Module 3- Pressure Measurement Standards and Pressure Flashcards
How is flow inferred from pressure
measure of the press dropped across a restriction
Define pressure
the measurement of force acting on the area of a surface
Pressure formula
Force/Area
Pressure units
pounds per square inch PSI
Pascals Pa
1 PSI in Pa
7000
What does pressure vary depending on
weather pressure fonts, sea level
Define Gauge pressure
the pressure measured relative to the atmospheric pressure. It is the difference between the absolute pressure of a system and the atmospheric pressure surrounding it
Gauge pressure Formula
Absolute pressure - Atmospheric pressure
A gauge pressure device will indicate zero when
bled down to atmospheric pressure
Define absolute pressure
the total pressure exerted on a system, measured relative to a perfect vacuum (where there is no pressure)
Absolute pressure formula
Gauge pressure + Atmospheric Pressure
When would an absolute pressure indicator indicate atmospheric pressure
when completely vented down to atmosphere and it would not indicate scale 0
When Absolute pressure is zero what does is Gauge pressure
-101.3 kPa(g)
When gauge pressure is 0 what is absolute pressure
101.3
What are the 3 basic functions of pressure detector
ICA
Indicate
Alarm
Control
List pressure sensor
BBC MS
Bourdon tube
Bellow
Pressure Capsule
Manometer
Strain gauge
Describe the manometer
a fluid-filled
tube where an applied gas pressure causes
the fluid height to shift proportionately
why is a manometer consider a differential pressure instrument
because it indicates the
difference between two pressures by a shift
in liquid column height
List the types of manometer
U tube manometer
Well manometer
Raised well manometer
inclined manometer
What equation is the manometer based on
P1- P2 = rho g h
Errors associated with manometer
manometer zero
meniscus
parallax
Vapourization of fluid
Three pressure standards used with manometer
a standard atmosphere
A vertical column of water
A vertical column of mercury
properties of manometer liquid
low temperature coefficient of expansion
low surface tension
low vapor pressure
immiscible with other liquids
What are the typical gauge elements
Bellows
Bourdon Tube
Metallic Diaphragms
Capsules
Bellows are extremely… and provide
extrmely sensitive and provide power for recording activating and indicating mechnisms
Define hookes law
s, the force required to stretch an elastic object such as a metal spring is directly proportional to the extension of the spring
Hookes law formula
F=-kx
Define the bellows
collapsable tank
consist of corrugated or pleated tubes that can expand and contract along their length
pressure is applied to the internal volume and as the pressure changes it expands or contracts to generate an an electrical signal that causes the gauge pointer to move
Pressure increase in bellows
If the pressure inside the bellows exceeds the external pressure, the bellows will expand.
Pressure decrease in bellows
If the external pressure is greater than the pressure inside the bellows, it will cause the bellows to contract.
Describe the make up of a bourbon tube
Thin arch shaped tube that is flattened so that is cross sectional area is that of an ellipse that is permanently fastened at on end
Principle of operation of a bourdon tube
When pressure is applied to the system is the tube cross section returns to a circular shape and this causes the tube to straighten, the tip of the tube traces a curve this tip movement generates an electrical signal to move theguage pointer
Types of bourdon
spiral and helical
Diaphragms
