LRS Micro-g LaCoste FG5, Manual, Page: 89 / 149

Adjustment and Maintenance
4
4.6.1.2.MOTOR DRIVE SELECTION
The motor driver circuit can be selected by an external switch with five positions:
OFF, WINDOW, AUTO, REMOTE, and MANUAL. This controls a DC motor
which can position the top of the main spring relative to the main bracket. The
position may need to be adjusted as the main spring slowly stretches over time,
or due to temperature or gravity changes. The DC motor can lift (lower) the test
mass so that the sphere position becomes more positive (negative). This motor
should only be used to position the mass but should not be activated during the
Superspring operation as a long period isolation device.
4.6.1.2.1.OFF
This setting disables the DC motor that positions the top of the main spring. The
Superspring should be left in this mode when the active servo is activated.
4.6.1.2.2.AUTO
The Superspring controller will try drive the DC motor using a feedback loop so
that the sphere signal is zero.
4.6.1.2.3.WINDOW
The Superspring controller will activate the motor when the sphere voltage is out
of range (larger than the window setting). The motor drives the sphere voltage to
zero and then is turned off. In principal the Superspring can be left in this mode
but it could re-zero during a measurement causing excess noise.
4.6.1.2.4.REMOTE
The Superspring can be made to zero using an external TTL signal.
4.6.1.2.5.MANUAL
In manual mode, the spring motor is controlled by the potentiometer (pot) on the
front panel. A setting greater than 5 will move the spring up less than 5 will
lower the spring. Moving the spring up will case the BNC Sphere out to move in
a positive direction while down will move voltage output in a negative direction.
4.6.1.3.Active Servo
The
filter is a band pass accomplished with a high pass (HP) and then a low pass
(LP) filter. The Q-value and frequency of each filter is adjustable via the on-
board trim pots. The phase lead and lag and the servo gain are also adjustable.
2
2
Nelson P.G., An Active Vibration Isolation System for Inertial Reference and Precision Measurement ,
Rev. Sci. Instrum., 1991, 62 , 2069-2075.
4-33