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Measuring the permittivity of a liquid

atferrari

Well-Known Member
Few hours ago I completed the journey started after reading this thread. I got interested in implementing such a device: a VFO fitted with a variable capacitor which inserted into a cuvette full of a certain liquid allows to calculate its permittivity.

For the reasoning supporting the measurement process and calculation, please refer to the posts there, in particular, the OP and the even more specific, #101 by member JimB . I would not dare to add anything.

Prior to starting I had to acquire a reasonable familiarity with VFOs and finally I got one decent BJT Clapp oscillator working in the 1,1 - 1,3 MHz range. The variable cap measures 4 to 144 pF in air. Not bad, considering that I had to revisit (bah, relearn) how to properly bias (resistor divider) a BJT amplifier. The sole "conditioning" of the VFO's output was providing a +2,5V offset prior to applying it straight to the TMR3CKI pin input of the micro. Circuit attached.

Frequency counter implemented with a PIC micro 18F2321 (TMR3 as a counter) with data displayed on a 2 x 24 LCD.

Following the nomenclature employed by member JimB , I got the following values:

fa small air: 1,306006 MHz
fb large air: 1,202345 MHz

fa small liq: 1,298703 MHz
fb large liq: 1,088448 MHz

K = 2,38 (for this particular oil stated as 2,5 to 2,6). I am not a chemist, far from that. Now you know.

BTW, the oil to test came from the kitchen: pure sunflower cooking oil. I manage to cook good tasty french fries with it.

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JimB

Super Moderator
Most Helpful Member
Wow, I am impressed.

I like your circuit board construction, excellent for RF experimentation.

But who is this little fellow?
Bench Gremlin.png


JimB
 

atferrari

Well-Known Member
Wow, I am impressed.
I like your circuit board construction, excellent for RF experimentation.
:eek::eek::):) Nothing less than flattering coming from you Jim. Gracias.

It took me time to learnt to give more space for eventual changes / additions. After ruining two small (actually too small) boards with the help of essential tremor, I got that one.

But who is this little fellow?
View attachment 127221
JimB
Not a local leprechaun but some TV's animated motion thing (USA I guess), following me in my bench for years. Have to ask my granddaughters. :)
 

atferrari

Well-Known Member

JimB

Super Moderator
Most Helpful Member
This has reminded me of something which I found in Italy some years ago.

As I parked my hire car for the night, I found this thing on the ground:
Ravenna Gremlin.JPG
The picture is bigger than the object, which is 60mm tall.

Obviously some childs plaything, I picked it up and stood it on the boot (trunk) of the car in case mother and child walked back past the car.
Next morning it was still there and so I put it in the car.
When I cleaned out the car at the airport, I just put the little gremlin in my briefcase, and here it is 20+ years later lurking on the shelf in my office/electronic workshop/radio shack.

An ugly little thing I think!

JimB
 

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