Non-contact Temperature Measurement Flashcards
Explain the principle of operation of pyrometers and state the applicable mathematical
formula.
The thermal radiation (energy) emitted by an object is a function of its absolute temperature.
𝑊 = €𝜎𝑇^4
Explain what a black body is (i.e. what is a perfect radiating body?).
Black body absorbs all radiation that it intercepts and radiates more energy than any other
body of the same temperature.
Explain what the emissivity factor represents.
The ratio of radiation emitted by the object compared to that of a Black Body at the same
temperature.
What factors affect emissivity?
- Shine / Reflection of the object
- Roughness
- Flatness
- Darkness
The radiation received by a pyrometer is the summation of what three sources?
The emittance E, the reflectance R, and transmittance T
To correctly measure the temperature of an object with a radiation pyrometer, the
radiation received should only be from what form?
The emittance # (ie; R & T should be zero)
What factors will effect the radiation that the detector in a broadband
pyrometer receives from the targeted object?
- Moisture that can create prizms
- Gasses like CO2 that absorb heat
- Particulate, smoke, and/or dust that will absorb wavelength
- Lens material
- Distance
What does 40” to 1” mean as it applies to radiation pyrometers?
At 40 inches in distance the object diameter that is being measured is 1 inch
What factors could effect the reading of a pyrometer?
- Emissivity
- Path condition
- Distance
- Angle of measurement
- Absorbed energy
- Change in environment / ambient temperature
- Movement of the target
What are the disadvantages of a pyrometer?
- Fragile
- Expensive
- Non-linear scale shape
- Emissivity needs to be compensated for (low E cause a higher temperature reading)
- Needs a consistent environment
How would a high temperature affect frequency and wave length?
Higher temperature = higher frequency and low wavelength
Describe perfect blackbody attributes.
- Dull
- Rough
- Flat (no curves)
- Black
What is the main function of a heat sensor?
Monitor for a flame loss or a failure to ignite
What is a conductivity flame sensor and what is the disadvantage
Conductivity flame sensor completes the loop and sends a current when flame is present closing the loop
Carbon plugging could fool the sensor between sensing elements
How does a rectification flame sensor work?
Senses a flame through an electrode. When a flame is cut off so is the fuel supply.
