From Atmosphere to Absolute: Demystifying Pressure Transmitter Types

Pressure transmitters are integral devices in various industries and applications, playing a crucial role in monitoring, controlling, and ensuring the safety of processes and systems. They are designed to measure pressure and convert it into an electrical signal, allowing for accurate and real-time pressure monitoring. Understanding the different types of pressure transmitters, their working principles, advantages, and disadvantages is essential for selecting the right one to meet specific application requirements.

In this comprehensive guide, we delve into the world of pressure transmitters, exploring the intricacies of Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters. We uncover the working principles behind each type, unravel their distinctive advantages and limitations, and examine the critical factors that influence their selection. Moreover, we provide real-world examples and scenarios to illustrate how these pressure transmitters find their place in a wide range of industries and applications.

By the end of this guide, you'll be equipped with the knowledge to make informed decisions when it comes to choosing the appropriate pressure transmitter type for your unique needs. Whether you're working in the realm of industrial processes, scientific experiments, meteorology, or any other field, the insights offered here will empower you to harness the power of pressure measurement with precision and confidence.

Fig 1. Pressure transmitter types

Absolute vs. Gauge vs. Differential Pressure Transmitters

Pressure transmitters are instruments used to measure and transmit information about the pressure of a fluid or gas in a system. There are three common types of pressure transmitters: Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters. Each type is used in specific applications and provides different information about pressure. Here's an overview of each type:

Absolute Pressure Transmitters:

Absolute pressure is the pressure of a fluid or gas relative to a perfect vacuum (i.e., absolute zero pressure).

Absolute pressure transmitters measure pressure relative to a full vacuum, which means they take into account atmospheric pressure. In other words, the pressure reading includes both the pressure of the fluid or gas and the atmospheric pressure.

They are often used in applications where it's essential to know the total pressure, such as in meteorology, altitude measurement, and certain scientific and industrial processes.

Gauge Pressure Transmitters:

Gauge pressure is the pressure measured relative to atmospheric pressure.

Gauge pressure transmitters measure the pressure of a fluid or gas relative to the local atmospheric pressure. This means they do not consider atmospheric pressure in their reading.

Gauge pressure transmitters are commonly used in various industrial applications, such as monitoring pressure in pipelines, tanks, and pneumatic systems. They are useful for determining whether the pressure is above or below atmospheric pressure.

Differential Pressure Transmitters:

Differential pressure is the difference in pressure between two points in a system.

Differential pressure transmitters measure the pressure difference between two points in a system. They have two ports, with one port connected to one point in the system and the other port connected to a different point. The transmitter then calculates the pressure difference between the two points.

Differential pressure transmitters are used in applications where it's essential to monitor changes in pressure, such as flow rate measurement, level measurement in tanks, and filter monitoring in HVAC systems.

In summary, the choice between absolute, gauge, and differential pressure transmitters depends on the specific requirements of your application. You should consider whether you need to measure pressure relative to a vacuum (absolute), relative to atmospheric pressure (gauge), or the difference in pressure between two points (differential) to select the appropriate type of pressure transmitter for your needs.

Fig 2. Different pressure types

What is an Absolute Pressure Transmitter?

An Absolute Pressure Transmitter is a type of pressure sensor or transducer designed to measure and transmit pressure readings relative to an absolute vacuum, as opposed to measuring pressure relative to atmospheric pressure or any specific reference point. In other words, it provides a measurement that includes the absolute zero pressure point.

Here are some key characteristics and uses of Absolute Pressure Transmitters:

• Reference to Absolute Vacuum: Absolute pressure transmitters measure the pressure of a fluid or gas relative to a perfect vacuum (zero pressure). Unlike gauge pressure transmitters, which measure pressure relative to atmospheric pressure, absolute pressure transmitters account for the entire range of pressure values, from absolute zero to the pressure of the medium being measured.
• Common Uses:
  • Meteorology: Absolute pressure measurements are important in meteorology for weather forecasting and studying air pressure systems.
  • Altitude Measurement: In aviation and aerospace, these transmitters are used to determine altitude above sea level.
  • Scientific and Laboratory Applications: Absolute pressure transmitters are used in scientific experiments and laboratory setups where precise pressure measurements are crucial.
  • Certain Industrial Processes: Some industrial processes require absolute pressure measurements, especially when dealing with vacuum systems and chemical reactions at specific pressure conditions.
• Atmospheric Pressure Compensation: It's important to note that absolute pressure transmitters can provide readings that are not affected by changes in local atmospheric pressure. Gauge pressure transmitters, on the other hand, provide pressure readings relative to local atmospheric pressure and are affected by atmospheric pressure variations.
• Pressure Units: Absolute pressure transmitters typically provide readings in units such as pascals (Pa), bar, psi (pounds per square inch), or millimeters of mercury (mmHg). The specific unit used can vary depending on the application and industry standards.

In summary, Absolute Pressure Transmitters are valuable instruments for applications where the precise measurement of pressure relative to a complete vacuum is necessary. They are commonly used in meteorology, aerospace, and various scientific and industrial processes requiring accurate and absolute pressure readings.

