JPH08166297A - Load cell type temperature compensation method - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a temperature compensation method capable of realizing highly accurate temperature correction without performing highly accurate temperature detection when performing digital correction based on the temperature detected by a temperature sensor. To aim. [Structure] A temperature correction resistor R _N is used to roughly adjust the temperature characteristic of sensitivity, and the output of the load cell 2 subjected to the coarse adjustment is multiplied by a coefficient by the microcomputer 4 based on the measured temperature obtained by the temperature sensor 3. Fine-tune.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature compensation method for a load cell type balance.

[0002]

2. Description of the Related Art A load cell is constructed by connecting a strain gauge attached to a flexure element to a bridge circuit.
The temperature characteristic of load cell sensitivity is almost determined by the material of the strain generating element and the type of strain gauge, but the characteristic value is about 3
It is as large as 00 to 600 ppm / ° C.

Specifically, the temperature sensation characteristic before correction is 600 pp.
If m LOAD / ° C, the temperature sensation correction coefficient is -6
Given as 00 ppm LOAD / ° C. If the output error of the temperature sensor is 1 ° C when the rated load is applied,
There is an error in the correction value by 600ppm from the rating. That is, 600 × 10 ⁻⁶ ≈ (1/1667) the error of the rated output.

Conventionally, temperature compensation is performed by any of the following. In FIG. 2, a temperature-sensitive resistor _RN is inserted from the excitation power source 1 to the input side circuit of the bridge circuit of the load cell 2,
The input voltage to the bridge circuit is given the temperature characteristic opposite to that of the load cell output to cancel the load cell output and the temperature characteristic.

Characteristic S of FIG.₀ Is the raw temperature of the load cell output
Degree characteristic. Actually, one temperature-sensitive resistor R_N Insert
However, due to various variations, the characteristic S₁ As shown in
I can only make adjustments, but not completely correct. Therefore, temperature sensitivity
Resistance R_N In parallel with the correction resistor R _P To make fine adjustments by connecting
The work is repeated to make fine adjustments.

[0006] sense Another adjustment method that does not use the hot resistor R _N is a temperature sensor 3 is disposed in the vicinity of the load cell, as shown in FIG. 4 in place of the temperature-sensitive resistor R _N, to the temperature detected by the temperature sensor 3 Based on this, the microcomputer 4 performs digital correction. In the microcomputer 4, a correction coefficient required to cancel the characteristic S ₀ is registered for each detected temperature.

In FIGS. 2 and 4, 5 is a preamplifier and 6 is an A / D converter.

[0008]

In the conventional method, the microcomputer 4 is based on the temperature detected by the temperature sensor 3.
In the case of digital correction with, it is not necessary to repeat fine adjustment of the correction resistor R _P , but the temperature detection accuracy of the temperature sensor 3 affects the accuracy of the scale, and if a detection error of 1 ° C. occurs, the rated output is Error of about 1/1500 to 1/3000 occurs.

Therefore, highly accurate temperature detection is required for digital correction. The present invention reduces the man-hours as compared with the conventional method, and when the microcomputer 4 digitally corrects the temperature based on the temperature detected by the temperature sensor 3, the high-accuracy temperature correction is not necessary. It is an object of the present invention to provide a temperature compensation method that can realize the above.

[0010]

According to a first aspect of the present invention, there is provided a temperature compensation method, wherein a strain gauge is attached to a strain-generating body, and a load acting on the strain-generating body is detected.
A temperature compensation resistor having a temperature characteristic is inserted in series in the excitation circuit of the strain gauge to roughly adjust the temperature characteristic of the sensitivity, and the output signal of the output circuit of the strain gauge is measured in the state of being roughly adjusted. The temperature characteristic of the sensitivity is stored, and the output signal of the output circuit of the strain gauge is multiplied by the correction coefficient based on the stored temperature characteristic and the operating temperature obtained by actually measuring the temperature at the time of use with the temperature sensor to obtain a fine value. It is characterized by adjusting.

According to a second aspect of the temperature compensating method, in a load cell type balance in which a strain gauge is attached to a strain-generating body and a load acting on the strain-generating body is detected, the temperature characteristic of the strain-generating material and the strain gauge are used. Based on the temperature characteristics of, the resistance value of the temperature correction resistor necessary for coarse adjustment by interposing in series with the excitation circuit of the strain gauge is obtained,
Measure the resistance value of the temperature compensation resistor used for mounting, calculate and store the correction coefficient necessary for fine adjustment of the output signal of the strain gauge output circuit based on this measured resistance value. It is characterized in that the output signal of the output circuit of the strain gauge is multiplied by the correction coefficient and finely adjusted based on the correction coefficient and the use temperature obtained by actually measuring the temperature at the time of use by the temperature sensor.

[0012]

According to the structure of claim 1, the temperature compensation resistor is used to roughly adjust the temperature characteristic of the sensitivity, and the output of the load cell subjected to the coarse adjustment is measured to obtain the temperature correction coefficient and the occasionally measured temperature. Fine tune based on.

According to the second aspect of the invention, when the temperature correction resistor is used for coarse adjustment, and the output of the load cell that has been coarsely adjusted is multiplied by the temperature correction coefficient according to the actually measured temperature, the fine adjustment is performed.
Measure the resistance value of the temperature compensation resistor used for mounting, calculate and store the compensation coefficient necessary for fine adjustment of the output signal of the strain gauge output circuit based on the measured resistance value, and then memorize it. To do.

