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.
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.