What is pressure transmitter ? Working principle of pressure transmitter

A pressure transmitter, also known as a pressure transducer, is a device that converts pressure into an analog electrical signal. Although there are various types of pressure transmitters, the most common works on the principle of piezoelectricity, which means the electricity is generated by applying pressure to piezoelectric materials.

The basic operation of a pressure transmitter involves the pressure sensor component, which senses the pressure (either absolute, gauge, or differential pressure) and converts it into a mechanical signal. This mechanical signal is then converted into an electrical signal by the transducer element, which can be processed and read by various types of control systems or display units.

Pressure transmitters are widely used in various industrial and non-industrial applications for monitoring and controlling pressures. They are essential in industries such as oil and gas, chemical manufacturing, power generation, and water treatment, among others, where precise control of pressure is critical for safety, efficiency, and process quality.

A pressure transmitter typically consists of several key components that work together to measure pressure and convert it into an electrical signal. The main components include:

1. Pressure Sensor: The core component of the transmitter, the pressure sensor detects the pressure applied to it and converts it into a mechanical signal. This sensor can be based on different technologies, such as strain gauge, piezoelectric, capacitive, or resonant silicon.
2. Diaphragm: A thin, flexible membrane that moves in response to changes in pressure. The diaphragm is an essential part of the pressure sensor, as the movement caused by pressure changes is what gets converted into an electrical signal. It can be made from materials like stainless steel, Hastelloy, Monel, Tantalum, or others, depending on the application’s requirements for chemical compatibility and durability.
3. Seal: Seals are used to protect the internal components of the transmitter, especially the pressure sensor, from the process medium (the fluid whose pressure is being measured). Seals must be compatible with the process medium to prevent corrosion or degradation.
4. Process Connection: This component allows the pressure transmitter to be connected to the process system where the pressure measurement is required. Common process connections include threaded connections (NPT, BSP), flange connections, and sanitary connections, among others.
5. Electrical Connection: The electrical connection is the part of the transmitter where the electrical signal is outputted. It can vary in type, including terminal blocks, cable glands, or connectors, and is used to connect the transmitter to the control system or display unit.
6. Housing: The housing encases the internal components of the transmitter, providing protection against environmental conditions such as dust, moisture, and the potential hazards of the specific industrial environment in which it is installed. Housings are typically made from durable materials like aluminum or stainless steel and are designed to meet specific standards for explosion-proof or intrinsically safe applications.
7. Transducer (or Transmitter Circuitry): The transducer converts the mechanical signal from the pressure sensor into an electrical signal. This component often includes signal conditioning circuitry to amplify, filter, and convert the signal into a standard output format, such as 4-20 mA, 0-10V, or a digital signal like HART, Foundation Fieldbus, or Profibus.
8. Display and User Interface (optional): Some pressure transmitters come equipped with a local display and user interface, such as buttons or a touchscreen, which allows for on-site monitoring of pressure readings and configuration of the transmitter settings.

These components work together to ensure that the pressure transmitter can accurately measure pressure and provide reliable data to control systems for process monitoring and control.

The working principle of a pressure transmitter involves converting the physical pressure variable into an electrical signal. The most common type of pressure transmitter uses a piezoresistive sensor or strain gauge as the sensing element.

Here’s a simplified explanation of the working principle:

1. Pressure Sensing: When pressure is applied to the pressure transmitter, it is first encountered by the primary sensing element. This element can be a diaphragm, a bourdon tube, or a piston, depending on the design and application of the transmitter. This component moves or deforms slightly in response to the pressure.
2. Transduction: The movement or deformation of the primary sensing element affects a secondary element, which is typically a strain gauge or piezoresistive sensor attached to or integrated with the primary sensing element. The strain gauge consists of electrical conductive wires or piezoresistive materials that change resistance when stretched or compressed.
3. Electrical Signal Generation: The change in resistance of the strain gauge or piezoresistive sensor alters the electrical characteristics in the sensor circuit. This change is usually in the form of a voltage, current, or frequency change and is proportional to the pressure applied. Common output signals include 4-20 mA current loops, voltage signals, or digital signals like HART or Fieldbus.
4. Signal Processing: The raw electrical signal generated by the sensor element is often processed by an internal circuit within the transmitter to produce a standardized and calibrated output signal. This processing might include temperature compensation, linearization, and amplification to ensure accuracy and reliability of the output signal.
5. Output: The processed signal is then transmitted to a control system, display, or other devices for monitoring, display, or further processing. This signal represents the measured pressure in a form that can be easily interpreted and used by the system.

This principle allows pressure transmitters to provide accurate and reliable measurements in various applications, from simple water pressure monitoring to critical measurements in high-pressure industrial processes.

Pressure transmitters are versatile devices used across a wide range of industries for monitoring and controlling pressure levels.

