Push to ON PUSH to OFF PLC program using NO NC and Coil
This is Interview question that every PLC programmer came across in his carrier. The Question is very tricky and shows the fundamentals (basic Ladder Laws) and depth of candidates knowledge.
Today we are going to discuss PLC program for Push to ON device and Push to Off Device. But the trick is that we have to use only Normally open(NO) ,Normally Close (NC) contacts ,and Coil as output only(No timer, Counter, OSR ).
In short there will be a single Push Button Input (X0) , and one Output (Y0). When user press Push button for 1st time output will be ON ,when user Presses Push Button for 2nd time output will be OFF. This is also called as “Push
to On Push to Off ” logic. Analogy can be provided with “TV” on and off Push Button.
We Can Break Sequence Like This :
1) Push Button Pressed (X0) ==> Output (Y0)On
2)Push Button Released (X0)==> Output (Y0) Latched
3)Push Button Pressed (X0)==> Output (Y0 )Off
4)Push Button Released (X0)==> Output (Y0) Off
Remember you can write PLC program in number of ways
- Using only NO,NC,Coil only
- Using Counter
- Using Pulse Instruction
- Using OSR (Rising Edge ,Falling Edge) Instruction
below PLC Ladder program is using NO,NC,Coil
Note:Do not Replace M0 with Y0
Below Program is using Counter instruction
Below Program is using PLS instruction
More Question asked on this are related to Scan time and rung interchange etc.