Tech Note 441 Detail

Theory of Operation - Temperature Sensors

Affected Products:

PS-2125 PASPORT Temperature Sensor
TD-8550A Thermoelectric Converter
PS-2135 PASPORT Fast Response Temperature Probe (3 pack)

Problem/Symptom:
How do the PASCO Temperature Sensors work?

PASCO Solution:

10 kOhm NTC Thermistors

The following equipment measure the resistance of a 10 kOhm ceramic metal-oxide negative temperature coefficient thermistor that was designed to have resistance of 10.00 kOhm at a temperature of 25.00 C:

The thermistor is connected between the tip and sleeve (base) of the TRS connector. The ring is not connected. The equation for the temperature in terms of the resistance is given by the (Steinhart-Hart) equation below:

Temperature[Celsius] = 1.0 / ( A + B ln(R) + C ln(R)^2 + D ln(R)^3 ) - 273.15
R = ThermistorResistance[Ohms] / 10000

Temperature
Range [°C]
A B C D
-35 to 135 3.354e-3 2.564e-4 2.388e-6 8.377e-8

100 kOhm NTC Thermistors

The following sensors use a version of the ceramic metal-oxide negative temperature coefficient thermistor that is designed to have a resistance of 100.0 kOhm at 25.00 C:

The equation for the temperature in terms of the resistance is given by the (Steinhart-Hart) equation below:

Temperature[Celsius] = 1.0 / ( A + B ln(R) + C ln(R)^3 ) - 273.15
R = ThermistorResistance[Ohms]

Temperature
Range [°C]
A B C
-50 to 0 8.312653413479670E-04 2.083082877047050E-04 8.162433729410980E-08
0 to 50 8.274918692383500E-04 2.087547277229870E-04 8.069870440386500E-08
50 to 100 8.252715954912970E-04 2.090759654020190E-04 7.970254981668580E-08
100 to 150 8.169484569941060E-04 2.105821263402370E-04 7.242814459308220E-08

Type K Thermocouples

The following sensors use Type-K (chromel-alumel) Thermocouples:

Type K thermocouples are good for measuring a much wider temperature ranges than NTC thermistors, but are less accurate. Thermocouples consist of a junction between two conductors with different work functions. Thermocouples output a voltage that is nearly proportional to the difference in temperature between the two conductors, and their non-linearity is well compensated. As thermocouples can only measure differences in temperature, the temperature at the cold side of the junction is typically measured by a thermistor to calculate the actual temperature.

Creation Date: 09/18/2003
Last Modified: 06/5/2014
Mod Summary: