Calibration - Reftek REF TEK Colt User Manual

Rev D

8 Calibration

Three in-series calibration coils, one for each component of the REF TEK Colt, are used
to examine or test its response. The calibration input signal is isolated from the
seismometer calibration coil by a relay that is switched on while the Cal Enable Pin is
pulled to ground (activated).
NOTE: When the Cal Enable pin is pulled to ground (activated), the
seismometer output automatically switched from orthogonal (Z/Y/X) to
symmetrical (U/W/V) outputs. When calibration is over and the Cal Enable
pin is pulled high (deactivated) the seismometer outputs will automatically
switch back to orthogonal (Z/Y/X) outputs.
Two kinds of calibration signals are commonly used:
•
Step Signal (wide pulse signal) – Used to check the self-resonant period of the seismometer.
•
Sine Signal – Used to check amplitude characteristics.
The expected seismometer output for a sine wave calibration input signal can be
calculated with the following formula:
Vpp_output = (Cal_Sensitivity * Sensitivity / frequency / 2 / pi) * A_input
Where:
Cal_Sensitivity = Calibration Sensitivity value from the supplied REF TEK Colt Datasheet.
Sensitivity = Seismometer UWV output sensitivity value from the supplied REF TEK Colt Data
Sheet.
Frequency = Frequency of the calibration sine wave input.
A_input = Calibration voltage input (Peak-to-Peak) / Resistance of the calibration coil
NOTE: Calibration coil resistance is different for different serial numbers
60 second
120 second
NOTE: The sensitivities provided on the Datasheet are on a per channel
basis, so the expected seismometer output signal can be calculated for each
channel.
Reftek Systems Inc.
REF TEK Colt™ Broadband Seismometer User Guide
117400-XX-UG
750 Ω
Before 202001
Before 203001
Ω
187.5
202001 and later
203001 and later
10/27/2021
24