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Alternative ways to measure self resonating freqency of coil?

Signalglow

New Member
Hi guys!
I am going to wind a multi tapped toroid coil from 29.9mH to 156mH
I would like to know how i can measure the SRF without an oscilloscope?
I know that i could use a dip meter and figure it out fast, but i dont have that.

What i have is a DE 5000 LCR meter, with test tone frequencies 100 Hz / 120 Hz / 1 kHz / 10 kHz / 100 kHz
a function signal generator with sine, triangle, square wave, frequency 1HZ to 500KHz
and a standard multimeter, and an external soundcard for my computer with line in, line out.

Can i use these tools to get the SRF?

Help is much appreciated.

Best regards.
 

Signalglow

New Member
Why do you want to know anyway? - presumably this is for your graphic equaliser?, so of what interest is the self resonant frequency?.
Hi Nigel,
This is for a DIY Pultec equalizer.
I want to know this, so i can calculate the parasitic capacitance in the coil.

Best regards.
 

ronsimpson

Well-Known Member
Most Helpful Member
Picture of a grid dip meter. It is a oscillator and some coils. You can scan from a low frequency to a high frequency and see if your unknown coil resonates at some frequency. Very handy tool.
120220
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hi Nigel,
This is for a DIY Pultec equalizer.
I want to know this, so i can calculate the parasitic capacitance in the coil.
Again WHY? - how will that help you in any way?.

I suspect a grid dip meter wouldn't help much, as they are for RF, and you're looking at MUCH lower frequencies, which is why it doesn't matter.
 

JimB

Super Moderator
Most Helpful Member
Q - How do you couple a Dip Meter to a toroid coil?

A - In my experience, with difficulty.

JimB
 

ronsimpson

Well-Known Member
Most Helpful Member
Read above
If I would/could read …..
I thought about putting the signal generator across the coil and also putting a a.c.-meter across the coil. But many meters will not measure 100khz ac.
what to do? ...….
Make a "RF probe" or a "demodulation probe" for your meter. Use the circuit from the internet. (ok most internet circuits do not work)
probe
Because we want to use it at a lower frequency than "RF" you might use 10x or 100x larger capacitors than normal.

Put the signal generator across the coil. The coil should short out the signal. Put the demodulation probe across the coil and set the meter to low voltage DC.
Sweep the signal generator and try to find a frequency where the coil 'opens up" and you get a large signal.
 

Signalglow

New Member
Again WHY? - how will that help you in any way?.

I suspect a grid dip meter wouldn't help much, as they are for RF, and you're looking at MUCH lower frequencies, which is why it doesn't matter.
Okay i have not looked a lot into dip meters yet..
The reason is that i want to wind these coils with the less parasitic capacitance as possible,
Using a progressive winding technique (reverse winding technique)
So i would like to know the capacitance, so i can use this technique.
Best regards

Do you have the part numbers or data sheet for the coils?
What equipment do you have? Scope? Signal generator?
I want to wind the coil myself.
I have a signal generator, LCR meter (DE 5000), and a standard multimeter.
Best regards
 

alec_t

Well-Known Member
Most Helpful Member
Whatever measuring kit you connect to the coil will introduce further capacitance and skew the measurement. How will you account/compensate for that?
 

ronsimpson

Well-Known Member
Most Helpful Member
I have done this to reduce the capacitance.
120223120222120221
The idea came from how high frequency flyback transformers are made. Slot winding makes the coil into several small coils.
120224
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Okay i have not looked a lot into dip meters yet..
The reason is that i want to wind these coils with the less parasitic capacitance as possible,
Using a progressive winding technique (reverse winding technique)
So i would like to know the capacitance, so i can use this technique.

Again, WHY? - wind the coils, build the graphic, job done - what difference do you imagine lowering the parasitic capacitance will make?. It's as if you've found the word on line somewhere, and imagine it's important for some reason.
 

Signalglow

New Member
Whatever measuring kit you connect to the coil will introduce further capacitance and skew the measurement. How will you account/compensate for that?
Well this is true, but i just want to get an idea.

I have done this to reduce the capacitance.
View attachment 120223View attachment 120222View attachment 120221
The idea came from how high frequency flyback transformers are made. Slot winding makes the coil into several small coils.
View attachment 120224
Very interesting thanks for the tip, i found this technique.

Again, WHY? - wind the coils, build the graphic, job done - what difference do you imagine lowering the parasitic capacitance will make?. It's as if you've found the word on line somewhere, and imagine it's important for some reason.
Trust me i want to just do the coil and just be done with it, but i really want to learn how to do this the best way possible, also for future projects.
What i want to avoid is unwanted oscillations, crosstalk and all the downsides of parasitic capacitance.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Well this is true, but i just want to get an idea.


Very interesting thanks for the tip, i found this technique.


Trust me i want to just do the coil and just be done with it, but i really want to learn how to do this the best way possible, also for future projects.
What i want to avoid is unwanted oscillations, crosstalk and all the downsides of parasitic capacitance.
I'll repeat again - you're doing the coils for low frequency and high inductance - nothing you're worrying about is a concern, and the original coils certainly won't have been wound in any special way. I suspect you're also going to have a lot of 'fun' winding high inductance values on a toroidal former :D

You mentioned in the first post you're making a tapped inductor - that's going to make it MUCH worse than any imaginary capacitance issues, you need a separate inductor for each one.
 

Signalglow

New Member
I'll repeat again - you're doing the coils for low frequency and high inductance - nothing you're worrying about is a concern, and the original coils certainly won't have been wound in any special way. I suspect you're also going to have a lot of 'fun' winding high inductance values on a toroidal former :D

You mentioned in the first post you're making a tapped inductor - that's going to make it MUCH worse than any imaginary capacitance issues, you need a separate inductor for each one.
Yes i cant wait to make this thing! :)
I guess this is the worst project i ever layed my hands on, the thing is, i am doing this by hand so this is a very time consuming task..
The inductor will be tapped, i dont have room for more inductors, but i will try it out, and see how it goes...
 

alec_t

Well-Known Member
Most Helpful Member
The inductor will be tapped
...... so each section will be affected by its neighbours. I don't see how the self-resonant frequency of a section in isolation could be determined in that case?
 

Signalglow

New Member
...... so each section will be affected by its neighbours. I don't see how the self-resonant frequency of a section in isolation could be determined in that case?
No you a totally right, the only way i can see this work is to check the parasitic capacitance after each layer , and use techniques on the next layer to reduce it.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Yes i cant wait to make this thing! :)
I guess this is the worst project i ever layed my hands on, the thing is, i am doing this by hand so this is a very time consuming task.
Why build such an antique design?, anything remotely 'modern' uses gyrators instead of inductors, and these cure all the problems with inductors (none of which is parasitic capacitance though).

The inductor will be tapped, i dont have room for more inductors, but i will try it out, and see how it goes...
So why all the concern about imaginary parasitic capacitance?, of vastly greater concern is that the inductors are all going to be coupled to each other as they are one big transformer. How tiny is your design?, there should be plenty of room for multiple inductors, which should be spaced apart anyway, in order to prevent interaction.
 

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