View Full Version : Question: Liquid Level Gauge?
Ok, this may be a stretch but I am out of ideas on where to look. I need to electronically detect the level of liquid inside a container, fairly accuratley, and with a sensor that will fit through a hole approximately 3/4" in diameter, and to a depth of about 9.5 inches.
The design I am using involves two wires, running down opposing sides of a thin tube submerged in the liquid from the top of the container. What I need now is a circuit/device that will be able to measure the difference in resistance between the two wires (due to the conductivity of the liquid) accuratley enough to display it on some sort of gauge or LCD meter.
I seem to remember some type of Ramsey display kit that would mimmick this, though I do not find anything now.
Any help, or pointers greatly appreciated.
Jack are you looking for something you can calibrate for a more or less accurate guage, or do you just need a low level [or high level] warning?
I know there are some plans out there for simple "water in the basement" detectors and the converse "low fluid in the windshield washer tank of the car" type applications. My suggestion would be the Ramsey minikit TS1. While it is designed for touch action - the description also refers to a well watered plant. Depending on the conductivity of the liquid - this might work just fine. Also its pretty inexpensive.
If you are looking more for a guage, well that could be trickier - however if you needed something that would let you know in steps e.g. full, 3/4, 1/2, 1/4, empty etc. you could use multiple TS1s powering LEDs. Remember the TS1 has two separate circuits, so 3 TS1s would allow up to 6 indications! Hey, 5 TS1s could provide 10 indications, probably much more accurate than most car gas guages!
Here is another bizarre thought that occured to me. You could try using a sensitive ohm meter with the probe you describe. When the liquid covers just the bottom portion of the probe, the resistance is likely to be less than say when all the probe is covered? If you have, or can borrow, a good old analogue type VOM, you could try that as an experiment. The old RS ones [like the one that is gathering dust at my Mom's house!] included a schematic that could be helpful for future modifications. Let's say this experiment sort of works e.g. the VOM is at infinity when the jar is empty, and reading 10 megaohms when full. You might want to track down a working VOM [a nice big sensitive one] at a flea market etc. Then you could try modifying it to be more sensitive. Hmm - changing the resistor values? Higher voltage battery? Seems my old rig at Mom's used an AA for all but the highest range, and a 9 volt for the highest, so why not try 2 or even 3 [we're getting really brave here!] 9 volt batteries in series [eek 18 or 27 volts!] to increase the sensitivity. DON'T try this with a digital display VOM, or with a precious analogue rig - this is for that $3.00 working special that you picked up at "Wade's Working Wired Wonders Emporium"! If you find that you can modify a VOM to provide a nice scale reading, you can always make a neat fluid volume guage dial out of paper or whatever and glue it on the old VOM [some of those meters you can open up the actual meter, install your new label, then reglue the plastic meter back together. It may not be pretty, but properly calibrated, it may be pretty accurate! Happy experimenting and good luck!
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