JPS6347627A - Temperature transducer - Google Patents

Abstract

PURPOSE:To enhance accuracy and to reduce cost, by a method wherein the voltage of a thermocouple is subjected to pulse width modulation to be converted to a pulse and an AND circuit is driven by said pulse to obtain the power of the voltage of the thermocouple and this voltage is added and subtracted in a predetermined ratio to perform error correction. CONSTITUTION:A differential circuit 4 outputs the difference voltage ET of the temp.-sensitive voltage of a thermocouple 1 and the correction voltage of a reference contact correction circuit 2. The voltage ET is converted to the pulse of the duty ratio proportional to the voltage ET by a pulse width modulation circuit 11 to be inputted to an AND circuit 13. Then, reference DC voltage is subjected to switching control based on the output pulse of the circuit 11 by a first switch S1 and smoothed by a first filter A1 to output average voltage E1. Further, average voltage E2 is formed from voltage E1 by a second switch S2 and a second filter A2 and, hereinafter, average voltages E1-En up to an n-th switch Sn and an n-th filter. An are formed. These voltages are added and subtracted in a predetermined ratio to calculate temp. subjected to error correction. By this method, measuring accuracy is enhanced and cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a temperature transducer using a thermocouple as a temperature sensing element.

[Conventional technology]

In a temperature transducer that uses a thermocouple as a temperature sensing element, the output voltage of the thermocouple does not have a linearly proportional relationship with the temperature, so error correction means is provided to correct this nonlinear error. is common. Conventional examples of this error correction means include one composed of a microcomputer including an A/D converter and ROM, and one composed of a resistor,
There were broken line approximation circuits made up of capacitors, diodes, etc. A conventional example of a thermometer using a thermocouple as a temperature sensing element is disclosed in Japanese Patent Application Laid-Open No. 129630/1983, and its configuration is shown in FIG. 3 in the figure, (
1) is a thermocouple, (2) is a reference junction compensation circuit, and (3) is an error correction means, which is a differential circuit in which the output of the thermocouple (1) and the output of the reference junction compensation circuit (2) are connected. 4), A/
It consists of a microcomputer (6) with a D converter (5) and a ROM (6M). (7) is a decoder circuit connected to the output of the error correction means (6), and (8) is a display circuit connected to the output of the decoder circuit (7).

Next, the operation will be explained. When measuring temperature, use a thermocouple (1
) and the reference junction compensation circuit (
The compensation voltages formed in step 2) are each applied to the error correction means (
3) is sent to the differential circuit (4), and the difference between the two types of pressure is obtained as the output of this differential circuit (4).

In thermometers using thermocouples, the reference junction is 0°C.
If you measure the temperature of the object at a temperature other than that, for example, the same temperature as room temperature, the measured value will be different from the value obtained when the temperature of the reference junction is held at 0°C. Therefore, a deviation occurs by an amount corresponding to the above room temperature. The compensation voltage mentioned above is for canceling out this deviation.

On the output side of the differential circuit (4), as described above, a voltage that is the difference between these compensation voltages and the voltage of the thermoelectromotive force appears. This difference voltage is transferred from the differential circuit (4) to the A/D converter (5).
) is sent to the microcomputer (6) as a temperature measurement signal, and its nonlinear characteristics are converted into linear characteristics. After that, it is added to a display circuit (8) having, for example, a liquid crystal element via a decoder circuit (c), so that the measured temperature can be displayed.This non-linear characteristic is converted into a linear characteristic. First, the analog temperature measurement signal input from the differential circuit (4) is sent to the A/D converter (5).
) and sent to the microcomputer (6). In this microcomputer (6), a thermocouple (1
) is stored, and this data is called at a predetermined timing and used to linearize the temperature measurement signal sent from the A/D converter (5). It performs arithmetic processing and then sends it to the decoder circuit (7).

[Problem that the invention seeks to solve]

Thermometers that use a microcomputer, such as the conventional temperature transducer described above, can perform complex arithmetic processing on the temperature measurement signal, improving measurement accuracy, but they have many relatively expensive parts and the equipment is expensive. There was a problem in that it became high. In addition, those using a line approximation circuit consisting of resistors, capacitors, diodes, etc. have low measurement accuracy due to drift due to temperature changes, and depending on the type of thermocouple, each constant that determines the line characteristic There were problems such as the need to experimentally determine the

This invention was made to solve the above-mentioned problems, and its purpose is to obtain an inexpensive and highly accurate temperature transducer.

