JP2000227343A - Measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring device capable of precisely compensating a measured error caused by the variation of parts at a low price to measure with high accuracy. SOLUTION: The measuring device is provided with a sensor 5 measuring a physical quantity to output an analog detection signal corresponding to the measuring value, a V/F converter 7 and a CPU 8 converting the detection signal from the sensor 5 into digital data, an EPROM 9 storing a compensation data to compensate the digital data from the V/F converter 7, and the CPU 8 reading out the compensation data from the EPROM 9 to compensate the digital data from the V/F converter 7 based on the compensation data. Then, the compensation absorbs all of measured errors in the pulse signal by computing the compensation at the CPU 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device for measuring various physical quantities.

[0002]

2. Description of the Related Art Conventionally, there are measuring devices for measuring various physical quantities. FIG. 9 is a circuit block diagram showing a measuring device for measuring weight, for example. This measuring device includes a sensor 21 for measuring weight, an amplifier circuit 22 including an amplifier, a V / F converter 23 for converting a voltage signal into a frequency signal, and a frequency signal output from the V / F converter 23. It is provided with a CPU 26 for inputting and converting into a weight value and displaying it on a display 25 via an interface 24.

Normally, in such a measuring apparatus, an error may occur in a measured value due to a variation in parts, an output error due to an operation of a circuit, or the like. For example, as shown in FIG.
And a strain gauge 27 senses a strain generated when a load is applied.

In this case, one or more strain gauges 27
If there is a variation in the resistance values, the bridge circuit loses its equilibrium state, an error voltage appears at the output terminal 28, and the true weight value may not be measured accurately. In addition, the amplification circuit 2
2 and the output of the V / F converter 23 may cause an error due to the operation of the circuit.

Therefore, in such a measuring apparatus, zero adjustment or the like is performed for each component or circuit to correct a measurement error due to variation. For example, in the sensor 21, as shown in FIG. 10, a volume resistor 29 is connected in parallel to a certain strain gauge 27, and the volume resistor 29 is adjusted so that the bridge circuit is in a balanced state.

However, since the above adjustment work is performed on the volume resistor 29 of each product, it is very troublesome and time-consuming. Therefore, the operation cost has been increased. Therefore, it is conceivable to use a high-precision part in order to suppress the dispersion of the parts, but such a part is usually expensive and causes a disadvantage such as an increase in the part cost.

[0007] Even if the measurement error is corrected by adjusting the individual parts, a further measurement error may occur depending on the condition when the product is assembled, and the measurement accuracy may be impaired as a product.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been conceived in view of the above circumstances, and is intended to accurately and inexpensively correct measurement errors due to variations in parts and perform high-accuracy measurement. It is an object of the present invention to provide a measuring device that can perform the measurement.

In order to solve the above problems, the present invention takes the following technical measures.

According to the first aspect of the present invention, a detecting means for measuring a physical quantity and outputting an analog detection signal corresponding to the measured value, and a converting means for converting the detection signal from the detecting means into digital data Storage means for storing correction data for correcting digital data from the conversion means, and correction means for reading the correction data from the storage means and correcting the digital data from the conversion means based on the correction data. A measurement device is provided.

The object to be measured by the detecting means can be weight, pressure, temperature, flow rate, etc., but is not limited to these.

According to a preferred embodiment, the correction means selectively reads the correction data from the storage means according to the digital data from the conversion means.

According to another preferred embodiment, the detecting means measures the weight.

According to another preferred embodiment, the storage means stores an error between a genuine physical quantity value and a previously measured value as correction data.

According to another preferred embodiment, the storage means stores, as correction data, a mathematical expression representing an error tendency obtained based on an error between a genuine physical quantity value and a previously measured value.

According to another preferred embodiment, there is provided display means for displaying the information corrected by the correction means.

According to the present invention, the detection signal representing the measured physical quantity is converted from an analog signal to a digital signal. Then, the correction data corresponding to the digital signal is read out, the digital signal is corrected based on the correction data, and a genuine physical quantity is obtained. Since the digital signal includes all measurement errors generated at the previous stage of the correction means, for example, due to variations in components and operation outputs of the circuit, by storing correction data in consideration of such measurement errors, Accurate correction can be performed, and a highly accurate measurement value can be obtained.

