A measurement circuit and method for a three-wire resistance sensor

Abstract

The present invention discloses a measurement circuit and method for a three-wire resistance sensor, wherein one end of a core resistance element of the resistance sensor is connected to a first interface of the resistance sensor, and the other end is connected to a second interface and a third interface of the resistance sensor; the circuit comprises: at least two resistance sensors; a first selector having at least two selection channels; a second selector having at least one selection channel; a first resistor; the first interface of each resistance sensor is connected to a first channel of the first selector and a data input end of a second channel, and an output end of the first channel of the first selector is connected to a power supply through a resistor; the output end of the second channel of the first selector is connected to a first data input end of the second selector; the second interface of each resistance sensor is connected to the ground through a first resistor, and an interface of the first resistor away from the ground is connected to a second data input end of the second selector; and the third interface of each resistance sensor is respectively connected to other data input ends of the second selector.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to a measurement circuit and method for a three-wire resistance sensor. Background Art

[0002] A resistance sensor is a sensor that converts non-electrical physical quantities such as displacement, force, pressure, acceleration, torque, etc. into changes in resistance. A three-wire resistance sensor is a packaged sensor product (i.e., a product that can be used directly without repackaging) with three interfaces, such as Figure 1 The PT100 temperature sensor shown. Figure 1 In the figure, the dotted box is a schematic diagram of the internal cross-section of the finished sensor. 1 is a thermocouple or thermal resistor, which is a core resistor element with two pins 2 and 3. When packaged as a finished sensor, pin 2 is led out through one lead, and pin 3 is led out through two leads, so that the finished sensor has three leads. In actual use, multiple sensors such as PT100 are often deployed, and their number is generally more than the controller, and the values ​​of each sensor need to be read frequently in order to grasp the environmental parameters in real time. How to read more sensor data in real time through fewer controllers, that is, how to achieve multi-channel acquisition of sensor data, is one of the research focuses in this field.

[0003] Taking the PT100 temperature sensor as an example, the existing technology generally adopts a full bridge (such as Figure 2 As shown), half bridge (as Figure 3 as shown) or a constant current source (as Figure 4 and Figure 5 The measurement of a three-wire resistance sensor can be realized by the method shown in Figure 2. Figures 2 to 5 In the figure, RT1, RT2, RT3, and RT4 are resistance sensors to be measured, R1, R2, R3, and R4 are standard resistors, and I1 and I2 are constant current sources.

[0004] The inventors found that although the full-bridge or half-bridge method is more accurate, it is necessary to calibrate at least two standard resistors, and the measurement process is relatively cumbersome; although the constant current source method does not require standard resistors, the constant current source circuit itself is relatively complex with high accuracy and low temperature drift. In addition, when the full-bridge, half-bridge and constant current source methods are used to collect multi-channel sensor data, it is necessary to add switching circuits and amplifier circuits on the basis of the multi-channel full-bridge, half-bridge or constant current source, which makes the existing measurement method have high material costs and complex circuits. Summary of the invention

[0005] In view of this, an embodiment of the present invention provides a measurement circuit and method for a three-wire resistance sensor to solve the problems of high material cost, complex circuit and calibration in the existing method of collecting multi-channel sensor data.

[0006] According to a first aspect, an embodiment of the present invention provides a measurement circuit for a three-wire resistance sensor, wherein one end of a core resistance element of the resistance sensor is connected to a first interface of the resistance sensor, and the other end is connected to a second interface and a third interface of the resistance sensor; the measurement circuit comprises: at least two resistance sensors; a first selector having at least two selection channels, each selection channel can realize M selection, wherein M is an integer greater than or equal to 2; a second selector having at least one selection channel, the selection channel can realize N selection, wherein N is an integer greater than or equal to 4; a first resistor; wherein the first interface of each resistance sensor is connected to the first channel of the first selector and the data input end of the second channel, and the output end of the first channel of the first selector is connected to a power supply through a resistor; the output end of the second channel of the first selector is connected to the first data input end of the second selector; the second interface of each resistance sensor is connected to the ground through the first resistor, and the interface of the first resistor away from the ground is connected to the second data input end of the second selector; the third interface of each resistance sensor is respectively connected to the other data input ends of the second selector; the output end of the second selector is connected to a data processing circuit.

