PRESSURE MEASUREMENT Flashcards by Aliya Baya

are concerned not only with determination of force per unit area but are also involved in
many liquid level, density, flow and temperature measurements.

Pressure measurements

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Pressure measurement is crucial in process industries for several reasons:

Safety
Process Control:
Efficiency:
Equipment Protection:

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Accurate pressure monitoring helps prevent over-pressurization,
which can lead to equipment failure, explosions, or the release of hazardous
substances. Maintaining proper pressure levels is essential for ensuring the safety of personnel and equipment.

Safety

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Pressure is a key parameter in many industrial processes.
Precise pressure measurement allows for better control of processes like chemical
reactions, fluid flow, and gas compression. This ensures that the process operates
within desired parameters, leading to consistent product quality.

Process Control

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Proper pressure management can optimize energy consumption
and reduce waste. For example, in a steam system, maintaining the correct
pressure can improve energy efficiency, reducing costs and minimizing
environmental impact

Efficiency:

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Continuous pressure monitoring helps protect sensitive equipment, such as pumps, compressors, and vessels, from damage due to abnormal pressure conditions. This extends the lifespan of the equipment and
reduces maintenance costs

Equipment Protection:

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Many process industries are subject to strict regulations regarding pressure levels. Accurate pressure measurement is necessary
to ensure compliance with industry standards and regulatory requirements.

Compliance and Regulation:

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Deviations in pressure can indicate potential problems, such as leaks, blockages, or equipment malfunctions. Early detection
through pressure monitoring allows for timely intervention, preventing costly
downtime or accident

Early Detection of Issues:

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force exerted per unit area on the surface of an object.

Pressure

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It is a measure of how much force are distributed in fluids (gases and liquids) and solids and
applied over a specific area and is typically expressed in units such as pascals (Pa),
atmospheres (atm), or pounds per square inch (psi).

Pressure

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Pressure can be measured in various ways depending on the application and the reference point used. Here are the main types of pressure measurement:

Absolute Pressure
Gauge Pressure
Differential Pressure
Atmospheric Pressure
Vacuum Pressure
Hydrostatic Pressure

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is the pressure measured relative to a perfect vacuum (zero
reference point).

Absolute Pressure

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Used in applications where a true reference point is needed, such as
in vacuum systems, altimeters, and when measuring atmospheric pressure.

Absolute Pressure

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is the pressure measured relative to the ambient atmospheric
pressure.

Gauge Pressure

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is the difference in pressure between two points in a system. It is used in flow measurement, filtration, level measurement, and in systems
where it’s important to know the pressure difference across components like filters or
orifices

Differential Pressure

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is the pressure exerted by the weight of the Earth’s atmosphere. It varies with altitude and weather conditions. It is used in weather forecasting, altimetry, and aviation

Atmospheric Pressure

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is the pressure lower than the atmospheric pressure. It is often
measured as a gauge pressure with reference to atmospheric pressure. It is used in vacuum systems, such as those in manufacturing, scientific research, and space applications

Vacuum Pressure

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is the pressure exerted by a fluid at rest due to the force of
gravity. It is relevant in applications involving liquids, such as in dams, water towers, and blood pressure measurement.

Hydrostatic Pressure

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Here are some common units of pressure:

Pascal (Pa):
Kilopascal (kPa):
Megapascal (MPa)
Pound per Square Inch (psi):
Pound per Square Foot (psf):
Bar
Atmosphere (atm):
Torr (Torr):
Millimeter of Mercury (mmHg):
Inch of Mercury (inHg):
Millibar (mbar):

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is uniform in all directions, so pressure measurements are
independent of direction in an immovable (static) fluid.

Static pressure

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applies additional
pressure on surfaces perpendicular to the flow direction, while having little impact on surfaces parallel to the flow direction.

Flow,

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This directional component of pressure in a moving (dynamic) fluid is called

dynamic pressure

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An instrument facing the flow
direction measures the sum of the static and dynamic pressures; this measurement is
called th

the total pressure or stagnation pressure.

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While static gauge pressure is of primary importance to d

determining net loads on pipe walls

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dynamic pressure is used to measure

flow rates and airspeed

Dynamic pressure can be measured by taking the

differential pressure between instruments parallel and perpendicular to the flow.

is a device used to measure pressure, typically of gases or liquids, by balancing the pressure against a column of liquid. The basic principle behind a manometer is that the pressure exerted by a fluid in a column is proportional to the height of the fluid column.

manometer

Manometers are simple, reliable, and widely used in various applications, particularly in

laboratories, HVAC systems, and industrial processes.

