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 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.

Check Video Demonstration of Above Program

Post a Comment

Aadil Khan said... 20 June 2015 at 12:57

I want to plc logic book for practic. Plz tell me

Anonymous said... 3 October 2015 at 10:41

Ooka wada karan na ooii. Ekko positive transition ekak daala hadapan naththan ooka gihin deepan lamayekuta.

Unknown said... 10 March 2016 at 19:43

i want wiring daigram of on/off lamp on only one push button without use plc

mhellier1 said... 11 May 2016 at 18:44

It will be cheaper to use a plc than use 500 contactors or build a logic board and power a contactor.
That's from a electrical contractors veiw

Bimantara Ksatria Putra said... 4 August 2016 at 13:51

Hi. I got the same question from my lecturer, but it is only use NO/NC with max 3 addresses, with one network. Can you help me find the answer