Calibration-free measurement method of three-wire sensor

Abstract

The invention relates to the technical field of sensor precision calibration measurement, and discloses a calibration-free measurement method for a three-wire sensor, and the method specifically comprises the following steps: S101, obtaining a three-wire sensor circuit, and the arrangement mode of sensor conduction resistance, sensor wire resistance and precision resistance in the three-wire sensor circuit; s102, acquiring a voltage value of a sensor wire resistor in the three-wire sensor circuit, and acquiring voltage values at two ends of a current sensor conduction resistor; s103, a plurality of acquisition points are arranged on the circuit, the voltage difference between the plurality of acquisition points is obtained, and the voltage difference between the two ends of the sensor on-resistor is calculated through the voltage difference between the acquisition points at the two ends of the sensor on-resistor; and S104, acquiring current voltages on the acquisition points at the two ends of the plurality of precision resistors. An equal-precision measurement method is adopted, voltage values of multiple points on a sensor circuit are collected for calculation, the influence of wire resistance on a measurement result is eliminated, and other non-linear variables are not introduced.

Description

Technical Field

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

[0002] In the prior art, for signal acquisition of three-wire sensors, a Wheatstone bridge circuit is generally used. The sensor to be measured is connected to the bridge, and the balance principle of the bridge is used to calculate the resistance of the sensor to be measured, and then derive other parameters.

[0003] However, in practical applications, the influence of wire resistance on measurement data cannot be completely eliminated, the nonlinear variables introduced by the bridge arm are difficult to handle, and changes in ambient temperature will also affect the accuracy of the measurement. When using it, it is necessary to consider different influencing factors according to different sampling requirements and different environmental conditions, and to correct and compensate the circuit or calculation method to obtain accurate measurement results.

[0004] It can be seen that the circuit design using the Wheatstone bridge circuit is more difficult and there are many influencing factors to consider when performing calculations. Summary of the invention

[0005] The purpose of the present invention is to provide a calibration-free measurement method for a three-wire sensor, which adopts an equal-precision measurement method to collect voltage values ​​at multiple points on the sensor circuit for calculation, eliminates the influence of wire resistance on the measurement result, and does not introduce other nonlinear variables. It aims to solve the problem in the prior art that when used, it is necessary to correct and compensate the circuit or calculation method according to different sampling requirements and different environmental conditions, and consider different influencing factors to obtain accurate measurement results.

[0006] The present invention is implemented in this way: the calibration-free measurement method of the three-wire sensor specifically comprises the following steps:

[0007] S101: Obtain a three-wire sensor circuit and an arrangement of a sensor on-resistance, a sensor wire resistance, and a precision resistor in the three-wire sensor circuit;

[0008] S102: Obtain the voltage value of the sensor wire resistance in the three-wire sensor circuit, and obtain the voltage value across the current sensor on-resistance;

[0009] S103: setting multiple collection points on the circuit to obtain voltage differences between the multiple collection points, and calculating the voltage difference between the two ends of the sensor on-resistance by collecting the voltage difference between the two ends of the sensor on-resistance;

[0010] S104: obtaining current voltages at collection points at both ends of the multiple precision resistors to obtain current voltage values ​​of the multiple precision resistors, and finally obtaining a total voltage value of the precision resistors in the three-wire sensor circuit;

[0011] S105: Obtaining a logical relationship between the sensor on-resistance and the precision resistor, and obtaining a resistance value of the sensor on-resistance based on the logical relationship, thereby completing calibration-free measurement of the three-wire sensor.

[0012] Further, in S101, a three-wire sensor circuit and an arrangement of sensor on-resistance, sensor wire resistance and precision resistor in the three-wire sensor circuit are obtained, including:

[0013] The three-wire sensor circuit includes a differential ADC acquisition circuit diagram and a single-ended ADC acquisition circuit diagram, wherein a single-pole double-throw switch is provided in the differential ADC acquisition circuit diagram to adjust the voltage values ​​at different acquisition points;

[0014] Get the sensor on-resistance R in the differential ADC acquisition circuit diagram and the single-ended ADC acquisition circuit diagram pt , the sensor wire resistance is R x1 =R x2 =R x3 =R x , R ref1 , R ref2 0.1%, 5-20ppm precision resistor, R ref1 , R ref2 According to R pt Select the appropriate value for the optimal working current.

