Instrument Consultant Program: Pressure Measurement

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Questions and Answers

Which pressure measurement unit is NOT referenced to a column of fluid?

torr

in Hg

in H₂O

psi (correct)

What is the conversion factor from bar to psi?

1.45038

14.5038 (correct)

0.06895

1.0

When converting 40 bar to psi, what is the correct psi value?

300.0

450.0

580.151 (correct)

200.0

Why is it important to note the temperature when measuring the density of a liquid?

Density changes with temperature. Signup and view all the answers

Which of the following pressure measurement units can safely be used for liquid applications?

all of the above Signup and view all the answers

What is one of the primary reasons for measuring pressure in industrial processes?

To ensure safety Signup and view all the answers

Which type of pressure measurement is primarily used to measure the pressure difference between two points?

Differential pressure Signup and view all the answers

What is the primary function of mechanical pressure gauges like the Bourdon tube?

To measure and display pressure in a readable format Signup and view all the answers

How does gas pressure relate to the container it occupies?

It is dependent on container volume and temperature Signup and view all the answers

Which of the following is NOT a type of electronic pressure transmitter?

Bourdon Tube Signup and view all the answers

What does the term 'head pressure' refer to in pressure measurement?

Pressure exerted by a column of liquid Signup and view all the answers

Which of the following is a benefit of accurate pressure measurement?

Cost savings in operations Signup and view all the answers

What is the primary distinction between absolute pressure and gauge pressure?

Gauge pressure includes atmospheric pressure, while absolute pressure does not Signup and view all the answers

What occurs to the pressure of a gas in a tank if the temperature is increased?

Pressure will increase as temperature increases. Signup and view all the answers

Which of the following is NOT a reason for measuring pressure in process industries?

Quality control of materials Signup and view all the answers

Why is accurate pressure measurement critical in preventing equipment failure?

It helps minimize equipment damage and leaks. Signup and view all the answers

What is an inferred measurement variable often associated with pressure measurement?

Density of the gas Signup and view all the answers

How does accurate pressure measurement contribute to cost savings?

By preventing pumps and compressors from operating unnecessarily. Signup and view all the answers

What risk does pressure measurement help reduce in process industries?

Personal injury and environmental leaks. Signup and view all the answers

What is the relationship between process efficiency and pressure control?

Efficiency is highest when pressures are controlled within narrow ranges. Signup and view all the answers

Which of the following statements regarding accurate pressure measurement is true?

It is essential for preventing operational inefficiencies. Signup and view all the answers

What happens to the pressure at the bottom of a liquid column when the density of the liquid remains constant?

It increases as the height of the liquid increases. Signup and view all the answers

How does a change in temperature generally affect the density of a liquid?

It causes the liquid to expand, decreasing its density. Signup and view all the answers

What is the specific gravity of a liquid with a density of 800 kg/m³?

0.8 Signup and view all the answers

What is referred to as top pressure in a closed tank application?

The pressure exerted by a gas present above the liquid. Signup and view all the answers

If gasoline has a specific gravity of 0.66, what is its density at 50 °F (10°C)?

660 kg/m³ Signup and view all the answers

In a vacuum above a liquid in a closed tank, what type of pressure exists on the surface of the liquid?

Less than atmospheric pressure. Signup and view all the answers

Which factor does NOT affect the hydrostatic pressure in a liquid column?

Shape of the container. Signup and view all the answers

Which formula correctly represents the relationship between mass, density, and volume?

$Density = Mass / Volume$ Signup and view all the answers

What pressure reference does a gauge pressure transmitter use?

Atmosphere Signup and view all the answers

How does the output of a gauge pressure sensor change?

Due to changes in atmospheric pressure Signup and view all the answers

What is a key advantage of differential pressure measurements?

They provide a more accurate measurement by comparing two pressures. Signup and view all the answers

How many connections do differential pressure-measurement instruments typically have?

Two Signup and view all the answers

What does the designation 'g' signify in pressure units?

Gauge pressure Signup and view all the answers

Why are differential pressure-measurement instruments less affected by atmospheric changes?

Both measured and reference pressures are equally influenced by the atmosphere. Signup and view all the answers

What might result when gauge pressure in a closed system is lower than atmospheric pressure?

Negative pressure reading Signup and view all the answers

What is the approximate atmospheric pressure in psi that gauge measurement references?

14.7 psi Signup and view all the answers

What is the specific gravity calculated by when measuring pressure?

Pressure in inches of water divided by height of liquid in inches Signup and view all the answers

In pressure measurement for density calculations, which liquid column height is standardly used?

Inches of water Signup and view all the answers

What phenomenon does an interface measurement identify?

The boundary between two immiscible fluids Signup and view all the answers

Which pressure measurement instrument is commonly used to measure atmospheric pressure?

Barometer Signup and view all the answers

What is the role of measuring pressure in fermentation processes?

To infer density from pressure measurement Signup and view all the answers

Which statement describes the relationship between oil and water in an interface measurement?

Oil floats on water due to lower density Signup and view all the answers

Which type of electronic pressure transmitter operates based on capacitance?

Variable capacitance Signup and view all the answers

What would you use to determine when to stop pouring off the top fluid in a tank?

