How to measure temperatures up to 300 deg.C

[misley]

I have problem with the heater for special ceramics...I have to measure temps 300-350 deg.C with +/- 5 deg. precision and present the result on the LCD... digital circuit is not a problem but temp. sensor is a biiig... Some help?
Bridges?

 

[Elavionic]

For that range of temperature the best way is to use thermocouple and not a discrete sensor. You need to make or buy a unit capable of converting the mV/T to a readblenit. For +/- 5ºC you can make some aproximation and design your converter. You you´d like more acurasy i advise you to buy a unit. See this links for more info about thermocouple.
http://instserv.com/rmocoupl.htm
http://www.picotech.com/applications/thermocouple.html

 

[misley]

Is there any chance for use some semiconductors...It's too hard to find thermocouples and usually, there is no any available data about them...
What do you think about bridges where one of Ohmic impedances is in closely contact with heater and other ones are on room temp...?

 

[Bert]

You can use an NTC or PTC resistor too. I don't think that semiconductors that stand your temperature requirement exist.

Bert

 

[Elavionic]

I don´t know any NTC or PTC for those ranges of temperature. The maximum i know is about 150ºC. Another way to mesure those temp, is using IV thermometer, but will have to buy one, isn't ease to bild one. The best way is thermocouple. Try RS or Farnell they usually have thermocouple probes already assembled.

 

[bobcat1]

Hi

You can use INFRA RED to measure hi temp

Go to melexis site @

**broken link removed**

ENJOY


Bobi

 

[pqtam]

Hi misley!
1. Semicon sensor: use 2N2222 or other silicone transistor in metal case, shorting collector and base, using base-emitter junction. Feed the sensor with simple constant current suply on FET (2N4856 for example). The linearity is quite good as you see in the datasheet. Don't use diode in plastic or glass case, since the heat gradient is high due to low heat conductivity.
3. You can make a thermocouple quite easy: use copper wire, twisted with a manganin wire, put under the acetylen welding nozle. The two wires will be welded.
This is your thermocouple with quite high linearity. Just calibrate it at ice point and boiling point of water. You can use other wires in pair.
3. Use Op-amp for amplification.
I've use both sensors and the result was OK.
Hope it help!