Yes leitmotif, this pump fills up the tank. You are right that the H floatswitch opens on rising, and I should have drawn it that way years ago. We always use a LL level to stop the pump from running dry.
Any ideas about analog control?
Well I can still read drawings - all right!!!!
Analog control
1. Why do you think you need it? Are you dispensing from this tank - dispense rate is proportional to level ?? - is it that critical??
2. If #1 is true, then what tolerance do you want on level (ie +/- one inch etc??)
3. Pick a tolerance that will meet your needs. 10% is a dollar, 5% is 20 dollar, 1% is 100 etc etc.
4. What is stuff in tank? Water or corrosive, flammable, how uhhh syrupy (??) is it? Does it have particulate in it or does it have medium to high concentration of dissolved solids (salt sugar etc) in it that may settle out or have differing concentrations at different levels or temperatures
5. Make sure the materials exposed to tank contents will not be affected by them.
6. There is no - I mean NO - maintenance free.
7. Are your in house maintenance folk able, trained and have the tools to deal with new sensing and control?
8. More spare parts to keep in stock?
9. Is volume proportional to height ie tank is an UPRIGHT cylinder without tapered (conical) bottom.
10. Tank volume and how often and for how long will pump pump? Maximum dispensation (outflow) rate??
You just may be better off staying with float switches??
If you really want to change then I would go with a sensor with 4 20 mA output feeding a VFD and control motor speed proportional to level (uhhh inversely proportional ie higher level = slower speed).
Nearly forgot - motor is 3 phase right??
If you do this:
1. Do NOT run pump less than 5 Hz or so (or make allowances for possible lack of motor cooling)
2. If a centrifugal pump - check pump curve to ensure pump will actually pump at low Hz (RPM) --- it MUST pump to keep the seals cool. Probably true for gear type pumps also.
Dan Bentler