[0015] Furthermore, in the differential ADC acquisition circuit, the sensor on-resistance R is obtained. pt The voltage value at both ends includes:

[0016] R x1 , R x2 , R x3 The voltage across the terminals is V Rx1 、V Rx2 、V Rx3 ;

[0017] Due to R x1 =R x2 =R x3 =R x , so V Rx1 =V Rx2 =V Rx3 =V Rx ;

[0018] Remember R pt The voltage across the terminals is V Rpt .

[0019] Furthermore, in the differential ADC acquisition circuit, the ab and ac voltage differences are obtained, including:

[0020] Pull the SPDT switch to pin 3 to collect the voltage difference between a and b, recorded as V ab ,

[0021] Then we have: V ab =V Rx1 +V Rpt =V Rx +V Rpt ;

[0022] Pull the SPDT switch to pin 2 to collect the voltage difference between a and c, record it as V ac ,

[0023] Then we have: V ac =V Rx1 +V Rx2 +V Rpt =2V Rx +V Rpt .

[0024] Furthermore, in the differential ADC acquisition circuit, the accurate sensor on-resistance R pt The voltage value at both ends includes:

[0025] Assuming 2V ab -V ac ;

[0026] Then we have: 2V ab -V ac =2V Rx +2V Rpt -2V Rx -V Rpt =V Rpt ;

[0027] This can accurately obtain R pt The voltage difference between the two ends is:

[0028] V Rpt =2V ab -V ac .

[0029] Furthermore, in the differential ADC acquisition circuit, the sensor on-resistance R is obtained. pt The resistance values ​​include:

[0030] Remember R ref1 and R ref2 The voltage across the terminals is V ref1 、V ref2 .

[0031] Assume R REF =R ref1 +R ref2 , V REF =V ref1 +V ref2 ;

[0032] Then we have: V REF =VCC-V ac

[0033] Infer that:

[0034] The available resistance is:

[0035] The sensor on-resistance R is accurately obtained from the above formula pt The resistance and voltage across it.

[0036] Furthermore, in the single-ended ADC acquisition circuit, the sensor on-resistance R is obtained. pt The voltage value at both ends includes:

[0037] R x1 , R x2 , R x3 The voltage across the terminals is V Rx1 、V Rx2 、V Rx3 ;

[0038] Due to R x1 =R x2 =R x3 =R x ,so:

[0039] V Rx1 =V Rx2 =V Rx3 =V Rx ;

[0040] Remember R ref The voltage difference between the two ends is V ref .

[0041] Furthermore, in the single-ended ADC acquisition circuit, the voltage difference between acquisition point a and acquisition point b is obtained, including:

[0042] The voltage value at point a is collected by ADC1 and recorded as V a , then:

[0043] V a =V Rx2 +V ref =V Rx +V ref ;

[0044] The voltage value at point b is collected by ADC2 and recorded as V b , then:

[0045] V b =V ref ;

[0046] Remember R pt The voltage difference between the two ends is V Rpt , then

[0047] V Rpt =VCC-V a -V Rx1 ; = VCC-V Rx -V ref -V Rx1 ; = VCC-2V Rx -V ref .

[0048] Furthermore, in the single-ended ADC acquisition circuit, the accurate sensor on-resistance R pt The voltage value at both ends includes:

[0049] Because: VCC-2V a +V b =VCC-2V Rx -2V ref +V ref ; = VCC-2V Rx -V ref ;

[0050] So: V Rpt =VCC-2V a +V b ;

[0051] That is, the sensor on-resistance R is obtained pt The exact value of the voltage across the terminals.

[0052] Furthermore, in the single-ended ADC acquisition circuit, the sensor on-resistance R is obtained. pt The resistance values ​​include:

[0053] According to R pt The logical relationship between the precision resistor and the

[0054] The sensor on-resistance is obtained

[0055] The sensor on-resistance R is accurately obtained from the above formula pt The resistance and voltage across it.

[0056] Compared with the prior art, the calibration-free measurement method of the three-wire sensor provided by the present invention has the following beneficial effects:

[0057] 1. The measurement method with the same precision as the technical solution is adopted to collect the voltage values ​​of multiple points on the sensor circuit for calculation, thereby eliminating the influence of the wire resistance on the measurement result and not introducing other nonlinear variables;

[0058] 2. Due to the use of precision resistors, changes in ambient temperature have little effect on them and basically have no effect on the measurement results. Therefore, the relevant parameters of the three-wire sensor can be accurately obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A schematic flow chart of the calibration-free measurement method for a three-wire sensor proposed by the present invention;

[0060] Figure 2 A schematic block diagram of a process for obtaining a three-wire sensor circuit in a calibration-free measurement method for a three-wire sensor proposed in the present invention, and an arrangement of a sensor on-resistance, a sensor wire resistance, and a precision resistor in the three-wire sensor circuit;

[0061] Figure 3 It is a differential ADC acquisition circuit diagram in the calibration-free measurement method of the three-wire sensor proposed by the present invention;

[0062] Figure 4 This is a single-ended ADC acquisition circuit diagram in the calibration-free measurement method of the three-wire sensor proposed by the present invention. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0064] The implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0065] The same or similar numbers in the drawings of this embodiment correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limitations on the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0066] Reference Figure 1-2As shown in the figure, the calibration-free measurement method of the three-wire sensor includes the following steps:

[0067] S101: Obtain a three-wire sensor circuit and an arrangement of a sensor on-resistance, a sensor wire resistance, and a precision resistor in the three-wire sensor circuit;

[0068] The three-wire sensor circuit and the arrangement of the sensor on-resistance, the sensor wire resistance and the precision resistor in the three-wire sensor circuit are obtained, including:

[0069] The three-wire sensor circuit includes a differential ADC acquisition circuit diagram and a single-ended ADC acquisition circuit diagram. A single-pole double-throw switch is provided in the differential ADC acquisition circuit diagram to adjust the voltage values ​​at different acquisition points.

[0070] Get the sensor on-resistance R in the differential ADC acquisition circuit diagram and the single-ended ADC acquisition circuit diagram pt , the sensor wire resistance is R x1 =R x2 =R x3 =R x , R ref1 , R ref2 0.1%, 5-20ppm precision resistor, R ref1 , R ref2 According to R pt Select the appropriate value for the best working current;

[0071] S102: Obtain the voltage value of the sensor wire resistance in the three-wire sensor circuit, and obtain the voltage value across the current sensor on-resistance;

[0072] S103: setting multiple collection points on the circuit to obtain voltage differences between the multiple collection points, and calculating the voltage difference between the two ends of the sensor on-resistance by collecting the voltage difference between the two ends of the sensor on-resistance;

[0073] S104: obtaining current voltages at collection points at both ends of the multiple precision resistors to obtain current voltage values ​​of the multiple precision resistors, and finally obtaining a total voltage value of the precision resistors in the three-wire sensor circuit;

[0074] S105: Obtain the logical relationship between the sensor on-resistance and the precision resistor, and obtain the resistance value of the sensor on-resistance based on the logical relationship, that is, complete the calibration-free measurement of the three-wire sensor. The measurement method with the same precision as the present technical solution is adopted to collect the voltage values ​​of multiple points on the sensor circuit for calculation, thereby eliminating the influence of the wire resistance on the measurement result and not introducing other nonlinear variables. Since precision resistors are used, the change of ambient temperature has little effect on it and basically has no influence on the measurement result. Therefore, the relevant parameters of the three-wire sensor can be accurately obtained.

[0075] Reference Figure 3 , in the differential ADC acquisition circuit, obtain the sensor on-resistance R pt The voltage value at both ends includes:

[0076] R x1 , R x2 , R x3 The voltage across the terminals is V Rx1 、V Rx2 、V Rx3 ;

[0077] Due to R x1 =R x2 =R x3 =R x , so V Rx1 =V Rx2 =V Rx3 =V Rx ;

[0078] Remember R pt The voltage across the terminals is V Rpt .

[0079] Get ab, ac voltage difference, including:

[0080] Pull the SPDT switch to pin 3 to collect the voltage difference between a and b, recorded as V ab ,

[0081] Then we have: V ab =V Rx1 +V Rpt =V Rx +V Rpt ;

[0082] Pull the SPDT switch to pin 2 to collect the voltage difference between a and c, record it as V ac ,

[0083] Then we have: V ac =V Rx1 +V Rx2 +V Rpt =2V Rx +V Rpt .

[0084] Accurate sensor on-resistance R pt The voltage value at both ends includes:

[0085] Assuming 2V ab -V ac ;

[0086] Then we have: 2V ab -V ac =2VRx +2V Rpt -2V Rx -V Rpt =V Rpt ;

[0087] This can accurately obtain R pt The voltage difference between the two ends is:

[0088] V Rpt =2V ab -V ac .

[0089] Get the sensor on-resistance R pt The resistance values ​​include:

[0090] Remember R ref1 and R ref2 The voltage across the terminals is V ref1 、V ref2 .

