Relative pressure transmitters are essential components in measurement and control technology – wherever the system pressure in a plant needs to be reliably monitored. In contrast to differential or absolute pressure sensors, they specifically measure the overpressure in relation to the ambient pressure, for example in hydraulic circuits, pneumatic controls, or process lines.
Our relative pressure transmitters are therefore used in hydraulics and pneumatics, process technology, and general machine and plant engineering. They provide precise measured values and standardized output signals such as 0–10 V or 4–20 mA – ideal for control, regulation, or monitoring systems.
In this guide, you will learn everything you need to know about function, areas of application, types, and accessories—explained in a compact and practical way.
What is a relative pressure transmitter?
A relative pressure transmitter, also known as a pressure transmitter, is a sensor that measures the excess pressure of a gaseous or liquid medium in relation to the ambient atmospheric pressure. Its main task is to convert this measured pressure value precisely into a continuous and proportional standard electrical signal, typically 0–10 V or 4–20 mA.
Unlike a simple pressure gauge, which only displays the pressure, or a pressure switch, which only switches at a predefined value, a transmitter provides a continuous signal. This signal can be further processed by higher-level systems such as a PLC control, a frequency converter, or a building management system to actively control, monitor, and log processes. This makes it an indispensable component for automated and safety-related applications in industry and technology.
How does relative pressure measurement work?
Relative pressure measurement is based on a simple but effective principle: measuring the process pressure against the ambient atmospheric pressure. At the heart of every relative pressure transmitter is a pressure-sensitive diaphragm. The pressure of the medium to be measured, for example the water pressure in a pipe, acts on one side of this diaphragm. The other side of the diaphragm is in direct contact with the ambient air, which serves as a constant reference point for the current air pressure.
If the diaphragm is deformed by the applied process pressure, an internal sensor element precisely detects this mechanical deflection. The transmitter's integrated electronics then convert this minimal physical change into a stable and standardized electrical signal, such as 0–10 V or 4–20 mA. This signal is directly proportional to the measured overpressure and can thus be reliably forwarded to a control or display device for continuous monitoring of the system pressure.
Typical applications for relative pressure sensors?
Relative pressure transmitters are indispensable in numerous industrial and technical areas due to their versatility and robustness. They are used wherever system or plant pressure must be reliably monitored and controlled.
The most important areas of application include hydraulic systems, where they ensure the operating pressure of aggregates and control circuits. In pneumatic systems, they monitor the supply pressure in compressed air networks and ensure the correct functioning of cylinders and tools. In general mechanical and plant engineering, they are a key component for controlling pressures in cooling circuits, lubrication systems, or process lines. In addition, they are used in water management for pressure monitoring in pumping stations and pipe networks, as well as in process engineering for regulating pressures in containers and reactors.
Types of relative pressure transmitters
Our relative pressure transmitters are housed in a compact and robust enclosure designed for direct installation in industrial environments. The primary difference between the types is whether or not they are equipped with an integrated local pressure display.
Transmitters without a display are the ideal choice for installation in control cabinets or at measuring points that are difficult to access, where the pressure values are recorded and visualized centrally in a control system. Their particularly compact design allows for space-saving and inconspicuous installation.
For applications where direct on-site monitoring of the system pressure is required or desired, we offer models with an innovative, plug-in LCD display. This display can be mechanically rotated and tilted to ensure optimum readability from any installation position. In addition, the displayed value can be rotated digitally, offering maximum flexibility during commissioning and maintenance. Regardless of the variant, all transmitters have a standardized G ½" process connection.
Technologies: Ceramic vs. stainless steel measuring cell
The heart of every relative pressure transmitter is the measuring cell, which converts the physical pressure into an electrical signal. Choosing the right technology is crucial for durability and measurement accuracy in your specific application. We distinguish between two proven principles:
Ceramic measuring cell: Our “ceramic” series transmitters use a robust measuring cell made of aluminum oxide. This material is characterized by its high hardness and good corrosion resistance to most common media. The ceramic measuring cell is the ideal and economical choice for a wide range of standard applications in hydraulics, pneumatics, and general mechanical engineering. An important exception is use with ammonia and freons, for which this technology is not suitable.
Stainless steel measuring cell: For more demanding industrial applications, our transmitters are equipped with a completely seal-free welded stainless steel measuring cell. This premium design does not require additional elastomer seals that could react with the medium. The result is superior media compatibility, high overload protection, and suitability for extended temperature ranges. This technology is the first choice when maximum robustness and chemical resistance are required.
Selecting the right measuring cell ensures that your transmitter will continue to operate accurately and reliably even under demanding conditions.
