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Topic: Calibrating thermistor (Read 368 times) previous topic - next topic

J35U51510V3

I'm trying to calibrate my thermistor and first way i'm trying is using a ds18b20 as source to calibrate the thermistor.

when reading the temperature from both sensors i noticed the thermistor is about 2.2 degrees off, so i added that 2.2 in thermistor temperature calculation, now the reading from both sensors are almost the same.

for example the reading right now is:

Thermistor: 26.42 C

DS18B20: 26.37 C

from 25 degrees to 35 degrees both sensors readings are similar (thermistor response is way faster to temperature change) but i didn't tested it below 25 degrees.

my question is how accurate this method of calibrating can be in huge temperature changes like -10 or +80? is it still gonna be as accurate as it is in 25-35 range of temperature?

 

pylon

Quote
my question is how accurate this method of calibrating can be in huge temperature changes like -10 or +80? is it still gonna be as accurate as it is in 25-35 range of temperature?
That depends on the thermistor used. As you didn't specify which type you're using and how you calculate the result it's hard the predict any result.

jremington

If you calibrate the thermistor correctly, using the DS18B20 as the reference, the readings should be within 1 degree of each other.

MarkT

#3
Aug 31, 2019, 11:27 pm Last Edit: Aug 31, 2019, 11:28 pm by MarkT
I'm trying to calibrate my thermistor and first way i'm trying is using a ds18b20 as source to calibrate the thermistor.

There are several sources of experimental error with temperature measurements.  Firstly sensors pick
up conducted heat and radiated heat, and in a ratio that depends on the sensor shape, construction and
surface materials.

Also the time constant for a sensor to equalize with its surroundings can be tens of seconds or even more.

You are best placing both sensors inside a small closed metal tube (to reflect radiant heat and spread
conducted heat), and use a rapidly stirred water-bath.  The temperature of the water should be raised
in steps, then the sensors allowed to equalize in temperature for a minute or so before taking each
measurement.

If you just have sensors on the bench I would expect upto 2 degrees error just because you are at the
bench radiating heat at them.

Quote
when reading the temperature from both sensors i noticed the thermistor is about 2.2 degrees off, so i added that 2.2 in thermistor temperature calculation, now the reading from both sensors are almost the same.

for example the reading right now is:

Thermistor: 26.42 C

DS18B20: 26.37 C

from 25 degrees to 35 degrees both sensors readings are similar (thermistor response is way faster to temperature change) but i didn't tested it below 25 degrees.

my question is how accurate this method of calibrating can be in huge temperature changes like -10 or +80? is it still gonna be as accurate as it is in 25-35 range of temperature?

 
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GolamMostafa

#4
Sep 01, 2019, 04:24 pm Last Edit: Sep 01, 2019, 04:25 pm by GolamMostafa
I would do the two points calibration taking DS18B20 as a reference. The two points are: 40C (ice water) and 1000C (boiling water).

MarkT

For the boiling water point you need to check the atmospheric pressure at the time and apply a correction for this.
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herbschwarz

A thermistor does not follow the change in
temperature in a linear manner. So, the wider
the difference in temperature from the calibration
point, the more error may be seen.
Herb

malinga5

It all depends on the type of thermistor you use as you didn't mention the type you used it is difficult to predict the results.
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