Temperature measurement using thermistor - Electronic Circuits Projects Diagrams Free

yasser11 · 29th September 2005, 08:33 AM

I have to use a wheatstone bridge with thermistor in one arm to detect change in the resistance of a thermistor for a temperature range of 0-100Celsius.And i have to use an instrumentation amplifier to obtain an output of 0-10V for the temperature ange of 0-100 Celsius.
Pls help me with this

Styx · 29th September 2005, 09:15 AM

and what is the problem? a bit more detail is required please

yasser11 · 29th September 2005, 10:08 AM

the problem is how to achieve that linear range 0-10 V as output of instrumentation amplifier corresponding to the temperature range 0-100 degree celsius.

Styx · 29th September 2005, 10:29 AM

is the thermister changing linerarly? if so a standard amplifier will do

if not the chances are it is exponential and you will have to construct a log-amp and have fun calibrating it unfortunetly

**Nigel Goodwin** · 29th September 2005, 10:32 AM

Quote:

Originally Posted by yasser11

the problem is how to achieve that linear range 0-10 V as output of instrumentation amplifier corresponding to the temperature range 0-100 degree celsius.

Well a thermistor isn't usually linear, so getting a linear range is going to be difficult.

But to get a 0-10V range from 0-100 degrees is easy enough:

1) Adjust the other half of the bridge to make it balanced at 0 degrees (zero volts out).

2) Use a differential input opamp to amplify the output from the bridge.

3) Adjust the gain of the opamp to give 10V out when the thermistor is at 100 degrees.

This will then be correct at 0 degrees, and at 100 degrees, but inbetween accuracy will vary due to the non-linearity of the rhermistor.

JimB · 29th September 2005, 02:20 PM

The resistance/temperature characteristic of a thermistor is non-linear, however a reasonable amount of linearisation can be done using series and parallel resistors. There will still be some non-linearity, but depending on your application it can be ignored.

Have a look at this link:
http://www.thermometrics.com/assets/images/ntcnotes.pdf

Around page 23 (if I remember correctly), is a good section on linearisation.

JimB

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29th September 2005, 08:33 AM	(permalink)
yasser11	Temperature measurement using thermistor I have to use a wheatstone bridge with thermistor in one arm to detect change in the resistance of a thermistor for a temperature range of 0-100Celsius.And i have to use an instrumentation amplifier to obtain an output of 0-10V for the temperature ange of 0-100 Celsius. Pls help me with this

29th September 2005, 09:15 AM	(permalink)
Styx	and what is the problem? a bit more detail is required please __________________ Nothing is impossible. Once a problem is realised, the rest is just details

29th September 2005, 10:08 AM	(permalink)
yasser11	the problem is how to achieve that linear range 0-10 V as output of instrumentation amplifier corresponding to the temperature range 0-100 degree celsius.

29th September 2005, 10:29 AM	(permalink)
Styx	is the thermister changing linerarly? if so a standard amplifier will do if not the chances are it is exponential and you will have to construct a log-amp and have fun calibrating it unfortunetly __________________ Nothing is impossible. Once a problem is realised, the rest is just details

29th September 2005, 02:20 PM	(permalink)
JimB	The resistance/temperature characteristic of a thermistor is non-linear, however a reasonable amount of linearisation can be done using series and parallel resistors. There will still be some non-linearity, but depending on your application it can be ignored. Have a look at this link: http://www.thermometrics.com/assets/images/ntcnotes.pdf Around page 23 (if I remember correctly), is a good section on linearisation. JimB __________________ Experience is directly proportional to the value of the equipment ruined.