JPH0127306Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to an improvement of a signal folding circuit.

(Prior art and its problems) Conventionally, as shown in FIG. 2, in this type of signal return (hereinafter abbreviated as loop) circuit, the relay is inactive during the non-loop period, and the loop monitoring relay contact 7 can be opened. Therefore, the voltage E is input to the negative logic element 5 through the pull-up resistor 9, and a logic signal "0" is output to the loop monitoring output terminal 11. On the other hand, during the loop, the relay is in operation, the relay contact 7 is connected to the ground, OV is input to the negative logic element 5, and a logic signal "1" is output to the loop monitoring output terminal 11. In order to monitor the loop as described above, a relay contact 7 is required in addition to the relay contacts 6 and 8 for the loop circuit, which has the disadvantage that the relay is expensive and large. In addition, since the loop circuit relay contacts 6 and 8 and the relay contact 7 are separate, if the loop relay contacts 6 and 8 operate and the relay contact 7 does not operate, an erroneous loop monitoring output signal is output. It was a possibility, but it was unreliable.

(Purpose) The present invention is characterized by outputting a loop monitoring signal at a loop circuit contact, and its purpose is to reduce the size of the loop circuit and realize it at low cost and with high reliability.

(Structure) To achieve this, the present invention provides a signal return circuit in which an input signal switching relay contact disconnects an input line, an output signal switching relay contact disconnects an output line, and a signal input terminal and a signal output terminal are connected. A resistor R ₁ is provided between the common terminal of the switching relay contact and ground, a resistor R ₂ is provided between the power source E and a make terminal that comes into contact with the common terminal when the input line is disconnected, and the common terminal is configured by connecting the input end of a negative logic element having an input threshold voltage V _TH to the input line, and when the input line is disconnected, the make terminal V _io =E/
Each element is provided with a signal return monitoring circuit selected so that {(R ₂ /R ₁ )+1} satisfies V _io <V _TH .

(Embodiment) FIG. 1 shows an embodiment of the loop circuit of the present invention. 1 is a signal output terminal, 2 is a signal input terminal, 3 is a signal output circuit, 4 is a signal input circuit, 5 is a negative logic element, 6 is a signal output switching relay contact, 8 is a signal input switching relay contact, 9 is a pull-up resistor (Hereafter R ₁
10 is a signal input termination resistor (hereinafter abbreviated as _R2 ), and 11 is a loop monitoring output terminal. When the relay is not operating, the signal from the signal output circuit 3 is sent to the signal output terminal 1 via the signal output switching relay contact 6.
The signal from the signal input terminal 2 passes through the signal input switching relay contact 8, is terminated at the _R2 resistor 10, and is input to the signal input line 4. At this time, since the signal input switching relay contact 8 is inactive, a voltage E higher than the threshold voltage of the negative logic element 5 is input to the negative logic element 5 via the _R1 resistor 9, and the loop monitoring output terminal 11 has signal input terminal 2
A logic signal "0" indicating that looping is not performed is outputted from the signal output terminal 1. While the relay is in operation, a signal from the signal input terminal 2 is outputted to the signal output terminal 1 via the signal output switching relay contact 6. At this time, since the signal input switching relay contact 8 is operating, the voltage V _io input to the negative logic element 5
becomes E/(R ₁ /R ₂ )+1. Here, R 1 and R ₂ are set so that the ratio of the threshold voltage V _{TH of} the negative logic element and E/(R ₁ /R 2 )+1 is V _TH > E/(R ₁ /R ₂ ) ₊₁ . If selected, the negative logic element 5 determines V _io as _LOW ,
A logic signal "1" indicating that the signal is looped from the signal input terminal 2 to the signal output terminal 1 is output to the loop monitoring output terminal 11.

(Effects) As explained above, according to the present invention, it is possible to monitor the loop status using the relay contacts for the loop circuit, so by reducing the number of relay contact circuits, the cost and size of the relay can be reduced. Furthermore, since the relay contact signal for the loop circuit directly becomes the loop monitoring output signal, the reliability of the monitoring output signal can be increased.

[Brief explanation of the drawing]

Figure 1 shows a loop circuit according to an embodiment of the present invention;
The figure shows a conventional loop circuit. 1...Signal output terminal, 2...Signal input terminal, 5
...Negative logic element, 6...Signal output switching relay contact, 8...Signal input switching relay contact, 9...Pull-up resistor, 10...Receiving signal terminating resistor, 11...
...Loop monitoring signal output terminal.

Claims (1)

[Claims for Utility Model Registration] In a signal folding circuit in which an input signal switching relay contact disconnects an input line, an output signal switching relay contact disconnects an output line, and connects a signal input terminal and a signal output terminal, the input signal switching circuit A resistor _R1 is provided between the common terminal of the relay contact and the ground, a resistor _R2 is provided between the make terminal and the power source E, which contacts the common terminal when the input line is disconnected, and a resistor R2 is provided between the power source E and the common terminal. The input terminal of a negative logic element having an input threshold voltage V _TH is connected, and the voltage at the make terminal when the input line is disconnected is V _io =E/(R ₂ /R ₁ )+1 is V _io A signal loopback circuit characterized by comprising a signal loopback monitoring circuit in which each element is selected such that <V _TH .