D
OCUMENT
301900,
R
EVISION
D
44
E
PI
S
ENSOR
U
SER
G
UIDE
The Etna
The only reason to use the differential output with the Etna is to take
advantage of its superior common-mode rejection in a high noise
environment.
When using the differential output, the EpiSensor will need either a separate
power supply or should use its single supply option and take power from the
Etna’s +12V. This is because the Etna can supply only +/-40mA on each
+12 and –12V power line.
The K2 & Mt. Whitney
The 6-channel K2 and Mt. Whitney can supply 75 mA from the +12
and –12V power lines for the sensors and any gain boards. Gain boards
draw approximately 5mA per rail. There is more than enough power for a
single EpiSensor connected to a 6-channel ADC/DSP board with additional
gain boards.
If you wish to use two EpiSensors on a 6-channel board you need to work
out the current requirement as shown in Table 10. In general, the system
will probably supply adequate quiescent current for both sensors with low-
noise amplifiers enabled, but there may be a problem with the dynamic
current at high g levels.
If this is the configuration you wish to use, we suggest using one of the
following solutions:
!
Run only one of the EpiSensors on the low-noise setting
!
Contact Kinemetrics about modifying the ADC/DSP board to
supply more power
!
Use the single supply option on the EpiSensors, powering the units
from the +12V battery power on the K2 or Mt. Whitney
!
Build your own power supply unit
Dual Gain Systems
Some users may want to use an EpiSensor and a 6-channel K2 with gain
boards as a dual gain system – for example, to record 2g strong motion on
channels 1 to 3, and a high gain channel on channels 4 to 6. To do this you
will need to build a special "Y" cable that allows one triaxial sensor package
to be connected to two-recorder input connectors.
The first of these is wired exactly per the instructions in this chapter. The
second only wires the signal connections for the X, Y, and Z outputs from
the EpiSensor. Set the EpiSensor for low-noise 20V differential output. On
the gain board for channels 1 to 3 (strong motion) set the gain board as an
attenuator with a gain of 0.125 and the gain to 1. See the gain board manual
for instructions on setting the gain board. This will reduce the 20V
differential input to the 2.5V input required for the ADC at full-scale.
