Multi-channel thermal resistance temperature acquisition circuit based on three-wire system differential compensation

Abstract

The invention relates to the technical field of industrial temperature measurement, in particular to a multichannel thermal resistor temperature acquisition circuit based on three-wire system differential compensation, which comprises a voltage source, a reference resistor, a multichannel thermal resistor, two groups of constant current circuits and two groups of analog switches, the positive end of each thermal resistor is respectively connected with one group of constant current circuit and the analog switch, and the negative end of each thermal resistor is respectively connected with the other group of constant current circuit, the analog switch and the reference resistor; the negative end of each thermal resistor is connected with the voltage source. And the two groups of analog switches are synchronously gated. According to the invention, the dual analog switch groups are integrated in the three-wire system differential compensation architecture to eliminate the resistance deviation, and while the advantages of multi-channel real-time acquisition are kept, the core problems of insufficient precision, weak interference resistance and the like of the traditional scheme are effectively solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of industrial temperature measurement, and in particular to a multi-channel thermistor temperature acquisition circuit based on three-wire differential compensation. BACKGROUND

[0002] For mechanical equipment such as bearing assemblies and power equipment that need multi-point temperature monitoring, there are currently three temperature measurement methods, namely, a thermocouple scheme, a single-channel thermistor scheme and a multiplexing scheme. However, the thermocouple scheme has non-linear errors and high electromagnetic interference sensitivity, which leads to insufficient reliability in a strong electromagnetic environment, and the structure characteristics of the thermocouple make its service life shorter than that of a thermistor; the traditional single-channel PT100 thermistor scheme has better linearity, but the resistance of the long wire used will cause large system errors, and the single-channel architecture increases the unit measurement cost and reduces the space utilization; and the multiplexing scheme using analog switches will produce a large theoretical error due to the 1:1 series relationship between the on-resistance and the PT100 reference resistance. SUMMARY

[0003] The application provides a multi-channel thermistor temperature acquisition circuit based on three-wire differential compensation, which integrates double analog switch groups in a three-wire differential compensation architecture to eliminate resistance deviation, while retaining the advantages of multi-channel real-time acquisition, effectively solving the core pain points of insufficient precision and weak anti-interference of traditional schemes.

[0004] The multi-channel thermistor temperature acquisition circuit based on three-wire differential compensation provided by the application includes a voltage source, a reference resistance, multiple thermistors, two groups of constant current circuits and two groups of analog switches. The positive terminals of the thermistors are respectively connected to one group of constant current circuits and the analog switches, and the negative terminals are respectively connected to another group of constant current circuits, the analog switches and the reference resistance; the negative terminals of the thermistors are also respectively connected to the voltage source; and the two groups of analog switches are synchronously selected.

[0005] Further, the multiple thermistors and the analog switches at both ends form multiple temperature acquisition channels.

[0006] Further, a microcontroller is further included, and the microcontroller is connected to the two groups of analog switches.

[0007] Further, an operational amplifier is further included, and the operational amplifier is connected to the microcontroller and the two groups of constant current circuits.

[0008] Further, the two groups of analog switches use CD4051BM / TR chips, and U2 and U3 are respectively used as one group of analog switches.

[0009] Further, the common port of the CD4051BM / TR chip is connected with the positive and negative terminals of the thermal resistance through S1-S8 terminal respectively.

[0010] Further, the control terminals of the two groups of analog switches share PA1-PA4 GPIO bus, and PA1-PA3 realizes channel synchronous switching to compensate the on-resistance.

[0011] Further, the constant current circuit converts the power supply voltage VCC = 5V into reference voltage VREF = 2.5V based on the CJ431 voltage stabilizing chip.

[0012] The above technical solutions of the present application have the following advantages: The multi-channel thermal resistance temperature acquisition circuit based on three-wire differential compensation provided by the present application has the following advantages: The multi-channel thermal resistance temperature acquisition circuit based on three-wire differential compensation provided by the present application has the following advantages:

[0013] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0014] Figure 1 The structural diagram of the multi-channel thermal resistance temperature acquisition circuit based on three-wire differential compensation provided by the present application is shown in the figure. Figure 2 The structural diagram of the analog switch provided by the present application is shown in the figure. Figure 3 The structural diagram of the voltage conversion module provided by the present application is shown in the figure. Figure 4 The structural diagram of the constant current circuit provided by the present application is shown in the figure. Specific embodiments

[0015] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, technologies, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

[0016] It is to be understood that the terminology "includes", "has", "holds", "contains" or "comprising", "including", "having" and the like, when used in the present specification and in the accompanying claims, are used to indicate included, has, holds, contains or comprises but do not exclude other integers or additional integers.

