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RC2000 Antenna Controller Interface Box
Dual-Speed Antenna Azimuth and Elevation Movement
The RC2000 antenna controllers use a pulse width modulation scheme to obtain slow speed movement
when interfaced to 36 volt DC motors. This pulse width modulation scheme is not compatible with the
interface box. When the RC2000 A and C model antenna controllers are used with the interface boxes
described here, antenna azimuth and elevation movement occurs at fixed speed(s) - the controller's pulse
width modulated speed control system must be disabled (from the keypad). These speed(s) are set by the
installer via potentiometers located in the RC2K90INT Interface Box. With Dual-Speed interface boxes,
two-speed motion is implemented by using the RC2000A's (former) polarotor output to specify the speed.
The polarotor output becomes the speed control bit when the ROTATING FEED PRESENT? CONFIG
Mode item is set to 1. If polarization control is required with a dual speed interface box, the RC2KPOL
option must be the polarization control entity. The RC2000 / 2K90INT system does support Polarotor-
servo type polarization control schemes but only when operating with a single-speed interface box. A
special version of the RC2000C code implements the dual-speed option.
2. Theory of Operation
The two issues which must be addressed to interface an RC2000 controller to a large antenna is the
application of power to the antenna motors and sensing of the antenna's position. Polarization control may
also be an issue. Applying power to the antenna will be addressed first.
2.1 Controlling the Motors
Figure 1 shows a schematic representation of a single axis (in this case azimuth) of the antenna control
system. The output of the RC2000 on the AZ1 and AZ2 terminals will be +/- 36 volts. When AZIM CCW
(east in the northern hemisphere) movement is specified, AZ1 will have the higher voltage, and when
AZIM CW (west in the northern hemisphere) movement is specified, AZ2 will have the higher voltage. In
a similar fashion, when down movement is specified, EL1 will be at the higher voltage, and when upward
movement is specified, EL2 will be at the higher potential. When east movement is specified, current will
flow out of the AZ1 terminal of the RC2000, through the dropping RESISTOR, R. The purpose of the
dropping resistor is to match the output voltage of the RC2000 (nearly 40 volts) to the voltage rating of the
relay coils. The current then continues through STEERING DIODE D1, through the east RELAY COIL,
through the EAST LIMIT SWITCH, through the WEST LIMIT SWITCH, and back into the AZ2 terminal
of the RC2000. Current flowing through the EAST RELAY COIL will activate the relay and close the
EAST CONTACT CLOSURE. This will configure the POWER CONTACTOR to move the antenna in
the east direction. When east current flows STEERING DIODE D2 keeps current from flowing through
the west RELAY COIL.
When the antenna is within the east limit, the EAST LIMIT SWITCH remains closed. When the east limit
is reached, the EAST LIMIT SWITCH will open. When this occurs, STEERING DIODE D3 will keep
east current from flowing, but will allow west current to flow. West movement limiting is accomplished in
a similar fashion. Note that limit switches are not required. The RC2000 series controllers maintain
logical limits based on the position count. Limit switches are pretty cheap insurance, however.
The circuit shown in Figure 1 shows the relay contacts activating power contactors that control the motor
drive power. The key part of the circuit outlined in Figure 1 is the use of the AZ1 and AZ2 outputs of the
RC2000, the dropping resistor, the relays, steering diodes, and the limit switches to generate contact
closures which can be used to control the antenna's azimuth motor.
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