To control 6 pump sets in sequence. what can be ladder logic for it ?

[hinddhindsa]

i need to control six pump sets.
initially 2 pump sets will run after two hours another two will run and later the third pair.
5 bar pressure has to be maintained,
Can you please help me, How can i achieve this.

Any hints and tips are welcome. plz help me.
thanks in Advcance.

 

[Prashant1707]

first use an acyclic timer. with on time of 2 hours and off time of 1 sec. Now use three counters. These counters will be triggered by the acyclic timers. Set counter one to be "ON" on count of 1 and "OFF" at Count of 2.
Set counter two to be "ON" on count of 2 and "OFF" at Count of 3. Set counter three to be "ON" on count of 3 and "OFF" at Count of 4. Reset all the counters during third OFF time pulse. To start the pumps AND the outputs of individuals counters with the pressure switch contact. Hope this will help you>

 

[chavak]

To start the pumps AND the outputs of individuals counters with the pressure switch contact. Hope this will help you>

That was a good start.

Well, 5 bars of pressure is to be maintained, so the pressure switch is not a condition, it is a requirement. It means more pumps have to be added in, or taken away in case the pressure drops/increase.

I would start with a simple drawing to understand the various situations.

Welcome to the forum guys.

Regards

 

[Anirban Hazra]

first use an acyclic timer. with on time of 2 hours and off time of 1 sec. Now use three counters.

In addition to a cyclic Timer, only 1 counter is needed.Then you just have to use "Equal" instructions on the counter accumulator value to turn on the pumps at the appropriate count.

 

[Prashant1707]

You are right we can do by one counter. But PLC such as siemens logo do not have the "Equal Instruction". Therefore using 3 counters for 3 pumps will solve the problem in just 3 FBD lines and will be basic program.

 

[Lancie1]

But PLC such as siemens logo do not have the "Equal Instruction".

That is a good point.

Hinddhindsa,
What PLC are you using? It does make a difference, because they all do not have the same instructions. Some have more, some have less. Which is yours?

This must be a student problem, because as Chavak pointed out, for a real pump system, maintaining a certain output pressure is more important than making sure each set of pumps runs exactly 2 hours. For example, a city water system will gladly run ALL pumps in order to keep adequate system pressure.

 

[Prashant1707]

i am keeping Siemens logo in mind, as i feel it is the simplest to begin with. i already designed it and telling you. use three counters for three outputs. use fourth counter to reset above three counters. use acyclic pulse generator and set 2hours on time and about 1 or 2 sec off time and use this at trigger input of all four counters. "AND" output of individual counters with the pressure switch. reset the three counters by using the fourth counter at the 3 rd count of the acyclic pulse generator and reset the fourth counter along with the three counters. thats it.

 

[Anirban Hazra]

If the original poster is working on a PLC whose instruction set does not have an "Equal" instruction then I think the simplest way to solve the timing problem is by using 3 Timers.

To do that build a logic like this:

1st set of pumps start Timer 1
Timer 1 timing out stops 1st set, starts 2nd set and Timer 2
Timer 2 timing out stops 2nd set, starts 3rd set and Timer 3
Timer 3 timing out stops 3rd set,restarts 1st set and Timer 1
and so on..

 

[Prashant1707]

anirban, how will u trigger the timer for first time when supply is put on or when supply resumes after failure.

 

[Anirban Hazra]

After failure/power cycle, if Start button is pressed then again the cycle will start from the first.But if you want the PLC to remember which set was turned ON last and for how much time after failure/power cycle, then you just have to use retentive timers and retentive memories.

 

[Prashant1707]

no one will bother to press start button in a pump room. and even if you use start button you have to hold it on and consequently you will have another issue to reset it..

 

[Anirban Hazra]

no one will bother to press start button in a pump room. and even if you use start button you have to hold it on and consequently you will have another issue to reset it..

I don't know what you are trying to say?

First of all,if you want to directly on the pumps on a power cycle without a start button, that can also be done in the logic that I said.

Secondly, why should anyone have to hold it? The pumps can be latched in the logic itself.

 

[Prashant1707]

that makes the logic more complicated. lets stick to automatic operation. for automatic operation any start button does not fit in the picture. usually the pumps are desired to run on their own. even after supply resumes the automatic operation should be continue. your second sentence just added more logic hence making it more complicated. my logic using counters can be used to sequence any number of pumps. only one logic line will increase if u add additional pump set.

 

[Prashant1707]

hinddhindsa,

check this logic in ur plc software.

 

[OkiePC]

I think this project calls for a program written on one sheet of paper as a flow chart. Once the details are all ironed out on paper, it easy simple substitution to translate that into bullet proof ladder logic.

Paul