JP4426046B2 - Electronic balance that performs creep correction using temperature correction means - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic balance type weighing device, an electronic balance such as a load cell type weighing device using a strain-generating body, and in particular, a change in sensitivity of the device due to the passage of time can be corrected using a temperature correction means. It relates to an electronic scale.
[0002]
[Prior art]
In a highly sensitive weighing device called a so-called electronic balance such as an electromagnetic balance weighing device or a load cell weighing device using a strain-generating body, the influence of disturbance is large due to its high sensitivity. In particular, temperature (change in temperature) is a major factor causing sensitivity changes.
[0003]
FIG. 4 shows an electromagnetic balance type weighing device (electronic balance) having a particularly high resolution among electronic balances. In this electronic balance, a magnet 21, a pole piece 22, and a yoke 23 form a magnetic circuit. When a load WN is applied to the weighing pan 24, the load WN tries to swing and displace the beam 26 about the fulcrum 25. This displacement is detected by the position sensor 28. In response to the displacement signal of the position sensor 28, the current control unit 29 causes a current to flow through the force coil 27, thereby balancing the beam 26. The current output to the force coil 27 is digitally output to the calculation means 33 via the A / D converter 31, and the measurement value of the load WN is calculated from the amount of electricity in the calculation means and displayed on the display means 34. In the figure, the roval mechanism and the like are omitted.
[0004]
In this electronic balance, the temperature coefficient of the magnetic field strength of the magnet 21 is as large as −200 to −300 ppm / ° C. Therefore, the temperature sensor 30 is provided in the vicinity of the magnet 21 in order to maintain sensitivity as a weighing device. The temperature data output from the temperature sensor 30 is output to the computing means 33 via the A / D converter 32, and the measured value is often temperature-corrected by this temperature data.
[0005]
[Problems to be solved by the invention]
The electronic balance, which reads the weight when the weight is stable and reads the measured value and immediately removes the load and displays the correct mass, also applies the sample for a long time. When the change with time is observed, the measured value of the load applied by the sample may cause a change different from the change due to the change with time of the sample itself .
[0006]
FIG. 5 shows the change of the measured value over time in the electronic balance. When the load is applied at time t1 and the load is removed at time t2, the change in the measured value of the load during the elapsed time Δt is shown. The diagrams L1 and L2 show examples of changes in the measured value, and L3 shows the true value of the applied load. As can be seen from the figure, a creep phenomenon occurs in which the measured value changes due to the passage of time .
[0007]
Conventionally, the temperature of the magnet 21 changes due to heat generated by passing a current through the force coil 27, and the magnetic field is changed by the magnet 21 due to the temperature change of the magnet 21, that is, only the temperature of the magnet 21 is the cause of the change. As described above, the measured value is corrected by correcting the temperature, and the position of the temperature sensor 30 is adjusted so that creep does not occur when a load is applied. However, the position of the temperature sensor adjusted in this way is not an optimal position from the point of detecting the temperature change around the electronic balance. In reality, there is a limit to ensuring the accuracy of the electronic balance only by temperature correction. . In addition, due to the stress applied to the mechanical part due to the load applied to the electronic balance, creep of components faster than the heat generation of the force coil may occur, and it is not possible to prevent the occurrence of creep simply by adjusting the position of the temperature sensor. There are also cases.
[0008]
For this reason, in order to obtain higher accuracy in a high-resolution weighing device, especially when correcting the creep, the creep characteristics of the weighing device are detected by a long-term test, and the detected data is separate from the temperature correction. Creep correction is performed by a simple arithmetic circuit. As a result, it cannot be denied that the arithmetic circuit is complicated and the entire apparatus is expensive.
