Research Concepts RC2500 - Manual (Page 152)

RC2500 Antenna Controller Appendix Q Working with the SA 8151 145
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Appendix Q – Working with the SA 8151
It is possible to use the RC2500 Antenna Control Unit (ACU) to replace the Scientific Atlanta SA 8040
Antenna Controller when operated with the SA 8151 Local Control Unit (LCU) and enjoy the industry-
standard RCI operator interface and added capabilities of inclined-orbit tracking, multiple stored locations,
and PC remote control. In order to be compatible with the Antenna and the LCU, resolvers are placed on
the azimuth, elevation and polarization (if required) pivot points. Information on the connection and use
of resolvers is found in section 3.3.1. The firmware version for this unit is: version 1.07wra-p, the date:
3.17.98, and the checksum: '34'. The RC2500 uses a modified 2_5KI_O1 as the interface PCB.
LCU Limit Status Outputs
The SA8151 LCU has four non-isolated outputs that are directly compatible with the limit inputs of the
RC2500. These outputs connect to the limit return lines of J6. A 5V source located in the LCU is
connected to all high-side limit input lines. The limits are directly connected to a normally open set of
contacts in the antenna-mounted limit switch. When the limit is reached, the contacts close, allowing
current to flow through the RC2500 optoisolator. The normally-closed side of the limit switch is used to
interrupt drive power to the motors. The “safe” operating region is defined as the non- conducting state
of the drivers. That is a pull-down occurring on the limit return line (5VDC is always on the limit input) of
the RC2500 input terminal indicates a limit has been reached. A high voltage (+5VDC) on the limit return
line indicates that a limit has not been reached. Note that this is different from other control schemes
where the conducting state indicates the safe operating region.
This “Local / Remote” switch located on the control panel of the LCU signals to the ACU with 5VDC when
the LCU is to be driven from the ACU. This 5VDC supply also powers the drive side interface. The LCU
is switched to “Local” the 5VDC goes to zero and, the RC2500 will flash “ALARM – MAINTENANCE” on
the LCD. In this state the RC2500 may not move the antenna. When the 5V signal is returned, the
flashing alarm message disappears, and control is resumed from the RC2500.
The limit inputs formerly used for AZ fault, EL fault, and EStop are wired out of the circuit.
ACU Drive Outputs
The Output circuitry of the RC2500 is modified to be compatible with the drive inputs to the SA 8151 LCU.
There are 4 drive inputs for the LCU. These are: AZ CW, AZ CCW, EL UP, and EL DOWN. Optionally,
POL CW, and POL CCW may also be controlled. They are active high, that is they move the antenna
when 5V is applied to the line. The RC2500 drives these lines with opto-isolated darlington drives in a
pull-up configuration.
The standard I/O drive board of the RC2500 is modified to adapt to the SA 8151 interface. VR1 and VR2
are removed from the circuit. A MPTE5 transient protection diode is installed between pins 1 and 2 and
a jumper is installed between pins 1 and 3 of VR1. A 0.2A-trip, resettable fuse is installed between pins 1
and 2 of VR2. IC’s U2, U4, and U6 are removed and replaced with DIP headers supporting connections
between pin 9 and pin 8, and between pin 10 and pin 6. The limit inputs formerly used for AZ fault, EL
fault, and EStop are wired out of the circuit by connecting U8 pin 12 to U8 pin 11, U8 pin 13 to U8 pin 14,
and .U9 pin 10 to U9.
The hardware interface between the RC2500 ACU and SA 8151 LCU is summarized in the following
tables showing all connections at J6 and J7 of the ACU.