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Old 01-21-2014, 08:17 PM   #1
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How to test holding tank sensors

My One Place external holding tank sensors manufactured by Precision Circuits Inc. worked great for the first year. My black tank recently started showing 1/3 even when empty then 2/3 too soon and for quite some time before reading full. I flushed my black tank with dawn, then Thedfords eco black tank cleaner at 400%. Each time letting it set for 24 hours and driving before dumping and flushing. No luck! Must be a bad sensor. I removed the two screws holding the black tank flush connection to see the 3 sensors. I used a long screw driver to reach in an touch each one. I wet my hand and touched the metal part of the screw driver to ground out each sensor while looking at the display. Touching two of them would change the display and one would not. Ok I knew I had a bad or blocked sensor. At dusk dark I used a very bright led pen with 6 LEDs and held it up behind the black tank and it made it transparent even with water it it. The attached photo's explains it all.

I cannot put ice in the tank and drive around. Thedford said that I would damage the electric toilet internally.

I will follow up with the rest of the story.

This is me trying to pay back to the forum. I am sure many know much more than me.

Thanks

Jesse
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Old 01-22-2014, 12:05 AM   #2
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I am also experiencing the same problem with my 2012 Ellipse. Mine will show full at the same time as the electronic toilet reads full. Goes to 2/3 when I empty the tank and run the tank flusher.
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Old 01-22-2014, 05:10 AM   #3
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There may be an adjustment you can make for being empty on the level panel or behind it on the circuit board. Before doing that I would get some bath salts and put in the tank with about 10 - 15 gallons of water, HOT water works great. Drive this around a bit to ensure that the tank is really clean. It may be possible that the area where the sensor is actually has a build up of crap blocking the sensor. It's also possible that the tank actually has a big buildup of crappy paper. Let it soak over night then drive it around and dump it after you add even more water or beter yet hook up the black tank flush and run that while dumping. If all else fails then the sensor could be bad and needs replacing.
Mine on the forward bath room had to be replaced and it was acting that way since we got her in August.
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Old 01-22-2014, 05:38 AM   #4
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Sensors and systems are different I know. But mine work perfectly after ten year use.

First using hot water in cleaning makes a huge difference. Second, I have one of those wands with the small perforations on the end to make a concentrated spray. Got it a CW. I put it down the toilet and simply move it around as far as I can snake it into the toilet. Just the action of water pressure cleans the sensors on mine and keeps the black tank clean most effectively than anything else I do.
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Old 01-22-2014, 07:07 AM   #5
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Quote:
Originally Posted by jmarr1 View Post
I am also experiencing the same problem with my 2012 Ellipse. Mine will show full at the same time as the electronic toilet reads full. Goes to 2/3 when I empty the tank and run the tank flusher.
Hi jmarr1
The controller doesn't know what position a sensor is, just how many are sensing. So if the middle and lower sensor is blocked it would do what yours is doing.
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Old 01-22-2014, 07:13 AM   #6
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Jmarr1
My one place doesn't have an adjustment. If you look it the tank with a lite and don't see it blocked then ground our each sensor and see if the display changes. The two that don't make any difference are blocked or bad.
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Old 01-22-2014, 12:09 PM   #7
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I am confused - my sensors are black squares adhered to the side of the tank at three levels with wire daisy chained between them.
I have the sensors shown HERE ,scroll down to PN 00-10023-000 Digi-Level Tank Sensor.
I don't see them in the picture you posted.

If you do have them the following info may be of interest:
There are three small black square sensors glued the side of the tank with a wire running between each sensor. A wire from the top sensor goes back to the display board. It supplies 12 volts from a resistor on the display board to the string of sensors. There is a wire from the bottom sensor going back to the display board ground.

The sensors are active devices - that is they contain an integrated circuit.
When the fluid reaches each one it - in effect - acts as a switch connected across a resistor and closes when the fluid is there and opens when it isn't.

A LM339 Low Power Low Offset Voltage Quad Comparator IC senses the voltage change and turns an LED on the display board on or off .
Note that the board really doesn't know which of the three sensors is involved since they are in series.
For example if the level is rising it turns on the 1/3 full sensor when any sensor closes. When another one closes it turns on the 2/3 full LED and so forth. This works well when all of the sensors are good but if one sensor fails open the display board will show 2/3 even when the tank is full. Conversely if any sensor fails closed the 1/3 LED will be lit when the tank is empty.

