JPH0233965B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature measurement method using a transducer with a temperature measurement function, and in particular to a strain gauge type transducer that converts a physical quantity other than temperature, such as a strain amount, into an electrical quantity and outputs the electrical quantity. This invention relates to a temperature measurement method using a converter with a temperature measurement function combined with a temperature-sensitive resistor.

Generally, in concrete structures and the like, strain gauge type transducers are installed to detect temperature, amount of strain, etc. and output them as electrical signals in order to investigate the behavior of the structure. Conventionally, there are two types of temperature measurement transducers: those that measure only temperature, and those that measure temperature only, and those that have a temperature measurement function added to the above-mentioned strain gauge type transducers.

This converter with temperature measurement function is shown in FIGS. 1 and 2. The temperature measuring function transducer 1 shown in FIG.
Connect the input/output lead wires _l1 to _l4 of the strain gauge type transducer 2, that is, the input lead wires _l1 , _l3 , the output lead wires _l2 , _l4 , and the temperature measurement lead wire _l5. is connected to the temperature sensitive resistor 3. This converter 1 with temperature measurement function measures the temperature with the temperature sensing resistor 3 connected between the output lead wire _{l 4} and _the temperature measurement lead wire l ₅ . Correction is required because it is affected by resistance changes due to resistance and temperature.

In addition, the temperature measurement function transducer 4 shown in FIG. 2 has three wires that can correct the resistance of the lead wires and resistance changes due to temperature when measuring using a strain gauge type transducer 5 consisting of a Wheatstone bridge circuit. For example, the temperature sensitive resistor 3 is connected between the output lead wire l ₄ and the temperature measurement lead wires l ₅ and l ₆ .

The effect of lead wire resistance as described above can be corrected by measuring the lead wire resistance in advance, but the correction value differs each time the lead wire length changes, and the lead wire resistance There is a problem in that the resistance must be measured every time the length changes. In addition, in the above-mentioned converter with a temperature measurement function, the number of lead wires, that is, the number of core wires of the cord increases due to the addition of the temperature sensing resistor 3, and if the lead wires are combined into one cord, it becomes thick and heavy. Further, there are problems in that the cost is high and the wiring work for the lead wires is complicated.

The present invention has been made to solve the above problems, and its purpose is to provide a strain gauge type transducer with a simple and inexpensive configuration in which a temperature sensitive resistor is added to a conventional strain gauge type transducer. To convert the behavior of an object to be measured into an electrical signal and output it without increasing the number of lead wires, and to perform predetermined calculations on the temperature near the object to be measured without being affected by the resistance of the lead wires. An object of the present invention is to provide a temperature measurement method using a converter with a temperature measurement function, which can be determined by the following.

In order to achieve the above object, the present invention provides a strain gauge type that has a Wheatstone bridge that includes a strain gauge on at least one side, detects the behavior of an object to be measured as a strain amount, converts the strain amount into an electrical signal, and outputs it. A temperature measurement method using a converter with a temperature measurement function, which is a combination of a converter and a temperature-sensitive resistor connected in series to at least one output end of the Wheatstone bridge, the method comprising one or more temperature-measuring functions. The amount of change in resistance per 1°C of the combined resistance of the temperature-sensitive resistor (Ro is the combined resistance of the temperature-sensitive resistor at 0°C, and α is the temperature coefficient of resistance of the temperature-sensitive resistor) is determined in advance by a temperature calibration test,
Furthermore, the resistance R _A ( ₀ ) and the resistance R _B ( ₀ ) at a temperature of 0° C. as seen from the output end and the input end of the Wheatstone bridge including the temperature-sensitive resistor on the output end side are measured in advance, actually measuring the resistance R _A (t) and the resistance R B (t) at a temperature t° C. when the temperature is measured as seen from the output end and the input end of the Wheatstone bridge including the temperature sensitive resistor on the output _end side; Amount of resistance change obtained as above
Ro・α, resistance R _A ( ₀ ), resistance R _B ( ₀ ), resistance R _A (t)
and the value of resistance R _B (t), t=
{R _A (t)−R _B (t)}−{R _A ( ₀ )−R _B ( ₀ )}/Ro・
The present invention is characterized in that the temperature t° C. at the time of temperature measurement is determined by substituting α into an arithmetic expression.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 3 is a circuit diagram showing the circuit configuration of an embodiment of a converter with a temperature measuring function used in carrying out the present invention. The temperature measuring transducer shown in Figure 3 is a so-called strain gauge type transducer that detects a physical quantity other than temperature, converts it into an electrical signal, and outputs it. It uses a converter. This converter 6 with temperature measurement function has 4
A strain gauge type transducer 7 (hereinafter simply referred to as a transducer) is formed by connecting strain gauges SG ₁ to SG ₄ to form a Wheatstone bridge. temperature sensitive resistor
R ₁ and R ₂ are each connected. In addition, 10,1
1 is an input terminal, 12 and 13 are temperature sensitive resistors R ₁ ,
This is the output end of the temperature measuring converter 6 to which _R2 is connected.

