How to measure SRF of a DD coil with Parallel Damping Resistor

[green]

Here is scope probe method (pi excites test coil DF)). 500-560KHz.

Reply#12 you got different SRF readings using two different methods. Are you now getting similar readings comparing PI excites and signal generator exciting. I measured SRF of two mono coils overlapped using the PI exciting method. Shorted the not wanted coil so only the wanted coil would excite and decay.https://www.geotech1.com/forums/show...019#post257019

[bklein]

I don’t understand what you are doing with two excited coils; one shorted?
In any case your readings are in MHz and mine KHZ so my coils must be pretty bad...

[green]

I don?t understand what you are doing with two excited coils; one shorted?
In any case your readings are in MHz and mine KHZ so my coils must be pretty bad...

The thread says DD so I assumed two coils, Tx and Rx. Don't know if your coils are bad just slower. Mine are without a lead wire, closer to 1MHz depending on lead length with a lead.

[dbanner]

Listen care fully. Srf is a function of the parameters of the coil. Without getting into too much details, what you are basically trying to determine is a zone of credible information.
I often wonder why results are disputable?
It comes down to the level of precise calibration of your rig.

[dbanner]

Any readings have to be taken with a pinch of salt.

[Polymer]

Any readings have to be taken with a pinch of salt.

Don't quite agree - I'd take a bag of salt or maybe a barrel ...

Sometimes the humidity here changes drastically from say 30% to 80% at short notice.
The measurements in that time are nutty ... sometimes I wonder if the mood of the neighbor's cat can skew results too ...

[green]

Listen care fully. Srf is a function of the parameters of the coil. Without getting into too much details, what you are basically trying to determine is a zone of credible information.
I often wonder why results are disputable?
It comes down to the level of precise calibration of your rig.

Test procedure can be as important as calibration, maybe more. I worked in a test lab where calibration and a defined test procedure was required. I'm guessing most don't have a recent calibration record for our equipment. One option is don't present data unless your scope, multimeter or inductance meter has a recent calibration sticker and you used a defined test procedure. It would be great if we had defined test procedures and our equipment had recent calibration records. I'm sure the metal detector manufactures do. How much of the manufactures data is presented on this forum? We could write some test procedures.