Hydraulics

Trafag pressure transmitters are used in applications from heavy construction and agricultural equipment to high accuracy test benches. They are proven for long term stability in extremely harsh environments from the dusty heat of deserts to the icy cold of sub-arctic forests. The reliable pressure transmitters with great long-term stability are highly prized for stationary hydraulics as well, for they avoid costly production interruptions.

Trafag’s products are used in hydraulics, for example:

• Agricultural and forestry machines
  Tractors, harvesting machines, transport machines
• Renewable energies
  Rotor control in wind power plants, solar tracking for photovoltaic systems
• Construction machines
  Excavators, mobile cranes, concrete pumps and mixers
• Communal and special vehicles
  Garbage collection, heavy transporters, firefighting vehicles
• Machine and plant construction
  Injection moulding machines, forming presses, stretch-blow machines
• Test and inspection installations
  Chassis test benches, material inspection systems, inspection of hydraulic components
• Hydraulic components and subsystems
  Valve block systems, power packs, tank monitoring

Pressure sensors for hydraulic applications - sometimes also called pressure transmitters or pressure transducers, (see also Pressure transmitters) measure the pressure of the medium hydraulic oil in valves, pumps, cylinders and pressure accumulators, etc.. They are therefore central elements for the control and regulation of hydraulic systems. These systems are often components of large and expensive machines or plants, where a standstill or even failure would have far-reaching consequences. For this reason, pressure transmitters for hydraulics must always function reliably - even under harsh conditions. Therefore, the robust design is very important.

Hydraulic applications are divided into two categories: The category of stationary hydraulics includes areas of application such as machine tools or lifts. The category of mobile hydraulics includes, for example, construction machinery and municipal vehicles.

Many requirements apply to both stationary and mobile applications. In mobile hydraulics, additional challenges must be mastered due to the harsh environmental conditions.

In hydraulic applications, a fluid pressure is generally measured, usually the pressure of the hydraulic oil. Because the fluid is only slightly compressible, pressure peaks caused by the system and the application are transmitted to the sensors almost unfiltered as hard shocks. This short-term, enormous pressure load can cause the sensors to be damaged or even burst. As a countermeasure, most manufacturers integrate so-called pressure peak damping elements in the pressure bore of the sensor. Because these have a smaller opening than the pressure bore in the part of the pressure transmitter that encounters the medium, they act like an orifice in front of the diaphragm and thus in many cases provide initial protection for the sensor against brief pressure surges.

In the case of extreme pressure surges, however, the damping elements are no longer sufficient, and the diaphragm must be built more robustly. The overpressure resistance, which is twice the measuring range or nominal range for commercially available pressure sensors, serves as the measured variable for the robustness of the diaphragm against pressure surges. Hydraulic pressure sensors from Trafag offer an overpressure resistance of three times the nominal pressure as standard, and an overpressure resistance of five times the nominal pressure is even available as an option.

Further information on the topic of "pressure peaks" and how pressure sensors can be protected against pressure peaks can be found here:

The high pressure in hydraulic systems places high demands on the mechanical strength and precise manufacture of the components of the pressure transmitter: For example, the connection parts must be precisely manufactured to ensure the seal with the counterpart and to prevent oil from escaping. In addition, the stainless steel used for the connection must have the necessary strength to withstand the acting forces even after several years of use under harsh environmental conditions.

The connection parts and diaphragms of the pressure sensor are made of stainless steel and are very compatible with the common hydraulic oils. Only in the case of elastomer seals is it necessary to ensure that the sealing material used is also compatible with the contacting oil. This applies not only to the seals in the process connection, but also to the seals on the housing and in the plug. This is because escaping oil, resulting from leaks or contamination during repair and maintenance work, can cause external components to come into contact with the oil as well.

The measured value is transmitted to the control via the output signal. Most in use are transmitters with the analogue output, such as 4 ... 20mA, because this is very cost-effective. However, digital signals, such as IO-Link or CANopen, are becoming more and more popular. They offer additional advantages besides the measured value evaluation. Because of their greater immunity to electromagnetic interference, digital signals offer the possibility of transmitting other parameters in addition to the measured pressure value, such as the device or media temperature (provided a temperature sensor in the transmitter makes the measured values available). In addition, digital signals can also transmit diagnostic data, which can be used for condition monitoring, for example.

Parameterisation is also very easy via the digital interface. It is of particular importance for pressure transmitters that have one or more switching outputs or for devices with a display. Trafag offers a pressure transmitter series (DPC 8380 and DPS 8381) with display. Various parameters can be configured easily and quickly via the smartphone app and the NFC interface on the display. In addition to the parameters for the switching outputs and the display, the measuring range can also be easily adjusted. In addition, the analogue output can be switched from a 4 ... 20 mA current signal to a 0 ... 10 VDC voltage signal. The data of the integrated logger can also be obtained via this interface.

Learn more about the parameterisation of pressure sensors with display in these whitepapers:

Mobile machines are used in harsh environments where significant shocks and vibrations are common This can lead to inappropriately selected pressure sensors providing inaccurate readings or even failing altogether. To reliably withstand vibrations, the internal structure of the pressure transmitters must be designed and produced to be correspondingly reliable. This is where Trafag pressure transmitters stand out with their reliable construction and connection techniques. Thanks to the high level of integration of many functionalities in the Trafag ASIC, the microchip developed in-house and ideally matched to the Trafag pressure sensor, the electronics of Trafag pressure transmitters require fewer components and are therefore more robust in the face of vibrations and therefore less prone to faults.

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