Here, the resistance R _A seen from the output terminals 12 and 13 of the temperature measuring converter 6 including the temperature sensitive resistors R and R ₂ ,
Letting the resistance R _B as seen from the input terminals 10 and 11 be expressed as R _A = R ₁ + R ₂ + Rout (1) R _B = Rin (2). However, Rout is the output resistance of the converter 7 seen from the output terminals 8 and 9, and Rin is the input terminal 10,
11 is the input resistance of the converter 7 as seen from 11.

If the value obtained by subtracting the above equation (2) from the above equation (1) is ΔR ₀ , it is expressed as the following equation (3).

△R ₀ = R _A − R _B = R ₁ + R ₂ + Rout − Rin (3) Now, the converter 7 and temperature sensitive resistors R ₁ and R ₂ are undergoing resistance changes due to temperature, and the temperature t Rout is the output resistance of the converter viewed from output terminals 8 and 9 at ℃.
(t), the input resistance of the converter viewed from the input terminals 10 and 11 is Rin (t), and the temperature sensitive resistors R ₁ and R ₂
The combined resistance R ₁ + R ₂ is R, and the combined resistance is 0°C.
When the resistance at time is R ₀ and the temperature coefficient of resistance is α, the above equations (1), (2), and (3) are expressed as follows.

R _A (t)=R ₀ (1+αt)+Rout(t) ………(1)′ R _B (t)=Rin(t) ………(2)′ △R ₀ (t)=R ₀ (1+αt )+Rout(t) −Rin(t) ………(3)′ However, R _A (t), R _B (t) and △R ₀ (t) are
These are the values of R _A , R _B and ΔR ₀ when the temperature is t°C.

Also, let the values of R _A , R _B and △R ₀ at 0°C be R _A (0), R _B (0) and △Ro (0), respectively, and the values of Rout and Rin at 0°C. Rout each value
(0), Rin (0), the above (1), (2) and (3)
The formula is expressed as follows.

R _A (0) = R ₀ + Rout (0) ......(1)'' R _B (0) = Rin (0) ...... (2)'' △R ₀ (0) = R ₀ + Rout (0) - Rin(0)
......(3)'' Here, the resistance change amount ΔR of the temperature sensitive resistor at t° C. with 0° C. as a reference is expressed as follows.

△R={R _A (t)−R _B (t)} −{R _A (0)−R _B (0)} ………(4) = △R ₀ (t)−△R ₀ (0) ………(5) = [R ₀ (1 + αt) + {Rout (t) − Rin (t)}] − [R ₀ + {Rout (0) − Rin (0)}] ………(6) = R ₀ αt+[{Rout(t)−Rout(0)} −{Rin(t)−Rin(0)}] ………(7) The second term on the right side of equation (7) above, which is the measurement error, is Since the only difference is the change due to temperature between the resistance on the output end side and the resistance on the input end side of the strain gauges _SG1 to _SG4 , it is sufficiently smaller than the value of the first term on the right side of the above equation (7). Therefore, the above equation (7) can be expressed as the following equation (8).

