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What is 3% means of a NTC resistor?

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tony_lth

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Hi,
In the datasheet of a TDK NTC resistor, its spec is as following:
-40deg ~ +125 deg, measure accuracy is 3%, etc.
So what is the 3% means here? Because its measure range is (125-(-40))=165 deg, does 3% mean 165*3%=5deg error?
Thanks.
Best,
Tony Liu
 

Hi,

Please post the link to the datasheet.
 

No NTC datasheet has percent measuring accuracy spec, the have resistance and possibly B coefficient spec. It can be converted in temperature accuracy which varies over temperature range. Due to B tolerance, least error is around reference temperatur, e.g. 25 °C.

Read complete datasheet.
 

    tony_lth

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Hi. Gurus,
I used the following TDK NTC.
In room temeprature at 27 deg, the NTC resistor value is about 8K, so conduct the temperature is 33deg, about 5 deg error.
So what is the B constant value here? How to conduct accuracy temperature?
Best,
Tony Liu
 

Attachments

  • NTCG063JH103 P2R050501 热敏电阻-40~125度 TDK.pdf
    136.6 KB · Views: 132

Hi,

In the datasheet there are 72 occurances of "3%"
* most of them clearly give the tolerance of the "B constant"
* the other clearly give the tolerance of the nominal "25°C initial resistance value".

Which one exactly do you mean? And what is unclear with it?

Klaus
--- Updated ---

...added

I just did an internet search for you "ntc b value calculations formula"
I came to this explanation: https://www.ametherm.com/blog/thermistors/thermistor-beta-calculations
Does this answer your questions?

Klaus
 
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    tony_lth

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Your type specification doesn't include the letter for resistance tolerance which can be either 3 or 5% according to datasheet. Exact B value and tolerance doesn't matter near 25 °C. For 8k you can calculate 31°C NTC temperature, deviation from expected 27 °C is much higher than explainable by resistor tolerance. Possible explanations
- inaccurate measurement
- NTC self heating. What's the sensor current?
 

    tony_lth

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Sorry, Gurus,
Finally we found the bug, there are some pull-up and pull-down resistors which should be removed, but not.
So after do so, we tested room tempereature 26.2 deg, and compared to a air-conditioner sensor's 26.4deg.
I am satisfied with the result.
BTW, do you think this TDK NTC can reach 1% measurement accuracy? from results, it seems very good.
But in datasheet, there are so many factors, so how to evaluate the accuracy from theory?
Best,
Tony Liu
 

you would have to calibrate it at 3 differing temps to get 1% or better ...
 

    tony_lth

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You didn't mention the temperature range. 1 K accuracy around 25 °C is possible without calibration.
--- Updated ---

In addition, you can buy NTC sensors like NTCLE203E3103SB0 https://www.vishay.com/docs/29118/ntcle203.pdf with 2.2% R and 0,5 % B tolerance that achieve 1 K accuracy over the full application temperature range (-55 to +150°C) without calibration. Although it's simple error propagation calculus, 1st years engineering stuff, but you'll find supplementing documents with accuracy calculations on the TDK or Vishay web sites.



 
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    tony_lth

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