuit are turned on, thereby reducing the equivalent resistance values of the first bridge arm resistor, the third bridge arm resistor, and the second bridge arm resistor, respectively. The bridge sampling circuit is adapted to a PT100 platinum resistance thermometer.
[0008] Furthermore, the driving circuit includes an isolation driving circuit and a logic conversion circuit; The input terminal of the isolation drive circuit is connected to the output terminal of the controller, and the output terminal of the isolation drive circuit is connected to the input terminal of the logic conversion circuit. The first output terminal of the logic conversion circuit is connected to the controlled terminal of the first resistor switching circuit and the controlled terminal of the third resistor switching circuit, and the second output terminal of the logic conversion circuit is connected to the controlled terminal of the second resistor switching circuit.
[0009] Furthermore, the isolation drive circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, an NPN transistor, and an optocoupler; The base of the NPN transistor is connected to the output terminal of the controller via the first resistor, the collector of the NPN transistor is connected to the cathode of the optocoupler, and the emitter of the NPN transistor is grounded. The second resistor and the first capacitor are connected in parallel between the base and emitter of the NPN transistor; The anode of the optocoupler is connected to the second reference power supply via the third resistor, the collector of the optocoupler is connected to the third reference power supply via the fourth resistor, the collector of the optocoupler is connected to the input terminal of the logic conversion circuit, and the emitter of the optocoupler is grounded.
[0010] Furthermore, the logic conversion circuit includes a fifth resistor, a first inverter, and a second inverter; The input terminal of the first inverter is connected to the output terminal of the isolation drive circuit via the fifth resistor, and the output terminal of the first inverter is connected to the controlled terminal of the first resistor switching circuit and the controlled terminal of the third resistor switching circuit. The output of the first inverter is connected to the input of the second inverter, and the output of the second inverter is connected to the controlled terminal of the second resistor switching circuit.
[0011] Furthermore, the first resistor switching circuit includes a sixth resistor, a seventh resistor, an eighth resistor, a first transient voltage suppressor, and a first P-MOS transistor; One end of the sixth resistor is connected to the first output terminal of the driving circuit, and the other end of the sixth resistor is connected to the gate of the first P-MOS transistor and one end of the first transient voltage suppressor. The other end of the first transient voltage suppressor is grounded. The seventh resistor and the eighth resistor are connected in parallel, with one end connected to the drain of the first P-MOS transistor and the other end connected to the end of the first bridge arm resistor that is closer to the second bridge arm resistor. The source of the first P-MOS transistor is connected to the first reference power supply.
[0012] Furthermore, the second resistor switching circuit includes a ninth resistor, a tenth resistor, an eleventh resistor, a second transient voltage suppressor, and an N-MOS transistor; One end of the ninth resistor is connected to the second output terminal of the driving circuit, and the other end of the ninth resistor is connected to the gate of the N-MOS transistor and one end of the second transient voltage suppressor. The other end of the second transient voltage suppressor is grounded. The tenth resistor and the eleventh resistor are connected in parallel, with one end connected to the drain of the N-MOS transistor and the other end connected to the end of the second bridge arm resistor closest to the first bridge arm resistor. The source of the N-MOS transistor is connected to the end of the second bridge arm resistor that is furthest from the first bridge arm resistor.
[0013] Furthermore, the third resistor switching circuit includes a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a third transient voltage suppressor, and a second P-MOS transistor; One end of the twelfth resistor is connected to the first output terminal of the driving circuit, and the other end of the twelfth resistor is connected to the gate of the second P-MOS transistor and one end of the third transient voltage suppressor. The other end of the third transient voltage suppressor is grounded. The thirteenth resistor and the fourteenth resistor are connected in parallel, with one end connected to the drain of the second P-MOS transistor and the other end connected to the end of the third bridge arm resistor closest to the platinum resistor. The source of the second P-MOS transistor is connected to the first reference power supply.
[0014] Furthermore, the operational amplifier circuit includes a first operational amplifier, a second operational amplifier, a third operational amplifier, a fifteenth resistor, a sixteenth resistor, a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a fifth capacitor, and a sixth capacitor; The non-inverting input of the first operational amplifier is connected to the common terminal of the first bridge arm resistor and the second bridge arm resistor. The inverting input of the first operational amplifier is shorted to the output. The output of the first operational amplifier is connected to the inverting input of the third operational amplifier through the sixteenth resistor. The non-inverting input of the second operational amplifier is connected to the common terminal of the third bridge arm resistor and the platinum resistance resistor via the fifteenth resistor. The inverting input of the second operational amplifier is short-circuited to the output. The output of the second operational amplifier is connected to the non-inverting input of the third operational amplifier via the seventeenth resistor. The fifth capacitor and the eighteenth resistor are connected in parallel between the inverting input and the output of the third operational amplifier; the sixth capacitor and the nineteenth resistor are connected in parallel between the non-inverting input of the third operational amplifier and the first reference power supply.
[0015] To achieve the above objectives, the present invention also provides a temperature sampling device for a platinum resistance thermometer, the temperature sampling device for the platinum resistance thermometer comprising the temperature sampling circuit of the platinum resistance thermometer as described in any of the preceding claims.
[0016] The technical solution of this invention uses a controller to send a unified mode selection signal, which, through a drive circuit, synchronously controls the switching on and off of a first resistor switching circuit, a second resistor switching circuit, and a third resistor switching circuit connected in parallel with the three bridge arm resistors in the bridge sampling circuit. This dynamically reconstructs the equivalent resistance values of the three bridge arm resistors in the bridge sampling circuit, enabling the same bridge sampling circuit to adapt to the impedance characteristics of both type 1 and type 2 platinum resistance thermometers. Since this invention requires only one set of hardware circuitry to achieve compatible sampling of both types of platinum resistance thermometers without the need for additional independent sampling circuits, it significantly reduces hardware costs and PCB footprint. Because it adjusts the equivalent resistance values of each bridge arm resistor in the bridge sampling circuit from the hardware level, achieving precise impedance matching between the bridge sampling circuit and the two types of platinum resistance thermometers, rather than relying on backend software gain compensation, it effectively improves the overall sampling accuracy of the system, fundamentally avoiding additional errors caused by software compensation. Since the sampling mode conversion can be completed solely through the mode selection signal output by the controller, without requiring modifications to the hardware circuitry, the operation is simple and convenient. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.
