JPH09280885A - Measuring device for characteristic value of fluid in pipeline - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a measurement accuracy to satisfy a requirement for practical use, at least, in frequently required measurement subsections and also to enable the measurement over a wide range. SOLUTION: By connecting a sensor 3 for a characteristic value measurement with an variable-gain amplifier 5 and control circuit 7, setting the control circuit 7 on one or more threshold values correspondingly to the measurement subsections over the whole measuring range, making the control circuit 7 form a control signal when an output of the sensor 3 exceeds the threshold value, setting the gain of the amplifier 5 to be more than two-stepped by the control signal, and thus, the measurement accuracy of the characteristic values can be changed over more than two-stepped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring a characteristic value of a fluid in a pipeline, and more particularly to an improvement in a technique for automatically measuring various characteristic values of a fluid such as high pressure air flowing in the pipeline. is there.

The above-mentioned characteristic values to be measured by the present invention include the pressure, temperature and flow rate of fluid, but in the following description, the case of pressure measurement will be described as a typical example. To do.

[0003]

2. Description of the Related Art Conventionally, in the automatic measurement as described above, an output signal of a pressure sensor is generally used as an amplifier (opamp).
Amplify with A / D conversion, then process with CPU,
Visible display on LCD.

Generally, in the case of measuring the fluid pressure in a pipeline,
For example, there is a practical demand for displaying with a measurement accuracy of 0.1 Kgf / cm ^{2 in} a measurement range of up to 20 Kgf / cm ² .

The measuring device to which the present invention is applied is often used in a narrow space of a complicated piping system, and a fixed power source may not be expected in such a space. Therefore, it is desirable that the device itself is small and highly portable, and that it has a built-in battery. Also, the use of self-contained batteries in such devices has become a common trend these days.

Regarding the resolution of the A / D converter, the desired resolution was achieved with 8 bits in consideration of cost.

[0007]

Here, for example, the pressure measurement range is 0 to 20 Kgf / cm ² , and the power supply voltage is 3
(V). Then, since the resolution of the 8-bit A / D converter is 256, the maximum output voltage of the amplifier is 1.5.
If it is set to (V), a maximum of 128 steps can be detected.

Looking at this at a maximum of 20 kgf / cm ² , the display resolution is 0.156 Kgf / cm ² , which is practically 0.2 Kgf / cm ² . That is, the above requirement "with accuracy of 0.1 Kgf / cm ² step" cannot be satisfied.

Further, for example, when a built-in battery having an output voltage of 1.5 (V) is used, even if two batteries are used, the power supply voltage is only 3 (V). Generally, the output voltage of the amplifier is 1.5 (V) subtracted from the applied voltage, so that the output voltage of the amplifier is 1.5 (V). The output voltage can be increased by increasing the number of batteries, but this will impair compactness and portability.

In view of the state of the art as described above, an object of the present invention is to provide a measurement accuracy that can meet practical requirements, in consideration of cost, compactness, portability, etc. in measuring characteristic values of fluid in a pipeline. , At least in the measurement subdivisions that are in high demand, and enabling measurement over a wide range.

[0011]

Therefore, in the present invention, a sensor for measuring characteristic values is connected to an amplifier whose gain can be changed and a control circuit, and the control circuit corresponds to a measurement subsection within the entire measurement range. Then, one or more threshold values are set, and when the output of the sensor exceeds the threshold value, a control signal is formed in the control circuit, and the gain of the amplifier is set to two stages or more by this control signal, The purpose of this is to switch the measurement accuracy of the characteristic value to two or more steps.

That is, in the present invention, the entire measurement range is divided into two or more measurement subsections, and the measurement subsections that are in high demand are measured with high accuracy and the other subsections are measured with lower accuracy. Of. For that purpose, the threshold value of the control circuit is set according to the measurement subsection.

Since a CPU is typically cited as an element for outputting a control signal in the control circuit, a case of using a CPU as the element will be described below as an example, but the present invention is not limited to this. is not. Although the CPU has an A / D converter,
The converter may be either a built-in type or a separate type.

[0014]

When the output signal of the sensor exceeds the first threshold value corresponding to the upper limit of the first measurement subsection, the CPU outputs the first control signal, and in response thereto, the gain of the amplifier becomes the first value.
Set to a stage to give the measurement accuracy of the first stage. When the output signal of the sensor exceeds the Nth threshold value corresponding to the upper limit of the Nth (N: positive integer) measurement subsection, the CPU outputs the Nth control signal, and in response thereto, the amplifier outputs Gain is Nth
Set to stage N to provide Nth stage measurement accuracy.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows the basic construction of the apparatus of the present invention. The sensor 3 for measuring the characteristic value is connected to the gain-changeable amplifier 5 and the control circuit 7. The element 6 shown in the figure is an A / D converter. This control circuit 7
Is set to a threshold value corresponding to the upper limit of each measurement subdivision in the entire measurement range. When the output of the sensor 3 exceeds any threshold value, the CPU in the control circuit 7 outputs the control signal S, which causes the control circuit 7 to set the gain of the amplifier 5. As a result, the measurement accuracy of the characteristic value can be switched between two or more steps.

2 and 3 show a first embodiment of the device of the present invention, in which the control circuit includes a CPU 71 and a voltage dividing setting circuit 10. The voltage division setting circuit 10 is provided in front of the sensor 3. That is, the sensor 3 is connected on the input side to the reference voltage generator 2 connected to the power supply 1 via the voltage dividing setting circuit 10. Here, by comparing the partial pressure VR and the value of I · RD, VR
The output voltage of the operational amplifier is set so that = I · RD, and this is applied to the sensor 3. Gain is changed by changing the voltage division ratio by the control signal S from the CPU 71.
As a result, the display resolution is changed.

The voltage division setting circuit 10 is composed of a transistor T and a resistor group, and the transistor T is CP.
It is connected to U71 and turned on / off by a control signal S from the CPU 71.

Here, the gain of the amplifier 5 is set to K, the voltage, current, resistance and the like of each part are determined as shown in the figure, and ΔR is the resistance change of the sensor 3.

The transistor T is turned off when the control signal S is not output from the CPU, and is turned on when the control signal S is output. The following relationships are established in the circuit of FIG.

[0020]

[Equation 1]

Here, the divided voltage VR will be compared for the case where the transistor T is turned off and the case where it is turned on. When the transistor T is off, the partial voltage VR is Vin · R2 /
(R1 + R2). When the transistor T is on, the partial voltage VR is Vin · {R2 · R3 / (R2 +
R3)} / {R1 + R2 · R3 / (R2 + R3)}. In this way, the partial pressure VR changes depending on whether the control signal S is output from the CPU or not. That is, the apparent gain changes and the output voltage changes. Therefore, the display resolution can be set to an appropriate value by changing the voltage division ratio.

The above-mentioned display resolution changing process will be described with concrete numerical values. For example, pressure 0 to 20 Kgf / cm
Within the range of ² , the first demand is 10 Kgf / cm ²
The divided voltage VR is set to VR1 so that the maximum value of the output voltage becomes 1.2 (V) in the following measurement subsections. Then, the display resolution is 10 × 3 / (2 ⁸ ) /1.2=0.098 Kgf
/ Cm ² . That is, it satisfies the requirement of "with measurement accuracy of 0.1 Kgf / cm ² step".

Then, when the pressure exceeds 10 Kgf / cm ² , the maximum value of the output voltage becomes VR (V).
The partial pressure VR is set to 2. Then the display resolution is 20 ×
0.0117 / 1.5 = 0.15 Kgf / cm ² . But this is a measurement subdivision with less demand, so
Even with this measurement accuracy, there is no practical problem.

Therefore, in practical use, first, the partial pressure VR
Is set to VR1 to read the pressure, and if it is 10 Kgf / cm ² or more, the output port of the CPU 71 is turned on, the transistor T is switched, the partial pressure VR is set to VR2, and the pressure is read.

The above case is one example of the method of carrying out the present invention, and as shown in FIG. 4, the entire measurement range is 0 to 20 kg.
The f / cm ² is divided into two, divided into measurement accuracy of the measurement of 0~10Kgf / cm ² accuracy and 10~20Kgf / cm ^2, in which the former was often measured subsection demand.