[0014]

EXAMPLES The temperature compensation method of the present invention will be described below based on specific examples. FIG. 1 shows a load cell type balance adopting the temperature compensation method of the present invention, in which a temperature sensitive resistor _RN is inserted from an exciting power source 1 to a circuit on an input side of the bridge circuit for coarse adjustment, and a temperature sensor 3 is used to load the load cell. The temperature in the vicinity of 2 is detected and digitally corrected by the microcomputer 4 for fine adjustment.

Specifically, the temperature-sensitive resistance R _N is calculated based on the theoretical value of the temperature coefficient determined by the material of the strain generating element and the theoretical value of the temperature coefficient determined by the material of the strain gauge.
Implement temperature sensitive resistor R _N which seems closer to a value obtained by calculation, and measured the span value of the load cell 2 by multiplying the actual load in a thermostat, micro calculates the digital correction factor based on the results Write to computer 4.

In this way, the output of the load cell 2 is roughly adjusted by the temperature-sensitive resistor R _N , and the output which is roughly adjusted and the inclination of the temperature characteristic of sensitivity is reduced is detected by the microcomputer 4 by the temperature detected by the temperature sensor 3. Since the digital compensation is further performed based on the temperature compensation method as compared with the conventional temperature compensation method in which the characteristic S ₀ having a large inclination is digitally compensated based on the detected temperature, high accuracy is achieved even if the temperature measurement accuracy is the same as the conventional one. The temperature compensation can be realized.

Moreover, by simply interposing the temperature sensitive resistor R _N ,
Unlike the conventional case, it is not necessary to repeat the work of connecting the correction resistor R _P and performing fine adjustment, and it is possible to reduce the number of steps. In the temperature compensation method described above, the digitally-corrected coefficient is obtained by mounting the calculated temperature-sensitive resistor R _N and measuring the roughly adjusted characteristic, but the digitally-corrected coefficient can also be obtained as follows.

This method of obtaining a digital correction coefficient without actually measuring the characteristics that have been roughly adjusted is based on the theoretical value of the temperature coefficient determined by the material of the strain generating element and the theoretical value of the temperature coefficient determined by the strain gauge material. The resistance R _N is calculated, and a theoretical digital correction coefficient based on each theoretical value is calculated.

Next, the resistance value of the temperature-sensitive resistor R _N , which is considered to be close to the calculated value, at the reference temperature is measured, and the theoretical digital correction coefficient is recalculated based on the measured value. In this recalculation, the temperature coefficient on the circuit side can be processed with a theoretical value, or can be processed based on the temperature coefficient measured by putting only the circuit board in the constant temperature bath.

Finally, the temperature sensitive resistor R _N is mounted and the recalculated digital correction coefficient is written in the microcomputer 4. According to this temperature compensation method, the number of types of temperature-sensitive resistors R _N prepared in advance can be reduced. Further, since a large constant temperature bath is not required, the equipment can be downsized.

[0021]

According to the first aspect of the present invention, the temperature compensation resistor is used to roughly adjust the temperature characteristic of sensitivity, and the output of the load cell that has been coarsely adjusted is measured with the temperature correction coefficient obtained from the actual measurement. Since the fine adjustment is performed based on the measured temperature, it is not necessary to repeat the troublesome adjustment work of the parallel resistance as in the case of temperature compensation using only the temperature correction resistor as in the past. Appropriate temperature correction can be realized without measuring the temperature with high accuracy as in the case of temperature compensation only by correction.

According to the second aspect of the invention, when the temperature is adjusted roughly by the temperature correction resistor and the output of the load cell which is roughly adjusted is multiplied by the temperature correction coefficient according to the actually measured temperature,
Measure the resistance value of the temperature compensation resistor used for mounting, calculate and store the compensation coefficient necessary for fine adjustment of the output signal of the strain gauge output circuit based on the measured resistance value, and then memorize it. Therefore, the above effect can be obtained even if the number of types of temperature-sensitive resistances prepared in advance is reduced. Further, since a large constant temperature bath is not required, the equipment can be downsized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a load cell type balance adopting a temperature compensation method of the present invention.

FIG. 2 is a configuration diagram of a load cell type balance adopting a conventional temperature compensation method using a temperature-sensitive resistance.

FIG. 3 is a temperature sensitivity characteristic diagram.

FIG. 4 is a configuration diagram of a load cell type balance adopting a conventional temperature compensation method by digital correction.

[Explanation of symbols]

1 excitation power source 2 load cell 3 Temperature sensor 4 microcomputer R _N temperature sensing resistor

Claims (2)

[Claims] 1. In a load cell type balance in which a strain gauge is attached to a flexure element and a load acting on the flexure element is detected, a temperature compensation resistor having a temperature characteristic is serially connected to an exciting circuit of the strain gauge. The temperature characteristics of sensitivity are roughly adjusted, and the temperature signal of sensitivity is stored by measuring the output signal of the output circuit of the strain gauge in the state of being roughly adjusted, and the stored temperature characteristics and temperature sensor are used. A temperature compensation method for a load cell type balance that finely adjusts the output signal of the strain gauge output circuit by multiplying it by a correction coefficient based on the operating temperature obtained by actually measuring the temperature. 2. A load cell type scale, wherein a strain gauge is attached to a strain-generating body and a load acting on the strain-generating body is detected, wherein the strain gauge is based on the temperature characteristic of the strain-generating material and the temperature characteristic of the strain gauge. Calculate the resistance value of the temperature compensation resistor required for coarse adjustment by inserting it in series with the excitation circuit of the strain gauge, and measure the resistance value of the temperature compensation resistor used for mounting. Calculate and store the correction coefficient necessary for fine adjustment of the output signal of the output circuit of the strain gauge based on the measured resistance value. A temperature compensation method for a load cell type balance in which the output signal of the output circuit of the strain gauge is multiplied by a correction coefficient and finely adjusted based on the operating temperature.