[0018] Figure 1 This is a structural block diagram of an embodiment of the temperature sampling circuit for a platinum resistance thermometer according to the present invention; Figure 2 for Figure 1 A schematic diagram of the circuit structure of one embodiment of the driving circuit; Figure 3 for Figure 1 A schematic diagram of the circuit structure of an embodiment of the first resistor switching circuit; Figure 4 for Figure 1 A schematic diagram of the circuit structure of an embodiment of the second resistor switching circuit; Figure 5 for Figure 1 A schematic diagram of the circuit structure of an embodiment of the third resistor switching circuit; Figure 6 for Figure 1 A schematic diagram of the circuit structure of an embodiment of the bridge sampling circuit; Figure 7 for Figure 1 Equivalent circuit diagram of the bridge sampling circuit adapted to PT1000; Figure 8 for Figure 1 The equivalent circuit diagram of the sampling circuit of the medium-voltage bridge adapted to the PT100.
[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0021] The technical solution of this invention uses a controller to send a unified mode selection signal, which, through a drive circuit, synchronously controls the conduction and cutoff of a first resistor switching circuit, a second resistor switching circuit, and a third resistor switching circuit connected in parallel with the three bridge arm resistors in the bridge sampling circuit. This dynamically reconstructs the equivalent resistance values of the three bridge arm resistors, enabling the same bridge sampling circuit to adapt to the impedance characteristics of both type 1 and type 2 platinum resistance resistors. This configuration allows the same hardware circuit to achieve compatible sampling of different types of platinum resistance resistors without any physical modifications. This not only significantly reduces hardware costs and PCB footprint but also reconstructs the impedance matching state of the bridge from the hardware perspective. In other words, this invention can replace two independent fixed circuits in the prior art with a single adaptively reconfigurable hardware circuit. While significantly saving costs and space, it solves the technical problems of noise amplification and poor sampling accuracy introduced by relying solely on backend software gain compensation, achieving a balance between high precision and high compatibility.
[0022] Example 1 Reference Figure 1 This invention provides a temperature sampling circuit for a platinum resistance thermometer, comprising a controller 10, a drive circuit 20, a bridge sampling circuit (not labeled), a first resistance switching circuit 30, a second resistance switching circuit 40, and a third resistance switching circuit 50, wherein: The bridge sampling circuit includes at least a first bridge arm resistor R1_1, a second bridge arm resistor R1_2, a third bridge arm resistor R1_3, and an operational amplifier circuit 60. The first bridge arm resistor R1_1 and the second bridge arm resistor R1_2 are connected in series between the first reference power supply VDD1 (e.g., +2.5V) and ground. The common terminal of the first bridge arm resistor R1_1 and the second bridge arm resistor R1_2 is connected to the inverting input terminal of the operational amplifier circuit 60. The third bridge arm resistor R1_3 is connected in series with an external platinum resistor (e.g., PT1000 or PT100) between the first reference power supply VDD1 and ground. The common terminal of the third bridge arm resistor R1_3 and the platinum resistor is connected to the non-inverting input terminal of the operational amplifier circuit 60. The first resistor switching circuit 30 is connected in parallel with the first bridge arm resistor R1_1; the second resistor switching circuit 40 is connected in parallel with the second bridge arm resistor R1_2; the third resistor switching circuit 50 is connected in parallel with the third bridge arm resistor R1_3; the input terminal of the drive circuit 20 is connected to the output terminal PT1k_CS of the controller 10, and the output terminal of the drive circuit 20 is connected to the controlled terminals of the first resistor switching circuit 30, the second resistor switching circuit 40, and the third resistor switching circuit 50.
[0023] This bridge sampling circuit converts the resistance change of an external platinum resistance thermometer caused by temperature variations into a differential voltage signal corresponding to the temperature. The bridge sampling circuit consists of two series-connected voltage divider branches: the first bridge arm resistor R1_1 and the second bridge arm resistor R1_2 are connected in series to form the fixed reference branch of the bridge, and their common terminal provides a stable reference voltage to the inverting input of the operational amplifier circuit 60; the third bridge arm resistor R1_3 is connected in series with the externally connected platinum resistance thermometer to form the sensor branch of the bridge, and the voltage at their common terminal changes with the temperature characteristics of the platinum resistance thermometer and is input to the non-inverting input of the operational amplifier circuit 60. The operational amplifier circuit 60 amplifies the voltage difference between its non-inverting and inverting inputs, outputting an analog voltage signal corresponding to the temperature. Furthermore, the output of the operational amplifier circuit 60 is connected to the analog-to-digital converter input pin of the controller 10. The controller 10 has pre-stored temperature-resistance-voltage calibration data or algorithms corresponding to two operating modes (such as PT1000 operating mode and PT100 operating mode). The controller 10 selects the mode corresponding to the signal based on the current output mode, calls the corresponding calibration data, and can then calculate the accurate temperature value.
[0024] The first resistor switching circuit 30, the second resistor switching circuit 40, and the third resistor switching circuit 50 are connected in parallel with the first bridge arm resistor R1_1, the second bridge arm resistor R1_2, and the third bridge arm resistor R1_3, respectively, to change the equivalent resistance values of the parallel-connected first bridge arm resistor R1_1, second bridge arm resistor R1_2, and third bridge arm resistor R1_3. Each resistor switching circuit includes at least one controlled electronic switching element, such as a MOSFET, a relay, etc., and a resistor. When the electronic switching element is controlled to be turned on, the resistor switching circuit connects its internal resistance in parallel with the corresponding bridge arm resistor, thereby reducing the equivalent resistance value of the bridge arm resistor; when the electronic switching element is turned off, the bridge arm resistor operates at its nominal resistance value.
[0025] The controller 10 may be a microcontroller, which is used to output a mode selection signal to the drive circuit 20.
[0026] The drive circuit 20 is used to receive the mode selection signal output by the controller 10, and perform corresponding electrical isolation, level conversion and power enhancement, and generate drive signals that can synchronously drive the switching elements in the three resistor switching circuits.
