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Old 27-07-2020, 11:16   #16
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Re: Looking at doing a DIY capacitive black water tank sensor

Have you seen this solution: https://tankedge.com/products.html

I'm considering using this for levels in 2 water tanks, diesel tank and holding tank.

I have no relationship with the company.
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Old 27-07-2020, 11:19   #17
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Re: Looking at doing a DIY capacitive black water tank sensor

I also installed a BlueSea ultrasonic sensor on my black water tank and am very satisfied with it. Works perfectly. If you decide to go this route, you could take a hybrid DIY approach and interface it to a non OEM gauge as the BlueSeas display is a bit spendy. Suffice it to say that BlueSeas buys these sensors from a sensor builder and the gauge can be interfaced to other gauges or displays with a bit of cleverness.
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Old 27-07-2020, 11:48   #18
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Re: Looking at doing a DIY capacitive black water tank sensor

This is a photo taken in the interior of my holding tank showing the PVC pipe that is the SCAD capacitance level sensor. Between cleanings, fouling causes the indicated level to drift higher as the thickness of the fouling increases. Adding citric acid to the tank slows the rate of buildup and will sometimes clean the sensor. Otherwise, it is don the rubber gloves time...

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Old 27-07-2020, 14:37   #19
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Re: Looking at doing a DIY capacitive black water tank sensor

The simplest is a silicon rubber or vinyl bag or balloon on the bottom of the tank under a retaining strap or containing a sinker, filled with coloured water or vegetable oil, and fastened to a tube leading to the bottom of a visual glass tube vertically mounted outside the tank wall. As the tank fills, the oil is forced up the gauge--approximately at the same level or just a little higher than the level of the waste in the tank.
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Old 27-07-2020, 15:02   #20
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Re: Looking at doing a DIY capacitive black water tank sensor

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Originally Posted by wsmurdoch View Post
This is a photo taken in the interior of my holding tank showing the PVC pipe that is the SCAD capacitance level sensor. Between cleanings, fouling causes the indicated level to drift higher as the thickness of the fouling increases. Adding citric acid to the tank slows the rate of buildup and will sometimes clean the sensor. Otherwise, it is don the rubber gloves time...



Bill


Do you know what.... that could have been done without the photo.
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Old 27-07-2020, 15:04   #21
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Re: Looking at doing a DIY capacitive black water tank sensor

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The simplest is a silicon rubber or vinyl bag or balloon on the bottom of the tank under a retaining strap or containing a sinker, filled with coloured water or vegetable oil, and fastened to a tube leading to the bottom of a visual glass tube vertically mounted outside the tank wall. As the tank fills, the oil is forced up the gauge--approximately at the same level or just a little higher than the level of the waste in the tank.


Iím trying to picture this (and get that previous photo out of my head). Does the pipe from the bladder need to exit the bottom of the tank or am I right in thinking it should still work if it exits the top, loops down to the bottom outside, then back up?
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Old 27-07-2020, 15:07   #22
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Re: Looking at doing a DIY capacitive black water tank sensor

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Stuff adheres to the outside of the pvc tube, not directly to the sensor material, but it does change the readings.



I do not have access to the outside of the tank, only the top.



I have a PhD in environmental engineering so I have little fear of my ability to properly handle wastewater. My years of academic research included the development and use of many electronic sensors, including ultrasonic. I have built and resurrected toilets in several developing countries during 12 years as adviser to the Engineers Without Borders chapter.



In this case I am simply accessing the top of the tank through an existing access plate that provides the vent and will actually leave a bit of an air gap from the max fluid level to the ultrasonic sensor to minimize fouling.



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Ah, right, ultrasonic, not capacitive.

I am keen to try capacitive before I go down the ultrasonic path.
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Old 27-07-2020, 20:12   #23
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Re: Looking at doing a DIY capacitive black water tank sensor

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Yes, I have units that fit into a pvc tube and stick down into the black water tank. I have issues with them fouling and giving poor readings. Good news is they function well near the top. However, I am now working on an ultrasonic sensor attached to a pi to measure the level.

