BitFlakey

I should have been more specific.

I'm using a S7-1200 controller. and TIA Portal V13

I want to perform an diagnostic function of an digital input such that I can check for feedback of the input line to tell if the wire is off or broken.

Similar to putting a resistor on the load to provide feedback.

Hi.

There are "safety" schemes that is best suited for what you ask. Communication capable devices for example where you receive On/Off state via communication.

When some devices switch "off" the signal you receive is not actually off, but rather at a voltage. In this case you could use an analog input instead of digital input and actually read the voltage.. in concept the same as 4 to 20mA.

Trouble comes when having a hardware switch. When switched to the off position, you have an open contact which you can not read a voltage from.... it look like a wire break.

In this case you could use x2 digital inputs, one to a normally open contact and another to normally closed. In this case PLC logic can monitor for a difference in signal within a short period.

Does these ideas help any?
w

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background info:
https://support.industry.siemens.com/cs/ww/en/view/109477921

If you want to know when a signal disappears (wire is broken -OR- signal is in OFF state), use the hardware interrupt for that input signal on the PLC module itself to detect signal went from hi to low.

If it is a safety function, wire it into your safety system in series with your safety inputs, or as a single signal to more comprehensive safety devices that monitor every safety input. 

BitFlakey

Clarification for Wire break function of digital inputs of S7-1200...

On the 1500 we have an input module 6ES7 521-1BH00-0AB0, that has a "wire Break" Diagnostic function.

Question: Is there a way to do that "Wire Break" function on the dig inputs of the S7-1200.