[0027] The technical solution of this invention sets two operating modes determined by hardware status, which are switched by a mode selection signal of the controller 10: First operating mode: When the mode selection signal output by the controller 10 is at the first level (e.g., high level), the drive circuit 20 controls the first resistor switching circuit 30, the second resistor switching circuit 40, and the third resistor switching circuit 50 to all disconnect. At this time, the resistors of each bridge arm in the bridge sampling circuit operate at their own nominal resistance values. The overall input impedance of the bridge sampling circuit is relatively high, making it suitable for temperature sampling of first-class platinum resistance thermometers such as PT1000.
[0028] Second operating mode: When the mode selection signal output by the controller 10 is at the second level (e.g., low level), the drive circuit 20 controls the first resistor switching circuit 30, the second resistor switching circuit 40, and the third resistor switching circuit 50 to all be turned on to connect to the bridge sampling circuit, respectively, and connect in parallel with the first bridge arm resistor R1_1, the second bridge arm resistor R1_2, and the third bridge arm resistor R1_3 in the bridge sampling circuit. This causes the equivalent resistance values of the first bridge arm resistor R1_1, the second bridge arm resistor R1_2, and the third bridge arm resistor R1_3 to be adjusted synchronously, reducing the overall input impedance of the bridge sampling circuit, making it suitable for temperature sampling of second-type platinum resistance thermometers such as PT100.
[0029] The technical solution of the present invention uses a controller 10 to send a unified mode selection signal, which is then controlled by a drive circuit 20 to synchronously control the switching on and off of the first resistor switching circuit 30, the second resistor switching circuit 40, and the third resistor switching circuit 50, which are connected in parallel with the three bridge arm resistors in the bridge sampling circuit. This dynamically reconstructs the equivalent resistance values of the three bridge arm resistors in the bridge sampling circuit, enabling the same bridge sampling circuit to adapt to the impedance characteristics of the first type of platinum resistance thermometer and the second type of platinum resistance thermometer.
[0030] This configuration allows the same bridge sampling circuit to achieve compatible sampling of different types of platinum resistance thermometers without any modifications. This not only significantly reduces hardware costs and PCB footprint but also adjusts the equivalent resistance of the bridge arms at the hardware level to achieve impedance matching. This ensures that the bridge sampling circuit precisely matches the impedance characteristics of both Type I and Type II platinum resistance thermometers at the hardware level. This direct impedance matching at the hardware level effectively improves the overall sampling accuracy of the system, fundamentally avoiding the additional errors caused by relying solely on backend software gain compensation. Furthermore, the sampling mode can be switched easily via the mode selection signal output by controller 10, making operation simple and convenient. This completely solves the technical problems of poor compatibility and low sampling accuracy caused by the significant differences in the base resistance of platinum resistance thermometers.
[0031] Example 2 This embodiment further defines the configuration of the output terminal of the driving circuit 20, the signal logic, and the specific connection relationship between the output terminal and the first resistor switching circuit 30, the second resistor switching circuit 40, and the third resistor switching circuit 50, and clarifies the correspondence between the level of the mode selection signal and the specific platinum resistance type.
[0032] The specific connection is as follows: the output terminal of the drive circuit 20 is configured to have a first output terminal and a second output terminal; its first output terminal PT1k_OE is simultaneously connected to the controlled terminal of the first resistor switching circuit 30 and the controlled terminal of the third resistor switching circuit 50, so as to control the first resistor switching circuit 30 and the third resistor switching circuit 50 to operate synchronously. Its second output terminal PT1k_nOE is connected to the controlled terminal of the second resistor switching circuit 40; The working principle is as follows: When the mode selection signal output by the controller 10 is high (corresponding to the first level), the first output terminal PT1k_OE of the drive circuit 20 outputs a high-level electrical signal to the first resistor switching circuit 30 and the third resistor switching circuit 50, and the second output terminal PT1k_nOE of the drive circuit 20 outputs a low-level electrical signal to the second resistor switching circuit 40, causing all three circuits—the first, third, and second—to be disconnected. The first bridge arm resistor R1_1, the second bridge arm resistor R1_2, and the third bridge arm resistor R1_3 all operate at their nominal resistance values. In this state, the overall input impedance and input signal range of the bridge sampling circuit are adapted to the sampling requirements of the PT1000 platinum resistance thermometer.
[0033] It should be noted that the first resistor switching circuit 30 and the third resistor switching circuit 50 have the characteristic of low-level conduction, while the second resistor switching circuit 40 has the characteristic of high-level conduction.
[0034] When the mode selection signal output by the controller 10 is low (corresponding to the second level), the first output terminal PT1k_OE of the drive circuit 20 outputs a low-level electrical signal, and the second output terminal PT1k_nOE of the drive circuit 20 outputs a high-level electrical signal. At this time, the first resistor switching circuit 30 and the third resistor switching circuit 50 are turned on by the low-level electrical signal of the first output terminal PT1k_OE, and the second resistor switching circuit 40 is turned on by the high-level electrical signal of the second output terminal PT1k_nOE. The resistors inside the first resistor switching circuit 30, the second resistor switching circuit 40, and the third resistor switching circuit 50 are respectively connected in parallel to the first bridge arm resistor R1_1, the second bridge arm resistor R1_2, and the third bridge arm resistor R1_3. The equivalent resistance values of the first bridge arm resistor R1_1, the second bridge arm resistor R1_2, and the third bridge arm resistor R1_3 after being connected in parallel are all reduced. The bridge sampling circuit was reconfigured to operate with lower input impedance and a wider range of compatible signals, thus precisely matching the sampling requirements of the PT100 platinum resistance thermometer.
[0035] Example 3 Reference Figure 2In one specific embodiment, the driving circuit 20 includes an isolation driving circuit 201 and a logic conversion circuit 202; wherein, the input terminal of the isolation driving circuit 201 is connected to the output terminal PT1k_CS of the controller 10, and the output terminal of the isolation driving circuit 201 is connected to the input terminal of the logic conversion circuit 202; the first output terminal PT1k_OE of the logic conversion circuit 202 is connected to the controlled terminal of the first resistor switching circuit 30 and the controlled terminal of the third resistor switching circuit 50, and the second output terminal PT1k_nOE of the logic conversion circuit 202 is connected to the controlled terminal of the second resistor switching circuit 40.
