JPH0844436A - Burnout detection method and apparatus for thermocouple input circuit - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a burnout detection method and device for a thermocouple input circuit, and more particularly, to detecting an n-channel by a burnout detection circuit provided on the output side of a thermocouple signal selection switch. To aim. A burnout detection method and device for a thermocouple input circuit according to the present invention simplifies the burnout circuit configuration by detecting burnout at the output side (O ₁ ) of a thermocouple signal selection switch (1). The configuration is such that noise leakage between channels is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burnout detection method and apparatus for a thermocouple input circuit, and more particularly to a burnout detection circuit provided on the output side of a thermocouple signal selection switch.
A new improvement for detecting channel burnout.

[0002]

2. Description of the Related Art Conventionally, as a burnout detecting method and device for a thermocouple input circuit of this type, which has been conventionally used, the structure shown in FIG. 6 has been adopted. That is, FIG.
Those represented by the reference numeral 1 in a thermocouple signal selection switch having an input terminal I ₁ ~I _n of n channels, this the input terminals I ₁ ~I _n, thermocouples T ₁ ~ n-channel
Time constant circuits G _{1 to} G _{n of} T _{n, a} resistor R, and a capacitor C, and burnout circuits B _{1 to} B _n are respectively connected.

[0003] Each input I ₁ ~I _n of the thermocouple signal selection switch 1, the external address of the internal selection circuit 2 C
By addressed by an external signal 3a for the channel setting from the computer 3 of the PU or the like, in which selectively outputs data 4a to one output terminal O ₁ is outputted, to the output terminal O ₁ is An amplifier 4 is connected via a pair of grounding resistors R ₁ and R _2, and output data 4 of this amplifier 4
a is A / D converted by the A / D converter 5 and converted data 5a
Has been incorporated into the computer 3. Therefore, the burnout (disconnection) of the thermocouples T _{1 to} T _n is detected by the burnout detection circuit B ₁ to _Bn provided for each channel.
This is done by checking the voltage charged to the capacitor C, each done by B _n .

[0004]

Since the conventional burnout detection method and device for a thermocouple input circuit are configured as described above, the following problems exist. In other words, since a burnout detection circuit is provided for each channel, the resistors provided in this circuit connect the channels, and if noise enters one of the channels, the other It also had an adverse effect on the channel. Further, providing the burnout detection circuit on each channel not only increases the number of parts as a hardware circuit, but also complicates the configuration and increases the cost, and the detection accuracy decreases due to the variation of each part. .

The present invention has been made to solve the above problems, and particularly, a burnout detection circuit provided on the output side of a thermocouple signal selection switch detects an n-channel burnout. It is an object of the present invention to provide a burnout detection method and device for a thermocouple input circuit.

[0006]

A burnout detection method for a thermocouple input circuit according to the present invention has n-channel input terminals to which thermocouples are connected, and the n-channel input terminals are connected by an external signal.
A burnout detection method for a thermocouple input circuit, comprising a thermocouple signal selection switch for selectively outputting one of the channels, wherein a burnout detection circuit detects the burnout of each thermocouple. In this method, the burnout is detected on the output side of the signal selection switch.

More specifically, the method uses one burnout detection circuit.

More specifically, the external signal is obtained from a computer connected to the output side.

A burnout detecting device for a thermocouple input circuit according to the present invention has an n-channel input terminal to which a thermocouple is connected, and a thermocouple for selectively outputting one of the n channels by an external signal. A burnout detection device for a thermocouple input circuit, comprising a signal selection switch, wherein the burnout detection circuit detects burnout of each thermocouple, wherein the burnout detection is performed on the output side of the thermocouple signal selection switch. The circuit is connected.

More specifically, a computer that outputs the external signal is connected to the burnout detection circuit, and output data obtained from the output side is input to the computer through an A / D converter. This is the configuration.

More specifically, the burnout detection circuit is provided with a select circuit to which a burnout detection mode signal from the computer is input.

