Water pump control with AB Micrologix 1500


Thread Starter

José Claudeni

Could anyone help me to elaborate a ladder program for AB Micrologix 1500 to control five pumps in turn?

Some especifications:
Theres is a watertank 920m above floor level) and a reservoir (under the groud), both with ultrasonic level sensors. The pumps (15HP) draw
the water to tank from the reservoir. They work in turn: when four of them work, the other one pauses for 24 hours. They power-on when the
level of the watertank is low and the level of the reservoir is not low. They power on from 15s to 15s one after the other. They can´t
power-off together.They power-off from 15s to 15s one after the other.
I must use RSLogix 500.
Forgive me for my poor English.

Jose Tolentino

You must ask somebody who is an experienced programmer. PLC programming is not about simple ladder circuit entry. PLC can be dangerous at times if its operation is not predictable.

Paul Dackermann

I feel I need to ask a few quesions to fully understand what you want to accomplish. My understanding of what is posted is that you have 5, 15 hp pumps which you plan to control. The pumps will normally be placed in operation with 1 standby and 4 ready. The standby pump will be alternated every 24 hrs. The operating scenario is such: When the elevated tank level requires a pump to be energized to introduce water into the tank(assuming the low-level interlock in the suction side of the pump is not disqualifing the operation),the 4 pumps in service shall energize in unison every 15 seconds. In turn when the required level is satisfied the pumps shall de-energize in unison every 15 seconds. With this understanding, my questions.

Have you considered the pump sequence? FIFO, Alternation during the 24 hr. period.

How many pump cycles are expected during a 24 hr interval? Consider the manufacturers spec. for the motor. There is much to say concerning
amount of cycles and the period of each.

Has consideration been given to the volume of the tank relative to the HP selection for the pump/motor train?

Returning to alternation. Give some thought to the order of the pump sequence so that the overall time is averaged an not maxing out a
single pump/motor. Further to as an example; the first shot would be 1,2,3,4 followed in the next sequence by 2,3,4,1 and so forth.

Above all, establishing the working model is important for the initiation for the programmer.

Good Luck!

Al Pawlowski

I would like to add a few more items to Paul's reply on this application.

Because pumps often get put in "Off" (maintenance etc.), it is often preferable to a base alternation on pump run time instead of just FIFO; the programming is a bit more complicated however.

In addition to sensing a pump's "run" condition, I have found it very useful to add a contact to the pump's HOA switch "A" position so that the
program can tell when a pump is not ready to be called. Such pumps are then normally moved out of the alternation scheme along with pumps that fail to start when called. Since it is so useful, a "HOA in A" sensor seems like a no-brainer, but you would be surprised at how many people forget about it. BTW, don't forget to work out the "pump fail" logic carefully, acccounting for start delays and should you have fail when called to stop, etc.

Think about energy management and peak demand running.

And finally, don't forget to take into account pump/control operation in the event of a powerfail, program restart and level sensor fail. You probably don't want all of your pumps to start at the same time on power up or when the level signal goes to zero.

Al Pawlowski, PE
[email protected]
dba ALMONT Engineering
Baton Rouge, LA USA