Research Concepts RC2000C - Manual (Page 22)

14 RC2000C Az/El Tracking Antenna Controller Chapter 3 Installation/Setup
Research Concepts, Inc. • 5420 Martindale Road • Shawnee, Kansas • 66218-9680 • USA www.researchconcepts.com
3.3 Optional Polarization Control
With the RC2KPOL daughterboard option, the RC2000C can control a rotating feed which employs a
24-volt DC polarization motor with potentiometer position feedback. This section describes the
installation and setup of a rotating feed compatible with the RC2KPOL option. It should be noted that
not all versions of the controller support polarization control. If a polarization control device is not
present or a Polarotor tm is used, make sure that the Rotating Feed Present CONFIG mode item is set to
0 and proceed to the next section
*** 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) or a Contelec PD 2205-5KO/J (5K ohm, 5 turn). To see if the potentiometer
is centered properly, the following procedure may be performed on a workbench.
Verifying Pot 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 ohmmeter between the wiper of the pot (terminal 2 on the Spectrol or Contelec) 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 ohmmeter 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 ohmmeter to insure that the pot's mechanical limit is not
reached. If the ohmmeter 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 ohmmeter 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 Pot
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 the allen screw that holds the shaft of the pot onto 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.
4. When the feed has been centered in its range of travel, connect the ohmmeter between the wiper
and one of the other terminals of the pot. Rotate the shaft of the pot until the resistance read from
the ohm meter is one half of the value of the pot's total resistance (obtained in step (1)).