recording hours on a pump with a vfd

[DRThorne]

whenever my pump is running, my plc starts a timer to record operating hours. It's very basic counter that counts the minutes the pump is on. The plc controls the pressure by an analog signal and variable speed drive and normally runs between 50% to 90% of full speed. Is it normal to create some logic to slow down the plc operating hour timer when the pump is not operating at full speed to reduce the maintenance intervals? for example, run the hour counter at 50%, 60%, 70%, 80%...

[Steve Bailey]

Implicit in that strategy is the assumption that an hour at full speed produces significantly more wear and tear than an hour at half speed. If your experience tells you that your scheduled PM is late on pumps that consistently run at higher speeds but OK when the pumps run slower, then by all means create a speed-weighted timer.

I've never run across anyone who set up a PM timer like that. I think most places would just take a worst-case scenario and set up their timer on that basis, figuring that the cost of doing a PM sooner than necessary is less than the consequences of doing it too late.

You just have to decide if it makes sense for your application.

[Jimmie_Ohio]

As an alternative to a "weighted" operating time based on load, since timers in the PLC are "free", you could also consider several timers, each within a specific load range.

For example, one each could record operating time in: "under 25% load", "25 to 50% load", "50 to 75% load", and "75% to full load".

This method may give you more significant operating data for maintenance considerations.