High temp thermometer.

As long as he's OK with +-5 degrees or so, and is smart about getting rid of the EMI, it might work fine--maybe almost as well as a calibrated light bulb.

Four stainless steel wires spot-welded to the pins on the light bulb would allow a four-wire resistance measurement that would probably be pretty good.

Light bulb filaments are usually made out of tungsten alloy with 5-10% other stuff like iron, nickel, and copper to improve its ductility. (Tungsten's ductility can stand a lot of improving.) ;)

The alloying will reduce its dR/dT, so getting good accuracy will require calibration, as others have noted.

Cheers

Phil Hobbs

No accuracy requirement was given in the original post. I didn't know I was bidding on a US gov't project.

Plain copper wire makes a nice RTD, if oxidation isn't too bad.

Nice post Syd. I'm planning to crimp steel or Cu wire to bulb leads. For insulation, I figured on Telfon or ceramic, but fiberglass sounds like a nice suggestion. Lot's of good posts to this thread fellas, Thanks Ken

A thermocouple starts to sound better and better. You can buy a cheap DVM that has a thermocouple input.

OP: Send me your e-mail and I'll send you a type K bead thermocouple.

They're rugged, have fast response, are trouble-free and just what the doctor ordered for this kind of application.

He can probably get away without cold-junction comp, but that's not hard. He'd get around 13 millivolts at 600F.

dynamics (at) uniserve.com

business address is

OT:Just got a new organizer, so I have room for more good stuff,

In application, the 'thermometer/thermocouple' goes to a triac controlled existing 'hot plate' heater. Regards Ken

An "ambition" is to remove methanol from ethanol, but I think a common diode series will do for that, otherwise quite true. Ken

It's cheaper to buy pure ethanol in the first place.

Ken S Tucker is famous for posting meaningless nonsense. This seems to be more of the same.

-- Bill Sloman, Nijmegen

Done.

A still?

Best regards, Spehro Pefhany

Except for the taxes. According to C. this was a common activity among the chemistry Uni students. Get it right and cheap booze, get it wrong and you go blind!

Best regards, Spehro Pefhany

BP of ethanol and methanol are 78.37°C/65°C so there's a reasonable separation. AFAIUI, denaturing uses more than one additive so as to make the process more difficult to reverse.

Best regards, Spehro Pefhany

Thermocouples are pretty good, usually better than their specs suggest. They are much more rugged than RTDs, and work to much higher temperatures.

The biggest practical problem is that most readout devices have miserable cold-junction sensing for any CJ temperature but 20C. If you do it right, it's remarkable how accurate thermocouples are.

Why do you reflexively add insults to most everything you post?

Amateurs! The Tulane chem department had an expensive IR absorption spectrometer, used for nothing but pre-party alcohol analysis. They were mostly looking for methanol and benzine.

other issues with thermocouple process units is they need to operating in the same ambient temperature as the device the probe is connected too. The cold junction reference will miss calculate otherwise..The seebeck effect is a basic thing, however, not very understood by a few, especially those that carry a name of "SLow-Man"

Jamie

I don't understand that. Why?

I don't think so. The 'cold' junction is inside the thermocouple readout device and its temperature is measured using an absolute device such as a thermistor, maybe a PRT. The 'cold' junction will often be made from fairly substantial material to damp any fast temperature changes and maintain an even temperature (an isothermal block) and to couple easily to the thermistor.

As long as your thermocouple wire is maintained all the way to the readout, either with thermocouple wire or appropriate compensating cable, and providing the connectors are of the correct material, then all is well.

Cheers

Thermocouple extension wire is normally what's used for longer runs, because it's cheaper. However, its composition isn't as accurately controlled as real thermocouple wire, so variations in ambient temperature along the run can cause errors.

But the main problems with TCs are low sensitivity to temperature and high sensitivity to EMI.

Cheers

Phil Hobbs