PID controller in lead and lag with pumps

richie

Member
Join Date
Aug 2005
Location
new jersey
Posts
27
I have a PID format controller with pump1 at 6 seconds lead and pump2 lag at 7 seconds my P is 100% default settings both pumps kick in at once the set point is 7.5 ft and process variable start at 4 feet any ideas why both pumps are kicking in ?
richie
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Last edited:
Like Ken, I too would need more information..... But GENERALLY speaking it sounds like there isn't enough "time" or "pressure" difference between the 2 pumps.

I start my lead at 4 seconds, followed by the lag about 10 seconds later (for a total of 14 seconds from the start threshhold). But that is with a pretty aggressive P, and a calculated starting point (based on actual pressure) for the pump.

There are ALSO accel and decel times in the drives to consider. If the drives are set too sluggish, the process won't be increased as fast as the PID tries to increase it, leaving a difference that the controller thinks requires another pump to achieve.

What are your "accel" and "decel" set to?

Stationmaster
 
The P setting is at 100% int the F&P manual it states 100% is the default setting. The lag is the I set at seven seconds and the lead "D"is set at 6 seconds they have the set point at 7.5 but the well is supposed to be 12 feet high and overflow at 11.5 and the pumps loose suction at 3.5 feet !!!!!!!! I can give you alarm settings tomorrow!!!!!!! thanks for responding
 
AS I told Ken people are giving me these parameters!!! THe lead the 'D' at six seconds the lag the "i" at 7 seconds the "P" IS AT 100% THE F&P MANUAL calls this the default setting the setpoint is at 7.0 to 7.5 depending on the person you speak to !!!!! The elevation of the tank is said to be 12 feet and overflow at 11.5 feet and cavation of pumps is 3.5 feet!!!!Thanks for responding I can get high and low alarm tomorrow !!!!!!again thanks !!!!
 
Are these Variable speed pumps or are you controlling a valve?
If not it sounds like a compete miss-use of PID to me.
PID is used for modulating not discrete Start/Stop.
Regards
Roy
 

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