Non Contact Vs Contact Temperature Measurement?

This is a common question – do I need a ‘probe’ thermometer or an infrared thermometer?

There are advantages and disadvantages to both of these methods of temperature measurement.

Temperature sensors are defined as contact or non contact. Understanding the difference is important in choosing the right thermometer for your needs and environment e.g. quality control in the food, pharmachem, engineering or environmental industries.

What are contact temperature sensors?

Contact sensors quite simply, measure temperature by making contact with the object to be measured  - via a ‘probe’ of some type. These can be penetration probes (the most common kind, with a pointed tip, often for inserting into food), immersion probes (for liquids), air probes (typically to measure ambient air in frozen/chilled/oven environments) and surface probes to measure flat surfaces e.g. hot plates, that pointed tip probes may have difficulty in making successful contact with.

There are different types of contact sensors that are used in these probe types to obtain measurement e.g.  thermocouples, thermistor or PT100 sensors.

Thermocouples are commonly used, due to their wide temperature range and measurement across a broad spectrum.  Thermocouples are typically low in cost, can be incorporated into small probe designs and have a quick response time.

Thermistor style sensors are generally used when higher accuracy is required. They have a narrower measuring range but they are regarded as one of the more precise everyday temperature sensors, offering high accuracy measurements of +/- 0.4°C or better.

PT100 sensors can offer higher accuracy still and are often used in laboratory applications or as a reference type measurement.

What are non contact thermometers?

Non contact thermometers measure surface temperature only and are often referred to as IR (Infrared), or Laser thermometers, due to that fact that many feature a laser sighting. These thermometers work by the principle that all objects above absolute zero, emit infrared energy and this is what non-contact thermometers measure, displaying as a temperature reading.

The fact that contact is not required with the object to be measured, can be an advantage for a few reasons e.g. Safety (if the object is electrically ‘live’) Accessibility (not all probes can access difficult to measure areas) & also product integrity (foodstuffs that may be damaged by probe insertion).

In a practical sense, the main differences between contact and non-contact thermometers can be summarised as follows:

Accuracy: Generally probe thermometers are considerably more accurate than IR thermometers

Response Time: IR thermometers are faster responding than probe thermometers – almost instant

Measurement capability: IR thermometers will only measure surface temperature (not core) so not always suitable for some food applications

Techris Systems have 35 years experience in the temperature measurement sector, we know your processes and applications and can advise you on which type of thermometer best suits your needs.