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

#### J35U51510V3

##### Aug 29, 2019, 02:48 pm
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

#1
##### Aug 29, 2019, 04:24 pm
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

#2
##### Aug 29, 2019, 04:27 pm
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 pmLast 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

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 pmLast 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

#5
##### Sep 02, 2019, 02:49 pm
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

#6
##### Sep 03, 2019, 04:46 pm
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

#7
##### Sep 04, 2019, 06:08 am
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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