RESEARCH CONCEPTS RC2000C Manual page 99

RC2000C Polar Tracking Antenna Controller Appendix F AC or Large DC Motors 93
The RC1000A and RC2000 antenna controllers count the number of rising and falling edges of the
waveform. The position count is decremented for azimuth ccw movement and incremented for
azimuth cw movement. The waveform's high level should be 4.5 to 5.7 volts, and the low level should
be 0.0 to 0.5 volts. The waveform's minimum high or low pulse duration should be at least 10
milliseconds. This means that pulses less than 10 milliseconds long may not be detected by the
antenna controller. The maximum number of counts from the antenna's azimuth ccw limit to its
azimuth cw limit should be less than 65000. Remember, each rising edge and each falling edge of the
sensor's output waveform is a separate count.
Many large antennas use a sensor attached directly to each of the fundamental axis of the antenna.
The sensor used may be a resolver, synchro, potentiometer, or a quadrature pulse encoder. A pulse
type sensor attached to the fundamental axis of the antenna is not suitable for use with the RC1000A
or RC2000 antenna controllers. The reason for this requires a bit of explanation.
When a rising or falling edge is detected on the antenna controller's sensor input, the antenna
controller must determine whether to increment or decrement the position count. Since single-phase
pulse sensors are used, the antenna controller must determine which way the antenna was last
commanded to move, and decrement or increment the count accordingly. With a pulse sensor
connected directly to the antenna's fundamental axis, when the antenna vibrates back and forth due to
wind, the pulse sensor produces a steady stream of pulses. The antenna controller will increment or
decrement the count depending on which way the antenna was last commanded to move. In reality
the antenna is just vibrating in the wind and not really moving. The result of this is an error in the
position count maintained by the antenna controller.
The antenna controllers are designed to work with 36-volt actuators. With these actuators the pulse
sensor is connected directly to the motor. The motor typically drives either a worm or screw type gear,
which will not allow forces applied to the antenna to cause rotation of the motor. Therefore, no false
counts are recorded by the antenna controller.
On a large antenna, the solution to the sensor dilemma is to place a sensor on the output of the motor.
Most motors attach to either gear reduction systems or linear actuators via a C56 type flange. There
are pulse sensors that may be placed between the motor and the transmission at this flange.
Remember that any pulse sensor used must conform to the requirements of the antenna controller,
which are: 1) the total number of rising and falling edges must not exceed 65000, 2) the duration of
the high and low segments of the waveform must be at least 10 milliseconds, 3) the high level of the
waveform must be 4.5 to 5.7 volts, 4) the low level of the waveform must be 0.0 to 0.5 volts, and 5)
sensor must be a zero speed type which will count rotation of the motor shaft at very low speed.
Inductive pickup type sensors do not generally meet the last requirement.
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