△R≒R ₀ αt ………(8) From the above equation (8), the temperature t is t≒△R/R ₀ α={R _A (t)−R _B (t)}−{R _A (0 )
−R _B (0)}/R ₀ α……(9). Therefore, the above R _A (t),
Measure the values of R _B (t), R _A (0), and R _B (0), and find the resistance change amount R ₀ α per 1°C of the combined resistance R of the temperature-sensitive resistor from a temperature calibration test. Accordingly, the temperature (t) can be obtained from the above equation (9).

Next, temperature measurement when the resistance r of the lead wire is taken into consideration will be explained. FIG. 4 shows a circuit similar to that in FIG. 3 when the resistance r of the lead wire is taken into consideration.

Now, if the resistance between the output terminals 12' and 13' is R _A ', and the resistance between the input terminals 10' and 11' is R _B ', then R _A '=R ₁ +R ₂ +Rout+2r ......(10) R It is expressed as _B ′=Rin+2r (11). Here, if the value obtained by subtracting equation (11) from equation (10) above is △R ₀ ′, then △R ₀ ′=R ₁ +R ₂ +Rout−Rin (12), and the resistance r of the lead wire becomes irrelevant. Therefore, R _A (t)−R _B (t), R _A (0)−R _B in the above equation (9)
(0) is also independent of the resistance r, and the temperature t can be determined independent of the resistance r of the lead wire.

Next, the influence of the temperature sensitive resistor on the strain measurement of the transducer will be explained.

First, a case will be explained in which a zero-point indicator is used. FIG. 5 shows an outline of the measurement circuit, and FIG. 6 shows its equivalent circuit. In FIG. 5, 14 is an indicator including a dial bridge 15, an amplifier 16, a meter M, etc. Also, in Figure 6,
Rg is the impedance of the bridge circuit, Rc is the impedance of the dial bridge, R _L is the input impedance of the indicator, e _g is the voltage generated by the bridge circuit, e _c is the voltage generated by the dial bridge,
e is the voltage across the input impedance of the indicator, R
is the resistance of the temperature sensitive resistor, and 2r is the reciprocating resistance of the lead wire.

The following equation is derived from the equivalent circuit shown in FIG.

e=R _L /Rg+R+2r+R _c +R _L (e _g +e _c ) ...... (13) The zero-order method sets e in the above equation (13) to zero. In other words, in the term on the right side of equation (13) above, (e _g +
e _c ) becomes zero, that is, e _c opposing e _g
Since _this is a measurement method that generates a No error occurs in the value.

Next, a case will be explained in which a deflection method indicator is used. FIG. 7 shows an outline of the measurement circuit, and FIG. 8 shows an equivalent circuit. From the equivalent circuit in Fig. 8, the voltage e across the input impedance R _L of the indicator 14 is expressed as e=R _L /R _g +R + 2r + R _L e _g (14), and depending on the values of R and 2r, e changes.

Here, if R _L is sufficiently large, e is hardly affected by R and 2r. For example R _L
=1MΩ, R=10KΩ, R _g =350Ω, 2r=79.6Ω
(If 0.5 mm ² 4-core lead wire is connected for 1000 m), e will be 0.99 times that without R and 2r, and the output will only decrease by 1%.

In the above embodiment, four strain gauges SG ₁ to _{SG 4} are used in the transducer constituting the bridge circuit.
Although we have explained an example using the strain gauge SG ₁ , there are other ways to use the
Fixed resistors may be used only for SG ₁ and SG ₂ on other sides of the bridge circuit.

Further, although two temperature-sensitive resistors are provided in series on the output side of the converter 7, they may be provided in series on only one of the output sides. As this temperature-sensitive resistor, for example, a thermistor or a metal wire (platinum wire, nickel wire, indium wire, etc.) temperature-detecting resistor, which has been widely used in the past, can be used, but recently developed porcelain 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 to use a complicated correction circuit such as an analog calculation circuit.