Installation and connection of relative pressure transmitters
The installation of our relative pressure transmitters is straightforward and designed for quick deployment in the field. Mechanical installation is carried out by screwing the transmitter directly into the pressure line via the standardized G ½ inch process connection.
The electrical connection is conveniently and securely made using the DIN connector included in the scope of delivery. This plug-in system not only enables quick and error-free commissioning, but also easy disassembly for maintenance purposes without having to disconnect the fixed cabling. This saves time and increases plant safety.
Performance and service life: What influences sensor quality?
The long-term performance and reliability of a relative pressure transmitter is determined by several factors. The correct selection of measurement technology plays a decisive role: The use of a stainless steel measuring cell for chemically demanding media or a ceramic measuring cell in the appropriate application area prevents corrosion and ensures stability. Equally important is choosing the right measuring range to avoid permanent overload of the sensor due to pressure peaks.
In addition, environmental conditions can influence service life. Strong vibrations, extreme temperatures outside the specified range, or high humidity can put strain on both the mechanical components and the electronics. Professional installation that avoids mechanical stress on the housing and a stable and correctly connected power supply are also essential for long-term precise and trouble-free operation.
What should you look for when choosing a relative pressure transmitter?
Choosing the right relative pressure transmitter is crucial for the process reliability and longevity of your system. To find the right model for your needs, you should answer four key questions:
- What pressure range do I need? The measuring range of the transmitter should match the maximum operating pressure of your application. Choose a range that safely covers the expected pressure to avoid overloading the sensor while ensuring high resolution of the measurement signal.
- What medium is being measured? This determines the choice of measurement technology. For most standard media in hydraulics and pneumatics, our ceramic measuring cell is the ideal choice. However, if you are measuring more chemically demanding or aggressive media, you should use the fully welded stainless steel measuring cell to guarantee maximum resistance.
- What output signal is required? Your control system determines whether you need a voltage signal (0–10 V) or a current signal (4–20 mA). The 4–20 mA signal is generally more interference-free and better suited for transmission over longer distances.
- Is a display on site required? If the current pressure value needs to be readable directly at the measuring point for commissioning, maintenance, or process control, a model with an integrated LCD display is the right choice. For measuring points that are only monitored centrally, a version without a display is sufficient.
By clarifying these points, you can ensure that you select the optimal transmitter for your application.
Where can I find all the technical data for the relative pressure transmitters?
All detailed technical data and relevant information about our relative pressure transmitters can be found directly on the respective product pages in our online shop. The official data sheets, operating instructions, and declarations of conformity are available for download there.
Frequently asked questions about relative pressure transmitters?
What is the difference between relative, absolute, and differential pressure?
Relative pressure measures the excess pressure in relation to the surrounding atmospheric pressure (e.g., tire pressure). Absolute pressure measures the pressure relative to a perfect vacuum (0 bar). Differential pressure measures the pressure difference between any two points (e.g., before and after a filter).
When should I use a 4–20 mA signal instead of a 0–10 V signal?
The 4–20 mA current signal is significantly less sensitive to electrical interference and voltage drops over long cable runs. It is the preferred choice when the transmitter is installed far away from the control system or is operated in an environment with high interference potential (e.g., due to frequency converters).
What is the difference between a ceramic and a stainless steel measuring cell?
The ceramic measuring cell is the robust and economical solution for most standard media such as hydraulic oil, water, or air. The fully welded stainless steel measuring cell offers superior chemical resistance and is the right choice for more demanding or aggressive media as well as for applications with high hygiene requirements.
Can I use the pressure transmitter for drinking water?
Yes, our relative pressure transmitters with stainless steel measuring cells are approved for drinking water in accordance with NSF/ANSI 61/372 and are therefore ideally suited for use in drinking water applications.
How do I install the pressure transmitter?
Installation is simple: the transmitter is screwed directly into the pressure line with its G ½" thread. The electrical connection is quick and secure using the DIN connector supplied.
Do I need a display on my transmitter?
A display is useful if you want to read the current pressure value directly on site for commissioning, maintenance, or process control. If the values are monitored exclusively in a central control room or control system, a model without a display is sufficient.
What does an accuracy of ± 0.3% of full scale mean?
This means that the maximum deviation of the measured value from the actual pressure value is no more than 0.3% of the total measuring range end value. It is a measure of the high precision of the sensor.
What happens if the pressure exceeds the measuring range?
Our transmitters are equipped with overload protection and can withstand pressures far above the nominal measuring range for a short time without being damaged. The exact values for the overload and burst pressure can be found in the respective data sheet.
