JPH0653830A - Method for automatically calibrating non-linear sensor connecting circuit - Google Patents

Abstract

PURPOSE:To provide a calibration method for circuits connected to a non-linear sensor capable of automatically and inexpensively executing highly accurate adjustment. CONSTITUTION:In the method for calibrating two processing circuits, i.e., a resistance/voltage converter 1 and an A/D converter 2, connected to the non- linear sensor 41 having non-linearity so as to process the measured output value of the sensor 41 and input their processed signal to a microcomputer 3, a known calibrating input value is inputted to the circuits 1, 2 to find out their circuit characteristics, the calibrated I/O relation of both the circuits 1, 2 is found out based upon the circuit characteristics, the calibrated output value of the circuits 1, 2 corresponding to the measured output value of the sensor 41 is found out based upon the calibrated I/O relation of the circuits 1, 2 and non-linear/linear conversion having characteristics reversed from that of the sensor 4 is executed by the microcomputer 3 based upon the calibrated output value of the circuits 1, 2, so that the automatic calibration of the circuit connected to the non-linear sensor 4 can be executed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for calibrating a circuit connected to a non-linear sensor.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram for processing an output signal of a conventional non-linear sensor, FIG. 5 is a circuit configuration diagram by a conventional calibration method, and FIG. 6 is a procedure diagram of the conventional calibration method. Is. In FIGS. 4 and 5, 11 is a resistance / voltage converter, 12 is an A / D converter, 13 is a microcomputer, 14 is a sensor resistance, 15 is a gain adjusting means, 1
6 is an offset adjusting means, 17 is a ROM data table, 18 is a switch, 50 is a measurement target, 52 is a variable, 5
4 is an electric quantity, 56 is a digital value, 58 is a measured value, 60 is a sensor, 62 is an analog circuit, 64 is an A / D conversion circuit,
66 is a non-linear conversion circuit.

Conventionally, the linearization of the signal of the non-linear element by the signal processing of the output of the non-linear element such as the non-linear sensor is performed as follows. For example, FIG. 4 shows a flow of processing of an output signal when a resistance temperature detector such as Pt100 or Ni500 is used as a non-linear sensor, and a measurement target 50 such as temperature is a resistance value of an element of the sensor 60. Change the variable of.

This variable 52 is converted into an analog electric quantity such as voltage or current by an analog circuit 62, and further A /
The D conversion circuit 64 performs analog / digital conversion into a digital value 56. The digital value 56 is non-linearly converted by the non-linear conversion circuit 66 having a characteristic opposite to the non-linearity of the non-linear sensor 66 itself, and a linearized measured value 58 is obtained.

In the signal processing of the output of the above-mentioned non-linear element, the analog circuit 62 and the A / D conversion circuit 64 have an electric quantity 54 which is an output value of those circuits and a digital value due to an error of component constants constituting the circuit. The value 56 will include an error. Therefore, the error is calibrated by the conventional circuit configuration shown in FIG. 5 according to the procedure shown in FIG.

In FIG. 5, the output of the sensor resistor 14 is connected to the resistor / voltage converter 11 via a switch 18,
The output voltage is analog-to-digital converted by the A / D conversion circuit 12 into a digital value, which is input to the microcomputer 13. A ROM data table 17 is connected to the microcomputer 13. Further, the resistance / voltage converter 11 has a gain adjusting means 15 and an offset adjusting means 1 in order to correct the error.
6 is provided.

Hereinafter, an example using a resistance temperature detector as the non-linear element will be described, but the same can be applied to other non-linear elements. The resistance value of the sensor resistor 14 changes with temperature, but the state of this change is not linear. For example, as shown in the graph 1 of FIG. 6, the change of the resistance value with respect to the temperature change is not a linear characteristic but a non-linear characteristic of the nonlinear element. The non-linear characteristic of this change is peculiar to the sensor, is predetermined, and is known.

The microcomputer 13 operates the switch 18 in response to the sensor input instruction signal, and the sensor resistor 14
Then, the resistance value of is input to the resistance / voltage converter 11. And
The resistance / voltage converter 11 converts the resistance value into a voltage. This resistance / voltage conversion is shown in graph 2 of FIG. However, as shown in graph 2 of FIG. 6, both the resistance / voltage converter 11 and the next A / D converter 12 perform gain adjustment and offset adjustment to change the circuit characteristic to a predetermined characteristic. There is a need. This is resistance /
This is because there are variations in the circuit constants that form the voltage converter 11 and the next A / D converter 12, and there is an error from the set value. Here, the resistance / voltage characteristic is adjusted by the volume adjustment of the gain adjusting means 15, the offset adjusting means 16, and the like.