[0007] Optionally, the measurement circuit further includes: a controller, an output end of which is connected to an address input end of the first selector and / or the second selector.

[0008] Optionally, an enable terminal of the first selector and / or the second selector is grounded.

[0009] Optionally, the measurement circuit further includes: a non-inverting amplifier, a non-inverting input terminal of which is connected to the output terminal of the second selector.

[0010] Optionally, the measurement circuit further includes: an AD conversion circuit, an input end of which is connected to the output end of the in-phase amplifier.

[0011] Optionally, the number of the resistance sensors is 4, M is 4, and N is 8.

[0012] Optionally, the resistance sensor is a PT100 temperature sensor.

[0013] According to a second aspect, an embodiment of the present invention provides a method for measuring a three-wire resistance sensor, which is applicable to the measurement circuit described in the first aspect, and the resistance value of each core resistance element of the resistance sensor is obtained in sequence by controlling the on and off of the first selector and the second selector; wherein the resistance value of one of the core resistance elements of the resistance sensor is obtained by the following steps: controlling the two data input terminals connected to the one resistance sensor in the first selector to be connected to the corresponding output terminals, and controlling the first data input terminal of the second selector to be connected to the corresponding output terminal, thereby obtaining the voltage V1 at the first interface of the one resistance sensor; controlling the second data input terminal of the second selector to be connected to the corresponding output terminal, thereby obtaining the voltage V2 at the interface of the first resistor away from the ground; controlling the data input terminal of the second selector connected to the third interface of the one resistance sensor to be connected to the corresponding output terminal, thereby obtaining the voltage V3 at the third interface of the one resistance sensor; and calculating the resistance value of the core resistance element of the one resistance sensor according to V1, V2 and V3.

[0014] Optionally, a predetermined code of 0 or 1 is input to the address input terminal of the first selector and / or the second selector through the output terminal of the controller to control the predetermined data input terminal to be connected with the corresponding output terminal.

[0015] The method provided in the embodiment of the present invention is based on a standard resistor to overcome the lead resistance of the lead wire to obtain the resistance value of the core resistance element of the resistance sensor. Calibration is not required or only needs to be calibrated once. The measurement process is relatively simple and the measurement result is relatively accurate. In addition, the measurement circuit has fewer peripheral components, lower material cost, simple production process, and is convenient for large-scale mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 The internal structure diagram of the three-wire PT100 temperature sensor is shown;

[0018] Figures 2 to 5 The following is a schematic diagram of the circuit structure of an existing measurement method of a three-wire resistance sensor;

[0019] Figure 6 A schematic diagram of the measurement circuit structure of a three-wire resistance sensor according to an embodiment of the present invention is shown;

[0020] FIG. 7A to FIG. 7C A schematic diagram showing a process of measuring one of the core resistance elements according to a measuring method according to an embodiment of the present invention;

[0021] Figure 8 A schematic diagram of a circuit for calculating a core resistance element according to a measurement method according to an embodiment of the present invention is shown;

[0022] 9A to 9C A schematic diagram of a process of measuring another core resistance element according to a measurement method according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0024] The embodiment of the present invention provides a measurement circuit of a three-wire resistance sensor. One end of the core resistance element of the resistance sensor is connected to the first interface of the resistance sensor, and the other end is connected to the second interface and the third interface of the resistance sensor. For details, please refer to Figure 1 .

[0025] like Figure 6 As shown, the measurement circuit includes at least two resistance sensors (RT1, RT2, RT3 and RT4 in the figure are core resistance elements of the resistance sensors), a first selector U1, a second selector U2 and a first resistor R1. The first selector U1 has at least two selection channels, each of which can realize M-selection, where M is an integer greater than or equal to 2; the second selector U2 has at least one selection channel, and the selection channel can realize N-selection, where N is an integer greater than or equal to 4.