[0018] Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is an external perspective view showing an example of a measuring device according to the present invention. The measuring device is a weight scale for measuring the weight of an object to be measured, for example, a person, and has a substantially rectangular main body 1, a display 2 disposed on the upper surface of the main body 1 and displaying the measured weight value, A push button type power switch 3 provided on the side surface of the main body 1. The upper surface of the main body 1
The boarding surface 4 on which a person boards is set.

FIG. 2 is a circuit block diagram of the weight scale shown in FIG. The scale includes a sensor 5 for measuring weight, an amplifier circuit 6 connected to the sensor 5 for amplifying a voltage, a V / F converter 7 connected to the amplifier circuit 6 and converting the voltage to a frequency. , V / F converter 7
Which is connected to the output and corrects the output of the V / F converter 7
U8 and an EE connected to the CPU 8 for storing correction data
A PROM 9 and a display 2 connected to the CPU 8 via the interface 10 and displaying measured values are provided. Although not shown, the CPU 8 has a ROM for storing an execution program for correcting the output of the V / F converter 7 and an R for temporarily storing variable data and the like.
AM is connected.

The sensor 5 is a weight sensor for measuring the weight of the measured object. The sensor 5 is a unit in which a bridge circuit including the strain gauge 27 shown in FIG. 10 is provided on a plastic base formed in a flat plate shape, and is covered with a laminate film or the like from above the unit. , On the back side of the boarding surface 4. However, in the present embodiment, the volume resistor 29 connected in parallel to the strain gauge 27 in FIG. 10 is omitted.

The sensor 5 senses a strain generated when a load is applied to the boarding surface 4 by a strain gauge 27.
That is, the strain gauge 27 changes its electrical resistance when detecting strain. As a result, the equilibrium state of the bridge circuit is lost, and a voltage value corresponding to the change in the electric resistance is output from the output terminal 28.

The amplifying circuit 6 is composed of an amplifier such as an OP amplifier and its peripheral circuits, amplifies the voltage value detected by the sensor 5 at a predetermined gain, and outputs the amplified voltage value to the V / F converter 7.

The V / F converter 7 converts an analog signal having a voltage value output from the amplifier circuit 6 into a pulse signal having a frequency corresponding to the voltage value.

The CPU 8 counts the number of pulses of the pulse signal output from the V / F converter 7, obtains a frequency value corresponding to the measured value, and corrects the frequency value based on the correction data read from the EEPROM 9. Then, the true weight value is calculated.

The display 2 is for displaying the measured weight value, and comprises a plurality of 7-segment LEDs and their peripheral circuits. The display 2 dynamically or statically displays display data given by the CPU 8 and representing a weight value.

The EEPROM 9 stores correction data for correcting a measurement error. The correction data is calculated when the true weight value (for example, the weight of the weight) is measured.
It is calculated in advance by examining a unique measurement error of the weighing scale, and is written in the EEPROM 9.

As will be described later in detail, the CPU 8 obtains the value of the frequency from the output of the V / F converter 7 at the preceding stage. For this reason, the EEPROM 9 stores a frequency-weight conversion table for converting a frequency value into a weight value, which is used when performing a correction operation. Instead of this table, a mathematical expression for converting a frequency value into a weight value may be stored.

Here, a method of calculating the correction data stored in the EEPROM 9 in advance will be described. In this calculation method, the weight is actually measured for each assembled product using a weight or the like serving as a weight reference, and the difference between the true weight value and the measured value is calculated as an error. Then, even when nothing is placed on the boarding surface 4, the weight is changed using a plurality of weights, and each error in a plurality of weights is calculated.

As described above, by calculating each error while changing the true weight value, the relationship between the true weight value and the measured value and the error tendency can be recognized. For example, in a certain product, as shown in FIG. 3, when the true weight value is W1,
It is assumed that the acquired frequency value (measured value) becomes f1.
Since the CPU 8 obtains the value of the frequency from the output of the V / F converter 7 in the preceding stage, the frequency is used as an equivalent to the measured value in FIG.

Here, the broken line A represents the ideal relationship between the weight value and the measured value, which is obtained by calculation in advance and has no error. Therefore, when the true weight value is W1, ideally, it is desirable that the true frequency value f0 is measured according to the solid line A. Therefore, in this case, the difference Δf1 between f1 and f0 is a measurement error.

By calculating the measured values for a plurality of genuine weight values by such a method and deriving the relationship between the genuine weight values and the measured values as shown by a solid line B, the product Is linear.

