Input Amplifier - Gecko Compact Product User Manual

Input Amplifier

The Gecko is, fundamentally, a high speed, high resolution Voltage data logger. It measures
the voltage across each channel's pair of wires, and it can measure from -20V to +20V DC
at 24-bit resolution. This 40V peak-to-peak range is read as a 24-bit number, producing a
value between 0 and 16,777,216 counts, which equates to 419,430.4 counts per volt.
If you are using a sensor with a 40Vpp output (for ±10V differential output sensors, such as
Nanometrics or Guralp seismometers) set the gain to x1.
If you have lower voltage output sensors, use the input amplifier to utilise the full dynamic
range of the Gecko - e.g. ±5V IEPE accelerometers or ±4V MEMS accelerometers (as used
in the Gecko SMA), could use a gain of x4 to stretch those output to ±20V or ±16V
respectively to record at higher resolution. Note that ground offsets will also be amplified.
If you are using a passive sensor (e.g. geophone) you can use even higher gains to see
smaller signals at higher resolution. For example, the Gecko Tremor's geophones (standard
sensitivity of 78.74 V/m/s) normally have a clip level of 254mm/s, but by using a gain of
x16 you can see smaller signals and get a similar effective sensitivity (1260 V/m/s) and clip
level (16mm/s) as a typical short period active seismometer.
Input Range
x1 (40Vpp)
> x2 (20Vpp)
x4 (10Vpp)
x8 (5Vpp)
x16 (2.5Vpp)
x32 (1.25Vpp)
x64 (625mVpp)
x128 (313mVpp)
x256 (156mVpp)
x512 ( 78mVpp)
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