Ultrasonic Tank Level

[Dockhead]

I have had a Maretron TLM-100 ultrasonic tank level sensor on board for a few years -- I bought it to replace the Wema sensor in my black water tank, which does not show level at all, just when the level is "high" or "full". I never got around to installing it.

A few days ago my water tank">fresh water tank level sender -- a Wema one which I replaced maybe 12 or 13 years ago -- failed. With just days to go before I throw off the lines for my summer cruise.

I replaced it with the TLM-100, and configured with a DLM-250. It was a big job because I have to take out my salon table to get to it, which requires unloading the watermaker compartment below it (used for storage since I don't have a watermaker) and holding nuts which can't be reached with human arms.

Well, I'm surprised at how well this works. It makes a very, very precise measurement of the level in the tank, and when you configure it, you can set the tank capacity, and the TLM-100 will put into the network % of tank capacity, and even liters of water remaining.

Obviously the boat must be motionless and level for this to be accurate, but at the dock, the accuracy seems amazing. I ran a load of laundry and the liters remaining went down by almost the exact amount of water consumption for that cycle according to the manual.

This is a big improvement over the Wema gauge which was quite vague, without even any marks on the scale besides "Full" and "Critically Low", so you couldn't tell even something like half full except vaguely, by the angle of the pointer. You may say you don't need more accuracy, and certainly I've lived with the old system for 15 years, but nevertheless this extra information seems really useful to me.

I'm really liking this, so thinking about buying a couple more for fuel and black water tanks.

[Pete7]

We tend to use the mast as a gauge. Stand in the middle of the cockpit and the angle of the mast tells me if we need to take on water. We do have a Wema gauge, but the tank is triangular shaped, so takes an age to go from full to half and then drops quickly. With a 10L spare water container and only coastal sailing, we don't have to worry too much.

Pete

[Ixium]

I wish those ultrasonic ones weren’t so expensive. 300 CAD each.

The top of my water tanks have no room for a normal sender to get in, so they’d be perfect. But can’t justify the cost when I can just open a cupboard and see the side of the tanks and guesstimate water levels.

[Dockhead]

Originally Posted by Ixium

I wish those ultrasonic ones weren’t so expensive. 300 CAD each.

The top of my water tanks have no room for a normal sender to get in, so they’d be perfect. But can’t justify the cost when I can just open a cupboard and see the side of the tanks and guesstimate water levels.

You can see into your tank? Then you certainly don't need any other gauge. Just mark levels on it, and it's not even guesstimating.

[BigAl.NZ]

Originally Posted by Dockhead

You can see into your tank? Then you certainly don't need any other gauge. Just mark levels on it, and it's not even guesstimating.

I got the Oceanic sender for our water tank and it can be calibrated through the Raymarine chart plotter. Similar to your impressions I was very happy with ours - calibrated to a irregular shape and its very very accurate.

[tanglewood]

I would caution against using them for black or gray water. I tried both and it was a complete failure. They seem to need a clean fluid surface to sound off of, and neither black or gray water provide that. I ended up removing mine and replacing them with submersible pressure transducers connected to Maretron pressure modules. The transducer sits on the bottom of the tank and measures the head (depth) of the fluid above it. They can be calibrated for different shape tanks to read in liters or silly US units. They work great for all types of fluids except petrol/gasoline.

[Dockhead]

Originally Posted by tanglewood

I would caution against using them for black or gray water. I tried both and it was a complete failure. They seem to need a clean fluid surface to sound off of, and neither black or gray water provide that. I ended up removing mine and replacing them with submersible pressure transducers connected to Maretron pressure modules. The transducer sits on the bottom of the tank and measures the head (depth) of the fluid above it. They can be calibrated for different shape tanks to read in liters or silly US units. They work great for all types of fluids except petrol/gasoline.

Interesting; thanks for that. Did you use all Maretron equipment for that? Including the pressure transducer?

[GordMay]

Originally Posted by tanglewood

I would caution against using them for black or gray water. I tried both and it was a complete failure. They seem to need a clean fluid surface to sound off of, and neither black or gray water provide that...

