hi q12,
Look at this sim.
Your Scope should be Earth free or if a dual scope, use A and B channels, Va and Vb added.
Note Vpeak across the inductor around 1.6kHz.
E

 

ok, then we are on the same page, because it is exactly what I was expecting to see from my setup. But all I got was random V garbage.
So, if this didnt work, then we should try something else then.
You might be on something, suggesting a higher voltage actually. My FNIRSI sig gen is a couple of 10's to 100's mV in amplitude. This might not be good enough for the circuit and create --probably-- all this random V noise ?!?
Im definitely very new to all this side of electronics ! Im more an automatization type of electronist than fv one. But I still need this tool component reading, and I believe it can be done with the stuff I already have.

 

You might be on something, suggesting a higher voltage actually. My FNIRSI sig gen is a couple of 10's to 100's mV in amplitude.

hi q,
I am using a 2Vpeak AC waveform to sweep the frequency
E

 

I can not add FM & AM signals. My fv gen is very limited. Again it is what FNIRSI can provide.

 

hi q.
That freq module outputs only a sweeping frequency, just like when you are adjusting the frequency control on your signal generator.

E

 

The original circuit using a transformer, a variable resistor, and 60 Hz mains power, is really going to provide any accuracy for inductors having a significant reactance at the mains frequency of 60Hz. To make it work at higher frequencies will require accuracy and resolution much greater than available to us.

 

There are generally two methods to determine: 1) To measure. Just connect a one of measurers and push the button Start. 2) To calculate. Just open an appropriate software and push button Start. Or open the appropriate book or website and apply it formula in Excel. I personally like rather much the software named the Coil.

 

That freq module outputs only a sweeping frequency

you are speaking about its output, I am speaking about its inputs.
Like I said, my fv gen is very limited and I can not provide that kind of FM and AM radio signals. I can only provide the function generated type of signals, like sine, square,triangle and 2-3 more I think.
-So, any other circuits ideas I should try? Or that's it?

 

Hello,

What function generator do you use?
You could use the given circuit by stepping the frequency.
Use large steps to get in range, then finer steps to find resonance.

Bertus

 

one an go real basic, without function generator

 

What function generator do you use?

FNIRSI 1014D waveform types:
1 Sine
2 Square
3 Triangle
4 Sawtooth1
5 Sawtooth2
6 Step
7 Half Wave
8 Full Wave
9 Exponential
10 Logarithmic
11 Exponential-Logarithmic
12 Square Root
13 Multi-Audio
14 Sync Pulse (Cinke pulse)
15 Custom Waveform

 

one an go real basic, without function generator
View attachment 335222

and how do I use it? provide some steps what to do, what to read, what to expect.

 

put switch in charge position (choose suitable voltage such as 5VDC or whatever). connect unknown coil, connect scope, flip switch to test position. read the frequency or if you like use cursors and place them on peaks. and measure time between them. that is period T.
frequency is f= 1/T

and as already stated you can calculate the L from known value of C and measured value for f.

 

btw you can measure period between either max or min points on the curve. and if you choose your points wider (several periods) you can divide by "several" to get better accuracy. here, several is 3

 

In circuit, this coil alone is rising the Amp in my PSU to its limit 2.5A that I set (middle). The coil started to heat up in seconds, but I didnt let it too long, like 2-3 sec and power off.
So I am forced to insert 100R in series with it. You can read its value if you really zoom in it.
You can clearly see on top of the coil it is 2.5mH marked. Here is my tester that is showing the same value. So the coil is GOOD. I was starting to think it might be burned, but then it couldn't conduct anything... so... these are the facts. These small mH range coils really need some limiter current resistors next to them ! This means, in our next formulas, will have to take 100R from the result.
This was the coil I tested all this time - for the record. It looks like a small transformer but its only 1 single coil. I think I scrapped this type of coils (multiple) from various power supplies, maybe even light bulb boards, I really dont remember where each was. And the majority has absolutely no markings on them. Im lucky to have markings on 2 or 3. And Im having them collected over the years and just sitting there, without proper marking, complete mysteries in a bag. Again, my tester is able to read --some-- of them but really, not all. Even here you can see that resistor-inductor symbol on the top of the screen, that he thinks is a resistor in there. While if Im testing other bigger coils, it is reading them more correctly than this one, showing only the inductor symbol, sign that he knows for sure what it is, while here, is uncertain, when showing this double symbol. Some others are showing this symbol but incoherent data or nothing, clean data screen. He definitely doesn't know how to read them. He only catches something, but not clear enough.
-Or, the other way of looking at it, it might actually read it correctly this one, showing more helpful data about it, that resistance, and then the inductance of it. Im very doubtful sometimes of its readings.

