Research Concepts RC2000C - Manual (Page 107)

RC2000C Az/El Tracking Antenna Controller Appendix F AC or Large DC Motors 99
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From this information the 3-dB beamwidth of the antenna can be determined to be: 0.28 degrees
To determine the total number motor revolutions which occur when moving from the antenna’s azimuth
ccw limit to the antenna’s cw limit and to get a rough idea of the number motor revolutions per each
degree of movement determine the time that it takes for the antenna to move through a known angle.
For this case, determine the time that it takes the antenna to move from limit to limit (100 degrees for
this example): use 110 seconds for this example
Determine the total number of motor revolutions per second: 1750 rpm / 60 seconds = 29.16 revolutions
per second.
Determine the number of motor revolutions required to move from limit to limit: 29.16 revolutions per
second x 110 seconds = 3208 motor revolutions.
Choose a Powermation pulse sensor with a one pulse per revolution characteristic and check to make
sure that the requirements outlined earlier are satisfied:
The duration of the pulse high and low level waveforms is greater than 10 milliseconds,
The total number of position counts encountered moving from limit to limit is less than 65000, and
There are at least 10 position counts that occur as the antenna is moved across its 3-dB beamwidth.
Make sure that the total number of position counts when moving from limit to limit are less than 65000.
This is easy. If there are 3208 motor revolutions, one pulse per revolution, and given the fact that the
controller counts both the rising and falling edge of each position pulse the total number of position
counts can be calculated to be:
3208 motor revolutions x 1 pulse per revolution x 2 edges per pulse = 6416 total position counts
This easily satisfies the requirement that there be less than 65000 total position counts.
Next make sure that the pulse waveform high and low duration is greater than 10 milliseconds. Use the
formula given above: 30000 / (1750 RPM x 1 PULSE PER REVOLUTION) = 17.14 milliseconds per
pulse. This satisfies the requirement that the pulse duration be greater than 10 milliseconds.
Next calculate the number of position counts which occur as the antenna moves over a 3-dB
beamwidth. If there are 6416 position counts over 100 degrees, the number of position counts per
degree is 6416 divided by 100 or 64.16 counts per degree. To calculate the number of position counts
that occur as the antenna moves over its 3-dB beamwidth (0.28 degrees), multiply the 64.16 counts per
degree by 0.28 degrees to obtain 17.96 position counts. This satisfies the requirement that there be at
least 10 position counts over the antenna’s 3 dB beamwidth.