Since the relationship between the true weight value and the measured value is linear, the value of the difference Δf1 is constant at any weight value, and the difference Δf1 is used as the correction data in the EEPROM.
9 (see FIG. 6A).

Further, as shown in FIG. 4, when it is recognized that the relationship between the genuine weight value and the measured value is non-linear (see the solid line B) in a certain product, a plurality of genuine weight values are obtained. Then, a plurality of difference values are calculated based on the difference.

For example, the difference Δ
The difference Δf3 is calculated for each of f2 and the frequency value f3, and these values are written to the EEPROM 9 as correction data (see FIG. 6B).

Further, as shown in FIG. 5, when the relationship between the true weight value and the measured value includes both a linear range and a non-linear range, correction data is stored for each range. I do. That is, the value of the frequency is f4 to f
In the range of 5, only one difference value Δf4 is stored in the EEPROM 9.
Write to. In the range where the frequency value is f5 or more,
Write a plurality of difference values Δf6, Δf7,... Corresponding to a plurality of frequency values f6, f7,... To the EEPROM 9 (see FIG. 6C).

The relationship between the true weight value and the measured value is
When it is recognized that the expression can be represented by a certain mathematical expression representing the error tendency, the mathematical expression is stored in the EEPROM 9 in the form of data. As described above, when the data is stored by using mathematical formulas, the number of data to be stored can be reduced, and the memory capacity can be reduced. Therefore, there is an advantage that the cost of parts can be reduced.

As described above, based on the relationship between the genuine weight value and the measured value, the correction value or the mathematical expression indicating the tendency of the error is stored in the EEPROM 9 for each product.

Next, the processing operation of the weight scale will be described with reference to the flowchart shown in FIG. First, when the user puts on the weight scale (S1), the sensor 5 detects the weight of the measured object as a voltage value (S2) and outputs the detection signal to the amplifier circuit 6. This detection signal includes a measurement error by the sensor 5, for example, an error due to a variation in resistance of the strain gauge 27.

The amplifier circuit 6 which has received the detection signal from the sensor 5 amplifies the detection signal at a predetermined amplification factor (S
3) Apply an amplified signal to the V / F converter 7. This amplified signal includes an output error of an amplifier or the like.

V / F receiving the amplified signal from amplifier circuit 6
The converter 7 converts an analog signal as an amplified signal into a digital signal (S4). Specifically, an amplified signal having a voltage value is converted into a pulse signal having a frequency value, and is supplied to the CPU 8.

The CPU 8 receiving the pulse signal from the V / F converter 7 counts the number of pulses of the pulse signal (S5), and obtains the value of the frequency of the pulse signal. That is, the number of falling edges of the pulse signal from “high” to “low” is counted, and the value of the frequency is obtained based on the number of falling edges in a fixed cycle.

Here, the pulse signal includes an error due to a variation in resistance of the strain gauge 27, an output error of the amplifier circuit 6, and an output error of the V / F converter 7. That is, a measurement error generated in all circuits connected to the preceding stage of the CPU 8 is included.

Next, the CPU 8 reads a correction value corresponding to the acquired frequency value from the EEPROM 9 (S6),
A correction value is added to or subtracted from the acquired frequency value (S7), and a frequency value corresponding to a genuine weight value is calculated. Then, the frequency value is converted into a weight value based on the frequency-weight conversion table to obtain a true weight value (S8).

Alternatively, instead of steps S6 and S7, a mathematical expression representing the error tendency is read from the EEPROM 9, and the obtained frequency value is applied to the mathematical expression to calculate a frequency value corresponding to a genuine weight value. Then, the frequency value is converted into a weight value based on the frequency-weight conversion table, and a genuine weight value is obtained.

Thereafter, in step S9, the CPU 8
Provides the corrected weight value to the display 2 via the interface 10, and the display 2 displays the corrected weight value. Alternatively, instead of providing the weight value to the display 2, the weight value may be supplied to an external device that performs predetermined data processing.

In the case where a finite number of correction values are stored in the EEPROM 9 as correction data, the frequency value actually measured and obtained does not always coincide with the frequency value corresponding to the correction value. Rather, it is more likely that they do not match.

Therefore, in the present invention, a correction value corresponding to the obtained frequency is calculated using the correction value of the frequency before and after the frequency stored in the EEPROM 9. That is, as shown in FIG. 8, when the measurement value f8 is obtained, the CPU 8 refers to the EEPROM 9 and searches for the frequency values f9 and f10 before and after the measurement value f8. Then, a numerical value distribution of the measured value f8 between the frequency values f9 and f10 is calculated, and a correction value corresponding to the measured value f8 is calculated based on the numerical value distribution.

