Presure Sensors to Measure Tank Fluid Level ?

[twistedtree]

I've got an update on this, and am seeking advice from anyone with N2K knowledge.

After much back and forth with Maretron (they were very helpful and engaged) the conclusion was that their TLA100 N2K tank sensor adapter could not be made to work with the Centroid tank senders. The Centroid senders have a voltage output, not a resistive output, and the TLA can't deal with it. The TLA has what they call "Gauge Mode" where it's designed to passively monitor the combination of a Sender and Gauge, and I remain puzzled why that isn't exactly what I need - after all the voltage output of the Centroid sender is just like the voltage one would measure on the Send terminal of a Sender and Gauge wired together - but Maretron steered me away from that configuration, and never really explained why it wasn't what I had hoped. I guess they know something I don't.

So where does this leave me? On my water tanks, I'm leaning towards the original pressure sender approach described in this thread. I would use more sensitive senders to get the desired accuracy. My hesitations are:

- I worry about the senders getting blocked by crud and requiring more service than I'd otherwise like.

- I need to add a number of fittings to the tank (elbows, shutoffs, reducers, etc) which will add about $25 - $50 for each tank, plus $125 for each Sender, plus $350 or so for the N2K adapter shared across both tanks. It adds up to being pretty expensive.

Just to answer the obvious questions, I can't use an ultrasonic or float sender due to the shape of the tank, and the Centroid Sender doesn't work well with water maker water, and guess what I just installed.

On the fuel tanks, I have a couple of choices. I could:

1) Use the pressure sender approach on them too. The same maintenance concerns apply, but there is the added problem of fitting the sender hardware when I have full tanks. I suppose I could have someone come pump them out, then fill them back up again, but what a nuisance. I think I read somewhere about using a shop vac on the filler while plugging the vent to create enough vacuum in the tank so the fuel won't flow out of the tap when I remove the plug.

2) Buy a Chetco N2K adapter which they say will work with the Centroid adapters, but the Chetco device is $1200, and it draws 0.75 A all the time which is a lot while at anchor

Any advice?

[twistedtree]

I had to wrap up abruptly on my last post, so here's some more...

The Chetco product has some interesting qualities, but it's very difficult to sort it out. Their website is largely unintelligible with lots of hand waving about what the product can do, but no details so one can understand Exactly what it does, what variations there are of the product, and which one should be ordered. It's a very stark contrast to Maretron's excellent web site and documentation. But once you figure out how to get a hold of the Chetco users manual, you cna start to figure it out. But if you are not an engineer, God help you.

Ok, with my frustrations vented, it does look like their product can interface to the Centroid senders which makes it a candidate for my fuel tanks. However they do not have support for low pressure senders configured as fluid gauges, so I would still have to use the Maretron stuff for my water tanks.

And as mentioned in my previous post, the Chetco box is $1200 or so. That's not so bad if you are using most or all of the 12 inputs, but it's very expensive when using only two as I would. Plus it's a power hog @ 750ma. Other sender interface devices are in the 50-100ma range. I have my N2K set up to be powered and running anytime I'm on the boat including while at anchor so power consumption matters a lot to me.

As a result of all this, I'm wondering if anyone knows of other N2K manufacturers who have tank interface devices that I might check out. Any pointers and/or experience would be welcome.

Thanks in advance,

Peter

[James S]

The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc. ........................

[Lancerbye]

Originally Posted by James S

The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc. ........................

+1

[hellosailor]

At that point, I think I'd take a new style toilet float valve (the kind that uses a "ring" around a vertical tube, not a ball float) and copy it.

Two stainless rods instead of the tube. A disc magnet or several bars, on a ring shaped float. Then some glass sealed reed switches running up the stainless rods.

As the float goes up/down it trips the reed switches. Each switch can trun on a segment on a small 8-10 segment LED bar array. Low voltage, one moving part, everything else very capable of being sealed. Resolution limited only by how many reed switches you want to use.

[twistedtree]

Originally Posted by James S

The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc.
The Tank Tender - by Hart Systems, Inc. ........................

Thanks for the pointer. If the gauges tied into n2k I'd consider them, but as they stand they are out for my needs.

I did find that Garmin has a tank adapter not unlike Maretrons. I might give it a try, but worry that it's and OEM version of the Maretron device and that I'll run into the same problems..

[twistedtree]

Well, I've come full circle on this subject and am in the process of fitting pressure sensors to all my tanks for fluid level measurement. As a quick recap....

I want my water and fuel tank levels on N2K, so that's what I'm trying to accomplish. Sounds easy, right? I wish.

My tanks all have Vee bottoms, and sender mounts that are offset from the bottom of the Vee. Looking straight down from the sender mount you see the sloped bottom of the tank. To "see" the very bottom (full depth), you have to "look" off at an angle from the sender mount. The result is that any sender that operates vertically (floats and ultrasonic senders) won't reach to bottom of the tank. Additionally, ultrasonic senders must reflect off a flat bottom.

