Simple MAF Sensor I made today..

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Grain alignment does wonders for metal strength.

?-)

Each to their own, i would braze a contact point on then solder to that. Just easier for me. Works best with an Oxy-MAPP or hotter torch.

?-)

spot welder?

I tried out some Phosphor bronze (0.005") and also, I tried 0.012 " which we use in house for production on some products that has a bronze braid, expensive stuff.

Both worked well, the 0.012 more demanding then need be but is ok in cases where you have enough space to coil that much for lowering the current.

This sensor will be in a ozone rich environment so we'll see how long it'll last :)

The other items on the list is how conductive is ozone? I may need to consider some thinking on the mechanical end that houses the sensing wire.

Jamie

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There are other alloys too. I like phosphur bronze becasue it's non- magnetic.

I might worry about the oxidation caused by ozone, maybe some alloy of stainless would work better?

George H.

Not really -- maybe with a torch, there's lots of interesting chemistry going on in a flame.

I've done it numerous times, in open air, inductive heated -- it probably helps that heating is relatively quick, but the flux was regular Handy Flux and the filler regular silver solder.

Works wonders on copper pipe, too (which we use a lot of, since, how else do you carry kiloamperes cheaply..), though a lot slower because the copper reflects magnetic fields so nicely.

Tim

Ok, I'll need to look up the TC of Stainless.

Jamie

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The same about 0.3% at 300K.

Opps forget that! Stainless (304, 310) looks pretty flat from room temp to 20 K.

I'm going to have to go back and re-read my solid state books. (There's never enough practical stuff in the physics ones.)

The pure elements all look pretty good... But not a whole lot too choose from.

The highest room temperature resistivity that I see is, (In units of 10^-8 ohm-meters)

Ti 42.7 Pb 21 Nb 14.4 Fe 9.7

Cu 1.68 (for comparison)

Have you looked how others are making MAF's... Steal whatever they use.

George H.

We had a 100 ft of 0.005" steel wire past through a FEP extrusion today, which put 0.0015 mill wall on it. Yes, that is thin but it past the hi-pot test. And then we subjected it to a environmental chamber for a while today, at maximum effect for 6 hours.

I only had an hour to test it afterwards but it looks good and responds very well.

The phosphor bronze also works out well but has a much lower R/1M so not so good for small area sensors but works great for door or window ways as a candle test. Then again, I didn't have the smallest gauge available of the phosphor bronze to start with.

Jamie

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Yeah, sorry about that. It looks most alloys have a 'zero temperature resistance' and that puts a limit on the 1/T behavior. But there may be 'alloys' that have a bigger temperature dependence. Thermistors for instance. Could you put a couple of thermistors on heat sinks coupled to the air flow?

George H. so

What problem did you have. Mine gave me problems until I learned how to adjust it. I sold mine in great condition 3 years ago.

Oh, one day I was driving along a ca freeway near La. Started to give out all kinds of black smoke. Found foam filter I put on got sucked in keeping the flap open!!!

Wasn't that thing designed by Bosch.

Greg

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Don't have one. Though i am thinking of buying a used dental spot = welder. Just the right size for the things i want to do.

?-)

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Maybe, i would worry about the ozone leaching the carbon out of the SS.

ok

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Got slightly interested, googled once, found this:

Seems pretty good, the company is reputable.

?-)

There are lots of plans on the web about how to use a microwave oven transformer. I built one and used a PAL to implement a cycle counter that controls a solid-state relay in the primary. So, I can select how many full cycles of AC it puts into the work. If you don't do that, you can get some significant variabilities due to the previous state of the core...saturation.

Worked great except that a low-voltage system like this depends greatly on the contact resistance. Open-circuit was only a couple of volts. I used it to weld battery tabs, but had repeatability issues.

A commercial CD welder was MUCH more repeatable because the much higher voltage makes the current much less a function of contact resistance. I can get 7V across a milliohm.

Don't know what technique they use in a dental welder. CD is much more repeatable than straight transformer/resistive.

If you're building one, a split-bolt connector or any kind of wire connector that uses a screw for compression might work just fine.