Trans-Cal Industries, Inc.

Model SSD120-(XX)A
&
Model SSD120-(XX)AE

All Solid State Altitude Encoder/Digitizer

Owner/Installation Manual
Operating Ceilings from 30,000 to 42,000 Feet.

T.S.O. C88a Approved

Trans-Cal Industries, Inc.

Van Nuys Airport
16141 Cohasset Street
Van Nuys, CA 91406-2908
(818) 787-1221 (800) 423-2913 FAX (818)787-8916
www.trans-cal.com

August 8, 2006 Document Number: 881000 Rev. D

8 2001 by Trans-Cal Industries, Inc.
This document may not be reproduced, transmitted, or copied in any form without the prior
written consent of Trans-Cal Industries. The data contained herein is subject to change without
notice.

Please Note:
It is the responsibility of the installer of this equipment, within a specific type or class of
aircraft, to determine that the aircraft operating conditions are within TSO standards.

Trans-Cal Industries, Inc.

16141 Cohasset Street
Van Nuys, CA 91406

818/787-1221
800/423-2913
FAX 818/787-8916
www.trans-cal.com

Ordering Information:
To receive additional copies of this publication, order Trans-Cal Industries
part number 881000 rev. C.

History of Revision
Revision Date Description
-- 07/98 Production release.
A 10/99 Added SL70 transponder data pg. 15.
B 12/01 Added GTX 327 transponder pg. 13. Corrected current pg. 3.
Clarified calibration '3.3.3 added diagram.
C 08/04 Updated Manual.
D 08/06 Updated warranty from 40 to 48 months.

2
 Table of Contents

Section 1.0 Introduction & Specifications...................................................................................... 4

1.1 Scope..................................................................................................................................... 4
1.2 Equipment Description ......................................................................................................... 4
1.3 Equipment Specifications ..................................................................................................... 4
1.3.1 Warm-Up Time:............................................................................................................. 4
1.3.2 Operating Altitude: ........................................................................................................ 4
1.3.3 Code Output. .................................................................................................................. 5
1.3.4 Accuracy. ....................................................................................................................... 5
1.3.5 Mechanical Characteristics. ........................................................................................... 5
1.3.6 Input Power Requirement. ............................................................................................. 5
1.3.7 Output Signal Characteristics. ....................................................................................... 5
1.3.8 Input Signal Requirements............................................................................................. 5
1.3.9 Environmental................................................................................................................ 6
1.3.10 Over Range. ................................................................................................................. 6
Section 2.0 Operation ..................................................................................................................... 6
2.1 General.................................................................................................................................. 6
2.2 Operating Instructions........................................................................................................... 6
Section 3.0 Installation and Calibration.......................................................................................... 7
3.1 Mechanical Installation......................................................................................................... 7
3.2 Electrical Installation ............................................................................................................ 7
3.3 Calibration ............................................................................................................................ 8
3.3.1 General........................................................................................................................... 8
3.3.2 Calibration Equipment Required. .................................................................................. 8
3.3.3 Calibration Procedures................................................................................................... 9
Altitude Digitizer to Primary Flight Altimeter ............................................................................. 10
Temperature vs. Warm-up Time:.................................................................................................. 11
Outline Drawing ........................................................................................................................... 12
Narco AT-50 and AT-50A Installation......................................................................................... 13
Encoder Interconnections ............................................................................................................. 14
Table I ............................................................................................................................... 14
Table II.............................................................................................................................. 15
Table III ............................................................................................................................ 16
Table IV ............................................................................................................................ 17
Table V.............................................................................................................................. 18
WARRANTY REGISTRATION ................................................................................................. 19

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Section 1.0 Introduction & Specifications
1.1 Scope

This manual provides detailed installation, calibration and operating instructions for the
Trans-Cal Industries= Model SSD120-(XX)A and SSD120-(XX)AE* (see note 1) series of
altitude encoders.
1.2 Equipment Description

This device is approved under F.A.A. T.S.O. C88a. The SSD120-(XX)A and SSD120-
(XX)AE series of altitude encoders are self contained solid state electronic devices
which, when connected to an aircraft static and electrical system, converts pressure
altitude into the digital data set forth in the International (ICAO) Standard for SSR
Pressure Altitude Transmission. In accordance with U.S. National Standards for
Common System Component Characteristics for the I.F.F. Mark X (SIF)/Air Traffic
Control Radar Beacon System SIF/ATCRBS.

