INDUCTANCE

[Mark-VA]

Is there a simple way to measure inductance in a homemade coil?

[sled]

depends on what equipment you have, i.e let us know what you got and we can tell you what you can do

- LC Meter
- Oscilloscope
- Frequency Generator
- Soundcard + PC
- Frequency counter
- Multimeter with RMS AC voltage measurement capabilities
- Arduino
- Some passive components (resistors, capacitors)

[Mark-VA]

Actually have an Oscilloscope (not used in 20+) years.
soundcard and PC

many components

Very interested in how a soundcard and pc would work.
But please inform me of both.



QUOTE=sled;218413]depends on what equipment you have, i.e let us know what you got and we can tell you what you can do

- LC Meter
- Oscilloscope
- Frequency Generator
- Soundcard + PC
- Frequency counter
- Multimeter with RMS AC voltage measurement capabilities
- Arduino
- Some passive components (resistors, capacitors)[/QUOTE]

[green]

Actually have an Oscilloscope (not used in 20+) years.
soundcard and PC

many components

Very interested in how a soundcard and pc would work.
But please inform me of both.



QUOTE=sled;218413]depends on what equipment you have, i.e let us know what you got and we can tell you what you can do

- LC Meter
- Oscilloscope
- Frequency Generator
- Soundcard + PC
- Frequency counter
- Multimeter with RMS AC voltage measurement capabilities
- Arduino
- Some passive components (resistors, capacitors)

[/QUOTE]

Using an oscilloscope. The way I do it. Lay scope probe near test coil. Bring a operating PI coil near test coil to excite resonance. Record coil self resonant frequency(1/time between peaks). Connect a 10nf capacitor across coil and repeat test. Coil inductance equals 2.53 million/frequency squared or 2.53 million times period squared(time between peaks squared). Example 10.5usec between peaks, 2.53 million times 10.5usec squared = 279uH.

[Koala]

All in 1 ESR Meter Transistor Tester Diode Triode Capacitance SCR Inductance com around £10 from eBay. Used it for transistor matching also.

[6666]

Using an oscilloscope. The way I do it. Lay scope probe near test coil. Bring a operating PI coil near test coil to excite resonance. Record coil self resonant frequency(1/time between peaks). Connect a 10nf capacitor across coil and repeat test. Coil inductance equals 2.53 million/frequency squared or 2.53 million times period squared(time between peaks squared). Example 10.5usec between peaks, 2.53 million times 10.5usec squared = 279uH.[/QUOTE]


Are you talking about the peaks in the ringing oscillations ? and not between the peaks in the TX pulses.

[green]

Using an oscilloscope. The way I do it. Lay scope probe near test coil. Bring a operating PI coil near test coil to excite resonance. Record coil self resonant frequency(1/time between peaks). Connect a 10nf capacitor across coil and repeat test. Coil inductance equals 2.53 million/frequency squared or 2.53 million times period squared(time between peaks squared). Example 10.5usec between peaks, 2.53 million times 10.5usec squared = 279uH.

Are you talking about the peaks in the ringing oscillations ? and not between the peaks in the TX pulses.[/QUOTE]

Yes

[bbsailor]

CALCULATING COIL INDUCTANCE CHANGES

If you know the inductance of your present coil and want to see what adding a few more turns would do to the inductance value, here is a quick way only using a calculator to figure it out. Let's say you have a 19 turn coil, 10" diameter that is 315 uH and you want to know how many more turns to add to make this a 500uH coil. Do this

1. Divide 500 by 315 and get 1.58730
2. Take the square root of the above number and get 1.259881
3. Multiply your initial 19 turn 315uH coil by the square root above and get 23.937749 turns.
4. Round off to the nearest full turn or in this case make the new coil 24 turns and your new 24 turn coil will be very,very close to 500uH.

Here is another method that will show you how much the inductance changes by adding various amounts of additional coil turns. First we must calculate the percentage increase the additional turns add. In this example I will add just one additional turn but this works for other amounts also. Here is a mental model to keep you on the right path. Doubling the turns makes the inductance change by the square of the increase or 4 (in this example). A change of 1 turn in 19 is equal to 1/19 or .052631 more or 5.2631 percent larger than the initial coil. The new 20 turn coil inductance is 1.052631 squared or 1.108032 larger inductance than the initial 315uH or 349.03uH.

Just use your particular coil numbers and the example methods above and enjoy experimenting with different coils.

Joseph J. Rogowski

[Mark-VA]

Not knowing the inductance of most PI detectors and certainly not the Whites TDI, but I'd hope this tester would provide enough range for the to test and build what I need.
What would the inductance of the stock 12" tdi coil be?

Thoughts welcome


http://www.mcmelectronics.com/produc...UUEaAoRd8P8HAQ

[FatBob]

Well in general you want to be able to measure 300uh accurately.

My cheapo Chinese one has a 20mh low range and it doesn't agree too well
with a good meter at work. It always seems to be off in the same direction
though so maybe just needs a better cal?

[6666]

I have 4 inductance meters,
they all give different readings on the same 300uH coil
2 have a high and a low Inductance setting,
they both give a different reading on high and low so its damn frustrating.

[Carl-NC]

Mark, the TDI is pretty tolerant to coil inductance. 300uH +/- 20% should work fine. Getting too far off 300 might result in sub-optimal damping but it'll still work. With that in mind, use a coil calculator like is posted in this forum to figure up how many turns you need for the diameter, and don't worry too much about being able to measure it. Yes, you can measure inductance with a 'scope by adding a parallel cap, but only within the tolerance of the cap, which is often 20%.