Dry and wet contacts

Dry contact and wet contact

1. What is dry contact ？
Passive switch ; It has two states of closing and opening ;2 There is no polarity between the two contacts , interchangeable .

Common dry contact signals are ：
1） Various switches, such as ： Limit switch 、 Travel switch 、 Foot switch 、 Rotary switch 、 Temperature switch 、 Liquid level switch, etc ;
2） Various keys ;
3） Output of various sensors , Such as ： Sensors in environmental power monitoring ： Water immersion sensor 、 Fire alarm sensor 、 The glass is broken 、 Vibration 、 Smoke and condensation sensors ;
4） Relay 、 The output of the clarinet ; If there is a dry contact, there is a wet contact .

2. What is wet contact ？
Active switch ; With and without electricity 2 States ;2 There is polarity between two contacts , You can't connect in reverse ;
Common wet contact signals are ：
1） If the above dry contact signal , Connect the power supply , Then follow the other pole of the power supply , As the output , It's the wet contact signal ; Industrial control , The voltage range of the commonly used wet contact is DC0～30V, The standard is DC24V;AC110～220V The output of can also be wet contact , Although it is less done ;
2） hold TTL The level output is used as the wet contact , Not too bad ; In general ,TTL Level requires buffered output , for example ：7407、245、244 etc. , And VCC And so on ;244、245 Also you can talk with gnd Make up the loop ; To drive the remote optocoupler .
3）NPN Collector output and output of triode VCC;
4） The collector output and output of Darlington tube VCC;
5） Output of infrared reflection sensor and infrared reflection sensor ;

3. In the field of industrial control , Advantages of using dry contact ：
1） Random access , Reduce engineering costs and engineering personnel requirements , Improve the engineering speed ;
2） Deal with a large number of dry contact switching values ;
3） The conductor connecting the dry contact will not damage the local control equipment even if it is short circuited for a long time , It won't damage distant equipment ;
4） Easy access , The interface is easy to unify .