E
PI
S
ENSOR
2
U
SER
M
ANUAL
D
OCUMENT
305801,
R
EVISION
A
corrects its offsets. When continuously powered, the sensor retains the same offset removal current
setting.
AUTOZERO requires higher quiescent power consumption (about 120 mW extra), and it increases self-
noise levels. Unless the user has special requirements (e.g., using a very low dynamic range digitizer
requiring the use of input preamplifiers),
we recommend leaving the AUTOZERO in its OFF state. Any
modern digitizer, as well as many data analysis algorithms, are not affected by DC-offsets in the signals,
or in the digital data.
Calibration (CAL)
Calibration is seamlessly supported through the digitizer connection. This includes a digital control line
for connecting the (differential) calibration input signals to the sensor elements, and use of the voltage
sources provided by the digitizer. For the EpiSensor2 (with DC-320+Hz bandwidth), random noise is an
excellent calibration stimulus source.
Retention of Settings
The current full-scale range and AUTOZERO status (ON or OFF) is stored in EEPROM within the sensor.
These settings are updated whenever the status is changed by the user (or the digitizer). Upon a system
Power-ON-RESET, or simple RESET, the sensor is restored to the the stored operating configuration. The
calibration status, however, is volatile. Following any RESET event, the calibration mode must be re-
entered using either the digitizer enable line, or an RS-232 command.
Sensor Response Values
Each sensor element is trimmed during manufacture, to provide a standard scalar response (Volts/g) on
each of the five (operating ranges). In addition, each sensor axis is trimmed to ensure that its response
bandwidth falls within a set range (-3 dB amplitude point at or above 320 Hz).
The scalar responsivity (G) is stored on the “RESPONSE” page that is described below. A command query
on this page (“status” command) will return the scalar response values for each element, at the current
full-scale range setting.
The Episensor2 frequency response can be described well by a simple set of conjugate pole pairs:
P1 =
-700+/-1250j (radians/second)
P2 = -1340+/-3350j (radians/second)
The full response is defined as:
V (s) = G |P1|
2
|P2|
2
(
s
– P1)(
s
– P1*)(
s
– P2)(
s
- P2*)
where G is the scalar responsivity (Volts/Standard g). (A standard g is defined as 9.81 m/sec
2
).
Input Power Requirements
The EpiSensor2 operates from a wide (9-36V) input supply range. The quiescent power consumption
(input power in the absence of significant seismic signals, with all LED indicators OFF, and with the RS-
232 interface disconnected) is under 350 mW. Typically, the current draw is 25 to 28 mA @ 12V.
Power consumption is temporarily higher when LEDs are illuminated. Also, a persistent RS-232
connection increases power consumption by 10 to 20 mW.
Page 13
August 2015