[0036] The isolation drive circuit 20 is the front-end processing module of the drive circuit 20. It uses opto-isolation to achieve electrical isolation between the high and low voltage sides, and at the same time completes the primary signal drive, blocking the influence of the power side interference of the subsequent stage on the front-end controller 10.
[0037] The logic conversion circuit 202 is a post-processing and output module of the driver circuit 20. It is used to receive the electrical signal output by the isolation driver circuit 201, complete logic level conversion, signal shaping and generate a pair of driver signals with opposite levels.
[0038] The specific working principle is as follows: When the mode selection signal output by the controller 10 is high (corresponding to the PT1000 operating mode), the isolation drive circuit 201 outputs a low-level electrical signal to the logic conversion circuit 202. The first output terminal PT1k_OE of the logic conversion circuit 202 outputs a high-level electrical signal to the first resistor switching circuit 30 and the third resistor switching circuit 50, and the second output terminal PT1k_nOE of the logic conversion circuit 202 outputs a low-level electrical signal to the second resistor switching circuit 40, thereby turning off the first resistor switching circuit 30, the third resistor switching circuit 50, and the second resistor switching circuit 40. The bridge sampling circuit is adapted to the impedance characteristics of the PT1000 platinum resistance thermometer.
[0039] When the mode selection signal output by the controller 10 is low (corresponding to the PT100 working mode), the isolation drive circuit 201 outputs a high-level electrical signal to the logic conversion circuit 202. The first output terminal PT1k_OE of the logic conversion circuit 202 outputs a low-level electrical signal to the first resistor switching circuit 30 and the third resistor switching circuit 50. The second output terminal PT1k_nOE of the logic conversion circuit 202 outputs a high-level electrical signal to the second resistor switching circuit 40, so that the first resistor switching circuit 30, the third resistor switching circuit 50 and the second resistor switching circuit 40 are all turned on. The equivalent resistance of each bridge arm resistor of the bridge sampling circuit is reduced, and the bridge sampling circuit is adapted to the impedance characteristics of the PT100 platinum resistance.
[0040] Example 4 Continue to refer to Figure 2 In one specific embodiment, the isolation drive circuit 201 includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first capacitor C1, an NPN transistor Q1, and an optocoupler U1. The specific connection relationship is as follows: The base of NPN transistor Q1 is connected to the output terminal PT1k_CS of controller 10 via the first resistor R1. The collector of NPN transistor Q1 is connected to the cathode of optocoupler U1, and the emitter of NPN transistor Q1 is grounded. The second resistor R2 and the first capacitor C1 are connected in parallel between the base and emitter of NPN transistor Q1. The anode of optocoupler U1 is connected to the second reference power supply VDD2 (e.g., +3.3V) via the third resistor R3. The collector of optocoupler U1 is connected to the third reference power supply VDD3 (e.g., +5V) via the fourth resistor R4. The collector of optocoupler U1 is connected to the input terminal of logic conversion circuit 202, and the emitter of optocoupler U1 is grounded.
[0041] The specific working principle is as follows: When the mode selection signal output by controller 10 is high (corresponding to the PT1000 operating mode), this high-level mode selection signal is injected into the base of NPN transistor Q1 after being current-limited by the first resistor R1, causing NPN transistor Q1 to saturate and conduct. At this time, the LED of optocoupler U1 emits light normally, and the potential of the collector of optocoupler U1 is pulled low to near ground potential. Accordingly, the isolation drive circuit 201 outputs a stable low-level signal to the subsequent logic conversion circuit 202.
[0042] When the mode selection signal output by controller 10 is low (corresponding to the PT100 operating mode), NPN transistor Q1 is reliably turned off. Because NPN transistor Q1 is off, no current flows through the LED of optocoupler U1, and it stops emitting light. At this time, the fourth resistor R4 pulls the potential of the collector of optocoupler U1 up to the voltage of the third reference power supply VDD3. Accordingly, the isolation drive circuit 201 outputs a stable high-level signal to the subsequent logic conversion circuit 202.
[0043] Example 5 Continue to refer to Figure 2 In one specific embodiment, the logic conversion circuit 202 includes a fifth resistor R5, a first inverter A1, and a second inverter A2; the input terminal of the first inverter A1 is connected to the output terminal of the isolation drive circuit 201 via the fifth resistor R5, and the output terminal PT1k_OE of the first inverter A1 is connected to the controlled terminal of the first resistor switching circuit 30 and the controlled terminal of the third resistor switching circuit 50; and the output terminal PT1k_OE of the first inverter A1 is connected to the input terminal of the second inverter A2, and the output terminal PT1k_nOE of the second inverter A2 is connected to the controlled terminal of the second resistor switching circuit 40.
[0044] When the mode selection signal output by controller 10 is high (corresponding to the PT1000 operating mode), the isolation drive circuit 201 outputs a low-level electrical signal. This low-level electrical signal is inverted by the first inverter A1 and becomes a high-level electrical signal, thereby controlling the first resistor switching circuit 30 and the third resistor switching circuit 50 to disconnect. Simultaneously, the high-level electrical signal output by the first inverter A1 is input to the second inverter A2, and after being inverted again, becomes a low-level electrical signal, thereby controlling the second resistor switching circuit 40 to disconnect.
[0045] When the mode selection signal output by controller 10 is low (corresponding to the PT100 operating mode), the isolation drive circuit 201 outputs a high-level electrical signal. This high-level electrical signal is inverted by the first inverter A1 and becomes a low-level electrical signal, thereby controlling the first resistor switching circuit 30 and the third resistor switching circuit 50 to conduct. Furthermore, the low-level electrical signal output by the first inverter A1 is input to the second inverter A2, and after being inverted again, becomes a high-level electrical signal, thereby controlling the second resistor switching circuit 40 to conduct.
[0046] Example 6 Reference Figure 3 In one specific embodiment, the first resistor switching circuit 30 includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a first transient voltage suppressor TVS1, and a first P-MOS transistor Q2.
