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.