JPH1137827A - Measuring device of load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable accurate correction of temperature, in a measuring device of load, which has a temperature dependence as output characteristic. SOLUTION: In a storage means 4, data on the output characteristic of a load measuring means 1, which changes according to a change in temperature and which is expressed by two accurate curves L1 and L2 based on a hysteresis brought about corresponding to an increase and decrease of the temperature are stored. An arithmetic means 3 detects temperature T1 on the occasion when the load measuring means 1 measures a load, by a temperature detecting means 5, and a comparing means 7 compares this temperature with the previous detected temperature T2 outputted from RAM 6 and determines whether or not the present detected temperature T1 has increased beyond the previous one. Either the curve L1 or L2 of the storage beans 4 is selected, a corrective value corresponding to the detected temperature T1 on the selected curve is obtained and a measured value of the load is corrected by this corrective value and displayed in a display means 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a load, and more particularly to an apparatus for displaying an accurate measured value by correcting a measured value outputted from a load measuring means in accordance with a change in temperature. The present invention relates to a load measuring device.

[0002] Among the devices for measuring loads, for example, a load cell type weighing device and an electromagnetic balance type weighing device, the load is converted into an electric signal, and the electric signal is converted into an electric signal through an A / D conversion circuit and various arithmetic circuits. There is provided an electronic load measuring device (hereinafter, the term "load measuring device" indicates the electronic load measuring device unless otherwise specified) which is converted into a measured load and displayed. Although this type of device has high measurement accuracy, a component having relatively large temperature dependency, such as a strain gauge or an electromagnetic unit, is used as a part of the device. Therefore, it is inevitable that both the span and the zero point change in response to the temperature change. That is, the measured load value output from the load measuring portion has a temperature-dependent output characteristic that its output changes in response to a temperature change. This characteristic can be neglected to some extent if the accuracy of the device is not very high. However, this output characteristic is corrected (temperature compensated) in accordance with the improvement of the accuracy of the device, and accurate measurement values are displayed. The need to do so increases. In response to such demands, several methods for correcting the temperature-dependent output characteristics have been proposed at present.

[0003]

For example, considering the above-mentioned output characteristics by taking a span as an example, in the above-mentioned apparatus, the model,
It is known that, although there is a difference in the configuration, the span generally changes so that the measured value output increases as the temperature increases. In this case, assuming that the change in span with respect to temperature is a straight line, a correction value for temperature change can be easily set, and correction can be performed with a small circuit configuration.

[0004] However, the span does not strictly change linearly, but shows a change approximating a quadratic curve.
That is, in the electromagnetic balance type weighing device, the span change approximates to a quadratic curve as the resolution increases, and similarly in the load cell type weighing device, the span change changes to a quadratic curve in a high resolution device of, for example, 1/10000 or more. It is expected that accurate correction will be difficult with the correction method that approximates and therefore assumes a straight line. Here, when an example of the span change is shown with reference to FIG. 1 for explaining the present invention, the span changes with a curve approximating a quadratic curve such as a curve L1. Therefore, in the conventional method in which the span change is corrected as a straight line, the correction is insufficient in a high-precision load measuring device.

Further, the inventors have confirmed that, in addition to the fact that the span changes in a curve as described above by performing a test described later, there is actually a hysteresis in the span change. That is, in FIG. 1, when the span change when the temperature rises is shown by a curve L1, the span change when the temperature falls does not follow this curve L1, but changes along another curve L2. Therefore, in order to perform more accurate correction, it is necessary to obtain not only a span change curve corresponding to a temperature change in one direction but also a span change curve in another direction in consideration of hysteresis. It has been confirmed that the change of the zero point also changes with the same curve as the change of the span, and also has the hysteresis.

[0006]

SUMMARY OF THE INVENTION According to the present invention, there is provided a load measuring apparatus configured to accurately correct a measured load value based on the above-described viewpoint. In a load measuring device that selects a correction value from a stored span change with respect to a temperature change and corrects a load measurement value, a unit that stores a change in a curvilinear span with respect to a temperature change in at least one direction, and a temperature detection unit. Based on the detected temperature obtained from the temperature detecting means, a correction value corresponding to the detected temperature is obtained from the means for storing the change in the curved span, and the load measurement value output from the load measuring means is corrected by the correction. Preferably, in addition to these, the storage means stores a span change curve in both directions of temperature increase and decrease, and stores the previously measured temperature. And comparing means for comparing the stored previous measured temperature with the current measured temperature to detect an increase or decrease in the measured temperature, and the calculating section stores the stored data based on a signal output from the comparing means. One of the curves stored in the means is selected, and a correction value for the measured temperature in the selected curve is selected to correct the load measurement value output from the load measurement means.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The inventors use a calibration weight to load one of the load cell scales produced by the inventors at 5 ° C. to 4 ° C.
In a temperature range up to 0 ° C., a change in span was measured at multiple points in a temperature increasing direction and a temperature decreasing direction. That is, as a result of measuring the span change at 18 points at intervals of 2 ° C., a curve indicating the state of the span change of the curve L1 in the temperature increasing direction and the curve L2 in the decreasing direction was obtained. By plotting the change in span measured at intervals of 5 ° C., it was possible to obtain almost the same curve as the above curve.

