RESEARCH CONCEPTS RC1500B Manual page 25

RC1500B Single Axis Tracking Antenna Controller
3.3.3.1 Verifying the Potentiometer Center Position
The most common problem experienced during installation of a rotating feed is damage to the
potentiometer due to the potentiometer reaching its mechanical limit before the feed reaches its
mechanical limit. This problem has occurred quite often with Seavey feeds.
Before using a Seavey ESA 124 rotating feed with the RC1500, 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 original pot used with the Seavey feed was a Spectrol model 533 (1K ohm, 3 turn). Later
models employ a Contelec PD2205-5K (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 ohm meter 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 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.)
4. 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".
5. 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 following paragraphs.
Centering the Pot
The procedure outlined here may be used to center the feed's range of travel within the pot's
mechanical limits.
Research Concepts, Inc.; 5420 Martindale; Shawnee, KS 66218
Chapter 3 Installation/Setup
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