1. Home
  2. Electronics Design
  3. How to make an 8mH inductor which can handle 13V peak square wave without saturation
  4. Page 2

How to make an 8mH inductor which can handle 13V peak square wave without saturation

The OP's thing may be mis-identified.

It seems that there is an angle transmitter from a piece of avionics.

The usual angle transmitters in avionics are: a three-phase synchro, a resolver (sine+cosine) and a sine-cosine potentiometer.

The drive level is suspect. An electronic synthetic shaft with two interconnected synchros can need so much. Another place where a magnetic core is heavily driven is a flux-valve compass sensor, but it does not have any moving parts (like the LVDT core).

John is right: What is the thing supposed to achieve?

Reply to
Tauno Voipio
Loading thread data ...

It is an artificial horizon called KI256. I need to attenuate the roll output a bit.

I have the circuits of the driver and circuits of the KI256. I measured the KI256 LVDT primary inductance, etc.

Some other data points are that another inductor but a small one, just did nothing and presumably saturated.

Crazy to have such a high drive level; I agree.

Reply to
Peter

It sounds kind of like the LVDT wanted to be a resolver.

Well that's a shame. You'll have to use a method that's suited to your application.

Reply to
Jasen Betts

Just an update.

I tested that 8mH coil from Mouser. Verified at 8mH with an LCR meter and with the $500 micro tweezer thingy.

Doesn't work!! It behaves like it was 20mH or something like that. The attenuation is way too high. But 8mH was the perfect value with that funny milspec 0-10mH box I got off Ebay, which was heavy enough to contain pretty big inductors.

So what is happening?

Must be something in the waveform which is buggering up the way these inductors behave, in conjunction with the demodulation scheme used to "decode" the LVDT position.

Maybe it is saturating, but saturation has the opposite effect: it

*lowers* the effective inductance.

So I bought a 2.5mH one from Mouser, again one which can do 1.5A or so, and will try that, after the potting compound has gone off :)

Reply to
Peter

An inductor in series with the excitation coils of an LVDT will shift the phase of the current going through the LVDT. If the output of the LVDT is being demodulated with a phase sensitive detector you'd need a matching shift in the phase of the drive to the demodulator to get a sensible (or useful) output.

A precision rectifier wouldn't have that problem, but they weren't all that precise decades ago, and not all that popular. They also don't reject noise and out-of-phase pick-up, so nobody sensible would have used one.

Worse - it could be saturating on part of the cycle and giving you a very funny current waveform going through the LVDT - actually a rotary variable transformer, but we've been through that,

Looking at the current waveforms is always a good idea, but not always all that easy.

More looking a what's actually going on might be a good idea - buying random parts before you had worked out exactly why the last one didn't work isn't good policy.

Reply to
Bill Sloman

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.