Stability and Linearity of PI Capacitive Position Sensors PI capacitive position sensor electronics incorporate a proprietary design providing superior linearity, low sensitivity to cable capacitance, low background noise and low drift.
The Integrated Linearization System (ILS) compensates for influences caused by errors, such as non-parallelism of the plates. A comparison between a conventional capacitive position sensor system and the results obtained with the PI ILS is shown in Figure 2 on this page. When used with PI digital controllers (which add polynomial linearization techniques) a positioning linearity of up to 0.003 % is achievable.
Figure 3 shows the linearity of a P-752.11C piezo flexure nanopositioning stage with integrated capacitive position sensor operated in closed-loop mode with an analog controller. All errors contributed by the mechanics, PZT drive, sensors and electronics are included in the resulting linearity of better than 0.02 %. Even higher linearity is achievable with PI digital controllers, see the E-710 on pp. see link ff.
The exceptional long-term stability of the PI capacitive position sensor and electronics design is shown in Figure 4.
Drawings & Images:
Fig 1. P-752.11C, 15 µm piezo nanopositioning stage with integrated capacitive position sensor.
Fig 2. Linearity of conventional capacitive position sensor system vs. PI ILS (integrated linearization system), shown before digital linearization.
Fig 3. Linearity of a P-752.11C, 15 µm piezo nanopositioning stage operated with E-500/E-509.C1 control electronics. The travel range is 15 µm, the gain 1.5 µm/V. Linearity is better than 0.02 %; even higher linearity is achievable with PI digital controllers.
Fig 4. Measurement stability of an E-509.C1 capacitive position sensor control board with 10 pF reference capacitor over 3.5 hours (after controller warm-up).
