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Signal conditioner for thermocouple

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bimbla

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signal conditioner of thermocouple

The range of thermocouple is 1200 degree celcius (50mv)

Initially I am getting negetive o/p.
Then when I heat the thermocouple, o/p increases in +ve direction.
Is this normal?

Is there a ref. ckt.?

thanks in advance.

bimbla.
 

jourval

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ntc signal contitioner

thermocouple is ultralow impedance source.
you can get negative output only, if inverting input
of operational amplifier connected to gnd via relatively high
resistor. In this case voltage drop on this resistor =
R x Iinput bias can be higher, than your signal.
So, - use lower resistors for feedback and all will be OK.
For precision measurements you'll need 0 ceelsius reference.
 

7rots51

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pt100 ad594

hi
for THC type J or K you can use AD594/5 from analog device ,For direct THC to digital you can use sigma delta ADCs and for cold junction compensation you can use NTC resistors.
 

arturt134

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use instrumentation amplifier as signal conditioner for thermocouple. Linear makes some good amplifiers (i.e. LT1101). Also you can look in Analog Devices.
Some times ago, I saw some good application notes about measuring temperature by THC, in linear www site.
 

bimbla

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Thermocouple Sig. Condt.

Thanks.

I will look into all the suggestions, make the necessary changes.

bimbla.
 

james

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bimbla said:
The range of thermocouple is 1200 degree celcius (50mv)

Initially I am getting negetive o/p.
Then when I heat the thermocouple, o/p increases in +ve direction.
Is this normal?

Is there a ref. ckt.?

thanks in advance.

bimbla.

bimbla,

As I realized you are not well accustomed about THC matters, I suggest to read "Industrial Temperature Primer" to this web:

http://www.wici.com/technical_info/articles/temp_prm/temp_primer.htm

You'll find there theory and some generality and you can download the document in pdf also.

Regardless the solution you will employ, analogue or digital, what is very important in THC signal conditioning is CJC implementation (Cold Junction Compensation) and signal linearization.

THC output is a function (not linear) of the temperature difference measured between hot junction (junction at temperature to be measured) and reference junction, the cold junction.

All reference standard tables are calculated with a cold reference junction at 0 deg C so provided that for industrial application is expensive to stabilize the CJC at 0 deg C using an ice batch for example, what you've to implement is a system to compensate for the additional error introduced by cold junctions at ambient temperature. As it has been said, compensation maybe done using analogue chips offered by a lot of manufactury or using a digital processing which supply a better accuracy if you measure the cond junction with a Pt100 class A. About linearization, again once, analogue chips can do the job if you don't need high accuracy. However with a digital processing you will achieve a better accuracy, usually better of 0.01 deg C of linearizing error.

If you need THC standard tables, as well as Pt100, or further infos you can find a lot here:

http://www.minco.com/support/
http://listserve.minco.com/sensorcalc/rtd/index.php?action=start
http://listserve.minco.com/sensorcalc/thrmcpl/index.php?action=start

Hope it helps
 

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