The input resistance value is converted into a voltage by the calibrated characteristic, and then A / D converted (see graph 3 in FIG. 6). This digital value is the microcomputer 1
Input to 3. The microcomputer 13 has a data table 17 (which can be mounted in a ROM or the like) having a nonlinear characteristic that is an inverse characteristic of the temperature / resistance characteristic of the nonlinear element as shown in graph 4 of FIG. 6 with respect to this digital value. , And obtains the temperature value measured by linear conversion.

Next, the resistance / voltage converter 11 and A /
The calibration in the D converter 12 will be described. FIG. 7 shows analog / digital conversion of an analog signal input (hereinafter referred to as “A
FIG. 3 is a block diagram showing a configuration of a system for inputting to a microcomputer.

In the figure, the analog input is input to the analog circuit 10 via the analog input connection switch 18, where it is converted to a predetermined level, and the A / D converter 12 is supplied.
Is converted into a digital value by and input to the microcomputer 13. Here, the portion formed by the analog circuit 10 and the A / D converter 12 is referred to as an A / D conversion circuit. The analog input connection switch 18 is used to select a plurality of analog inputs when there are a plurality of analog inputs, and can be omitted in FIG. 7.

In this system, in order to input an accurate digital value corresponding to an analog input to the microcomputer 13, the level conversion in the analog circuit 10 and the A / D conversion in the A / D converter 12 are performed with high accuracy. It is necessary. However, since the analog circuit 10 and the A / D converter 12 have an output error due to a variation error in the component constants forming them, it is necessary to correct them. Hereinafter, this point will be described.

FIG. 8 shows an analog circuit 10 and an A / D converter 1.
FIG. 3 is an input / output characteristic diagram of the A / D conversion circuit including 2 and. In the figure, the broken line shows an ideal input / output characteristic with no error in the variation of component constants, where x is an analog input and f ₁ (x) is a digital output: f ₁ (x) = a ₁ x + b ₁ ... (1) In other words, A when the analog input is x
When the / D converted value is f (x), the A / D converted value can be expressed by a linear expression of analog input. (This relationship is obtained because the relationship between the analog input and the A / D conversion output is linear, such as when the analog input is a low-frequency signal.) However, there is a variation error in the component constants. Therefore, in reality, the input / output characteristics are different from the ideal characteristics shown by the solid line. This characteristic is represented by f ₂ (x) = a ₂ x + b ₂ (2).

Here, a ₁ and a ₂ are amplification factors, and b ₁ and b ₂
Is an offset value. It can be seen from FIG. 8 that the amplification factor a ₁ and the offset value b ₁ are ideal values, but in reality, the amplification factor is a ₂ and the offset value is b ₂ . Also,
To obtain an accurate A / D conversion value for analog input,
It is understood that the correction of a ₂ → a ₁ and b ₂ → b ₁ should be performed.

FIG. 9 is a block diagram for explaining a conventional method for calibrating an A / D conversion circuit. The variable resistor 15 'on the input side of the A / D converter 12 changes the amplification factor from a ₂ to a.
Adjusted to ₁ to adjust the offset value from b ₂ to b ₁ by a variable voltage power source 16 '.

[0016]

However, the above-mentioned conventional method of calibrating the circuit connected to the nonlinear sensor has the following problems. In order to perform predetermined conversion in resistance / voltage conversion and A / D conversion in a circuit connected to a conventional non-linear sensor, it is necessary to perform gain adjustment and offset adjustment in order to correct errors in component constants and the like. Since this adjustment requires manpower, there are problems in labor saving and adjustment accuracy.

An object of the present invention is to solve the above-mentioned problems and to provide a method of calibrating a circuit connected to a non-linear sensor capable of performing highly accurate adjustment automatically and at low cost.

[0018]

To achieve the above object, the present invention is connected to a non-linear sensor having non-linearity to process a measured output value of the non-linear sensor and input the processed signal to a microcomputer. In the method of calibrating the processing circuit, the known input value for calibration is input to the processing circuit to obtain the circuit characteristic of the processing circuit, and the calibrated input / output relationship of the processing circuit is calculated from the circuit characteristic of the processing circuit. Then, the calibrated output value of the processing circuit with respect to the measured output value of the non-linear sensor is obtained from the calibrated input / output relationship of the processing circuit, and the calibrated output value of the processing circuit is compared with the non-linear sensor in the microcomputer. The non-linear / linear conversion of the inverse characteristic is performed to automatically calibrate the non-linear sensor connection circuit.