Some of the key applications include:

1. Process Control in Manufacturing: They are extensively used in the manufacturing industry to monitor and control the pressure of liquids and gases within pipes and vessels to ensure optimal operating conditions, product quality, and safety.
2. Oil and Gas Industry: In the oil and gas sector, pressure transmitters are critical for drilling operations, pipeline monitoring, and refining processes, where precise pressure measurements are crucial for efficiency and safety.
3. Chemical Industry: They are used to control reaction pressures in reactors, monitor storage conditions, and ensure the safe transfer of chemicals through pipelines.
4. Water and Wastewater Treatment: Pressure transmitters help in managing water supply systems by monitoring water pressure in pipelines and storage tanks, controlling pumps, and ensuring consistent water flow and treatment processes.
5. HVAC Systems: In Heating, Ventilation, and Air Conditioning (HVAC) systems, they are used to maintain optimal air pressure, ensuring comfort and energy efficiency in buildings.
6. Automotive Industry: They are used in various systems within vehicles, including tire pressure monitoring systems (TPMS), engine management systems, and fluid pressure monitoring in braking systems.
7. Aerospace: In the aerospace industry, pressure transmitters are used to monitor and control cabin pressure, hydraulic systems, and fuel systems in aircraft and spacecraft.
8. Food and Beverage Industry: They are used to monitor and control the pressure in cooking, pasteurization, and bottling processes, ensuring product quality and safety.
9. Pharmaceuticals: In pharmaceutical manufacturing, pressure transmitters ensure that processes such as fermentation, distillation, and tablet pressing occur under precise pressure conditions to maintain product efficacy and safety.
10. Power Generation: They are critical in monitoring steam pressure in boilers and turbines in power plants, ensuring efficient and safe power generation.

These applications highlight the importance of pressure transmitters in various industrial and commercial processes, where accurate pressure measurements are essential for operational efficiency, product quality, safety, and environmental protection.

An industrial pressure transmitter serves several critical functions in various industrial processes:

1. Pressure Measurement: The primary function of an industrial pressure transmitter is to accurately measure the pressure of gases, liquids, or vapors in a system. This can include absolute pressure, gauge pressure, or differential pressure, depending on the application.
2. Process Control: By providing precise pressure readings, pressure transmitters help maintain optimal conditions in industrial processes. This can involve regulating the flow of materials, controlling the operation of pumps and valves, and ensuring that processes operate within safe and efficient pressure ranges.
3. Safety: Pressure transmitters play a crucial role in safety systems by monitoring pressure levels to prevent unsafe conditions. For example, they can trigger alarms or shut down systems if the pressure exceeds or falls below predetermined safety limits, preventing accidents, equipment damage, and potential hazards to personnel.
4. Efficiency Optimization: By enabling the precise control of processes, pressure transmitters help optimize the use of energy and materials, reduce waste, and improve overall efficiency. This is particularly important in industries such as chemical manufacturing, oil and gas, and power generation, where small improvements in efficiency can lead to significant cost savings and reduced environmental impact.
5. Quality Assurance: In many manufacturing processes, the pressure conditions directly affect the quality of the final product. Pressure transmitters ensure that these conditions are maintained consistently, leading to higher quality products and fewer defects.
6. Data Collection and Monitoring: Modern industrial pressure transmitters often come equipped with digital communication capabilities, allowing them to collect and transmit data for monitoring and analysis. This data can be used for predictive maintenance, process optimization, and historical record-keeping, contributing to better decision-making and process improvements over time.

Overall, industrial pressure transmitters are integral components in managing and optimizing industrial operations, ensuring safety, efficiency, and quality in a wide range of applications.

When selecting a pressure transmitter for a specific application, several key specifications and factors must be considered to ensure compatibility, accuracy, and reliability.

Here are the primary specifications to consider:

1. Pressure Range: The transmitter should be capable of measuring the expected pressure range of the application, including any potential pressure spikes. It’s important to select a transmitter with a maximum range slightly above the maximum expected pressure to avoid overranging and potential damage.
2. Accuracy: This specifies how close the transmitter’s readings are to the true value. It’s usually expressed as a percentage of the full scale or in specific units of pressure. The required accuracy will depend on the application’s tolerance for deviation.
3. Process Connection: The type of connection needed to attach the transmitter to the process (e.g., flanged, threaded, sanitary) must be compatible with existing equipment and capable of withstanding the process conditions.
4. Output Signal: The transmitter’s output must be compatible with the control system or data acquisition system it will connect to. Common outputs include 4-20 mA, 0-10 V, or digital signals like HART, Foundation Fieldbus, or Profibus.
5. Media Compatibility: The materials in contact with the process media (diaphragm, body, seals) must be compatible with the media to avoid corrosion or degradation. Common materials include stainless steel, Hastelloy, Monel, and Teflon.
6. Operating Temperature: The transmitter must be able to operate within the temperature range of the process and the environment. Extreme temperatures may require special models or additional protection.
7. Overpressure Limit: The maximum pressure the transmitter can withstand without permanent damage or degradation in performance, even if it exceeds the specified range.
8. Response Time: The time it takes for the transmitter to respond to a change in pressure. Faster response times may be necessary for dynamic processes.
9. Electrical Connections: Consideration for the type of electrical connection required (e.g., cable glands, terminal blocks, connectors) and any necessary ingress protection (IP) ratings against dust and water.
10. Certifications and Standards: Depending on the industry and location, certain certifications may be required for safety, hazardous area operations (e.g., ATEX, IECEx), and quality standards (e.g., ISO, NIST).
11. Stability and Drift: The transmitter’s ability to maintain accuracy over time without recalibration, affected by factors like temperature fluctuations and aging.
12. Vibration and Shock Resistance: In industrial environments with high vibration or shock, the transmitter must be robust enough to maintain accuracy under these conditions.