Fig 3. An absolute pressure transmitter

What is a Gauge Pressure Transmitter?

A Gauge Pressure Transmitter is a type of pressure sensor or transducer designed to measure and transmit pressure readings relative to local atmospheric pressure. It is one of the most common types of pressure transmitters used in various industrial and commercial applications. Here are some key characteristics and uses of Gauge Pressure Transmitters:

• Reference to Atmospheric Pressure: Gauge pressure transmitters measure the pressure of a fluid or gas relative to the local atmospheric pressure. In this context, "gauge pressure" refers to the pressure above or below atmospheric pressure. When the measured pressure is equal to atmospheric pressure, the gauge pressure reading is zero.
• Common Uses:
  • Industrial Monitoring: Gauge pressure transmitters are widely used in industrial applications to monitor and control processes, such as in pipelines, tanks, and pneumatic systems.
  • Pressure Safety: They are often employed to ensure that pressure levels in systems remain within safe operating ranges.
  • HVAC Systems: In heating, ventilation, and air conditioning (HVAC) systems, gauge pressure transmitters monitor and control air and refrigerant pressures.
  • Automotive: In vehicles, they are used for tire pressure monitoring systems (TPMS) to indicate when tire pressure is too low.
  • General Pressure Measurement: Many pressure measurement applications require the comparison of the measured pressure to atmospheric pressure, making gauge pressure transmitters appropriate.
• Atmospheric Pressure Variation: Gauge pressure readings are affected by changes in local atmospheric pressure. Therefore, they are ideal for applications where you need to know the pressure differential from the local environment.
• Pressure Units: Gauge pressure transmitters typically provide readings in units such as psi (pounds per square inch), bar, kPa (kilopascals), or other pressure units relevant to the specific application.

In summary, Gauge Pressure Transmitters are commonly used in a wide range of applications to measure and monitor pressure relative to local atmospheric conditions. They are valuable for ensuring the safe and efficient operation of industrial processes and systems, as well as for applications like tire pressure monitoring in vehicles.

Fig 4. A gauge pressure transmitter

What is a Differential Pressure Transmitter?

A Differential Pressure Transmitter is a type of pressure sensor or transducer designed to measure and transmit the difference in pressure between two points in a fluid or gas system. This type of pressure transmitter is used to monitor changes in pressure between two reference points and is widely employed in various industrial and commercial applications. Here are some key characteristics and uses of Differential Pressure Transmitters:

• Measurement of Pressure Difference: Differential pressure transmitters measure and provide output signals that represent the pressure difference (delta P) between two points in a system. They typically have two ports, with one port connected to one reference point and the other port connected to a different reference point within the system.
• Common Uses:
  • Flow Rate Measurement: Differential pressure transmitters are frequently used to determine flow rates in pipes and ducts. The pressure drop across an obstruction (such as an orifice plate or venturi tube) is related to the flow rate, and a differential pressure transmitter can provide this information.
  • Level Measurement: In applications like tank and vessel level measurement, differential pressure transmitters are used to monitor the pressure difference between the bottom of the tank and the vapor space or reference point.
  • Filter Monitoring: They are used to monitor the clogging or saturation of filters, such as in HVAC systems or industrial filtration units.
  • Differential Pressure Control: These transmitters are also used in systems where it's important to control and maintain a specific differential pressure between two areas, like cleanrooms or containment facilities.
• Pressure Units: The pressure units used by differential pressure transmitters are typically the same as those used for absolute and gauge pressure transmitters, including psi (pounds per square inch), bar, kPa (kilopascals), and more, depending on the specific application.
• Atmospheric Pressure Compensation: Differential pressure transmitters are not inherently affected by changes in atmospheric pressure because they focus on measuring the pressure difference between two points within the same system.

In summary, Differential Pressure Transmitters are essential instruments for applications where monitoring changes in pressure between two reference points is critical. They are commonly used in flow rate measurement, level measurement, and filter monitoring, as well as in systems where maintaining a specific differential pressure is necessary for safety and efficiency.

Fig 5. A DP transmitter

Comparing Absolute, Gauge, and Differential Pressure Transmitters

Comparing based on the working principle

Pressure transmitters, including Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters, operate based on different working principles. Here's a comparison of these pressure transmitter types based on their working principles:

Absolute Pressure Transmitter:

Working Principle: Absolute pressure transmitters measure the pressure relative to a perfect vacuum (absolute zero pressure). They rely on a reference chamber that is maintained at a vacuum to provide an absolute pressure reading. The sensor inside the transmitter measures the pressure difference between the vacuum reference chamber and the pressure of the medium being measured.

Key Points: This type of transmitter provides readings that include both the pressure of the fluid or gas and atmospheric pressure. It is often used in applications where knowing the total pressure is crucial, such as in meteorology, altimeter instruments, and scientific experiments.

Gauge Pressure Transmitter:

Working Principle: Gauge pressure transmitters measure the pressure of a fluid or gas relative to the local atmospheric pressure. They typically contain a reference chamber that is exposed to the local atmosphere. The sensor inside the transmitter measures the pressure difference between the process pressure and the atmospheric pressure.

