JP2013024808A - Measuring apparatus and measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring apparatus which does not require an analog amplifier, and can highly precisely measure the physical amount of an object to be measured with simple and inexpensive circuit configuration irrespective of an environmental change such as a change in temperature.SOLUTION: A measuring apparatus 100 measures the physical amount of an object T to be measured by calculating the physical amount of the object to be measured from a frequency of an output signal of an oscillation part 120 connected by a resistance element 110 for detection by an operation part 130. The oscillation part 120 has at least one of reference resistance elements 121 having an already-known electrical resistance value, and the resistance element 110 for detection and the reference resistance element 121 can be connected by switching.

Description

  The present invention relates to a measuring device using a detection resistance element that converts a change in a physical quantity to be measured into a change in electrical resistance value, and in particular, converts the electrical resistance value of the detection resistance element into a frequency to measure the physical quantity to be measured. The present invention relates to a measuring apparatus and a measuring method for measuring the above.

Conventionally, a resistance element for detection that converts changes in physical quantities such as strain gauges into changes in electrical resistance is fixed to the measurement object, and changes in physical quantities such as strain are measured as changes in electrical resistance. Is well known.
As a method for measuring the electrical resistance value of the resistance element for detection, a method of converting to a voltage change using a resistance bridge such as a Wheatstone bridge is commonly used, and the voltage is amplified by an analog amplifier to perform A / D conversion. A device that converts a digital value and outputs the digital value is known (see Patent Document 1, etc.).

However, since the change in the electrical resistance value of the detection resistance element is minute and the change in voltage after conversion is also minute, an analog amplifier for amplifying this is highly accurate and has little characteristic change due to the environment such as temperature. There is a problem that the circuit scale is increased for stabilization, compensation, and the like, and expensive parts are required by using high-precision parts.
In order to solve such problems of the analog amplifier, a circuit configuration in which the analog amplifier is omitted by converting the change in the electric resistance value of the detection resistance element into a change in frequency using an oscillation circuit and outputting the change. Are known (see Patent Document 2).

JP 2000-163683 A Japanese Patent Laid-Open No. 2005-300519

However, according to the known Patent Document 2, an expensive analog amplifier is not required, but the frequency characteristics of circuit elements including a capacitor included in the oscillation circuit, and changes in characteristics due to the environment such as temperature, make the measurement value accurate. There was a problem of affecting.
In particular, since the change in the electrical resistance value of the detection resistance element is minute, the influence of the state change of the circuit itself, such as the internal resistance of the circuit itself, is extremely large, and the influence on the accuracy of the measurement value is extremely large. there were.
In order to reduce these effects, it is necessary to make the oscillation circuit less susceptible to changes in characteristics due to the environment such as temperature, etc., and use complicated parts with high precision parts for stabilization and compensation. There was a problem that it would be extremely expensive.
In addition, when monitoring changes in the physical quantity of the measurement target over a long period of time, it is difficult to completely eliminate these characteristic changes. I couldn't cope with the extensive monitoring.

  Accordingly, the present invention solves the above-described problems, eliminates the need for an analog amplifier, and with a simple and inexpensive circuit configuration, allows the physical quantity to be measured to be accurately measured even when there is an environmental change such as temperature. An object of the present invention is to provide a measuring device and a measuring method capable of measuring.

  According to the first aspect of the present invention, a detection resistance element that converts a change in a physical quantity to be measured into a change in electrical resistance value, and an output signal having a frequency corresponding to the electrical resistance value when the detection resistance element is connected. The measuring device includes an oscillating unit that outputs, and an arithmetic unit that calculates a physical quantity to be measured from the frequency of the output signal, and measures the physical quantity to be measured, wherein the oscillating unit has a known electrical resistance value. The above-mentioned problem is solved by having at least one reference resistance element having the above-mentioned and being configured to be connectable by switching between the detection resistance element and the reference resistance element.

  In the invention according to claim 2, in addition to the configuration of the measurement device according to claim 1, the oscillation unit includes a plurality of reference resistance elements having different electric resistance values, and the detection resistance element and the plurality of the resistance elements By switching the reference resistance element and being connectable, the above-described problems are solved.