[0017] In addition, in the description of the present specification and the accompanying claims, the terms "first", "second", "third", etc. are used only to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0018] In the present specification, the expression "one embodiment" or "some embodiments" or the like means that a specific feature, structure or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Thus, the expressions "in one embodiment", "in some embodiments", "in other some embodiments", "in yet some embodiments" and the like appearing in various places in the specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments" unless otherwise specifically stated. The terms "include", "comprise", "have" and their conjugates mean "including but not limited to", unless otherwise specifically stated. "Multiple" means "two or more".

[0019] The present application is directed to the problem that the gating resistance will cause large measurement error when the multi-channel is expanded in the industrial temperature measurement system, and proposes to eliminate the resistance deviation by integrating the double analog switch group in the three-wire differential compensation architecture. Specifically solve: ① temperature measurement deviation caused by analog switch on-resistance ② long distance wire resistance influence ③ the contradiction between multi-channel real-time acquisition and cost control. Compared with the traditional thermocouple scheme, the electromagnetic interference sensitivity is reduced, and the system linearity is improved.

[0020] The specific embodiments of the present application are described in further detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application, but are not used to limit the scope of the present application.

[0021] The present application provides a multi-channel thermistor temperature acquisition circuit based on three-wire differential compensation, as shown in Figure 1As shown, including a voltage source, a reference resistance, a plurality of thermal resistances, two groups of constant current circuits, two groups of analog switches; the positive end of each of the thermal resistances is connected with a group of the constant current circuits and the analog switch, respectively, and the negative end is connected with another group of the constant current circuits, the analog switch and the reference resistance, respectively; the negative end of each of the thermal resistances is also connected with the voltage source, respectively; the two groups of the analog switches are synchronously selected.

[0022] In some embodiments, the plurality of thermal resistances and the two ends of the analog switches form a plurality of temperature acquisition channels.

[0023] In some embodiments, further comprising a microcontroller, the microcontroller is connected with the two groups of analog switches, respectively.

[0024] In some embodiments, further comprising an operational amplifier, the operational amplifier is connected with the microcontroller and the two groups of constant current circuits, respectively.

[0025] In some embodiments, the two groups of analog switches adopt CD4051BM / TR chips, U2 and U3 are used as a group of the analog switches, respectively.

[0026] In some embodiments, the common ports of the CD4051BM / TR chips are connected with the positive end and the negative end of the thermal resistances through S1-S8 terminal connections, respectively.

[0027] In some embodiments, the control ends of the two groups of analog switches share PA1-PA4 GPIO buses, PA1-PA3 realize synchronous switching of channels to compensate for the on-resistance.

[0028] In some embodiments, the constant current circuit converts the power supply voltage VCC = 5V into the reference voltage VREF = 2.5V based on the CJ431 voltage stabilizing chip.

[0029] The multi-channel thermal resistance temperature acquisition circuit based on three-wire differential compensation includes a plurality of temperature acquisition channels, two groups of constant current source circuits, two groups of analog switches, an operational amplifier and an MCU control unit. Two analog switches select the positive and negative leads of the thermal resistance, respectively, and the third lead is directly connected to the power supply port, forming a three-wire structure. By synchronously controlling the on-state of the analog switch, the selected resistance is included in the lead resistance compensation system, and the differential voltage is used to eliminate the on-resistance error. The formula of the compensation mechanism is as follows: ΔV = I×(R_rtd + R_on) - I×(R_ref + R_on) = I×(R_rtd - R_ref), wherein ΔV is the differential voltage, I is the constant current value, R_rtd is the thermal resistance value, R_ref is the reference resistance value, and R_on is the on-resistance value of the analog switch.

[0030] In the field of industrial temperature measurement, existing technologies have significant limitations: thermocouple solutions suffer from nonlinear errors and are susceptible to electromagnetic interference, affecting temperature measurement accuracy. Single-channel RTD solutions exhibit significant measurement deviations due to wire resistance, especially in applications with long wires, potentially exceeding the allowable error range. Multiplexed solutions, by simulating the on-resistance of a switch, introduce excessively large temperature errors, directly leading to the loss of sensor range effectiveness.

[0031] To address this, this application innovatively proposes a three-wire differential compensation architecture. By using a dual analog switch group synchronous selection technology, the on-resistance is incorporated into the compensation system. Based on the differential algorithm of ΔV = I×(R_rtd-R_ref), the mathematical elimination of the selection resistance is achieved. While retaining the advantages of multi-channel real-time acquisition, this effectively solves the core pain points of traditional solutions, such as insufficient accuracy and weak anti-interference.

