Differential pressure transmitter - principle of operation

The differential pressure transducer of pressure is a device used to measure the difference in pressure between two points in the system, for example, between the inside of a pipe and the outside. At its heart is a sensor that responds to the pressure difference, converting it into an electrical signal. This signal is proportional to the measured pressure difference. Depending on the type of pressure transducer, the sensor can use different methods to measure pressure, such as capacitance change in the case of capacitive transducers, material deformation in strain gauge transducers, or voltage generation in piezoelectric transducers. The output signal is then sent to a control or display system, where it is interpreted, allowing the pressure measurement in a given system to be monitored and controlled.

Types of Differential Pressure Transducers

Differential pressure transducers come in two basic types, which differ in operating principles and applications:

• Capacitive Transducers: This type of transducer consists of two capacitors, each with a movable plate that responds to pressure. A change in pressure alters the capacitance of one or both capacitors, which is then converted into an electrical signal. These transducers are valued for their high accuracy, sensitivity, and stability. Due to these properties, they are used in precise environments such as laboratories, the semiconductor industry, and technological process control. However, their measurement accuracy can be affected by changes in temperature and humidity, so this should be considered in the calibration and usage process.

• Piezoresistive Transducers: Most differential pressure transducers rely on the piezoresistive effect, which involves a change in the electrical resistance of a material caused by stress or pressure. In this type of transducer, materials (usually silicon sensors) are used that generate an electrical voltage under pressure. They are ideal for rapid and dynamic measurements, such as vibration monitoring. All piezoresistive sensors for measuring differential pressure are practically free from drift. Examples of such devices in our range include: the multi-range differential pressure transducer for inert gases, SIRAS P21 DP with SIL/PL approval, and MIDAS DP10 for gases and low-aggressiveness liquids.

Choosing the right type of transducer depends on the requirements of the application, including accuracy, measurement range, and environmental resistance.

Differential Pressure Transducer – Applications

Differential pressure transducers are crucial in various industrial sectors, playing an essential role in the precise monitoring and control of processes:

Oil and Gas Industry

Pipeline Monitoring: One of the common applications of differential pressure measurement is determining flow rate in pipelines using an orifice plate. This constriction reduces the pipe's cross-section, increasing flow velocity and causing a change in static pressure. Pressure is measured before and after the orifice, and the measured pressure difference is used to determine the flow rate. Such pressure monitoring in pipelines enables leak detection and optimization of raw material flow.

Extraction Processes: Help maintain stable extraction conditions, minimizing the risk of hazardous situations, such as gas explosions.

Chemical Industry

Reactor Monitoring: Crucial for monitoring pressure in chemical reactors, increasing safety and process efficiency.

Flow Systems: Facilitate the regulation of chemical flows, ensuring continuity and safety of production processes.

Pharmaceutical Industry

Process Control: Essential for monitoring conditions in production processes, especially in the manufacture of medicines and vaccines.

Clean Systems: Used to maintain appropriate environmental conditions in sterile environments, such as operating rooms or laboratories.

Flow Measurement and Filter Monitoring: Used for accurate measurement of substance flow and monitoring the condition of filters.

Engineering and Automation

HVAC Systems: Used in managing air conditioning and ventilation, controlling airflow in buildings, maintaining optimal conditions. For example, in ventilation systems, differential pressure measurement is used to assess filter cleanliness. By measuring pressure on both sides of a filter, its condition can be determined. When the filter is contaminated, resistance to the passing air or other medium increases, resulting in a greater pressure difference. This increase in resistance is a direct indicator of the filter’s contamination level, allowing for an assessment of the need for its replacement or cleaning.

Process Automation: Used to monitor and regulate pressure in devices, enhancing production efficiency and safety.

Water and Wastewater Engineering: Responsible for monitoring and controlling water systems, from managing water levels to detecting leaks.

Rail Industry

In rail transport, these transducers are used to monitor pressure in braking systems, ensuring safety and reliability. Precise pressure measurements are critical for the proper functioning of brakes and other crucial rail systems.

In each of these applications, differential pressure transducers provide accurate information necessary for effective process management, enhancing safety, energy efficiency, and overall operational performance.

Level measurement in closed tanks using differential pressure transducers

Differential pressure transducers are also used as hydrostatic probes to measure levels in closed tanks. This measurement technique is crucial in many industries, from the chemical industry to food processing. They work by measuring the pressure difference between two points in a tank - at the bottom and top. This pressure difference is directly related to the height of the liquid column, allowing the level of the liquid to be accurately determined. This method is particularly useful in conditions where direct contact with the fluid is undesirable or impossible, such as with toxic, corrosive or high-pressure substances. This technique is highly effective even under difficult conditions, such as agitation of the fluid, the presence of foam, extreme temperatures or varying tank pressure. Using differential pressure transducers for this purpose not only ensures accuracy, but also increases safety and operational efficiency in tank management. In addition, they feature easy installation and quick start-up, making them extremely convenient for daily use.

Differential Pressure Transducers for Explosion-Hazard Areas

Differential pressure transducers designed for use in explosion-hazard areas, known as Ex zones, must meet strict safety and durability standards. They are engineered to operate safely in potentially dangerous environments where flammable gases, liquids, or dusts are present. Key aspects of these devices include:

• Certification: Differential pressure transducers for Ex zones must comply with international and local Ex equipment standards, such as ATEX in Europe, IECEx internationally, and other national standards.
• Explosion-Proof Enclosure: They are equipped with specially designed explosion-proof enclosures that prevent the penetration of sparks or excessive heat into the environment, which could trigger an explosion.
• Environmental Resistance: These transducers are typically robust against extreme environmental conditions, including high and low temperatures, moisture, vibrations, and other challenging industrial conditions.
• Temperature Range: They must be capable of operating within a broad temperature range, both ambient and the medium they contact. Their design takes into account the maximum and minimum operational temperatures.
• Materials and Construction: Made from corrosion-resistant materials such as high-quality stainless steel to ensure long-lasting and reliable operation in harsh industrial environments.
• Functionality and Programmability: Often equipped with advanced features such as integrated LCD displays for presenting measurement data, programming capabilities, and adaptability to specific application requirements.

It is important to note that specific requirements may vary depending on the specifications of a particular model and the operating conditions in which it will be used.

An example of a differential pressure transducer meeting the above requirements is the dTRANS p20 DELTA Ex d.

The permissible ambient temperature for JUMO dTRANS p20 differential pressure transducers varies depending on the version:

• II 1/2G Ex d: from -40 to +60°C
• II 1/2D Ex d: from -40 to +70°C
• II 1/2G Ex d: from -40 to +85°C.

Additionally, the maximum permissible temperature of the medium with which the transducer can operate also varies depending on the temperature class:

• For class T6: +70°C
• For class T5: +85°C
• For class T4: +110°C
• For class T105°C: +100°C

About the author

My name is Ewelina Szmit and I have been working in the field of content marketing for several years, combining my professional skills with my passion for writing. I believe that even the most technical topics can be presented in an interesting and accessible way for everyone. Outside of work, I develop my creativity by creating newspaper collages. I like to spend my free time most actively, walking my dog or running.