Measurement Principle NTC sensing

General
This article gives an introduction into the temperature measurement by NTC Sensors.


Measurement principle
A NTC Sensor is a temperature sensitive resistance with a Negativ Temperature Coefficient (NTC). Therefore, the resistance of the sensor can be measured and converted into the corresponding temperature value. The higher the temperature, the lower the sensors resistance.

NTC and PTC characteristic curve

RMS Devices
Rotronic offers two Minilogger based on NTC sensing.

• RMS-MLOG-T-868/915 -> fix internal NTC sensor
• RMS-MLOG-T10-868/915 -> external NTC sensor connectable

NTC sensors
Rotronic also offers various types of NTC sensors for several ranges and applications for the Minilogger.
Overview: https://service.rotronic.com/manual/...?sensors4.html


NTC Sensor Parameters

• B is a sensor material specific constant and stands for the electrical conductivity. As higher B as more isolating the material is.
• R25 – Nominal resistance of the sensor at 25°C – also a material specific constant.

If the application requires the use of a different sensor than listed above, both parameters of the sensor need to be read out from the datasheet and be edited into the device properties of the Minilogger.
Ranges and Parameters: https://service.rotronic.com/manual/...up-tables.html


Advantages of NTC

• Robustness of the sensor
• Wide range / extreme temperatures possible to measure
• Lower price than a Platinum sensor PT (e. g. PT100)

Disadvantage of NTC

• Less accuracy than a PT sensor
• Bigger measurement deviation between identical sensor types. A higher tolerance range needs to be considered e. g. for Alarming.

Accuracy
The measurement accuracy consists of the electronical accuracy of the Minilogger and the accuracy of the sensor.

• Sensor datasheets : https://www.rotronic.com/de-ch/produ...wnload?id=1783
• Accuracy of Minilogger: https://service.rotronic.com/manual/...ication15.html

If the application requires the use of a different sensor than listed above, the accuracy of the desired sensor (see the relevant datasheet) is to be considered.