The method of carrying out the present invention is not limited to this. For example, as shown in FIG.
20Kgf / cm ² is divided into three, 0-10Kgf / c
The measurement accuracy of m ^2, the measurement accuracy of 10 to 15 Kgf / cm ² , and the measurement accuracy of 15 to 20 Kgf / cm ² may be used. In this case, 0 to 10 Kgf / cm ² is the demanded measurement accuracy.

FIG. 6 shows an example of the configuration of the voltage dividing setting circuit 10 in the case where the entire measurement range is divided into three measurement accuracies corresponding to the method of implementation shown in FIG. In this case, two transistors T1 and T2 are used to connect to the CPU 71, respectively. For example, the first control signal from the CPU 71 first turns on the first transistor T1 and the second control signal turns on the second transistor. Other points are the same as those in FIG.

FIG. 7 and FIG. 8 show a second embodiment of the apparatus of the present invention, in which the control circuit includes a CPU 71 and a gain setting circuit 20. The gain setting circuit 20 is provided on the rear side of the sensor 3. That is, the sensor 3 has the gain setting circuit 20 on the output side.
It is connected to the amplifier 5 via. The display resolution is changed by changing the gain of the amplifier 5 according to the control signal S from the CPU 71.

The gain setting circuit 20 is composed of two transistors T1 and T2 and resistor groups R1 to R3. The transistors T1 and T2 are connected to the CPU 71 and are turned on by a control signal S from the CPU 71. Turned off. That is, when no control signal is output, both transistors turn off and shut off,
When the control signal is output, both transistors are connected to the CPU 71 so as to be turned on and conductive.

Here, the voltage, current, resistance, etc. of each part are determined as shown in the figure. First, when the control signal S is not output from the CPU 71, both transistors T1 and T
2 is off and shut off, and the following relationship holds.

[0031]

[Equation 2]

When the control signal S is output from the CPU 71, both the transistors T1 and T2 are turned on and become conductive, and the following relationship is established.

[0033]

(Equation 3)

That is, the gain of the amplifier is changed from K to K '. By setting the gain in this way, the output voltage can be changed, and the display resolution can be appropriately set.

FIG. 9 shows an example of the configuration of the gain setting circuit 20 when the entire measurement range is divided into three measurement accuracies. In this case, four transistors T1 to T4 and resistor groups R1 to R4 are used, and the transistors are connected to the CPU 71, respectively. Other points are the same as those in FIG.

[0036]

[Effects of the Invention] While satisfying the requirements of cost, compactness and portability, the high measurement accuracy required for practical use is maintained in the measurement subsections with high demand, and more than that in the measurement subsection with low demand. By using low measurement accuracy,
It is possible to measure over a wide range.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of an apparatus according to the present invention.

FIG. 2 is a block diagram showing the configuration of the first embodiment of the device of the present invention.

FIG. 3 is a circuit diagram of the same.

FIG. 4 is a graph showing an example of a method of implementing the present invention.

FIG. 5 is a graph showing another example of the same.

FIG. 6 is a circuit diagram showing a modification of the first embodiment.

FIG. 7 is a block line showing a configuration of a second embodiment of the device of the present invention.

FIG. 8 is a circuit diagram of the same.

FIG. 9 is a circuit diagram showing a modification of the second embodiment.

[Explanation of symbols]

 1: Power supply 2: Reference voltage generator 3: Characteristic value measuring sensor 5: Amplifier 6: A / D converter 7: Control circuit 10: Voltage dividing setting circuit 20: Gain setting circuit 71: CPU T: Transistor R: Resistance S: Control signal

Claims (3)

[Claims] 1. A sensor for measuring a characteristic value is connected to a gain changeable amplifier and a control circuit, and the control circuit has one or more threshold values corresponding to measurement subsections in the entire measurement range. Is set, a control signal is formed in the control circuit when the output of the sensor exceeds the threshold value, and the gain of the amplifier is set to two stages or more by this control signal.
As a result, the characteristic value measuring device for the fluid in the pipeline is characterized in that the accuracy of measuring the characteristic value can be switched in two or more stages. 2. The apparatus according to claim 1, wherein the control circuit includes a voltage division setting circuit. 3. The apparatus of claim 1, wherein the control circuit includes a gain setting circuit.