Precise Position Monitoring

Inductive position sensors enable non-contact, precise position measurement in industrial systems. They are used, among other things, for valve and actuator monitoring in demanding environments.

Reliable position measurement is a key requirement for safe and stable operation in many industrial facilities. In particular, monitoring valve positions, actuator movements, and structural displacements plays a crucial role in this regard.

Inductive position sensors have been used successfully for this purpose for many years. Their non-contact measurement principle enables precise detection of linear movements while minimizing mechanical wear. Thanks to their robust design, they are particularly well-suited for demanding operating environments such as power plants, industrial machinery, and infrastructure systems.

The sensors discussed here are manufactured by Schreiber Messtechnik and distributed by abj sensorik, which also provides application engineering support, including on an international scale.

Use in Power Plants and Valve Monitoring

A classic application for inductive position transducers is position feedback from control valves in power plant systems. These include, in particular, high-pressure steam bypass valves and water injection valves in steam turbines.

The valve position must be precisely measured across the entire stroke range and transmitted to the plant control system as a standardized signal, such as 4 to 20 mA. This results in high requirements for accuracy, temperature stability, ease of installation, and reliable long-term operation.

Since mechanical tolerances can occur within the valve mechanism, individual adjustment of the measurement ranges is often necessary. Programmable position sensors allow this to be done directly during commissioning via a teach-in procedure.

Measurement Principle and Robust Sensor Architecture

Inductive position sensors operate on the differential inductance principle (half-bridge). The position of a moving core changes the inductance of two coil sections. This change is detected electronically and converted into a proportional output signal.

The design comprises a hollow coil body with symmetrically wound coils, a high-permeability magnetic shield, a stainless steel housing, and a movable push rod with a nickel-iron core. The entire interior is filled with potting material, resulting in a particularly robust and sealed sensor design.

The non-contact measurement principle prevents mechanical wear and ensures a long service life as well as stable measurement results. The movable core has no stop and can be fully withdrawn from the sensor without causing damage.

Signal Processing and Flexible Integration

In programmable versions, the analog measurement signal is digitized via a 16-bit A/D converter and processed by a microcontroller. Corrections are made based on calibration data stored in an EEPROM. The signal is then converted back into standardized output signals, such as 0(4)–20 mA or 0–10 V, via a 16-bit D/A converter.

The measurement range can be flexibly configured using a teach-in procedure, allowing different mechanical strokes to be mapped using identical sensor types.

Various designs are available for mechanical integration, such as articulated joints, protective tubes, or probe pins with return springs. Electrical connection is provided either via plug-in connectors or potted cables up to protection class IP68. Typical supply voltages range from 10 – 32 VDC with a measurement accuracy of approximately 0.1 %.

Versatile Industrial Applications

In addition to valve monitoring in power plants, inductive displacement transducers are also used in many other applications. These include position feedback for mechanical actuators, the detection of lever movements, feedback systems in hydraulic proportional valves, and test benches for vibration and material testing.

Their combination of robust construction, high accuracy, and wear-free operation makes them particularly well-suited for applications where long-term stability and reliability are critical.

Conclusion

Inductive displacement transducers are a proven technology for precise position and displacement measurement in industrial systems. Thanks to their non-contact measurement principle, robust construction, and flexible measurement range adjustment, they can be integrated in a variety of ways.

Sensors from Schreiber Messtechnik, distributed by abj sensorik, are used worldwide in applications where reliable position monitoring must be ensured over the long term.