In operation, with the encoder connected to the aircraft=s transponder in mode AC@
operation and interrogated by an air traffic control station, the transponder will utilize the
encoder data to reply with the aircraft=s altitude referenced to 29.92 In. Hg. (1013 MB.)

1.3 Equipment Specifications

1.3.1 Warm-Up Time:

SSD120-(XX)A +20EC to +70EC No warm-up time.

-20EC to +20EC See figure 1.

SSD120-(XX)AE -55EC to -20EC See figure 1.

1.3.2 Operating Altitude:

Model SSD120-30A or SSD120-30AE -1000 to +30,000 feet.

Model SSD120-35A or SSD120-35AE -1000 to +35,000 feet.
Model SSD120-42A or SSD120-42AE -1000 to +42,000 feet.

See High Altitude Series manual for the units listed below:
Model SSD120-50A or SSD120-50AE -1000 to +50,000 feet.
Model SSD120-62A or SSD120-62AE -1000 to +62,000 feet.
Model SSD120-65A or SSD120-65AE -1000 to +65,000 feet.
Model SSD120-80A or SSD120-80AE -1000 to +80,000 feet.

* Note 1: (E) Extended operating temperature range: -55EC to +70EC.

4
1.3 Equipment Specifications (continued)
1.3.3 Code Output.
The encoder=s digitized output code is in accordance with the U.S. National
Standard for Common System Component Characteristics for the IFF Mark X
(SIF) Air Traffic Control Radar Beacon System, SIF/ATCRBS, as amended 8
March 1971.
1.3.4 Accuracy.

The encoder accuracy is "50 feet from -1000 to 30,000 feet and "75 feet from
30,000 feet to 42,000 feet, when measured from the altitude transition points of
the digital code and referenced to 29.92 In. Hg. (1013 MB.)

1.3.5 Mechanical Characteristics.

Weight: 10 oz. Dimensional: See outline drawing.

1.3.6 Input Power Requirement.

The SSD120-(XX)A or SSD120-(XX)AE models operating up to 42,000 feet will

operate on either 14 or 28 VDC at 0.600 Amps.

1.3.7 Output Signal Characteristics.

The encoder=s output is provided by the Auncommitted@ collectors of a transistor

array and must be Apulled-up@, through a resistive load by the transponder. The
pull-up voltage may be 3 to 50 VDC at 50 ma sink current.

1.3.8 Input Signal Requirements.

Pin 6 of the altitude encoder must be either grounded or connected to the

transponder strobe (output enable.)

5
 1.3 Equipment Specifications (continued)
1.3.9 Environmental.

All SSD120-(XX)A and SSD120-(XX)AE encoders have been designed, tested

and approved to meet the requirements of TSO-C88a, in accordance with RTCA
Document DO-160b, dated July 1984 (specifics provided upon request.)

Operating Temperature: SSD120-(XX)A -20E to +70EC.

SSD120-(XX)AE -55E to +70EC.

Storage Temperature (non-operational): -60E to +85EC.

1.3.10 Over Range.

The SSD120-(XX)A or SSD120-(XX)AE series of altitude encoders will not be

damaged when operated beyond their specified maximum altitude up to 100,000
feet MSL, or over pressured to 18 psi maximum.

Section 2.0 Operation

2.1 General

The SSD120-(XX)A and SSD120-(XX)AE series of altitude encoders are designed to be

mounted within a pressurized or non-pressurized, but temperature controlled location
within aircraft operated up to 42,000 feet MSL. Usually remotely located, the encoder is
fully automatic in operation and normally controlled by the transponder.

2.2 Operating Instructions

Place the transponder in mode AC@, altitude reporting mode, and apply power to the
encoder. In some installations the encoder will automatically be supplied power when the
transponder is energized; in others, power to the encoder may be supplied through a
separate circuit breaker. If power to the encoder is provided directly from the avionics
buss, follow the power-up procedures recommended by the transponder manufacturer.

