thermocouple for industrial application

[binojkumar]

Hi friends im in search of a thermocouple(500degree or above capability) that can produce an out put of 0-3 or 0-5 volt out put. If anybody knows abt it pls inform me.

Thnks in advance.
Binoj

 

[FvM]

Did you understand the operation principle of thermocouples? They are generating a voltage according to a temperature difference and the thermoelectric potential of the material pair. For high temperatures, it's limited to about 5 mV/100°C per couple. To generate 5 V without an amplifier, you need a thermopile made of about 200 junctions. Such devices are sometimes used for control purposes to actuate valves or relays without external power supply, but not as measuring device. For temperature measurement, a single industry standard thermocouple with a suitable amplifier would be used.

 

[binojkumar]

Thanks , can u pls tell me wht type of amplifier used? pls suggest some examples.

 

[sixtus]

Thanks , can u pls tell me wht type of amplifier used? pls suggest some examples.

as commented by FvM the thermocopule is a junction (j) of two different metals which generate a voltage according the Seebeck proportionality coefficent (a) and following formula: vj = a*tj - a*TRef (TRef = cold junction temperature measured at thermocoupule vs instrument connection points)
Unfortunately also the Seebeck coefficent changes with the temperature then the thermocopules are non linear sensors (as RTD).
The temperature range depend of the type of metals used for the junction.
So, there are many differents thermocopule types.
For Your application I think You can use a "J" type thermocouple (Iron vs Chopper-Nikel) which have a temp sensivity about of 52mV/°C, temperature range from 32°F to 1382°F (0°C to 750°C).
The ampli than You can use may be a differential chopper stabilized MAX420.
To convert the "J" thermocopule voltage to a temperature You must use a polinomial formula :
T°C = a0+a1*vj+a2*vj^2+a3*vj^3+a4*vj^4+a5*vj^5
where :
a0 = -0,048868252
a1 = 19873.14503
a2 = -218614.5353
a3 = 11569199.78
a4 = 264917531.4
a5 = 2018441314

:-D