NW S.O.A.R.

Northwest Society Of Amateur Radio

KD7WBP

Notes on W7DU capacity Measurement system

This is  one of my more satisfactory home made measuring systems.  I have been using it for about 20 years. It is based on a type 555 integrated circuit which is still available. It puts out a signal the  frequency of which is inversely proportional to the capacitance of a condenser.  I find it is fairly useful for a range from about 25 PF to many microfarads provided that you can measure its frequency output down to very low values.  My home made counter is capable of reading frequency in cycles per second and also in units of time per cycle.

The unit has one variable resistor which must be adjusted to calibrate it.

I set mine to obtain one cps with a one mfd capacitor under test.  If your counter wont measure that frequency use a 0.01 mfd at100 hz or 0.001mfd at 1000 hz etc.  I found a setting of approximately 0.209 megohm was required in
my case.

--W7DU