Temperature Measurement devices in laboratories

Hand held infra red laser thermometer

Temperature is defined as the degree of hotness or coldness of a body. In a laboratory temperature measurements are used to establish purity of substances (melting point and boiling point), control over distillation processes, reaction kinetic studies and in several other measurements such as viscosity, density, phase transition studies, determination of flash points of flammable oils, etc. A single temperature measurement device is not applicable across all situations. The article discusses some of the common temperature measurement devices for different laboratory applications.

Liquid in glass thermometers

A liquid in glass thermometer is the most commonly used temperature measuring device used in laboratories .A liquid should have the following desirable properties for use in glass thermometers:

• Uniform coefficient of thermal expansion over the temperature range of the device
• Low freezing and high boiling point so as to cover large temperature range.
• Good conductor of heat for fast response to heat changes i.e. its specific heat should be low.
• Free flowing and should not wet the glass surface.

The two commonly used liquids are mercury and alcohol

Mercury in glass thermometer

Mercury in glass is the most predominant temperature measurement device in laboratories as it meets requirement of most common applications. Mercury remains in liquid state from  and has all the desired properties listed above. Its only disadvantage is its toxicity and requires special cleanup procedures in case of breakages.

Alcohol in glass thermometer

Alcohol in glass thermometers finds major applications in measurement of low temperatures as alcohol has a freezing point of  and a boiling point of . Its use above ambient temperatures is not recommended as it is not as good a conductor of heat as mercury and expands more than mercury. As alcohol is colorless a dye is added to aid clear visibility.

Probe Thermometers

Probe thermometers have specially designed probes to permit immersion or penetration in viscous or semi solid porous materials such as oils, grease and foods. Apart from use in laboratories such thermometers are used in manufacturing industries, food catering establishments and retail outlets. Probe thermometers are provided with digital display and are portable for convenience of use by field staff.

Infra Red Thermometers

Infrared thermometers are a class of non contact measurement hand held devices. These are based on measurement of radiation from a hot object. They are also called laser thermometers as a laser beam is used to target the probe to the centre of the measurement area. Infrared thermometers find application in measurement of high temperatures beyond .

Temperature data loggers

Temperature data loggers can be set for temperature recording and display on continuous basis or at pre-set time intervals. The data output can be in digital or graphical formats and can be shared online or stored for subsequent review. Such devices find use in storage areas of temperature sensitive chemicals and standard reference materials as well in stability chambers used for evaluating shelf life studies.

Resistance Thermometers

Resistance Thermometers or Resistance Temperature Detectors (RTD’s) measure temperature through changes in electrical resistance of a pure metal wire due to change in temperature. Common materials are Platinum, Copper or Nickel. The pure metal wire is wound around an inert ceramic or glass core. Platinum is the most widely used material as it has a large resistance change over temperature range measured. The temperature ranges from  to  with an accuracy of 

Platinum resistance thermometer or PRT finds global acceptance as a temperature measurement and calibration reference standard because of its high accuracy and precision of measurements.