Jump to content



Recommended Posts



Hi !!


Assuming we have PLC designed for 24VDC inputs and due to long length of cable, or any other reason the input voltage drops to 16 volts, what will be the effect on input state?


In other words....what is the threshold voltage below which the input state will shift from "1" to "0".


Any thoughts..




Link to comment
Share on other sites

That is going to vary widely by brand and even by module selection. The only valid answer should be in the specifications for your specific PLC and the DI module you need. For example, Allen Bradley SLC 500 digital inputs for DC have a range of 10-30VDC for some modules, 15-30V for others. Automation Direct has one that goes from 10.2V to 26.4VDC, and another that goes from only 20-28VDC.
"He's not dead, he's just pinin' for the fjords!"
Link to comment
Share on other sites

  • 3 weeks later...

Dear chaterpilar, :)

Welcome to the forum.


Jraef is right. It depends upon the brand of Plc. We have Allen Bradley Plc with 24vdc input module. We have also such a problem of voltage drop. But this module can accept 10-30vdc signal. At some inputs, voltage dropped bellow the range, we have connected a Transistor C1383 with 15K input resister and controlled that problem. You can also do it.


Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...