Hi Experts,

I have confusion on the automatic duty change operation of pumps when they are controlled by a PLC in auto mode.

I have seen in control panels that there are 2 modes auto and manual. Manual is the regular start and stop function controlling the pumps. I have confusion on how pumps operate in auto mode controlled by PLC?

Hearing for your valuable response.

Thanks,
Akash

 

Dear Akash,

There must be some parameters in PLC which tells PLC to stop/start pumps in auto mode. It can be level of liquid, pressure, temperature ... depend of process PLC controls. If you don't have manuals or HMI to set parameters, then you must look at program in PLC.

Best regards,
Vedran

 

What you have there is a H-O-A station, for "HAND" "OFF" and "AUTO" operation. In "HAND" mode, or manual, you are forcing on the pump regardless of what it should be doing.

"OFF" is obvious.

"AUTO" mode allows the pump to be operated by a program resident in the PLC that takes an input from some sensor, usually a pressure or level sensor, and turns on the pump, or pumps, as required by the program.

So, you are pumping from a wet well. You have several level set points connected to the PLC. As the water reaches each set point, another pump is turned on to slow or reverse the rise in level. It will also work in reverse if you are pumping to a wet well.

The PLC may also have a sequencer program which will choose each pump based on cumulative run time data, so it may bring on Pump 3 as lead pump, Pump 4 as lag pump, etc. Next cycle it might be Pump 4 as lead, and so on.

Does that help?

Walt

Walt Boyes, FInstMC, Chartered Measurement and Control Technologist
Life Fellow, International Society of Automation
Editor in Chief, Control and ControlGlobal.com
[email protected]