[0026] like Figure 6As shown, the first interface of each resistance sensor (i.e., one end of the core resistance element) is connected to the first channel of the first selector U1 and the data input end of the second channel, and the output end of the first channel of the first selector U1 is connected to the power supply through a resistor (which can be any resistor); the output end of the second channel of the first selector U1 is connected to the first data input end of the second selector U2; the second interface of each resistance sensor (i.e., the other end of the core resistance element) is connected to the ground through the first resistor R1, and the interface of the first resistor R1 away from the ground is connected to the second data input end of the second selector U2; the third interface of each resistance sensor (i.e., the other end of the core resistance element) is respectively connected to the other data input ends of the second selector U2; the output end of the second selector U2 is connected to the data processing circuit.

[0027] Below Figure 6 The circuit shown in the figure measures RT1 and then switches to measure RT2 as an example to illustrate the measurement method of the measurement circuit (please refer to FIG. 7A to FIG. 7C ).

[0028] like Fig. 7A As shown, firstly, the data input terminal X0 connected to RT1 in the first selector U1 is controlled to be connected to the corresponding output terminal X, the data input terminal Y0 is controlled to be connected to the corresponding output terminal Y, and the first data input terminal X0 of the second selector U2 is controlled to be connected to the corresponding output terminal X, thereby forming Fig. 7A The current path shown by the thick solid line in the figure. That is, the power supply VREF is connected to the ground through the resistor R2 (any resistor), the core resistor element RT1 and the first resistor R1 in sequence. At the same time, the first interface of the resistance sensor (note that it is not the core resistor element) is connected to the data processing circuit through the first selector U1 and the second selector U2. Thus, the voltage V1 at the first interface of the resistance sensor (note that it is not the core resistor element) can be obtained.

[0029] like Figure 7B As shown, the second data input terminal X1 of the second selector U2 is controlled to be connected to the corresponding output terminal X, at which time the data input terminal X0 of the first selector U1 is kept connected to the corresponding output terminal X, and the data input terminal Y0 is kept connected or disconnected to the corresponding output terminal Y. Thus, the voltage V2 at the interface of the first resistor R1 away from the ground can be obtained.

[0030] like Figure 7C As shown, the data input terminal X5 connected to the third interface of RT1 in the second selector U2 is then controlled to be connected with the corresponding output terminal. At this time, the data input terminal X0 of the first selector U1 and the corresponding output terminal X remain connected, and the data input terminal Y0 and the corresponding output terminal Y may remain connected or not connected, thereby obtaining the voltage V3 at the third interface of RT1.

[0031] Since the pins of the core resistor element are often led out through long leads inside the resistor sensor, the resistance value of the lead resistance has a great influence on the measurement results and cannot be ignored. FIG. 7A to FIG. 7C As shown in r in , the lead resistance of a three-wire resistance sensor is usually three equal-valued resistors. Figure 8 A simplified circuit diagram showing the lead resistance and the circuit in which the voltage is measured is shown. Figure 8 As shown, since the subsequent circuit of the data input terminal X5 is usually a high impedance circuit when acquiring V3, the lead resistance (i.e. Figure 8 There is no voltage drop on the lead resistance r) in the lower left corner, so the voltage difference between V3 and V2 is the lead resistance connected to resistor R1 (i.e. Figure 8 The voltage drop on the lower right lead resistor r). Assuming the circuit in the circuit is I, then according to Figure 8 You can get:

[0032] V2=I·R1——(1)

[0033] V3-V2=I·r——(2)

[0034] V1-V2=I·(RT1+2·r)——(3)

[0035] According to the above three formulas, we can get:

[0036] It can be seen from this that the method provided in the embodiment of the present invention is based on a standard resistor R1 and can overcome the lead resistance of the lead resistance to obtain the resistance value of the core resistance element of the resistance sensor. Calibration is not required or only needs to be calibrated once. The measurement process is relatively simple and the measurement result is relatively accurate. In addition, the measurement circuit has fewer peripheral components, lower material costs, and a simple production process, which is convenient for large-scale mass production.