[0047] Among them, one end of the sixth resistor R6 is connected to the first output terminal PT1k_OE of the drive circuit 20, and the other end of the sixth resistor R6 is connected to the gate of the first P-MOS transistor Q2 and one end of the first transient voltage suppressor TVS1. The other end of the first transient voltage suppressor TVS1 is grounded. The seventh resistor R7 and the eighth resistor R8 are connected in parallel, one end of which is connected to the drain of the first P-MOS transistor Q2, and the other end is connected to the end of the first bridge arm resistor R1_1 near the second bridge arm resistor R1_2 (i.e., the common terminal PT100_1C of the first bridge arm resistor R1_1 and the second bridge arm resistor R1_2). The source of the first P-MOS transistor Q2 is connected to the first reference power supply VDD1.
[0048] The first resistor switching circuit 30 is used to dynamically adjust the equivalent resistance value of the first bridge arm resistor R1_1. The first P-MOS transistor Q2 is turned off or on based on the level of the electrical signal at the first output terminal PT1k_OE of the driving circuit 20, thereby determining whether to connect the parallel seventh resistor R7 and eighth resistor R8 into the circuit, thus changing the equivalent resistance value of the first bridge arm resistor R1_1.
[0049] The working principle is as follows: When the first output terminal PT1k_OE of the drive circuit 20 outputs a high-level electrical signal, this high-level electrical signal is applied to the gate of the first P-MOS transistor Q2 through the sixth resistor R6. Since the P-MOS transistor is a switching device that conducts at a low level, the first P-MOS transistor Q2 is in the off state when the gate is high. At this time, the first bridge arm resistor R1_1 operates at its nominal resistance value (corresponding to the PT1000 operating mode).
[0050] When the first output terminal PT1k_OE of the drive circuit 20 outputs a low-level electrical signal, this low-level electrical signal is applied to the gate of the first P-MOS transistor Q2 through the sixth resistor R6, causing the first P-MOS transistor Q2 to conduct. At this time, the parallel seventh resistor R7 and the eighth resistor R8 are connected to the bridge sampling circuit and are connected in parallel with the first bridge arm resistor R1_1 in the bridge sampling circuit, thereby reducing the equivalent resistance value of the first bridge arm resistor R1_1 (corresponding to the PT100 operating mode).
[0051] Example 7 Reference Figure 4 In one specific embodiment, the second resistor switching circuit 40 includes a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a second transient voltage suppressor TVS2, and an N-MOS transistor Q3; one end of the ninth resistor R9 is connected to the second output terminal PT1k_nOE of the driving circuit 20, and the other end of the ninth resistor R9 is connected to the gate of the N-MOS transistor Q3 and one end of the second transient voltage suppressor TVS2, and the other end of the second transient voltage suppressor TVS2 is grounded; after the tenth resistor R10 and the eleventh resistor R11 are connected in parallel, one end of the tenth resistor R10 is connected to the drain of the N-MOS transistor Q2, and the other end of the tenth resistor R10 is connected to the end of the second bridge arm resistor R1_2 close to the first bridge arm resistor R1_1 (i.e., the common terminal PT100_1C of the second bridge arm resistor R1_2 and the first bridge arm resistor R1_1); the source of the N-MOS transistor Q2 is connected to the end of the second bridge arm resistor R1_2 away from the first bridge arm resistor R1_1 PT100_1B.
[0052] The working principle is as follows: When the second output terminal PT1k_nOE of the driver circuit 20 outputs a low-level electrical signal, this low-level electrical signal is applied to the gate of the N-MOS transistor Q3 through the ninth resistor R9. Since the N-MOS transistor is a switching device that conducts at a high level, it is in the off state when its gate is low. At this time, the N-MOS transistor Q3 is turned off, and the second bridge arm resistor R1_2 operates at its nominal resistance value (corresponding to the PT1000 operating mode).
[0053] When the second output terminal PT1k_nOE of the drive circuit 20 outputs a high-level electrical signal, this high-level electrical signal is applied to the gate of the N-MOS transistor Q3, causing the N-MOS transistor Q3 to conduct. At this time, the parallel tenth resistor R10 and the eleventh resistor R11 are connected to the bridge sampling circuit and are connected in parallel with the second bridge arm resistor R1_2 in the bridge sampling circuit, thereby reducing the equivalent resistance value of the second bridge arm resistor R1_2 (corresponding to the PT100 operating mode).
[0054] Example 8 Reference Figure 5 In one specific embodiment, the third resistor switching circuit 50 includes a twelfth resistor R12, a thirteenth resistor R13, a fourteenth resistor R14, a third transient voltage suppressor TVS3, and a second P-MOS transistor Q4; one end of the twelfth resistor R12 is connected to the first output terminal PT1k_OE of the drive circuit 20, and the other end of the twelfth resistor R12 is connected to the gate of the second P-MOS transistor Q4 and one end of the third transient voltage suppressor TVS3, and the other end of the third transient voltage suppressor TVS3 is grounded; after the thirteenth resistor R13 and the fourteenth resistor R14 are connected in parallel, one end of the thirteenth resistor R13 is connected to the drain of the second P-MOS transistor Q4, and the other end of the thirteenth resistor R14 is connected to the end of the third bridge arm resistor R1_3 near the platinum resistor (i.e., the common terminal PT100_1A of the third bridge arm resistor R1_3 and the platinum resistor); the source of the second P-MOS transistor Q4 is connected to the first reference power supply VDD1.
[0055] The working principle is as follows: When the first output terminal PT1k_OE of the drive circuit 20 outputs a high-level electrical signal, this high-level electrical signal is applied to the gate of the second P-MOS transistor Q4 through the twelfth resistor R12, and the second P-MOS transistor Q4 is in the off state. At this time, the third bridge arm resistor R1_3 operates at its own nominal resistance value (corresponding to the PT1000 operating mode).
[0056] When the first output terminal PT1k_OE of the drive circuit 20 outputs a low-level electrical signal, this low-level signal is applied to the gate of the second P-MOS transistor Q4, causing Q4 to conduct. At this time, the parallel thirteenth resistor R13 and fourteenth resistor R14 are connected to the bridge sampling circuit, and are connected in parallel with the third bridge arm resistor R1_3 in the bridge sampling circuit. This reduces the equivalent resistance of the third bridge arm resistor R1_3 (corresponding to the PT100 operating mode).
