Basic OR gate operation explanation using electrical wiring diagram and PLC ladder diagram

Application:-In electrical panel there are two switches given for panel ON lamp. Both the switches are optional, the lamp can be ON either by switch 1 or switch 2.Draw truth table, electrical wiring diagram and write PLC program for this application.

Components:-Programmable logic controller, Electrical panel, wires, 24vDC switches with NO contacts, 24VDC indication lamp, 24 VDC relay.

Diagram:-Electrical wiring diagram and truth table of OR operation

Explanation:-

As per our application, we can use above application for OR gate explanation. In application we are using two switches and one lamp for indication. If switch 1 or switch 2 pressed, indication lamp should be ON. So in above electrical wiring diagram we have used S1 and S2 in parallel connection so electrical supply can flow either from S1 or S2.

In truth table we can easily understand the conditions of OR gate,

As per truth table,

If S1=ON OR S2=ON, then R=1

If S1=ON OR S2=OFF, then R=1

If S1=OFF OR S2=ON, then R=1

If S1=OFF OR S2=OFF, then R=0

So the output will be OFF only in the last condition.

PLC program:-

Write the ladder program for OR gate operation using ladder diagram language. Here for ladder logic we can use any PLC system. For PLC logic we need digital inputs and outputs.

For our application all switches are digital inputs and lamp is digital output. So define digital input address and output address as per below explanation,

Digital inputs:-

S1=I0.0

S2=I0.1

Digital Output:-

Lamp=Q0.0

Memory coil:-

Memory bit-M0.0

PLC program Explanation:-

In network 1 we have considered two digital inputs for two switches S1 and S2. So we have taken NO contact of S1 (I0.0) in parallel with S2 (I0.1) for OR operation. So when S1 or S2 ON, memory bit (M0.0) will be ON.

In network 2 we have taken NO contact of memory bit (M0.0) to operate panel ON lamp (Q0.0).