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] Example like Figure 1 The multi-channel RTD temperature acquisition circuit shown includes eight three-wire RTD acquisition channels. Each RTD is connected to the VCC power supply and two sets of analog switches. The positive terminal of the RTD is connected to the constant current circuit of the reference terminal via analog switch U3, and the negative terminal is connected to the constant current circuit via analog switch U2. The dual analog switches form a symmetrical loop in the three-wire architecture, and their on-resistance is equivalent to the wire resistance and incorporated into the differential compensation system. The MCU outputs a 3-bit binary code (000-111) through the PA1-PA3 GPIO bus to cyclically select the channel. Under constant current excitation, it generates a sensing voltage U = R×I. This signal is processed by an operational amplifier (OPA) to extract the differential voltage, which is then converted into a temperature value by the microcontroller's ADC module and output via serial port.

[0034] Figure 2Further show the specific connection mode of the dual analog switch: the dual analog switch group is realized by using a CD4051BM / TR chip, U2 and U3 are respectively used as the first and second analog switches, the common ports (Z ends) of the two are connected to the negative and positive ends of the thermal resistance through S1-S8 terminal connections, and the negative end of the thermal resistance is directly connected to a 5V power supply to form a three-wire structure, and the R11 resistor is connected in the path to play a current limiting role. The control ends of the two groups of analog switches share the PA1-PA4 GPIO bus, PA1-PA3 realize synchronous switching of the channel to compensate the on-resistance, and PA4 provides 5V power supply enable control. This topology structure has no specific limitation on the model of the analog switch and the compensation mechanism is universal.

[0035] Figure 3 and Figure 4 The circuit for providing a constant current value is shown, the power supply voltage VCC = 5V is converted into a reference voltage VREF = 2.5V based on a CJ431 voltage stabilizing chip, the reference voltage VREF is driven by a voltage follower U1A to make the field effect transistor Q1 work in the saturation region, and the resistance R9 controls the constant current value of the output to provide an excitation current for the thermal resistance.

[0036] The core of the embodiment is the three-wire differential compensation mechanism and the on-resistance compensation architecture: through the synchronous gating technology of the dual analog switch group (U2 / U3), the gating resistance R_on is converted into a common mode signal. Based on the differential algorithm of ΔV = I x (R_rtd-R_ref), the on-resistance is mathematically eliminated in the formula derivation and is offset in real time to resist the resistance fluctuation and thermal potential drift, thereby improving the measurement accuracy and also ensuring the reliability of the system.

[0037] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above functional units and modules is exemplified, and in actual application, the above functions can be completed by different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. In addition, the specific names of each functional unit and module are only for easy distinction, and do not limit the protection scope of the application.

[0038] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A multi-channel resistance temperature acquisition circuit based on three-wire differential compensation, characterized in that, It includes a voltage source, a reference resistor, multiple thermal resistors, two sets of constant current circuits, and two sets of analog switches; The positive terminals of each of the thermal resistors are connected to one set of constant current circuits and the analog switches, respectively, and the negative terminals are connected to another set of constant current circuits, the analog switches, and the reference resistor, respectively; the negative terminals of each of the thermal resistors are also connected to the voltage source; the two sets of analog switches are synchronously selected.

2. The multi-channel RTD temperature acquisition circuit based on three-wire differential compensation as described in claim 1, characterized in that, The multiple thermal resistors and the analog switches at both ends form a multiple temperature acquisition channel.

3. The multi-channel RTD temperature acquisition circuit based on three-wire differential compensation as described in claim 1, characterized in that, It also includes a microcontroller, which is connected to each of the two sets of analog switches.

4. The multi-channel RTD temperature acquisition circuit based on three-wire differential compensation as described in claim 3, characterized in that, It also includes an operational amplifier, which is connected to the microcontroller and the two sets of constant current circuits respectively.

5. The multi-channel RTD temperature acquisition circuit based on three-wire differential compensation as described in claim 1, characterized in that, The two sets of analog switches use the CD4051BM / TR chip, with U2 and U3 serving as one set of analog switches respectively.

6. The multi-channel RTD temperature acquisition circuit based on three-wire differential compensation as described in claim 5, characterized in that, The common port of the CD4051BM / TR chip is connected to the positive and negative terminals of the thermal resistor via the S1-S8 terminals, respectively.

7. The multi-channel RTD temperature acquisition circuit based on three-wire differential compensation as described in claim 5, characterized in that, The control terminals of the two sets of analog switches share the PA1-PA4 GPIO bus, and PA1-PA3 realize channel synchronous switching to compensate for the on-resistance.

8. The multi-channel RTD temperature acquisition circuit based on three-wire differential compensation as described in claim 1, characterized in that, The constant current circuit uses a CJ431 voltage regulator chip to convert the power supply voltage VCC = 5V into a reference voltage VREF = 2.5V.

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