Tc978 Test And Calibration; Local Voltage Supply Test; Tc978 Altitude Encoder Calibration; Calibration Equipment - FreeFlight ADS-B FDL-978 Series Installation Manual

ADS-B FDL-978 Series and
Lite Series Installation Manual
Document No. 87343 Rev F
3.7

TC978 Test and Calibration

3.7.1 Local Voltage Supply Test

The TC978 Controller of the FDL-978-XVR utilizes a DC supply voltage of 5.5V to 8V. The
display typically shows the supply voltage between 6.5V to 7.1V as shown below.
There is no option or configuration to be entered or selected in this step. Press the ENT button
or the FN button and move to the next configuration item in the setup mode.

3.7.2 TC978 Altitude Encoder Calibration

The TC978 includes a built-in altitude encoder. The TC978 Controller reports pressure altitude
on pin 4 of the DB-9 male connector on the back of the TC978 as RS-232 serial data, at 9600
bps, using the format commonly called "Icarus" format (See Section 6.1.1). The installation
manual provides further details of interfacing the altitude encoder with the primary static
pressure of the aircraft altimeter. The calibrate altitude encoder setup allows the recalibration of
the altitude encoder. This ensures that the altitude seen on the pilot's primary altimeter is the
same as what is transmitted out of the FDL-978-XVR. The maximum allowed difference
between the primary altimeter and the altitude encoder is 125 feet in European Technical
Standard Order (ETSO) C88a and TSO C88b. The altitude encoder in the TC978 Controller is
accurately calibrated in the factory to be within 50 feet of the applied pressure altitude at all
altitudes, whereas the allowed error in the primary altimeter increases with altitude, and above
18,000 feet the altimeter error alone may exceed 125 feet. It is therefore possible that the
combination of the allowed errors in the encoder and the primary altimeter may exceed 125 feet,
in which case the altitude encoder must be adjusted to correspond to the primary altimeter.
The purpose of calibrating the encoder is to make the output correspond to the
primary altimeter. The encoder calibration procedure must therefore only be
undertaken after the primary altimeter has been tested and found to comply with
the relevant standards.

3.7.2.1 Calibration Equipment

To calibrate the encoder the TC978 must be powered up and you will need a pitot-static test set
with the appropriate adapters to connect to the static port on the aircraft. The pitot-static test set
should be able to drive the altitude down to sea level, and above the service ceiling of the
aircraft.
No test set is required – the calibration procedure displays all the information you need on the
screen of the TC978 Controller.

3.7.2.2 Calibration Procedure

There are two adjustment points on the altitude encoder, a low altitude adjustment point, and a
high altitude adjustment point. The low altitude point adjusts the correspondence at sea level,
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