JPS58134394A - Physical quality measuring apparatus with function of measuring temperature - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring physical quantities such as strain and temperature of an object to be measured using a bridge circuit using a strain gauge or the like and a temperature-sensitive resistance element.

2. Description of the Related Art Conventionally, a device shown in FIG. 1 has been known as a device for measuring the temperature of an object to be measured and a certain physical quantity, such as strain, using a temperature-sensitive resistance element and a bridge circuit. This device is roughly divided into a sensor section 10, an extension cord section, and a measuring device main body.

The sensor unit 10 is a part that converts the amount of strain and temperature of the object to be measured into electrical quantities, that is, resistance values, and includes a bridge circuit B consisting of four strain gauges SG, SG, SG, SG, SG, and SG. , and a temperature-sensitive resistance element R. Between the extension cord parts, there are 6 core wires Is + lx,
Is H4e Is * /e, and input terminals 1, 2 . . . of the bridge circuit 13, respectively. Same output terminal 3, 4
．． It is connected to both terminals 5 and 6 of the temperature sensitive resistance element R. Also, each core wire l, ~I! 6 is the same standard and the same length,
Each has a resistance r. The measuring device main body I includes a constant current source S1 that supplies a constant current to the input side of the bridge circuit B, an amplifier A1 that amplifies the voltage across the output side of the bridge circuit B, and a voltage connected to the output terminal of the amplifier A1. and a meter SM that displays the strain of the object to be measured. In addition, the voltage drop due to the measuring device body) ffil C, t, the constant current source S that supplies a constant current to the temperature-sensitive resistance element R, and the composite resistance 2r of the temperature-sensitive resistance element l (and the core wire /, , , 26). It has an amplifier A2 for amplification, and a meter TM, which is a voltmeter connected to the output terminal of the amplifier A8, and for measuring the temperature of the object to be measured.

Next, the operation of the above conventional example will be explained. First, strain gauge 5
( ) 1 to SG are attached to the part to be measured by, for example, adhesive. For example, adjacent strain gauges in bridge circuit B may
The strain gauges on opposite sides of the strain gauge are attached to each other in the same direction of elongation of the object to be measured. In this case, if strain gauge S01 is stretched at a certain point, strain gauge SG,
Strain gauge SG2.
SG is attached at a position where it will shrink. and constant current source S
When a current is supplied from 1 to bridge circuit B, the voltage between terminals 3 and 4 changes depending on the strain of the object to be measured, and after this voltage is amplified by amplifier A, meter SM is driven. Therefore, the amount of strain on the object to be measured is displayed on the meter SM.

' On the other hand, a temperature-sensitive resistance element R is also attached to the object to be measured, and as the temperature of the object to be measured increases,
Its resistance value changes greatly. Therefore, as the temperature of the object to be measured changes, the input voltage of the amplifier A2 changes, and after amplifying this, the voltage value displayed on the meter TM is determined by the measurement error of the core wire is, due to the 1 m resistor 2r. By subtracting the voltage value corresponding to the voltage drop, the temperature of the object to be measured at that time can be determined.

However, in the conventional example described above, four core wires are sufficient when measuring only the strain of the object to be measured, but two core wires are required when measuring strain and temperature. Of course, it is possible to change the circuit configuration and share the core wires 1 and 1, but even if that happens, the number of core wires will increase. By increasing the number of extension cords, 20
．． 7) A problem arises in that the shape becomes thicker and the weight increases. In addition, in the above conventional example, the core wire J@, 1 m resistance 2-
The temperature of the object to be measured is determined by subtracting the voltage drop caused by the current flowing through r, and the resistance 2r changes each time the length of the extension cord 20 changes. Therefore, there is a problem in that if the length of the extension cord changes, the correction value for temperature measurement must also be changed.

