Download FG5 Absolute Gravimeter User`s Manual - Micro

Micro-g LaCoste FG5 User’s Manual
4 Adjustment and Maintenance
With proper and careful setup and operation, the FG5 should provide accurate and
reliable results. However, if you suspect that there is a problem, before attempting
repairs or adjustments yourself, it is usually a good idea to first contact Micro-g LaCoste
at
www.microglacoste.com/contact.htm
So, while a full list of all adjustments is beyond the scope of this manual, listed below are
some common issues, their explanation, and their resolutions…
4.1 Superspring
Superspring problems usually manifest themselves as either an inability to zero properly
or through high drop scatter and strange residuals. In some cases it will be necessary to
open the Superspring to ascertain the source of the problem.
4.1.1 Removing the Superspring Cover
If it is necessary to open the Superspring, place it in its tripod, level it, make sure it is
travel locked, and loosen the 6 screws at the bottom of the main can, and remove the
whole can and lid straight up together. Note that there are punch marks to indicate
the orientation of the can relative to the Superspring base.
Note. Do not open the cover by removing the bottom flange! This will damage the
internal electrical connections through the service ring.
4.1.2 The Spring Position is off the Detector
If, for some reason, the mass is extremely far from the center of its range (e.g. due to
an extreme change in either temperature or local gravity), the spring controller may
appear to be behaving incorrectly: it may appear to go the “wrong way” (e.g. more
negative, even though the motor is set to lift the mass – See Figure 12). This is
because all of the light from the LED is not actually on the detector. As more light
misses the detector (either going off the top or bottom), the absolute value of the
voltage becomes less and less, making it appear that the spring is nearer zero than it
actually is. (Note that this problem is handled automatically in the newer
Superspring controllers.)
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