CMG-DM24 Mk1 Datalogger Standalone

The Mk1 Standalone versus a CMG-3TD with integrated Mk1

CMG-DM24 Mk1 dataloggers have the same FIR filter cascade and tap table lookups as CMG-DM24 Mk2 dataloggers. Sensitivities for the Mk1 standalone datalogger (wired for differential output) matches that of the Mk2 wired for single-ended output. Mk1 dataloggers integrated into the CMG-3TD were wired with single-ended output. For these instruments, use these responses for the Mk1 standalone and updated the datalogger gain (SEED stage 3) and total gain (SEED stage 0) by dividing by two.

Tap Table Lookup Numbers

The DM24 generates sample rates for each channel by cascading decimation filters to create up to 6 successive "taps" or sample rates. Some or all of these sample rates may be output.

The FIR filters used for a given sample rate is determined by the tap sequence programmed into the datalogger at startup time. Each unique combination of taps is referenced by a "Tap Table Lookup (TTL) Number". Knowning this number is necessary to locate the correct instrument response, since a single sample rate can be generated in a variety of ways.

The TTL can be found in one of these ways:

1. running Guralp's EAMs program
• selecting "GDI channels display from the tools menu
• choosing the data stream of interest and
• clicking "View details".
• The "Metadata" table in the resulting display lists the "gcf-tap-table-lookup".
2. retrieving the TTL byte by web interface (instructions here)
3. reading the Decimation Index (TTL) from the Scream "ViewInfo" window (instructions here)

CMG-DM24 Mk1 Standalone

Mary Templeton 12/6/2017