Why O why are inductors described by the turns?!!?

[DigiTan]

This has always bugged me. It seems over half the schematics I see describe their inductors by turns rather than plain old inductance (not even an estimate). I know inductance meters are expensive, but seriously--what's the deal with this?

And is there a way for me to estimate the inductance just from the number of turns and gauge? That's about all the info I've got.

 

[bloki]

When inductance is described with number of turns, coil diameter, wire diameter and maybe pitch then it is easy to reproduce such an inductor. This is specially throught for less experienced homebrewers. Professionals rather give data about inductance.
Questions like how to make an inductor or what inductance coil has are usuall. There are number of programs that can do the job in both directions. One of such programe is Calcoil for air core single or multilayer inductors.
**broken link removed**

 

[bryan1]

Hiya Digitan,
Eh mate back in feb 2004 EPE did a project on an inductance/capactance/frequency meter, I found a website where a bloke built one and compared it next to his commercial one and the epe kit beat it hands down. It's based on a 16f628 and doesn't look like a hard project to make so take a look I'm sure you'll like it as much as I do.

Cheers Bryan

 

[stevez]

Something to think about - by describing the inductor and how it's made the author covers nearly all of the characteristics of the inductor. Inductance is only one of several important characteristics of an inductor. A 10 microhenry inductor that is air wound is different than one on a toroidal core (and which core makes a difference). For some applications the difference isn't a problem - in others it matters.

 

[Nigel Goodwin]

This has always bugged me. It seems over half the schematics I see describe their inductors by turns rather than plain old inductance (not even an estimate). I know inductance meters are expensive, but seriously--what's the deal with this?

It's done this way because it's by far the best, the coil is simple to make yourself, and the value itself is fairly irrelevant.

This only happens at VHF and above, where the coil only requires a few turns, and because of stray inductance and capacitance (which is appreciable at these frequencies) you can't do normal calculations on the circuit anyway (as you've no way of knowing the values, except for building it and measuring the resonant frequency).

You can easily calculate the ENTIRE values from the frequency, but these won't be the values of the inductor and capacitor used, so there's not much point?.

 

[Roff]

My avatar is St.Feelalot Born AD 533 Excomminucated AD 653

She was excommunicated when she was 120 years old? Was she still alive? Can one be excommunicated after he/she dies?
These are weighty questions.

 

[bryan1]

She was excommunicated when she was 120 years old? Was she still alive? Can one be excommunicated after he/she dies?
These are weighty questions.

Hi Ron,
Well my avatar came out of a travel guide book on a country called Monrovia. The book is a light hearted look at an Imaginary country where everything but the norm goes on. It's a top read and when I saw that pic and the description I finally decided to stop being naked and put up an avatar. Oh and when I tell ppl what your avartar is when they see it :shock: it always results in a different response

Cheers Bryan

 

[DigiTan]

Hiya Digitan,
Eh mate back in feb 2004 EPE did a project on an inductance/capactance/frequency meter, I found a website where a bloke built one and compared it next to his commercial one and the epe kit beat it hands down. It's based on a 16f628 and doesn't look like a hard project to make so take a look I'm sure you'll like it as much as I do.

Cheers Bryan

Bryan, I think you just beat me to my next question. I was going to ask if anyone had managed to build a meter using a uC. Can anyone explain how those were built? I was thinking you could check the phase difference between V and I, but those meters use way fewer parts than I expected.

 

[Nigel Goodwin]

Hiya Digitan,
Eh mate back in feb 2004 EPE did a project on an inductance/capactance/frequency meter, I found a website where a bloke built one and compared it next to his commercial one and the epe kit beat it hands down. It's based on a 16f628 and doesn't look like a hard project to make so take a look I'm sure you'll like it as much as I do.

Cheers Bryan

Bryan, I think you just beat me to my next question. I was going to ask if anyone had managed to build a meter using a uC. Can anyone explain how those were built? I was thinking you could check the phase difference between V and I, but those meters use way fewer parts than I expected.

They simply use the inductance in an oscillator circuit (the EPE one used a simple CMOS gate design for this), and measure the output frequency. Another pair of gates were used for a capacitance measuring oscillator as well in the EPE design.

However, it (obviously) didn't go low enough for high frequency inductors like you're talking about - basically for the same reasons I gave earlier.

 

[DigiTan]

Ah, that's pretty darn clever. I need to try some kind of digital frequency meter for my AVR, then. Did they ever post a schematic or parts list for those projects? I've heard of getting the amplitude of a signal digitally, but not the frequency.

 

[Nigel Goodwin]

Ah, that's pretty darn clever. I need to try some kind of digital frequency meter for my AVR, then. Did they ever post a schematic or parts list for those projects? I've heard of getting the amplitude of a signal digitally, but not the frequency.

No idea for an AVR?, but PIC ones are common, in fact MicroChip did a datasheet for a 50MHz auto-ranging frequency counter using a 16C55 (or similar old PIC?) a great many years ago - it's been updated over the years by various people, and versions based on the 16C84 or 16F84 are available.

Frequency counting is simple, just count the input pulses over a certain time period, or (for low frequencies) measure the width of the pulses, and calculate from there.

The old PIC design was clever, because it used a sneaky method of reading the 16 bit counter/timer, when only one half of it is readable!.

In fact, in this months EPE, they have a project for measuring the speed and power produced from a propeller - it counts the rotation of the propeller by breaking a light beam (in software). The power produced is measured by pushing against a spring, which in turn pushes a ferrite rod into a coil, arranged as an oscillator. So the frequency changes in relation to the power of the push, this frequency is measured using a counter/timer.

 

[DigiTan]

Alright, looks like I'll be checking with avrfreaks for this one. So were two oscillators used (one for RC/one for RL), or did have use some other circuit. (Maybe a waveform gen chip?)

 

[bloki]

There are a lot of projects on the web about PIC LC Meter. They are all using comparator LM311 as oscillator and PIC as a counter. Accuracy and resolution of such devices is pretty good.

 

[DigiTan]

Okay, it looks like one hombre already did one using the AVR2313 I had in mind. And it's well-documented too. I'll be sure to give one the once-over maybe two or three times. 8)