Specifically, for example, when the measured value f8 is a value that divides the preceding and following frequency values f9 and f10 by a ratio of 1: 2, the correction value corresponding to the preceding and following frequency values f9 and f10 Is also proportionally distributed in a ratio of 1: 2. For example, if the correction value of the previous frequency value f9 is “± 0” and the correction value of the rear frequency value f10 is “+3”, the correction value of the measurement value f8 is “+1”.

The greater the number of correction values to be stored, the more
Since the error tendency can be more closely approximated, the accuracy of correction increases, and the measurement accuracy of the weight scale also improves. But,
If the number of correction values is too large, a memory capacity is also required, so that it is desirable to store an appropriate number of correction values.

As described above, the pulse signal input to the CPU 8 includes an error due to variation in the resistance of the strain gauge 27, an output error of the amplifier circuit 6 and the V / F converter 7, and the like. That is, it includes measurement errors generated in all circuits connected to the preceding stage of the CPU 8. Therefore, in the present invention, the CPU 8 performs the calculation of the correction so that all the measurement errors included in the pulse signal are absorbed in the correction. That is, since the value of the frequency is obtained from the pulse signal and the calculation is performed based on the correction data corresponding to the value of the frequency to obtain the true weight value, accurate measurement without measurement errors can be performed.

In addition, since it is not necessary to adjust the variation for each part or to adjust for an error when assembling, etc.
Production time can be reduced. Furthermore, since it is possible to prevent an increase in component costs due to the use of high-precision components,
As a result, the production cost can be reduced.

Of course, the scope of the present invention is not limited to the above embodiment. For example, the measuring device described in the above embodiment is not limited to a scale,
Alternatively, a weighing device may be used.

The above-described correction method may be applied to an apparatus for measuring not only weight but also other physical quantities, for example, an apparatus for measuring other physical quantities such as pressure, temperature and flow rate. Good. In this case, the sensor 5 is not limited to a weight sensor.

In the above embodiment, the CPU 8 obtains the frequency value, but may obtain the voltage value. The V / F converter 7 is not limited to this, and may be, for example, an A / D converter that outputs 8-bit data in parallel.

[Brief description of the drawings]

FIG. 1 is an external perspective view showing an example of a measuring device according to the present invention.

FIG. 2 is a circuit block diagram of the measuring device shown in FIG.

FIG. 3 is a diagram showing a case where a relationship between a weight value and a frequency value is linear.

FIG. 4 is a diagram illustrating a case where a relationship between a weight value and a frequency value is nonlinear.

FIG. 5 is a diagram showing a case where a range in which the relationship between a weight value and a frequency value is linear and a range in which the relationship is nonlinear are mixed.

FIG. 6 is a diagram showing an example of a table for storing correction data stored in an EEPROM.

FIG. 7 is a flowchart showing an operation procedure of the measuring device.

FIG. 8 is a diagram for explaining a method of calculating a correction value.

FIG. 9 is a circuit block diagram of a conventional measuring device.

FIG. 10 is a circuit diagram of a conventional weight sensor.

[Explanation of symbols]

 2 Display 5 Sensor 7 V / F converter 8 CPU 9 EEPROM

Claims (6)

[Claims] A detecting means for measuring a physical quantity and outputting an analog detection signal corresponding to the measured value; a converting means for converting a detection signal from the detecting means into digital data; and a digital data from the converting means. Storage means for storing correction data for correcting the data, and correction means for reading the correction data from the storage means and correcting the digital data from the conversion means based on the correction data. , Measuring equipment. 2. The measuring apparatus according to claim 1, wherein the correction unit selectively reads the correction data from the storage unit according to digital data from the conversion unit. 3. The measuring device according to claim 1, wherein the detecting unit measures a weight. 4. The measuring device according to claim 1, wherein the storage unit stores a difference between a genuine physical quantity value and a previously measured value as correction data. 5. The storage unit according to claim 1, wherein the storage unit stores, as correction data, a mathematical expression representing an error tendency obtained based on a difference between a genuine physical quantity value and a previously measured value.
The measuring device according to any one of the above. 6. The measuring device according to claim 1, further comprising a display unit for displaying information corrected by said correction unit.