Key Points: Gauge pressure transmitters provide readings that are affected by changes in local atmospheric pressure. They are commonly used in various industrial applications to monitor processes and systems relative to the local environment.

Differential Pressure Transmitter:

Working Principle: Differential pressure transmitters measure the pressure difference between two reference points within a system. They typically have two ports, with one port connected to one reference point and the other port connected to a different reference point. The sensor inside the transmitter calculates the pressure difference between the two points.

Key Points: Differential pressure transmitters do not reference atmospheric pressure. They provide readings that focus on the difference in pressure between two points, making them valuable for applications like flow rate measurement, level measurement, and filter monitoring. Changes in atmospheric pressure do not directly impact their readings.

In summary, these three types of pressure transmitters differ in their working principles and the reference points they use for measurement. Absolute pressure transmitters reference a vacuum, gauge pressure transmitters reference atmospheric pressure, and differential pressure transmitters focus on the difference in pressure between two points within the same system. The choice of pressure transmitter type depends on the specific application and the information required for accurate pressure measurement.

Comparing table

Here's a comparative table summarizing the key differences between Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters based on various aspects:

Table 1. Comparison based on the working principle

Aspect	Absolute Pressure Transmitter	Gauge Pressure Transmitter	Differential Pressure Transmitter
Pressure Reference Point	Perfect Vacuum (Absolute Zero)	Local Atmospheric Pressure	Two Reference Points
Reading Includes Atmosphere	Yes	No	No
Atmospheric Pressure Impact	None	Yes	None
Common Applications	- Meteorology - Altitude Measurement - Scientific Experiments - Certain Industrial Processes	- Industrial Monitoring - Pressure Safety - HVAC Systems - Automotive (e.g., tire pressure monitoring)	- Flow Rate Measurement - Level Measurement - Filter Monitoring - Differential Pressure Control
Units of Measurement	pascals (Pa), bar, psi, mmHg, etc.	psi, bar, kPa, etc.	psi, bar, kPa, etc.
Atmospheric Pressure Variations Compensation	No	No	No (Not impacted directly by atmospheric changes)

This table provides a clear comparison of the three types of pressure transmitters, highlighting their unique characteristics and common applications. The choice between these transmitters depends on the specific requirements of the application and whether you need pressure measurements relative to a vacuum, local atmospheric pressure, or the difference between two reference points.

Fig 6. Different Pressure transmitters

Comparing based on the Application

Each type of pressure transmitter—Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters—has specific applications where they are most suitable due to their unique characteristics. Here's a comparison based on typical applications for each type:

Absolute Pressure Transmitters:

Applications:

• Meteorology: Used in weather stations to measure atmospheric pressure and predict weather patterns.
• Altitude Measurement: Used in aviation and aerospace to determine altitude above sea level.
• Scientific Experiments: Employed in laboratories for precise pressure measurements in experiments.
• Certain Industrial Processes: Utilized in processes where measuring absolute pressure is essential, such as vacuum systems and chemical reactions under specific pressure conditions.

Key Advantage: Provides pressure readings that include both the pressure of the medium and atmospheric pressure, making it suitable for applications requiring absolute pressure values.

Gauge Pressure Transmitters:

Applications:

• Industrial Monitoring: Widely used in industrial settings to monitor and control processes, such as in pipelines, tanks, and pneumatic systems.
• Pressure Safety: Ensures that pressure levels in systems remain within safe operating ranges.
• HVAC Systems: Monitors and controls air and refrigerant pressures in heating, ventilation, and air conditioning systems.
• Tire Pressure Monitoring: Used in vehicles to indicate when tire pressure is too low (TPMS).

Key Advantage: Ideal for applications where monitoring pressure relative to the local atmospheric environment is important.

Differential Pressure Transmitters:

Applications:

• Flow Rate Measurement: Used in pipes and ducts to determine flow rates by measuring the pressure difference caused by obstructions like orifice plates or venturi tubes.
• Level Measurement: Applied in-tank and vessel level measurements to monitor the pressure difference between the bottom of the tank and a reference point.
• Filter Monitoring: Monitors the clogging or saturation of filters in HVAC systems and industrial filtration units.
• Differential Pressure Control: Maintains a specific pressure difference between two areas, such as in cleanrooms or containment facilities.

Key Advantage: Suitable for applications where monitoring changes in pressure between two reference points is essential for control or measurement.

The choice of pressure transmitter type should align with the specific requirements and goals of the application. Absolute, gauge, and differential pressure transmitters serve distinct purposes, and selecting the right type ensures accurate and reliable pressure measurements in various industries and contexts.

Comparing table

Here's a comparative table that summarizes the key differences between Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters based on their typical applications:

Table 2. Comparison based on the Application

Application	Absolute Pressure Transmitter	Gauge Pressure Transmitter	Differential Pressure Transmitter
Meteorology	✓
Altitude Measurement	✓
Scientific Experiments	✓
Industrial Processes	✓	✓
Industrial Monitoring	✓	✓
Pressure Safety	✓
HVAC Systems	✓
Automotive (e.g., TPMS)	✓
Flow Rate Measurement	✓
Level Measurement	✓
Filter Monitoring	✓
Differential Pressure Control	✓

Note: In the table, "✓" indicates the primary suitability of each pressure transmitter type for a specific application. However, there can be some overlap in applications, and the choice of transmitter may depend on the specific requirements and preferences of the user.

