Follow, Drift, And Drive Error Sensing; Timekeeping - RESEARCH CONCEPTS RC4600 Operator's Manual

RC4600 ACU Board Set Chapter 2 Hardware

3.2.4.1 Follow, Drift, and Drive Error Sensing

The RC4600 continuously monitors the axis positions to detect incorrect movement of the antenna. If an
axis has been commanded to move and the RC4600 detects that the movement is not "following" the
calculated path, the controller will declare a "FOLLOW" condition and not allow further movement until the
condition has been reset.
Similarly, if the RC4600 is holding position in an axis and the position "drifts" away from the held position
and the controller cannot correct it out, the RC4600 will declare a "DRIFT" condition and not allow further
movement until the condition has been reset.
The RC4600 also continuously monitors the azimuth and elevation motor drive current. If at any time the
current sensed rises above the value set in the system configuration, the RC4600 will declare a "DRIVE"
condition and not allow further movement until the condition has been reset.

3.2.5 Timekeeping

There are several versions of time (system, sidereal, display and GPS) discussed within this manual.
System time is maintained by the RC4600's real time clock. The real-time clock is backed up by battery
so that system time is available as soon as the RC4600 powers up. The system time is used to calculate
sidereal time for maintaining track tables. Since satellite's do not experience time shifts (such as from
Standard Time to Daylight Savings Time or when moving from one time zone to another), it is
recommended that system time not be modified while active track tables are present. If system time is
changed, the information stored in track tables for inclined orbit satellites will no longer be valid.
The RC4600's system time is set to approximately Universal Coordinated Time (UTC) at the factory. It
will vary from UTC due to the tolerance of the real-time clock.
If the optional GPS receiver is installed, the RC4600 parses UTC from the data sent by the GPS receiver.
This data is only available when the GPS receiver is sufficiently locked on to GPS satellites to determine
UTC. The RC4600 allows the user to synchronize system time to the UTC reported by the GPS receiver.
The period of a satellite's motion is one sidereal day (approximately 23 hours 56 minutes 4 seconds).
Entries in the track table for an inclined orbit satellite are stored at intervals of 1/48th of a sidereal day.
The RC4600 determines at what point in a sidereal day (with respect to the RC4600 reference) it is by
calculating how many sidereal days have passed from January 1, 1992 until the present system time.
In several screens the RC4600 displays a display time. The user may designate a three letter time zone
designation and an hourly offset from system time. This allows the user to display local time or some
other time without modifying system time. If system time is maintained close to UTC, the time displayed
may be of use to operators for coordinating events.
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