  In the invention according to claim 3, in addition to the configuration of the measurement device according to claim 1 or claim 2, the oscillating unit automatically switches between the detection resistance element and the reference resistance element. It solves the problem.

  In the invention according to claim 4, in addition to the configuration of the measuring device according to any one of claims 1 to 3, the oscillating unit further includes a temperature compensating resistance element whose temperature influence characteristic is known. This solves the problem.

  In the invention according to claim 5, in addition to the configuration of the measuring device according to any one of claims 1 to 4, the calculation unit counts the wave number of the output signal for a predetermined time, and calculates the predetermined wave number from the wave number. The problem is solved by calculating an average frequency of time and calculating a physical quantity to be measured.

  In addition to the configuration of the measurement apparatus according to claim 5, the invention according to claim 6 solves the above-described problem by the calculation unit being configured to be able to change and set the predetermined time.

  According to the seventh aspect of the present invention, in addition to the configuration of the measuring device according to any one of the first to sixth aspects, the oscillation unit includes a CMOS inverter, and the electrical resistance of the connected detection resistive element The problem is solved by outputting a pulse signal having a frequency corresponding to the value.

  The invention according to claim 8 is a detection resistance element that converts a change in a physical quantity to be measured into a change in electrical resistance value, and an output signal having a frequency corresponding to the electrical resistance value to which the detection resistance element is connected. A measuring method for measuring a physical quantity to be measured, comprising an oscillating section for outputting and a computing section for computing a physical quantity to be measured from the frequency of the output signal, wherein the oscillating section has a known electrical resistance value The reference resistance element having at least one of the reference resistance elements is configured to be connectable by switching between the detection resistance element and the reference resistance element, the frequency of the output signal when the reference resistance element is connected, and the reference resistance The function is set so that the product becomes a linear function of the frequency from the product of the electrical resistance value of the element, and the frequency when the detection resistive element is connected is substituted into the function to calculate the electrical resistance of the detection resistive element. The resistance value is calculated and the calculated electricity By measuring the physical quantity of a measurement target from the anti-value, it is to solve the above problems.

  In the invention according to claim 9, in addition to the configuration of the measurement method according to claim 8, the oscillating unit includes a plurality of reference resistance elements having different electric resistance values, and is a linear function of the frequency. When the function is set to, the product of the electrical resistance values of the plurality of reference resistance elements and the respective measured frequencies is obtained, and the product becomes a linear function of the frequency by the least square method from the obtained plurality of products. By setting the function as described above, the above-mentioned problem is solved.

According to the measuring apparatus according to claim 1 and the measuring method according to claim 8, it is possible to switch to a reference resistance element having a known electric resistance value before or during measurement of a physical quantity to be measured. By measuring the frequency when the reference resistance element is connected, the characteristics of the oscillation circuit due to changes in the environment, such as temperature, are identified as needed, and the relationship between the measured frequency and the physical quantity to be measured is easily calibrated. can do.
Therefore, there is no need to use high-precision parts to stabilize or compensate for environmental fluctuations of the oscillation circuit, or to make a complicated circuit configuration. However, the physical quantity to be measured can be measured with high accuracy.
According to the configuration of the ninth aspect, the relationship between the measured frequency and the physical quantity to be measured can be calibrated with higher accuracy, and the physical quantity to be measured can be measured with higher accuracy. Become.

According to the configuration of the second aspect of the present invention, by measuring the frequency when a plurality of reference resistance elements having known electrical resistance values are connected, the influence of characteristic changes due to environmental changes such as temperature can be more accurately performed. Can be specified, and the relationship between the frequency measured more accurately and the physical quantity to be measured can be calibrated.
According to the configuration of the third aspect of the present invention, even when monitoring the change in the physical quantity of the measurement target over a long period of time, it is automatically switched to the reference resistance element at an appropriate interval without manual intervention. In addition, it is possible to always measure the physical quantity of the measurement target with high accuracy by specifying the characteristic change due to the environmental change such as temperature and accurately calibrating the relationship between the measured frequency and the physical quantity of the measurement target.
According to the configuration of the present invention, even if there is a change due to temperature such as the reference resistance element, the electric resistance value inside the circuit, or the capacitance, it can be further calibrated by the temperature compensating resistance element. This makes it possible to accurately calibrate the relationship between the measured frequency and the physical quantity to be measured, and without using an expensive reference resistance element that does not change characteristics due to temperature. It becomes possible to measure.