Keep in mind that while this table provides a general overview of common applications, individual situations may vary, and other factors, such as the pressure range, accuracy requirements, and environmental conditions, should also be considered when selecting the appropriate pressure transmitter for a given application.

Fig 7. Pressure sensor application

Comparing based on the pressure range

Pressure transmitters are designed to operate within specific pressure ranges, and the choice of the right type depends on the application's pressure requirements. Here's a comparison of Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters based on pressure range considerations:

Absolute Pressure Transmitters:

• Pressure Range: Absolute pressure transmitters can measure pressures below atmospheric pressure (vacuum) and extend to higher pressures, depending on the specific design and calibration. They are often used for very low-pressure measurements in the millibar or pascal range to high-pressure measurements in bar or psi ranges.
• Suitable Applications: Ideal for applications that require the measurement of both sub-atmospheric and super-atmospheric pressures, such as vacuum processes, altimeter instruments, and scientific experiments.

Gauge Pressure Transmitters:

• Pressure Range: Gauge pressure transmitters are generally designed to measure pressures above atmospheric pressure. The pressure range can vary widely, from a few psi (for low-pressure applications) to several thousand psi (for high-pressure applications). The specific range depends on the transmitter's design and calibration.
• Suitable Applications: Commonly used in applications where the pressure is above atmospheric pressure, such as in industrial monitoring, HVAC systems, and automotive tire pressure monitoring (TPMS).

Differential Pressure Transmitters:

• Pressure Range: The pressure range of differential pressure transmitters depends on the specific application. They are often used to measure relatively low-pressure differentials, ranging from a fraction of an inch of water column (inH2O) to a few thousand psi. The choice of range depends on the specific use case and the pressure difference to be measured.
• Suitable Applications: Used in applications where monitoring the pressure difference between two points is crucial. The pressure range is selected based on specific requirements, such as flow rate measurement, level measurement, and filter monitoring.

The suitability of each pressure transmitter type depends on the application's pressure range and whether the pressure measurement needs to be relative to a vacuum (absolute), relative to atmospheric pressure (gauge), or focused on the pressure difference between two points (differential). Proper selection ensures accurate and reliable pressure monitoring in various industrial and scientific settings.

Fig 8. Absolut, Gauge, and Differential Pressure

Comparing based on installation and maintenance

The installation and maintenance requirements for pressure transmitters can vary depending on the type and specific application. Here's a comparison of Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters based on these considerations:

Absolute Pressure Transmitters:

• Installation:
• Installation can be straightforward in many cases, as they are mounted in a location where atmospheric pressure is always accessible.
• For accurate measurements, they may require calibration adjustments to account for variations in atmospheric pressure.
• Maintenance:
  • Maintenance requirements are generally low because they do not directly reference atmospheric pressure.
  • Periodic calibration and testing may be necessary to ensure accurate absolute pressure measurements.

Gauge Pressure Transmitters:

• Installation:
• Installation often involves mounting the transmitter at the desired measurement point, ensuring that the reference chamber is open to the local atmosphere.
• Proper installation and calibration are crucial to account for changes in local atmospheric pressure, especially in applications where accuracy is critical.
• Maintenance:
  • Maintenance can be moderate, as gauge pressure transmitters need occasional calibration to compensate for fluctuations in atmospheric pressure.
  • Routine inspection and recalibration may be required to maintain accuracy, particularly in critical applications.

Differential Pressure Transmitters:

• Installation:
• Installation may be more complex, as these transmitters require connection to two different reference points within the system.
• Proper installation, including tubing and port connections, is essential to ensure accurate differential pressure measurements.
• Maintenance:
  • Maintenance requirements can vary widely based on the application and the system's characteristics.
  • Regular inspection, cleaning, and calibration may be needed, especially in applications where precision is crucial for process control or safety.

In summary, the installation and maintenance requirements for each type of pressure transmitter depend on factors such as the specific application, environmental conditions, and the need for precision. Absolute pressure transmitters are relatively straightforward to install and maintain, gauge pressure transmitters require attention to atmospheric pressure changes, and differential pressure transmitters can have more complex installation and maintenance needs but offer precise measurements of pressure differentials. Proper installation and regular maintenance are essential to ensure the accuracy and reliability of pressure measurements in any application.

Comparing table

Here's a comparative table summarizing the installation and maintenance considerations for Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters:

Table 3. Comparison based on the Installation

Aspect	Absolute Pressure Transmitter	Gauge Pressure Transmitter	Differential Pressure Transmitter
Installation Simplicity	Moderate to Simple	Moderate to Simple	Moderate to Complex
Calibration for Atmospheric Pressure	Occasional adjustment to account for atmospheric pressure variations	Requires regular calibration to compensate for atmospheric pressure changes	Calibration is needed to maintain accuracy, but not directly affected by atmospheric pressure
Maintenance Requirements	Generally low	Moderate	Variable (depends on application)

Please note that the actual installation and maintenance requirements may vary depending on the specific model of the pressure transmitter, the application, and the manufacturer's recommendations. It's important to follow the manufacturer's guidelines and industry best practices to ensure accurate and reliable pressure measurements and transmitter performance.

