DC temperature sensor NTC, which method makes more sense?
Hello.
A measurement is to be carried out with a resistor, more precisely a temperature-dependent resistor. There are the following possibilities:
On the one hand, there is the use of any bridge where one of the four resistors is represented by the temperature-dependent resistor and is operated in the adjustment process.
Then there is the direct measurement of current and voltage on the resistor.
Which method do you consider more useful and why?
Thank you in advance.
(No Ratings Yet)
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The advantage of the Wheatstone bridge is the independence from the operating voltage.
The disadvantage is that one knows the resistance ratios between NTC and the bridge resistances, but still not the absolute size of the NTC resistance.
With direct measurement of current and voltage one has the problem that one cannot measure both exactly at the same time.
In both methods, the resistance value is known with good luck, but the temperature must then be calculated. NTCs have a very nonlinear characteristic.
So both procedures are quite unusable in practice.
I recommend a voltage divider made of NTC and a temperature-independent known resistor. The voltage at the NTC is then measured with an ADC ratiometrically against the applied voltage. Then the resistance of the NTC is known and a microprocessor is instructed to calculate the temperature. This is not exactly trivial because you have to calculate logarithms for this.
Thank you very much. How is the independence of the operating voltage advantageous?
And if you had to take one of the two methods, which one would you prefer?
Many thanks for the detailed answer.
I would build a voltage divider with an NTC and a temperature-independent resistor. An ADC measures the voltage at NTC.
The voltage at the voltage divider must be at the same time reference voltage of the ADC, because an ADC measures (normally) the ratio between input voltage and reference voltage.
(This is called rational measurement.)
The measured value is thus independent of the accuracy of the reference voltage.
Thank you very much.