RESEARCH CONCEPTS RC3000 Especificaciones descargar pdf (Pagina 7)

I 1PPS output, TTL compatible

Hand Held Remote

Connector J10 (DB-25 female) provides an interface to the optional hand-held remote control (designated RC3000HRC). The

RC3000HRC option allows an operator to jog the antenna and view antenna limit indications. Antenna position information is

not displayed on the hand-held remote. The remote is housed in a 3” x 6” x 1.75” aluminum chassis and interfaces to the

RC3000 via a 25’ multi-conductor cable (included with the handheld remote).

Pulse Sensors for Inclined Orbit Satellite Tracking Applications

The RC3000 supports interfaces to analog position sensors (azimuth potentiometer, elevation inclinometer, polarization

potentiometer). The analog sensors provide good absolute position accuracy and are used for open loop antenna pointing.

The analog sensors, however, do not provide the resolution needed for inclined orbit satellite tracking. The RC3000TRK

option allows the RC3000 to track inclined orbit satellites using step track and memory track algorithms. For inclined orbit

satellite tracking, the antenna mount must be equipped with azimuth and elevation pulse type position encoders (in addition

to the analog position sensors).

The output of a pulse encoder is a voltage waveform that transitions between two levels (‘high’ and ‘low’) as the encoder shaft

is rotated. There are two types of pulse encoders: single phase and quadrature.

A single phase pulse encoder produces a single channel pulse output. By looking at the output of a single phase encoder

an antenna controller cannot determine which way the shaft of the encoder is being rotated. The controller has to increment

or decrement the position count for that axis by knowing which way the antenna is commanded to move. If pulses occur

when the antenna is not commanded to move (or is not in the coast interval immediately following a move), the controller

does not know whether to increment or decrement the position count. For this reason, single phase pulse encoders can

only be used reliably when they are placed at a point in the antenna drive train that does not experience backdrive. In this

context, backdrive refers to forces applied to the antenna reflector that cause the shaft of the encoder to rotate. In a typical

RC3000 inclined orbit tracking application, single phase Hall effect pulse sensors are placed on the az/el drive motor shafts

and the pulse encoders essentially count motor revolutions. A typical gear ratio for a mobile antenna mount (motor

revolutions to antenna revolutions) is 5000:1 or greater. Backdrive is typically not a problem when the sensors are directly

attached to the antenna az/el drive motors. The Powermation Digital Tachometer is a single phase pulse encoder designed

for use on 56C type motor mounting flanges. The Powermation unit has been used successfully for inclined orbit tracking

with the RC3000. A datasheet describing the Powermation sensor is included with this document.

A quadrature pulse sensor produces two channels of pulse information as the encoder shaft is rotated. One channel is offset

90 degrees from the other when the input shaft of the sensor is turning in a given direction. With a quadrature sensor it is

possible to determine which way the sensor shaft is turning by looking at the phase relationship between the two output

pulse waveforms. This characteristic allows quadrature sensors to be attached directly to the antenna mount’s az/el pivot

points – as the antenna blows around in the wind the outputs from the quadrature pulse encoder are properly accumulated by

the antenna controller. Quadrature pulse encoders are usually equipped with a third channel that produces an index pulse.

The index pulse is active only when the sensor shaft is at a reference position. The index channel can be used by a

controller to initialize the controller’s internal pulse position count.

At the present time the RC3000 does not support quadrature type pulse encoders. The controller can interface to single

phase pulse position encoders whose power supply requirements are compatible with 5.7 volts DC (200 milliamps max).

Note that other pulse position encoder power supply voltages are available, please contact the factory for details). The

RC3000 controller counts both the rising and falling edges of the pulse output waveform (i.e. each pulse provides two position

counts). The position count is decremented for azimuth ccw (elevation down) movement and incremented for azimuth cw

(elevation up) movement. The waveform's high level amplitude should be 4.5 volts or greater and the waveform’s low level

amplitude should be less than 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 in duration may not be detected by the antenna controller.

The controller can accumulate a maximum of 65000 pulses about either the azimuth or elevation axis. Note that for single

phase pulse sensors that count motor revolutions (such as the Powermation unit), a one pulse per revolution sensor

characteristic is almost always appropriate.

Shielded cables equipped with a bare drain wire that provides a connection to the shield must be employed to interface the

controller to the position encoders. The drain wire must be connected at the controller to the AZ PULSE SHEILD and EL

PULSE SHIELD terminals provided on the J4 connector. The drain wire and shield must not be allowed to come in contact

with earth ground or the vehicle chassis. Use heatshrink at the sensor to prevent the frayed ends of the shield or drain wire

from making contact with the sensor body or connector. If the drain wire is allowed to come in contact with earth ground a

ground loop will be formed (the controller SHIELD terminals are connected to the vehicle chassis). With a ground loop

current flowing in the earth ground plane or vehicle chassis can flow through the sensor shield and cause stray counts to be

induced in the controller’s pulse input circuits. If the sensor cable is spliced be sure to splice the drain wire and insulate the

connection to prevent a ground loop.

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