[0009]
[Means for Solving the Problems]
The present invention is configured in view of the above-described problems. The displacement or deformation due to a load is converted into an electric quantity, the load is measured, the temperature of the displacement part or the deformation part is measured, and the measured temperature and There is a temperature correction means that corrects the weighing load according to the temperature coefficient of the displacement part or deformation part, and the measurement value changes due to the creep phenomenon caused by the continuous load of the load on the deformation or displacement part. the electronic balance assumes the amount of metered value changed due to the creep phenomenon, in terms of the temperature values resulting in a change in the weight value of the change and the same amount of weight value with the creep assuming that the factor of temperature, and means for the conversion value and the correction value (equivalent temperature), the correction of the change in weight value with the creep phenomenon, the temperature correction means an equivalent temperature the calculated as the correction value An electronic balance for the creep correction using the temperature correction means, characterized by being configured to positive.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
For example, in an electronic balance, a temperature sensor for temperature correction is provided in an electromagnetic part, particularly a magnet of the electromagnetic part. When a load of a weighing object is applied during the adjustment of the electronic balance, the load time of this load is measured, and the change in the measured value of this load is measured with the passage of time as a factor .
[0011]
As a result of this measurement, the measured value when the measured value after loading is stabilized is used as a reference, and when this measured value changes over time, the amount of change is measured as creep. The amount of change in the measured value is based on the temperature characteristics of the electronic balance, directly based on the temperature coefficient of the magnet of the electronic balance electromagnetic part, and the measured value that occurs when the magnet temperature actually changes. It is converted into a temperature corresponding to the amount of change (hereinafter referred to as "equivalent temperature") Ru is the correction value.
[0012]
When the equivalent temperature is calculated, the equivalent temperature data is output to the temperature correction means, and the change in the measurement value due to the passage of time is used as a correction value. Correct. Also in this case, if the actual measured temperature of the magnet is also changed to correct the metered value as a temperature compensation by the temperature compensation means, including the actual measurement temperature and the equivalent temperature.
[0013]
【Example】
FIG. 1 is a block diagram of an electronic balance showing an embodiment of the present invention.
In the figure, when the load WN of the weighing object is loaded, the displacement of the beam due to this load is detected by the position sensor 1, and the current control means 2 sends a current to the force coil of the electromagnetic unit 3 in response to the displacement signal, This balances the beam. The current output from the current control means 2 is output as a weight digital signal WS1 to the temperature correction means 9 via the A / D converter 4.
[0014]
On the other hand, a temperature sensor 7 is disposed in the electromagnetic unit 3, particularly the magnet of the electromagnetic unit 3 (see also FIG. 4) to detect the temperature of the magnet, and this temperature data passes through the A / D conversion unit 8 and is measured temperature digital. The signal TS1 reaches the temperature correction means 9. The temperature correction means 9 performs temperature correction of the weight value from the weight digital signal WS1 and the measured temperature digital signal TS1, and outputs the weight digital signal AW after temperature correction to the calculation means 5. The calculation means 5 calculates the weight value of the weighed product from the weight digital signal WS1 and outputs it to the display means 6 as the weight value digital signal WS2, and the display means 6 displays the weight value.
[0015]
Next, at the time of adjustment of the electronic balance, reference numeral 10 denotes a clock means for measuring the output time of the measurement value digital signal WS2 output from the calculation means 5. 11 is a measurement value change measuring means, which measures the change of the measurement value with respect to the true value when the load time of the load of the weighing object on the electronic balance becomes a certain time or more. Reference numeral 12 denotes equivalent temperature calculation means, which is used when the amount of change of the measured value that has changed due to the passage of time is the same as the amount of change of the measured value that changes when the change in temperature is assumed to be a factor . It is a means for calculating an equivalent temperature which is a temperature.
[0016]
FIG. 2 is a flowchart showing an example of the operating state of the above-described configuration. The operating state will be described together with the configuration of FIG.
At the time of adjustment, first, the output of the equivalent temperature digital signal TS2 is stopped in order to avoid the influence of the already set equivalent temperature (Sa1). In this new state, the weight WN of the weighing object is applied while the temperature sensor 7 is measuring the magnet temperature of the electromagnetic unit 3 (Sa2). The weight digital signal WS1 based on the load is calculated by the temperature correction unit 9 and the calculation unit 5 as a measurement value of the weight of the weighing object, and the measurement value digital signal WS2 is output to the display unit 6.