In some installations, the transponder controls the encoder by enabling and disabling the
encoder outputs. In still other installations, the encoder=s output is not controlled by the
transponder and is continually enabled, (pin 6 of the altitude encoder is grounded.)

6
Section 3.0 Installation and Calibration

3.1 Mechanical Installation

The SSD120-(XX)A and SSD120-(XX)AE series of altitude encod ers may be mounted
in any attitude within the internal structure of the aircraft. DO NOT mount the encoder in
the direct airstream or either hot or cold air ducts. The mounting position should allow
for a short pressure line from the encoder to the altimeter, and allow access to the
encoder=s adjustments.

Use #4-40 machine screws, sheet metal screws, or pop rivets to attach the encoder or the
mounting tray to the airframe. Secure the mating connector to the encoder housing using
the captive #4-40 screwlock assembly provided. Refer to the outline drawing for
mechanical dimensions and the installation block diagram.

3.2 Electrical Installation

The altitude encoder is designed to operate on either 14 or 28 VDC power source. These
voltages can be A+ switched power provided by the transponder or can be provided by
the avionics buss. If using the avionics buss, protect the circuit with a 1 Amp fuse or
circuit breaker. Ground, pin 15, should be connected to aircraft ground (A-).

The encoder label and the outline drawing provide electrical connector/function
information. Use this data when connecting the altitude encoder to the transponder.

In some installations where older transponders are used, the transponder may not provide
an Aaltitude disable@ function. In this case, an instrument panel mounted switch for this
function may be required.

7
3.3 Calibration

3.3.1 General
Ref: FAR 91.217; FAA Advisory Circular 43-6A
FAR 91.413; FAR 43-Appendix E and F.

Each altitude encoder is calibrated to an NIST traceable pressure datum;

however, when the unit is installed in an aircraft for use as the transponder=s mode
AC@ altitude encoder, it must be recalibrated for correspondence to the aircraft=s
primary flight altimeter as required by FAR 91.217 and 91.413.

Model SSD120-(XX)A and SSD120-(XX)AE altitude digitizers are designed to

be field calibrated to meet this requirement, as per the procedure described in
'3.3.3. The correspondence required for digitizers is fully addressed in SAE
Aerospace Standard AS8003 '3.11. This correspondence standard requires
altitude digitizer=s to report within "125 feet of the primary flight altimeter=s
reading when the pressure datum is set to 29.92 In. Hg., (1013 MB) absolute.

The standard further requires a transition accuracy of "75 feet of the nominal
transition point for that altitude. A transition is defined as the point at which the
digitizer changes from one altitude to the next, either increasing or decreasing
altitude. This nominal transition point occurs 50 feet prior to the altitude in
question. See figure 1.

3.3.2 Calibration Equipment Required.

A pitot-static test set capable of exercising the altimeter and the altitude encoder
over a range of -1000 feet to the maximum altitude of the encoder, and a test set
(ramp tester) capable of interrogating the transponder are required.

8
3.3.3 Calibration Procedures.

1. Connect the pitot-static test equipment to the aircraft=s static line, and the
transponder test set per the manufacturer=s recommendations. The encoder=s
two adjustment potentiometers are identified as L and H, meaning Low and
High altitude. The low adjustment is closest to the edge of the housing, and
the high adjustment is closer to the center of the housing.
(Note: Changing either potentiometer will affect the other. An adjustment
made to the low potentiometer, correcting the low transition point, will move
the high transition point, and require an adjustment of the high
potentiometer.)

2. Apply power to the altitude encoder/transponder.

3. Set the primary flight altimeter barometric pressure to 29.92 In Hg (1013

MB).

4. Interrogate the transponder with the ramp tester, while observing the altitude
code, decrease pressure to the point where the altitude code just makes the
transition to the maximum altitude encoded. Verify that the digitizer is within
"125 feet of the altimeter=s reading. If not, adjust the high potentiometer until
the digitizer=s transition point is within "30 feet of the nominal transition
point; 29,950 feet for a 30,000 foot digitizer.