[0037] The above gives the process of measuring RT1. When you need to switch to measuring RT2, you only need to do the following after the above process is completed (please refer to 9A to 9C ):

[0038] like Fig. 9A As shown, firstly, the data input terminal X1 connected to RT2 in the first selector U1 is controlled to be connected to the corresponding output terminal X, the data input terminal Y1 is controlled to be connected to the corresponding output terminal Y, and the first data input terminal X0 of the second selector U2 is controlled to be connected to the corresponding output terminal X, thereby forming Fig. 9AThe current path shown by the thick solid line in the figure. That is, the power supply VREF is connected to the ground through the resistor R2 (any resistor), the core resistor element RT2 and the first resistor R1 in sequence. At the same time, the first interface of the resistance sensor (note that it is not the core resistor element) is connected to the data processing circuit through the first selector U1 and the second selector U2. Thus, the voltage V1 at the first interface of the resistance sensor (note that it is not the core resistor element) can be obtained.

[0039] like Fig. 9B As shown, the second data input terminal X1 of the second selector U2 is controlled to be connected to the corresponding output terminal X. At this time, the data input terminal X1 of the first selector U1 is kept connected to the corresponding output terminal X, and the data input terminal Y1 is kept connected or disconnected to the corresponding output terminal Y. Thus, the voltage V2 at the interface of the first resistor R1 away from the ground can be obtained.

[0040] like Fig. 9C As shown, the data input terminal X4 connected to the third interface of RT2 in the second selector U2 is controlled to be connected with the corresponding output terminal. At this time, the data input terminal X1 of the first selector U1 and the corresponding output terminal X remain connected, and the data input terminal Y1 and the corresponding output terminal Y may remain connected or not connected, thereby obtaining the voltage V3 at the third interface of RT2.

[0041] Calculate the resistance value of RT2 based on the above V1, V2 and V3.

[0042] The resistance values ​​of resistors RT3 and RT4 can also be measured in the above manner, thereby realizing multi-channel acquisition of resistance sensors.

[0043] It should be noted that the selector in the present application may be a 74 series chip or other types of chips currently sold on the market, or may be a unit or module that can implement the selector function in the present application.

[0044] Optionally, the measurement circuit provided in the present application further includes a controller, an output end of which is connected to an address input end of the first selector U1 and / or the second selector U2.

[0045] Optionally, an enable terminal of the first selector U1 and / or the second selector U2 is grounded.

[0046] Optionally, the measurement circuit provided in the present application further includes a common-phase amplifier (high impedance device), a common-phase input terminal of which is connected to the output terminal of the second selector U2.

[0047] Furthermore, the measurement circuit provided by the present application also includes: an AD conversion circuit, whose input end is connected to the output end of the in-phase amplifier. The output end of the AD conversion circuit can be connected to the input end of the controller, so that the resistance value of the core resistance element is calculated by the controller.

[0048] As an optional implementation of this embodiment, the number of resistance sensors is 4, M is 4, and N is 8.

[0049] As an optional implementation of this embodiment, the resistance sensor is a PT100 temperature sensor.

[0050] The embodiment of the present invention also provides a three-wire resistance sensor measurement method, which is applicable to the above-mentioned measurement circuit. The measurement method sequentially obtains the resistance value of each resistance sensor core resistance element by controlling the on and off of the first selector U1 and the second selector U2; wherein the resistance value of one resistance sensor core resistance element is obtained by following the steps S1 to S4:

[0051] S1: Control the two data input terminals connected to a resistance sensor in the first selector U1 to be connected to the corresponding output terminals, and control the first data input terminal of the second selector U2 to be connected to the corresponding output terminal, so as to obtain the voltage V1 at the first interface of a resistance sensor.