[0012]

In the burnout detection method and apparatus of the thermocouple input circuit according to the present invention, the burnout detection circuit is provided on the output side of the thermocouple signal selection switch to which the n-channel thermocouple is connected. Whether or not there is burnout of the thermocouple for each channel switched by the signal is detected by a common burnout detection circuit on the output side. Also, on this output side,
The output data in the thermocouple signal measurement mode is A / D converted by the A / D converter via the amplifier, and is taken into the computer as converted data.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a burnout detection method and apparatus for a thermocouple input circuit according to the present invention will be described in detail below with reference to the drawings. Those represented by the reference numeral 1 in FIG. 1 is a thermocouple signal selection switch having an input terminal I ₁ ~I _n of n channels, this the input terminals I ₁ ~I _n, n
Channel thermocouples T _{1 to} T _n, resistor R and capacitor C
The time constant circuits G _{1 to} G _n are connected to each other.

[0014] Each input I ₁ ~I _n of the thermocouple signal selection switch 1, the external address of the internal selection circuit 2 C
By addressed by an external signal 3a for the channel setting from the computer 3 of the PU or the like, in which selectively outputs data 4a to one output terminal O ₁ is outputted, to the output terminal O ₁ is One burnout detection circuit B ₁ is connected, and this output data 4a is A / D converted by the A / D converter 5 via the amplifier 4 and is taken into the computer 3 as converted data 5a. The burnout detection circuit B ₁ is provided with a select circuit Bs, which is connected to a grounded terminal A or a burnout voltage V _B by a burnout detection mode signal 3b from the computer 3. The switching piece B _K can be switched to any one of the terminals B. Therefore,
Detection of burnout of the thermocouples T ₁ through T _n (disconnection) is switched for each channel specified by an external signal 3a, the output data 4a from the output terminal O ₁ is an amplifier 4, and the A / D converter The converted data 5a is input to the computer 3 via 5.

The detection of burnout of each thermocouple T _{1 to} T _n will be described. First, when the terminal A of the select circuit Bs is selected, the burnout detection circuit B ₁ does not operate, and the thermocouple measurement signal is output as the output data 4a. When the terminal B is selected, the burnout voltage V _B is supplied to enter the burnout detection mode. Therefore, as described above, the burnout detection circuit B
_By the select circuit B _S of 1, the switching piece B _K is connected to the terminals A and B.
If it is switched to the terminal B, the capacitor C is charged by the burnout voltage V _B. After that, when this charging is repeated for each detection scan, when the thermocouple is burned out, the voltage of the capacitor C gradually increases and is compared with the reference value of the set predetermined threshold value (by the computer 3). By doing this, disconnection can be detected.

Next, the state in which the above-mentioned thermocouple burnout is detected will be described in more detail with reference to the timing chart of FIG. That is, tB in FIG. 2 is the burnout voltage charging time, and tD is the burnout voltage discharging time.

The equivalent circuits shown in FIGS. 3 to 5 are the burnout voltage application mode in the normal state when there is no disconnection in FIG.
FIG. 4 shows the burnout voltage discharge mode (measurement of the thermocouple signal is performed after the above tD), and FIG. 5 shows the burnout voltage application mode when the thermocouple is disconnected.

Therefore, in the case of FIG.
A voltage of V _C = (R + _RTC ) / (2 · RB + R + _RTC ) · V _B is charged for tB time, but since there is no disconnection of the thermocouples T _{1 to} T _n , it is normal, so as shown in FIG. Discharge time tD
During this period, the voltage V _C charged in the capacitor C is discharged by R + _RTC . The time tD is determined so that the voltage V _C is within the thermoelectromotive force measurement error, and after the time tD elapses, thermocouple signals from the normal thermocouples T _{1 to} T _n (not shown). No.) is A / D converted by the A / D converter 5 and taken into the computer 3.

