JPS623629A - Reference contact connection box - Google Patents

Abstract

PURPOSE:To transmit the thermoelectromotive force of a thermocouple to an instrument body without being affected by the variation of the temperature of a reference contact and the noise, by providing an electrophoto converting circuit having a light emitting element, a detecting circuit which detects the variation of temperature, and a temperature compensating circuit. CONSTITUTION:In a connection box 1, the thermoelectromotive force of each thermocouple 2 is converted to a corresponding optical signal by an electrophoto converting circuit 6 and is transmitted to the instrument body through an optical fiber 14. In this case, a part of the optical signal emitted from a light emitting element 12 of the electrophoto converting circuit 6 is received by a detecting circuit 16 to detect the temperature variation of the electrophoto conversion efficiency of the light emitting element 12. The detection signal outputted from the detecting circuit 16 in accordance with the temperature variation of the light emitting element 12 is used as a temperature compensating signal. That is, the thermoelectrpmotive force changed by the temperature of the reference contact of the thermocouple 2 is compensated with respect to temperature on a basis of the detection signal given form the detecting circuit 16. Thus, data of the thermoelectromotive force obtained by the thermocouple 2 is transmitted to the instrument body without being affected by the variance of the temperature of the reference contact and the noise.

Description

[Detailed description of the invention] (a) Industrial application field The present invention is applicable to multi-point temperature measurements using thermocouples.
The present invention relates to a reference junction connection box interposed between the thermocouple and a measuring instrument body in order to compensate for thermoelectromotive force that changes depending on the temperature of the reference junction of the thermocouple.

(b) Prior art and its problems In general, for example, in various equipment industrial plants, etc., when monitoring the operating conditions of heat treatment equipment,
Multipoint temperature measurements are performed using thermocouples. In such a case, if the measurement point where the thermocouple is installed and the measuring instrument body that processes the temperature data obtained from this are far from each other, connect the reference junction near the measurement point as shown in Figure 4. A configuration is adopted in which a box a is provided, each thermocouple is temporarily assembled in this reference junction junction box a, and then connected from this reference junction junction box a to the measuring instrument main body d via a copper conducting wire C.

The thermoelectromotive force of a thermocouple changes depending on the temperature of its reference junction. Therefore, it is necessary to compensate for changes in the thermoelectromotive force depending on the temperature of the reference junction, so conventionally, the terminal portion connecting the thermocouple and the copper conductor C is heated or cooled to keep the temperature constant. Alternatively, as shown in FIG. 4, a thermocouple e is separately provided to measure the temperature at the connection part of the reference junction junction box a with the thermocouple, and this thermocouple e is extended to the side of the measuring instrument main body d. Based on the temperature data obtained by the thermocouple e, measures are taken to compensate for the thermoelectromotive force that varies depending on the temperature of the reference junction of the thermocouple.

However, in such a conventional configuration, the voltage of several mV to
Since it is necessary to transmit a minute voltage signal of several tens of IRv over a long distance from the reference junction junction box a to the measuring instrument main body d via the copper conductor C, it is easily affected by noise during transmission. In addition, the number of copper conductive wires C corresponding to each thermocouple is required, and thermocouples e for temperature measurement may also need to be provided, which increases the number of wires and increases the cost of wiring work. There is a problem.

The present invention has been made in view of these circumstances, and is capable of transmitting the thermoelectromotive force of a thermocouple to the measuring instrument body without being affected by temperature changes at the reference junction or noise during transmission. Moreover, the wiring cost can be reduced, and the reference junction can reliably compensate for changes in the thermoelectromotive force of the thermocouple depending on the temperature of the reference junction, without the need for a dedicated sensor for temperature compensation. The purpose is to provide connection boxes.

(c) Means for Solving the Problems In order to achieve the above object, the present invention provides an electro-optical conversion circuit having a light emitting element that converts the thermoelectromotive force of a thermocouple into an optical signal corresponding to the electromotive force of the thermocouple, a detection circuit that receives a part of the optical signal from the light emitting element of the circuit and detects a temperature change in the electro-optic conversion efficiency of the light emitting element; The reference junction junction box includes a temperature correction circuit that corrects thermoelectromotive force that changes due to temperature changes.

(D) Function In the reference junction junction box of the present invention, the thermoelectromotive force of each thermocouple is converted into a corresponding optical signal by an electro-optical conversion circuit, and the optical signal is transmitted to the measuring instrument body via an optical fiber. At that time, a part of the optical signal emitted from the light emitting element of the electro-optical conversion circuit is received by the detection circuit, and a temperature change in the electro-optical conversion efficiency of the light emitting element is detected.

Then, a detection signal outputted from this detection circuit in response to a temperature change of the light emitting element is used as a temperature correction signal. That is, the temperature correction circuit corrects the thermoelectromotive force that changes depending on the reference junction temperature of the thermocouple based on the detection signal provided from the detection circuit.

