One of the broad categories in engineering disciplines is instrumentation. Electrical, mechanical, and civil engineering heavily depend on instruments to control and monitor operations. One of the key parameters in engineering is temperature. Many devices have been invented to measure temperatures and one of them is a Pyrometer. A device is used to measure temperature from a remote location. It is a combination of two words, ‘pyro’ which is a Greek word for ‘heat’, and ‘meters’ a Greek word for ‘measure’. The measurement is done without the meter coming into contact with it which is the main advantage. It usually measures high temperatures.
It is a simple instrument made of two main parts namely;
- The optical system – consists of an optical lens that concentrates radiation from the source to the detector. A concave mirror is used for the purpose.
- Detectors- it is a sensor that converts heat from radiation rays into an electrical signal for measurement. The sensor can convert the signal into an electrical signal by focussing the heat on a thermopile. A collection of thermocouples makes a thermopile.
There are two main types of these meters, they are;
- An optical pyrometer- is used to measure temperatures from devices that emit visible radiation. The radiation is focussed by an optical lens and the resulting heat is directed to a detector.
- Infra-Red/ Radiation pyrometer- the detector responds to infra-red signals from the source. The heat is converted to measurement signals such as electrical signals.
Principle of operation
Key to note is that both types of operation on the principle of emission of radiation by objects were studied by scientist Stefan Boltzmann’s law. His work led him to come up with a law of emissivity and emissivity constant that is used to date. All objects above absolute zero temperature (0 degrees’ kelvin) emit radiation either in the visible or the infra-red spectrum. The radiation contains heat which when measured gives a measure of the temperature of an object. Radiation flux is directly proportional to proximity to the object and the temperature of a distant object.
Unlike liquid thermometers and thermocouple thermometers, a pyrometer does need to make contact with the object to take the reading. It was invented as a solution to measuring high temperatures of furnaces and metal smelting factories where contact thermometers were unable.
- Some of the advantages include;
- Require no contact to take readings
- Can measure very high temperatures.
- Fast to take readings.
- It has stable operation in a rugged environment.
- Can take the reading of moving objects.
- It is an expensive instrument.
- It is complex in construction.
- Its accuracy is affected by dust, smoke, and stray thermal radiation.
- Unsuitable for very low-temperature readings.
There is a wide array of applications for this wonderful instrument. Most of its usage is in high heat generation environments. They are highly preferred as compared to their contact-making counterparts. Some of them include;
- Smelting plants
- Metallurgy industry
- Steam boilers
- Furnace temperature reading
- Hot air balloon temperature taking.
- Liquid metal temperature reading.
- Heat leakage detector.
A pyrometer is an indispensable temperature meter that has taken instrumentation convenient and easy. Indeed temperature is a key parameter in the physical world, it is responsible for changing the state of objects. For objects to function well, they need to be at the right working temperatures. The control of this temperature must begin by measuring the actual temperature. Kudos to Stefan Boltzmann who carried incredible work in the field of pyrometry. With technological advancement, the heat signal from the sensor can be converted to an electrical signal and transmitted remotely.