An optical pyrometer is a non-contact device for measuring devices. The device allows you to measure the temperature of objects that are typically difficult or seem impossible to measure with contact devices. For instance, an optical pyrometer measures the temperature of devices like rotating components, hazardous elements, and objects in high voltage environments. According to Process Parameters (https://www.processparameters.co.uk/high-temperature-pyrometer/), it can even be used to measure the temperature of furnaces, molten metals, and overheated liquids.
The working principle of an optical pyrometer
The working principle of an optical pyrometer is based on the comparison of the brightness intensity of visible radiation emitted by a heated object with radiation energy emitted by a source with known brightness or intensity. In a nutshell, it works by matching an object’s brightness to the filament inside the optical pyrometer.
How does an optical pyrometer work?
It features a lens that focuses radiated energy from a heated object and redirects or targets or aims it on the electric filament lamp. The intensity of the electric filament depends on the amount of current that passes through it. This is why the current is adjusted until the brightness of the filament is equal to that of the object. When this happens, the filament’s outline disappears completely. On the other hand, the filament typically looks brighter when the temperature is more than the source. Additionally, the filament usually looks darker if the temperature is less than required to attain equal brightness.
Construction of an optical pyrometer
This non-contact temperature measuring device is made up of the following construction;
- Internal cylinder- this is where the lens and the eyepiece are located. The lens and eyepiece are usually located on opposite sides of the optical pyrometer. The internal cylinder also consists of the lamp.
- The power source- it is made up of a battery, rheostat, and millivoltmeter or ammeter connected to the temperature bulb
- The lamp- this part goes in between the eyepiece and lens.
- The filter- this component is usually placed in front of the eyepiece. Its role is to help get monochromatic light. It also also in narrowing the wavelengths band.
- Absorption screen- this component goes between the temperature lamp and the objective lens. Its role is to increase the temperature range to measure the object’s temperature.
What are the advantages of optical pyrometers?
The primary advantages of optical pyrometers are;
- They are great for high-temperature applications
- You can use an optical pyrometer to check the temperature of distant and moving objects
- The temperature measuring device is highly accurate
- It can be used to measure temperature without connecting with the target
- It is lightweight and easy to use
- It is highly flexible and portable
- It provides fast responses
- It is less sensitive to changes in emissivity
What are the disadvantages of optical pyrometers?
While optical pyrometers are highly beneficial, they also feature significant downsides. Below are the primary disadvantages of optical pyrometers;
- The radiation of the thermal background and other elements like dust and smoke can affect the accuracy of optical pyrometers
- The devices do not apply the temperature measurements of burning gasses because the energy they emit is not visible
- Optical pyrometers are expensive to acquire
- They are not great for evaluating object temperatures below 8000C. This is because the amount of energy generated at less temperature is usually low.
Applications of optical pyrometers
The most common applications of optical pyrometers are;
- Measuring the temperature of highly heated materials
- Measuring furnace temperatures
- Measuring temperatures in critical processes like furnaces, glass manufacturing, and heat treating
- Measuring the temperature at the top of a hot air balloon
- Measuring the steam temperature in steam boilers
- Measuring the temperature of liquid metals and highly heated materials
- Optical pyrometers are also used in the smelting and metallurgy industries
What is the optical pyrometer range?
The operating range of optical pyrometers ranges from 700 degrees Celsius to 4000 degrees Celsius. The range may differ depending on the type of pyrometer, the design, and construction.
Optical Pyrometer Wrap Up
There are two types of pyrometers; optical and infrared pyrometers. They measure temperatures remotely y measuring radiation from an object instead of physical contact. Both types belong to a class of thermometers that are only used for measuring high temperatures. Optical pyrometers are the most commonly used and versatile in industrial and laboratory uses.