 

put switch in charge position (choose suitable voltage such as 5VDC or whatever). connect unknown coil, connect scope, flip switch to test position. read the frequency or if you like use cursors and place them on peaks. and measure time between them. that is period T.
frequency is f= 1/T

Alright ! I think I got it. But it was the 20-est time !!!! this waveform to --finally-- catch it. It was very obscured or hidden in the settings of the oscilloscope, I had to do A LOT of knobs tweaking until I got it like that. Also the waveform doesn't appear just like that, it is randomly appearing, so only sometimes, not at every button press. So that was also a disadvantage I didn't know I had it. I got lucky to catch it, while I was doing something else, playing with the knobs. And then I bring it big into focus like is here in the picture. WOW. This is the first time in my LIFE!!! when Im catching such nice waveform. Again, guided only by pure luck. Wow. I cant believe my eyes I got such glorious waveform there. But everyone here helped me formulate what to expect and when I seen a glimpse of it, I jump on it like a tiger on fire. So your participation, helped, everyone so far.
So... look in the Top-Left corner, where it says T=4.20us and F=238kHz - this was from my button pressing, not from the fv gen. WOW. NOICE.

You can spot 2 vertical green cursors placed on peaks like you suggested! I had to re-learn how to make that single shot oscilogram again. Its a bit tricky. So that helped immensely to get to this point.
So for this image to get I had to tweak the osc H&V knobs as follows: V=
- And now what? What should I do from this point? But now YOU have the data, you do the math for me, then show it here and Ill get your point after that. Remember that I inserted 100R in series with the inductor ! Because right now I don't know precisely how to continue it.
Hey-thanks ! Genius idea with the button and the oscillations ! I hope it will give us the right inductance. phuuuu....

 

So, you said something about conversion, right?

Actually now I realize that this conversion is already done by the FNIRSI software. Hmmm, who knew? Haha.

Oh well, I double confirm it then.
>
So 4.20us = 238.09kHz and we used this formula:
L = 1 / ((2π * fv)^2 * C)
L = 1 / ((6.238 * 238090)^2 * 0.0000001) (where 0.0000001F=100nF)
L = 1 / ((1485205.42^2) * 0.0000001)
L = 1 / (2205835139597.3764 * 0.0000001)
L = 1 /220583.51395973764
L = 4.5334304454580489720197126249374e-6
L = 0.0000045334
L = 4.5334uH (gaaaaaaah - wrong!) - it should be 2.5mH
and I didnt include that 100R - ha - but where to put it?

 

looks good to me... using multiple periods errors get divided even if cursor placement is less than perfect.
so i get frequency to be about 225kHz (much closer to 228kHz shown by scope) and from that computed inductance is 5uH.
if you think value should be different, are you sure that capacitor value is really 100nF and not 220nF for example?

 

wait, are you sure? The original formula was L = 1 / ((2π * fv)^2 * C)
now you show me that L = 1 / (2π^2 * fv^2 * C) which is different:
L = 1 / (2π^2 * fv^2 * C)
L = 1 / (9.8690 * 238090^2 * 0.0000001)
L = 1 / (9.8690 * 56686848100 * 0.0000001)
L = 1 / 55944.25038989
L = 1.78749e-5
L = 0.0000178749
L = 17.8uH (gaaaaaaah - still wrong!) - it should be 2.5mH

wait -100R but where?
L = 100 / (2π^2 * fv^2 * C) -I'll put it here
L = 100 / 55944.250
L = 0.00178
L = 1.78mH -yah, very close to the truth ! (should be 2.5mH)

 

are you sure that capacitor value is really 100nF and not 220nF for example?

i measured it before installing, and is 101nF, to be very precise.
---
I used your measurement from before of the 225kHz !
L = 100 / (2π^2 * fv^2 * C)
L = 100 / (9.8690 * 225000^2 * 0.0000001) with 225kHz
L = 100 / (9.8690 * 50625000000 * 0.0000001)
L = 100 / 49961.8125
L = 0.002001
L = 2.001mH <<< NOICE !!! Very-very close.
My tester was:
Now, that we find the formula and the way to measure it, -How to increase the reading resolution on it?
My osc is not letting me read too deep/zoomed in because is showing a blank if its too zoomed in.
I have to keep a certain distance (from the H knob) to actually display anything.