This is very important to understand about wet contact relays, outside the head, for instrument / automation or electrical engineers. This is because it relates to the remote control method on many devices, almost all.
Internal Wet Contact Relay on a Remote Device
Below is a diagram showing an internal wet contact relay in a Digital Output Module on the Air Compressor device. in the figure, a controller is used for data acquisition about the “Run / Off” status of an air compressor, the controller can only accept “wet contact”. incidentally the air compressor is able to provide it from the Digital Output.
Dry Contact Relay
The following is a picture of a dry contact relay, where a controller is used to monitor the on-off condition of the air compressor. However, the controller of the PLC can only accept dry contact signals. Because the air compressor has a wet contact internal relay digital output, then an interposing relay must be provided so that will change the signal from wet to dry contact.
Wet Contact Relay for Command
This is a wet contact wiring relay diagram for the remote command application.