Solid state relays are "normally open" devices. You can use an IO module to create an inverse situation where N.O. behaves as N.C. and N.C behaves as N.O. The IO module is an IO-IDC-028-P (DC field signal) or an IO-IAC-280-P (AC field signal). Data pages: IO modules, DC switching SSRs, or AC switching SSRs.


In this drawing, the customer has a field signal ON and the solid state relay is in the OFF state. In the white IO module, terminal 4 is capable of sinking up to 100mA.

The power supply can be any voltage between 4-28VDC. For bench top testing of the circuit, you can use a 9 volt battery.

normally open solid state relay

In this drawing, the customer's field device is OFF, which permits the SSR to turn ON.

normally closed solid state relay