Selecting a pressure transmitter with the appropriate specifications ensures that the device will perform as required, offering reliable and accurate pressure measurements for the specific industrial application.

Pressure transmitters, like many industrial devices, must comply with a variety of codes and standards to ensure safety, reliability, and interoperability. These standards may vary by region, industry, and application, but some of the most commonly referenced include:

1. IEC 61508: This is an international standard for the functional safety of electrical/electronic/programmable electronic safety-related systems. It is applicable to all kinds of industry where safety is a concern, including pressure transmitters used in safety-critical applications.
2. IEC 61000: This series of standards covers electromagnetic compatibility (EMC), providing limits and testing methods for the emission and immunity of electrical and electronic equipment, including pressure transmitters, to ensure they do not interfere with or are not susceptible to electromagnetic interference.
3. ANSI/ISA S82 and ANSI/ISA S84: These are standards from the International Society of Automation (ISA) related to electrical equipment for measurement, control, and laboratory use (S82), and the application of safety instrumented systems for the process industries (S84).
4. ATEX Directive (EU) and IECEx Scheme (International): These standards relate to equipment intended for use in potentially explosive atmospheres. The ATEX directive is for the EU, while IECEx is an international certification accepted in many countries. Both include requirements for the design and manufacture of pressure transmitters used in hazardous areas.
5. NEMA Standards: The National Electrical Manufacturers Association (NEMA) sets standards for the protection of electronic equipment, including pressure transmitters, against environmental conditions through different enclosure types (e.g., NEMA 4X for watertight and corrosion-resistant enclosures).
6. API Standards: The American Petroleum Institute (API) provides standards for the oil and natural gas industry, including specifications for pressure measuring devices used in drilling, production, and refining.
7. ASME B31 Series: The American Society of Mechanical Engineers (ASME) B31 series covers the design and construction of piping systems, including considerations for pressure transmitters used within these systems.
8. FM Global and UL Standards: Factory Mutual (FM) and Underwriters Laboratories (UL) provide certification for products used in hazardous locations, ensuring they meet specific safety criteria.
9. CE Marking: In Europe, pressure transmitters must comply with relevant European Directives to earn CE marking, indicating conformity with health, safety, and environmental protection standards.
10. PED Directive (EU): The Pressure Equipment Directive (2014/68/EU) applies to the design, manufacture, and conformity assessment of pressure equipment and assemblies with a maximum allowable pressure greater than 0.5 bar, including pressure transmitters.

Compliance with these codes and standards is crucial for manufacturers and users of pressure transmitters, not only to fulfill legal requirements but also to ensure the safety and efficiency of industrial processes.

There are numerous manufacturers around the world that specialize in the design, development, and production of pressure transmitters, catering to a wide range of industries and applications. Some of the most well-known manufacturers include:

1. Emerson Electric Co.: Emerson is known for their Rosemount series of pressure transmitters, which are widely used in various industries for reliable pressure measurement.
2. Endress+Hauser: A leading supplier in measurement instrumentation, Endress+Hauser offers a wide range of pressure transmitters for process and level measurement.
3. Siemens AG: Siemens provides a variety of process instrumentation products, including pressure transmitters that are used in many industrial applications.
4. ABB Ltd: ABB offers a comprehensive range of pressure transmitters known for their accuracy and reliability, suitable for a variety of industrial applications.
5. Honeywell International Inc.: Honeywell’s pressure transmitters are used in many sectors, including oil and gas, chemicals, and power generation, for their robust performance.
6. Yokogawa Electric Corporation: Yokogawa is known for high-quality industrial automation and control products, including pressure transmitters that offer precision and durability.
7. WIKA Alexander Wiegand SE & Co. KG: WIKA offers a broad portfolio of pressure measurement instruments, including pressure transmitters for a wide range of applications.
8. Danfoss: Danfoss manufactures pressure transmitters that are used in various applications, including refrigeration, air conditioning, heating, and hydraulics.
9. Schneider Electric: Schneider Electric offers pressure measurement devices that are designed for robustness and performance in challenging industrial environments.
10. Foxboro (now part of Schneider Electric): The Foxboro brand is known for its reliable and accurate pressure transmitters, used in diverse industrial processes.

Each of these manufacturers has its own range of products tailored to specific industrial needs, including general process measurement, high-precision applications, hazardous area installations, and sanitary requirements for the food and pharmaceutical industries. When selecting a pressure transmitter, it’s important to consider the specific requirements of the application, including the type of pressure measurement, the range, accuracy, material compatibility, and any relevant industry standards or certifications.