Looking at doing a DIY capacitive black water tank sensor

[GILow]

Hi all,

I am getting a little tired of playing the "guess the blackwater tank level" game, even more tired of getting it wrong.

I've looked at some of the options for monitoring the level, and the one that looks like it will work best with my particular setup is a capacitive sensor.

There are many good articles on DIY capacitive tank sensors, but most are for somewhat "cleaner" environments than a blackwater tank.

I am curious to see if anyone is using a submerged capactive sensor for their tank, and if so, how does it perform over time? Does it block up in any way (no need to go into horrible details here), has it proved reliable over time?

If you went DIY, which approach did you take with the construction?


Edit: I am not entirely settled on a submersible capacitance sensor. I will try external sensing (timber and fibreglass tank), but it seems from some reading here on CF that the external sort get into trouble from the walls of the tanks become... er... messy.

Thoughts and experience of the external sort, particularly DIY would also be helpful.


Matt

[wefleenor]

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.

Bill
Double-Wide

[chrisr]

why does the mix of 'DIY' and 'black water' send shivers down my spine ?



cheers,

[GILow]

Originally Posted by wefleenor

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.

Hmmm... I feared this would be an issue. Do you think the dielectric gap has an influence on the probability of fouling or is it simply “stuff” adhering to the electrodes?

Did you try the external sensor approach?

I’ll be interested to hear how your ultrasonic sensor works out. It was my preferred approach initially, but it seems there can be problems with the surface being a little... err... “fluffy” from time to time and preventing a good reading. Also lots of complaints about needing to clean the sensors, even though they are not submerged.

[GILow]

Originally Posted by chrisr

why does the mix of 'DIY' and 'black water' send shivers down my spine ?







cheers,

Yeah, some room for trouble, no doubt about that.

Touch wood, no major problems with my DIY holding tank so far (less than a year), aside from keeping track of the capacity remaining.

[chrisr]

can you see the tank easily ? is there room for an external sight glass - or even a translucent panel in the tank

would have the added advantage of seeing what you had for dinner last night...



cheers,

[RaymondR]

Have a look at Jaycar Cat ZD1904, let your imagination loose and see what happens.

[GILow]

Originally Posted by RaymondR

Have a look at Jaycar Cat ZD1904, let your imagination loose and see what happens.

That would be a good option if I had an outlet at the bottom of the tank, but I don’t, and for fairly obvious reasons I’m kind of reluctant to start drilling holes.

I’ve see the approach of using a pressure sensor combined with a dip tube with an opening at the bottom, but in most cases it seemed it was hard to maintain pressure over time, so the readings become increasingly inaccurate, just when you’d really rather they were not.

[GILow]

Originally Posted by chrisr

can you see the tank easily ? is there room for an external sight glass - or even a translucent panel in the tank



would have the added advantage of seeing what you had for dinner last night...







cheers,

I can’t find the vomit emoticon, darn it.

Although access to the tank is very good on three of the four sides, I think I’ll give that approach a miss.

[RaymondR]

Originally Posted by GILow

That would be a good option if I had an outlet at the bottom of the tank, but I don’t, and for fairly obvious reasons I’m kind of reluctant to start drilling holes.

I’ve see the approach of using a pressure sensor combined with a dip tube with an opening at the bottom, but in most cases it seemed it was hard to maintain pressure over time, so the readings become increasingly inaccurate, just when you’d really rather they were not.

You could put a sounding tube in from the top and have one of those things they use to pressure up the blood pressure cuff to pump air in and have a calibrated U tube full of water to read off the depth. Or use the pressure transducer and a meter.

[AKA-None]

I’ve thought of possibly adding Some way of flushing fresh water down past the electrodes not sure how that would work but a thought

[rslifkin]

I haven't messed with a capacitive sensor for black water, but I've got the Blue Sea ultrasonic sensor in my tank and it's been pretty good. Occasionally it'll seem to lose reading or get a bit funky, but it's only happened twice and both times has self-resolved fairly quickly, so I'm not sure what's causing it. The rest of the time, it's very accurate (when compared to visually looking at the slightly translucent plastic tank).

[Miket99]

I have been looking at this Gobius Pro, Bluetooth Level Indicator, Marine Sanitation in Wash state carries them, but have not made the jump. My thought was try one at the top of my tank so that it would alarm when 75% full. Anyone else used them?

[John De Bree]

I used on my old boat a float switch off a submersible septic pump and it worked well. Never had a problem with it.

[wefleenor]

Originally Posted by GILow

Hmmm... I feared this would be an issue.

Did you try the external sensor approach?

.

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.

Bill
Double-Wide