gopal_amlekar
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Yes, I suggested it as an option.FvM, Will it help to increase resolution by using amplifier and range switching?
The thermistor characteristic is approximately following this equationWill linearization (hardware or software) help in increasing the resolution?
FvM, But how will it help actually? If I bias the thermistor with a 3.3V supply through a resistor, I can connect the thermistor voltage directly to ADC input. What difference it will make by adding an amplifier?Yes, I suggested it as an option.
A short remark about oversampling. It's generally an option, but has a principle limitation in the DNL (differential non-linearity) of the ADC. I won't expect too much from a PIC ADC in this regard.
Yes, that really makes sense! I had overlooked that dynamic range without an amplifier.Assume a simple voltage divider with a fixed resistor (to 3.3V) and the thermistor (to GND). You can chose e.g. a high resistor value, that gives a sufficient resolution at low temperatures. Then the voltage across the thermistor will be a few 10 mV maximum at high temperatures. By adding a programmable gain amplifier (PGA), you get sufficient resolution for low voltages, too.
oversampling seems really attractive option as you say. Are there any "cons" using this technique? Why do people go for 16-bit / 24-bit then? Thanks for good suggestion. I will study it...
Cons:
1. Lower speed (you need multiple samples)
2. Aditional care to inject proper noise (usually needs some additional hardware)
3. Additional filtering of input signals (you need low pass filter on the input, preferably hardware filter)
BTW, this is the way how most electronic human body thermometers work - they achive 0.01 degree despite that there is stupid cheap silicon inside.
Siniša;796801 said:0.1º resolution is not the problem, but accuracy ±0.1º over -40º to 140º is. I don't think you'll be able to get anything close to that without using Pt sensors. Even with Pt sensors it is challenging to design accurate system. Using some specialized IC's for this purpose might help.
Theoretically, ADC non-linearity involved with multi-bit oversampling ADC can be corrected, as it is usually done with multi-bit Sigma-Delta-ADC. You can find a respective chapter in Schreyers SD anthology. But it requires a table the holds the exact linearity deviation of each ADC step, measured with intended final oversampling resolution.Theoretically with oversampling you can achieve any resolution you want with simple 10 bit ADC.
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