Calibration; Sine Wave Calibration Example - Reftek 151D User Manual

Rev A

8.2 Calibration

Three in-series calibration coils, one for each component of the 151D, 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 activated.
Two kinds of calibration signals are commonly used:
• Step Signal (wide pulse signal) – Used to check the period of the
seismometer.
• Sine Signal – Used to check amplitude characteristics.
8.2.1

Sine Wave Calibration Example

The expected seismometer output for a sine wave calibration input signal can
be calculated with the following formula:
Vpp_output = Cal_Sensitivity * Sensitivity* A_input / (frequency * PI)
Where:
Cal_Sensitivity
Sensitivity
A_input
If you have a calibration sine wave input with amplitude = 5 Volts (10Vpp)
and a frequency of 1 Hz, the expected Peak-to-Peak Output voltage of the
seismometer with nominal Cal Sensitivity and Output Voltage Sensitivity
would be:
Vpp_output = 10 * 2000*(5 / 47500) / (1*3.14)
Vpp_output =
0.67
Note: Values 10 (Cal Sensitivity) and 2000 (Output Voltage Sensitivity)
should be taken from the 151D Seismometer Data Sheet
The 180 Wrangler recorder can be used to generate a calibration signal for
confirmation. This can be accomplished in the WebUI through the
Parameters>Sensor Calibration Signal menu. Select signal enable
checkbox for the relevant channels and a duration of 30s, amplitude of 5V and
signal type of Sine. Select a Sine Frequency of 1 Hz. Press Send to confirm
these parameters (note this does not send the signal).
Reftek Systems Inc.
REF TEK 151D Broadband Seismometer Users Guide
151D-UG
From the supplied 151D Data Sheet.
Seismometer sensitivity from the supplied 151D Data
Sheet.
Calibration voltage input amplitude / Resistance of the
calibration coil in ohms (Calibration coil resistance is
nominally 47.5 kΩ)
Vpp (Nominal
12/4/2023
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