They can be fooled when enough wet gunk builds up on the tank wall.
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Old 01-23-2014, 06:34 PM   #8
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Quote:
Originally Posted by Clay L View Post
I am confused - my sensors are black squares adhered to the side of the tank at three levels with wire daisy chained between them. I have the sensors shown HERE ,scroll down to PN 00-10023-000 Digi-Level Tank Sensor. I don't see them in the picture you posted. If you do have them the following info may be of interest: There are three small black square sensors glued the side of the tank with a wire running between each sensor. A wire from the top sensor goes back to the display board. It supplies 12 volts from a resistor on the display board to the string of sensors. There is a wire from the bottom sensor going back to the display board ground. The sensors are active devices - that is they contain an integrated circuit. When the fluid reaches each one it - in effect - acts as a switch connected across a resistor and closes when the fluid is there and opens when it isn't. A LM339 Low Power Low Offset Voltage Quad Comparator IC senses the voltage change and turns an LED on the display board on or off . Note that the board really doesn't know which of the three sensors is involved since they are in series. For example if the level is rising it turns on the 1/3 full sensor when any sensor closes. When another one closes it turns on the 2/3 full LED and so forth. This works well when all of the sensors are good but if one sensor fails open the display board will show 2/3 even when the tank is full. Conversely if any sensor fails closed the 1/3 LED will be lit when the tank is empty. They can be fooled when enough wet gunk builds up on the tank wall.



That's a good explanation, so it's kind of a dumb system that just counts how many sensors are closed.



One thing I found when my Tecma Thetford toilet display read "yellow" instead of "green" when the tank was empty. The "one place" display did read empty. I found that the toilet display read from its own set of sensors, redundant to the "one place sensors". One of the Tecma Thetford sensors was delaminating from the tank. The adhesive did not adhere to the tank properly. The dealer had some special two sided tape to repair the sensor.
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Old 01-23-2014, 06:53 PM   #9
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I suspect your tank is 'dirty' around the sensor area. A tech at Forest City advised us to dump dishwasher power that contains enzymes down the toilet after each dump. The hot water and this trick may solve your problem. We use septic tank toilet paper and usually dump not long after we read 2/3. I back flush well and close the black valve while running the flush cleaner for a while then dump again. I always leave some fresh water in the tank and then add a cup or so of the detergent. I also use about a cup of backing soda to sweeten things up. We have been in this coach full time since May and are having great success with this method. (I close the grey valve the day before I dump as a hose flush after I dump the black tank.)
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Old 01-23-2014, 10:31 PM   #10
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We have been in our coach full time since February 2013. The holding tank sensors just started acting up 2 weeks ago. We always use RV toilet paper and I always run the tank flusher after each dump (and that is much more frequent with the Techma toilet than any of the older style we have had in the past). I add a holding tank deodorizer and enzyme each dump. I'm hoping that JBMSR, the original author of this thread, resolves his problem and posts the resolution since he has the same coach as me. I suspect my sensors have failed and will test them to be sure.
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Old 01-25-2014, 09:23 AM   #11
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Quote:
Originally Posted by Jbmsr View Post
My One Place external holding tank sensors manufactured by Precision Circuits Inc. worked great for the first year. My black tank recently started showing 1/3 even when empty then 2/3 too soon and for quite some time before reading full. I flushed my black tank with dawn, then Thedfords eco black tank cleaner at 400%. Each time letting it set for 24 hours and driving before dumping and flushing. No luck! Must be a bad sensor. I removed the two screws holding the black tank flush connection to see the 3 sensors. I used a long screw driver to reach in an touch each one. I wet my hand and touched the metal part of the screw driver to ground out each sensor while looking at the display. Touching two of them would change the display and one would not. Ok I knew I had a bad or blocked sensor. At dusk dark I used a very bright led pen with 6 LEDs and held it up behind the black tank and it made it transparent even with water it it. The attached photo's explains it all.

I cannot put ice in the tank and drive around. Thedford said that I would damage the electric toilet internally.

I will follow up with the rest of the story.

This is me trying to pay back to the forum. I am sure many know much more than me.

Thanks

Jesse

Follow up:

1. Filled the tank with the eco black tank cleaner from CW and used 4 times as much as requested. let sit then lowered a bit for slosh room then drove and inspected. still no difference.
2. Filled the tank with water and added dawn and cascade. let sit then lowered a bit for slosh room then drove and inspected. still no difference. BTW FYI the second baths sink drains into the black tank.
3. Filled the tank with very hot water and then drove and inspected. still no difference.
4. Filled the tank with 12 gallons of bleach then and water, let sit then lowered a bit for slosh room then drove and inspected. still no difference.
5. Removed the lower gate valve assembly to gain access to the tank and used a long brush with pinesol on it and with the light I could see the brush scrubbing the area needed but did nothing was happening!
6. OK NOW I AM ANGRY!. I put straight muriatic acid into a pump sprayer and taped a wire to the plastic hose to bend to the desired angle and sprayed into the tank onto the sensor area. The pictures tell it all.