Therefore, the present invention aims to reduce the number of core wires in an extension cord and to reduce the number of core wires in an extension cord in a device that measures physical properties such as strain and temperature of a measured object using a bridge circuit using a strain gauge and a temperature-sensitive resistance element. In order to automatically correct the resistance of the extension cord during measurement, a temperature-sensitive resistance element is installed in series on the output side of the bridge circuit, and two constant current sources that flow the same current are installed. , the input side of the bridge circuit is short-circuited, one of the constant current sources is connected between the input side and one end of the output side of the bridge circuit via a temperature-sensitive resistance element, and the input side and the output side are connected. The other end of the constant current source is connected between the other end and the other end of the constant current source. - Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings. Note that the same members are given the same reference numerals. FIG. 2 is a circuit diagram showing one embodiment of the present invention.

The sensor unit 11 includes a bridge circuit B including strain gauges SG, ~SG, and one output terminal 4 of the bridge circuit B.
A temperature-sensitive resistance element R connected to is provided. Strain gauges SG, to SG are of the same standard. In addition, the temperature-sensitive resistance element l (has a resistance value of 100Ω
, 1 when the temperature coefficient of resistance is 4J100 ppm/”C
, "The one with a resistance change per C of 04 Ω is used. Note that 1 and 2 are the input terminals of the bridge circuit B, and 3 and 4 are the output terminals of the bridge circuit.

The extension cord section 21 has four core wires l, ~I! 4 are provided, and their core wire resistances are all r. Also, each core wire/1゜z
t, ls*/4 are terminals 1.2, 3. The extension cord section 21 has a maximum length of 1000 m using the 05- core wire.

Bridge input side terminal 11゜2' in the measuring device main body 31
, the same output side terminals 3' and 4' are core wires e and H1x, respectively.
.

It is connected to 1H1a. The constant current sources S, , S, are for passing the same current to each other, and the switch fS is for connecting terminal 2' to terminal 1' or constant current source S, and is a switch. SW2 is for connecting constant current source S1 to terminal 3' or terminal 2, and switch SW3 is for connecting constant current source S2 to terminal 4' or no load (or connecting to terminal 2). The switches sw, , and sw are interlocked with each other. That is, switch SW.

sw2. When measuring temperature, sw shorts the input side 1' and 2' of the bridge circuit B, and connects the input side 1' and one end 4' of the output side of the bridge circuit B via the temperature-sensitive resistance element R. A constant current source S2 is connected, and a constant current source S is connected between the input side 1' and the output side 3'. During strain measurement, the switches sw, , sw, , sw connect constant current source S1 (and/or '1..
I. connects S2) and outputs 3' and 4 of the bridge circuit B.
The constant current sources S, , and S are not connected to '.

The amplifier A3 amplifies the voltage between the terminals 3'' and 4', and has a sufficiently high input impedance.

The meter M is calibrated for strain amount and temperature.

Next, the operation of the above embodiment will be explained. First, a case will be described in which the strain of the object to be measured is measured. This case is similar to strain measurement using the conventional constant current method.

That is, switch S~fox.

sw, , Switch all the vortices to the contact side. An equivalent circuit in this case is shown in FIG. In the figure, core wire 11゜l,
Since the constant current source S1 (and/or S2) is connected to the right end of the resistor r and the bridge circuit 13. A constant current i is flowing through the resistor r. and strain cages SG, and S
G,, SG, and SG are considered to always change resistance in the same way, and the strain gauge S('i.

and SG, which combined resistance and strain gauge S G , and S
C+.

As it is considered to be almost the same as that of (after all): Party A,
, The combined resistance of ridge circuit B is considered to be approximately constant. Therefore, it may be considered that a constant voltage is always applied between the input terminals 1 and 2 of the bridge circuit B. Then, depending on the deformation of the object to be measured, the bridge circuit I (output terminal 3-
The voltage between 4 changes.

