JPS6250629A - Detecting circuit for input disconnection of resistance bulb - Google Patents

Abstract

PURPOSE:To detect the disconnection of any cable securely by comparing the output voltage of a bridge circuit formed of a resistance bulb with a voltage based upon a supply voltage. CONSTITUTION:The bridge circuit is formed of the resistance bulb 1 of a cable A, proportional resistances 2 and 3, addition/subtraction side resistance 4 of a cable B, etc. A fine output voltage generated by this bridge circuit is processed by a differential amplifier 6 to measure temperature. The output voltage of this bridge circuit is compared by a comparator 9 with a reference voltage obtained by dividing the supply voltage to the bridge through analog switches 7 and 8 by resistances 10 and 11. Then, when the cables A and B, and a ground connection cable C are all not disconnected, the output of the comparator 9 decreases and when one or two of the cables A-C are disconnected, the output of the comparator 9 is nearly equal to the supply voltage; when all the cables including the ground connection cable are disconnected, that is detected securely.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a resistance temperature detector that detects disconnection in a cable to which the resistance temperature detector is connected by utilizing the change in resistance value due to temperature. This invention relates to an input disconnection detection circuit.

[Conventional technology]

FIG. 2 shows a conventional resistance temperature detector input circuit. In the figure (1) is a three-wire resistance temperature detector pt, 100 II, (
21, (3) is a proportional side resistor, (4) is an adjustable side resistor,
(5) is the input filter, (6) is the amplification of the minute voltage generated by the bridge circuit consisting of the resistance temperature detector (1), the proportional side resistor (2) (3), and the rheostat (4). 2), -), and (C) are cables that connect the resistance temperature detector to the differential amplifier.

Next, the operation will be explained. The proportional side resistor (2
), (3), a rheostat (4), and a resistance temperature sensor (1) form a bridge circuit, and the change in resistance value according to the temperature of the resistance temperature sensor (1) is extracted as a minute voltage. The voltage is amplified by a differential amplifier (6) through an input filter (5) to a standard voltage, and the temperature can be determined from this voltage value. Furthermore, since the relationship between the resistance value of the resistance temperature detector (1) and the temperature is generally not linear, linear live is required.

Now, in Figure 2, if the cable () and extension) are disconnected for some reason, the bridge circuit described above becomes unbalanced, and the input voltage to the differential amplifier (6) becomes a value far from the normal value. becomes. Therefore, the -differential amplifier (6) is saturated in the positive or negative direction.

This makes it possible to detect wire breakage.

[Problem that the invention seeks to solve]

Since the conventional resistance temperature detector input circuit is configured as described above, it is possible to detect the disconnection even if only the cable (4) or cable (C) is disconnected, or if the cable (C) is disconnected. , cable (A) CB) (C)
If any two or all three wires are disconnected, there is a problem in that no potential difference appears at the input end of the input filter (5) and the disconnection cannot be detected.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a resistance temperature detector input disconnection detection circuit that can reliably detect disconnection in any case.

[Means for solving problems]

The resistance temperature detector input disconnection detection circuit according to the present invention connects an analog switch to the output end of the bridge circuit, and uses the analog switch and a comparator to compare the output voltage of the bridge circuit with the voltage supplied to the bridge circuit. K so that disconnection of any cable can be reliably detected.
This is what I did.

[Effect]

The resistance temperature detector input disconnection detection circuit according to the present invention can detect disconnection in any case by comparing the output voltage of the bridge circuit with the voltage supplied to the bridge circuit.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, il+ is a resistance temperature sensor pt100 Q, f
2) (3) is a 10Kg proportional side resistor, (4) is a 100Kg proportional side resistor.
A bridge circuit is composed of the resistance temperature measuring resistor (1), the proportional side resistor (21 (3), and the rheostatic resistor (4)). (5) is the input filter, (6 )
is a differential amplifier that differentially receives and amplifies the minute voltage generated by the bridge circuit, (7) and (8) are analog switches that are connected to the output terminal of the bridge circuit and can be turned on and off using digital signals. 9) is this analog switch <
71 Comparator that compares the voltage from (8) with the divided voltage of the voltage supplied to the bridge circuit and outputs a logic level voltage, (II is 100 R17) resistor, I
is a 10KJ resistor.

Next, the operation will be explained. In the case of normal temperature measurement, the analog switches (7) and (8) are turned off and the output voltage of the bridge circuit is measured. In other words, the measurement is performed by extracting the change in resistance value of the resistance temperature detector Il+ as a minute voltage according to the temperature, passing it through an input filter (5), amplifying it with a differential amplifier (6) to make it a standard voltage, and measuring with this voltage value. It is used to know the temperature.

Next, one of the analog switches (7) and (8) is turned on to detect a disconnection. In this case, when there is no disconnection, the voltage applied to the analog switches (7) and (8) is on the order of several mV, which is small compared to the voltage divided by the resistor (Al am), but the voltage applied to the cable (5) C
B) When either (C) r or both or all of them are disconnected, the voltage applied to analog switch (7) or (8) is equal to the supply voltage to the bridge. The voltage value will be around 15V. Therefore, resistance αQ
When compared with the voltage divided by aυ, either or both of the voltages of the analog switches (7) and (8) will be larger than the divided voltage, and this will be detected by the comparator (9).

In the above embodiment, the case of one resistance temperature detector input was explained, but in the case of multi-point input, the same can be achieved as in the above embodiment by receiving the input with a multi-prefner or the like and providing this detection circuit at the subsequent stage. It is clear that this method has the following effects.

〔Effect of the invention〕

As described above, according to the present invention, the output voltage of the bridge circuit supplied to the analog switch is compared with the voltage obtained by dividing the voltage supplied to the bridge circuit using a comparator. It is possible to detect any kind of disconnection in the cable connected to the resistance temperature sensor, increasing reliability and having the effect of being able to detect it digitally.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a resistance temperature detector input circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional resistance temperature detector input circuit. (1 is a resistance temperature sensor, (2) (3) (4) al)
am) is a resistor, (5) is an input filter that removes noise, (6) is a differential amplifier that amplifies the output voltage of the bridge, ()) (8) is an analog switch, and (9) is a voltage comparison It is a comparator that In the figures, the same reference numerals indicate the same parts. Patent applicant Mitsubishi Electric Corporation Representative Patent Attorney 1) Hiroshi Sawa Shoji゛″1 (R
2-4) -'・) L-+ + +- Procedural amendment (voluntary) 1937 1°-A Day

Claims (1)

[Claims] From the output end of a bridge circuit consisting of a pair of proportional side resistors, a rheostat, and a three-wire resistance temperature detector that detects the measured temperature, the resistance value changes according to the temperature of the temperature detector. is converted into a minute voltage value, extracted, passed through an input filter, and amplified by a differential amplifier to obtain a standard voltage.In a resistance temperature detector input disconnection detection circuit that detects temperature from this voltage value, a voltage is applied to the output terminal of the bridge circuit. 1. A resistance temperature detector input disconnection detection circuit, comprising: a comparator connected to an analog switch and comparing a voltage from the analog switch with a voltage supplied to the bridge circuit.