Appendix F - Controlling Antennas Powered By Ac Or Large Dc Motors - RESEARCH CONCEPTS RC2000C Manual

90 RC2000C Polar Tracking Antenna Controller Appendix F AC or Large DC Motors

Appendix F - Controlling Antennas Powered by AC or Large DC Motors

The RC1000A, RC2000A, and RC2000C antenna controllers are designed to control satellite
antennas powered by 36-volt DC motors that use pulse type position sensors. The RC1000A is
designed for use with single axis polar mount antennas. The maximum output current from the
RC1000A is 5 amps. The RC1000A has a built-in interface for a Chaparral type Polarotor. The
RC2000A and RC2000C are dual axis antenna controllers designed for use with elevation over
azimuth or azimuth over elevation type mounts as well as polar mounts with a motorized elevation
(latitude angle) or motorized declination adjustment. The RC2000C has all of the features of the
RC2000A as well as support for tracking inclined orbit satellites via step track and memory track
algorithms. The RC2000A and RC2000C share a common motherboard. In the text that follows the
term RC2000 will be used to refer to both versions. The maximum actuator drive current available from
the RC2000 is 8 amps. The RC2000 has a built-in interface for a Chaparral type Polarotor. There is
an optional interface (designated RC2KPOL) for a 24 volt DC polarization motor which uses a
potentiometer for feedback. With this option the output current available to the polarization motor is
approximately 200 milliamps. This option was designed to be used with Seavey motorized feeds.
The two issues which must be addressed to successfully interface one of these controllers to a large
antenna is the application of power to the antenna motors and sensing the antenna's position. This
paper describes a technique to use the antenna controller's +/- 36-volt output voltage to activate AC
and higher voltage DC motors as well as the selection and placement of pulse type position sensors
that are compatible with these antenna controllers. This paper also includes a description of the
products available from Research Concepts, Inc. (RCI) which implement the motor control scheme
outlined in this paper and a sensor design example.
Controlling the Motors
Please refer to figure 1. The azimuth motor drive output of the RC2000 on the AZ1 and AZ2 terminals
will be +/- 36 volts. When azimuth ccw movement is specified, AZ1 will have the higher voltage, and
when azimuth cw movement is specified, AZ2 will have the higher voltage. (Note that the sense of
antenna azimuth movement is as seen by an observer located above the antenna). 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 azimuth ccw movement is specified,
current will flow out of the AZ1 terminal of the RC2000, through the dropping RESISTOR, through
STEERING DIODE D1, through the AZ CCW RELAY COIL, through the AZ CCW LIMIT SWITCH,
through the AZ CW LIMIT SWITCH, and back into the AZ2 terminal of the RC2000. Current flowing
through the AZ CCW RELAY COIL will activate the relay and close the AZ CCW CONTACT
CLOSURE. This will configure the POWER CONTACTOR to move the antenna in the azimuth ccw
direction. When azimuth ccw current flows STEERING DIODE D2 keeps current from flowing through
the azimuth CW RELAY COIL.
When the antenna is within the azimuth CCW limit, the AZ CCW LIMIT SWITCH is closed. When the
azimuth ccw limit is reached, the AZ CCW LIMIT SWITCH will open. When the AZ CCW LIMIT
SWITCH is open, STEERING DIODE D3 will keep azimuth ccw current from flowing, but will allow
azimuth cw current to flow to move the antenna out of the ccw limit. Azimuth cw movement is
accomplished in a similar fashion. Note that limit switches are not required. The RC1000A and
RC2000 maintain logical limits based on the position count. Limit switches are pretty cheap insurance,
however.
The purpose of the dropping resistor is to match the output voltage of the RC1000A or RC2000 (36
volts) to the voltage necessary to activate the relay coils. A common relay coil voltage is 24 volts. If
the relays have 24 volt coils, the dropping resistor should be selected so that at the relay's rated coil
current the voltage drop across the resistor will be 12 volts. If 36 volt relays are used the dropping
resistor is not needed.
A number of products are available from Research Concepts which implement the motor control
scheme outline above. See the section below entitled Motor Control Interface Products for a
description of these products.
Research Concepts, Inc. • 5420 Martindale Road • Shawnee, Kansas 66218-9680 • USA www.researchconcepts.com