Types of Thermometer

Here at Hanna Instruments, we offer a range of four different types of thermometer: thermistor thermometers, thermocouple thermometers, Pt100 thermometers and infrared thermometers. They all vary slightly from one type to the next, each designed for specific tasks.

Thermistor Thermometers

the thermistor is a semi-conductor device whose resistivity (r) varies as a function of temperature (T)

r = r₀ (1+aT),  where

r₀ = characteristic resistivity of material

a = temperature resistance coefficient of material

It is possible to determine the temperature by applying a potential difference and measuring the resistance. Thermistor thermometers offer extremely accurate measurements (tenths of a degree) due to the sensitivity of the sensor. They are suitable for the range -50 to 150 °C (-58 to 302 °F), higher temperatures may damage the semiconductor sensor.

Thermocouple Thermometers

The thermocouple consists of the junction of two wires of different metals. At a given temperature, a potential difference results at the opposite extremes of the two wires (the Seebeck effect), with the respective variations linearly related within small intervals. It is therefore possible to determine the temperature given the potential difference and characteristics of the two metals.

Although not quite as accurate as the thermistor thermometer, the thermocouple thermometer has a much wider range of temperatures in which it can operate, making it more suitable in certain applications.

Pt100 Thermometers

The operating principle of resitance thermometers is based on the increase of electrical resistance of metal conductors (RTD: Resistance Temperature Detectors) with temperature. Among the various metals to be used in the construction of resistance thermometers, platinum (Pt, hence the name of the thermometer), a noble metal, is the one that can measure temperatures throughout a wide range, from -251 °C (-419.8 °F) to 899 °C (1650.2 °F) with a linear behaviour.

The main disadvantage of RTD probes is the resistance connection cable. This resistance prevents the use of standard two-wire cables for lengths over a few meters, since it affects the accuracy of the reading. For this reason, to obtain high levels of accuracy in industrial and laboratory applications, the use of a three or four wire system is reccomended. 

For all of our Pt100 thermometers and probes, we have chosen the multiple wire technology for higher accuracy. This means if you require a thermometer to measure a large temperature range to a igh degree of accuracy, the Pt100 thermometers are for you.

Infrared Thermometers

All objects emit a radiant energy in the infrared (IR) spectrum that falls between visible light and radio waves. In the ealry 20th century scientists were able to quantify IR energy, and discovered that this energy is proprtional to the 4th power of the object's temperature.

IR instrumentation almost exclusively uses an optic device that detects the heat energy generated by the object that the sensor is aimed at. This is then amplified, linearised and converted into an electronic signal which in turn shows the surface temperature in Celsius or Fahrenheit degrees.

Infrared measurements are particularly suitable for areas where it is difficult or undesirable to take surface measurements using conventional contact sensors. Applications for IR meters include non-destructive testing of foodstuffs, moving machinery, high temperature surfaces and hazardous areas, such as high voltage wires.

See our shop to see which of our thermometers is right for you.

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