Water depth gauge using capacitance?

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Pommie

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I need to keep track of water depth from 0 to 100mm (4") in a container. Initial calculations show that a pair of 100mm square conductors placed 5mm apart will vary from approx 20pF to 1.4nF. There are designs on the net that will measure capacitance down to 20pF - See The second circuit here. I'm thinking of laminating aluminium foil so it's water proof and 3D printing a mesh to keep the separation fixed. I don't really care how accurate the measured capacitance is, just if I can calibrate it to give a reasonable reading of depth.

Anyone any thoughts on this approach? Is there an easier way - not float switch. At what separation will capillary action become a problem?
BTW, I'll be using an esp8266.

Mike.
 
Hi Mike

I had a brief foray into depth gauges last year when I was trying to measure the contents of our IBC's.

I made two differing models .. Probe 2 is a capacitance probe which is linked to a moving coil meter which worked OK; however, since the liquid content of the IBC's was a form of soap I ended up using a sonic probe and an Arduino which was much better for our use.

If either of those appeals to you I can look out the details and send them on

S
 

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I didn't think of that, I've got an ultrasonic distance measuring device. Now, where did I put it?

Mike.
 
+1 on ultrasonic sensor.

By the way, the level of an IBC can be determined by the sound reflected back from a container - you must use a range of frequencies as the source, and as the echo is received, filter out each original wavelenth and compare the intensity changes. It was quite cleaver - the original company making it has gone out of business but I heard the successor company is refocusing their business model and giving up drum/ibc monitoring for opportunities that can be more easily justified economically.
 
Would you typically submerge the ultrasonic depth sensor pointing up so it reflects off the water-air boundary? Or have unsubmerged pointing down so it reflects off the air-water boundary?
 
Pommie said:
I've got an ultrasonic distance measuring device.
Click to expand...
I think you'll find most of those have a minimum range which is considerably greater than the distance you are trying to measure.
 
I'm going to persevere with the capacitive device - just to see if it works. Seems like a nice challenge.

Mike.
 
alec_t said:
I think you'll find most of those have a minimum range which is considerably greater than the distance you are trying to measure.
Click to expand...

The simple maker-quality unit from Parallax and the cheap knock-offs from eBay have a minimum of range below 2cm. Resolution is quite good but, if comparing ranges over a long period of time, the temperature changes can be A significan factor - but not so much over a 40 mm delta if the transceiver is also within a few cm of the highest liquid level. It will make a difference if sensor is several feet from the liquid.
 
i was able to get some good readings when i stuffed a pvc pipe with tinfoil on one digital pin(keep it dry), and put a wire in my tank with an anchor on the other digital pin.
i think 2 pieces of flat foil on each side of the container will work fine.

I used a sampling code to read it and switch the bias of the pins and measure the charge/discharge times ... no analog, just a measurement of how long the digital pin transitioned from 0 to 1,
 
Externet said:
I would discard capacitive.
Click to expand...


The capacitive example I showed above as 'Probe 2' is closely based on the experiments that JimB has detailed and works very well, is quite accurate and easy to use.
The only reason for opting to use an ultrasonic device (HC-SR04) was that the liquid concerned was actually a liquid soap which got the probe rather messy.

dknguyen said:
Would you typically submerge the ultrasonic depth sensor pointing up so it reflects off the water-air boundary? Or have unsubmerged pointing down so it reflects off the air-water boundary?
Click to expand...

The device was built into an ABS enclosure which was wide enough to span the screw cap air vent on the top of the IBC .. ..



The HC-SR04 is not visible on this picture, but it is mounted in the bottom edge of the case.

Temperature variation never raised any issue, but condensation, if the unit was left in situ too long was another story.

S
 

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