NTC is a contact resistance sensor, the thermocouple generates temperature-dependent voltage and the infrared sensor assesses the surface temperature from radiation. The choice depends on what you actually want to measure.

What to check out

• Specify temperature range, required accuracy, response and possibility of physical contact.
• For NTC you need an appropriate measuring input and R/T-caracteristics. MAX31855 is not a NTC converter.
• For the thermocouple, use the correct version of the converter, type of probe and appropriate connections and compensation of the cold joint.
• Infrared measurements check the emissivity, field of vision, distance and ambient reflections.

A Practical Example

The temperature of the liquid can be measured using an appropriately installed contact probe. It is interesting for a moving surface IR-measurement, but it must be checked for its material and measurement geometry.

Common error

Light metal may be IR-it gives a misleading result. Also, the nominal range of the converter does not demonstrate the same range of the whole probe and cable.

For further reading

• Analog Devices: converter for thermocouples MAX31855 (English). Example of an interface for thermocouples with cold joint compensation and fault detection.

Compatibility check products

Select products according to the above criteria; the list is not a confirmation that they are all interchangeable.

• Inox probe NTC sensor for a temperature of 10K 0,5m cable
• Module Infrared Thermometer MLX90614ESF-DCC for Arduino