[0091] Assume R REF =R ref1 +R ref2 , V REF =V ref1 +V ref2 ;

[0092] Then we have: V REF =VCC-V ac

[0093] Infer that:

[0094] The available resistance is:

[0095] The sensor on-resistance R is accurately obtained from the above formula pt The resistance value and the voltage at both ends are measured by using the differential ADC acquisition circuit accuracy measurement method. The voltage values ​​at multiple points on the sensor circuit are collected for calculation, eliminating the influence of the wire resistance on the measurement results and will not introduce other nonlinear variables.

[0096] Reference Figure 4 , in the single-ended ADC acquisition circuit, obtain the sensor on-resistance R pt The voltage value at both ends includes:

[0097] R x1 , R x2 , R x3 The voltage across the terminals is V Rx1 、V Rx2 、V Rx3 ;

[0098] Due to R x1 =Rx2 =R x3 =R x ,so:

[0099] V Rx1 =V Rx2 =V Rx3 =V Rx ;

[0100] Remember R ref The voltage difference between the two ends is V ref .

[0101] Obtain the voltage difference between collection point a and collection point b, including:

[0102] The voltage value at point a is collected by ADC1 and recorded as V a , then:

[0103] V a =V Rx2 +V ref =V Rx +V ref ;

[0104] The voltage value at point b is collected by ADC2 and recorded as V b , then:

[0105] V b =V ref ;

[0106] Remember R pt The voltage difference between the two ends is V Rpt , then

[0107] V Rpt =VCC-V a -V Rx1 ; = VCC-V Rx -V ref -V Rx1 ; = VCC-2V Rx -V ref .

[0108] Accurate sensor on-resistance R pt The voltage value at both ends includes:

[0109] Because: VCC-2V a +V b =VCC-2V Rx -2V ref +V ref ; = VCC-2V Rx -V ref ;

[0110] So: V Rpt=VCC-2V a +V b ;

[0111] That is, the sensor on-resistance R is obtained pt The exact value of the voltage across the terminals.

[0112] Get the sensor on-resistance R pt The resistance values ​​include:

[0113] According to R pt The logical relationship between the precision resistor and the

[0114] The sensor on-resistance is obtained

[0115] The sensor on-resistance R is accurately obtained from the above formula pt The resistance value and the voltage at both ends are measured by the single-ended ADC acquisition circuit accuracy measurement method. The voltage values ​​at multiple points on the sensor circuit are collected for calculation, eliminating the influence of the wire resistance on the measurement results and will not introduce other nonlinear variables. Due to the use of precision resistors, changes in ambient temperature have little effect on them and basically will not affect the measurement results. Therefore, the relevant parameters of the three-wire sensor can be accurately obtained.

[0116] This technical solution adopts an equal-precision measurement method to collect voltage values ​​at multiple points on the sensor circuit for calculation, eliminating the influence of wire resistance on the measurement results and not introducing other nonlinear variables. Due to the use of precision resistors, changes in ambient temperature have little effect on them and basically have no effect on the measurement results, thereby accurately obtaining the relevant parameters of the three-wire sensor.

[0117] In this embodiment, the entire operation process can be controlled by a computer, and with the addition of a PLC, etc., automated operation control can be achieved. In each operation link, sensors can be set up to provide signal feedback to achieve sequential execution of steps. These are all common knowledge of current automated control and will not be described in detail in this embodiment.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A calibration-free measurement method for a three-wire sensor, characterized in that: The specific steps include: S101: Obtain a three-wire sensor circuit and an arrangement of a sensor on-resistance, a sensor wire resistance, and a precision resistor in the three-wire sensor circuit; S102: Obtain the voltage value of the sensor wire resistance in the three-wire sensor circuit, and obtain the voltage value across the current sensor on-resistance; S103: setting multiple collection points on the circuit to obtain voltage differences between the multiple collection points, and calculating the voltage difference between the two ends of the sensor on-resistance by collecting the voltage difference between the two ends of the sensor on-resistance; S104: obtaining current voltages at collection points at both ends of the multiple precision resistors to obtain current voltage values ​​of the multiple precision resistors, and finally obtaining a total voltage value of the precision resistors in the three-wire sensor circuit; S105: Obtaining a logical relationship between the sensor on-resistance and the precision resistor, and obtaining a resistance value of the sensor on-resistance based on the logical relationship, thereby completing calibration-free measurement of the three-wire sensor.

