7
3 GROUND LOOPS
The single greatest danger to your nanopositioning system is a ground loop between the
stage and the mounting surface. Ground loops can be the source of noise in the HS1,
and in some cases the oscillations may be severe enough to permanently damage the
piezoactuators.
3.1 Prevention and identification of ground loops
Ground loops may sometimes be detected by a digital Voltmeter and can usually be
detected by using the differential mode of a dual channel oscilloscope.
Prevention of ground loops can be achieved in two ways. An effective and simple
method is to insulate the stage from the mounting surface (e.g. mylar or paper between
the stage and the mounting surface combined with non-conductive mounting screws).
The second method is to connect the PIEZOCONCEPT's controller
ground to the
mounting surface. The stage is connected directly to the ground of the
PIEZOCONCEPT's controller, which in turn is connected to the ground of the AC power
cord. The PIEZOCONCEPT's controller
enclosure is also at ground potential. Attaching a
grounding wire between any of the PIEZOCONCEPT's controller
enclosure screws and
the mounting surface may short-circuit the ground loop. In a few cases, this may not be
an effective method. When this occurs, please identify high current sources returning to
ground through your mounting surface. Mounting surfaces should never be used as the
electrical ground current path for any instrumentation (such as vacuum pumps,
computers, etc.).
Should you observe unexpected oscillations in your nanopositioning stage after you have
switched on the power, this likely indicates the continued presence of a ground loop or
excessive sample mass (see Section 2).
SWITCH THE SYSTEM OFF IMMEDIATELY
AND SEARCH FOR THE SOURCE OF THE GROUND LOOP. SHOULD THE
PROBLEMS CONTINUE PLEASE CONTACT PIEZOCONCEPT FOR TECHNICAL
ASSISTANCE.
4 OPERATING THE NANOPOSITIONING STAGE
The HS1 comes complete with a position sensitive detector for closed loop operation. In
closed loop operation, achieved using the PIEZOCONCEPT controller, the effects of
creep and hysteresis are removed and the position is held constant at the command
position.
4.1 Operating in closed loop mode
The HS1 comes with a 9 pin D-type connector and uses the PIEZOCONCEPT's
controller
for complete positioning control. To operate in closed loop mode use the
following procedure :
•
Install the HS1 as discussed in
Section 2
.
•
Turn the PIEZOCONCEPT's controller
power off.