The main purpose of a manometer is to

compare the pressure of a fluid with a known reference pressure.

It typically consists of a glass tube or a flexible diaphragm that reacts to pressure changes. The device can measure both positive and negative pressures, providing valuable information for different systems and processes

Manometer:

In all forms of manometers (U tubes, well-types, and inclines) there ______ surfaces

are two liquid

consists of a U-shaped glass tube filled with a liquid, usually mercury or water. One end of the tube is open to the atmosphere or a reference pressure, while the other end is connected to the pressure source being measured

U-Tube Manometer

It is used to measure small pressure differences, such as in laboratory experiments or ventilation systems.

U-Tube Manometer:

What is the principle of the manometer?

pressure to be measured is applied to one side of the tube producing a movement of liquid, as shown in figure above

is a specialized type of manometer designed to measure small pressure differences with greater accuracy and sensitivity than standard U-tube manometers

Inclined Manometer:

It is commonly used in applications where precise lowpressure measurements are required

Inclined Motor

What is the key feature of inclined manomater?

The key feature of an inclined manometer is the inclination of the tube, which allows for a larger scale of measurement for small pressure changes, making it easier to detect and measure minute pressure differences.

What does the inclined manometer consists?

The inclined manometer consists of a transparent tube filled with a liquid, typically water or a low-density oil. The tube is mounted on a scale that is inclined at a specific angle to the horizontal plane. One end of the tube is connected to the pressure source, and the other end is open to the atmosphere or connected to another pressure source for differential pressure measurement

more sensitive to low pressures.

inclined manometer

The inclination allows for finer resolution in measurement, making it easier to read small changes in pressure.

inclined manometer

is a variant of the traditional U-tube manometer, designed to measure pressure with enhanced readability and convenience, especially for larger pressure ranges.

Well-Type Manometer:

What are manometer used for larger pressure ranges?

Well-Type Manometer

This type of manometer is commonly used in both industrial settings and laboratories due to its ability to provide clear and accurate pressure readings.

Well-Type Manometer

A _____ uses a large reservoir or "well" on one side of the tube, which helps stabilize the liquid level, making the measurement process easier and more reliable.

well-type manometer

The larger area leg in a well type manometer is called the

"well"

s do not rely on a hydrostatic balance of fluids (water/mercury) in order to detect pressure. Rather, they come with a component known as a pressure transducer that converts the level of pressure observed into an electric signal/value; the value can then be recorded as the amount of pressure present

Digital Manometer

There are usually three types of electrical variables used by pressure transducers:

resistive, capacitive, and inductive

Digital manometers represent a significant advancement in pressure measurement technology, offering

high accuracy, ease of use, and a range of features that make them suitable for various applications

Despite their higher cost and complexity, the benefits of _____ make them a valuable tool in modern industry and research

digital manometers

It is most widely used as a pressure sensing element.

Bourdon Tube:

The pressure is applied at the other end which is open and fixed. The tube is formed into a curve, a flat spiral or a helix.

Bourdon Tube:

The angle between the connecting link and the sector tail is called the t

travelling angle

Frequently used bourdon tube materials include

bronze, alloy and stainless steel.

The advantages of Bourdon tube pressure gauges are that

they give accuratenresults

are simple in construction and their cost is low

Bourdon tubes

They are safe even for high pressure measurement and the accuracy is high especially at high pressures.

Bourdon tubes

Limitations of Bourdonn Tubre Pressure Gauges

They respond slowly to changes in pressure. They are subjected to hysteresis and are sensitive to shocks and vibrations. As the displacement of the free end of the bourdon tube is low, it requires amplification. Moreover, they cannot be used for precision measurement

consists of a diaphragm isolator and a general pressure gauge.

Diaphragm pressure gauge

It is suitable for measuring the pressure of media that are highly corrosive, high temperature, high viscosity, easy to crystallize, easy to solidify, and have solid floating substances, and direct measurement of the media must be avoided

Diaphragm Pressure Gauge

is a type of pressure measuring instrument that uses a bellows-like expansion and contraction mechanism to measure the pressure of gases or liquids.