[0052] S2: Control the second data input terminal of the second selector U2 to be connected to the corresponding output terminal, so as to obtain the voltage V2 at the interface of the first resistor away from the power supply.

[0053] S3: Control the data input terminal connected to a resistance sensor in the second selector U2 to be connected to the corresponding output terminal, so as to obtain the voltage V3 at the third interface of the resistance sensor.

[0054] S4: Calculate the resistance value of a core resistor element of a resistor sensor according to V1, V2 and V3.

[0055] The above steps can be specifically referred to FIG. 7A to FIG. 7C , 9A to 9C Related description.

[0056] Optionally, a predetermined code of 0 or 1 is input to the address input terminal of the first selector U1 and / or the second selector U2 through the output terminal of the controller to control the predetermined data input terminal to be connected with the corresponding output terminal.

[0057] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A measurement circuit for a three-wire resistance sensor, characterized in that: One end of the core resistor element of the resistor sensor is connected to the first interface of the resistor sensor, and the other end is connected to the second interface and the third interface of the resistor sensor; the measuring circuit includes: at least two of said resistance sensors; A first selector has at least two selection channels, each of which can realize M selections, where M is an integer greater than or equal to 2; The second selector has at least one selection channel, each selection channel can realize N-selection, where N is an integer greater than or equal to 4; a first resistor; Wherein, the first interface of each of the resistance sensors is connected to the data input terminals of the first channel and the second channel of the first selector, the output terminal of the first channel of the first selector is connected to the power supply through a resistor; the output terminal of the second channel of the first selector is connected to the first data input terminal of the second selector; the second interface of each of the resistance sensors is connected to the ground through the first resistor, and the interface of the first resistor away from the ground is connected to the second data input terminal of the second selector; the third interface of each of the resistance sensors is respectively connected to the other data input terminals of the second selector; the output terminal of the second selector is connected to the data processing circuit; The resistance value of each core resistance element of the resistance sensor is obtained in sequence by controlling the on and off of the first selector and the second selector; wherein, the resistance value of one core resistance element of the resistance sensor is obtained by the following steps: controlling the two data input terminals connected to the one resistance sensor in the first selector to be connected to the corresponding output terminals, and controlling the first data input terminal of the second selector to be connected to the corresponding output terminal, thereby obtaining the voltage V1 at the first interface of the one resistance sensor; controlling the second data input terminal of the second selector to be connected to the corresponding output terminal, thereby obtaining the voltage V2 at the interface of the first resistor away from the ground; controlling the data input terminal of the second selector connected to the third interface of the one resistance sensor to be connected to the corresponding output terminal, thereby obtaining the voltage V3 at the third interface of the one resistance sensor; and calculating the resistance value of the core resistance element of the one resistance sensor according to V1, V2 and V3.

2. The measuring circuit according to claim 1, characterized in that: Also includes: A controller has an output terminal connected to the address input terminal of the first selector and / or the second selector.

3. The measuring circuit according to claim 1, characterized in that: An enable terminal of the first selector and / or the second selector is grounded.

4. The measuring circuit according to claim 1, characterized in that: Also includes: A non-inverting amplifier has a non-inverting input terminal connected to the output terminal of the second selector.

5. The measuring circuit according to claim 4, characterized in that: Also includes: The AD conversion circuit has an input end connected to the output end of the in-phase amplifier.

6. The measuring circuit according to claim 1, characterized in that: The number of the resistance sensors is 4, the M is 4, and the N is 8.

7. The measuring circuit according to any one of claims 1 to 6, characterized in that: The resistance sensor is a PT100 temperature sensor.

8. The measuring circuit according to claim 1, characterized in that: A predetermined code of 0 or 1 is input to the address input of the first selector and / or the second selector through the output of the controller to control the predetermined data input terminal to be connected with the corresponding output terminal.

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