JPS5838824A - Temperature measuring system - Google Patents

Abstract

PURPOSE:To perform the accurate temperature measurement, by measuring the temperature at the same one position by two pairs of different thermocouples, and obtaining the measured temperature from the thermal electromotive forces. CONSTITUTION:The temperature at the same one position is measured by temperature measuring contact points A and D of two pairs of the different thermocouples 1 and 2. The thermal electromotive forces at reference contact points B, C, E, and F are inputted into a receiving meter 5, and the temperature is computed by an operator. Since two pairs of the thermocouples 1 and 2 are used for determining the temperature, no compensation error is present and the accurate temperature measurement is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature measurement system that uses thermocouples to measure temperature.

As is well known, when the temperature of a reference junction (cold junction) of a thermocouple changes, errors occur in the measurement results. Conventionally, the following measures have been taken to compensate for this measurement error.

(1) Method of keeping the reference junction at a constant temperature. Figure 1 shows the schematic configuration of a temperature measurement system using this method.

In this figure, numerals 1 and 2 are thermocouple wires, and numeral 2 is their contact point, that is, a temperature measuring junction. Thermocouple wire 1 and copper conductor wire 4
The contact point 1 between the thermocouple iI2 and the copper conducting wire 4b are both reference junctions, and are inserted into the freezing point bath 3 and maintained at 0°C. According to such a configuration, a thermoelectromotive force determined only by the temperature of the temperature-measuring contact point can be obtained at the open end of the copper conducting wire. The temperature is measured by measuring this thermoelectromotive force with a receiving instrument.

(8) A method of performing temperature compensation of the reference junction using the input circuit of the receiving instrument. As shown in Figure 2, the thermocouple wire 1.2 is directly input to the receiving instrument, and in this case the temperature of the reference junction λO cannot be kept constant.To compensate for this, for example, the input circuit is made into a bridge circuit, and As part of the resistance, a reference junction temperature compensation resistor R(l) having an appropriate temperature coefficient is provided near the reference junction 1, a.

Such a configuration compensates for measurement errors. When the remote temperature tl is constant, this method is often used by connecting compensation conductors 7.8 in series with the thermocouple wires 1.2, as shown in FIG.

By the way, the conventional temperature measurement system described above has the following drawbacks.

In the method (1), the freezing point tank 3 for keeping the temperature of the reference junctions B and 0 at the freezing point is expensive and troublesome to maintain. A tank 3 is often required, which has the drawback of increasing costs and maintenance work.

In the method (2), the error of compensation by the compensation conductor 7.8 and the error of the reference junction compensation circuit in the input circuit of the receiving instrument 6 are added to the error inherent in the thermocouple, resulting in a reduction in measurement accuracy. Furthermore, if the distance between the measuring point and the receiving instrument 6 is long, a large number of expensive compensating conductors are required, resulting in increased costs.

In view of the above-mentioned circumstances, the present invention provides a temperature measurement system that can accurately measure the temperature of a point to be measured without using a freezing point bath, a compensation conductor, or a compensation circuit. The temperature is measured using two different pairs of thermocouples, and the temperature is measured based on the different thermoelectromotive forces obtained from these thermocouples.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a schematic configuration diagram showing the configuration of an embodiment of the present invention. In this figure, α is a thermocouple having a thermocouple wire 1.2 and a temperature measuring junction M which is the connection point of these wires, and the thermocouple M
The reference junctions 1, C of 1, 2 are connected to the input terminals of the receiving instrument 5 via copper conductors 10&, respectively. Also, β is a thermocouple 1i made of a different material from the thermocouple wire 1.2! 11
．． 12 and a thermocouple having a temperature measuring junction which is the connection point of these, and the reference junction X%A of each thermocouple wire 11. It is connected to the. The receiving instrument 5 is configured using, for example, a microprocessor, and receives thermoelectromotive force 1 obtained from the thermocouple α.
α and the thermoelectromotive force Iβ obtained from the thermocouple β are measured,
Calculation is performed based on this measurement result and the measured temperature t! 11.

Next, the calculation operation in the receiving instrument 5 will be explained.

Generally, the thermoelectromotive forces Z and V of a thermocouple are set at a reference junction temperature of 0°C.
Then, it is a function of the temperature measuring junction temperature t'', and is expressed by the following equation.

IC=t(t)...
...(1) Furthermore, the form of the function r(t) is "0 from J
1602 Thermocouple", each thermocouple is shown in the form of numbers and formulas.

