310201e Non-Contact Temperature Measurement Flashcards
What is a diode
Diodes are two terminal devices that permit current flow in one direction
Can you use a diode as a temperature measurement sensor?
Yes
As the temperature of the diode increases, its internal resistance to current flow decreases
The drop in diode resistance allows a higher value of current, which the ammeter measures
Another method with a diode is to measure the voltage across the diode. In this case, as the temperature of the diode increases, the voltage measurable across it decreases.
What is a transistor?
Transistors are three-terminal, solid state electronic deviced that are usually made of silicone, gallium arsenide or germanium
They are commonly used for amplification and for switching integrated circuits
They can also be used for temperature measurement because transistors are sensitive to temperature change
What materials are transistors usually made of?
Silicone
Gallium arsenide
Germanium
What is a pyrometer?
A pyrometer is a non-contact radiant energy detector
Pyrometers measure the intensity of the radiant energy and produce a signal proportional to the radiating objects temperature
Where are three applications where you would measure non-contact temperatures with a pyrometer?
- Where temperatures are above the limits of conventional detectors
- Objects are moving
- Accessibility is difficult or impossible
Define incident radiation
Incident radiation is the energy hitting the surface of a body in the form of waves or particles through space
Define absorbed radiation
Absorbed radiation is the radiant energy absorbed by a body
Define reflected radiation
Radiant energy reflected by the surface of a body
Define transmitted radiation
Transmitted radiation is the radiant energy transmitted through a body
What is the value of fractional reflection associated with a black body?
0%
What is the value of fractional absorption associated with a black body
100%
What is the value of fractional transmission associated with a black body
0%
What is the Stefan-Boltzmann equation for all bodies including non-black bodies?
Define emissivity
Emissivity is the ratio of radiant energy that an object emits divided by the radiant energy that a black body emits at the same temperature
What is a Gray Body?
A gray body is an object with an emissivity of less than one
The emissivity is the same at all wavelengths
Most solids and liquids are gray bodies
What is a Non-Gray Body?
A Non-Gray Body is an object whose emissivity factor varies with wavelength
Glass, metals and plastic films are non-gray bodies
What is the wavelength range for IR radiation?
0.7 micro-meters to 1 millimeter
What is the wavelength range for visible light?
0.4 micro-meters to 0.7 micro-meters
When you use a diode as a temperature sensing device, what happens to the internal resistance as the temperature increases?
As temperature increases, the internal resistance decreases
When you use a diode as a temperature sensing device, what happens to the internal resistance as the temperature decreases?
As temperature decreases, the internal resistance increases
How many terminals does a transistor have
3
What field of instrumentation commonly uses semiconductor sensors for temperature measurement and why?
HVAC because of their low cost compared to other sensors
Name an application of an IC transistor used for industrial temperature measurement?
Reference junction temperature compensation in thermocouple circuits
What do non-contact pyrometers measure?
The intensity of radiant energy
Define a black body
A black body is a theoretical ideal radiating body
It absorbs all radiation that it intercepts and it radiates more energy than any other body at the same temperature
Measurement error becomes greater or smaller as the wavelength increases with many metals?
With many metals, the measurement error becomes greater as the wavelength increases
List three accessories required when pyrometers are exposed to high operating temperatures
- Water cooling jacket
- Special cable connections
- Air blowing attachment
A pyrometer has a distance to spot (D:S) ration of 100 to 1
What does this ratio mean?
This ratio is the relationship between the distance of the measuring device from the target and the diameter of the spot
Ex. When the pyrometer is 100m from the target, the target diameter is 1m
When you compare thermal and quantum detectors used in pyrometers, which detector provides the fastest response to a change in temperature?
The quantum detector
List three types of quantum detectors
- Photomultiplier tubes
- Photoconductive cells
- Photovoltaic cells
Which type of pyrometer is unaffected by airborne contamination such as smoke or water vapour?
A ratio pyrometer
What is the lowest temperature that a manual optical pyrometer can read?
760°C
Below 760°C, not enough energy radiates in the visible spectrum for this method to work
What is the highest temperature that a manual optical pyrometer can read?
3500°C
What are the two types of black body calibrators used in pyrometry?
- Cavity
- Flat plate
What are the three components of a pyrometer?
- Optical system
- Detector
- Associated electronics
Whqt are the primary and secondary method of calibration for a pyrometer?
Primary - simulated black body
Secondary - comparing to another pyrometer calibrated to a black body
What are two advantages and disadvantages of a radiation pyrometer?
Pros - physical contact not needed, fast reponse
Cons - expensive, non-linear scale
How does an optical pyrometer work?
Compares a heated filament to the light given off by an object
