- All of the temperature-measuring methods discussed before need physical contact of the thermometer with the body whose temperature is to be measured.
- However, at temperatures exceeding 1400°C, the thermometer may melt as a result of direct physical contact.
- To solve these problem a non-contact temperature sensing method is used.
- This method is also useful for moving bodies.
- Pyrometry is a method of measuring temperature without making physical contact.
- Pyrometry is a method of determining the temperature of a body by measuring its electromagnetic radiation.
- Two types of pyrometers:
- Radiation Pyrometers.
- Optical Pyrometers.
- Infrared Pyrometers.
Optical Pyrometer
- The optical pyrometer is another device for measuring high temperatures in the range of 600 to 3000°C.
- Optical pyrometers are very useful for checking and calibrating radiation pyrometers.
Optical Pyrometer Principle
Operation of optical pyrometer based on the comparison of the intensity (brightness) of the visual radiation emitted by the hot body with the radiation emitted by the source of known intensity.
Optical Pyrometer Construction
The pyrometer has a cylindrical shape, and its parts mostly include an eyepiece, a power source, an absorption screen, and a red filter.
- On both sides of the instrument, an eyepiece and an object's lens are placed.
- A temperature bulb is connected to a battery, millivoltmeter, and rheostat.
- To enhance the temperature range, an absorption screen is placed between the reference temperature lamp and the objective lens, and his range can be determined using the device.
- The red filter is placed between the lamp and the eyepiece so that the lamp only allows for a narrow band with a wavelength of 0.65mui.
Optical Pyrometer Working
Optical Pyrometer Diagram
As shown in Fig. 1,
- The intensity of radiation emitted by the hot body whose temperature to be measured, is matched with the intensity of a calibrated reference (lamp) whose temperature is known.
- It consists of hot body, lamp placed in line.
- It uses lens to pick-up the radiant heat waves.
- The brightness of the hot substance is matched to brightness of an incandescent lamp.
- The comparison is made by eye, and the brightness of the lamp is manually adjusted by manipulating a variable resistor.
- The amount of adjustment needed to match the two sources of light is a measure of temperature.
- The position of the resistor is indicated on a dial graduated in units of temperature.
- When the resistor has been positioned so that the light sources are equal in brightness, the temperature can then be read directly on dial.
Optical Pyrometer Advantages
Advantages of Optical pyrometer are as follows.
- Flexibility and convenient to use.
- Light in weight.
- Useful for monitoring the temperature of moving objects and distant objects.
- No need for contact with target of measurement.
- As long as the size of the item whose temperature is to be measured corresponds to the size of the optical pyrometer, the distance between the two is not an issue. As a result, the device is suitable for remote sensing.
- Electrical objects' temperatures can be measured, which is critical when dealing with contact type measurements such as HT panels and transformers.
- The instruments can be used in situations where physical access is difficult. At roof heights, there could be small ducts or some other objects.
- It can measure the moving objects.
- Useful for high temperatures.
- Good accuracy.
- It has a very good accuracy of +/-5 degrees Celsius.
Optical Pyrometer Disadvantages
Disadvantages of Optical pyrometer are as follows.
- Not useful for measuring the temperature of clean burning gases that do not radiate visible energy.
- The device is dependent on light intensity, it can only be used in applications with a minimum temperature of 700 degrees Celsius.
- The device is ineffective for recording continuous temperature measurements at small intervals.
- Expensive.
- Causes human error.
- Emissivity errors.
Application of Optical Pyrometer
Applications of Optical pyrometer are as follows.
- Optical pyrometer is used to measure high temperatures.
- It is used to determine the temperature of extremely hot materials.
- It is helpful for measuring furnace temperatures.
- It is used in critical process measurements of crystal growth, furnace control semiconductor, medical, induction heat treating, glass manufacturer, etc.
Conclusion
As a result, this is simply an overview of the optical pyrometer. Finally, we can conclude from the above article that this is a type of noncontact temperature measuring device. This device works by matching the intensity of an object to the intensity of the filament used in the pyrometer.
FAQs
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Pyrometry is a method of estimating the temperature of a body by measuring its electromagnetic emissions.
Pyrometry is a method of measuring temperature that does not require physical contact.
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It is used in a variety of industrial applications to measure non-contact high temperatures.
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The operation of an optical pyrometers is based on a comparison of the intensity (brightness) of the visual radiation emitted by the hot body with the radiation emitted by the source known intensity.
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The optical pyrometers is another instrument for measuring the high temperatures in the range of 600 to 3000°C.
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A red filter is placed between the eyepiece and the reference bulb to help in narrowing the wavelengths band.
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A thermocouple is a transducer made of two different metals welded together at each end that produces a voltage proportional to the temperature difference between the two junctions (one of which is normally held at a known temperature), whereas a pyrometer is a thermometer designed to measure high temperatures.
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The optical pyrometers are useful for high temperatures and It is useful for monitoring the temperature of moving object and distant objects.