LRS Micro-g LaCoste FG5, Manual, Page: 98 / 149

Troubleshooting
5
5.2.3.SUPERSPRING
A Superspring problem usually results in gravity data with a large drop-to-drop
scatter. A chart recorder is very helpful in monitoring the status of the
Superspring. A two channel recorder can monitor both sphere and coil output.
However, if a one channel recorder is used, it is best to monitor coil output. A
plot of the coil output can also be helpful in identifying seismic activity or
unusually large environmental noise, which produce a larger than average drop-
to-drop scatter. During setup, the operator should exercise care in leveling the
Superspring. Also, if the change in gravity from one site to the next is very large,
it is common for the test mass to be out of range (as indicated by an LED on the
front panel of the Superspring controller). If the change in gravity from the most
recent station to the present one is positive and the sphere is out of range, the
spring will be low and should be driven up into range. If the change in gravity is
negative, the spring should be driven down into range. It is always very
important to monitor the voltage at the front panel BNC of the Superspring
controller marked SPHERE OUT while the servo loop is still open. The sphere
position should be moving substantially (+/- voltage) when the loop is open and
the Superspring is unlocked. This indicates that the test mass is hanging freely.
See Chapter 3, paragraph 53-54 for more details. Table 5-3 lists possible
problems and solutions pertaining to the Superspring.
Problem Solution
Test mass can be driven in one
direction but cannot be adjusted in the
other direction. Limit switch is limiting the motion.
The solution is either to widen the
range for the limit switch or adjust
the coarse position of the main
spring using the nut on the top of
the flexure.
Sphere shows no oscillations when
unlocked and cannot be driven into
range. Upper flexure on main spring is
broken and needs replacement or a
delta rod bent.
Spring sphere signal looks quiet but the
gravity data is still noisy as if the
Superspring is not isolating.
The mass is not in range of the
detector.
The Superspring is still locked.
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