The processing circuit is an analog circuit or an A / D.
A converter may be included, and the input control to the processing circuit of the known input value for calibration and the measured output value of the non-linear sensor is performed by a microcomputer. Further, the non-linear / linear conversion can be performed by a storage means that stores non-linear characteristics.

[0020]

According to the present invention, a method for calibrating a processing circuit which is connected to the above-described non-linear sensor, processes the measured output value of the non-linear sensor, and inputs the processed signal to the microcomputer is adopted. Therefore, the calibration of the processing circuit, which is conventionally performed manually, can be automatically calibrated using a microcomputer.

Thus, even in a circuit in which a non-linear sensor signal is used as an input signal, the circuit can be automatically calibrated.

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a block diagram illustrating a method of calibrating a circuit connected to a nonlinear sensor according to an embodiment of the present invention, and FIG. 2 is an A / D conversion circuit of a circuit connected to a nonlinear sensor according to an embodiment of the present invention. It is a block diagram explaining a calibration method.

In the figure, 1 is a resistance / voltage converter, 2 is an A / D converter, 3 is a microcomputer, 10 is an analog circuit, 11 to 13 are connection switches, 41 is a sensor resistance, 42 is a reference resistance α, 43 is a reference resistance β, 44 to 46
Is a connection switch. The configuration of the present invention will be described below.
In FIG. 1, the configuration of the present invention includes a portion 41 of the nonlinear sensor.
~ 43 and circuit parts 1 to 3 for processing the output signal from the non-linear sensor.

The portion of the non-linear sensor in this section corresponds to graph 1 in FIG. 6, and the circuit portion for processing the output signal from the non-linear sensor corresponds to graphs 2 to 4 in FIG. First, the principle of the method of analog automatic calibration of a linear signal according to the present invention will be described with reference to FIG. 2 by a circuit portion that processes an output signal from a non-linear sensor. FIG. 2 shows that the resistance / voltage converter 1 in FIG.
The input to 0 is separated from the output signal from the non-linear sensor into a general input signal.

In the input / output characteristic diagram of FIG. 8, the following relationships are derived as described above. In the figure, the broken line shows an ideal input / output characteristic with no error in the variation of component constants, where x is an analog input and f ₁ (x) is a digital output: f ₁ (x) = a ₁ x + b ₁ ... (1) In other words, A when the analog input is x
When the / D converted value is f (x), the A / D converted value can be expressed by a linear expression of analog input. (This relationship is obtained because the relationship between the analog input and the A / D conversion output is linear, such as when the analog input is a low-frequency signal.) However, there are variations in the components. Therefore, in reality, the input / output characteristics are different from the ideal characteristics shown by the solid line. This characteristic is represented by f ₂ (x) = a ₂ x + b ₂ (2).

Here, a ₁ and a ₂ are amplification factors, and b ₁ and b ₂
Is an offset value. It can be seen from FIG. 8 that the amplification factor a ₁ and the offset value b ₁ are ideal values, but in reality, the amplification factor is a ₂ and the offset value is b ₂ . Also,
To obtain an accurate A / D conversion value for analog input,
It is understood that the correction of a ₂ → a ₁ and b ₂ → b ₁ should be performed.

In the above relational expression, when x = 0, f ₂ (0) = b ₂ (3) When x = α, f ₂ (α) = a ₂ α + b ₂ (4) From the above equations (3) and (4), a showing the characteristics of the circuit
₂ and b ₂ are as follows: a ₂ = {f ₂ (α) −f ₂ (0)} / α (5) b ₂ = f ₂ (0) (6)

The value of the input x when f ₂ (x) is known as the output value of the A / D converter 2 is x = {f ₂ (x) -b ₂ } / a from the equation (2). ₂ becomes (7). Here, the circuit characteristic value a ₂ of the equations (5) and (6),
Substituting b ₂ into the equation (7), x becomes x = α {f ₂ (x) -f ₂ (0)} / {f ₂ (α) -f ₂ (0)} (8).

That is, the A / D converted values f ₂ (0), f
₂ (α) and α, and the output value f of the A / D converter 2
The analog input value x at that time can be obtained from ₂ (x). Substituting this analog input value x into the ideal input / output characteristic equation (2) with no component variation error, f ₁ (x) = a ₁ α {f ₂ (x) −f ₂ (0)} / { f ₂ (α) -f ₂ (0)} + b ₁ (9), which is an A / D in which the circuit error is calibrated for the input value x.
The converted value f ₁ (x) can be obtained.