[0057] Example 9 Reference Figure 6In one specific embodiment, the operational amplifier circuit 60 in the bridge sampling circuit includes a first operational amplifier U2, a second operational amplifier U3, a third operational amplifier U4, a fifteenth resistor R15, a sixteenth resistor R16, a seventeenth resistor R17, an eighteenth resistor R18, a nineteenth resistor R19, a fifth capacitor C5, and a sixth capacitor C6. The specific connection relationship is as follows: The non-inverting input of the first operational amplifier U2 is connected to the common terminal PT100_1C of the first bridge arm resistor R1_1 and the second bridge arm resistor R1_2. The inverting input and output of the first operational amplifier U2 are shorted. The output of the first operational amplifier U2 is connected to the inverting input of the third operational amplifier U4 via the sixteenth resistor R16. The non-inverting input of the second operational amplifier U3 is connected to the common terminal PT100_1A of the third bridge arm resistor R1_3 and the platinum resistance thermometer via the fifteenth resistor R15. The inverting input and output of the second operational amplifier U3 are shorted. The output of the second operational amplifier U3 is... The seventeenth resistor R17 is connected to the non-inverting input of the third operational amplifier U4; the fifth capacitor C5 and the eighteenth resistor R18 are connected in parallel between the inverting input and the output of the third operational amplifier U4; the sixth capacitor C6 and the nineteenth resistor R19 are connected in parallel between the non-inverting input of the third operational amplifier U4 and the first reference power supply VDD1; the externally connected platinum resistor is connected between node PT100_1A and node PT100_1B, and its resistance changes with temperature, thereby changing the voltage value of the common terminal PT100_1A of the third bridge arm resistor R1_3 and the platinum resistor.
[0058] In this embodiment, the first operational amplifier U2 forms a voltage follower. The non-inverting input of the first operational amplifier U2 is connected to the common terminal PT100_1C of the first bridge arm resistor R1_1 and the second bridge arm resistor R1_2. This connection is used to provide impedance isolation and signal buffering for the sampling voltage of this bridge arm, preventing subsequent circuitry from interfering with the load of the sampling point of the preceding bridge arm. The buffered signal is then input to the inverting input of the third operational amplifier U4 through the sixteenth resistor R16.
[0059] The second operational amplifier U3 also forms a voltage follower. The non-inverting input of the second operational amplifier U3 is connected to the common terminal PT100_1A of the third bridge arm resistor R1_3 and the platinum resistance resistor via the fifteenth resistor R15. On the one hand, the fifteenth resistor R15 achieves input current limiting, and on the other hand, it provides impedance isolation and buffering for the sampling voltage on this side. The buffered signal is input to the non-inverting input of the third operational amplifier U4 via the seventeenth resistor R17.
[0060] The fifth capacitor C5 and the eighteenth resistor R18 are connected in parallel and then connected across the inverting input and output of the third operational amplifier U4 to form an RC feedback network. The eighteenth resistor R18 is a feedback resistor used to set the gain of the differential amplifier circuit, and the fifth capacitor C5 is used to suppress high-frequency noise and prevent circuit self-oscillation.
[0061] The sixth capacitor C6 and the nineteenth resistor R19 are connected in parallel. One end is connected to the non-inverting input of the third operational amplifier U4, and the other end is connected to the first reference power supply VDD1. This forms a non-inverting input bias and filtering network, which is used to provide a stable DC bias voltage to the non-inverting input of the third operational amplifier U4 and to filter out high-frequency interference in the transmission path.
[0062] In this embodiment, the operational amplifier circuit 60 achieves distortion-free buffering of the bridge sampling signal through the high input impedance characteristics of the front-stage voltage follower; the subsequent differential amplifier circuit amplifies the difference between the two input signals and outputs a voltage signal that is linearly related to the measured temperature.
[0063] Furthermore, the bridge sampling circuit also includes a first clamping diode D1, a second clamping diode D2, a third filter capacitor C3, and a fourth filter capacitor C4; the positive terminals of the first clamping diode D1 and the second clamping diode D2 are grounded, the negative terminal of the first clamping diode D1 is connected to the common terminal PT100_1A of the third bridge arm resistor and the platinum resistance, and the negative terminal of the second clamping diode D1 is connected to the end PT100_1B of the second bridge arm resistor R1_2 away from the first bridge arm resistor R1_1; the third filter capacitor C3 is connected between the common terminal PT100_1C of the first bridge arm resistor R1_1 and the second bridge arm resistor and ground, and the fourth filter capacitor C4 is connected between the common terminal PT100_1A of the third bridge arm resistor R1_3 and the platinum resistance and ground.
[0064] The first clamping diode D1 and the second clamping diode D2 of the bridge sampling circuit are used to provide overvoltage protection for critical nodes of the sampling circuit, preventing damage to the operational amplifier and other components due to excessive voltage. The third filter capacitor C3 and the fourth filter capacitor C4 are used to passively filter the voltage at the sampling points of the bridge arms, further improving the sampling accuracy and stability of the platinum resistance thermometer.
[0065] To more clearly illustrate the inventive concept of this invention, the following description is provided in conjunction with specific component parameters.
[0066] In the bridge sampling circuit, the first bridge arm resistor R1_1 is set to 10k ohms, the second bridge arm resistor R1_2 is set to 1k ohms, and the third bridge arm resistor R1_3 is set to 10k ohms.
[0067] First resistor switching circuit 30: the seventh resistor R7 is 1.2k ohms, and the eighth resistor R8 is 15k ohms; Second resistor switching circuit 40: Tenth resistor R10 is 1.5k ohms, eleventh resistor R11 is 120 ohms; The third resistor switching circuit 50: the thirteenth resistor R13 is 1.2k ohms, and the fourteenth resistor R14 is 15k ohms.
