How should I connect an optically isolated input and voltage supply to a dry contact output?

Sealevel’s SeaI/O modules are a good choice for this application. For example, using a SeaI/O-430 module with 32 isolated inputs, we can connect the dry contact output to an optically isolated input in the following way:

  • Connect output terminal A to the voltage supply’s “-” terminal.
  • Connect output terminal B to the SeaI/O module’s input 1 terminal.
  • Connect the voltage supply’s “+” terminal to the “C” (Common) terminal for inputs 1-4 on the SeaI/O module.

This arrangement is safe, easy to troubleshoot and easy to modify.

  • The “+” output of the voltage supply is protected by each input’s current limiting resistor.
  • Connecting the voltage supply’s “+” terminal to the common terminal of the four inputs reduces the likelihood of accidentally connecting multiple voltage supply outputs to the same bank of inputs.
  • Using additional outputs with the same voltage supply is now a snap – just connect the next dry contact between supply “-” and the input.

The safety, reliability, and ease of modification make this a nearly unbeatable arrangement for connecting dry contact outputs to optically isolated inputs.