That is, the respective outputs f with respect to the reference value inputs 0 and α for calibrating the analog input A / D conversion output
_{If 2} (0) and f ₂ (α) are obtained, the ideal conversion value for any analog input can be calculated backward. This back-calculation may be performed by substituting the A / D conversion value f ₂ (x) for the arbitrary analog input value x into the equation (9), and calculating the component constant in the analog circuit or the A / D conversion circuit. It is possible to absorb the error of the offset value and the amplification factor due to the variation error.

In the above calculation, the A / D converted value can be calculated using a microcomputer or the like. Further, an instruction of inputting 0 or α for calibration can also be performed by the microcomputer. FIG. 3 is a flowchart showing a method of analog automatic calibration of a linear signal in the embodiment of the present invention.

The method of analog automatic calibration of a linear signal of the present invention is performed by the following steps. Step S1: First, the microcomputer 3 is A / D
An A / D conversion instruction is given to the converter 2. Here, the connection switch 12 for inputting the first reference value is turned on, and the voltage corresponding to the reference value α is input to the analog circuit 10.

Step S2: Next, the microcomputer 3 gives an A / D conversion instruction to the A / D converter 2. A /
The D converter 2 outputs the A / D conversion output f with respect to the reference value α.
₂ (α) is output. Step S3: Next, the microcomputer 3 gives an input instruction of the reference value 0 to the switch 11 for inputting the second reference value. Here, the second reference value input switch 11 is turned on to ground the input of the analog circuit 10.

Step S4: Next, the microcomputer 3 gives an A / D conversion instruction to the A / D converter 2. A /
D converter 2 outputs A / D conversion output f with reference value 0
₂ (0) is output. Step S5: Next, the microcomputer 3 gives an input instruction of the analog input x to the switch 13 connecting the analog input.

Step S6: Next, the microcomputer 3 gives an A / D conversion instruction to the A / D converter 2. A /
The D converter 2 is an A / D conversion output f for the analog input x
₂ (x) is output. Step S7: Next, the microcomputer 3 f
₂ (x) is calculated using the above-mentioned calibration value calculation formula (9) as f
Calibrate to ₁ (x).

In the above description, 0 and α are used as the existing calibration values for the sake of easy understanding, but any known value β can be obtained in the same manner instead of 0. The calibration calculation formula f ₁ (x) in this case is f ₁ (x) = a ₁ [(β-α) f ₂ (X)-{βf ₂ (α) -αf ₂ (β)}] / {f ₂ (Β) −f ₂ (α)} + b ₁ (10), and the true value can be calculated by this calibration calculation formula.

Although the analog input has been described on the assumption of a voltage, the current or resistance value can be handled in the same manner. The linear automatic analog calibration method of the present invention according to the above description is such that the signals are switched and input to the analog circuit 10 by the connection switches 11 to 13 in FIG. 2, but this method is the same as in FIG. The invention can be applied in a circuit portion that processes an output signal from a nonlinear sensor.

In FIG. 1, a sensor resistance is applied as a non-linear sensor, and the reference value input 0, the reference value input α, and the analog input of FIG. 2 are a reference resistance β43, a reference resistance α42, and a sensor resistance r41, respectively. The resistance value from is input. In this example,
Although the sensor resistance is used as the non-linear sensor, other non-linear sensors can be applied.

Input of the reference resistance β43, the reference resistance α42, and the sensor resistance r41 to the resistance / voltage converter 1 is selected by inputting a reference value 1 from the microcomputer 3.
Reference value 2 input instruction and instruction signal of sensor input instruction,
Each reference resistance α42, reference resistance β43, and sensor resistance r
It is performed by inputting to the connection switches 44 to 46 provided in 41.

The nonlinear sensor input circuit shown in FIG.
Is shown in the actual measurement circuit.
Sensor 41 and reference resistors 42 and 43 and resistance / voltage converter
Figure to correct the effect of cable resistance between
Although a circuit configuration such as 10 is adopted, in this explanation,
This will be described with reference to 1. Microcomputer 3 is the standard value
Known as reference resistance α42, reference resistance β43 and measurement
Input instructions sequentially to the target sensor resistance r41,
Through the resistance / voltage converter 1 and the A / D converter 2,
Corresponding A / D conversion value f₂(Α), f ₂(Β), and f
₂(R) is obtained.

