Chapter 1 - Introduction to instruments

Question 1

Describe the troposphere?

Answer 1

• Extends upwards from sea level to approximately 5 to 9 miles
• Contains approximately 80% of the Earth’s atmosphere
• Characterised by turbulent weather conditions

Question 2

Describe the stratosphere?

Answer 2

• Extends from tropopause to approximately 31 miles above sea level
• Conditions are considered tranquil or non-turbulent
• High velocity winds such as the jet stream, but they are steady not gusty

Question 3

What is the standard atmospheric pressure at sea level?

Answer 3

• 14.69 psi
• 1013.25 hPa

Question 4

At what height is the atmospheric pressure approximately half of sea level pressure?

Answer 4

18,000 feet

Question 5

At what height is the atmospheric pressure approximately a quarter of sea level pressure?

Answer 5

Tropopause (about 36,000 feet)

Question 6

What is the international lapse rate for temperature in the atmosphere?

Answer 6

Up to a height of 36,090 feet (the tropopause) is given at a rate of 1.98°C per 1000 feet

Question 7

What is the temperature from the tropopause up to about 65,000 feet?

Answer 7

-56.5°C

Question 8

How does the ability of air to hold water vapour change with air temperature?

Answer 8

Increases with air temperature

Question 9

Why does humidity affect air density?

Answer 9

Water vapour is less dense than air

Question 10

What is the density of water vapour under standard sea level conditions as compared to perfectly dry air?

Answer 10

Water vapour - 0.7600 Kg/m³

Perfectly dry air - 1.225 Kg/m³

Question 11

What is the maximum amount of water vapour that air can contain?

Answer 11

5% by volume

Question 12

What is the international standard temperature?

Answer 12

15°C

Question 13

What is diffusion?

Answer 13

Property of gases whereby they are able to pass through certain solids

Question 14

What is Boyle’s Law?

Answer 14

Relationship between volume and pressure at constant temperature

Question 15

What is Charles’ Law?

Answer 15

Relationship between volume and temperature at constant pressure

Question 16

What is the Pressure Law?

Answer 16

Relationship between pressure and temperature at constant volume

Question 17

What is the relationship between volume and pressure, where temperature is kept constant?

Answer 17

Inversely proportional

Question 18

What is the equation for Boyle’s Law?

Answer 18

P₁V₁=P₂V₂

Question 19

What is the relationship between volume of a fixed mass of gas to its absolute temperature?

Answer 19

Proportional

Question 20

What is the equation for Charles’ Law?

Answer 20

V₁/T₁=V₂/T₂

Question 21

What is the combined Gas Law equation?

Answer 21

V₁P₁/T₁=V₂P₂/T₂

Question 22

What are the two types of pressure measurement indicators?

Answer 22

• Direct reading
• Remote indicating

Question 23

What would the absolute pressure of a fluid be equal to, taking account of the measured pressure?

Answer 23

Indicated pressure + atmospheric pressure

Question 24

What is the calculation for gauge pressure?

Answer 24

Absolute pressure - atmospheric pressure

Question 25

Where accuracy is of prime importance, which type of barometer will be used?

Answer 25

Mercurial barometer

Question 26

What is the height of mercury at sea level?

Answer 26

760 mm

29.92”

Question 27

What are the standard conditions, which should be inscribed on each barometer?

Answer 27

0 °C

980.665 cm s^-2

Question 28

What is the simplification of what an aneroid barometer is?

Answer 28

A barometer without liquid

Question 29

What does an aneroid barometer consist of?

Answer 29

Sealed capsule from which the air has been partially removed

Question 30

Where a diaphragm is used to indicate air pressure, how is greater movement achieved?

Answer 30

Corrugations in the diaphragm

Question 31

How does the number and depth of corrugations affect an indicator?

Answer 31

Greater the number and depth, the more nearly linear is its deflection and the greater the sensitivity

Question 32

How are capsules, essentially two diaphragms joined together, employed generally?

Answer 32

Low pressure measuring device

Question 33

What is the advantage of a capsule over a single diaphragm?

Answer 33

More sensitive

Question 34

What can a bellows be used for?

Answer 34

High, low or differential pressure measurement

Question 35

What is the purpose of a spring, which may be fitted internally or externally in a bellows?

Answer 35

• Increases the ‘spring-rate’
• Assist the bellows to return to its natural length when the pressure is removed

Question 36

What is generally used where high pressure is required to be measured?

Answer 36

Bourdon tube

Question 37

How is the sensitivity of a bourdon tube controlled?

Answer 37

Ratio between the minor and major axes

Larger ratio providing greater sensitivity

Question 38

How does pressure change the geometry of a Bourdon tube?

Answer 38

With increasing pressure, the cross section of the tube tends to change from elliptical to circular, and the tube then tends to straighten out

Question 39

What forms might a Bourdon tube take?

Answer 39

• ‘C’
• Flat spiral
• Helical spiral
• Twisted

Question 40

How might the movement of the Bourdon free end be used to indicate pressure?

Answer 40

• Directly to move a pointer across a scale
• Move the slider of a potentiometer
• Move the iron rod core in a linear variable differential transmitter (LVDT)

Question 41

Describe a Bourdon tube used for high pressure ranges?

Answer 41

• C-shaped tubes
• Almost rectangular cross section
• Made from brass or phosphor bronze

Question 42

How do spherical or helical tubes compare to the simple ‘C’ shape?

Answer 42

Greater sensitivity but less of a pressure capability