Positive or Negative logic inputs in Z-Purge application?

[rmore]

I have a system that requires a number of switch inputs in a machine that is going into a Z-Purge environment. My options are use positive input logic, with a common 24 V which will need to go to each switch on the machine, or use negative logic, where the common is ground.

This is my first PLC design and I'm slit as to which way to go as there appears to be distinct advantages and disadvantage to both.

Any advise?

 

[controlsdude]

Most PLC manufacturers provide 24vdc input and output modules. Where on the inputs it looks for 24vdc lvl to turn on the input. Where on the outputs it provides a 24vdc lvl to turn on the device in the field.
These input and output cards are common to all PLC manufacturers.

Now the other type which is not so common and most times has lead times of a month or more is just the opposite.

Where on the inputs it looks for a 0v common to turn on the input. Where on the outputs it provides 0v common to turn on the device in the field. This is probably harder to troubleshoot since your looking for a common not a 24vdc signal.

If you need further education look up on google Source/sinking devices are it refers to PLCs.