Logic of Standby pump

Shabbir

Member
Join Date
Jul 2002
Posts
1
I am new at the plc programming and want a logic of two pumps, they start on auto and manual and if one pump fails the other pump starts.

Thanks
 
Originally posted by Shabbir ...if one pump fails the other pump starts.QUOTE]

That's it Shabbir. You've told us the answer wright there!

Wether in Auto mode or Man mode, something act as a Star signal.

You have to direct this signal to one pump OR the other...

You have to figure out in the same way, with your own words, what make this sytem determine that a pump does not start.

Overload?, Montion sensor? Pressure or flow switch?

Then you switch pumps with this signal and you keep it there.

During this thincking, you have to play a game of What if...

What if both pumps fail?... before they start, after a switch,, etc...
What if I want to alternate pumps every day or every 100 hours?
What if my sensor fail?
What if on is in Àuto and the other in Man mode?
What if it's only not primed and it take longer to get a reading?
What if I switch mode during operation?
 
Re: Re: Logic of Standby pump

Pierre said:
Originally posted by Shabbir ...if one pump fails the other pump starts.QUOTE]

Thank you Pierre. You have started me thinking. At the moment i would to make following logic:

1. Manually any pump can be started
2. if the p#1 trips, p#2 will start if it is on Auto
3. if one pump is running and demand increase other p#2 will start
4. I want to alternate pumps every day or every 100 hours?

Thanks
 
Aziz...

BE THE COMPUTER!

Put yourself, mentally, in a dark room with nothing more than a Stop-watch, a pencil and paper, a few lights indicating status on the outside world, and a few switches for you to operate.

YOU are the computer! How would you respond to what you see?

Think very carefully and pay attention to every detail!

DO NOT ACT ON WHAT YOU THINK YOU KNOW!!!

ACT ONLY ON WHAT YOU SEE!!!
 
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Ok, I am in this dark room and I can't see the stopwatch or the paper, now what do I do?

-just kidding

I forgot to plug the power cord into the computer

-hee hee

P.S. That is a very good analogy to .. "act on what you see and not what you think". - I like; - I will try.
 
what I have done

I set up a normal motor run circuit for each of the pumps, just as if they were both always running simultaneously. This circuit of course has all of the faults that will inhibit the pump from running, and of course the auto input. Where I work, the jog circuit is almost always hardwired and is not done from the PLC.

Next, I set up a Flip Flop circuit to flip a bit back and forth. You can drive this flip flop with whatever you want, in order to switch the pump priorities. The bit from the Flip flop will determine which pump is the standby (lag) or main (lead) pump. I call this bit the Pump is Lead bit. This means that when the bit is on, pump A is the main, and B is the standby. When the bit is off, pump B is the main, and A is standby. I switch lead and lag pumps when either both pumps are running or both pumps are stopped. You can switch the lead and lag pump run commands based off of run hours if you want.

Next I determine how many pumps I want to run. 0, 1, or 2 pumps. For my application, I determine how many pumps I want to run based off the level of the tank that the pumps are pumping liquid from. The level of the tank turns on a bit that says run lead. When the level goes higher, it turns on a bit that says run lag. If both bits are on then two pumps run, if only the run lead pump bit is on, then only 1 pump (the main pump) runs. And of course, if no bits are on, then neither pump runs.



Logic that is placed in front of the Pump run logic for pump A

Run Pump A Pmp A Etc. Run
Lead is Lead Fault Pmp A
--| | |-----| | --------------|/|-------| |----------( )
| |
| Run Pump A |
| Lag is Lead |
--| | |-----|/|----------


Run Pump A Pmp A Etc. Run
Lead is Lead Fault Pmp B
--| | |-----|/| --------------|/|-------| |----------( )
| |
| Run Pump A |
| Lag is Lead |
--| | |-----| |----------






What this says is ..... If you are calling for the lead pump to run
and pump a is the lead/main pump, then run A. If you are calling for
the lag/standby pump to run, and A is the standby, then run A.

It says the same for B. ie. if b is lead and calling for lead, then run b etc.

I hope this helps get you started in your thinking. It is almost 9:00pm on a Friday night, and I am tired of working. I also had some logic to Run the Lag pump in case the lead pump failed to run, but I don't remember what it looks like. I think I just added another branch on both pumps and said that if the lead pump failed to run and this pump is the lag, then run or something.

Let me know if you want some more advice. I really shouldn't get on here under the influence of alcohol.
 
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