This document discusses using eddy-current displacement sensors to actively dampen unstable running characteristics in liquid-filled industrial centrifuges. The sensors, oriented 90 degrees to each other, measure the deflection of the centrifuge rotor, which is used as input for controllers regulating a magnetic bearing. Key reasons for using this system are the non-contact measurement, high accuracy and temperature stability, 10 kHz bandwidth, and insensitivity to strong magnetic fields.

1. A086_e
Eddy-current displacement sensors
eddyNCDT
Active damping of liquid-cooled centrifuges
At certain configurations of speed, filling level and Technical details
design parameters, liquid-filled industrial centrifuges - Measuring range: 2,000 µm
tend to produce unstable running characteristics - Resolution: 1 µm
which can lead to failure of the centrifuge. The - Accuracy: 4 µm
instability, which arises due to interaction between - Bandwidth: 10 kHz (- 3dB)
the fluid and the centrifuge, cannot be rectified by
passive means (dampers), so therefore the instability Ambient conditions:
is corrected actively with the aid of a magnetic - Temperature: 15°C to 25°C
bearing and suitable closed-loop controllers. The - Medium: airI
deflection of the rotor, which is acquired with two - Interference fields: strong magnetic fields
eddy-current sensors orientated at 90° to one
another, is used as input information for the
controller. System setup
2 x S2 1 x OS510
Reasons for the system selection: 2 x C3 2 x DL 504
- Non-contact measurement 2 x BC - S2m 6 x FP 507
- High accuracy and temperature stability 1 x RS 584
- Bandwidth 10 kHz (-3 dB) 1 x DD 500
- Insensitive to strong magnetic fields
eddyNCDT
sensors S2
rotor
PC
controller-
card
magnetic
bearing
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