Research Concepts RC2000A - Manual (Page 24)

24 RC2000A Dual Axis Antenna Controller Chapter 3 Installation
3.3 Optional Polarization Control
This section describes how to configure the RC2000A to control motorized feeds with potentiometer
feedback. If this installation uses a Chaparral type polarotor servo, or has no polarization adjustment,
proceed to section 3.4.
The controller has an internal expansion port which can accept optional daughter boards. Two
daughter boards are available which can provide polarization control: RC2KPOL and RC2KHPP. The
RC2KPOL is designed for use with the Seavey model ESR-124D motorized feed with potentiometer
feedback. The Seavey feed requires 24 volts DC at 500 milliamps. The RC2KHPP option is designed
for motorized feeds with up to 3 amps. Version 1.50 of the software supports the RC2KPOL option.
Version 1.51 supports the RC2KHPP option. If either of these options is installed in the unit, a 5
position connector labelled J4 will be present on the back panel of the unit above the pots labelled
AGC1 and AGC2.
*** CAUTION ***
Before using a Seavey rotating feed with the RC2000, it is recommended that the user verify that the
feed's range of mechanical movement is within the position sense potentiometer's range of mechanical
movement. If the mechanical limit of the pot is reached before the mechanical limit of the feed is
reached, the torque of the motor can destroy the pot. The pot used with the Seavey feed is a Spectrol
model 533 (1K ohm, 3 turn). To see if the potentiomter is centered properly, the following procedure
may be performed on a workbench.
Verifying Potentiometer Center Position
1. Verify the total resistance of the potentiometer. This may be done by either reading the value
written on the side of the pot, or by measuring between the two non-wiper terminals of the pot. For
the Spectrol pot this will be terminals 1 and 3.
2. Connect an ohm meter between the wiper of the pot (terminal 2 on the Spectrol) and one of the
other two terminals. Note that when the shaft position of the pot is near one of the pot's mechanical
limits, the ohm meter will read either less than 25 ohms, or the value found in step 1.
3. With a bench power supply, automobile battery charger, or some other voltage source, carefully
apply power to the feed's DC motor to move it towards one mechanical limit or the other. (Note that
the feed motor for the Seavey feed nominally requires 24 volts DC at approximately 150 ma. The
feed motor should move with an applied voltage of 6 to 12 volts DC.)
While movement is in progress monitor the ohm meter to insure that the pot's mechanical limit is not
reached. If the ohm meter indicates that the pot's mechanical limit is being approached, quickly
disconnect the power source and perform the procedure outlined in the section entitled "Centering the
Pot".
4. If the feed can safely move to one of its mechanical limits, reverse the power supply leads and
move the pot towards the other mechanical limit. Once again, monitor the ohm meter to insure that
the pot's mechanical limits are not exceeded. If the feed cannot be moved to its mechanical limit
without approaching the pot's mechanical limit, perform the procedure outlined in the section
entitled "Centering the Pot".
Centering the Potentiometer
The procedure outlined here may be used to center the feed's range of travel within the pot's
mechanical limits.
1. Find the total resistance of the pot. See step (1) above.
2. Loosen up the allen screw which holds the shaft of the pot to the gear.
3. Apply power to the feed motor (as in step (3) above) to center the feed in the middle of its range of
travel. As the feed rotates, make sure that the shaft of the pot does not turn.
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