Research Concepts RC2500 - Manual (Page 162)

RC2500 Antenna Controller Appendix S Andrew Plug Compatible Controller 155
Research Concepts, Inc. • 5420 Martindale Road • Shawnee, Kansas 66218-9680 • USA www.researchconcepts.com
Soft Limits Theory of Operation
The RC2500 is designed to interface with antenna’s that employ resolver type position sensors. The
controller employs a resolver to digital converter (RDC) to convert the electrical outputs of the resolver to
a 16 bit digital word. (0 to 65535 – referred to as the resolver position count) This digital word represents
the angular deflection of the resolver input shaft relative to a reference position, 0.00 to 359.99 degrees.
When the resolver output reaches 359.99 (65535) it rolls over to 0.00 (0), this is termed the resolver
rollover point.
The controller displays azimuth positions as an angular value between 0.00 and 359.99 degrees. For the
elevation axis the range of displayed values is –99.99 to 260.00. For the polarization axis, the range of
displayed values is –99.9 to 260.0. The key to understanding the mapping of resolver position to display
angle is to recognize that an indicated position of –99.99 degrees is equivalent to 260.01 degrees.
The resolver input shaft is attached to the antenna pivot points. The controller expects the sensed
position to increase as the antenna moves azimuth CW, elevation UP, or polarization CW. The Reverse
Az/El/Pol Sensor Direction CONFIG mode items can be set to 1 to reverse the sense of the resolvers
indicated direction of rotation. When the Reverse Sensor Direction flag is set to 1 for a given axis, the 16
bit output of the RDC is subtracted from 65535 and the result becomes the resolver position count.
It is advantageous for operators if the antenna controller displays the antenna’s actual azimuth, elevation,
and polarization pointing angles. If the couplers that connect the shafts of the resolvers to the antenna
pivot points are carefully adjusted the resolvers can directly indicate the antenna pointing angles about
each axis. This can cause problems, however, because the RC2500’s auto move routines cannot
operate properly if the resolver rollover points occur in the antenna’s active range.
The Azim/Elev/Pol Display Offset CONFIG mode items specify an angle that is added to each resolver’s
sensed position (adjusted for the Reverse Sensor Direction CONFIG mode items). The Display Offset
values can be any value between –179.99 and 180.00 degrees. The addition of the Offsets is performed
in a modulo 360 manner. The offset is added to the adjusted resolver reading and the result is adjusted
by adding or subtracting 360 degrees so that the display angle lies in the range of values appropriate for
that axis: 0.00 to 359.99 for the azimuth axis and –99.99 to 260.00 for the elevation and polarization axis.
The user specifies a soft limit by entering an angle at the soft limit CONFIG mode prompt. That angle
corresponds to a display angle for the axis whose limit is being entered. The controller will accept any
valid display angle for the axis whose limit is being set for either limit associated with that axis if the offset
associated with that axis is valid (a valid offset means that the checksum – described later in this
paragraph - agrees with the offset value and the offset is greater than –180.00 and less than or equal to
+180.00). If the angle entered is not a valid display angle for the axis associated with the limit or the
offset associated with that axis is not valid the controller will display ‘INVALID DATA’ when the user hits
the ENTER key to terminate the data entry. The offset for that axis is subtracted from the value entered.
The resulting angle is converted into a resolver position count and that value is stored in the controller’s
non-volatile memory. Also stored in memory is a checksum. The checksum is mathematically related to
the resolver position count that corresponds to the limit that is being set. The purpose of the checksum is
to allow the controller to periodically test the limit value to see if the controller’s non-volatile memory has
been corrupted.
When the user is prompted to set a soft limit the data entry field for the soft limit will contain the current
value of the soft limit for that axis if the following are true…
a) The checksum for both limits associated with that axis are valid.
b) The offset for the axis being set is valid (the offset value agrees with its checksum and the
value of the offset is greater than –180.00 and less than or equal to +180.00).
c) The value of the upper limit associated with that axis (azimuth CW, elevation up, or
polarization CW) is greater than or equal to the lower limit associated with that axis (azimuth
CCW, elevation down, or polarization CW).
If these conditions are not met the data field will contain ‘*’ characters. The last condition implies that a
soft limit value that is accepted by the controller will not be displayed at the data prompt if its magnitude
relative to the other limit associated with that axis does not meet the criteria outlined in item c above.
For a given axis, limit indications will be displayed and antenna motion disabled when operating outside
the region defined by the limits if the conditions outlined in items a, b, and c above are met and RDC
alarm is not active. If an RDC alarm is active the position display field for that axis will contain ‘*’