Fig 9. Differential pressure transmitter installation

Pressure transmitters come in various types, each suited to different applications and operating principles. Here's a comparison of Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters based on their types:

Absolute Pressure Transmitters:

Types:

Piezoelectric: Use the piezoelectric effect to convert pressure into an electrical signal. Common in high-precision applications.

Capacitive: Utilize changes in capacitance to measure pressure. They are suitable for high-pressure and high-temperature applications.

Strain Gauge: Measure strain on a diaphragm due to pressure and is often used for accurate absolute pressure measurement.

Resonant: Measure the change in the resonant frequency of a vibrating element due to pressure changes. Found in precise applications.

Applications by Type:

Each type can be used in a range of applications, but the choice depends on factors like pressure range, accuracy, and environmental conditions.

Gauge Pressure Transmitters:

Types:

Piezoresistive: Employ changes in resistance due to pressure to measure pressure differentials. Commonly used in industrial applications.

Microelectromechanical Systems (MEMS): Miniaturized silicon-based sensors suitable for compact applications.

Strain Gauge: Also used for gauge pressure measurement, where the reference is atmospheric pressure.

Applications by Type:

Gauge pressure transmitters are typically used in applications where pressure is measured relative to atmospheric pressure, such as industrial monitoring, HVAC, and tire pressure monitoring.

Differential Pressure Transmitters:

Types:

Diaphragm: Use a diaphragm to measure pressure differences in applications like flow rate and level measurement.

Bellows: Suitable for measuring very low differential pressures and in applications requiring high accuracy.

Orifice Plate: Used in flow rate measurement, especially in industrial settings.

Applications by Type:

• Differential pressure transmitters are primarily used in applications where the focus is on measuring the pressure difference between two reference points. The type chosen depends on the specific requirements, accuracy, and pressure range.

In summary, the choice of pressure transmitter type depends on the specific application's pressure range, accuracy requirements, and environmental conditions. Each type has various subtypes with specific advantages and suitability for particular situations. Selecting the right type and subtype is crucial for obtaining accurate and reliable pressure measurements in various industries and contexts.

Fig 10. Different types of pressure sensor

Comparing based on Advantages

Each type of pressure transmitter—Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters—comes with its unique advantages depending on the application's requirements. Here's a comparison of these pressure transmitter types based on their advantages:

Absolute Pressure Transmitters:

• Advantages:
  • Provides the absolute pressure value, which includes both the pressure of the medium and atmospheric pressure.
  • Useful for applications where it's essential to know the total pressure, such as meteorology and altitude measurement.
  • Allows for accurate measurements in vacuum processes and specific scientific experiments.
  • Not directly affected by variations in atmospheric pressure, making it ideal for some laboratory settings.

Gauge Pressure Transmitters:

• Advantages:
  • Well-suited for applications where pressure measurements are made relative to local atmospheric conditions.
  • Often used in industrial monitoring, HVAC systems, and automotive tire pressure monitoring (TPMS).
  • The simplicity of operation and easy installation in many cases.
  • Cost-effective and readily available for a wide range of pressure measurement needs.

Differential Pressure Transmitters:

• Advantages:
  • Provides precise measurements of pressure differences between two points within a system.
  • Valuable for flow rate measurement, level measurement, and filter monitoring.
  • Used in applications where the pressure difference is more critical than the absolute pressure.
  • Offers high accuracy in measuring pressure differentials.

Ultimately, the choice of pressure transmitter type depends on the specific application and the information required for accurate pressure measurement. Consider the advantages of each type in the context of your application's needs, and select the one that best aligns with your goals for pressure monitoring.

Comparing table

Here's a comparative table summarizing the advantages of Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters:

Table 4. Comparison based on the Advantages

Aspect	Absolute Pressure Transmitter	Gauge Pressure Transmitter	Differential Pressure Transmitter
Provides Absolute Pressure Value	✓
Suitable for Total Pressure Measurement	✓
Not Affected by Atmospheric Pressure Variations	✓	✓
Simplicity of Installation	✓
Cost-Effective	✓	✓
Suitable for Industrial Monitoring	✓	✓
Ideal for Flow Rate Measurement	✓
Precise for Pressure Difference Measurement	✓

Please note that the "✓" indicates the primary advantages of each type, but the choice of transmitter should align with the specific requirements and goals of the application. Selecting the appropriate type ensures accurate and reliable pressure measurements in various industrial, scientific, and commercial settings.

Comparing based on disadvantages

Each type of pressure transmitter—Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters—comes with certain disadvantages or limitations depending on the application and operating conditions. Here's a comparison of these pressure transmitter types based on their disadvantages:

Absolute Pressure Transmitters:

• Disadvantages:
  • Cannot provide pressure differentials or variations; they only measure absolute pressure.
  • Not suitable for applications where pressure variations or fluctuations are critical.
  • Typically more complex and expensive than gauge pressure transmitters for common applications.
  • Require regular calibration to account for atmospheric pressure changes.

