# Calculating temperature using NTC thermistor

• KaK's_SLiM
In summary, the Steinhart-Hart equation can be used to predict the resistance of a thermistor at another temperature.
KaK's_SLiM
Hello,
i was doing a practical experiment using NTC thermistor. I recorded the resistance at different voltages (1v, 2v, 3v, etc) and to find the temperature i need to use the temperature coefficient formula "The Steinhart-Hart equation":

R(T) = R(T0) * [ 1 + a(T - T0) ]

where
T0 = reference temperature (deg Celsius)
T = temperature of interest (deg Celsius)
R(T0) = resistance at reference temperature (ohm)
R(T) = resistance at temperature of interest (ohm)
a = temperature coefficient of resistivity (1/deg Celsius)

i am confused to how calculate the temperature.
i know: T0 = room temperature (20 degrees C)
a = for copper wire is 0.004041
T = is what I am trying to find
R(T0) = ?? my thermistor says "resistance value to be 2kΩ" is this the value of R(T0)?
R(T) = this is the resistance value i get when passing current through copper wire

in some books I've seen the values of T to be in kelvin and sometimes in celcius. which is the correct way in this case? and instead of resistance some books replace it with "rho" for resistivity.

does anyone know where i can find some example worked questions to understand this.

Slim

$$R(T) = R(T_0) \cdot [1 + a(T - T_0)]$$

Where,

$$R(T)$$ = resistance at temperature of interest
$$R(T_0)$$ = resistance at reference temperature
$$a$$ = temperature coefficient of resistivity
$$T$$ = temperature of interest
$$T_0$$ = reference temperature

This equation is for predicting the resistance at another temperature based on a resistance at a reference temperature. The resultant resistance is due to the temperature increase at the temperature of interest.

Example:

$$R(55) = R(20) \cdot [1 + 0.004041(55 - 20)$$

$$= 223.75 \cdot 1.14143$$

$$= 255.396$$ $$\Omega$$

The temperature should be in Celsius.

I'm not 100% sure if there is a way to relate your measured voltages to temperature using this equation so I'll let an EE chime in.

CS

I suggest you to take a look at the following application notes:
Analog Devices AN 709 (right now can be found here http://www.analog.com/UploadedFiles/Application_Notes/2001119207465975025AN709_0.pdf )
Microchip AN685 - http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en011704

Anyway, I don't understand what you are trying to achieve.
The formula you posted is NOT the Steinhart-Hart formula. The proper one is here http://en.wikipedia.org/wiki/Steinhart-Hart_equation

If you want to measure temperature using the NTC thermistor, check the app. notes above. Basically, you connect a resistor and NTC thermistor in series and measure a voltage drop on one of these components.
It is easy to get the NTC resistance then. If you know coefficients of Steinhart-Hart equation of your particular NTC, it is easy to work out the temperature of the NTC.

good luck
meereck

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## What is a NTC thermistor?

A NTC thermistor is a type of temperature sensor that uses a material with a negative temperature coefficient, meaning that its resistance decreases as the temperature increases. This makes it suitable for use in temperature measurement and control applications.

## How does a NTC thermistor calculate temperature?

A NTC thermistor calculates temperature based on its resistance. As the temperature increases, the resistance decreases, and vice versa. By measuring the resistance of the thermistor, the temperature can be determined using a mathematical formula or a lookup table.

## What factors can affect the accuracy of temperature calculation using a NTC thermistor?

There are several factors that can affect the accuracy of temperature calculation using a NTC thermistor. These include the self-heating effect, which can alter the temperature of the thermistor itself, and the non-linear nature of the resistance-temperature relationship of the thermistor. The accuracy can also be affected by the quality of the thermistor and any external factors such as humidity or vibrations.

## How can I calibrate a NTC thermistor for accurate temperature measurement?

To calibrate a NTC thermistor, you will need to determine the resistance at several known temperatures and create a calibration curve. This can be done using a temperature-controlled environment and a multimeter to measure the resistance. The calibration curve can then be used to convert resistance readings into accurate temperature values.

## What are the advantages of using a NTC thermistor for temperature measurement?

One advantage of using a NTC thermistor is its small size, making it suitable for use in compact devices. It also has a fast response time, making it useful for temperature control applications. Additionally, NTC thermistors are relatively inexpensive and have a wide temperature range, making them versatile for various applications.

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