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Forum Index : Microcontroller and PC projects : Sludge level measurement
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| akashh Senior Member  Joined: 19/01/2014 Location: IndiaPosts: 115 |
Good morning, I have set up a wattmon sludge monitoring and control system with 5 different sludge settling tanks, each with 3 level sensor floats. The tanks are spread out, the longest run is about 600 meters. I read the floats over digital inputs (optically isolated) over a 24v bus that runs across a utp cable. I can also power an SSR at the pump location over the same cable. Everything worked beautifully for the first month, but then sludge buildup on the float sensors caused erratic behaviour, they seem to get stuck a lot and so the pumping is a mess. These are normal low cost filtered water probes that work great in clean water (i have another setup which is running for well over a year). So I'd like to see if anyone has any bright ideas about how to solve this? Things I came up with are: 1) Extend the arm of the float and put a bigger float at the end (such as a golf ball) to give it more leverage 2) stick bare wires (24V DC) into the tank instead - current isnt more than a few ma 3) get an ultrasound distance sensor mounted at the top, but how to get this data to the wattmon over a cable of 600 meters? 4) get rid of the whole monitoring part and just use a float locally (large armature one) connected to the pump directly as is traditionally done 5) figure out a contraption with levers so that the actual sensors can be mounted outside the water but some type of floating rods will push them up at appropriate levels Any other ideas, suggestions are welcome! Akash |
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| hitsware Guru  Joined: 23/11/2012 Location: United StatesPosts: 535 |
what tolerance ? gps ? |
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| akashh Senior Member Joined: 19/01/2014 Location: IndiaPosts: 115 |
I am not sure i understand the questions... The system is located in Calcutta, India if you are asking about the location. The system requires 2 digital I puts for the hysteresis. The 3rd triggers an alarm when the water gets above the top probe. |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2946 |
Hi Akashh, Could you use an ultrasonic distance sensor? Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5111 |
Or a pressure sensor at the bottom of the tank? Pressure reading will be proportional to sludge level. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| akashh Senior Member Joined: 19/01/2014 Location: IndiaPosts: 115 |
Hi, Just for clarification I've included a diagram of the cabling: 
So, I would need to figure out how to get a ground wire (I only have 24V, which is looped back through the float switch to the opto)... |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5111 |
Is the sludge conductive? Could you use a stainless steel probe? The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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halldave Senior Member Joined: 04/05/2014 Location: AustraliaPosts: 121 |
I would think that a waterproofed pressure sensor would give you the correct depth BMP085 in some waterproof container perhaps regards David |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
I vote for ultrasonic. When I had a boat I hooked up the manually operated bilge pump to an ultrasonic sensor. It was waterproof (and probably sludge proof) and worked brilliantly when tested. I had it set up for automatic operation to engage the bilge pump, sound a piezo alarm, and turn on a red light when it detected contact with fluids. One day I set off and forgot to close the drain hole. I got several hundred metres to sea and all hell broke loose but the bilge pump cleared the water and kept it afloat until I went over the side and put the plug in. Unfortunately it was mid winter in Melbourne and the water was very cool. Long time back now and I don't know if you can still get these sensors but it was good. It operated when the water contacted the bottom surface and had a run on time (hysteresis) of 30 seconds after no longer sensing water. It was much better than mechanical sensing. |
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| halldave Senior Member Joined: 04/05/2014 Location: AustraliaPosts: 121 |
The second part of the problem is interesting How to get the reading back over 600 meters of utp Various wireless transceivers tap out at around 300m according to spec Anyone have a long distance 2 wire protocol Weigand comes to mind- may need to bit bang it Regards David |
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| halldave Senior Member Joined: 04/05/2014 Location: AustraliaPosts: 121 |
Sorry it's 3 wire |
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| VK2MCT Senior Member Joined: 30/03/2012 Location: AustraliaPosts: 120 |
For option #5 - How about mounting a spring loaded microswitch (or sensors) above the top of the tank. Connect & drop a 'fishing line' with a weight near the end of the line. Attach a floating rubber duck (or similar) to the end of the line. When duck floats sufficiently, it lifts the weight and switches the microswitch/sensor. John. |
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| akashh Senior Member Joined: 19/01/2014 Location: IndiaPosts: 115 |
Thanks for all the ideas so far! The spring loaded micro switch seems like the most easily doable solution since it does not involve any change in basic design. For the other ultrasonic solution, I suppose a completely separate controller with three relays could solve it but I am trying to find a low cost low tech solution that is retrofitable. How would one go about ensuring that the three lines for the various heights don't get entangled? The pressure sensor idea isn't clear to me, if its in a waterproof box which is airtight, how would the pressure affect the reading? Is the pressure inside the airtight box affected by the amount of water on top of the box? |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2946 |
Akashh, A few questions I have? How high are these tanks? How `sludgy' is sludge? ie. will there be car tyres/ dead animals/ tree branches or just `grey water'? How far from the lip of the tanks do you want the sensors? Or what levels do you want to sense? Is there any turbulence to consider? Regards, Mick EDIT *** I would do something like this: 
The Pivot and microswitch are OUT of the tank and the long part of the arm is in the tank.. Use the most appropriate sized ball for the job.. BASKETBALL for huge tanks (held on by a wire cage) or pingpong ball if only small tanks. You can add a threaded bolt onto the top of the gimble to give your self some adjustment. Good Luck Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6220 |
As much as I like electronics, I agree with Mick. As well as a longer arm and bigger float, you could try a large float on a rope going over a pulley. The other end of the rope has a counterweight on the outside of the tank. This acts as a visual indicator and you can use it to operate the microswitches. Jim VK7JH MMedit |
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| akashh Senior Member Joined: 19/01/2014 Location: IndiaPosts: 115 |
Bigmic, the tanks are big, about 4 meters by 4 meters by 3 meters deep minimum. They are made of solid concrete, with a manhole and a side hole for the wires and pipes. I have a long aluminium flat bolted to side of the manhole and probes are attached to that at fixed intervals. The water is grey, it has already gone through a couple of settling tanks so no leaves even, just a bit viscuous. I like the ball idea, but I was wondering if it wouldn't then make sense to just extend what I have now first to see if that helps? The floats are magnetic I think, they have an electrical contact when closed and they are fully waterproof. So I thought just extending the arm to give it more lift and weight would perhaps solve it? I will certainly do some more thinking about the pulley idea, maybe putting the float in a PVC pipe would avoid different probes from getting tangled... |
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