Contents
What is meant by dry contact output?
No current: A dry contact is the synonym of volt free — it is not “wetted” by a voltage source. Dry contact can refer to a secondary set of contacts of a relay circuit which does not make or break the primary current being controlled by the relay. Dry contacts means a relay that does not use mercury-wetted contacts.
What is dry contact output?
A dry contact (also known as a volt free contact or potential-free contact) is defined as a contact in which power/voltage is not directly provided from the switch but is instead always being supplied by another source. Dry contacts are known as passive contacts, as no energy is applied to the contacts.
What happens when the output of an open collector changes?
The output of the open collector has changed states, and this change in state can then be used to trigger the automation/security system, logic system, or energize the coil of a relay. “Pull to ground” and “current sink” are other terms used to describe the open collector circuit. Take a look at these diagrams of open collector circuits.
What makes a PLC module a dry contact?
PLC modules are always dry contacts, regardless of whether they are relay or digital output types. Just because a PLC module says 24V, don’t expect it to supply that voltage simply by activating the output terminal. The output points are driven by the 5V logic from the processor, the power for the loads always comes from an external source.
How are dry contacts used in relay terminals?
The relay terminals will make use of a COM and either a normally open or normally closed contact, two wires. Dry contacts are not directly provided with power from the switch and are used in switching devices which provide isolation and give a wide variety of output voltage options.
What makes a dry contact a wet contact?
If a control device with some sort of switching action has terminals for only two wires, this most likely indicates that it is a dry contact, and the switching action is performed within the body of the larger device. Most variable frequency drives contain a programmable relay output to be switched when a certain action occurs.