[0068] The specific working principle is as follows: When the mode selection signal output by the controller 10 is high (PT1000 mode), the first output terminal PT1k_OE of the drive circuit 20 outputs a high-level electrical signal to the gates of the first P-MOS transistor Q2 and the second P-MOS transistor Q4, and the second output terminal PT1k_nOE of the drive circuit 20 outputs a low-level electrical signal to the gate of the N-MOS transistor Q3, causing the first resistor switching circuit 30, the third resistor switching circuit 50, and the second resistor switching circuit 40 to all disconnect. At this time, the first bridge arm resistor R1_1, the second bridge arm resistor R1_2, and the third bridge arm resistor R1_3 all operate at their nominal resistance values and are not connected to any parallel adjustment network. In this state, the equivalent diagram of the bridge sampling circuit can be found by referring to... Figure 7 As shown, Ra=R1_1=10kΩ, Rb=R1_2=1kΩ, Rc=R1_3=10kΩ. The bridge sampling circuit exhibits a high input impedance and a specific voltage division ratio, thereby accurately adapting to the sampling requirements of the PT1000 platinum resistance thermometer and ensuring optimal signal amplitude and signal-to-noise ratio in the PT1000 operating mode.
[0069] When the mode selection signal output by the controller 10 is low (PT100 mode), the first output terminal PT1k_OE of the drive circuit 20 outputs a low-level electrical signal to the gate of the first P-MOS transistor Q2 and the gate of the second P-MOS transistor Q4, and the second output terminal PT1k_nOE of the drive circuit 20 outputs a high-level electrical signal to the gate of the N-MOS transistor Q3. At this time, the first resistor switching circuit 30, the third resistor switching circuit 50 and the second resistor switching circuit 40 are synchronously turned on.
[0070] At the same time, the seventh resistor R7 (1.2 kΩ) and the eighth resistor R8 (15 kΩ) connected in parallel in the first resistor switching circuit 30 are connected to the bridge sampling circuit and are connected in parallel with the first bridge arm resistor R1_1 (10 kΩ). After the three are connected in parallel, the equivalent resistance of the first bridge arm resistor R1_1 is reduced to 1 kΩ.
[0071] At the same time, the tenth resistor R10 (1.5 kΩ) and the eleventh resistor R11 (120 Ω) connected in parallel in the second resistor switching circuit 40 are connected to the bridge sampling circuit and are connected in parallel with the second bridge arm resistor R1_2 (1 kΩ). After the three are connected in parallel, the equivalent resistance of the second bridge arm resistor R1_1 is reduced to 100 Ω.
[0072] Meanwhile, the thirteenth resistor R13 (1.2 kΩ) and the fourteenth resistor R14 (15 kΩ) in the third resistor switching circuit 50 are connected in parallel and then connected to the bridge sampling circuit. They are also connected in parallel with the third bridge arm resistor R1_3 (10 kΩ). After the three are connected in parallel, the equivalent resistance of the third bridge arm resistor R1_3 is reduced to 1 kΩ.
[0073] In this state, the equivalent diagram of the bridge sampling circuit can be referenced. Figure 8 As shown, Ra=1kΩ, Rb==100Ω, Rc=1kΩ. At this point, the overall input impedance of the bridge sampling circuit is significantly reduced, and its common-mode operating point and differential signal sensitivity are recalibrated, thus accurately matching the sampling requirements of the PT100 platinum resistance thermometer. This hardware reconfiguration ensures that, in PT100 operating mode, the circuit can provide a matching excitation to the sensor and generate a signal with appropriate amplitude and high linearity, ultimately achieving high-precision temperature measurement at the same level as the PT1000 mode.
[0074] The present invention also provides a temperature sampling device for a platinum resistance thermometer, the temperature sampling device comprising the temperature sampling circuit of the platinum resistance thermometer as described in any of the preceding embodiments. The detailed structure of the temperature sampling circuit of the platinum resistance thermometer can be referred to the above embodiments, and will not be repeated here. It is understood that, since the above-described temperature sampling circuit of the platinum resistance thermometer is used in the temperature sampling device of the platinum resistance thermometer of the present invention, the embodiments of the temperature sampling device of the platinum resistance thermometer of the present invention include all the technical solutions of all embodiments of the temperature sampling circuit of the platinum resistance thermometer, and the achieved technical effects are also completely the same, and will not be repeated here.
[0075] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.
Claims
1. A temperature sampling circuit for a platinum resistance thermometer, characterized in that, include: A bridge sampling circuit includes a first bridge arm resistor, a second bridge arm resistor, a third bridge arm resistor, and an operational amplifier circuit. The first bridge arm resistor and the second bridge arm resistor are connected in series between a first reference power supply and ground. The common terminal of the first bridge arm resistor and the second bridge arm resistor is connected to the inverting input terminal of the operational amplifier circuit. The third bridge arm resistor and the platinum resistance thermometer are connected in series between the first reference power supply and ground. The common terminal of the third bridge arm resistor and the platinum resistance thermometer is connected to the non-inverting input terminal of the operational amplifier circuit. The first resistor switching circuit is connected in parallel with the first bridge arm resistor; The second resistor switching circuit is connected in parallel with the second bridge arm resistor; The third resistor switching circuit is connected in parallel with the third bridge arm resistor; Controller, used to output mode selection signal; The driving circuit has its input terminal connected to the output terminal of the controller, and its output terminal connected to the controlled terminals of the first resistor switching circuit, the second resistor switching circuit, and the third resistor switching circuit. When the mode selection signal is at the first level, the driving circuit drives the first resistor switching circuit, the second resistor switching circuit and the third resistor switching circuit to disconnect, and the bridge sampling circuit is adapted to the first type of platinum resistance. When the mode selection signal is at the second level, the driving circuit drives the first resistor switching circuit, the second resistor switching circuit and the third resistor switching circuit to conduct, thereby adjusting the equivalent resistance values of the first bridge arm resistor, the second bridge arm resistor and the third bridge arm resistor respectively. The bridge sampling circuit is adapted to the second type of platinum resistance.