Further, as shown in FIG. 5, in the burnout voltage application mode when the thermocouple is broken, τ = 2R _B ·
The capacitor C is charged for the time tB with the time constant of C, but since the discharge as shown in FIG. 4 does not occur, the voltage V _C continues to be charged to the capacitor C at each detection scan cycle, so that the output signal 4a is output. By comparing the thermocouple signal measurement voltage with the above-mentioned reference value by the computer 3, the thermocouple disconnection can be detected.

Experimental Example The applicant of the present invention set the above-mentioned tB to 60 msec, and the CR time constant circuit G
The time constant of _{1 to} G _n is 200 msec, (C: 100 μF, R:
2KΩ), tD for 6 seconds, R _B : 1 megohm, and the number of channels n was 13. As a result, the voltage V _C of the capacitor C at the time of thermocouple disconnection could be detected in about 80 seconds.

[0021]

Since the method and apparatus for detecting the burnout of the thermocouple input circuit according to the present invention are configured as described above, the following effects can be obtained. That is,
Since the burnout detection circuit is provided on the output side of the thermocouple signal selection switch, only one is required, and since each channel is isolated, noise in one channel adversely affects other channels. It is possible to perform highly accurate thermocouple signal measurement without affecting the temperature.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an apparatus to which a burnout detection method for a thermocouple input circuit according to the present invention is applied.

FIG. 2 is a timing chart.

FIG. 3 is an equivalent circuit in a normal state.

FIG. 4 is an equivalent circuit in a normal state.

FIG. 5 is an equivalent circuit at the time of disconnection.

FIG. 6 is a configuration diagram showing an apparatus to which a conventional burnout detection method for a thermocouple input circuit is applied.

[Explanation of symbols]

1 thermocouple signal selection switch O ₁ output side T _{1 to} T _n thermocouple I ₁ to 1 _n input terminal B ₁ burnout detection circuit 3a external signal 3 computer 4a output data 5 A / D converter 3b burnout detection mode signal B _S select circuit

Claims (6)

[Claims] 1. An n-channel input terminal (I ₁ -I _n ) to which each thermocouple (T ₁ -T _n ) is connected, and one of the n channels is selected by an external signal (3a). Burnout detection circuit with thermocouple signal selection switch (1) for selective output
(B ₁ ) in the burnout detection method of the thermocouple input circuit, which detects the burnout of each of the thermocouples (T _{1 to} T _n ), in the output side of the thermocouple signal selection switch (1) ( O ₁ )
The method for detecting burnout in a thermocouple input circuit, comprising: detecting the burnout. 2. The burnout detection method for a thermocouple input circuit according to claim 1, wherein one burnout detection circuit (B ₁ ) is used. 3. The burnout detection of a thermocouple input circuit according to claim 1, wherein the external signal (3a) is obtained from a computer (3) connected to the output side (O ₁ ). Method. 4. An n-channel input terminal (I ₁ -I _n ) to which each thermocouple (T ₁ -T _n ) is connected, and one of the n channels is selected by an external signal (3a). Burnout detection circuit with thermocouple signal selection switch (1) for selective output
In the burnout detection device of the thermocouple input circuit, which detects the burnout of each thermocouple (T _{1 to} T _n ) at (B ₁ ), the output side of the thermocouple signal selection switch (1) ( O ₁ )
The burnout detection device for a thermocouple input circuit, wherein the burnout detection circuit (B ₁ ) is connected to the burnout detection circuit. 5. A computer (3) for outputting the external signal (3a) is connected to the burnout detection circuit (B ₁ ), and output data (4a) obtained from the output side (O ₁ ). Is A /
The burnout detection device for a thermocouple input circuit according to claim 4, wherein the burnout detection device is configured to be input to the computer (3) through a D converter (5). 6. The burnout detection circuit (B ₁ ) is provided with a burnout detection mode signal from the computer (3).
6. The burnout detection device for a thermocouple input circuit according to claim 4, further comprising a select circuit (Bs) to which (3b) is input.