Pump Alternation

MuayThaiDCS · Jun 14, 2007

Looking for some advice...

The scenario:
I have two discrete pumps used to empty a tank.
The lead pump is requested to run once a high level condition is met. The lag pump is requested to run once a high high level condition is met. The lag will stop running when the high high is no longer true. The lag will shut off when a low condition is satisfied. They are also required to alternate lead to lag once they are shut off (by the low condition). I am looking for the most efficient way to program the alternation. I have ideas, but want to see what others think...

DBLD99 · Jun 14, 2007

This is got to be one of the easiest things to code.// Use a counter and the .ACC of the counter with the call to run to Alternate the pumps.

BobB · Jun 14, 2007

Use a modified flip flop. If you search here flip flop has been covered many times. It is pretty easy code for what you require.

Oakley · Jun 14, 2007

Not necessarily related to the pump control (as this has been discussed numerous times in the past - try a search for pump control or pump rotation), but be smart about the programming vs alarming. You don't want your pump control to be the same as the alarm - just think about it - an alarm is to annunciate an abnormal condition that requires action. Normal operation of draining a tank isn't typically defined as an alarm. Consider not using your HiHi level, but rather a Hi level that has your alarming on the outside of operation range. Then you could determine if a single pump is not working (failed) and/or if the second pump is necessary.

silva.foxx · Jun 14, 2007

We had a similar set-up in a previous company where we had two Vaughan wet-well vertical chopper pumps pumping effluent into the first of three cascaded sediment tanks. The pumps were on a 3-hour cyclic timer to alter lead-lag duty. There was four floats; low, lead, lag and high-level alarm. The control was relay logic. I've lately been messing with coding it in S7 and using PLCSim.

You could alternate duty after x cycles.

What are your ideas, Muay?

Kim Gold · Jun 14, 2007

If you are turning the lag pump on and off based on high-high level, what will happen on a pump failure?

i.e. If the duty pump fails and the high-high level is reached the lag pump will turn on. Then when high-high level is off the lag pump will stop. You could get into a starting and stopping situation that could damage you pump, assuming you still have flow coming into tank.

If you have some way of sensing a duty pump failure, you could switch the standby pump to duty. If the standby pump is only starting to assist to bring the level down, you may want to pump down to some intermediate level before having it shut off.

Kim

TConnolly · Jun 14, 2007

I sincerely hope that I didn't just answer a homework question, but on the off chance that it is not, here is a very simple solution.

All you have to do is count in binary. Each time you count up the least signficant digit changes state, 0, 1, 0, 1, 0, 1, 0, 1, etc. You can use a counter or a flip flop.

In the examples below I have assumed that all of the float switches make on rising tank level.

Here is one way you could do it with a flip flop.

You can add the logic necessary to the pump seal in branch of each of the rungs it you want the lag pump to shut down when the high level switch is not made.

Saturn_Europa1 · May 8, 2016

What does the bit ] [ C5:0.ACC/0 denote? I am unsure when this would be true or false.

Thank you

OkiePC · May 8, 2016

It is a "bit of word". Each time the value of C5:0.acc increments, the least significant bit will change states creating a "slick" form of a flip flop. I call it slick, because it is eloquent and simple and a little bit abstract to the casual observer, not to denigrate it in any way.

With Allen Bradley SLC and PLC-5 addressing, the"/" is the bit delimiter. "/0" means "bit zero".

So restating the answer for clarity, each time the value of C5:0.ACC is odd the value of C5:0.ACC/0 would be "1" and each time it is an even number, the value of C5:0.ACC/0 would be "0"

jraef · May 8, 2016

Lol, all that code to replace a simple cheap alternating relay...

T Gibbs · May 8, 2016

Do more and Productivity have a flip flop instruction.

Pump Alternation

MuayThaiDCS

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DBLD99

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BobB

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Oakley

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silva.foxx

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Kim Gold

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TConnolly

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Saturn_Europa1

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OkiePC

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jraef

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T Gibbs

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