I would not recommend anyone using muriatic acid without proper knowledge, protection and assistance.

I realize that I need to do things differently from now on to keep the tank clean. I have designed a failsafe black tank flush without having to run another hose. what's the point of having a hose real when you have to drag another out to flush. I will follow up soon with the details if anyone is interested.

Thanks

Jesse
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Old 01-27-2014, 10:29 PM   #12
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Jesse, a lot of hard, dedicated work on your part to attempt resolving your sensor issue. I would hope to never deal with the issue, but your efforts are worth knowing about should we experience false sensor readings. Speaking of which, we learned about the mid-deck bath sink being tied into the black tank in an unfortunate way. While dry camping we checked the OnePlace LCD tank level readings more than once each day, and trusted that the Tecma toilet switch LED would indicate a full black tank when they illuminate red. Though both bathroom switches indicated amber, a flush in the mid-deck bathroom one morning pushed black water up into that bathroom's sink. Yuck! I immediately checked the OnePlace and sure enough it indicated Full. We had CW investigate, and they discovered the Tecma upper sensors are mounted too high, higher than the OnePlace sensor on the black tank sidewall. New sensors are on order by CW for replacement to ensure accurate readings and prevent another unpleasant backwash into the sink. Best regards.
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Old 01-30-2014, 10:27 PM   #13
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Quote:
Originally Posted by Jbmsr View Post
My One Place external holding tank sensors manufactured by Precision Circuits Inc. worked great for the first year. My black tank recently started showing 1/3 even when empty then 2/3 too soon and for quite some time before reading full. I flushed my black tank with dawn, then Thedfords eco black tank cleaner at 400%. Each time letting it set for 24 hours and driving before dumping and flushing. No luck! Must be a bad sensor. I removed the two screws holding the black tank flush connection to see the 3 sensors. I used a long screw driver to reach in an touch each one. I wet my hand and touched the metal part of the screw driver to ground out each sensor while looking at the display. Touching two of them would change the display and one would not. Ok I knew I had a bad or blocked sensor. At dusk dark I used a very bright led pen with 6 LEDs and held it up behind the black tank and it made it transparent even with water it it. The attached photo's explains it all.

I cannot put ice in the tank and drive around. Thedford said that I would damage the electric toilet internally.

I will follow up with the rest of the story.

This is me trying to pay back to the forum. I am sure many know much more than me.

Thanks

Jesse
Madred this might help you.

Jesse
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Old 02-04-2014, 07:35 PM   #14
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Originally Posted by Jbmsr View Post

Follow up:

1. Filled the tank with the eco black tank cleaner from CW and used 4 times as much as requested. let sit then lowered a bit for slosh room then drove and inspected. still no difference.
2. Filled the tank with water and added dawn and cascade. let sit then lowered a bit for slosh room then drove and inspected. still no difference. BTW FYI the second baths sink drains into the black tank.
3. Filled the tank with very hot water and then drove and inspected. still no difference.
4. Filled the tank with 12 gallons of bleach then and water, let sit then lowered a bit for slosh room then drove and inspected. still no difference.
5. Removed the lower gate valve assembly to gain access to the tank and used a long brush with pinesol on it and with the light I could see the brush scrubbing the area needed but did nothing was happening!
6. OK NOW I AM ANGRY!. I put straight muriatic acid into a pump sprayer and taped a wire to the plastic hose to bend to the desired angle and sprayed into the tank onto the sensor area. The pictures tell it all.

I would not recommend anyone using muriatic acid without proper knowledge, protection and assistance.

I realize that I need to do things differently from now on to keep the tank clean. I have designed a failsafe black tank flush without having to run another hose. what's the point of having a hose real when you have to drag another out to flush. I will follow up soon with the details if anyone is interested.

Thanks

Jesse
Works well. One minute = 5 gallons
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Old 02-04-2014, 07:50 PM   #15
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Flows after hose reel through two cut offs, a one way valve, and a spring loaded flush lever to activate. Also has a cut off Y to supply a separate hose and sprayer
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Old 02-05-2014, 11:09 AM   #16
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Flows after hose reel through two cut offs, a one way valve, and a spring loaded flush lever to activate. Also has a cut off Y to supply a separate hose and sprayer
After I rotated your picture and saw what you have I was even more confused. I have no idea what you are gaining with all of this extra plumbing. The sani-flush port is a standalone fitting. It is intended for a separate non-potable use hose to be fitted to.

What am I missing in what you have done?
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