JPS5826210B2 - Contact information input circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a contact information input circuit for inputting ON/OFF information of a relay contact into an IC circuit.

When controlling a process using a digital computer, it is necessary to capture information on a large number of relay contacts on the process side.

Circuits for this purpose are conventionally known as shown in FIGS. 1 and 2.

Figure 1 shows an IC with 4 pull-up resistors for the 20 inputs of the IC gate.
The voltage is raised to the same voltage as power supply terminal 3. When relay contact 1 is off, IC gate 20 input is kept at high level, and when relay contact 1 is on, IC gate 2 input is kept at high level.
is grounded and the input changes to low level.

In this way, the on/off information of the relay contact can be transmitted using the so-called T
Although it is used for converting to a TL level, contact circuits are generally routed for a long time, making it easy for noise to enter from the outside.

Therefore, a common measure against noise is to insert a low-pass filter 7 consisting of a series resistor 5 and a parallel capacitor 6, as shown in FIG.

Although this circuit is somewhat improved compared to the circuit shown in FIG. 1 because the noise is attenuated by the low-pass filter 7, it has the following disadvantages.

(1) The higher the resistance value of the series resistor 5 of the low-pass filter 7, the greater the noise suppression effect as a filter, but as an IC circuit, the DC voltage at low level increases.
Conversely, malfunctions due to noise are more likely to occur.

(2) It is possible to increase the value of the parallel capacitor 6 without increasing the value of the series resistor 5 too much, but this will be disadvantageous in terms of reliability and cost.

(3) The conditions for using relay contact 1 are that the voltage when off is approximately 5 volts, and the current when on is approximately 1 milliampere; however, from the point of view of contact reliability, it is preferable to use larger voltages and currents. In this case as well, malfunctions due to noise are likely to occur.

As described above, the input circuit using only the pull-up resistor 4 and the low-pass filter 7 does not have a sufficient noise suppression effect.

The present invention aims to provide a contact information input circuit with a high noise suppression effect, and in addition to the conventional combination of a pull-up resistor and a low-pass filter, two diodes are connected between the relay contact and the IC gate. It is characterized by the interposition of a switch circuit.

An embodiment of the present invention will be described with reference to FIG.

One terminal of the relay contact 1 is connected to a negative power supply terminal 12, and the other terminal is connected to a diode switch circuit 10 via a resistor 11.

The diode switch circuit 10 is composed of a series diode 8 and a parallel diode 9.

First, a case where relay contact 1 is off will be explained.

In this case, obviously no current flows through diode 8, and since diode 9 is connected to positive power supply terminal 3 via resistors 5 and 4, it is reverse biased and becomes non-conductive.

Therefore, the input voltage to the IC gate 2 is kept equal to the voltage at the power supply terminal 3 (5V).

The non-conducting resistance of a diode is extremely large (usually several hundred to θ
) Therefore, the cutoff frequency of the low-pass filter composed of the resistor 11, the non-conducting resistor of the diode 8, and the low-pass filter 7 becomes very low.

That is, the effect of suppressing external noise entering the transmission line between the relay contact 1 and the resistor 110 becomes extremely large.

Next, a case where relay contact 1 is turned on will be explained.

In this case, current flows from the ground point 13 to the negative power supply terminal 12 via the diodes 9 and 8 and the resistor 11.

Therefore, diodes 8 and 9 become conductive, and the cathode potential of diode 90 is negatively biased by the forward voltage drop (0.7 V in the case of a silicon diode). Therefore, by setting resistors 4 and 5 to appropriate values, IC gate 2
The input to is approximately Ov.

The noise suppression effect when relay contact 1 is on will be explained.

Resistor 11 and diode 8 (since they are in a conductive state, the resistance value is small and can be ignored compared to resistor 11.

), a diode 9 forms an attenuation circuit.

At this time, since the resistance of the diode 9 is also small, the attenuation amount of the attenuation circuit can be set large, and external noise is suppressed here.

Furthermore, since the low-pass filter 6 also has a noise suppressing effect, the noise suppressing effect is significant even when the relay contact 1 is on.

FIG. 4 shows another embodiment of the invention.

In this embodiment, a parallel resistor 14 and a parallel capacitor 15 are provided at the cathode of a diode 80, and a positive power supply terminal 16 is further provided.

The capacitor 15 forms a new low-pass filter together with the resistor 11, and a noise suppressing effect can be obtained here as well.

With the configuration of this embodiment, by appropriately setting the value of the resistor 14 and the voltage applied to the power supply terminal 16, the contact current value when the relay contact 1 is on and the contact current value when the relay contact 1 is off can be adjusted. The voltage value can also be set to a value that is preferable in terms of reliability of the relay contact 1.

In this case, it is necessary to set the voltage value of the power supply terminal 16 to a voltage value higher than the voltage value of the power supply terminal 3 (for example, 24 V).

This is to maintain the diode 8 in a non-conductive state when the relay contact 1 is off, thereby providing a noise suppressing effect.

As explained above, according to the present invention, it is possible to suppress noise and accurately convert the IC gate input voltage (5■ when the relay contact is off, 0■ when the relay contact is on).
A highly reliable contact information input circuit can be obtained.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams of a conventional example, FIG. 3 is an explanatory diagram of one embodiment of the present invention, and FIG. 4 is an explanatory diagram of another embodiment of the present invention. 1...Relay contact, 2...IC gate, 4,5゜11...Resistance, 6...Capacity, 8,9... ·diode.

Claims (1)

[Claims] 1 A negative power supply is connected to one end 12 of the relay contact 1, and a diode switch circuit 10 consisting of a series resistor 11, a series diode 8 and a parallel diode 9, and a low frequency circuit consisting of a series resistor 5 and a parallel capacitor 6 are connected to the other end in order. filter 7 and
A parallel resistor 4 and an IC gate are connected, and a series diode 8 and a parallel diode 9 are connected in opposite directions when viewed from the relay contact 1 side, and a parallel diode 9 is connected to the IC gate.
is grounded, and the parallel resistor 4 is connected to a power supply.