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Old November 27th, 2010, 09:45 PM   #1
Moosebreath94
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Analog Pump Control



This newbie would like to replicate the tank level controller below, with an analog pressure transmitter and an IDEC SmartRelay FL1E,(NON Ladder logic) instead of float switches and relays.

I have been working on it all day and not making terrific progress. The scaling is not an issue, it is what combination of boolean and special operations would acheive the same result as the relays. I have been using analog triggers, latching relays and boolean operators without the desired result.

Any help would be appreiated, and adding the logic for HH and LL alarms would be a plus.
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Old November 27th, 2010, 10:42 PM   #2
leitmotif
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I would place maintain contact in parallel with high level to allow pumpdown to low level. The way you have it wired the low level will never stop the pump. ASSUMING pump pumps down tank.

If pump fills tank the high limit should be drawn as normally closed (opens on high level)

Hmm also assumes I am interpreting the symbols correctly.

Dan Bentler

Regardless if you keep the float switches or not I would always have a low level switch to stop pump from running dry.
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Old November 27th, 2010, 11:19 PM   #3
Moosebreath94
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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?
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Old November 27th, 2010, 11:49 PM   #4
leitmotif
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Quote:
Originally Posted by Moosebreath94 View Post
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

Last edited by leitmotif; November 27th, 2010 at 11:58 PM.
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Old November 28th, 2010, 07:33 AM   #5
Moosebreath94
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Analog pump control

Dan,

The revised drawing is below.The convention of opens on rising is the same as closes on falling.

We need analog control for a number of reasons;

1. For adjustability in the field
2. Cost for simple transducers has become lower than for a float switch tree. Labor and I/O count is reduced.
3. It helps keeps away riff raff that are trying to bid the project.
4. I can't afford to hire a Controls PE for many of these small projects, only the big ones.

Yes, a second pump is dispensing from this tank, and the level in the tank varies quite a bit.

A VFD on the filling pump is not compatable with the filling process machinery.

The filling pump machinery is constant rate.
The tank level analog monitoring is Rosemont / AB,
or in this case China / SmartRelay / inhouse.

Jim Herbert
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Old November 28th, 2010, 03:13 PM   #6
Mike Lamond
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Jim,

From your description, in the smart relay program the float switches will be replaced with contacts from two internal relays, let's call them CRH and CRL. These are the results of comparing the tank level analog input to high level and low level setpoints. The coils are on when the condition is true. (This may not be in exact IDEC mnemonics.)

'High Level - Greater Than or Equal comparison
GEQ(Tank_Level, SP_High) COIL(CRH)
'Low Level - Less Than or Equal comparison
LEQ(Tank_Level, SP_Low) COIL(CRL)

In the CR rung, the high level float will be replaced by an normally closed CRH contact while the low level float will be replaced by a norrmally open CRL contact.

If this is all you need to do, a digital process meter with relay output will do job and also display level and output state.

Mike
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Old November 28th, 2010, 04:17 PM   #7
Moosebreath94
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Analog pump control

Thanks Mike, I'll get working on it. I have yet to find any > or < operators, but I'll keep looking.

The SmartRelay "Function Block Diagrams" are kind of a mess, so I'm switching to Ladder Logic.

My old Relay Control ladder and IDEC's version of it are shown below;
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File Type: jpg ST Pump Fill Ladder.jpg (32.0 KB, 26 views)
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