[0017]
When the weighing object WN is loaded (Sa2), the measurement value digital signal WS2 is measured by the clock unit 10 (Sa3), and is measured for a predetermined time (Sa4). And a time value tS is output from the clock means 10 and a change in the measured value due to the passage of time is measured (Sa9). As a result, for example, data of change in the measured value due to the passage of time as shown in a diagram L1 in FIG. 5 is obtained. In this case, the change amount of the measured value with respect to the true value of the load of the weighed item is calculated. It should be noted that the measured value when the measured value of the weighed material after loading is stabilized substantially corresponds to this true value.
[0018]
The measured creep amount, at a temperature at which the change amount of the change in the weight value as a factor of the elapsed time as described above, and the amount of change in weight value that changes when the cause of the change in temperature becomes the same When an equivalent temperature, that is, a change in the measured value that is not attributed to the temperature, is regarded as a change in the measured value due to a temperature change, in other words, it is the same as the amount of change in the measured value when it is assumed that the temperature has changed. The temperature ( dummy temperature) that is the amount of change in is calculated as an equivalent temperature (Sa11). Using this equivalent temperature as a correction value, or when there is an actual temperature change, this actual temperature change data is added to create correction temperature data as the final equivalent temperature (Sa12). This correction temperature data is output as the equivalent temperature digital signal TS2 to the temperature correction means 9 (Sa6), and actually the creep correction due to the passage of time is used as the temperature correction due to the temperature change. Then, correction is performed using only the temperature correction means 9 without providing a creep correction means (Sa7), and this correction value is displayed as a measured value (Sa8).
[0019]
In the above description, there is no change in the temperature data outputted from the temperature sensor 7 in order to clarify the contents of the creep correction, that is, the case where there is no need to use the actual temperature data measured Example Explained. A case where temperature correction by the measured temperature digital signal TS1, which is actually measured temperature data due to a temperature change, also needs to be performed will be described using a specific example described later.
[0020]
Next, the flow will be described more specifically using specific numerical values.
First, the electronic balance has a weight of 100 g and a minimum display of 0.0001 g. In order to make the explanation easy to understand, the temperature coefficient of the magnet of the electromagnetic part is −200 ppm / ° C., the current of the force coil is zero when there is no load, that is, the weight data W is zero, and the weight data W at 100 g load is 1 , 000,000. As a result of tests by the inventors, the influence of the magnetic field generated by passing a current through the force coil on the magnetic field of the magnet is related to the value of the current value of the force coil and the weight value of the loaded load. Many of them have a quadratic function or a relationship close to this, but for the sake of simplicity, this point will be described below assuming that the influence of the magnet on the magnetic field is proportional to the current value.
[0021]
When adjusting the electronic balance, a load of 100 g was applied to display 100.0000 g (weight data Ws = 1,000,000) and finally converged to 100.010 g (weight data We = 1,000,010). And The temperature data at this time is also stored as Ta. From these changes in measured values, it can be considered that the magnetic field generated by the magnet is reduced by -10 ppm as shown in the following formula.
(Ws−We) / Ws = −10 / 1,000,000 = −10 ppm (1)
Here, since the temperature coefficient of the magnet is −200 ppm / ° C., the temperature change of −10 ppm is expressed by the following equation.
−10 ppm / −200 ppm / ° C. = 0.05 ° C. (2)
[0022]
That is, according to the above formula (2), when the weight data W is 1,000,000, this change can be regarded as a temperature change of 0.5 ° C., and the temperature data (equivalent temperature) is used to determine the temperature. It shows that creep correction is possible.
Therefore, the relationship between the maximum value Δtmax for correcting the temperature data in the temperature correction and the weight data W is expressed by the following equation (3).
Δtmax = 0.05 × W / 1,000,000 (3)
[0023]
When the amount of change of the load during the continuous load is affected by the temperature, the temperature change is added as a factor to the above equation (3). Since the temperature at the time of measurement is t and the temperature at the time of adjustment is Ta as described above, the amount of change at the time of continuous load is expressed by the following formula (4) as being linear with respect to the temperature. Here, k represents a constant that determines the sensitivity of the change amount of the measured value when the load is continuously applied to the temperature.