The calculating means responds to the detected temperature from the span change curve stored in the storage means in accordance with the temperature signal output from the temperature detecting means and the temperature increase or decrease signal output from the comparing means. The correction value to be performed is selected, and the measured load value output from the measuring means is corrected by the selected correction value. Further, in this case, when two span change curves corresponding to the hysteresis are stored in the storage means, the comparison means detects an increase or decrease in the current detection temperature with respect to the previous detection temperature, and responds to the increase or decrease. One of the span change curves is selected, and a correction value corresponding to the detected temperature is selected from the selected span change curve to perform the correction.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. First, the configuration of the load measuring device according to the present invention will be described with reference to the block diagram shown in FIG. Reference numeral 1 denotes a load measuring means. In the case of a load cell type load measuring device, it indicates a flexure element and a strain gauge provided in the flexure element. Then, a load measurement signal is output to the calculating means 3 via the A / D converter 2.

Reference numeral 4 denotes storage means for storing a change in the span and zero point of the load measuring device with respect to a change in temperature (hereinafter, a change in the span will be described as an example). Specifically, assuming that the change in span of the load measuring device is as shown by the diagram shown in FIG. 1, the change in span shown by this curve is stored in the storage means 4. In order to obtain the span change curve shown in FIG. 1, it is necessary to measure span changes at multiple points in the temperature increasing direction and the temperature decreasing direction in the temperature range of, for example, 5 ° C. to 40 ° C. as described above. For example, by measuring the span change at 18 points at 2 ° C. intervals in the above temperature range, it is possible to obtain the curve indicating the state of the span change indicated by the curve L1 in the temperature increasing direction and the curve L2 in the decreasing direction.

As described above, it is not always easy to measure the span change of the load measuring device at multiple points at the stage of the user of the load measuring device. Therefore, the change in span is preferably measured by the manufacturer of the load measuring device, and the change in span is stored in the storage means before the device is shipped. Also, in this case, it is the most desirable method to measure the span change for all the devices in consideration of the instrumental differences of the devices, and to store the results in the individual load measuring devices. A method is also possible in which the span change is measured by some randomly selected devices and the measurement result is stored in the storage means of another device.

5 is a temperature detecting means, 6 is a second storage means,
7 is the last detected temperature output from the storage means 6;
Comparing means 8 for comparing the current detected temperature output from the temperature detecting means 5 with the present detected temperature, and display means 8 for displaying the measured load value calculated and corrected by the calculating means.

The operation of the apparatus having the above configuration will be described below with reference to the flowchart of FIG. At the same time when the load is measured by the load measuring means 1, the temperature detecting means 5 detects the temperature T1 at the time of measuring the load (S1). This detected temperature T1 is output to the calculating means 3 and also to the comparing means 7. The comparing means 7 determines whether or not the detected temperature T1 and the previous detected temperature T2 output from the storage means 6 (S2) are the same (no change) (S3). In this case, the load signal W output from the load measuring means 1 is corrected (S5) using the previous correction value Nn as it is (S4).

On the other hand, the current detection temperature T1 and the previous detection temperature T
2 is different, the magnitude of T1 and T2 is determined (S
6) If T1 is large, the current detection temperature T1 is higher than the previous temperature T2, so the curve L1 is used among the curves L1 and L2 stored in the storage means 4 (S7).
Further, a correction value Na corresponding to the detected temperature T1 is selected from the curve L1 (S8). If the current detected temperature T1 is low, the detected temperature T1 is lower than the previous temperature T2, so the curve L2 is adopted from the curves L1 and L2 stored in the storage means 4 (S9), and This curve L
2, a correction value Nb corresponding to the detected temperature T1 is selected (S10). When the predetermined correction value is selected in this way, the load signal W output from the load measuring means 1 is corrected using the correction value Na or Nb (S5), and the corrected load measurement value is output (S5). S11). With the above configuration, the load measurement signal W output from the load measuring means 1 is corrected with an appropriate correction value in response to a temperature change, and an accurate display of the load is performed.

