Supervised Inputs

D

Thread Starter

Don Zunti

We are working with a spec that calls for 4-state discrete input supervision (open, close, short fault, open fault) on a switch that has internal series/parallel resistors. The short fault must be distinguished from a closed contact.

Has anyone used any brand of PLC that has this available? I know of Modicon (Quantum, Momentum) and AB (ControlLogix) that provide a line break supervision, but not a short circuit.

Even if we have to use 2 PLC inputs per switch, that would be OK. Using analogs would be costly since there are over 500 of these switches to monitor.

Thanks

Don Z.

 
S

Steve Bailey

Have you checked to see if any sensors for any of the Fieldbusses like DeviceNet or Profibus have the capabilities you're looking for. Either of these busses certainly have the bandwidth to handle the data.
 
S

Steve Bailey

Would a sensor that has both NO and NC contacts satisfy the spec? There are four states, two of which are valid, the other two are not.
 
> Would a sensor that has both NO and NC contacts satisfy the spec? There are four states, two of which are valid, the other two are not.

We thought that as well, and is they way we initially designed it. Then after the tender closed they issued an addendum stating that it must be resistive.

Don Z.
 
Your requirement of Open, closed, short circuit, open circuit are generally met by any fire alarm panel I/O card. I have worked with Simplex 4100 series fire alarm panels with such feature and it is a very common spec.. requirement in Fire Alarm specs. As you pointed out, it is possible to make
it with AI cards and utilize 2 mA and 22 mA for Open circuit and short circuit settings, but this is expensive.

Regards,

Sundar
 
Top