Δtmax = [0.05 + k × (t−Ta)] × W / 1,000,000 (4)
[0024]
Since the measured value gradually changes with the lapse of time after the load is applied, the temperature data is corrected in consideration of the time factor in the Δtmax. This can be realized by taking Δtmax as an input and passing this through a low-pass filter, and the degree of change can be realized by adjusting the strength of the low-pass filter. A simple method for functioning as a low-pass filter is a moving average process, and the strength of the low-pass filter can be adjusted by changing the number of data to be averaged. In the above example, data [Delta] t with time factor added to [Delta] tmax is obtained, and the temperature correction means adds or subtracts this data [Delta] t from the temperature data to correct the change due to the load continuation load.
[0025]
FIG. 3 is a flowchart specifically showing the calculation from the equivalent temperature calculation (Sa11) to the display (Sa8) in the flow shown in FIG. 2 in relation to the above specific example.
First, temperature data t is sampled and stored as a measured temperature digital signal TS1 output via the A / D converter 8 (Sb1). Similarly, the weight data W is sampled and stored by the weight digital signal WS1 output via the A / D converter 4 (Sb2). The maximum value Δtmax of the temperature data correction value for the weight data W and the temperature data t is calculated by a calculation formula using the weight data W and the temperature data t as variables (Sb3). In the formula shown as step Sb3, a, Wb, k, and Ta mean data at the time of adjusting the electronic balance and specific constants set for each model of the electronic balance. As described above, as a result of the test, as a result of the test, the expression of step Sb3 is more in accordance with the actual change if it is a quadratic expression of W. In this case, a specific secondary expression based on each test is used. Is shown in step Sb3.
[0026]
Next, in order to add a time element to Δtmax, an equivalent temperature Δt is obtained as an output signal TS2 through a low-pass filter as described above (Sb4). The strength of the low-pass filter is adjusted for each electronic balance model in accordance with the changing speed of the measurement value of the load that is continuously loaded.
[0027]
Subsequently determined temperature data t _c for use in temperature correction from the correction value Δt of the temperature data t and temperature data (Sb5), obtain Dt _c and temperature correction weight data W at this temperature data t _c (Sb6). This Dt _c becomes weight data in which an error due to the continuous load of the load is corrected. The weight data Dt _c is further subjected to various necessary corrections such as linearity and calibration (Sb7), and the final measured value D is displayed. (Sb8).
[0028]
As described above, correction of creep due to the passage of time using temperature data is equivalent to placing a temperature sensor at a position where no measurement error occurs when there is a continuous load load, And since the temperature sensor which detects actual temperature is previously arrange | positioned in the position which can measure the temperature of temperature measuring object correctly, naturally temperature correction itself can also be performed correctly.
[0029]
Although the present invention has been described mainly using an electronic balance as an electromagnetic parallel weighing device as an example, for example, a load cell weighing device using a strain generating body also has creep characteristics unique to the strain generating body, and temperature correction is performed. Of course, the present invention can be implemented with any load cell type weighing device. Moreover, even if no temperature correction has been performed in the past, the effect of temperature cannot be ignored due to the improved resolution of the load cell type weighing device. In parallel with the temperature correction system, a creep correction system is installed in this temperature correction system. It is possible to mount a built-in correction system.
[0030]
【The invention's effect】
As described above with reference to the embodiments, the present invention calculates the change in the measured value due to creep as an equivalent temperature corresponding to the change in the measured value when the temperature changes, and uses this equivalent temperature to correct the temperature. Since the creep correction is performed by the means, no special calculation means for performing the creep correction is required, and therefore the creep correction can be performed without complicating the calculation circuit.
[0031]
In addition, since creep correction is performed using temperature data, it is easy to change the measured value due to continuous load loading, or to change the actual temperature simply by changing the temperature data. It is possible to respond.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a flowchart showing an example of an operating state of the present invention.
FIG. 3 is a flowchart specifically showing from correction flow data creation to display in the flow shown in FIG.
