BULLETIN BOARD - D5

GPS SYNCHRONIZATION

IN RMS INSTRUMENTS' DATA SYSTEMS
AND AADCII COMPENSATOR

From their inception, RMS Instruments' DAS8 and DGR33A Data Systems have allowed for synchronization of recorded data to GPS time with an accuracy of approximately 10 msec. The 1-PPS signal from the GPS receiver is used to drive one of the (3) scans in the system, whose main function is to record the "system time" corresponding to the occurrence of the PPS signal. By recording also the GPS message that includes the time tag for the PPS in addition to position and time fixes, one can establish, post-flight, (GPS) time tags for the data recorded.

For applications where better accuracy is desired, and/or where implementation of software for data re-arrangement at processing time represents a problem, or where simply, it is desired to have all data structuring and time-tagging taken care of in real time, a different approach is required.  For these applications, RMS Instruments implemented a scheme for synchronization of the data systems and AADCII Compensator to the 1-PPS signal from a GPS receiver, which uses the event input port in a modified version of the Analog Input Module, RMS4185A-PPS.

The module generates a 10 Hz (or 20 Hz) timing signal, synchronized to the PPS from the GPS receiver, which is used to trigger both the (fast rate) scan in the data system, and the AADCII Compensator. Sampling of all signals in the system remains synchronized to GPS time, and the drifting between the system's (real-time) clock and GPS time becomes inconsequential.

RMS4185A-PPS modules may be purchased directly from RMS Instruments, or alternatively, RMS4185 and RMS4185A modules may be converted. The latter must be done at the factory, since in addition to a special firmware revision, some hardware modifications on the DPR board are required.

For further information, please contact RMS Instruments.

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