Dry Contact sensors
A dry or Volt-free contact is a contact without any voltage going through it. This effectively is a switch, meaning that if a sensor has a dry contact output, the switch will close when the sensor is triggered due to the presence of what it is measuring.
Dry contact sensors do not give a value. They detect the presence of something, whether it is gas, door close, smoke, water leak etc.
These types of sensors are normally connected to products that are monitoring events and act upon them, either by sending an alert or triggering a relay for example.
Although the output of the dry contact sensor is virtually volt-free, most require a DC voltage supply to operate. This power is either taken from the monitoring system, or connecting the sensor to a wall socket.
Sensors with Dry Contact Output
A family of low cost industrial sensors with dry contact output