JPH0636010B2 - Alarm monitoring circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alarm monitoring circuit, and more particularly to an alarm monitoring circuit that monitors an alarm signal guided to a remote location by a cable as well as a cable disconnection and the like.

(Prior Art) In an alarm monitoring circuit that monitors an alarm signal or the like transmitted to a remote point through a conventional cable, the alarm signal itself is monitored, and even a cable break or a connection failure at a connection point such as a connector is also included. It is not generally done to monitor.

(Problems to be Solved by the Invention) That is, in the above-described conventional alarm monitoring circuit, the received alarm signal and the like are monitored under the assumption that the cable or the connector is properly connected. However, there is a drawback in that it is impossible to monitor the disconnection of the cable or the connector.

(Means for Solving the Problem) An alarm monitoring circuit according to the present invention is associated with a bridge circuit in which an alarm relay circuit and a resistor are incorporated on one side via a cable, and an imbalance of the bridge circuit due to the operation of the relay circuit. A detection circuit for detecting a generated voltage level, a comparison circuit for comparing the detected voltage level with two predetermined reference voltage levels, and a detection circuit having a detection voltage level higher than either of the two reference voltage levels. , Between the two reference voltage levels, and
A display circuit for identifying when the voltage is smaller than any one of the two reference voltage levels and performing output display corresponding to the identified three states.

(Example) Next, this invention is demonstrated with reference to drawings.

FIG. 1 is a circuit diagram showing an embodiment of an alarm monitoring circuit according to the present invention.

In FIG. 1, the contact 1 of the relay is closed when an alarm is generated and is open when the alarm is normal (when no alarm is generated). In the open / closed state of the relay contact 1, the resistance change due to the presence of the resistance 2 is changed to the resistance 5.
6.7.8. It is supplied to a so-called bridge circuit composed of the variable resistor 4 and the power supply 29. At the normal connection point of the circuit by the cable 3, the variable resistor 4 is initially adjusted so that the voltages Va and Vb across the resistor 8 are equal, that is, the bridge circuit is balanced.

Resistors 9, 10, 11 and field effect transistors 12, 1
Reference numeral 3 represents a high input impedance differential amplifier circuit, which is configured so as not to be involved in the balance condition of the bridge circuit. Further, the resistors 14, 15, 16 and the transistor 17 constitute a constant current circuit, and the field effect transistor 1
The sum of the drain currents 2 and 13 is configured to be constant regardless of the changes in the voltages Va and Vb across the resistor 8.

The voltage V at the connection point between the resistor 9 and the field effect transistor 12
c is supplied to the level comparators 18 and 19, respectively, and level comparison is performed with the reference voltages 20 (Vr +) and 21 (Vr-), respectively. The level comparators 18 and 19 are respectively V
When c> Vr + or Vc> Vr−, a logical “1” is output, and when Vc <Vr + or Vc <Vr−, a logical “0” is output.

The logic of the level comparators 18 and 19 is the inverter circuit 2
2. The light-emitting diode 25 which emits red light and the light-emitting diode 26 which emits green light are decoded by the NAND circuits 23 and 24 and are controlled by the decoded signals. Also, resistor 2
Reference numerals 7 and 28 limit the currents flowing through the light emitting diodes 25 and 26, respectively.

The connection point voltage Vc changes depending on the alarm status, the connection status of cables, etc., but in FIG. 2, the case <1> alarm occurs and the relay contact 1 is closed, and the case <2> alarm does not occur. , The voltage Vc and the reference voltage Vr are in the normal state including the connection of the cable and the like, and <3> when the cable is broken or the connection of the connector or the like is defective.
The relationship between the voltage levels of + and Vr- is shown. FIG. 3 shows the relationship between each of the above states and the light emitting diodes 25 and 26 being turned on (lighted) and turned off (light off). As is clear from FIG. 3, according to the present invention, it is possible to monitor the alarm operation including the disconnection of the cable.

(Effects of the Invention) As described above, the present invention is provided with the bridge circuit in which the alarm relay circuit and the resistor are incorporated on one side via the cable, and is accompanied by the imbalance of the bridge circuit caused by the operation of the relay circuit. By comparing the generated voltage change with the two reference voltages, it is possible to quickly determine the connection failure of the alarm generation cable or the like. For example, depending on the lighting state of the light emitting diode that emits red light and the light emitting diode that emits green light, when only the red light emitting diode is lit, an alarm is generated at a remote point, and when only the green light emitting diode is lit, cables etc. are also connected. Including that it is normal,
When both are off, it is possible to determine that there is a cable break or a connection failure in the connector, etc., and there is an effect that an alarm monitoring circuit including a cable break etc. can be configured with an inexpensive circuit. .

[Brief description of drawings]

FIG. 1 is an alarm monitoring circuit diagram showing an embodiment of the present invention,
FIG. 2 shows the connection point voltage Vc and the reference voltages Vr +, V shown in FIG.
FIG. 3 is a diagram showing a relation with r−, and FIG. 3 is a diagram showing a light emitting diode which is light-emitted and displayed according to a magnitude relation between a voltage Vc and two reference voltages. 1 ... Relay contacts, 2, 5-11, 14-16, 2
7, 28 ... Resistor, 3 ... Cable, 4 ... Variable resistor, 12, 13 ... Field effect transistor, 17 ... Transistor, 18, 19 ... Level comparator, 20, 21
... reference voltage, 22 ... inverter circuit, 23,24 ...
... Nand circuit, 25,26 ... Light emitting diode, 29 ...
…Power supply.

Claims (1)

[Claims] 1. A bridge circuit in which an alarm relay circuit and a resistor are incorporated on one side via a cable, a detection circuit for detecting a voltage level caused by an imbalance of the bridge circuit due to an operation of the relay circuit, and A comparator circuit for comparing the detected voltage level with two predetermined reference voltage levels; when the detected voltage level is higher than either of the two reference voltage levels; and when it is between the two reference voltage levels. An alarm monitoring circuit, comprising: a display circuit that distinguishes between the two reference voltage levels and when the voltage is smaller than either of the two reference voltage levels, and displays an output corresponding to the identified three states.