To reach the bottom of the tank, the sender probe needs to bend to reach the bottom. The only senders I've found that can bend and operate at any angle are capacitive senders, and that's what my boat is currently equipped with. However, the capacitive senders have a voltage output, not a resistive output. As such, none of the N2K gauge adapters can interface to my senders. I've spent weeks trying with lots of help from various vendors, but the final conclusion is that it's can't be supported.

I've also come across another issue, which is that the capacitive senders (at least the brand my boat is equipped with) do not work reliably with water maker water. The water is too pure. I just installed a water maker, and want gauges that work, so this means the capacitive senders need to be replaced with something else at least for my two water tanks. This leaves no other alternative but to use pressure sensors. At least there is no alternative that I can find.

For my fuel tanks, I have two choices.

1) I could buy a replacement sent of capacitive senders, except get ones that have a resistive interface that will work with available N2K adapters.

2) Or I can outfit the fuel tanks with pressure senders, just like the water tanks.

The main objection to pressure senders originally - at least the one that caused me to reject them - was that the pressure range was too wide and resulted in less that desirable accuracy. However, Maretron chimed in a source for senders with a narrower range, and hence greater accuracy. With the accuracy issue solved, I've decided to move ahead with the pressure senders.

I'll outfit my water tanks first since they are drained and easy to work on. Both tanks have drain plugs on their sides right at the bottom of the tank, and my plan is to fit a shutoff, then a Tee to the pressure sender and to the drain plug. With that arrangement I'll have a shutoff for servicing the pressure sender, and still have the drain available as well.

The fuel tanks also have tapped and plugged holes, and I plan to outfit them the same way as the water tanks. The catch, however, is that my tanks are full. I'll either have to get someone to pump them out, wait while I fit the shutoff, then fill them back up again, or I'll wait until I'm into the boating season and run my tanks down enough so I can pump one tank over to the other until the first is dry, fit the shutoff, then pump back over to the other tank. Either way it's a pain in the butt.

By the way, I'll be leaving the whole existing gauge system in place as a backup.

[s/v Jedi]

Very nice Twisted... I'll be close behind you doing the same thing... doing canvas projects at the moment but will get that done quickly

ciao!
Nick.

[twistedtree]

Originally Posted by s/v Jedi

Very nice Twisted... I'll be close behind you doing the same thing... doing canvas projects at the moment but will get that done quickly

ciao!
Nick.

I think we live in parallel universes. We both did electronics refits about the same time and ended up building almost identical system. Now N2K tank monitoring, and I'm just finishing up a canvas project too. And I won't even mention DSLRs (oops, I just did). Spooky.

[twistedtree]

Here's a quick follow up on this little project. I've been cruising now for about 6 weeks with the pressure sensor gauges in my two water tanks. They work and correlate within a few gallons with the original Computank gauges which I left in place. I have, however, encountered a anomalies that anyone else trying this should take into consideration. If only I could see ahead as well as I can see backwards......

Issue #1 is related to the way my tanks are configured adn may not be applicable to anyone else. My aft tank sits higher than my forward tank, and via a balancing line drains into the forward tank. The water pump draws only from the forward tank. As a result of all this, the aft tank empties first, then the forward tank draws down. Where this gets funky is that as the aft tank fills it creates additional head on the forward tank. Initially the forward tank reading pegs at 160G (full), but as the head builds, the pressure sender on the forward tank goes out of range and I get "---" on the tank level display. FWIW, the display is a Maretron DSM-250. It's not the end of the world since I know that "---" means the forward tank is full, but it's a rough edge I wish weren't there.

Issue #2 has to do with tank venting, and is again perhaps a bit specific to my boat. My tank vents apparently do not rise steadily as they work their way through the boat, and trap water in them at the low spot(s). Because this water does not drain out, it creates back pressure in the tanks when you fill them, and a vacuum when you empty them. When filling the tanks, I can hear the vent gurgling and the back pressure creates a falsely high reading. Long term I'll try to re-do my vents so they drain back properly, but in the mean time I need to open the deck fills for both tanks to vent them properly when filling. Aside from the false level readings, the poor venting also prevents proper water flow from the aft to the forward tank, so this is a problem even without the pressure level sensors.

So I guess my short advice is to check your tank venting to be sure it drains back and provides full, proper venting. Mine doesn't.

[James S]

Yep...they gotta vent right...pretty much like all the other storage tanks on board...and its not easy, especially when you take into account heal...
Thanks Twisted.

[GordMay]

Originally Posted by twistedtree

... My tank vents apparently do not rise steadily as they work their way through the boat, and trap water in them at the low spot(s). Because this water does not drain out, it creates back pressure in the tanks when you fill them, and a vacuum when you empty them ...
... So I guess my short advice is to check your tank venting to be sure it drains back and provides full, proper venting. Mine doesn't.

For all practical purposes, your tanks are not effectively vented.

[twistedtree]

Yes, I agree this is a basic venting problem with the boat. It just has broader consequences with the pressure sensor tank gauges.