D
OCUMENT
301900,
R
EVISION
D
E
PI
S
ENSOR
U
SER
G
UIDE
11
2.
Gently
insert a hex ball (5/64" or 2mm) wrench,
perpendicular to
the case,
as far as it will go into the adjustment hole and make very
minimal adjustments – counterclockwise for negative adjustments
and clockwise for positive.
Important:
Give the unit a moderate tap with a screwdriver
handle. The adjustment screws can have a residual
stress that may cause an offset in data during a large
earthquake. Tapping eliminates this residual stress.
3. When the offset is in an acceptable range based on the above table,
carefully remove the hex wrench and replace the access hole screw.
Note
: One turn changes the output by about 1g.
Repeat this process for the X and Y axes.
Table 1: Reasonable zero offset voltages
Full-scale
range
Single-ended
"
2.5V output
Single-ended
"
10Voutput
Differential low-
noise amp.
Differential
"
20V output
1/4g
50 mV
200 mV
100 mV
400 mV
1/2g
25 mV
100 mV
50 mV
200 mV
1g
25 mV
50 mV
25 mV
100 mV
2g
25 mV
25 mV
25 mV
50 mV
4g
25 mV
25 mV
25 mV
25 mV
Note on Full-Scale Range
All of our full-scale ranges are stated as the voltage you would measure
with a voltmeter between the + and – outputs for the sensor when full-scale
acceleration is applied to the unit. For example, with a differential low-noise
amplifier and output of
"
20V on a range of 1g, you would m20V if
you applied 1g to the sensor. If you applied –1g you would measure –20V.
Thermal Insulation Shield
(Optional)
The EpiSensor possesses a very large dynamic range and increasingly we
are finding customers are interested in recording both strong motion and
weaker motion signals on the instrument. To fully exploit the performance
of the instrument for recording weak motion it is necessary to treat it more
like a broadband seismometer than a strong motion accelerometer! One
important area is to thermally insulate the unit so that variations in ambient
temperature and air currents do not cause “noise” by causing temperature