The ideal A / D conversion value for the input r is f ₁
Assuming that (r), f ₁ (r) is expressed by the following formula (1). f ₁ (r) = a ₁ r + b ₁ (11) Therefore, f ₁ (r) is calculated from the calibration equation (10) as follows: f ₁ (r) = a ₁ [(β−α) f ₂ (X) − { βf ₂ (α) -αf ₂ (β)}] / {f ₂ (β) -f ₂ (α)} + b ₁ (12)

The A / D conversion value f ₁ (r) obtained by the equation (12) can be a linear value with respect to the resistance r. However, the A / D converted value f ₁ (r) is not a linear value with respect to the temperature to be originally measured due to the non-linearity of the sensor. To return this non-linear value to a linear temperature, a method similar to the conventional one can be applied. That is, the microcomputer 3 can read the corresponding temperature and obtain the measured temperature by referring to the data table such as the ROM in which the temperature corresponding to the calibrated A / D converted value f ₁ (r) is recorded. .

Next, a second embodiment of the present invention will be described. FIG. 11 is a block diagram of a second embodiment illustrating a method for calibrating a circuit connected to the nonlinear sensor of the present invention. In the first embodiment of FIG. 1, the sensor resistance r41, the reference resistance α42, and the reference resistance β4 are connected to the resistance / voltage converter 1 by the connection switches 44 to 46 as inputs.
Although 3 is selected and input, in the second embodiment shown in FIG. 11, the sensor resistance r4 is left connected to the resistance / voltage converter 1 and the measurement target itself measured by the sensor resistance r4 is To change. The measurement object itself is changed by a measurement value input instruction, a reference value 1 input instruction, and a reference value 2 input instruction from the microcomputer 3.

The present invention is not limited to the above embodiments, and various modifications can be made within the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0045]

As described above, according to the present invention,
By adopting a method of connecting to the non-linear sensor to process the measured output value of the non-linear sensor and calibrating the processing signal by the microcomputer, the following effects can be obtained. (1) According to the present invention, even for a non-linear sensor signal, the input section to the A / D conversion output can be automatically calibrated by a microcomputer or the like, so that it can be omitted and the cost can be reduced. (2) Further, the adjustment accuracy can be improved by omitting manpower.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a method of calibrating a circuit connected to a non-linear sensor according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram illustrating a method of calibrating an A / D conversion circuit of a circuit connected to a non-linear sensor according to an exemplary embodiment of the present invention.

FIG. 3 is a flowchart showing a method for analog automatic calibration of a linear signal according to an embodiment of the present invention.

FIG. 4 is a block diagram for processing an output signal of a conventional non-linear sensor or the like.

FIG. 5 is a circuit configuration diagram according to a conventional calibration method.

FIG. 6 is a procedure diagram of a conventional calibration method.

FIG. 7 is a block diagram in which an analog signal input is A / D converted and input to a microcomputer.

FIG. 8 is an input / output characteristic diagram of the A / D conversion circuit.

FIG. 9 is a block diagram illustrating a calibration method of a conventional A / D conversion circuit.

FIG. 10 is a measurement circuit diagram using a non-linear sensor.

FIG. 11 is a block diagram of a second embodiment illustrating a method of calibrating a circuit connected to the inventive non-linear sensor of the present invention.

[Explanation of symbols]

 1 resistance / voltage converter 2 A / D converter 3 microcomputer 4 sensor resistance 10 analog circuit 11-13 connection switch 41 sensor resistance 42 reference resistance α 43 reference resistance β 44-46 connection switch

Claims (5)

[Claims] 1. A method for calibrating a processing circuit which is connected to a nonlinear sensor having nonlinearity, processes a measurement output value of the nonlinear sensor, and inputs the processed signal to a microcomputer, comprising: (a) A known input value is input to the processing circuit to obtain a circuit characteristic of the processing circuit; (b) a calibrated input / output relationship of the processing circuit is obtained from the circuit characteristic of the processing circuit; and (c) the processing circuit. A calibrated output value of the processing circuit with respect to the measured output value of the non-linear sensor from the calibrated input / output relationship of A method for automatically calibrating a non-linear sensor connection circuit, characterized by performing non-linear / linear conversion having an inverse characteristic of a sensor. 2. The automatic calibration method for a non-linear sensor connection circuit according to claim 1, wherein the processing circuit is a circuit including an analog circuit. 3. The automatic calibration method for a nonlinear sensor connection circuit according to claim 1, wherein the processing circuit is a circuit including an A / D conversion circuit. 4. The input control of the known input value for calibration and the measured output value of the non-linear sensor to the processing circuit includes:
The method for automatically calibrating a non-linear sensor connection circuit according to claim 1, which is performed by the microcomputer. 5. The method for automatically calibrating a non-linear sensor connection circuit according to claim 1, wherein the non-linear / linear conversion is performed by a storage unit that stores the non-linear characteristic.