Next, the change in span of the load measuring device may be due to aging, in addition to the above-described temperature dependence. As described above, since the span change curve stored in the storage device 4 is, for example, fixedly stored as a ROM at the time of product shipment, the device changes over time due to long-term use of the load measuring device, and the span change curve changes. It is assumed that accurate correction becomes difficult even if a curve is used. In this case, for example, the curve shown in FIG.
The load is measured at intervals of, for example, 5 ° C.
The corrected load measurement value is checked using the span change curve stored in. At this time, if the display of the load measurement value differs by more than the allowable range despite the correction, it is no longer appropriate to use the span change curve stored in the storage means 4.

In the above case, the calculation means 3 rewrites the span change curve stored in the storage means 4 so as to correspond to the current calibration, and stores this data in another storage means (R
AM) 10. In this case, since the aging depends on a certain limited element such as a slight change in the strain characteristic of the strain gauge in the load cell type load measuring device, the state of the span change, that is, the shape of the span change curve itself. No noticeable change occurs. For this reason, for example, as shown in FIG.
1, L2 can be dealt with by performing an arithmetic process so as to move in parallel to the curves L1 ′, L2 ′, and the calculation of replacing the span change curve can be simplified. In the configuration shown in FIG. 3, the first span change curve is stored in the ROM to form a so-called firmware. However, the first span change curve is stored in the RAM, and thereafter, the data of the span change curve is stored in accordance with the calibration. Of course, it is also possible to configure to rewrite.

The load measuring apparatus according to the present invention has been described above by taking as an example the measurement value correction accompanying a span change. However, as described first, the change of the zero point also changes along the same curve as the change of the span, and the hysteresis also changes. Similarly, the above configuration can be used for adjusting the zero point as it is.

[0018]

As described above, the present invention provides a correction value in consideration of the fact that the span and the zero point change with respect to the temperature change are actually curves and have a hysteresis with respect to the increase and decrease of the temperature. Therefore, the load measurement value output from the load measurement means can be corrected more accurately, and a more accurate load measurement value can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between an output output from a load measuring unit and a temperature in both a temperature increasing direction and a temperature decreasing direction.

FIG. 2 is a diagram showing a state where the diagram shown in FIG. 1 is translated and moved by calibration.

FIG. 3 is a block diagram of the load measuring device showing an example of the configuration of the load measuring device according to the present invention.

FIG. 4 is a flowchart showing an example of an operation state of the load measuring device according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 load measuring means 3 calculating means 4 (first) storing means 5 temperature detecting means 6 (second) storing means 7 comparing means

Claims (5)

[Claims] 1. A load measuring device which corrects a measured load value output from a load measuring means using data of an output characteristic change depending on a temperature change of the load measuring means, and stores the data. Output characteristic data which changes as a curve corresponding to a change in temperature is stored in the storage means, and the calculating means selects a correction value corresponding to the detected temperature from the curve based on a temperature signal output from the temperature detecting means. ,
A load measuring device configured to correct a load measured value output from a load measuring means with the correction value. 2. The storage means includes a first curve representing an output characteristic that changes in response to an increase in temperature, and a second curve representing an output characteristic that changes in response to a decrease in temperature. The temperature detecting means is provided with a second storage means for storing at least the last detected temperature T2 of the detected temperatures outputted, and the detected temperature T measured at the time of load measurement.
A comparison means for comparing the detected temperature T1 with the previous detected temperature T2 is provided, and the arithmetic unit is configured to store the first or second stored in the storage means in accordance with a detected temperature increase signal or a decrease signal output from the comparison means. 2. The load measuring device according to claim 1, wherein a curve is selected, a correction value corresponding to the detected temperature T1 in the selected curve is selected, and the load measurement value is corrected by the correction value. . 3. A load for calibration whose true value is known is added to the load measuring means, and the value obtained by correcting the load measurement value of the calibration load by the correction value and the calibration A means for comparing the true value of the load for use is added, and the comparing means determines whether the difference between the corrected measured load value and the true value is within an allowable value, and when the value exceeds the allowable value. 3. The load measuring device according to claim 1, wherein the output characteristic curve stored in the storage means is replaced with a new curve. 4. The load measuring device according to claim 1, wherein said load measuring means is a load cell and a strain gauge provided on said load cell. 5. The load measuring device according to claim 1, wherein the load measuring unit is an electromagnetic unit that generates an electromagnetic force corresponding to the applied load.