TruTrak Digitrak Install and User Guide - Manual (Page 5)

TruTrak flight systems DigiTrak Installation Manual
October 2009 3 8300-009 Rev B
Magnetic Considerations
Because the autopilot contains a built-in magnetometer for a backup source of heading in the event of GPS loss, it is important
to try to locate the programmer away from known sources of magnetic disturbance. The calibration procedure can account for a
moderate amount of fixed disturbance (for example, nearby iron objects) but it cannot adjust for changing magnetic fields such
as would be generated by aircraft compasses or certain electrical devices. One such source of such problems is the “Flag”
mechanism in some older DG or HSI devices. These units use a solenoid to hold the flag out of sight, and the magnetic field
will then change when the flags come and go. If at all possible, place the autopilot so as to be as far as possible from such
devices. A hand-held compass can be used to assist in finding fixed or variable disturbances prior to installation of the
autopilot. Even a few inches can make an appreciable difference in the magnetic disturbance level. It should be noted also that
strobe light controls, landing lights, navigation lighting, pitot heat, generate very strong currents in their wiring, thus they will
create a periodically pulsating magnetic field disturbance. Shielding has no effect on this problem; the only solution is to keep
wiring as far away as possible from any electronics which can be affected by pulsating magnetic fields.
RFI/EMI considerations
The autopilot programmer is shielded and does not generate any appreciable level of electromagnetic interference. Moreover,
the servo lines (except for power and ground) are low-current and cannot contribute to RF interference. The servo power and
ground lines do have switching currents through them, but so long as there are no parallel runs of servo power and ground lines
with such things as poorly-shielded antenna lines or strobe light power lines, there is no need to shield the servo harnesses.
The autopilot itself has been internally protected from RF interference and has been tested under fairly extreme conditions,
such as close proximity to transmitting antennas. However, it is always good practice to insure that such antennas are properly
shielded and not routed directly over or under sensitive panel-mounted electronic equipment. Most problems in this area are the
result of improper RF shielding on transmitting antennas, microphone cables, and the like. The most sensitive input to the
autopilot is the Control Wheel Switch input. This line should not be routed in parallel with transmitting antennas or other
sources of known RF interference. If necessary, it can be shielded with the shield connection to pin 8 of the autopilot
connector.
Specific connections for certain commonly-used in-panel GPS units
Note that the information in the tables is based upon the best information available from each manufacturer’s documentation at
the time of publication. Please consult the appropriate installation manual for confirmation of wiring information.
GPS Setup Guide
Portable GPS’s
Many new handheld GPS’s have adequate output required to fly a TruTrak autopilot. Although most support data
output not all handhelds will provide consistent and reliable information required to fly all TruTrak autopilots. Therefore,
some handhelds will not fly the airplane well. Performance may decline by putting the processor in high-load situations.
We require a data output rate of once per second for best performance. Some handhelds output data at longer intervals
than once per second. These handhelds will cause the autopilot not to perform well in turns and it may cause overshooting and
hunting. If the baud rate is selectable the optimum setting is 4800. Most handhelds will require a data cable that plugs into the
handheld and provides a medium for data output. This is an accessory and is available from your GPS manufacturer. The
setup procedures are in your GPS manual. If your GPS is not listed here consult your GPS manual for NMEA output setup.
The autopilot must have a direct connection with the handheld GPS to provide the autopilot with RS-232. To allow the
handheld GPS to be removed easily you should add a connector in your panel. We recommend that you use a 9 pin D
subminature connector in your panel that will mate to the harness from the GPS. This will also allow you to wire power and
ground and use the aircraft electrical system to power your handheld GPS.
Magellan GPS 315 A
The Magellan GPS 315 A requires a Power/Data Cable (Magellan Product Number 730276) to provide data output.
The Magellan GPS 315 A must be configured to provide the correct output to the autopilot.
Press the MENU key then select “Setup. Press ENTER. Select “NMEA” and press ENTER. Select “V2.1 GSA” then
press ENTER. Next we must set the baud rate. Press MENU then select “SETUP” and press ENTER. Next Select
“BAUD RATE” and press enter. Select 4800 for the baud rate. Press ENTER.
Garmin GPS III
The Garmin III requires a Power/data cable (Garmin Part Number 010-10082-00) to provide data output.
The Garmin III must be configured to provide the correct output to the autopilot.
Press the MENU key twice. Select ‘Setup’. Press ENTER. Select the ‘Interface’ tab. Press ENTER. Select the NMEA
format.