tuning an LC

A better word for it is "emulation". ...Jim Thompson

On a sunny day (Thu, 21 Nov 2013 12:43:50 -0500) it happened Phil Hobbs wrote in :

Sorry that does not parse here.

Usually no, sometimes yes.

On a sunny day (Thu, 21 Nov 2013 10:47:42 -0700) it happened Jim Thompson wrote in :

Yes.

We're measuring Theta-ja in a manner that's mostly independent of actual temperature. There are some second-order effects that we could correct for, but it's pretty good as-is.

I was impressed myself.

Our modules plug into commercial VXI crates that have fans. We don't furnish those crates. We want to measure air velocity at our module and report that to the users, so they can tell if a fan fails or if air flow is blocked or inadequate or something.

We put the parts on the board layout, figuring that, if it actually worked, we could provide the air flow register and advertise the feature. It works pretty well.

Jan could do that on his airplane maybe, if he can afford a few hundred mW of power.

Gosh, I thought this was an electronics discussion group. Is it bad form to introduce topics to discuss?

Since you never do, maybe it is a bad thing to do, to start technical threads. We should follow your example and restrict ourselves to redneck political rants and wine rack repairs.

It's called "designing." It involves exploring various possible solutions, some conventional and some goofy. I'm doing it in public.

Why don't you design something and open it for discussion?

I've got an intern working on that now. Grunt work, ideal for an intern.

I thought I mentioned that, when you suggested the variable inductors. Under an ohm is OK. I might add a zero-ohm jumper, just in case the customer ever wants to kill the Q.

Call it whatever you like. To my ear, "emulation" sounds more like a digital thing. Someplace I probably still have a PIC 17C456A ICE, for instance. Hanging a gyrator on a capacitor gives you what everyone calls a "simulated inductor", so I claim that it's more idiomatic to call this a "simulated transducer" than an "emulated transducer".

If somebody giving an active filter talk was going on about "emulated inductors", everybody in the audience would be chuckling.

Of course, after 200ish posts, the gist of the matter has been clear for some days now.

Cheers

Phil Hobbs

In this thread, isn't Larkin emulating a transducer... that is...

...IMITATION? ...Jim Thompson

Variable-reluctance sensors usually use DC drive and detect AC, I think, and it would be strange to need 50V swing for that. My guess is that it's a magnetostrictive drive, and they're using the resonance to match the acoustic impedance of whatever it's driving. But we don't know for sure.

Cheers

Phil Hobbs

You know, Jim, it would really be better to just admit that

Say we take L to be 1 uH, which is about the inductance of a 1-foot diameter loop in free space.

E_L = 0.5*1e-6*(30 mA)**2 = 450 pJ.

This, when deposited on a 20 pF drain capacitance would be

V_d = sqrt(2*450 pJ/20pF) = 6.7 V,

and that isn't even counting the self-capacitance of a piece of wire that big, which would be of the same order.

The 2N7000 is a 60-volt FET. You'd need a loop half the size of a football field to blow it out at 30 mA, even if it had no capacity whatsoever to absorb a nanojoule avalanche nondestructively.

When you lose your temper like this, you say silly things that you wouldn't say otherwise, and you make yourself look bad. As the wise man said, "When you find yourself in a hole, stop digging."

Cheers

Phil Hobbs

I explained it. No point to doing it again.

What's this have to do with "emulation" (this thread)?

And there are lots of other scenarios... what's 1uH with 1Amp dumped into 20pF? ... It's 158V

Why the resistance to good engineering practice, rather than squatting and saying, "you can get away with..."?

But I guess that's the way you do things? ...Jim Thompson

A la "Red October" ?>:-} ...Jim Thompson

Calculating rather than spouting off? Yes, absolutely.

Cheers

Phil Hobbs

And ignoring my 158V ?>:-}

I think it's time for _you_ to stop digging ;-) ...Jim Thompson

Your 150V is just fogging--you pulled that number out of your, um, lower back.

The point at issue was 30 mA for a relay, not an automotive ignition, or a contactor, or a pyrotechnic igniter. That 6.7 volts isn't much like a kilovolt in my lexicon. It isn't even 1% of a kilovolt.

Cheers

Phil Hobbs