Guralp Systems CMG-40T - Manual (Page 9)

Operator's guide
Calibration
You can calibrate a 40T sensor through the HCU by connecting a signal
generator across the yellow and green CALIBRATION SIGNAL inputs and
setting the adjacent switch to ON. The sensor's response can now be monitored
or recorded, and calibration calculations carried out. See
Chapter 4, “Calibrating
the 40T” for full details.
Control commands
If you have ordered a 40T with the remote null facility, you can zero its mass
position offsets from the HCU.
1. Select the component you want to centre from the CENTRING SELECT
dial.
2. Switch the signal meter dial to one of the MASS POS settings.
3. Switch the rightmost switch to 1 SEC VEL to enable the centring lines.
4. Press the +/– switch towards – to centre a mass from a positive value, or
towards + to centre it from a negative value.
Banana plugs
The remainder of the HCU provides useful connections for each of the signal
lines from the instrument, for attaching to your own equipment as necessary.
2.3 Zeroing the instrument
Before installing the 40T, you should check that the mass positions are not
significantly offset from zero. The mass position offsets can be affected by any
tilt to the instrument, as well as handling during transportation. The normal
range of the mass positions is ±10 V; you should zero the instrument if any
mass reads more than around ±3.5 V when the sensor is stationary.
The velocity outputs of the 40T are set at the factory to a nominal value below
±3 mV. Once the instrument is installed and has reached thermal equilibrium
with its environment, these outputs should be similar to the factory-set value.
Adjusting the mass position offsets manually
The 40T has three potentiometers (“pots”) accessible within its casing, which
should be used to remove any DC offsets electronically:
1. Bring the instrument into 1 second response mode by applying a voltage
across the Acc/Vel and Signal Ground pins of the input. If you are using
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