310201e Non-Contact Temperature Measurement

Question 1

What is a diode

Answer 1

Diodes are two terminal devices that permit current flow in one direction

Question 2

Can you use a diode as a temperature measurement sensor?

Answer 2

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.

Question 3

What is a transistor?

Answer 3

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

Question 4

What materials are transistors usually made of?

Answer 4

Silicone
Gallium arsenide
Germanium

Question 5

What is a pyrometer?

Answer 5

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

Question 6

Where are three applications where you would measure non-contact temperatures with a pyrometer?

Answer 6

1. Where temperatures are above the limits of conventional detectors
2. Objects are moving
3. Accessibility is difficult or impossible

Question 7

Define incident radiation

Answer 7

Incident radiation is the energy hitting the surface of a body in the form of waves or particles through space

Question 8

Define absorbed radiation

Answer 8

Absorbed radiation is the radiant energy absorbed by a body

Question 9

Define reflected radiation

Answer 9

Radiant energy reflected by the surface of a body

Question 10

Define transmitted radiation

Answer 10

Transmitted radiation is the radiant energy transmitted through a body

Question 11

What is the value of fractional reflection associated with a black body?

Answer 11

0%

Question 12

What is the value of fractional absorption associated with a black body

Answer 12

100%

Question 13

What is the value of fractional transmission associated with a black body

Answer 13

0%

Question 14

What is the Stefan-Boltzmann equation for all bodies including non-black bodies?

Answer 14

Question 15

Define emissivity

Answer 15

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

Question 16

What is a Gray Body?

Answer 16

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

Question 17

What is a Non-Gray Body?

Answer 17

A Non-Gray Body is an object whose emissivity factor varies with wavelength
Glass, metals and plastic films are non-gray bodies

Question 18

What is the wavelength range for IR radiation?

Answer 18

0.7 micro-meters to 1 millimeter

Question 19

What is the wavelength range for visible light?

Answer 19

0.4 micro-meters to 0.7 micro-meters

Question 20

When you use a diode as a temperature sensing device, what happens to the internal resistance as the temperature increases?

Answer 20

As temperature increases, the internal resistance decreases

Question 21

When you use a diode as a temperature sensing device, what happens to the internal resistance as the temperature decreases?

Answer 21

As temperature decreases, the internal resistance increases

Question 22

How many terminals does a transistor have

Answer 22

3

Question 23

What field of instrumentation commonly uses semiconductor sensors for temperature measurement and why?

Answer 23

HVAC because of their low cost compared to other sensors

Question 24

Name an application of an IC transistor used for industrial temperature measurement?

Answer 24

Reference junction temperature compensation in thermocouple circuits

Question 25

What do non-contact pyrometers measure?

Answer 25

The intensity of radiant energy

Question 26

Define a black body

Answer 26

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

Question 27

Measurement error becomes greater or smaller as the wavelength increases with many metals?

Answer 27

With many metals, the measurement error becomes greater as the wavelength increases

Question 28

List three accessories required when pyrometers are exposed to high operating temperatures

Answer 28

1. Water cooling jacket 2. Special cable connections 3. Air blowing attachment

Question 29

A pyrometer has a distance to spot (D:S) ration of 100 to 1 What does this ratio mean?

Answer 29

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

Question 30

When you compare thermal and quantum detectors used in pyrometers, which detector provides the fastest response to a change in temperature?

Answer 30

The quantum detector

Question 31

List three types of quantum detectors

Answer 31

1. Photomultiplier tubes 2. Photoconductive cells 3. Photovoltaic cells

Question 32

Which type of pyrometer is unaffected by airborne contamination such as smoke or water vapour?

Answer 32

A ratio pyrometer

Question 33

What is the lowest temperature that a manual optical pyrometer can read?

Answer 33

760°C Below 760°C, not enough energy radiates in the visible spectrum for this method to work

Question 34

What is the highest temperature that a manual optical pyrometer can read?

Answer 34

3500°C

Question 35

What are the two types of black body calibrators used in pyrometry?

Answer 35

1. Cavity 2. Flat plate

Question 36

What are the three components of a pyrometer?

Answer 36

1. Optical system 2. Detector 3. Associated electronics

Question 37

Whqt are the primary and secondary method of calibration for a pyrometer?

Answer 37

Primary - simulated black body Secondary - comparing to another pyrometer calibrated to a black body

Question 38

What are two advantages and disadvantages of a radiation pyrometer?

Answer 38

Pros - physical contact not needed, fast reponse Cons - expensive, non-linear scale

Question 39

How does an optical pyrometer work?

Answer 39

Compares a heated filament to the light given off by an object