Furthermore, since the input impedance of amplifier A is sufficiently high, despite the presence of the composite resistance 2r of core wires e, , i, and the resistance Rx of temperature-sensitive resistance element R, terminals 3'-4'
The voltage between them is practically the same as that between terminals 3 and 4. Therefore, the needle of meter M swings according to the strain of the object to be measured.
The amount of strain can be visually confirmed from the indication of this needle.

Next, we will explain the case of measuring the temperature of the object to be measured.1
, in this case, the switches sw, , sw, , sw
8 to the contact a side. An equivalent circuit in this case is shown in FIG. In the figure, Z1 is the combined resistance between terminals 4 and 1', B is the combined resistance between terminals 3 and 1', and E is the combined resistance between terminals 4'.
-1' is the voltage between terminals 3' and 3', and 3' is the voltage between terminals 4' and 3'. Therefore, Eo2I' = + E+ = (rr -) - RXq
-4-Z, ・+ )-(r・1+12・1) =l(x-i1 Otsu・i −Z, ・i = Rx-1+(
Z, -Z, )i#Rx,i.

Here, (2, -2,) can be ignored with respect to the resistance change due to temperature of the temperature-sensitive resistance element R. For example, if a 350Ω gauge is used in the bridge circuit B, approximately 1400Xl0 per side is used. -' When strain is applied and the output is quadrupled, the value is within the range of ±0002Ω, and when converted to temperature, the value is within the range of ±o, o o s 'c.

Also, the voltage between terminals 4' and 3' when o'o is tz(
0゛C), and the same voltage at t'c is ug (1°C)
If ΔE0 is the voltage change between terminals 4' and 3' when changes from O'O to t 'c, then ΔEo
= Eo(t′c)−E, (o゛c)=[(0(1−
t-ctt)i-Ro-1-Ro-a-i-t
becomes.

From this equation, the voltage change ΔE has a proportional relationship with the temperature t. By amplifying this voltage with an amplifier A and displaying it on a meter M, the temperature of the object to be measured can be visually checked. in this case,
Measurements can be made without being affected by the resistance r of the core wire IBL+.

However, in these calculation processes, the combined resistance (Z, -z2) is considered to be zero, so this amount appears as an error. However, the error is at most ±0.0 (15'O).Furthermore, although it can measure the strain and temperature of the object to be measured, four core wires are sufficient, so compared to the conventional device. The cord becomes thinner, reducing the need for electric switches.

The above embodiment is suitable for measuring, for example, the curing process of concrete and its behavior after curing. In other words, the stress in the concrete can be measured using a strain gauge, and the temperature at that time can be measured using a temperature-sensitive resistance element.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the invention.

For example, in the above embodiment, the bridge circuit 13 has four
Two strain gauges G, ~SG, were used.
,. Other than that (26, 呵mi, 'step:, -9SG, (7
) Mi*r;= &i Strain SG, , SG, only, and fixed resistors may be used on the other sides of the bridge circuit B.

In addition, two temperature-sensitive resistance elements R are connected in series with terminals 4 and 3, respectively.
Alternatively, only the terminal 3 may be provided in series. In strain measurements, amplifier A.

In relation to the input impedance, measurement accuracy will be improved if the combined impedance viewed from terminals 3'-4' to the left is made smaller.

As this temperature-sensitive resistance element, for example, a thermistor or a metal wire (platinum wire, nickel wire, indium wire, etc.) resistance temperature sensor, which has been widely used in the past, can be used, but recently developed magnetic It is desirable to use a temperature-sensitive resistor whose surface is coated with a special metal film and insulated with a special resin. In other words, thermistors have non-linear temperature characteristics, and their accuracy and repeatability are not very high. In order to make the temperature characteristics linear, it is necessary to add a correction resistor or use a complex correction circuit such as an analog calculation circuit. Become.