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Back in my days as an integrator, one of our customers had several waste-treatment plants. They used capacitive probes, too. These units had two concentric PVC tubes. There was a gap between the two tubes so clean water could be forced into the space. This was done as part of the level-check cycle. Water was forced through for about 30 seconds; the water was then shut off and the pressure vented. It usually took less than 60 seconds for the new level to stabilize. This was done every ten minutes, all under control of a SCADA (System Control And Data Acquisition) system. Once the holding tank reached about 80% capacity, it was pumped out into the next stage.
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Old 27-07-2020, 20:56   #24
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Re: Looking at doing a DIY capacitive black water tank sensor

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Back in my days as an integrator, one of our customers had several waste-treatment plants. They used capacitive probes, too. These units had two concentric PVC tubes. There was a gap between the two tubes so clean water could be forced into the space. This was done as part of the level-check cycle. Water was forced through for about 30 seconds; the water was then shut off and the pressure vented. It usually took less than 60 seconds for the new level to stabilize. This was done every ten minutes, all under control of a SCADA (System Control And Data Acquisition) system. Once the holding tank reached about 80% capacity, it was pumped out into the next stage.


Wefleenor appears to be using an ultrasonic sensor at the top of the tube, not capacitance sensing.

The idea of being able to flush the tubes has merit, though the complexity would be starting to build, and, with it, the change of odours escaping the tank.

I think Iíll start with external sensing of capacitance, and see how that goes.

Some posters are using a commercial version of this with good reports, so I reckon it is worth trying.
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Old 27-07-2020, 23:55   #25
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Re: Looking at doing a DIY capacitive black water tank sensor

There is another thread on holding tank monitoring with some interesting stuff. This contributor appears to like the pneumatic solution.

Re: Holding tank monitoring options?
Another product that I have seen people in this forum recommend is “Tank Tender” Hart Systems - Home . Ofcourse none boating specific priced devices are available in the industrial market such as Afriso Unitel Pneumatic Tank Gauge .
Both these installation details shows the capillary tube into the top of the tank ( which you do not want) However you could install it via a tee the pump outlet line of the waste tank (if from bottom) but would have to valve off upstream on the outlet line when you want to obtain the level of the tank, so the pneumatic pressure signal goes to the tank (level) not venting overboard . If you are DYI guy then you can build yourself something similar with a squeeze bulb pump, 1/4 “ check valve, 2” pressure gauge from a trade shop and some nylon tubing. All work on the principal that the pressure created by the pump is equal to the liquid head pressure in the tank. Due to your tank configuration, to calibrate any of the above you would need to fill the tank to get the 100% reading , empty for the 0%m then mark your gauge accordingly 25%, 50 % ,75% based on the number of flushes required from 0 to 100%.
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Old 28-07-2020, 04:33   #26
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Looking at doing a DIY capacitive black water tank sensor

Itís funny you should mention the number of flushes, but one way i have considered solving this one is digitally. My toilet has one of those timer flush circuits and I know how many flushes (roughly) the tank can take.

So one option is a simple counter circuit.
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Old 28-07-2020, 07:43   #27
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Re: Looking at doing a DIY capacitive black water tank sensor

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Itís funny you should mention the number of flushes, but one way i have considered solving this one is digitally. My toilet has one of those timer flush circuits and I know how many flushes (roughly) the tank can take.

So one option is a simple counter circuit.


Do you have multiple sources into one tank? Otherwise this might be close enough
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Old 28-07-2020, 13:54   #28
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Re: Looking at doing a DIY capacitive black water tank sensor

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Another product that I have seen people in this forum recommend is ďTank TenderĒ Hart Systems.
We have a TankTender on our holding tank. Works great. Reliable and accurate. Just make sure you get one with the purge valve option. If you already have a TankTender, the very nice folks at Heart will send you all the parts needed to add the purge valve option.
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Old 28-07-2020, 15:53   #29
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Re: Looking at doing a DIY capacitive black water tank sensor

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Do you have multiple sources into one tank? Otherwise this might be close enough


Just the one loo. Itís my fallback plan at the moment, you are correct, it may well be close enough.
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