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Section 9.0 Frequently Asked Questions
1. How often must the Altitude Digitizer be calibrated; is there periodic maintenance required?
There is no periodic maintenance required. The Digitizer is tested and calibrated, if
required, during the aircraft's biennial certification of the transponder and static system.
2. How many devices may be driven off of the parallel ICAO Altitude data port?
The number of devices that may be connected to the Digitizer ICAO altitude output is a
function of the current and power required. The Digitizer parallel data outputs are
"uncommitted" collectors of a transistor array which are "pulled-up" through a resistive
load by the transponder (or other device) to some positive voltage. This voltage may
range from about +3 to +40Vdc. Each Digitizer data output line (i.e. D4, A1, A2, A4 etc.)
is capable of providing 35 mA (0.035 Amperes) with a "not to exceed" power rating of
100mW (0.1 Watts), when it is "sinking" current in the "on" position. Typical modern
applications require about 1 milliampere or less per data line, per device.
DI GI TI ZER PARALLEL DATA OUTPUT
CI RCUI T 1 OF 10
D4 THRU C4
BASE
LOGI C
In the circuit illustrated below, the current is calculated as 0.9mA at 8.1mW. At
this current and power rating, a total of 12 identical devices could be connected
to the digitizer. Given the wide variety of input circuits capable of interfacing with
the Digitizer and the possibility of cross-talk, careful planning of the electrical
loads acting upon the Digitizer output is advised.
=
V
I
R
=
V
(
I
)
P
COLLECTOR
EMITTER
PIN 6
STROBE/OUTPUT
ENABLE
9
Vdc
10000
Ohms
×
9
Vdc
. 0
0009
Amps
TYPI CAL TRANSPONDER PAR
DATA I NPUT CI RCUI T
+9Vdc
10K
45
=
. 0
0009
Amps
=
. 0
0081
Watts
1 OF 10
D4 THRU C
4
LOGI C
ALLEL
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