What Is Coil Contact In Ladder Logic And How To Use It In PLC Programming

As we have discussed about the normally open and normally contact in ladder programming, we are today going to discuss here about the coil contact in ladder logic programming. For going ahead to coil discussion, let's revise the normally open and normally close contact to make better understanding about the coil. Normally open is like a circuit breaker, when we switch ON the circuit breaker, the current start flowing to the circuit and output will be switched ON. This is same we have normally open contact in ladder logic, in the ladder logic programming, we have a normally open contact, when this contact (normally open NO) energize, it start allowing current to flow from the circuit.


On the other hand, the normally close contact is like we have stop button in an electric circuit. When the stop button is switch ON, current stop flowing in the circuit and circuit is dis-energize. This is how the normally close contact works in ladder logic programming. When this normally close contact is pressed, or get signal, it stop current to flow from the circuit and circuit will dis-energize.


Read Here: Normally Open and Normally Close Contacts in Ladder Logic Programming


Now, the coil contact is actually we have the output in ladder logic programming. Let's explain it with a simple example below.

Drawing # 1

Drawing # 2

Let's explain this electric circuit. There are three components we have in this circuit, 1 stop switch, 1 on switch and one coil/output. First we have placed an normally close contact which is stop button. Then, we have placed a ON button which will switch ON the circuit. The output will tell us current is flowing or not.

Same we have in the ladder logic programming. We will use a normally close contact (as a stop button), then a normally open contact (which will start flowing current in the circuit), and the coil is output. When current start flowing in the circuit, the coil which is connected to the output will be energized and the output terminal of the PLC hardware will be energized.