Contacts and coils are often associated with the physical inputs outputs on the plc.
Normally open contact in plc.
Difference between normally closed and normally open inputs.
Normally open contacts would represent relay contacts that would perform a connection upon receipt of a signal.
Rising edge asks if a bit just turned from 0 to 1.
Concepts normally open and normally closed contact ought to be clarified and explained in detail in the example of a plc controller input and output.
If a contact is tied to an input then when the power at the input changes it s contact value in the ladder logic will change.
Normally closed nc contacts allow current through when the relay or contactor is not energized.
To illustrate that with the normally open contact you can think of the two sides of the contact as an input and an output.
The easiest way to explain them is in the example of a relay.
A relay contact in the ladder diagram can be normally open or normally closed and there is no limit to the number of contacts a relay can have.
The ladder logic symbols look almost like the electrical symbols for normally open and normally closed contacts and the function of these are the.
Normally open asks if a bit is 1.
Relays and contactors have two types of contacts each suited for different applications.
The normally closed nc contact is in plc programming referred to as an examine if open instruction xio.
As before the in switch stop virtual contact is in the closed state when no one presses the stop switch enabling the motor to start any time the.
Notice that both of the input push buttons are normally open but the ladder logic inside the plc has one normally open contact and one normally closed contact.
Normally closed asks if a bit is 0.
Often they are referred to as examine if closed xic and examine if open xio.
A plc output is really just an internal relay with a physical connection that can supply electrical power to control an external load.
Do not think that the ladder logic in the plc needs to match the inputs or outputs.
In order for the plc program to work properly with this new switch wiring the virtual contact for in switch stop must be changed from a normally closed nc to a normally open no.
But for stop functions it can be bad.
Normally open no contacts allow current when the relay or contactor is energized.
Normally open is a contact that does not flow.
In other words when voltage is applied to the relay contactor terminals this contact closes.
This is because normally open contacts can create dangerous situations when they fail let me explain that a little further.
Examine if closed is an instruction that examines a bit for the off condition.
Many beginners will get caught trying to make the ladder logic match the input types.
Just like the input actuators you have both normally open and normally closed contacts available in plc programming.
Using normally open contacts as plc inputs is good.
