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Pump Control with a PLC (Part 3)

By Walt Boyes

E-Zine December 2015

Click here to read “Pump Control with a PLC (Part 1)”
Click here to read “Pump Control with a PLC (Part 2)”

Al Pawlowski suggests that it is also very useful to add a contact to the HOA switch “auto” position so that the PLC can tell when the pump is not ready to be called. A pump can be out of service for maintenance, or it can have previously failed. Pulling in this contact moves the pump out of the alternation scheme until the contact breaks again. This is all part of working out the pump failure logic, which, of course, an old-fashioned pump controller did automatically for you out of the box.

Finally, Pawlowski warns, “don’t forget to take into account pump/control operation in the event of a power failure, program restart and/or level sensor failure. You probably don’t want all your pumps to start at the same time on power up, or when the level signal goes to zero.”

When you design a PLC-based pump controller, you have complete control over what the controller will do. This means that you have to be sure you’ve thought out the entire functionality you want the controller to have. It is too late when you start the pump station up and pumps go on and off when you don’t want them to.

The good news is that you won’t be the first to use a PLC instead of buying a pump controller. Your PLC vendor should be able to help you find already written code that will at least start you on your way.

From Flow Control (April 2002)

ISSN 1538-5280

Spitzer and Boyes, LLC
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