An ultrasonic level sensor emits a high frequency acoustic pulse, from its transducer. The pulse travels through the air gap, reflects against the liquid surface, and returns to the transducer. The ultrasonic level sensor measures the pulse time of flight, and converts this into level height, or distance.

Ultrasonic level sensors can generally provide reliable level measurement, of non-foaming, stable [non-turbulent] chemical, water, wastewater, and petroleum based liquids.

Condensation, on the antennas, can sometimes amplify inaccuracy issues, so the antenna shape can be tapered, to discourage accumulation, making it easier to shed condensation; and they can be coated with non-stick Teflon material, to be [somewhat] self-cleaning.


All, of which, reminds me:

Why do people call it “raw sewage”?
Do some people actually cook that stuff?

Mud treatments are good for the skin.
But, I saw a sign, the other day, saying: "Sewage Treatment Works".
Trust me, it doesn't.

[tanglewood]

Originally Posted by Dockhead

Interesting; thanks for that. Did you use all Maretron equipment for that? Including the pressure transducer?

Yes, all Maretron. They have two (maybe even three now) submersible transducers covering different ranges of tank depths. For best accuracy you want the sensor that covered the smallest depth range without going lower than you required depth. The price on the Maretron sensor is better than any commercial equivalent that I could find. They also include an adapter place that fits over a standard SAE tank sender aperture. You thread the sender cable through a grommet in the cover, lower the sender to the bottom of the tank, then secure the cover. It’s a very clear replacement for a typical wema or other sender. And they seem to survive the environment just fine.

[Franziska]

We use some of these glue on thermometer strips.
https://amzn.eu/d/08TKR9th


We glued a number of them horizontal and at a few cm/in of vertical distance on the side of our tank.



Now if we look at the side of the 120l stainless drum which we use as fuel tank and we can see the temperature difference between the full and empty section and from this know the fill level.



We tried this also with temperature sensors and an Arduino. Unfortunately it did fail after a while. So we went for a simpler solution.



We can't access the top of our tank, so we can't install a sensor there. A glued on ultrasound sensor at the bottom did not work either and we do suspect the stainless being the reason...

[Dockhead]

Small update:


I'm more and more pleased with this, the more I use it. I realize there is a bit of false precision in the "liters remaining" indicator but it's still worlds better than the old Wema gauge which didn't even have any lines on it. It's much easier to see how the water consumption is going. And even if the "liters remaining" is only accurate to 10 liters (or even 20), it's really valuable information.


I'm now thinking about updating my other tanks. I will look into the pressure ones Tanglewood so helpfully posted about.

[FlyingScot]

This is good info. We bought them for out two water tanks and two fuel tanks. Both easy to see if you look at the tank. But the water tanks are up forward and the fuel tanks are under each aft bed.

I haven't installed them yet, but it's on the list!

[Zhent]

Thanks for this. We recently received a new cat and neither of the blackwater tanks have sensors in them of any kind - not even quarters or empty/full reporting. The tanks cannot be seen through the access panels for the discharge system, so trying to find a good solution for reporting out their level. Unfortunately they are not rectangular so we need something that can be fairly customized to the volume of the tank.

[rslifkin]

I've had good luck with the Blue Sea ultrasonic sensor in my black water tank. It occasionally loses reading, but 99% of the time it reads the level just fine. And after 5 years it hasn't needed cleaning or anything.

[Dockhead]

Originally Posted by Zhent

Thanks for this. We recently received a new cat and neither of the blackwater tanks have sensors in them of any kind - not even quarters or empty/full reporting. The tanks cannot be seen through the access panels for the discharge system, so trying to find a good solution for reporting out their level. Unfortunately they are not rectangular so we need something that can be fairly customized to the volume of the tank.

Note the comments from someone above about using the Maretron pressure sensor for black water tanks. Probably a hot tip.


The Maretron sensors, both pressure and ultrasonic, can all be custom programmed to suit an odd shaped tank.


Note that you will need a Maretron MFD or an N2K to USB adapter to configure it.