Guralp Systems CMG-5T Compact - Manual (Page 9)

Operator's Guide
instrument makes it suitable for use in hazardous environments where
electrical discharges due to the build up of static charge could lead to the
ignition of flammable gasses. To ensure safe operation in these
conditions, the metal case of the instrument must be electrically bonded
('earthed') to the structure on which it is mounted, forming a path to
safely discharge static charge.
Where electrical bonding ('earthing') is required during the installation of
a 5T Compact instrument, the central mounting hole that extends
through the instrument should be used as the connection point. This is
electrically connected to all other parts of the sensor case. Connection
can be made by either a cable from a local earthing point terminated in a
8mm ring tag or by the mounting bolt itself.
2.4 Removing offsets from the 5T Compact
Once installed the sensor needs to be as level as possible to ensure the
output offset is minimised. Levelling is carried out by adjusting the feet
until the bubble level on the top of the sensor has the bubble completely
within the scribed ring.
When power is applied to the CMG-5T Compact, offset adjustments are
carried out automatically.
For more information on offsets go to:
http://www.guralp.com/articles/20060315-howto-sensor-zeroing
Should there be a need to reset the offsets, the simplest method is to
power cycle the sensor. If this is not possible the following methods can
be used.
2.4.1 Manual offset removal
Early versions of the CMG-5T Compact had a port in the
sensor lid to allow for manual offset adjustment. If the
sensor has a knurled screw cover then there is a manual
offset adjustment option.
1. Remove the screwed cover protecting the level adjusters. The
cavity contains three adjustment screws.
2. Power up the sensor and connect a digital multimeter to its low-
gain vertical outputs (pins A and B). Alternatively, use a
Hand-held Control Unit (see Section 2.5, page 11) to monitor the
outputs more easily.
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