[Means for solving problems]

The temperature transducer according to the present invention converts the voltage of the difference between the compensation voltage and the voltage of the temperature sensing element into a pulse width modulation signal I, and converts the average voltage E1 of the logical product of the reference DC voltage 22 and the pulse width modulation signal into the pulse width modulation signal I. 1 circuit, and a second circuit to create an average voltage E2 of the AND of the average voltage E1 and the pulse width modulation signal,
Below, the average voltage up to tube n...in is created up to the nth circuit, and the average voltage is.

E2. ...Fin is added or subtracted at a predetermined ratio and error correction is performed to obtain a DC voltage proportional to temperature.

[For production]

The temperature transducer according to the present invention has an average voltage E1 of the AND of a pulse width modulation signal and a reference DC voltage KT corresponding to the difference between the compensation voltage and the voltage of the temperature sensing element, and an average voltage E1 of the AND of the pulse width modulation signal and the reference DC voltage KT. The error-corrected temperature is calculated by adding and subtracting the average voltage E2 of the logical product and the average voltage .

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) is a thermocouple, (2) is a reference junction correction circuit, (6 is an error correction means, and (4) is a thermocouple (1).
) is a differential circuit to which the output of the reference junction compensation circuit (2) is connected, (11) is a pulse width modulation circuit to which the output of the differential circuit (4) is connected, and (15) is a pulse width modulation circuit. (1
1) is an AND circuit connected to the output; (14) is an addition/subtraction circuit connected to each output of the AND circuit (13).

In addition, as in FIG. 5, a decoder circuit and a display circuit for displaying the measured temperature are provided on the output side of the addition/subtraction circuit (1), but are not shown here. This is a diagram showing the AND circuit (16) in Figure 1 in more detail. In the figure, Kz is the reference DC voltage, (Sl
) is the first switch to which the reference DC voltage 'Hz is connected,
(A1) is the first filter to which the output of the first switch (Sl) is connected, (Sl) is the first filter (A1)
(A2) is a second filter to which the output of the second switch (Sl) is connected;
Below, switches and filters are connected in series, (Sn
) is the n-th switch connected to the output of the (n-1')-th filter (not shown), and An is the n-th switch (Sn
) is connected to the nth filter. The output of the pulse width modulation circuit (11) is connected to the control terminals of the first to nth switches (s+)t(82), . . . (Bn).

Next, the operation will be explained. In Figure 1, a thermocouple (
1), the reference junction compensation circuit (2) and the differential circuit (4) operate in the same way as the circuit shown in Figure 5 above, and a thermocouple is installed on the output side of the differential circuit (4). A voltage ET corresponding to the difference between the thermoelectromotive force (1) and the compensation voltage of the reference junction compensation circuit (2), that is, the temperature to be measured, is obtained.

This voltage ET is pulse width modulated by a pulse width modulation circuit (11) and converted into a pulse with a duty ratio proportional to the voltage X. This pulse satisfies the following equation (1), assuming that it has an on period T+ and an off period T2.

This pulse is input to the next AND circuit (13).

This AND circuit (13) is constructed as shown in FIG. 2, and its operation is as follows. The reference DC voltage XZ is controlled on and off by the output pulse of the pulse width modulation circuit (11) in the first switch (Sl), and the output 11 is converted into a pulse as shown in Fig. 3 (1).

The pulse output 11 is smoothed by the following first filter (A1), and its average voltage E1 is expressed by the following equation (2).

Next, the output voltage E1 of the first filter (A1) is applied to the output voltage E1 of the pulse width modulation circuit (11) (for example, the output of the photocoupler in the output stage of the pulse width modulation circuit (11)) at the second switch (Sl). Controlled on/off by pulse, its output L
2 is converted into a pulse as shown in Figure 6 (2). The pulse output 12 is smoothed by the following second filter (A2), and its average voltage E2 is expressed by the following equation (3).