Bellows Pressure Gauge:

The bellows, which is a flexible metal element, responds to changes in pressure by

expanding or contracting.

Bellows pressure gauges are often used in applications where

high sensitivity and accuracy are required

The ______ is a cylindrical, accordion-like structure made of thin, flexible metal.

bellows

When pressure is applied to the inside of the bellows, it ___ and when pressure decreases, it ______-

expands,contracts

The working principle of a bellows pressure gauge is based on the

expansion and contraction of the bellows due to pressure changes.

As the bellows expands or contracts in response to pressure variations, the pointer moves along the dial, indicating the pressure reading

Bellows Pressure Gauge:

is used to measure vacuum pressure

McLeod Gauge i

The components of McLeod gauge include a

reference column with reference capillary tube.

consists of a metal wire open to the pressure being measured

The Pirani gauge

These gauges are the most sensitive gauges for measuring very low pressures or high vacuum

Ionization Gauge:

The principle of operation of these gauges sensing pressure of gas by measuring the electrical ions produced when the gas is bombarded with electrons.

Ionization Gauge:

The electrons are generated by

thermo ionic emissions

The ionization gauges are of two types, the

hot cathode ionization gauges and the cold cathode ionization gauges.

The _______ works on the principle that at low pressure the thermal conductivity of a gas is a function of pressure

thermal conductivity vacuum gauge

The _____ is basically a pressure producing and pressure measuring device. It is used to calibrate pressure gauges

dead weight tester

. The ________ consists of a piston cylinder combination fitted above the chamber as shown in Figure 13. The chamber below the cylinder is filled with oil. The top portion of the piston is attached with a platform to carry weights. A plunger with a handle is provided to vary the pressure of oil in the chamber. The pressure gauge to be tested is fitted at an appropriate place as shown

dead weight tester apparatus

is a fine wire which changes its resistance when mechanically strained.

Strain Gauge Pressure Transducer:

The capacitance between two metal plates changes if the distance

between these two plates changes

But they are sensitive to high temperatures and are more complicated to setup than most pressure sensors. Their performance is also affected by the dirt and dust as they change the dielectric constant.

Capacitive Pressure Transducer: T

The __________ provides a simplemethod for obtaining an electrical output from a mechanical pressure gauge

potentiometric pressure sensor

The device consists of a precision potentiometer, whose wiper arm is mechanically linked to a Bourdon or bellows element

Potentiometric Pressure Sensors:

The movement of the wiper arm across the ________ converts the mechanically detected sensor deflection into a resistance measurement, using a Wheatstone bridge circuit.

potentiometer

Each time the wiper makes and breaks contact with a turn of wire, it causes an extra electrical signal

noise

An __ is an electronic device that converts pressure into an electrical signal through the principle of inductance.

inductive pressure transducer

This type of transducer is commonly used in industrial and automotive applications where precise and reliable pressure measurements are required.

Inductive Pressure Transducer:

work by using the principle of inductance, where the electrical inductance of a coil is affected by the position of a movable core or diaphragm that changes in response to pressure

Inductive pressure transducers

is an instrument used to measure atmospheric pressure, which is essential for weather forecasting, altitude determination, and various scientific applications.

barometer

The barometer has been a fundamental tool in meteorology since its invention in the 17th century by

Evangelista Torricelli

operate on the principle that atmospheric pressure exerts a force on a fluid or mechanical element, and this force can be measured to determine the pressure.

Barometers

The two most common types of barometers are the

mercury barometer and the aneroid barometer.

consists of a glass tube that is sealed at one end and open at the other, with the open end immersed in a reservoir of mercury.

mercury barometer

The height of the mercury column is measured in

millimeters or inches of mercury (mmHg or inHg).

An __ does not use liquid.

aneroid barometer

, it contains a small, flexible metal box called an aneroid cell.

aneroid barometer

ASME meaning

American Society of Mechanical Engineers

provides guidelines on Pressure Indicated Dial Type and Pressure Digital Indicating Gauges, Diaphragm Seals, Snubbers, and Pressure Limiter Valves.

B40.100

provides instructions and guidance for the accurate determination of pressure values in support of the ASME Performance Test Codes

PTC 19.2

B40.100-2013:

Pressure gauges and Gauge attachments.

PTC 19.2-2010 :

The Performance test code for pressure measurement.