FIG. 4 is a conceptual diagram of an electromagnetic parallel electronic balance showing a conventional temperature correction system.
FIG. 5 is a diagram showing creep of an electromagnetic parallel electronic balance.
[Explanation of symbols]
3 Electromagnetic part 5 Calculation means 6 Display means 7 Temperature sensor 9 Temperature correction means 10 Clock means 11 Measurement value change measurement means 12 Equivalent temperature calculation means AW Digital signal after temperature correction tS Time signal TS1 Measurement temperature digital signal TS2 Equivalent temperature digital signal WN Load WS1 Weight digital signal WS2 Weighing value digital signal

Claims (6)

The displacement or deformation due to the load is converted into an electric quantity, the load is measured, the temperature of the displacement part or the deformation part is measured, and the measurement load is determined by the measured temperature and the temperature coefficient of the displacement part or the deformation part. In an electronic balance having a temperature correction means adapted to correct, and the measured value changes due to the creep phenomenon caused by the continuous load of the deformation or the displacement part , the amount of the measured value changed by the creep phenomenon , in terms of the temperature values resulting in a change in the same metric and the change in weight value with the creep when assuming the temperature and factors comprises means for the converted value to the equivalent temperature, weighed by the creep phenomenon the correction of the change in value, using a temperature compensation means, characterized by being configured to correct the temperature correction means an equivalent temperature the calculated as the correction value click An electronic scale to the-loop correction. An electric quantity that balances the displacement of the electromagnetic part due to the load is output, the load is measured from the electric quantity, the temperature of the electromagnetic part is measured, and the measured value is calculated by the measured temperature and the temperature coefficient of the electromagnetic part. In an electromagnetic balance type electronic balance having a temperature correction means for correcting, and having a phenomenon in which a measured value changes due to the passage of time due to a creep phenomenon caused by a continuous load of a load on the electromagnetic part. the amount of metered value changed due to the creep phenomenon, in terms of the temperature values resulting in a change in the same metric and the change in weight value with the creep assuming that the factor of temperature, and the converted value equivalent temperature and means for, especially that the correction of the change in weight value with the creep phenomenon, and configured to correct the temperature correction means an equivalent temperature the calculated as the correction value Electronic scales for the creep correction using the temperature correction means to.   3. An electronic balance for performing creep correction using temperature correction means according to claim 2, wherein at least one of means for measuring the temperature of the electromagnetic part is disposed on a magnet of the electromagnetic part. The strain body is deformed by the load, the deformation is changed into an electric quantity, the load is measured, the temperature of the deformed part is measured, and the measured load is corrected by the measured temperature and the temperature coefficient of the deformed part. In a load cell type electronic balance having a temperature correction means configured to perform and having a phenomenon in which a measured value changes due to the passage of time due to a continuous load applied to the deformed portion, the measurement changed due to a creep phenomenon The amount of the value is converted into a temperature value that causes a change in the measured value that is the same as the change in the measured value due to the creep phenomenon when the temperature is assumed as a factor, and has a means for setting the converted value as an equivalent temperature , creep the correction of the change in the weight value due to creep phenomenon, by using the temperature correction means, characterized by being configured to correct the temperature correction means an equivalent temperature the calculated as the correction value Electronic scales to the positive. Means for measuring the load time of the load of the weighing object, means for measuring a change in the measured value due to the passage of time, and means for calculating an equivalent temperature corresponding to the amount of change in the measured value, during adjustment of the electronic balance, the load time of the load the load time of the load measured by the means for measuring the weighed materials by the means for determining the change in the weight value to cause the passage of time of the weighing Measure the change and calculate the equivalent temperature corresponding to the amount of change, and in normal use of the electronic scale, the measured value that causes the passage of time as a temperature correction in the temperature correction means by the calculated equivalent temperature An electronic balance that performs creep correction using the temperature correction means according to claim 1, wherein the change in temperature is corrected.   The measurement value data and the time data are output to the measurement value change measurement means when it is determined by the means for measuring the load time of the load of the weighing object that the load time has reached a preset time. An electronic balance that performs creep correction using the temperature correction means according to claim 5.

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