I have a question using markvie pdio card

How to pdio recognize digital input

For example limit switch , pressure switch

Our digital input voltage is 125vdc wetting system

When i check the voltage the pdio terminals, but i always check the + 62.5vdc, -62.5vdc even if the switches are off

Then how can pdio recognize the digital input "true"

 

The PDIO senses current (microamperes) flowing through the closed contacts and it interprets that as a closed contact. When the contacts are open, the current flow is stopped (interrupted) and the PDIO senses that as an open contact.

It is simply the absence or presence of current (again, a very small amount of current—a few microamperes) flowing through the switch contacts that the PDIO uses to determine if the switch contacts are open or closed, respectively.

The polarity of the voltage at the sensing input terminal of the terminal board the PDIO is attached to changes when the contact opens or closes—but it’s the current flow at the sensing input terminal that the PDIO detects that the PDIO uses to know if the switch contacts are open or closed.

 

Oh i got it. I really aprreciate you