How does the dry contact input PLC work?

Hello, I have a Dry input type digital input in my controller,
could someone explain to me how it works and what I can actually connect to it?

Dry contact module)More precisely: like most modules, it allows the use of these inputs in DRY CONTACT (NO contact) as well as WET CONTACT mode. Operation in DRY CONTACT mode (changing the state of a given digital input when it is shorted to ground) entails the module's internal pull-up (voltage source plus diode and resistor) to a high state. That is, at the moment when:

• we connect nothing to a given output: we get a high state
• we connect a given input to ground: we get a low state
to a given input we apply a voltage above the threshold: we get a high state
• to a given input we apply a voltage below the threshold: we get a low state
the sea attachment will lighten the situation.

Thanks for the answer but that didn't solve the problem. I have this situation: connect straight from the power supply to digital input dry contact on plus 24v and on minus 0v. The light from the relay input then blinks, something must be wrong, I will add that when I connect the inductive sensor in this way everything is ok. Is it all about the current? Should I add a resistor?

good dry contact track 4..20 mA current is determined by the documentation of the particular controller e.g. SuperBrain max. 150 mA

izeusz wrote:

I connect straight from the power supply to the digital input Dry Contact to plus 24v and to minus 0v.

Please do not do this! A colleague may damage this input, if it has not already been damaged.

With the Dry Contact input, the necessary voltages are applied through this input.
Shorting the Dry Contact input (H) to the ground of this input (N) will cause the controller to perceive this as a change from the "0" state to the "1" state.
In practice, this type of input is used with devices that have a pair of contacts (contacts) connected only and exclusively to the Dry Contact input - usually NO - Normally Open.
Changing the operation of this device, i.e. closing the contacts, will change the state of the Dry Contact input.
A typical example here is a relay, but also can be an auxiliary contact of a contactor or a reed switch.

demirko wrote:

good dry contact track 4..20 mA current

What is a colleague writing about here? What has analog current input to Dry Contact digital input?
Could a colleague explain this?

izeusz wrote:

The relay input light then blinks, something must be wrong,

As I wrote above. The colleague simply shorted both input terminals of this input. The state of the input should have changed to the "1" state.

Thank you, this is exactly the explanation I was looking for.
Connecting the input to ground actually changes the state.

Then I have one more question:
Why does connecting an inductive sensor change the state. The sensor has 3 wires one is connected to +24V the other to the input ground, while the third is connected to the H dry contact input. When the ind. sensor is triggered, a voltage of +24V appears on the third wire and the input state changes from 1 to 0

Please specify the model of this sensor.

The sensor is marked IMPOL ICZ-D5 CNP3
.

izeusz wrote:

Why connecting an inductive sensor changes the state. The sensor has 3 wires one is connected to +24V the second is connected to the input ground and the third is connected to the H dry contact input. When the ind. sensor is tripped, +24V appears on the third wire and the input state changes from 1 to 0

The issue is quite simple. As I mentioned above ...

Polon_us wrote:

connected only to Dry Contact input - usually NO - Normally Open .

Please consider the situation (and this is actually the case) that the sensor is equipped with NC contact - Normally Closed i.e. Normally Closed.