Need Help With Linear Control - RSLogix 5000

DBLD99

Member
Join Date
Oct 2003
Location
USA
Posts
230
Hello guys, need some input. I have 2 sets of setpoints min and max. 1 set of setpoints is for 1 pump running, and the other setpoints is for when both pumps are running. The speed is to be the same for all pumps if there running. I need to control the speed using a linear ramp between min and max setpoints in direct proportion to wet well level.
wet well level is 0-10ft
speed setpoints is 0-60hz

any input would be appreciated, thanks for your time

I need it to modulate back and forth between min and max setpoints
setpoints are for the speed of the pumps
example setpoint
min_sp_1_pump = 40hz
max_sp_1_pump = 55hz
wet well level=5ft
i need the pump to be running inbetween 40 and 55hz since the wet well level is 5ft. if the wet well level was 2 ft i would need the pump to be running about a 1/4 inbetween 40-55 so say 41 or 42 hz
sorry if im making it sound confusing
 
Last edited:
First off, what are your setpoints for - the speed of the pump, or the level of the well?

Second, when you are running one pump, what is your control strategy?
--PID to maintain a setpoint (if so, which one - MIN, MAX, or halfway between)?
-- On/Off control (Off when at MAX, back on when at MIN) - this assumes that setpoint is a function of level?
-- Modulate from Min to Max and back?
-- Something else?

It sound like you are looking for a strategy for how to handle things when you have one pump running at one speed, and the other pump off, and you want to both change setpoints AND change the speed of both pumps at the same time.

If so, there are lots of approaches, depending on how your system can handle disruptions:

-- Simulatneously ramp the running pump down to the new setpoint and ramp the new one up to the same one.
-- Keep the running pump running at whatever the current speed is (disabling PID control even, if used) and bring the second to that speed. THEN change setpoints and let both pumps run at the same speed.
-- etc.

There's so much that I don't know about your system and how you want to control it that it's impossible to answer effectively.
 

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