2. The calibration-free measurement method of a three-wire sensor as claimed in claim 1, characterized in that: In S101, a three-wire sensor circuit and an arrangement of a sensor on-resistance, a sensor wire resistance, and a precision resistor in the three-wire sensor circuit are obtained, including: The three-wire sensor circuit includes a differential ADC acquisition circuit diagram and a single-ended ADC acquisition circuit diagram, wherein a single-pole double-throw switch is provided in the differential ADC acquisition circuit diagram to adjust the voltage values ​​at different acquisition points; Get the sensor on-resistance R in the differential ADC acquisition circuit diagram and the single-ended ADC acquisition circuit diagram pt , the sensor wire resistance is R x1 =R x2 =R x3 =R x , R ref1 , R ref2 0.1%, 5-20ppm precision resistor, R ref1 , R ref2 According to R pt Select the appropriate value for the optimal working current.

3. The calibration-free measurement method of a three-wire sensor as claimed in claim 2, characterized in that: In the differential ADC acquisition circuit, the sensor on-resistance R is obtained. pt The voltage value at both ends includes: R x1 , R x2 , R x3 The voltage across the terminals is V Rx1 、V Rx2 、V Rx3 ; Due to R x1 =R x2 =R x3 =R x , so V Rx1 =V Rx2 =V Rx3 =V Rx ; Remember R pt The voltage across the terminals is V Rpt .

4. The calibration-free measurement method of a three-wire sensor as claimed in claim 3, characterized in that: In the differential ADC acquisition circuit, the ab and ac voltage differences are obtained, including: Pull the SPDT switch to pin 3 to collect the voltage difference between a and b, recorded as V ab , Then we have: V ab =V Rx1 +V Rpt =V Rx +V Rpt ; Pull the SPDT switch to pin 2 to collect the voltage difference between a and c, record it as V ac , Then there is: V ac = V Rx1 + V Rx2 + V Rpt = 2V Rx + V Rpt .

5. The calibration-free measurement method of a three-wire sensor as claimed in claim 4, characterized in that: In the differential ADC acquisition circuit, the accurate sensor on-resistance R pt The voltage value at both ends includes: Assuming 2V ab -V ac ; Then we have: 2V ab -V ac =2V Rx +2V Rpt -2V Rx -V Rpt =V Rpt ; This can accurately obtain R pt The voltage difference between the two ends is: V Rpt =2V ab -V ac 。 6. The calibration-free measurement method of a three-wire sensor as claimed in claim 5, characterized in that: In the differential ADC acquisition circuit, the sensor on-resistance R is obtained. pt The resistance values ​​include: Remember R ref1 and R ref2 The voltage across the terminals is V ref1 、V ref2 . Assume R REF =R ref1 +R ref2 , V REF =V ref1 +V ref2 ; Then we have: V REF =VCC-V ac Infer that: The available resistance is: The sensor on-resistance R is accurately obtained from the above formula pt The resistance and voltage across it.

7. The calibration-free measurement method of a three-wire sensor as claimed in claim 6, characterized in that: In the single-ended ADC acquisition circuit, obtain the sensor on-resistance R pt The voltage value at both ends includes: R x1 , R x2 , R x3 The voltage across the terminals is V Rx1 、V Rx2 、V Rx3 ; Due to R x1 =R x2 =R x3 =R x ,so: V Rx1 =V Rx2 =V Rx3 =V Rx ; Remember R ref The voltage difference between the two ends is V ref .

8. The calibration-free measurement method of a three-wire sensor as claimed in claim 7, characterized in that: In the single-ended ADC acquisition circuit, the voltage difference between acquisition point a and acquisition point b is obtained, including: The voltage value at point a is collected by ADC1 and recorded as V a , then: V a =V Rx2 +V ref =V Rx +V ref ; The voltage value at point b is collected by ADC2 and recorded as V b , then: V b =V ref ; Remember R pt The voltage difference between the two ends is V Rpt , then In Rpt =VCC-V a -V Rx1 ; =VCC-V Rx -V ref -V Rx1 ; =VCC-2V Rx -V ref 。 9. The calibration-free measurement method of a three-wire sensor as claimed in claim 8, characterized in that: In the single-ended ADC acquisition circuit, the accurate sensor on-resistance R pt The voltage value at both ends includes: Because: VCC-2V a +V b =VCC-2V Rx -2V ref +V ref ; =VCC-2V Rx -V ref ; So: V Rpt =VCC-2V a +V b ; That is, the sensor on-resistance R is obtained pt The exact value of the voltage across the terminals.

10. The calibration-free measurement method of a three-wire sensor as claimed in claim 9, characterized in that: In the single-ended ADC acquisition circuit, obtain the sensor on-resistance R pt The resistance values ​​include: According to R pt The logical relationship between the precision resistor and the The sensor on-resistance is obtained The sensor on-resistance R is accurately obtained from the above formula pt The resistance and voltage across it.

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