Gauge Pressure Transmitters:

• Disadvantages:
  • Measure pressure relative to local atmospheric conditions, making them unsuitable for applications where the absolute pressure value is required.
  • Susceptible to changes in atmospheric pressure, which can affect accuracy in some situations.
  • It may not be suitable for vacuum or low-pressure applications.
  • More susceptible to errors in high-altitude environments with varying atmospheric pressure.

Differential Pressure Transmitters:

• Disadvantages:
  • Requires proper installation, which can be more complex than single-point pressure transmitters.
  • Limited to measuring pressure differences between two points and may not provide absolute pressure readings.
  • Can be costlier and less straightforward to install compared to single-point pressure transmitters.
  • May require regular maintenance and calibration to maintain accuracy.

It's important to note that the disadvantages mentioned for each type are not absolute limitations but rather considerations for specific applications. The choice of pressure transmitter type should be made based on the specific requirements and constraints of the application to ensure accurate and reliable pressure measurements.

Comparing table

Here's a comparative table summarizing the disadvantages of Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters:

Table 5. Comparison based on Disadvantages

Aspect	Absolute Pressure Transmitter	Gauge Pressure Transmitter	Differential Pressure Transmitter
Limited to Absolute Pressure	✓
Affected by Atmospheric Pressure Variations	May require calibration due to atmospheric pressure changes	Vulnerable to atmospheric pressure fluctuations	Not directly affected by atmospheric pressure
Suitable for Vacuum or Low-Pressure Applications	Not ideal for precise measurements in vacuum or low-pressure conditions
Complexity of Installation	Installation can be more complex due to the need for two reference points
Calibration Needs	May require periodic calibration to account for atmospheric pressure variations	Regular calibration may be necessary to compensate for atmospheric pressure changes	Calibration may be needed, depending on accuracy requirements

Please note that the "✓" indicates the primary disadvantages or considerations for each type based on specific aspects. The choice of the transmitter should be made based on the specific requirements and constraints of the application to ensure accurate and reliable pressure measurements.

Fig 11. Absolute and Gauge pressure transmitters

Comparing based on easy-to-use

The ease of use of pressure transmitters can vary depending on the type and application. Here's a comparison of Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters based on their ease of use:

Absolute Pressure Transmitters:

Ease of Use:

Typically straightforward to install in applications that require absolute pressure measurements.

May require periodic calibration to account for variations in atmospheric pressure.

Generally, less affected by atmospheric pressure changes, simplifying data interpretation.

Suitable for applications where the absolute pressure value is the primary concern.

Gauge Pressure Transmitters:

• Ease of Use:
  • Often considered user-friendly due to their installation simplicity in applications that measure pressure relative to atmospheric conditions.
  • May require regular calibration to compensate for atmospheric pressure variations, which can be a maintenance consideration.
  • Well-suited for applications where monitoring pressure relative to the local environment is necessary.
  • Widely available and cost-effective for a variety of common pressure measurement needs.

Differential Pressure Transmitters:

• Ease of Use:
  • Installation can be more complex than single-point pressure transmitters because they require connection to two reference points within the system.
  • Proper installation, including tubing and port connections, is essential for accurate measurements.
  • Calibration may be required, depending on the application's accuracy needs.
  • Valuable for applications where monitoring pressure differences between two points is crucial.

In summary, the ease of use for each type of pressure transmitter depends on the specific application and the user's familiarity with the equipment. Absolute pressure transmitters may be easier for some applications, gauge pressure transmitters are user-friendly in many cases, and differential pressure transmitters require careful installation but offer valuable pressure difference measurements. The choice should align with the specific requirements and the user's experience with pressure measurement equipment.

Comparing table

Here's a comparative table summarizing the ease of use for Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters:

Table 6. Comparison based on the Easy to use

Aspect	Absolute Pressure Transmitter	Gauge Pressure Transmitter	Differential Pressure Transmitter
Ease of Installation	Generally straightforward for applications requiring absolute pressure measurements	Often user-friendly due to installation simplicity for gauge pressure monitoring	Installation can be more complex due to the requirement for two reference points
Calibration Needs	Periodic calibration may be needed to account for atmospheric pressure variations	Regular calibration may be necessary to compensate for atmospheric pressure changes	Calibration may be required, depending on accuracy requirements
Susceptibility to Atmospheric Changes	Generally less affected by atmospheric pressure changes	Affected by variations in atmospheric pressure	Not directly affected by atmospheric pressure
Suitable for Absolute Pressure Measurement	✓
Suitable for Relative Pressure Measurement	✓
Suitable for Differential Pressure Measurement	✓

Please note that the "✓" indicates the primary advantage or suitability for each type based on ease of use, but the choice of the transmitter should be made based on the specific requirements and constraints of the application to ensure accurate and user-friendly pressure measurements.

Factors influencing the selection between these types

The selection of a pressure transmitter type—whether Absolute Pressure Transmitter, Gauge Pressure Transmitter, or Differential Pressure Transmitter—depends on various factors. These factors influence the choice and are essential for ensuring the transmitter is well-suited to the application. Here are the key factors that influence the selection:

Measurement Requirements:

The primary factor is the specific measurement requirements of the application. Determine whether you need to measure absolute pressure, gauge pressure, or pressure differentials.