(e) Examples Hereinafter, the present invention will be explained in detail based on examples shown in the drawings.

FIG. 1 is a block diagram showing the configuration of a reference junction junction box according to an embodiment of the present invention. In the figure, reference numeral 1 designates the entire reference junction junction box, which is composed of an electro-optical conversion circuit 6, a detection circuit 16, and a temperature correction circuit 24, which will be described later. 2 is a large number of thermocouples connected to this reference junction junction box 1, and 4 is a multiplexer for selecting the connection of each thermocouple 2.

6 is an electro-optical conversion circuit that converts the thermoelectromotive force of each thermocouple 2 into a corresponding optical signal. This electro-optical conversion circuit 6 includes an A/D converter 8 that digitizes the thermoelectromotive force of each thermocouple 12 inputted via the multiplexer 4;
A parallel-to-serial conversion circuit IO and a parallel-to-serial conversion circuit 10 serialize the voltage signal digitized by the IO and send it out in a time division manner.
The light emitting element I2 is a laser diode in this example. The light emitting element 12 is mounted close to the multiplexer 4 in order to maintain the same temperature conditions as the reference junction of the thermocouple 2.

14 is an optical fiber for transmitting the optical signal from the light emitting element 12 to the measuring instrument in this example.

A detection circuit 16 receives a part of the optical signal emitted from the light emitting element 12 of the electro-optical conversion circuit 6 and detects a temperature change in the electro-optical conversion efficiency of the light emitting element 12. This detection circuit 1
Reference numeral 6 denotes a photodiode 18 that receives a part of the optical signal emitted from the light emitting element I2, a peak hold circuit 20 that holds the peak level of the output signal from the photodiode 18, and a peak level held by the peak hold circuit 20. and a comparator 22 that compares the level with a predetermined value and outputs a detection signal corresponding to the level difference between the two.

Reference numeral 24 denotes a temperature correction circuit for temperature-correcting the thermoelectromotive force that varies depending on the reference junction of the thermocouple 2 based on the detection signal from the detection circuit 16. This temperature correction circuit 24 is
a power control circuit 26 that outputs a power control signal for controlling the current value of the light emitting element 12 so that the peak value of the light emission power of the light pulse of the light emitting element 12 is constant based on the detection signal i from the comparator 22; The temperature correction calculation circuit 30 corrects the voltage signal based on the thermoelectromotive force from the thermocouple 2 based on both the power control signal output from the power control circuit 26 and the detection signal from the comparator 22. be done.

Further, 32 is a first alarm device that monitors the optical signal emitted from the light emitting element 12, and outputs an alarm signal if no optical signal is detected for a certain period of time or more.

Further, 34 is a second alarm device that monitors abnormalities in the control of the light emitting power, and outputs an alarm signal when the detection signal level from the comparator 22 deviates to a value exceeding a prescribed setting range. 36 is an OR circuit to which the first and second alarm devices 32 and 34 are connected in common, and the output terminal of this OR circuit 36 is connected to one input terminal of the multiplexer 4.

FIG. 2 is a block diagram of the signal input part of the main body of the measuring instrument that inputs the optical signal transmitted from the reference junction junction box l through the optical fiber 14 and measures the temperature at each measurement point detected by the thermocouple 2. It is. In the same figure, 40 is an optical fiber 14
42 is a serial/parallel conversion circuit that converts the pulse signal from the photodiode 40 into a parallel signal;
4 is a D/A converter that converts the signal parallelized by the serial/parallel converter circuit 42 into an analog signal.

The operation of each part of the reference junction junction box 1 having such a configuration will be explained.

The thermoelectromotive force of each thermocouple 2 is sequentially switched by a multiplexer 4 and input to the reference junction junction box 1. The thermoelectromotive force that changes depending on the input reference junction temperature is corrected by the temperature correction calculation circuit 30 and then
The signal is input to the D converter 8. The voltage signal input to the A/D converter 8 is converted into a digital signal here and then provided to the parallel-to-serial conversion circuit 10. The parallel-to-serial conversion circuit IO is
The input digital signal is serialized, time-divided, and output. The signal from the parallel-to-serial conversion circuit IO is converted into an optical signal by the next stage light emitting element 12, and this optical signal is transmitted to the measuring instrument main body via the optical fiber 14. On the measuring instrument main body side, a photodiode 40 receives an optical signal transmitted through an optical fiber 14, and a serial-to-parallel conversion circuit 42 parallelizes a pulse signal output according to the optical signal received from the photodiode 40. Then, convert this signal to D/
After converting into an analog signal by the A converter 44, various controls are performed based on the detected temperature at each measurement point.

