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10/11/10 13:07
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 		 #179043 - Measure temperature @0.1deg resolution using thermistor
Hello all,

I would like to get expert suggestions on whether it is possible to design a circuit for:

1. Temperature measurement using a NTC thermistor
2. 10-bit ADC (Max. input 3.3V)
3. Resolution of 0.1 degree celsius
4. Temperature range of -40 to +100 degree celsius


I studied a thermistor (10K, Beta value 2490) datasheet http://www.vishay.com/docs/29003/23816154.pdf.
If I use this thermistor in a voltage divider circuit biased from a 3.3V supply, I get a minimum step size of only 536uV for a 0.1 degree change in temperature.This step size varies through the range as the characteristics are nonlinear.

For a 10-bit ADC, minimum step size is 3.2mV.

Is there some way out or some other trick like amplifying voltage obtained across thermistor and / or changing gain of this amplifier dynamically etc. or some software manipulation / linearization etc.

Please guide..

Regards,
Gopal

List of 24 messages in thread
TopicAuthorDate
Measure temperature @0.1deg resolution using thermistor            01/01/70 00:00      
   Sorry - doesn't work            01/01/70 00:00      
      Thermistors aren't such bad...            01/01/70 00:00      
         Remember the original requirement of 0.1°C            01/01/70 00:00      
   Resolution is not there...            01/01/70 00:00      
      What about the Termistor            01/01/70 00:00      
      RE: Resolution is not there...            01/01/70 00:00      
         one-wire sensors are still quite expensive than thermistors            01/01/70 00:00      
            Thermistor Vs one-wire sensor cost            01/01/70 00:00      
               Your processor has a voltage reference good enough?            01/01/70 00:00      
                  Voltage reference            01/01/70 00:00      
                     That voltage reference has large error...            01/01/70 00:00      
                  Vref is Not Needed            01/01/70 00:00      
                     Depends            01/01/70 00:00      
                        Ah but,            01/01/70 00:00      
                           Still not trivial            01/01/70 00:00      
         The normal fluke doesn't give 0.1C correct readings            01/01/70 00:00      
         I think your customer ...            01/01/70 00:00      
            quite common problem with resolution/precision            01/01/70 00:00      
         linearing only solves one issue            01/01/70 00:00      
            Precision            01/01/70 00:00      
               hm            01/01/70 00:00      
               Not an opamp            01/01/70 00:00      
               Comparison with Fluke a big problem            01/01/70 00:00      

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