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NTC-1.php    13411 Bytes    23-04-2024 11:24:46


What's all this NTC stuff anyhow ?


NTC Basics, #1



NTC Resistors (Thermistors) are a negative temperature coefficient resistor that significantly reduces its resistance value as the heat/ ambient temperature rises.


NTC
NTC
NTC

"Classic THT"

Model to be screwed

SMD, 1206 (EPCOS)




✈ Applications




• Temperature Measurement -40 °C to +300 °C
• Temperature Control
• Inrush Current Limiting, see this Application Note from TDK
• Surge Suppression




✈ Temperature Characteristics




As the name suggests, those devices have a negative temperature coefficient. This is opposite to the usual experienced rise in resistance with temperature. (PTC).

B as a measure for the slope. Drawing courtesy TDK
Unfortunately their R(T) characteristics are very non-linear.

Fortunately it can be described with an exponential function and the knowledge of two parameters. One is the Resistance at 25 °C, the other is some kind of slope-parameter. This is the Thermistor Constant B or sometimes β. And yes, Temperatures are in Kelvin. (°C +273.15)





The javascript below lets you draw curves for your device.



Graph

Minimum Temperature
  [°C]
 
Maximum Temperature
  [°C]
 
Resistance at 25 °C
  [kΩ]
 
Thermistor Constant B
  [K]
 




Resistance [kΩ] versus Temperature [°C]






✈ Linearising this with a Voltage Divider




Possible configuration with an ADC
When used in this configuration, the curve gets much more linear, because we look only at a smaller range, and smart as we are, use an R1 almost the same value as the NTC in the middle of the operating range. (First iteration, see curve below). And yes, what is labelled "Reference" is identical to the +5V in the drawing ...






Graph

Minimum Temperature
  [°C]
 
Maximum Temperature
  [°C]
 
Resistance at 25 °C
  [kΩ]
 
Series Resistance R1
  [kΩ]
 
Thermistor Constant B
  [K]
 




Percentage of Reference [%] versus Temperature [°C]






✈ Tips & Tricks (as of 2009 aka "Hacks")




Four NTC's improve the accuracy by a factor of two
The accuracy of a single NTC is about 1% at 25 °C. If you want to improve this, you can increase the number of NTC's. If you take four of them, accuracy improves to 0.5% - this is about ± 0.1 °C (NTC Epcos B57374V2104F60).










✈ Share your thoughts



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Your Browser says that you allow tracking. Mayst we suggest that you check that DNT thing ?

 
t1 = 6585 d

t2 = 269 ms

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