According to the configuration of claim 5, even if high frequency noise or the like is included in the output signal output from the oscillating unit by calculating an average frequency within a predetermined time and calculating a physical quantity to be measured, The influence can be eliminated, and the physical quantity to be measured can be measured with high accuracy with a simple configuration without adding a filter circuit or the like.
According to the configuration of the sixth aspect, even when the measurement sampling cycle is increased when monitoring a minute change in the physical quantity of the measurement target over a long period of time, by setting the predetermined time longer, the time other than the measurement time It is possible to detect a change in the physical quantity of the measurement target temporarily generated as a change in the average frequency within a predetermined time, and it is possible to obtain a measurement value corresponding to the measurement mode of the physical quantity of the measurement target.
According to the configuration of the seventh aspect of the invention, since the output signal is in a pulse shape, even if noise is included in the output signal of the oscillating unit, the wave number can be accurately adjusted without providing a complicated filter circuit or the like. Counting is possible, and the configuration of the oscillation unit and the calculation unit can be simplified.

The basic composition schematic of the measuring device of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit explanatory diagram of an oscillation unit of a measuring apparatus according to a first embodiment of the present invention. Explanatory drawing which shows the measurement result at the time of continuous monitoring. The comparison figure of the measurement result by the presence or absence of correction | amendment by a reference resistance element.

As schematically shown in FIG. 1, the measuring apparatus 100 according to an embodiment of the present invention attaches a strain sensor 110 that is a detection resistance element to a measurement target T, and measures the electrical resistance value of the strain sensor 110. Thus, the distortion of the measurement target T is measured.
The strain sensor 110 is connected to the oscillation unit 120, and the oscillation unit 120 outputs a pulse signal having a frequency corresponding to the electrical resistance value of the strain sensor 110 as an output signal.
The output signal output from the oscillation unit 120 is input to the calculation unit 130, and the calculation unit 130 counts the pulse wave number of the output signal for a predetermined time (hereinafter referred to as “gate time”) that is arbitrarily set. The average frequency in the gate time is calculated, and the distortion amount of the measurement target T is calculated from the frequency.
Note that the distortion amount of the measurement target T calculated by the calculation unit 130 may be displayed directly by the calculation unit 130 with a display unit, or may be further output to the outside as measurement data.
In addition, a storage unit may be provided in the calculation unit 130 so that measurement data of a plurality of times is stored in the calculation unit and held as a history.

As a specific form of the measuring apparatus 100, the strain sensor 110, which is a resistance element for detection, may be conventionally used, and the oscillation unit 120 and the calculation unit 130 may be the same case even if they are separate cases. Any form may be employed as long as the functions of the oscillation unit 120 and the calculation unit 130 exist.
In addition to the functions of the oscillating unit 120 or the arithmetic unit 130, various additional functions may be incorporated, and the functions of the plurality of oscillating units 120 or the arithmetic units 130 are physically realized in one apparatus. May be.

  As shown in FIG. 2, the oscillating unit 120 connects the output of the preceding CMOS inverter 124 to the input of the subsequent CMOS inverter 125, and connects one terminal of the strain sensor 110, which is a detection resistive element to be measured, The other terminal of the strain sensor 110, which is a detection resistive element to be measured, is connected to the output of the preceding CMOS inverter 124 (the input of the subsequent CMOS inverter 125) via the input of the preceding CMOS inverter 124 and the capacitor 126. By connecting to the output of the subsequent CMOS inverter 125, a pulse-like output signal having a frequency corresponding to the electric resistance value of the strain sensor 110, which is a resistance element for detection, is measured from the output of the subsequent CMOS inverter 125. 127 is generated.

The strain sensor 110 to be connected is configured to be able to be switched to a plurality of reference resistance elements 121 having a known electric resistance value (three reference resistance elements 121 having different electric resistance values in this embodiment) by a switching circuit 122. ing.
The internal resistor 123 is shown as a representative internal resistor that affects the frequency of the oscillation circuit, and the power supply circuit supplied to the CMOS inverters 124 and 125 is not shown.

