Dry Contacts & Wet Contacts

Definition of dry Contact:
Passive switch, 2 states with closure and disconnection, no polarity between 2 contacts, can be interchanged;
Common dry contact signals are:
1, various switches such as: limit switch, stroke switch, foot switch, rotary switch, temperature switch, liquid level switch, etc.
2, various keys;
3, a variety of sensor output, such as: Environmental power monitoring sensors: water immersion sensor, fire alarm sensor, glass crushing, vibration, smoke and condensation sensors;
4, relay, reed tube output;

Wet contacts are defined as:
Active switch, 2 states with electricity and no power, 2 contacts have polarity, can not reverse;
Common wet contact signals are:
1, if the above dry contact signal, connected to the power supply, and another pole of the power supply, as the output, is the wet contact signal; Industrial control, commonly used wet contact voltage range is dc0~30v, compared to the standard is the output of dc24v;ac110~220v can also be wet contact, although this is relatively small;
2, the TTL level output as a wet contact, also can not be; In general, the TTL level needs to be buffered output, such as: 7407, 245, 244 and so on, and VCC and other components of the circuit, 244, 245 may also form a circuit with GND, to drive the remote Optocoupler. 3, the NPN transistor collector output and VCC;
4. The collector output and VCC of the Darlington tube;
5, infrared reflection sensor and the output of the sensor;

Dry contact, nonpolar, interchangeable (requires external power supply)
Wet contacts, polarity, non-interchangeable (no external power supply required)

Dry Contacts & Wet Contacts