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mmcl26554 08-18-2012 01:37 PM

Fresh water sensor in my 1992 Holiday Rambler, how does it work?
The fresh water sensor in my 92 HR looks as if it is a surface mount without any penetration into the tank, does anybody know how these work? I believe it is OEM sensor. Anyway it only senses up to 3/4 never full.\

Jim_HiTek 08-18-2012 02:13 PM

It would be cool if you could post a picture of the assembly attached to the tank.

Just guessing here, but I wonder if it isn't several sets of infrared transmitters and detectors. Could be measuring the index of refraction thru the tank plastic and water. If that's the case, you would have a 12V wire and a ground wire going to the device as well as 4-5 wires going to the display. If that's the case, then either a transmitter or a detector is bad or not properly connected.

mmcl26554 08-18-2012 07:47 PM

There are only 3 wires. The sensor has one rectangular 1x1.5 inch box between 2 wires which lead to some metal duct tape. One on either side of the box. The wires do not appear to go all the way to the top or bottom of the holding tank, unless the wires are very small and I cannot feel them under the tape. It isn't a big deal that it won't register full because it is accurate below 3/4 and I wouldn't spend a dime to fix it, but I am just curious how it works. I will try to post a picture tomorrow, but we are getting ready for a trip to Niagara Falls Monday, so if I don't get it posted I will ASAP.

Jim_HiTek 08-18-2012 11:34 PM

Interesting. I would think that two of those wires would be +12V and ground. The 3rd wire could be either a digital or analog output signal going to the display circuitry. The metal tape would be the sensor.

I can think of 3 possible methods, but my best guess would better if I could see a picture of the sensor, box, and display.

For a '92, sounds kind of sophisticated. Perhaps this is a prototype of the SeeLevel detection system: Sensor Board - For use with all model 709 tank monitor systems

mmcl26554 08-19-2012 09:19 AM

2 Attachment(s)
OK here are the pictures.

Jim_HiTek 08-19-2012 10:10 AM

Very, very interesting. Those sensors are so far apart that it would be difficult to adjust that circuit in the testing phase. Even with precision parts it would be hard to maintain much accuracy. If there is a small slotted adjusting screw peeking out of the potting material, that's how you'd readjust it. I can't see if it has an adjustment from the pictures, but if it does, you could tweak it a little. Mark it first. Then 1/4 turn per test.

My best guess is that it is using the tape as a electrically tiny capacitor. Which is a main component of a high frequency oscillator. As water fills the tank, it changes the capacitance a tiny amount, which changes the frequency of the oscillator. That is converted to a voltage sent to the display which, using comparators, toggles the lamps.

If it were mine, I'd 'black box' it by measuring the output while connecting my O'scope to the two white wires. And filling the tank while monitoring.

You might be able to affect a small change by cleaning those foil sensors. Might make enough difference in the output to bring it back in line. I remember the olden days when we used large 'air gap' rotating capacitors to tune in radio stations. If the plates of the capacitor had developed a coating of dust and gunk, it would shift the frequency a bit.

Does it appear to you to be original equipment? Is there any name tag on that black box or on the display?

Gary RVRoamer 08-19-2012 10:18 AM

Garnet Technologies makes a similar contact system, called the See Level Gauge. Works great (I have them). Maybe some info on their web site would give a clue.

jspande 08-19-2012 11:35 AM

Looks like the Tech-Edge system - try a Google search on "Tech-Edge".

Jim_HiTek 08-19-2012 12:00 PM

Clicky for Tech-Edge:

mmcl26554 08-19-2012 05:33 PM

Jim, that is it! I sent Tank edge an email asking if I can recalibrate it I'll see what they say. I assume my other holding tanks have this same technology and they work just fine. It surely is a great idea, no dirty sensors!

mmcl26554 09-07-2012 03:45 PM

I was able to contact the manufacturer tech-edge, they sent me a user's manual and there is a trimmer pot. I have made the adjustment and it is now accurate.

Jim_HiTek 09-08-2012 05:52 PM

Very cool, Michael, but where was that adjustment? In the display or in that little box near the sensors?

mmcl26554 09-08-2012 06:35 PM

It was on the display. There was a black plug just above the button to press, which is easy to pry out with a small screwdriver. The pot can be reached with the same small screwdriver and adjusted while holding the button down. There is one for each item displayed, fresh water, black water, gray water and propane. If anyone needs a picture I can post one.

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