A measurement operation of the measurement apparatus 100 having the above configuration will be described.
The calculation unit 130 stores and holds a relationship between the frequency of the output signal 127 of the oscillating unit 120 and the electrical resistance value, an arithmetic expression of the relationship between the electrical resistance value and the distortion amount of the measurement target T, or a direct correspondence map. ing.
Since the characteristics of the internal resistance 123, the CMOS inverters 124 and 125, and the capacitor 126 change due to environmental changes such as temperature, the reference resistance element 121 is connected by the switching circuit of the oscillation unit 120 prior to actual measurement, and the oscillation unit 120 The frequency of the output signal 127 is measured, and the relationship between the stored frequency of the output signal 127 and the electrical resistance value is calibrated.
At this time, it is possible to calibrate more accurately by connecting a plurality of reference resistance elements 121 having different electric resistances and measuring the frequency of the output signal 127 of each oscillation unit 120.
Further, at least one of the plurality of reference resistance elements 121 is a temperature compensation resistance element having a known relationship between temperature and electric resistance value, thereby enabling more accurate calibration.

The frequency of the output signal 127 of the oscillation unit 120 in the arithmetic unit 130 is measured by calculating the average frequency in the gate time by counting the pulse wave number of the output signal 127 of the gate time that is arbitrarily set. It is configured.
Therefore, even if the distortion of the measurement target T is increased or decreased, the influence of the measurement error due to noise or the like can be reduced by setting the gate time longer.
In addition, when monitoring the distortion of the measurement target T over a long period of time, the above-described calibration operation is automatically performed at an appropriate period, so that accurate measurement can always be performed even when an environmental change occurs.

Furthermore, even when the sampling period of the measurement value during long-term monitoring is set long, by setting a gate time equivalent to the sampling period, a change in distortion of the measurement target T during the sampling period is also measured. It is possible to measure as a change in average frequency.
For example, as shown in FIG. 3, a sampling period is set such that measurement is performed at time points t1 and t2, and a change in distortion of the measurement target T changes from A to B between t1 and t2, and then changes to A again. In such a case, in the measurement using the conventional Wheatstone bridge or the like, the measurement value is A at both t1 and t2 as shown in FIG. 3A, and therefore the distortion of the measurement target T during the sampling period is A. It will be estimated, and it cannot be detected that there has been a change.
However, according to the embodiment of the present invention, as shown in FIG. 3 (b), the number of waves from t1 to t2 is counted and the sampling is performed from the average frequency by making the gate time G equal to the sampling period. It is possible to estimate that the average value of the distortion of the measurement target T during the period is C, and it is possible to detect the change.

Next, an embodiment of the measuring method of the present invention will be described.
First, in the measurement apparatus 100 described above, a plurality of reference resistance elements 121 are switched and connected before measurement by the strain sensor 110, and the output signal 127 of the oscillation unit 120 when each reference resistance element 121 is connected is switched. The frequency is measured by the calculation unit 130.
The arithmetic unit 130 obtains a product of the electrical resistance values of the plurality of reference resistance elements 121 and the respective measured frequencies so that the product becomes a linear function of frequency by the least square method from the obtained plurality of products. Set the function.
Thereafter, the strain sensor 110 is connected, the frequency of the output signal 127 of the oscillation unit 120 is measured by the calculation unit 130, the electric resistance value of the strain sensor 110 is calculated by substituting the frequency into the set function, A physical quantity to be measured is measured from the calculated electrical resistance value.

FIG. 4A shows the measurement result of the physical quantity to be measured based only on the theoretical value of the measuring device without performing calibration with the reference resistance element 121, and FIG. 4B shows the measurement result with the reference resistance element 121. The measurement result of the physical quantity to be measured when the measurement is performed and calibrated is shown.
In both figures, the measurement results of the physical quantity to be measured by the bridge circuit with high measurement accuracy are indicated by ◆.

