I am doing a project which require to build a moisture sensor to measure wood chip moisture content. I built the the cylinder and put all the capacitor plate around it and I was able to measure the capacitance of the wood chip. However, I do not know how to convert capacitance that i got to the moisture content. I did a lot of research online but they do not talk briefly about it. Is there any specific equation or way to convert capacitance to moisture content?
Electronic – Calibrating a capacitive moisture sensor
calibrationcapacitancehumiditysensor
Related Solutions
There is almost certainly some part of the motor mechanism that is accessible and which can be used to return a periodic signal. This could be eg
- a rotating shaft with a "bump that will trigger a magnet plus Hall sensor,
- or the flywheel on the motor which will probably have some part which differs enough to trigger a sensor.
- or the flywheel surface can be given a white soot of paint etc or a strip of reflective tape to trigger an optical pickup.
You can buy optical tachometers which will repond happily to a periodically varying surface and the silvered tape trick is a standard one with them.
Some of the available tachometers will have some form of output (RS232?) or will be more acceptably hackable than the treadmill.
OR you could build your own without too much effort:
Another home made optical tachometer
More complex crcuit than is needed but the front end gives ideas.
This (from above) plus an Arduino is about enough - or just the sensor with care.
Arduino in the sky with clothespegs - actually a really simple optical interface optical tachometer with Arduino based optical tachometer with numerous clothes pegs assisting.
Wow !!! - Vast list or Arduino application with link to above project (at least)
Sample of commercial unit - Australian seller $A80 rtail. I have one of these. Goes OK. No external interface. Hackable.
Identical unit at Farnell UK 43 GBP ;-(.
A likely mechanism for the operation of the sensor is by creating a Galvanic Cell battery out of the probe electrodes, with the moisture in the soil acting as the electrolyte / "salt-bridge".
From the Wikipedia page referenced above:
The "sensor probe" would consist of two dissimilar metals such as Zinc and Copper, which @JimDearden correctly surmises in his answer.
However, the actual current flow due to Galvanic redox reactions is what would create the energy to deflect the needle of the sensor, rather than conductivity of the moist soil alone. The moisture here works merely as an electrolytic medium for the electrochemical reaction.
This sensor would fail if used in distilled or otherwise very pure water, or moisture containing no dissolved salts / electrolytes.
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Best Answer
There's not going to be an equation online for you to just plug in your values, as it's going to depend on your specific device, how you're measuring the capacitance, and probably even the wood you're using. Instead, you're going to need to calibrate it yourself, so you'd collect a bunch of points at known moisture values (ex. 0%, 10%, 20%, ...) and measure the capacitance for each. Assuming they form a smooth curve, you can then interpolate between capacitance/moisture values to get your reading