| ??? 10/14/10 04:19 Read: times |
#179095 - Precision Responding to: ???'s previous message |
Neil Kurzman said:
if you bias it with just a resistor you may get .1C at one end but 1C at the other. maybe a selection of different divider resistors. So I should better use a op-amp and a switching IC for gain switching, right? Neil Kurzman said:
And remember the fluke does not have any beter accuracy then the thermistor it is using. So even fluke also uses a thermistor only? Or something like DS1820 or DS2438? Per Westermark said:
If the Vref is used to feed both ADC and a voltage divider containing the thermistor, then the error will cancel. Steve M. Taylor said:
Then you run the constant current source through the thermistor and a reference resistor which generates Vref for the ADC Unfortunately my processor has no provision for external VREF. So VDD is only option. So I can generate the current for thermistor as well from VDD only. Erik Malund said:
I think your customer is confusing resolution with precision. Yes, he was confusing these two parameters. Erik Malund said:
the Fluke is NOT .1 degree precise. So comparison with fluke will not be a big problem then. Per Westermark said:
The customer don't know what he needs/wants except that it should look good. Why else require that it matches the reading of a Fluke? Fully agree. |