2. The temperature sampling circuit for a platinum resistance thermometer as described in claim 1, characterized in that, The output terminals of the drive circuit include a first output terminal and a second output terminal. The first output terminal is connected to the controlled terminal of the first resistor switching circuit and the controlled terminal of the third resistor switching circuit, and the second output terminal is connected to the controlled terminal of the second resistor switching circuit. When the mode selection signal is high, the first output terminal outputs a high level, the second output terminal outputs a low level, the first resistor switching circuit, the third resistor switching circuit and the second resistor switching circuit are disconnected, and the bridge sampling circuit is adapted to PT1000 platinum resistance. When the mode selection signal is low, the first output terminal outputs a low level, the second output terminal outputs a high level, and the first resistor switching circuit, the third resistor switching circuit, and the second resistor switching circuit are turned on, thereby reducing the equivalent resistance values of the first bridge arm resistor, the third bridge arm resistor, and the second bridge arm resistor, respectively. The bridge sampling circuit is adapted to a PT100 platinum resistance thermometer.
3. The temperature sampling circuit for a platinum resistance thermometer as described in claim 2, characterized in that, The driving circuit includes an isolation driving circuit and a logic conversion circuit; The input terminal of the isolation drive circuit is connected to the output terminal of the controller, and the output terminal of the isolation drive circuit is connected to the input terminal of the logic conversion circuit. The first output terminal of the logic conversion circuit is connected to the controlled terminal of the first resistor switching circuit and the controlled terminal of the third resistor switching circuit, and the second output terminal of the logic conversion circuit is connected to the controlled terminal of the second resistor switching circuit.
4. The temperature sampling circuit for a platinum resistance thermometer as described in claim 3, characterized in that, The isolation drive circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, an NPN transistor, and an optocoupler. The base of the NPN transistor is connected to the output terminal of the controller via the first resistor, the collector of the NPN transistor is connected to the cathode of the optocoupler, and the emitter of the NPN transistor is grounded. The second resistor and the first capacitor are connected in parallel between the base and emitter of the NPN transistor; The anode of the optocoupler is connected to the second reference power supply via the third resistor, the collector of the optocoupler is connected to the third reference power supply via the fourth resistor, the collector of the optocoupler is connected to the input terminal of the logic conversion circuit, and the emitter of the optocoupler is grounded.
5. The temperature sampling circuit for a platinum resistance thermometer as described in claim 3, characterized in that, The logic conversion circuit includes a fifth resistor, a first inverter, and a second inverter; The input terminal of the first inverter is connected to the output terminal of the isolation drive circuit via the fifth resistor, and the output terminal of the first inverter is connected to the controlled terminal of the first resistor switching circuit and the controlled terminal of the third resistor switching circuit. The output of the first inverter is connected to the input of the second inverter, and the output of the second inverter is connected to the controlled terminal of the second resistor switching circuit.
6. The temperature sampling circuit for a platinum resistance thermometer as described in claim 2, characterized in that, The first resistor switching circuit includes a sixth resistor, a seventh resistor, an eighth resistor, a first transient voltage suppressor, and a first P-MOS transistor; One end of the sixth resistor is connected to the first output terminal of the driving circuit, and the other end of the sixth resistor is connected to the gate of the first P-MOS transistor and one end of the first transient voltage suppressor. The other end of the first transient voltage suppressor is grounded. The seventh resistor and the eighth resistor are connected in parallel, with one end connected to the drain of the first P-MOS transistor and the other end connected to the end of the first bridge arm resistor that is closer to the second bridge arm resistor. The source of the first P-MOS transistor is connected to the first reference power supply.
7. The temperature sampling circuit for a platinum resistance thermometer as described in claim 2, characterized in that, The second resistor switching circuit includes a ninth resistor, a tenth resistor, an eleventh resistor, a second transient voltage suppressor, and an N-MOS transistor; One end of the ninth resistor is connected to the second output terminal of the driving circuit, and the other end of the ninth resistor is connected to the gate of the N-MOS transistor and one end of the second transient voltage suppressor. The other end of the second transient voltage suppressor is grounded. The tenth resistor and the eleventh resistor are connected in parallel, with one end connected to the drain of the N-MOS transistor and the other end connected to the end of the second bridge arm resistor closest to the first bridge arm resistor. The source of the N-MOS transistor is connected to the end of the second bridge arm resistor that is furthest from the first bridge arm resistor.
8. The temperature sampling circuit for a platinum resistance thermometer as described in claim 2, characterized in that, The third resistor switching circuit includes a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a third transient voltage suppressor, and a second P-MOS transistor; One end of the twelfth resistor is connected to the first output terminal of the driving circuit, and the other end of the twelfth resistor is connected to the gate of the second P-MOS transistor and one end of the third transient voltage suppressor. The other end of the third transient voltage suppressor is grounded. The thirteenth resistor and the fourteenth resistor are connected in parallel, with one end connected to the drain of the second P-MOS transistor and the other end connected to the end of the third bridge arm resistor closest to the platinum resistor. The source of the second P-MOS transistor is connected to the first reference power supply.
9. The temperature sampling circuit for a platinum resistance thermometer as described in claim 1, characterized in that, The operational amplifier circuit includes a first operational amplifier, a second operational amplifier, a third operational amplifier, a fifteenth resistor, a sixteenth resistor, a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a fifth capacitor, and a sixth capacitor; The non-inverting input of the first operational amplifier is connected to the common terminal of the first bridge arm resistor and the second bridge arm resistor. The inverting input of the first operational amplifier is shorted to the output. The output of the first operational amplifier is connected to the inverting input of the third operational amplifier through the sixteenth resistor. The non-inverting input of the second operational amplifier is connected to the common terminal of the third bridge arm resistor and the platinum resistance resistor via the fifteenth resistor. The inverting input of the second operational amplifier is short-circuited to the output. The output of the second operational amplifier is connected to the non-inverting input of the third operational amplifier via the seventeenth resistor. The fifth capacitor and the eighteenth resistor are connected in parallel between the inverting input and the output of the third operational amplifier; the sixth capacitor and the nineteenth resistor are connected in parallel between the non-inverting input of the third operational amplifier and the first reference power supply.
10. A temperature sampling device for a platinum resistance thermometer, characterized in that, The temperature sampling device for the platinum resistance thermometer includes the temperature sampling circuit for the platinum resistance thermometer as described in any one of claims 1 to 9.