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Previously known as “Input Mode” the SIG+ Mode setting tells the Gecko whether or not
power needs to be applied to the sensor channel positive wires (pins C, E, G and S on the
Gecko sensor connector). For most sensors, this mode should be set to “Normal”, but if you
are using an IEPE sensor, you can select “25V” which will put a 25V of DC power at 4mA out
to the sensor channel.
WARNING! Enabling SIG+ 25V output to non-IEPE sensors may damage your sensor
Previously known as “Sensor Wiring” the SIG- Mode tells the Gecko whether the sensor
channel negative wires (pins D, F, H & T on the sensor connector) need to be connected to
power ground or not. Most sensors require you to measure the difference between the
positive and negative wires, so the “Normal” setting would be used in most cases. If your
sensor requires the negative channel wire to be connected to power ground (e.g. for IEPE
sensors) then select “Ground”.
The DC Offset filter when enabled electrically removes signal offset by introducing a low
order high pass (~1.6Hz) frequency filter. For most sensors, it is best to leave this setting
as “Normal”. Do not enable this filter for long-period or broadband seismometers.
Some sensors (e.g. IEPE accelerometers) only output positive voltages, often over a 0-5V
range. At rest the signal will often sit at mid point of this range (known as “Bias voltage” but it
can be anywhere from about +2.5V to +12V DC. As the sensor moves, the voltage output
moves up or down from this DC offset by up half of the sensor’s range. The Gecko can remove
a number of counts from the signal after digitisation, but half of the -20V to +20V input range
of the Gecko is wasted. By enabling the DC Offset Filter, the pre-digitised signal is brought
down to almost 0V, and the digitised signal then moves between negative and positive
voltages around the zero level. This allows you to use a higher Input Amplifier setting (for
example of x8 to stretch a ±2.5V range to the Gecko’s full ±20V) to utilise the full dynamic
range of the Gecko’s 24-bit resolution.
Sensor Serial No.
A 20-character field is available to record your sensor’s serial number. This information is
stored in the station status text file for future reference. Upper and lower case letters,
numbers, and some special characters are available.
Mass Lock, Unlock, & Centre
Guralp 3-series seismometers have motorised mass controllers that allow the delicate
sensor components to be locked in place for transport and unlocked after installation. See
the sensor manual for more information. Activating Lock , Unlock and Centre controls
simply connects the corresponding pin on the sensor connector to Ground for 5 seconds, so
the feature could be used for other purposes if required.
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