Griekspoor piston positioning system LPM® (Linear Positioning Measurement)

The Griekspoor Linear Positioning Measurement system (LPM) is composed of a combination of one special sensor and a rod with a specific profile below the coating surface. There are two magnetic strength transducers in the sensor that “look” through the coating to the underlying rod profile. When the rod moves in either direction the transducer generates an incremental block signal that is processed in a counter.

Each transducer in the sensor immediately produces a block signal. The combination of both transducer signals give a 90° shifted block-patterned signal. This signal can be processed by standard available reading units and counters, because the signal is similar to that of an incremental rotary encoder or pulse encoder.

Edge detection causes quadrupling of the signal providing direction recognition. After all, when reversing direction, the sequence of “0” and “1” changes. The level of the signal depends on the supply voltage used for the sensors. The required supply voltage has to be at least 10VDC and at most 30VDC (28VDC maximum with ATEX-version, ATEX certificate: BVS 07 ATEX E 030 II 2 G Ex ib IIB T).


Important parameters:

Power supply: +10.. 30 VDC
Max. output current per channel: 40 mA (Block signal, short-circuit resistant)
Output frequency: 0.. 25 kHz
Measuring Distance*: 0.5 ± 0.3 mm compared to coating
Working temperature: - 40° to +125°C
Protection class: IP68
Max. cable length (without amplifier): 100 metres
Housing: Stainless steel, material 1.4305
Compressive strength (measuring side): 5 bar.
Max. vibration acceleration (EN61373): 200 m/s2
Shock resistance (EN61373): 2,000 m/s2

* Recommended measuring clearance for 0,3mm coating thickness

Cable selection for the position measuring system

When used under harsher conditions (in and on the ground, with the likelihood of mechanical stress, mud, etc.) is recommended to equip the sensor with a PUR cable. (Choice of type key is “N”). The cable's outer casing will then consist of Radox EM104. This is one of the best materials available for a cable jacket.

Exceptional properties for harsh environmental conditions

Radox is a specially developed insulation material that is highly resistant to thermal, chemical and mechanical loads. These specific material properties are achieved when the molecules of the plastic are three-dimensionally and mutually cross-linked by an electron beam. Radox materials are also resistant to abrasion, ozone, and UV radiation, are dimensionally stable, flexible, have very little shrinkage and a long lifespan. Thanks to the halogen-free Radox EM104 outer sheath, these can be used with high and/or low temperatures, and they are fire resistant. In the event of a fire, these cables will remain operational for at least 180 minutes.


NEK 606: 2004 (Norwegian industry standard for Offshore Oil and Gas, Ship & Marine)

  • IEC 60092-359 SHF1 (Electrical installations in ships)
  • IEC 60092-359 SHF2 (Electrical installations in ships)
  • IEC 60331-25 (Remain operational for 180 minutes)
  • IEC 60332-1-2 (Fire extension)
  • IEC 60332-3-25 (Fire extension)
  • IRM 902 (oil resistance)
  • SHF Mud (oil resistance IRM 903, Calcium Bromide Brine, Carbo Sea)
  • Temperature range of -40 °C to +120 °C

More information?

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