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Old February 27th, 2015, 09:25 AM   #1
remullis
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sump level control with hi level and lo level float

Hi,

I have a basic sump tank with a hi level float and a lo level float. I want to control the level of this sump using a pump that is pumping out. I'm using RSlogix5000.

I would like to latch the output on when the system is in auto and the hi level is reached, so I have programmed as such. I want this system to unlatch when the low level is reached. Easy enough.

The problem I have is when the operators put this system in manual sometimes the water level goes past the low level float basically(NO contacts). I need this swt to be ignored as the water rises because the bit will change states and then once the swt opens back up(XIC green) then it triggers and unlatches pump. Could I use a OSF in this case and if so what do you use for the storage bit and output bit.

Second, I could make this a one float control using time, but the time could get sketchy depending on the amount of flow coming into the sump. Any thoughts.
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Old February 27th, 2015, 09:55 AM   #2
Lancie1
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There was a thread here in the past 2 months about sump level control. Search for that because it had several PLC program for sump control.

Best I remember, it used only the High Level switch to start the pump, and the Low Level switch to stop the pump. If you set it up like that, the Low Level switch is always ignored until the level goes High. Them the pump starts, and the Low Level only comes into the picture as the level drops.

http://www.plctalk.net/qanda/showthr...control&page=2

Last edited by Lancie1; February 27th, 2015 at 09:58 AM.
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Old February 27th, 2015, 10:05 AM   #3
Bering C Sparky
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If your Low Level and HIgh Level Switches are both N/O.
(Circuit open when float is hanging in down position)
Then see if this is what you are looking for.
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File Type: jpg Sump_Rung.jpg (30.4 KB, 77 views)
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Old February 27th, 2015, 10:35 AM   #4
remullis
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Bering C, Actually in that setup once the hi level goes off then the pump goes off. I need it to run until it gets to the low. Both are NO.
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Old February 27th, 2015, 10:44 AM   #5
Bob O
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Notice the Sump_Pump contacts in parallel with the High Float. This is being used as a seal-in so the pump will continue to run until your low float drops out.
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Old February 27th, 2015, 11:10 AM   #6
Bering C Sparky
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Hello,

Like Bob O pointed out, it will work with the example I show here.

In auto the low level float will close first as the sump fills.
Then the high level float will close, this will complete the rung logic and make the pump output true.
Once the pump output is true then the XIC (Sump_Pump) on the branch extension under the high level float will also be true. This seals in the rung and keeps the pump on.
Once your low level float falls (opens) the low level XIC will become false and break the rung logic, thus making the output false.

Manual switch on bypasses all instructions and pump runs regardless of float positions.

BCS
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Last edited by Bering C Sparky; February 27th, 2015 at 11:16 AM.
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Old February 27th, 2015, 11:40 AM   #7
remullis
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Bob and Sparky,

I see what your talking about now. This will work. I appreciate your help. I need to start sketching this stuff out I do believe and following the "And, Or, Then, NOT .... etc strategies. Geez. Thanks again guys!
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Old February 27th, 2015, 11:46 AM   #8
Bering C Sparky
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No worries,

This is a much better way to write your logic instead of using Latch and Unlatch, if you are able.

It took me a bit to realize this also, but once I started using this method I found it much better and easier.

It is the same thing as wiring a contactor using two momentary buttons for start and stop.

You push the start button and it pulls in the contactor.
You have your power run through a N/O aux contact on the contactor and use this to hold (seal-in) the contactor once you let go of the start button.

Then when you press the stop button it breaks the circuit and the contactor opens.

Same exact principal, just looks a little different when you write it in Ladder.(See below contactor wiring example)

BCS
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Old February 27th, 2015, 07:30 PM   #9
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I will admit to not reading all of this thread, so forgive if I repeat anyone else's thoughts....

The "system" automatically controls the level in the sump using two float switches (I read that far at least)... Some questions...

Why is there a "manual" option ?

What can the operators achieve in manual mode that can't be achieved in auto ?

Do the operators absolutely need to override the automatic level control ?
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Old February 28th, 2015, 07:14 AM   #10
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The Switch change to Push Button for both Operation,

Set Timer to allow manual operation run,

series signal with low level for restore Auto.

indicator lamp for Auto and Man.
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Old February 28th, 2015, 07:15 AM   #11
Bering C Sparky
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Not sure in the OP's case but I can speak from my own experience.

1) The floats in the sump usually sit higher than the actual sump pump/motor (if motor is submersible). So if you want to clean out the sump or work on the motor/pump, or just get a chain fall hooked to the top of the motor/pump so it can be hoisted out, or drop something in the sump and want to retrieve it, it is nice to be able to do these things without going swimming, so yes you may want to put the sump in manual and drain it down further than the low level switch would allow.

2) If the float should fail for some reason and you find yourself suddenly seeing water (or what ever you might be pumping with this sump) in places that it should not be, then it is nice to be able to simply turn a switch and get the sump pumping again to stop the ever rising whatever it is you are pumping.

3) I have even seen some (3 phase applications) that have a reverse feature in case something gets stuck in the pump, you can reverse it and see if it will free the object without having to pull the pump/motor. You would need to have manual mode for this also.

4) Many times during our production if the ship has a large list, then the water is pouring into the sump at such a rate that it will cycle the motor on and off excessively, so we will put the pump in manual and let it run continuosly until the list can be compensated for.

It is kind of like the same way and elevator has a service mode.
99% of the time you will run it in automatic, but there is that 1% that you need to switch it over and run it in manual, for maintenance and the occasional oh s#!T.

Edit: Just started thinking, I dont believe that there is one piece of equipment on this entire ship that has a "Automatic Mode" Only and will not allow the operator to switch over and take control if they so choose.
I will give this some more thought and let you know if I come up with something that is Auto Only.

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Last edited by Bering C Sparky; February 28th, 2015 at 07:36 AM.
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