On the other hand, a part of the optical signal emitted from the light emitting element 12 is received by the photodiode I8 of the detection circuit 16.

Therefore, the photodiode 18 outputs a signal corresponding to the light emission power of the optical signal emitted from the light emitting element 12. That is, the signal output level of the photodiode 18 is proportional to the light emission power of the light emitting element 12. This signal output level is then held by the peak hold circuit 20.

The comparator 22 compares the signal output level of the photodiode 18 held by the peak hold circuit 20 with a predetermined value set in advance, and outputs a detection signal corresponding to the level difference between the two. This detection signal is then transmitted to the power control circuit 26.
and temperature correction calculation circuit 30, respectively. The power control circuit 26 outputs a power control signal based on the input detection signal to the light emitting element 12 and the temperature correction calculation circuit 30, respectively. Thereby, the current value of the light emitting element 12 is controlled by the power control circuit 26 so that the light emitting power is constant.

Incidentally, there is a correlation between the light emitting power p1, current value, and temperature θ of the light emitting element 12 as shown in FIG.

Therefore, in order to always maintain the light emission power of the light emitting element I2 at a constant value, it is necessary to control the current value i flowing through the light emitting element 12, and at this time, the current value i becomes a function of the temperature θ.

For example, in FIG. 3, the emission power is set to a constant value p. When the current value flowing through the light emitting element 12 is i, the temperature at that time is θ2, and if the current value is 14, the temperature at that time is θ4. Therefore, if the current value i flowing through the light emitting element 12 and the light emitting power p are known, the temperature θ can be calculated.

The power control signal output from the power control circuit 26 and the detection signal from the comparator 22 are commonly input to the temperature correction calculation circuit 30 . The power control signal is transmitted to the light emitting element 12
Since the detection signal corresponds to the light emitting power p, the temperature correction calculation circuit 30 calculates the temperature θ based on both the manually inputted signals, and the calculated temperature θ
The thermoelectromotive force that changes depending on the reference junction temperature of the thermocouple 2 is corrected based on the following. Therefore, the temperature correction calculation circuit 30
From then on, the thermoelectromotive force corrected for the temperature change at the reference junction is always applied to the electro-optical conversion circuit 6.

Note that the output of the photodiode 18 of the detection circuit 16 is also given to the first alarm device 32, so if the light signal is not output from the light emitting element 12 for a certain period of time or more, the first alarm device 32 detects a transmission abnormality. An alarm signal is output.

Furthermore, since the detection signal output from the comparator 22 is given to the second alarm device 34, an alarm signal is output from the second alarm device 34 when an abnormality in the control of the light emitting power occurs.

The alarm signal output from the first alarm device 32 or the second alarm device 34 is manually inputted to the multiplexer 4 via the OR circuit 36, so that an optical signal is sent together with the voltage signal from the thermocouple 2 to the light-to-light conversion circuit 6. It will be converted into and transmitted to the measuring instrument main body.

(F) Effects As described above, according to the present invention, data on thermoelectromotive force obtained with a thermocouple can be transmitted to the measuring instrument body without being affected by temperature changes at the reference junction or noise. 7, the wiring cost can be reduced.

Furthermore, even without the provision of a sensor dedicated to temperature compensation, significant practical effects can be achieved, such as the ability to compensate for the temperature of the thermoelectromotive force that changes due to temperature changes at the reference junction of the thermocouple.

[Brief explanation of drawings]

Figures 1 to 3 show embodiments of the present invention. Figure 1 is a block diagram showing the configuration of a reference junction junction box, and Figure 2 is a measurement system that receives optical signals from the reference junction junction box. A block diagram showing the light-receiving part of the instrument body, Figure 3 is a characteristic diagram showing the temperature dependence of the light-to-light conversion efficiency of the light emitting element, and Figure 4 shows the connections of the conventional thermocouple, reference junction junction box, and measuring instrument body. It is an explanatory diagram showing a state. DESCRIPTION OF SYMBOLS 1... Reference junction junction box, 2... Thermocouple, 6... Electro-optical conversion circuit, 12... Light emitting element, 16... Detection circuit, 2
4...Temperature correction circuit.

Claims (1)

[Claims] (1) In a reference junction junction box provided to compensate for changes in the thermoelectromotive force of the thermocouple due to temperature changes at its reference junction, the thermoelectromotive force of the thermocouple is converted into an optical signal corresponding to this. an electro-optical conversion circuit having a light-emitting element; a detection circuit that receives a part of the optical signal from the light-emitting element of the electro-optical conversion circuit and detects a temperature change in the electro-optical conversion efficiency of the light-emitting element; A reference junction junction box comprising: a temperature correction circuit that corrects a thermoelectromotive force that changes depending on the reference junction temperature of the thermocouple based on a detection signal.