On the other hand, metal wire resistance thermometers such as platinum wire and Mockel wire have low resistance values (for example, platinum resistance thermometers are 50Ω and 100Ω as specified in JISC1604), so contact resistance and signal circuits are There are disadvantages such as the wire resistance has a large effect, it is easily affected by external influences, the output signal is small, and the size is large, making it difficult to instrument.

In contrast to these, the above insulation coating type temperature sensitive resistor is
A thin metal film with a temperature-sensitive function on a special porcelain insulator that is electrochemically stable at high temperatures and has excellent thermal conductivity (the film material consists mainly of nickel, iron, chromium, etc., and several other metals). is added as an additive to obtain the desired resistance value and temperature coefficient of resistance) by vacuum evaporation, sputtering, etc., and these 7 are further coated with epoxy resin for protection. / Electrical resistance characteristics are linear, ranging from low resistance (several ohms) to high resistance (about 10 ohms)
For example, when using a wire with relatively high resistance, the contact resistance and the wire resistance of the signal circuit will not be a problem, and the resistance change rate is relatively large, which is advantageous against noise. It can also respond to temperature changes.

Furthermore, instead of the strain gauges SG, -SG=, other conversion elements such as differential transformers and differential inductances can be used to measure temperature as well as physical quantities other than V degrees, such as load, force, pressure, acceleration, etc. It may also be possible to make measurements.

Incidentally, a differential transformer is composed of a negative coil and a pair of secondary coils, and when the moving part moves depending on the physical quantity to be measured, the degree of magnetic coupling between the negative secondary coil and the pair of secondary coils changes. Then, the difference between the voltages induced in the secondary coil in proportion to the amount of movement of the movable part is detected. Also strain gauge SG,
-8G, for example cd s (cadmium sulfide)
If a photoelectric conversion element such as a photoelectric transducer is used, temperature can also be measured in addition to light stitching.

Note that the contacts of the switch S and the contacts of the switch SXS may be connected in advance.

As described above, the present invention provides an output of the bridge circuit in a device for measuring the physical quantity and temperature of a measured object using a bridge circuit constituted by an element that converts a physical quantity other than temperature into an electrical quantity and a temperature-sensitive resistance element. A temperature-sensitive resistance element is installed in series on the side, and two constant current sources are installed that send the same current to each other, and when the temperature is measured by switching the switch, the input end of the bridge circuit is shorted, and the input side and the output side of the bridge circuit are connected. One of the constant current sources is connected between one end of the input side and the other end of the output side via a temperature sensitive resistance element, and the other constant current source is connected between the input side and the other end of the output side. , it is possible to automatically correct the temperature measurement error caused by the core wire resistance of the extension cord, and it is also possible to improve the temperature measurement accuracy.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the Juto device, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is an equivalent circuit diagram of the above embodiment during strain measurement, and Fig. 4 is the above embodiment. FIG. 3 is an equivalent circuit diagram when measuring temperature. 10.11...Sensor part, 20, 21...
...Extension cord part, :so, 31...
・Measuring device body, S(i, ~S(i,...strain gauge, k...temperature-sensitive resistance element, l, ~16
・・・・・・Core wire of extension cord, S, , S,...
... Constant current source, A1-A3 ... Amplifier,
M SM 'I''M...Meter, B...
...Bridge circuit, sw, , sw2. sw3
····switch. Box permit applicant: Kyowa Co., Ltd. IL Industry Yuhito IPiuUi-i':i' TJJ
Al! A'l= Paste Q'f, 11.1 1st
Figure 2 [ (Figure 3

Claims (1)

[Claims] A temperature-sensitive resistance element provided in series on the output side of the bridge circuit, two constant current sources that flow the same current to each other, and a short-circuit between the input side of the bridge circuit and the bridge circuit when measuring temperature. One of the constant current sources is connected between one end of the output side of the circuit via the temperature sensitive resistance element, and the other of the constant current sources is connected between the input side and the other end of the output side. A physical quantity measuring device with a temperature measuring function, characterized in that it is provided with a connecting switch.