Pressure Range:

The pressure range of the application is crucial. Different types are suitable for various pressure ranges, from very low pressures to extremely high pressures.

Accuracy Requirements:

Consider the required accuracy of pressure measurements. Some types offer higher accuracy than others, and the choice should align with the desired precision.

Environmental Conditions:

The operating environment plays a significant role. Consider factors like temperature, humidity, and the presence of corrosive substances or hazardous conditions. Some transmitters are better suited to harsh environments than others.

Installation:

The ease of installation and the available infrastructure can influence the selection. Differential pressure transmitters, for example, can be more complex to install due to the requirement for two reference points.

Cost:

Budget constraints are a practical consideration. Different types of transmitters vary in cost, so it's important to balance the performance requirements with the budget.

Maintenance:

Consider the maintenance requirements. Some transmitters may require more frequent calibration or maintenance than others, which can impact operating costs.

Application Type:

The specific application also guides the choice. For example, industrial monitoring, HVAC systems, and meteorological equipment may require different types of pressure measurements.

Compatibility with Existing Systems:

If the application is part of an existing system, ensure that the chosen transmitter is compatible with the existing infrastructure and other measurement devices.

Regulatory and Safety Compliance:

In some industries, regulatory compliance and safety standards are paramount. Ensure that the selected transmitter type meets all necessary regulations and safety requirements.

Future Expandability:

Consider whether the application may need to expand or adapt in the future. The choice should be capable of accommodating potential changes.

Industry Standards:

Certain industries have established standards for pressure measurement. Ensure that the selected transmitter type complies with these standards.

Data Communication and Integration:

Consider how the pressure data will be communicated or integrated into control and monitoring systems. Some transmitter types may be better suited for specific communication protocols or integration methods.

In summary, the selection of a pressure transmitter type is a multi-faceted decision that depends on the specific requirements and constraints of the application. Carefully evaluating these factors and their relative importance will lead to the most appropriate choice for accurate and reliable pressure measurements.

Fig 12. Differential pressure transmitter used in tank

Real-world examples and scenarios for choosing the appropriate type

Selecting the appropriate type of pressure transmitter—Absolute, Gauge, or Differential—depends on the specific requirements and conditions of real-world applications. Here are some real-world examples and scenarios for choosing the right type:

Meteorological Station:

Scenario: A meteorological station needs to measure atmospheric pressure accurately for weather forecasting.

Appropriate Type: Absolute Pressure Transmitter.

Why: Absolute pressure transmitters provide measurements relative to an absolute vacuum, which is essential for accurate meteorological data.

Industrial Boiler Monitoring:

Scenario: An industrial facility needs to monitor the steam pressure in a boiler.

Appropriate Type: Gauge Pressure Transmitter.

Why: Gauge pressure transmitters are ideal for monitoring pressures relative to the local atmospheric conditions in industrial settings.

HVAC System:

Scenario: An HVAC system in a building requires pressure sensors to monitor air pressure and ensure the system's efficiency.

Appropriate Type: Gauge Pressure Transmitter.

Why: Gauge pressure transmitters are suitable for HVAC applications, where pressure is measured relative to local atmospheric conditions.

Flow Rate Measurement in a Chemical Plant:

Scenario: In a chemical manufacturing plant, the flow rate of a specific fluid needs to be accurately measured.

Appropriate Type: Differential Pressure Transmitter.

Why: Differential pressure transmitters are used with flow measurement devices (e.g., orifice plates) to calculate flow rates accurately.

Altitude Measurement in Aviation:

Scenario: An aircraft's altitude needs to be determined for navigation and safety.

Appropriate Type: Absolute Pressure Transmitter.

Why: Absolute pressure transmitters provide altitude measurements relative to sea level by considering atmospheric pressure.

Tire Pressure Monitoring in Automobiles:

Scenario: An automobile's tire pressure needs to be monitored for safety and performance.

Appropriate Type: Gauge Pressure Transmitter.

Why: Gauge pressure transmitters are used to measure tire pressure relative to the local atmospheric conditions.

Controlled Environment in Pharmaceuticals:

Scenario: A pharmaceutical laboratory requires pressure monitoring in cleanrooms to maintain controlled environments.

Appropriate Type: Differential Pressure Transmitter.

Why: Differential pressure transmitters are essential for ensuring specific pressure differences between cleanrooms and adjacent areas.

Hydraulic System in a Construction Vehicle:

Scenario: A construction vehicle's hydraulic system requires pressure monitoring for the operation of heavy equipment.

Appropriate Type: Gauge Pressure Transmitter.

Why: Gauge pressure transmitters are suitable for industrial machinery and hydraulic systems where pressures are relative to the atmosphere.

Scientific Experiment in a Laboratory:

Scenario: A laboratory conducts a scientific experiment that requires precise pressure measurements.

Appropriate Type: Absolute Pressure Transmitter.

Why: Absolute pressure transmitters provide accurate absolute pressure values, making them ideal for precise experiments.

Tank Level Measurement:

Scenario: A tank storing liquid or gas needs level measurement for inventory management.

