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Conundrum

Sun Sept 27 2009, 12:04PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Hi all.

was dicussing this a while back on IRC...

wonder if the same idea would work for low melt alloys, possibly even >100C?

-A

Sulaiman

Sun Sept 27 2009, 06:39PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Wouldn't it be easier to convert electrical to heat energy directly,
e.g. wrap resistance wire around the end and pass a variable current etc.

doctor electrons

Sun Sept 27 2009, 10:16PM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

Not sure if this will be any help to you but here goes!
I have worked with countless induction heaters while building the automation equipment my company manufactures. Never have i seen an induction coil that was made of wire. Varnished magnet wire or otherwise. I was told by an electrical engineer at Pillar the reason for that is emissivity. He said all of their designs are a flat rectangular coil due to better thermal transmission (more surface area than a round conductor). The coils can be bare because the windings do not touch each other. That would eliminate the smoking varnish that your instructor spoke of. For low emissivity materials they used alloy steel coils and for high they used copper coils. I am no expert but maby you could look up some of the equipment pillar makes. The last units i worked with were water cooled and could turn an xray tube commutator near white hot in about 3 seconds.
Also, a ceramic coil body would be ideal.

Conundrum

Mon Sept 28 2009, 05:08PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

hmm, ok.

Just received some gallium, seems that adding 2% Ga to metal alloys such as BiInSn Makes the alloy flow better which could be useful for very precise dispensing... also Ga wets most materials including glass (and clothing, yechh!)

doctor electrons

Mon Sept 28 2009, 11:52PM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

Here's a bit of info that may be interesting to you!
When you measure temperatures of target parts or target materials in an induction heating application sensors can be accurate but they are not the way to go. The only "true" way to monitor temperatures "accurately" are through the use of thermal imaging cameras. They eliminate the errors that occur in all sensor technologies (even expensive lasers) ie; atmospheric effect on thermocouples and the like (mass of couple cooling long before mass of target) The effect of emissivity on lasers renders them near useless. (ever see the waves of heat above a weber grill, it has a type of field effect just like magnetic fields can effect sensors)
Just wanted to share this info because of the type of project. If if helps GREAT, if not, put it in the circular file.

Conundrum

Tue Sept 29 2009, 07:27PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

very interesting... reckon that a PIR sensor chopped with a pager motor and interrupter would work? if so this is a very handy technique to save $$$.

regards, -A

doctor electrons

Tue Sept 29 2009, 08:41PM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

I cannot answer that question unfortunately. However that question surely can be answered by someone else here. There are quite a number of people here who know waaayyyy more about electronics than i do, maby including yourself! I am very familiar with the sensor end of things because i use them every day. Hope i at least gave you some creative input. By the way, induction heating is cool! heh!

Steve Conner

Wed Sept 30 2009, 11:48AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Can you explain your claim that a thermal imaging camera isn't affected by emissivity?

Proud Mary

Wed Sept 30 2009, 02:48PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Don't the better quality non-contact thermometers have adjustment controls for target emissivity, line of sight path obscuration, drift of ambient temperature, and access to a black body simulator/calibrator of some kind?

In any case, shouldn't we first ask what percentage of accuracy is needed for this experiment, and how much money can be spent upon it? I should have thought the choice of thermometry technique would flow from these initial decisions.

MinorityCarrier

Wed Sept 30 2009, 03:41PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

Optical pyrometers instruments, hand-held and otherwise, have an emissivity setting input, and usually a table in their user-manual on where to set the emissivity value, for different substrates in order to get an accurate temperature measurement readout.

I wrote a spew for this thread yesterday about emissivity/blackbody ratios, but decided not to post it. I do not believe you can accurately optically measure a materials' surface temperature without factoring in the emissivity ratio of that material.

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