Can a dry contact input be a closed circuit?
As long as the cable between the alarm and IO board is relatively short, you should not have any problems. You wrote: “If the digital output relays are close, my dry contacts will become a closed circuit and current will flow because the digital outputs are rated 250VAC/30 VDC, 2A??
Can a PNP sensor be mixed with a NPN sensor?
In most PLC’s it’s possible to configure cards as PNP or NPN. Another thing to note, is that NPN and PNP sensors should never be mixed on a PLC input card. Furthermore, if you have a specific type of PLC input card that’s NPN or PNP, It’s important to make sure that you choose sensors that match.
What kind of current do I need for a dry contact?
I don’t want it too high so that a standard open collector output (30V/50mA-100mA) can work on it as well. A dry contact can sometimes require what is known as a wetting current. This means that when the contact closes, a current is available to flow through the contact of a certain amount (usually specified by the vendor).
What’s the difference between a PNP and a NPN?
First, select a [&Sensor&] that matches your PLC Input Card (discrete DC INPUT) and has the same Circuit Wiring type ([&PNP&] or [&NPN&]). For this example, we’ll wire a 3-wire [&proximity&] [&sensor&] to a Discrete DC Input Card and walk through [&both&] [&PNP&] and [&NPN&] wiring types. 2. Next, check the data sheet for your [&sensor&].
What does dry contact and Volt free mean?
Volt-free and dry contact mean the same thing. If a control system supplier offers a dry contact for you to read as a status bit, then he is offering to close a contact (relay or contact output) that is nothing more that a stand-alone set of contacts with no voltage, current, or anything else impressed across the contact set.
When do digital outputs close in a relay?
As shown in the diagram, the digital outputs are Form A relays that “are closing contacts with one common terminal (C) and one normally open terminal (NO). The terminals are isolated from signal ground.”. So the digital outputs are normally open and I suppose will close only when there’s an alarm.
Which is an example of a dry contact?
Basically, a “dry” contact is a switch with no shared power source or supply integral to the control. A common example would be the contacts in a compressor contactor. The contactor has a 24v coil (in residential), but the power supply through the contacts doesn’t have any connection to the coil.