Regarding the two different types of thermocouples a1β,
Each thermoelectromotive force ma・1β is x a= t a(t)...
(2) Eβ=fβ(1) Song...(3)
becomes. Now, the temperature measurement junction temperature of thermocouples α and β are both 70℃.
, the reference junction temperature is tr℃, the thermoelectromotive force 1ta% Mβ of each thermocouple is 1ia-'g(tm'
fa(tr) ・・・・・・(4) Tobi β=fβ(1
m) -1β(tl) ......It is fitted according to the formula (5). Since the thermoelectromotive force lα and Iβ are obtained by measurement, it is (4)%.Equation (5) is an unexpressed number t.

For simultaneous equations with and tr, there is generally a solution.

If tr is eliminated from equations (4) and (5), 'a(fa(
tm3 Ig)-/'jβ(tl(t,)-1β)=
0...-(III) Therefore, by solving equation (6) by the arithmetic unit, such as a microprocessor, in the receiving instrument 6, υ and the measured temperature t can be obtained. Since the uncalculated number tr (reference junction temperature) is eliminated in equation (6), the calculation result t,! l is determined by 1 thermoelectromotive force, Σβ, and the reference junction temperature tr
It can be seen that it is not affected at all.

Incidentally, if the receiving instrument already has an arithmetic function, this can be used for the tt, and there is no need to take the trouble to provide a new receiving instrument for this embodiment.

In the above embodiment, if one thermocouple wire 2.11 of each of the thermocouples α and β is made of the same material, the thermocouple wire 2.11e made of the same material as shown in FIG. It may be configured in common.

In this linear wire configuration, the thermoelectromotive force error of the thermocouples α and β is based on the uniformity, heterogeneity, thermoelectromotive force characteristic force stability, etc. of the commonly used thermocouple wires 2.11. There is an advantage that the thermoelectromotive force error has little influence on the final result since it equally affects the pair a1β. Further, since it has a five-wire configuration, there is an advantage that the number of extension wires (copper conductive wires) and input terminals of the receiving instrument 5 can be reduced. Specifically, a combination of thermocouples that can be configured in this manner is a combination of thermocouple 1 and thermocouple J according to the standard.

Furthermore, in the case of such a 51m structure, it is also possible to measure the voltage between two wires that are not common, and to estimate the measured temperature t from this result.

Further, in this embodiment, the thermoelectromotive force K measured by the receiving instrument 5
a,! Based on β, various calculations are performed to determine the measured temperature tm1
However, there is a chart for easily determining the measured temperature 131,
Create a table or formula in advance and measure the temperature [
1, is also possible. Figure 6 shows an example of such a diagram.

This chart is 1 stipulated in "J Engineering 801602 Thermocouple"
This is a chart for calculating the measured temperature ft from the thermoelectromotive force of both using a thermocouple and a J thermocouple. For example, the thermoelectromotive force of 1 thermocouple is 52-06mV, and the thermoelectromotive force of W thermocouple is 23.52mV.
m V, the measured temperature t is determined from the coordinates of the intersection point.
! It can be seen that Il is 4〒5℃. Furthermore, if this chart is enlarged and created, the measured temperature t can be measured with an accuracy of 1 to 2°C.

In addition, in this embodiment, when there are many measurement points, if the output of the thermocouple installed at each measurement point is switched immediately after each thermocouple or near the input terminal of the receiving instrument 6, the receiving instrument 5 can be Since only a single measuring point is required, the price of the system with one measurement point can be further reduced.

By the way, if both tel and fβ are functions extremely close to a straight line, both the values of the measured temperature t and the reference junction temperature t1 are the thermoelectromotive force m,...! It goes without saying that it cannot be determined uniquely from β. Immediately after the temperature starts to rise), the disadvantage is that the measurement error increases.

That is, in 'm'Wtr, in the above formula (4), I a 'q O, lβ-O, tyo and t
The value itself is indefinite while maintaining the condition that l is approximately equal. Therefore, mathematically, even if solutions to equations (4) and (6) exist, the obtained values will have a large error. This means that the thermoelectromotive force becomes smaller in Figure 6.
This is clear from the fact that the isotherms become denser.

On the other hand, s ty (usually exact t in '-4tr,
The value of is not required and is often sufficient as long as it does not deviate significantly from the true value. Therefore, the following method can be considered as a temperature measurement method at tm-tr.