On the other hand, metal wire resistance thermometers such as platinum wire and nickel wire have low resistance values (for example, platinum resistance thermometers are 50Ω and 100Ω as specified in JISc ₁₆₀₄ ), so contact resistance and wires in signal circuits There are disadvantages such as resistance having a large effect, being susceptible to external influences, small output signal, and poor instrumentation due to the large size.

In contrast to these, the above-mentioned insulation-coated type temperature-sensitive resistors are electrochemically stable at high temperatures and are made of a special porcelain insulator with excellent thermal conductivity. Materials include nickel, iron,
The main component is chromium and several other metals are added as additives to obtain the desired resistance value and temperature coefficient of resistance). The temperature/electrical resistance characteristics are linear, and resistances ranging from low resistance (several Ω) to high resistance (about 10KΩ) can be obtained. For example, use a relatively high resistance one. In this case, the contact resistance and the line resistance of the signal system circuit are not a problem, and the rate of change in resistance against noise is advantageous because it is relatively large, and it can also cope with minute temperature changes.

As explained above, according to the present invention, the lead wires of the strain gauge type transducer can be connected easily and inexpensively by simply adding a temperature sensitive resistor in series to the output end of the conventional strain gauge type transducer. The behavior of the object to be measured is accurately converted into an electrical signal and output without increasing the number of lead wires, and the temperature near the object to be measured is calculated based on a predetermined calculation formula without being affected by the resistance of the lead wires. It is possible to provide a temperature measurement method using a converter with a temperature measurement function that can be obtained by performing the following steps.

Note that the above calculations are not limited to manual calculations, and can of course be easily performed using a computer.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams showing a conventional converter with a temperature measurement function, Figure 3 is a circuit diagram showing an embodiment of the present invention, and Figure 4 shows how to reduce the influence of lead wire resistance. A circuit diagram for explanation, Figure 5 is a measurement circuit diagram when using a zero point method indicator, Figure 6 is a measurement circuit diagram when using a zero point method indicator.
The figure is an equivalent circuit diagram of Figure 5, Figure 7 is a measurement circuit diagram when using a deflection method indicator, and Figure 8 is an equivalent circuit diagram of Figure 7.
FIG. 2 is an equivalent circuit diagram of FIG. SG ₁ to _{SG 4} ...Strain gauge, 6...Transducer with temperature measurement function, 7...Strain gauge type transducer, _R1 ,
R ₂ ...temperature sensitive resistor.

Claims (1)

[Scope of Claims] 1. A strain gauge type transducer that has a Wheatstone bridge that includes a strain gauge on at least one side, detects the behavior of an object to be measured as a strain amount, converts the strain amount into an electrical signal, and outputs it; A temperature measuring method using a converter with a temperature measuring function, which is combined with a temperature sensitive resistor connected in series to at least one output end of the Wheatstone bridge, comprising: 1
1°C of the combined resistance of one or more of the temperature sensitive resistors
The amount of resistance change Ro・α (where Ro is the combined resistance of the temperature-sensitive resistor at 0°C, and α is the temperature coefficient of resistance of the temperature-sensitive resistor) is determined in advance by a temperature calibration test, and then Resistance R _A at a temperature of 0°C as seen from the output end and input end of the Wheatstone bridge that includes the temperature-sensitive resistor on its output end side
( ₀ ) and resistance R _B ( ₀ ) are measured in advance, and the temperature at t°C at the time of temperature measurement as seen from the output end and input end of the Wheatstone bridge including the temperature sensitive resistor on its output end side is determined. Resistance R _A (t) and resistance
Actual measurement of R _B (t), resistance change amount Ro・α obtained as above, resistance R _A ( ₀ ), resistance R _B ( ₀ ), resistance
Let the values of R _A (t) and resistance R _B (t) be t=
{R _A (t)−R _B (t)}−{R _A ( ₀ )−R _B ( ₀ )}/Ro・
A temperature measurement method using a converter with a temperature measurement function, characterized in that the temperature t° C. at the time of temperature measurement is obtained by substituting into an arithmetic expression α.