Appropriate Type: Differential Pressure Transmitter.

Why: Differential pressure transmitters are used for level measurement by monitoring the pressure difference between the tank bottom and the reference point.

These examples illustrate how the choice of pressure transmitter type aligns with the specific requirements and conditions of real-world applications, ensuring accurate and reliable pressure measurements.

Fig 13. Rosemount pressure transmitters

Conclusion

In this comprehensive guide on pressure transmitters, we have explored the various types—Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters—along with their working principles, applications, advantages, disadvantages, and the factors influencing their selection. Let's summarize the key takeaways:

• Working Principles: Each pressure transmitter type operates on distinct principles. Absolute pressure measures pressure relative to a perfect vacuum, gauge pressure measures relative to local atmospheric pressure, and differential pressure measures the pressure difference between two reference points.
• Applications: The choice of pressure transmitter type depends on the specific application. Absolute pressure transmitters are suited for meteorology, altitude measurement, and scientific experiments. Gauge pressure transmitters find use in industrial monitoring, HVAC systems, and automotive tire pressure monitoring. Differential pressure transmitters excel in flow rate measurement, level measurement, and filter monitoring.
• Advantages: Each type offers its unique advantages. Absolute pressure transmitters provide absolute pressure values, gauge pressure transmitters are user-friendly in many applications, and differential pressure transmitters offer precise measurements of pressure differences.
• Disadvantages: It's essential to consider the disadvantages when selecting a pressure transmitter. Absolute pressure transmitters may require calibration for atmospheric pressure changes, gauge pressure transmitters are vulnerable to atmospheric pressure fluctuations, and differential pressure transmitters can have complex installations.
• Selection Factors: The choice of pressure transmitter type is influenced by factors such as measurement requirements, pressure range, accuracy needs, environmental conditions, installation and maintenance complexity, budget considerations, regulatory compliance, and more.
• Real-World Scenarios: Real-world examples helped illustrate how different pressure transmitter types are applied in various industries and applications. Selecting the appropriate type is crucial for accurate and reliable pressure measurements.

In conclusion, the selection of the right pressure transmitter type is a critical decision that depends on a thorough understanding of the application's unique requirements and constraints. By carefully considering these factors, users can ensure that pressure measurements are accurate, reliable, and suitable for their real-world applications, ultimately contributing to safety, efficiency, and precision in a wide range of industries and contexts.

To recap

1. What is a pressure transmitter?

A pressure transmitter is a device used to measure and convert pressure into an electrical signal, making it easier to monitor, control, or record pressure values.

2. What are the main types of pressure transmitters?

The main types of pressure transmitters are Absolute Pressure Transmitters, Gauge Pressure Transmitters, and Differential Pressure Transmitters.

3. How does an Absolute Pressure Transmitter work?

Absolute Pressure Transmitters measure pressure relative to an absolute vacuum. They typically use sealed reference chambers to measure pressure without any reference to atmospheric conditions.

4. Where are Gauge Pressure Transmitters commonly used?

Gauge Pressure Transmitters are often used in applications where pressure measurements are relative to local atmospheric conditions. Common uses include industrial monitoring, HVAC systems, and tire pressure monitoring in vehicles.

5. What is the primary advantage of Differential Pressure Transmitters?

Differential Pressure Transmitters are ideal for measuring pressure differences between two reference points. Their primary advantage is high accuracy in measuring pressure differentials.

6. How do I choose the right pressure transmitter type for my application?

The choice depends on factors like measurement requirements, pressure range, accuracy needs, environmental conditions, installation complexity, budget constraints, and the application type. Evaluate these factors to make an informed choice.

7. Are there any disadvantages to using an Absolute Pressure Transmitter?

Yes, one disadvantage is that they do not provide information about pressure variations or pressure differences. They also require calibration for atmospheric pressure changes in some applications.

8. What kind of applications require Differential Pressure Transmitters?

Applications that require monitoring pressure differences between two points within a system benefit from Differential Pressure Transmitters. Examples include flow rate measurement, level measurement, and filter monitoring.

9. Do pressure transmitters need regular maintenance?

The maintenance requirements depend on the specific application and the type of pressure transmitter. Some may require periodic calibration and maintenance, while others may have lower maintenance needs.

10. What is the main goal of selecting the appropriate pressure transmitter type?

The primary goal is to ensure accurate and reliable pressure measurements in real-world applications. Selecting the right type is essential for safety, efficiency, and precision in various industries and contexts.

References

https://realpars.com/pressure-transmitter/

https://www.transmittershop.com/blog/absolute-and-gauge-pressure-transmitters-overview-working-principle/

https://instrumentationandcontrol.net/whats-the-difference-between-absolute-gauge-and-differential-pressure.html

http://www.calscan.net/school_pressure_modes.html

https://www.emerson.com/en-in/automation/measurement-instrumentation/pressure-measurement/pressure-transmitters-and-transducers/about-rosemount-3051-pressure-transmitter-family

https://www.nuovafima.com/en/prodotti/mtom-dn100-en/

https://heinrichs.eu/en/products/pressure/differential-pressure-transmitter-pad/