Appropriate t for cabinets with tll1-1r>0 and 1m-1r=0
Set the thermoelectromotive force of either thermocouple and set this value]! ! 0, Iα≦Eo (or lβ
≦Io), the reference junction temperature tr is set in advance to a certain constant value tro, and this tre is substituted into tr in the above-mentioned equation (4) or (5) to obtain the measured temperature t! Calculate Il. (In addition, from both equations (4) and (6), the measured temperature Wt
m may be determined and these values may be averaged. ) That is, when the calculation result is tmitIl11, equation (7) is obtained.

tm+=? 'a(f*(tro)+Ia)
``'' (7) When Kg>Io, two obtained from equation (6) is M6M.

Now, let t,1 obtained from equation (7) be tI! Let it be l.

When the t values obtained in this way are plotted as a graph with χα as an independent variable, it becomes as shown in FIG. In this figure, the song 111rJ1 represents equation (6), and the curve L! represents the (Te) expression. Also, in this figure (6)
The value of 1β in the equation is the value when tr is fixed at a certain constant value, but when %tr changes, the song *Ls changes as shown by the broken line in the figure.

As can be seen from the figure, at a depth f4°, the spider) formula, (7)
tlII 0% t12+1, which are obtained from the equations, are generally discontinuous, and this discontinuity is inconvenient, for example, when temperature control is performed on the object to be measured.

For this reason, 1α! . At tyo. Set a function that gives tm mushrooms that are continuous with 0. For example, the following equation satisfies this.

If this equation (8) and the above-mentioned equation (6) are reduced to 7, they become continuous at the point 1m, 1o, as shown in Figure 8.
As can be seen from equation (8), when tag is near l a tx Q, the influence of tWO, which has a large error, does not become O at all in this vicinity, which causes an error in the measurement result. Therefore, to avoid this, o <m D<!
. Set l that satisfies, and t in the range of α≦ID! ,
Using the (Ma) formula, which has no shadow change of lo, in the range of ID
lllll and continuous function t1. Introducing la.

For example, the following formula satisfies this condition.

In this way, the range is divided into three depending on the value of IeeIl, and a different formula is used in each range to calculate the measured temperature tI.
llt-calculate. In the range of X > 10 (6
) expression 1! iI) ◇-ku! . Expression (9) within the range of m,
Figure 9 shows a graph when the measured temperature t is calculated using the formula () within x ranges.
) is continuous over the entire range. Note that in the above explanation, the measured temperature ftm is the thermoelectromotive force 1. Although treated as a function of , of course, it may also be treated as a function of thermoelectromotive force 1β.

In this way, the above method generates thermoelectromotive force α (mojiku is 1β)
Depending on the value taken, the measured temperature ft! Since the formula for calculating l is changed, the measured temperature [1,] can be calculated extremely accurately regardless of the magnitude of the thermoelectromotive force 1a (or lβ).

As explained above, according to the present invention, the temperature at the same location is measured with two different pairs of thermocouples, and the -j constant temperature is determined from one thermoelectromotive force obtained as a result of both thermocouples. , the following effects can be obtained.

■ A reference junction device such as a freezing point tank is not required, so the warm mm running system is easy to maintain and its configuration is simple. - Compensating conductors are not required; instead, ordinary copper conductors can be used instead, reducing the cost of constructing the system, especially in the case of telemetry systems. ■No compensation conductor is required, and there is no need for a reference junction compensation circuit in the input circuit of the receiving instrument, so there is no compensation error caused by them.
Therefore, highly accurate gIAll! Be able to make decisions.

[Brief explanation of the drawing]

Figures 1 to 2 are schematic diagrams showing the configuration of a conventional one-time measurement system, Figure 4 is a schematic diagram showing the configuration of an embodiment of the present invention, and Figure 3 shows the thermocouple a5 Figure 6, which shows the configuration when the i configuration is used, is 1N! Constant temperature 1. from each thermoelectromotive force of a thermocouple and 1 thermocouple. Diagram for finding
Figures 7 to 9 show the measured temperature t for the thermoelectromotive force 1α.
FIG. 1 is a diagram showing a change in number. α, β...Thermocouple, 5...Receiving instrument. Figure 1 Figure 7 / Figure 8

Claims (1)

[Claims] L. It is characterized by comprising a thermocouple that measures the temperature at the same measurement point and generates two types of thermoelectromotive force, and measures the temperature at the measurement point based on the two types of thermoelectromotive force obtained by the thermocouple. temperature measurement system.