As shown in FIG. 4, when the output of the oscillation unit 120 is converted into a physical quantity using only the theoretical value as it is, the measurement accuracy is significantly lowered, whereas when the calibration is applied using the measurement method of the present invention, the accuracy is reduced. It can be seen that is significantly improved.
In other words, even if there are unknown internal resistance values and capacitance fluctuation errors, by setting the function using the least square method from the product of multiple electrical resistance values and frequencies, including those errors Calibration is possible, and accuracy is greatly improved.
In the strain sensor 110 whose change in electrical resistance value is about several percent, sufficient accuracy can be obtained even by the linear function approximation as described above. Naturally, the function may be set as a polynomial so as to further improve the accuracy. good.
Further, as apparent from FIG. 4, when there is no load, there is almost no error in the measurement result of the physical quantity to be measured. Therefore, the measurement by the reference resistance element 121 is performed only once with one reference resistance element 121. As an alternative, a linear function may be set to shorten the calculation amount and processing time for calibration.

  In the measurement apparatus and the measurement method of the present invention, in the above embodiment, the strain sensor 110 is used as the detection resistance element and the strain of the measurement target T is measured. However, as the detection resistance element, temperature, pressure, magnetic Any other physical quantity whose resistance varies depending on any other physical quantity may be used, and it can be used as a measuring device and a measuring method for various physical quantities as well as distortion.

DESCRIPTION OF SYMBOLS 100 ... Measuring device 110 ... Strain sensor (resistive element for detection)
120 ... Oscillator 121 ... Reference resistance element 122 ... Switching circuit 123 ... Internal resistance 124 ... CMOS inverter 125 ... CMOS inverter 126 ... Capacitor 127 ... Output signal 130 ..Calculation unit

Claims (9)

A detection resistance element that converts a change in a physical quantity to be measured into a change in electrical resistance value, an oscillation unit that is connected to the detection resistance element and outputs an output signal having a frequency corresponding to the electrical resistance value, and the output signal A measurement device that measures a physical quantity of a measurement target, having a calculation unit that calculates the physical quantity of the measurement target from the frequency of
The oscillation device includes at least one reference resistance element having a known electrical resistance value, and is configured to be able to connect the detection resistance element and the reference resistance element by switching. .   The oscillation unit includes a plurality of reference resistance elements having different electric resistance values, and is configured to be connectable by switching between the detection resistance element and the plurality of reference resistance elements. 1. The measuring device according to 1.   The measuring apparatus according to claim 1, wherein the oscillation unit automatically switches between the detection resistance element and the reference resistance element.   The measuring device according to claim 1, wherein the oscillating unit further includes a temperature compensating resistance element whose temperature influence characteristic is known.   5. The calculation unit according to claim 1, wherein the calculation unit counts the wave number of the output signal for a predetermined time, calculates an average frequency for the predetermined time from the wave number, and calculates a physical quantity to be measured. The measuring device according to any one of the above.   The measurement apparatus according to claim 5, wherein the calculation unit is configured to change and set the predetermined time.   The said oscillation part has a CMOS inverter, and outputs the pulse signal of the frequency according to the electrical resistance value of the said resistance element for a detection connected. Measuring device. A detection resistance element that converts a change in a physical quantity to be measured into a change in electrical resistance value, an oscillation unit that is connected to the detection resistance element and outputs an output signal having a frequency corresponding to the electrical resistance value, and the output signal A measurement method for measuring the physical quantity of the measurement object, comprising a calculation unit that calculates the physical quantity of the measurement object from the frequency of
The oscillating unit has at least one reference resistance element having a known electric resistance value, and is configured to be connectable by switching between the detection resistance element and the reference resistance element,
From the product of the frequency of the output signal when the reference resistance element is connected and the electrical resistance value of the reference resistance element, set the function so that the product is a linear function of the frequency,
Substituting the frequency at the time of connecting the resistance element for detection into the function, the electric resistance value of the resistance element for detection is calculated,
A measurement method characterized by measuring a physical quantity to be measured from the calculated electrical resistance value. The oscillation unit has a plurality of reference resistance elements having different electrical resistance values,
When setting the function to be a linear function of the frequency, obtain the product of the electrical resistance values of the plurality of reference resistance elements and the respective measured frequencies,
9. The measurement method according to claim 8, wherein a function is set from a plurality of obtained products so that the product becomes a linear function of frequency by a least square method.

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