hodges - 13-7-2006 at 16:00
I wish to measure temperatures at which various substances melt and boil. However, I wish to stick to using small amounts (a few ml in a test tube).
Can anyone thing of a good way of doing this? The temperature range would be say -20C to 200C. I know there are lab themometers that cover this
range, but all the ones I have seen are huge and need to be immersed in at least several inches of liquid.
Thanks,
Hodges
Elawr - 13-7-2006 at 18:50
maybe thermistors?... Simple diodes as well can measure temp, iirc. These components can be very tiny, and are easily encapsulated for immersion into
liquids.
12AX7 - 13-7-2006 at 19:14
Small thermocouple (with suitable meter and/or amplifier to make use of the small voltage) could do it, too.
Electronics professionals I know have spoken of invisibly sized temp sensors, thermistor or otherwise. Size isn't an issue!
Tim
Twospoons - 13-7-2006 at 19:57
I agree with 12AX7 - the sensing tip on a thermocouple is usually only 1-2 mm in diameter, and the wire is only 1.5mm diameter. And thermocouples
are very cheap and easy to buy.
hodges - 14-7-2006 at 17:01
Almost all the thermisters I have seen are only good up to 125C. A thermocouple is good up to flame temperatures, but the output is only something
like 40uV per degree C so I would need to build an amplifier or dedicated circuit to use this.
Hodges
hinz - 15-7-2006 at 09:55
Look here:
http://www.omega.de/produkt/t2/unsheat.html
There are NiCr thermocouples with a diameter of 0,01mm for 46 Euro, a bit expensive but the next thicker one is cheaper.
hodges - 16-7-2006 at 13:40
Thanks guys. I think I found something that is going to work, for a reasonable price ($25 on EBay):
Offered here is a digital hi temperature probe thermometer. This instrument delivers a very wide temperature range. It is ideal for monitoring the
temperature in the lab, greenhouse and a variety of industrial applications.
Features
Water Proof
On / Off Switch
°C / °F Switch
Data Hold
Polycarbonate Case
Stainless Steel Probe
Auto power off
Specifications:
Range
-58° to 536°F
-50° to 280°C
Accuracy
±2°F / ±1°C
Resolution
0.1°
Probe Length:
Diameter:
Overall:
5.0" / 12.7 cm
0.137" / 3.5 mm
8.0" / 20.3 cm
Sampling Time
0.5 second
Power Source:
1 "LR44" battery
Battery Life:
5000 hours
Supplied with
Battery
Sheath with Pocket Clip
Hodges