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Working with Responses to Get Units of Ground Motion

Necessary information:

Sensor: sensitivity and passband (velocity transducer) or scaling (accelerometer)

Datalogger: Analog-to-Digital (A/D) conversion factor (aka bit weight) and Gain 

  • Quanterra model Q330: 419,430 counts/volt, or 2.384 uV/count at a Gain of 1
  • RefTek model RT130: 629,327 counts/volt, or 1.58997 uV/count at a Gain of 1


Example: Counts to Ground Velocity Conversion within the Passband


The appropriate conversion within the passband would be:


    Amplitude(counts) * A/D conversion factor(V/counts)
ground velocity (m/s) = ----------------------------------
    Gain * Sensitivity (V/m/s)


Suppose your sensor is an STS-2 and your datalogger is an RT130 with its Gain set to 1.


      (1.58997E-06 V/counts)
ground velocity = Amplitude(counts) * --------------------------------
      1 * (1500 V/m/s)


For information on SENSOR sensitivity and passband, see the Sensor Comparison Chart along with the Sensor Response Plot.