Fail-safe switch value discrete input state acquisition circuit

Abstract

The invention discloses a fail-safe switch value discrete input state acquisition circuit which comprises an oscillating circuit, an optocoupler as well as a voltage dividing resistor, wherein the oscillating circuit is connected to a switch value discrete input end, and outputs dynamic oscillation pulse through voltage division of the resistor and the isolation of the optocoupler when the input electrical level is high. The fail-safe switch value discrete input state acquisition circuit can acquire the state of the switch discrete input value safely, has rapid acquisition speed and less power consumption, as well as can operate individually under the premise that a safe side and a dangerous side are defined.

Description

technical field [0001] The invention belongs to the technical field of electronic circuit design, and specifically refers to a fail-safe discrete input signal acquisition circuit applied to industrial control systems, safety signal systems and other systems. Background technique [0002] In industrial control systems and safety signal systems (applied to avionics, railway signals, nuclear power and other industries), the system usually collects the status of the equipment switch through the input channel, and the controller realizes the monitoring of the external equipment through the input channel. [0003] The input state of the external device to the system is often a discrete quantity of the switch, that is, there are only two states of on and off. Input positive voltage when it is turned on, and no voltage input when it is turned off. [0004] Such as figure 2 As shown, it is a common design structure of a switching value discrete input state acquisition circuit. The ...

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Problems solved by technology

The problem with this solution is that when the optocoupler 1 is normally on or off, it may cause an error in the external state collected by the system logic circuit, which may lead to a dangerous output caused by an error in the calculation of the output by the safety system

However, the back end of optocoupler 1 is on the side of the input channel, and it is difficult to use a 3.3V or 5V TTL or CMOS fast optocoupler, which leads to a slow frequency response of the circuit to the calibration waveform, and it is difficult to set the calibration waveform at Frequency above 10KHz

If the system has high real-time requirements, it is difficult for this circuit to meet the requirements

[0008] 2. The circuit needs to be input by the verification waveform of the logic circuit, and it cannot work independently without the input of the verification waveform, which increases the complexity of the logic circuit part of the system

[0009] 3. The back end of the optocoupler 1 often needs a large current (5~10mA) to achieve a good working state. If the voltage of the input channel is high when the input channel is turned on, the power of the entire circuit will be relatively large

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