Data Acquisition System (DAS)

Leap Second's effect on PASSCAL RT-130 and Q330

Summary:

Q330:

Data time starting at 2017:001:00:00:00 is +1 second from truth for 1-2 minutes (seen in controlled tests) until a clock correction, followed by a gap of 2-40 seconds per channel depending on sample rate.

RT-130:

Data time starting at 2017:001:00:00:00 is +1 second from truth for 15min - 9:42hrs (seen in controlled tests) until a clock correction. Some data (~6secs in tests) around the time correction is mistimed, sometimes 11 years in the future, or missing.

This note concerns only those stations utilizing a remote autonomous power system and solar panels. Systems that will be using AC power should contact the PIC staff for more information on safely using these types of power sources.

Grounding of DAS units should only be attempted in extreme cases where static charge is a problem (for example, failing equipment such as external GPSes). Attempts to ground DAS units can lead to ground loops if not properly done, or even if done to best practices!  It should only be attempted when the sensor itself has been isolated from ground by a non-conducting plate such as a tile or phenolic pad.  Pads which are not part of the original vault design can also cause stability/noise problems, and must be well coupled to the base of the vault or concrete.

To record seismic data during the extremely cold Polar nights, the IRIS PASSCAL Polar Group relies on the Quanterra Q330 digitizer due to its exceedingly low temperature tolerance.   The Q330 is a 24 bit, 3 or 6 channel digitizer. In addition to its very low temperature tolerance, its very low power consumption makes it ideal for year round experiments in the Antarctic deep field.

The Reftek RT-130 is a 24bit, low power, robust and very portable seismic data recorder.  It is well suited for deployment in harsh climate environment and is easy to program and retrieve data in the field.  It can have 3 or 6 channels and records data on Compact Flash (CF) cards.

Suitable for seismic reflection, refraction, downhole, crosshole, tomography, surface wave, or marine surveys, and seismic monitoring. System is housed in portable, ruggedized case with built-in, daylight-visible 800x600 color LCD and thermal graphics printer.

Operates under Windows XP multi-tasking OS and runs on Pentium-class processor.

High-speed over-sampling combined with digital signal processing provide a 24-bit result using Crystal Semiconductor sigma-delta A/D converters.

GEODE 24-CHANNEL IN-FIELD SEISMOGRAPH.

System consists of one 24-channel Geodes, with two built-in high-speed connections to interface with other Geodes and a PC-compatible controller or the StrataVisor NZ seismograph.

Suitable for reflection, refraction, downhole, crosshole, surface wave, and tomography surveys, and seismic monitoring.