Similarly, switches and filters are successively connected in series, and the output Ln of the n-th switch (Sn) has the waveform shown in Figure 6-4>, and the output Ln of the n-th filter (An)
The average voltage En is expressed by the following equation (4).

However, in equation (4), En-1 indicates the output voltage of the (n-1)th filter (A211-1). In this way, in the AND circuit (15), the DC voltages E+ and E2 are proportional to the power of the voltage ET corresponding to the temperature to be measured.
, . . . En is obtained. Each output voltage E+, E2 . of the next AND circuit (13). ...in is an addition/subtraction circuit (14
) is added or subtracted at a predetermined ratio to obtain the output voltage Eo shown by the following equation (5).

E (1=ICIEj+ to 21!!2+---10Kn
En=zz (K+ET 10 to 21!i ding 10--...+Kn
KT")" (51 When obtaining a DC voltage that is linearly proportional to temperature from the temperature-output voltage characteristics of a thermocouple, +, [2,... the magnitude of Kn and the positive and negative The sign can be determined according to the curve of each thermocouple. Therefore, in the circuits shown in FIGS. ) for each coefficient +, K2...K
If n is selected according to the characteristic curve of the thermocouple, a DC voltage proportional to the input temperature l can be obtained. Note that the switch in Figure 2 is a 0-MOS analog switch or a 111F switch.
The T filter can be constructed from a simple circuit such as an OR integration circuit or an integration circuit combining an operational amplifier, a capacitor, a resistor, etc.

In the above embodiment, the reference voltage E2 and the first switch (Sl) are provided independently, but as shown in FIG.
- A similar effect can be obtained by using a MOS inverter, WAND gate, or other logic.

〔Effect of the invention〕

As described above, according to the present invention, the error correction means pulse-width modulates the voltage from the thermocouple, and uses this pulse to drive an AND circuit consisting of a switch and a filter in series, thereby adjusting the voltage from the thermocouple. The system is configured to correct errors in the temperature-output voltage characteristics by obtaining the power of
Moreover, effects such as being able to calculate addition/subtraction coefficients depending on the type of thermocouple can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a temperature transducer according to an embodiment of the present invention, FIG. 2 is a configuration diagram of an AND circuit in FIG. 1,
FIG. 3 is an explanatory diagram of the operation of the AND circuit in FIG. 2, FIG. 4 is a configuration diagram showing another embodiment of the first switch (Sl) in FIG. 2, and FIG. FIG. 2 is a configuration diagram of a transducer. In the figure, (1) is a thermocouple, (2) is a reference junction correction circuit, (4) is a differential circuit, (11) is a pulse width modulation circuit,
(13) is an AND circuit, (1 is an addition/subtraction circuit, (30)
is error correction means, (S+) to (Sn) are switches, (
A+) to (An) are filters. In each figure, the same reference numerals indicate the same or similar parts. Figure 2 Figure 4 x Figure 5

Claims (1)

[Claims] A thermoelectromotive force generated by heat applied to the temperature-sensing element using a thermocouple whose reference junction is temperature-compensated by a compensation voltage from a reference-junction compensation circuit. In a temperature transducer that outputs a DC voltage proportional to temperature by passing the DC voltage through an error correction means, the error correction means is configured to output a DC voltage proportional to the temperature by adjusting the difference between the compensation voltage from the reference junction compensation circuit and the voltage from the temperature sensing element. A differential circuit that outputs a voltage proportional to the output voltage, a pulse width modulation circuit that outputs a pulse with a duty ratio proportional to the output voltage of this differential circuit, a reference power supply that outputs a reference DC voltage Ez, and a reference power supply that is connected to this reference power supply. A first switch whose opening/closing is controlled by the output pulse of the pulse width modulation circuit, and a voltage having a peak value Ez outputted from this first switch is smoothed to obtain a first DC voltage E_
1, a second switch connected to the output side of the first filter and whose opening/closing is controlled by the output pulse of the pulse width modulation circuit, and a peak value E_1 output from the second switch. a second filter that smoothes the voltage of the second DC voltage E_2 and outputs the second DC voltage E_2; an AND circuit including switches and filters sequentially arranged in series up to the n-th filter; and the first, second, . . .・nth DC voltage E_1
, E_2, . . . En as input, and an addition/subtraction circuit that performs addition and subtraction at a predetermined ratio.