Measuring Inductance with a Neon

If you rearrange the circuit a bit, you can get the resonant circuit's signal down at ground so it is easier to put a scope onto.

Unfortunately, your subject line is a bit misleading. The neon isn't doing the measurement. A second neon bulb and a calibrated transformer in series with the inductor would fix this.

Re-arrangement not needed if there's a sense loop through the coil. But I'll admit, my bench circuit puts the tank at the bottom for no particular reason..I used an isolation xformer for power. Re-arrange as needed.

One benefit is that circuit can work without an isolation transformer when a sense loop through Ltest is used. No power supply, just plug it in. Bit of a zap hazard though..

Yeah.. I should have entitled this 'Neon Lamp Oscillator for Inductance Measurement by Measuring Resonant Frequency '

Why a 2nd neon?

I've been able to measure the resonant frequency of 30 turn inductors. btw..my bench circuit flashes. That happened due to limited part selection from the junk box.

D from BC myrealaddress(at)comic(dot)com BC, Canada

That makes the circuit less general. You can only use it where there can be the added turn.

You can isolate with a transformer on the signal side instead but then you would have dangerous voltages on the inductor wires.

Perhaps.

With the isolation transformer and a second neon, you really can use the neon to measure the inductance. The first neon puts a known step on the series combination of the unknown inductor and the known transformer. The voltage on the secondary of the transformer depends on the inductance of the unknown. An NE-2 has a know striking voltage so the second NE-2 gives you a one bit digital inductance measurement.

True..

Yup.. that's a twist.

I think I get it.. I have to do more thinking.

D from BC myrealaddress(at)comic(dot)com BC, Canada