Interface measurement Signup and view all the answers

Study Notes

Pressure Measurement Units

Pascal (Pa) is the SI unit of pressure, defined as one Newton per square meter (N/m²) and is not referenced to a column of fluid.
Conversion factor from bar to psi: 1 bar = 14.5038 psi
Conversion of 40 bar to psi: 40 bar * 14.5038 psi/bar = 580.152 psi

Density and Temperature

Temperature affects liquid density: A liquid's density changes with temperature, increasing as temperature decreases and vice versa.

Pressure Measurement Units and Applications

Safe for liquid applications: Units like psi, bar, and kPa are commonly used for measuring liquid pressures.
Primary reason for industrial pressure measurement: Process control, monitoring, and safety are key reasons for measuring pressure in industrial settings.
Differential pressure measurement: Used to gauge the pressure difference between two points, often for flow measurement or level indication.

Mechanical Pressure Gauges

Function of Bourdon tube gauges: These gauges translate pressure into physical movement of a pointer across a calibrated scale.
Gas pressure and container: Gas pressure is directly related to the volume of the container it occupies; an increase in volume leads to a decrease in pressure, and vice versa.

Types of Electronic Pressure Transmitters

Strain gauge: One of the common types of electronic pressure transmitters.

Pressure Measurement Terms and Concepts

Head pressure: Refers to the pressure exerted by a column of liquid due to its height and density.
Benefit of accurate pressure measurement: Optimal process efficiency, reliable system performance, and improved safety.
Distinction between absolute and gauge pressure: Absolute pressure measures pressure relative to a perfect vacuum, while gauge pressure measures pressure relative to atmospheric pressure.
Effect of increased temperature on gas pressure: An increase in temperature leads to an increase in gas pressure within a tank.

Importance of Pressure Measurement in Process Industries

Reasons for pressure measurement: Safety, process control, monitoring, equipment protection, and efficiency analysis.
Preventing equipment failure: Accurate pressure measurements help prevent system overpressure or underpressure conditions that can lead to equipment damage.
Inferred measurement variable associated with pressure: Flow, level, and density are inferred variables often associated with pressure measurement.

Cost savings and Risk Reduction through Pressure Measurement

Cost saving: Efficient process control leads to reduced waste, improved efficiency, and lower energy consumption.
Risk reduction: Accurate pressure measurement mitigates risks associated with equipment failure, process instability, and safety hazards.
Process efficiency and pressure control: Precise pressure control directly contributes to optimizing process efficiency.

Pressure Measurement Accuracy and its Significance

True statement about pressure measurement: Maintaining accurate pressure measurement ensures reliable process control and minimizes safety risks.
Pressure at the bottom of a liquid column: When density remains constant, the pressure increases linearly with the height of the liquid column.

Density, Specific Gravity, and Pressure

Effect of temperature on liquid density: Generally, a liquid's density decreases with increasing temperature.
Specific gravity of a liquid: The specific gravity is 0.8 for a liquid with a density of 800 kg/m³ (water density at 4°C is 1000 kg/m³).
Top pressure in a closed tank: Refers to the pressure at the surface of the liquid in a closed tank.
Gasoline density: Gasoline with a specific gravity of 0.66 has a density of 660 kg/m³ at 50 °F (10°C).
Pressure in a vacuum above a liquid: The pressure at the surface of the liquid in a vacuum is near absolute zero pressure.

Hydrostatic Pressure and its Factors

Factor not affecting hydrostatic pressure: The shape of the container holding the liquid does not influence hydrostatic pressure.
Equation for mass, density, and volume: Mass = Density * Volume

Types of Pressure Transmitters and Their Characteristics

Reference for gauge pressure transmitters: Gauge pressure is relative to atmospheric pressure.
Output of a gauge pressure sensor: The output of a gauge pressure sensor reflects the difference between the measured pressure and atmospheric pressure.
Advantage of differential pressure measurements: They are less susceptible to fluctuations in atmospheric pressure.
Connections in differential pressure instruments: Differential pressure instruments typically have two connections, one for high pressure and one for low pressure.
Significance of 'g' in pressure units: 'g' denotes gauge pressure, which is referenced to atmospheric pressure.

Pressure Measurement Applications and Considerations

Reason behind lower gauge pressure than atmospheric pressure: A potential vacuum condition exists within a closed system.
Approximate atmospheric pressure in psi: Atmospheric pressure is around 14.7 psi at sea level.
Specific gravity calculated in pressure measurement: Measured density divided by a reference liquid density (often water).
Standard liquid column height for density calculations: 1 meter (3.28 feet)

Interface Measurement and Applications

Interface measurement identification: Determines the boundary line between two immiscible liquids based on their densities.
Atmospheric pressure measurement instrument: A barometer is used to measure atmospheric pressure.
Role of pressure measurement in fermentation: Monitoring pressure helps control the fermentation process, as it can indicate the production of gases or pressure buildup within the fermentation vessel.
Oil and water relationship in interface measurement: Oil typically floats on top of water due to its lower density, providing a clear interface.

Electronic Pressure Transmitters and Other Applications

Capacitance-based pressure transmitter: A capacitance-based electronic pressure transmitter operates based on changes in capacitance caused by pressure variations.
Determining when to stop pouring off top fluid: You would use a level sensor or interface sensor to determine when to stop pouring off the top fluid in a tank.

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Description

This quiz covers the fundamentals of pressure measurement within the Level 1 training program for process control. Topics include the definition of pressure, pressure variables, terminology, and the importance of pressure in industrial processes. Test your knowledge on these critical concepts and ensure a comprehensive understanding of pressure measurement techniques.