5. Increase pressure until the digitizer=s output just makes the transition from 100
feet to 0 feet. Verify that the altitude digitizer reads within "125 feet of the
altimeter. If not, adjust the digitizer=s low potentiometer until the digitizer=s
transition point is within "30 feet of the nominal transition point (+50 feet) as
read on the altimeter.

6. Repeat steps (D) and (E) until the "125 tolerance is achieved for the
maximum calibration altitude and the minimum calibration altitude.

7. Exercise the aircraft=s static system over the operating range of the altitude
encoder and, with increasing and decreasing pressure, verify at a minimum of
ten test points that the altitude digitizer and primary flight altimeter is within
the "125 foot tolerance. If correspondence is not achieved at any test point the
altimeter may need calibration.

8. Verify that the altitude digitizer=s output is disabled when the transponder is
not in mode AC@, or when the AAltitude Disable@ switch is in the disable
position.

9
Altitude Digitizer to Primary Flight Altimeter

Figure 1
Altitude Digitizer to Primary Flight Altimeter
Correspondence
Reference TSO-C88a and SAE AS8003

9 1
1 0MBAR.
13
8 500 2
54
7 29.92
In. Hg.
3
6 4
5

10
Temperature vs. Warm-up Time:

Figure 3
Temperature vs. Warm-up Time
Degrees Celsius

Seconds (±20%)

11
 This document contains proprietary information of Trans-Cal
Industries, Inc. Any reproduction, use or disclosure of this
document without the written permission of Trans-Cal
Industries, Inc. is expressly prohibited. D Redrawn in entirety. 09/30/99 J.F.

Mounting Tray
(Optional Mounting
Outline Drawing

Method)

DA15-P Installation
D-Subminiature SSD120 Block Diagram
Connector

Transponder
(Optional, see note 2) Altimeter
DE9-S
D-Subminiature Interconnecting
Static Cable Assembly
Connector
Line

H
Altitude
Increase

L
1/8-27 NPT
Fitting

12
DA15-P Connector DE9-S Connector (Opt.)
High Alt. Adj. Pin Function Pin Function Pin Function
1 D4* 9 B2 1 Ground
Low Alt. Adj. 2 A1 10 B4 2 10 ' Resolution Select
3 A2 11 C1 3 Calibration Use Only
4 A4 12 C4 4 TxD 1
5 B1 13 C2 5 Ground
6 Output 14 14/28V 4 6 Protocol Select
Enable Input 7 Protocol Select
7 ---- 15 Ground 8 Ground
4 8 14/28V 9 TxD 2
Input
* Above 30,700 feet only.

Part Number Designations

Part No. Max Altitude
1 SSD120-30A 30,000 Ft. Mounting Tray P/N: 881022 Dimensions

SSD120-35A 35,000 Ft. Drawn:

4. Pins 8 & 14 connected internally. H. Smith 07/12/98 TRANS-CAL INDUSTRIES, INC.

SSD120-42A 42,000 Ft. Checker:
3. Manufactured in accordance with TSO-C88a. G. Pannullo 07/12/98
2. RS232 Serial port on model SSD120-(XX)A-RS232 Engineer:
Outline Drawing
1. An "E" suffix in part no. (eg. SSD120-30AE) designates J. Ferrero 07/12/98 SSD120-XXX
Tolerances:
full temperature range. (-55°C to +70°C). .XX ±.030
Notes: C SSD120-XXA( ) D
.XXX ±.010 None Inch 1 of 1
Narco AT-50 and AT-50A Installation

Narco AT-50 and AT-50A Installations

The Narco AT-50 or AT-50A transponder will not accept data from the Trans-Cal
SSD120-(XX)A until the following modifications have been completed:

1. The strobe modification as outlined in Narco service bulletin no. AT-50A-5 dated 19 February
1975 has been performed on the transponder.

2. A modification to the Trans-Cal SSD120-(XX)A removing the data line decoupling capacitor
network.

The SSD120-(XX)A may be ordered from the factory with Mod. 1 completed, or the altitude digitizer
may be modified in the field as outlined below.

Instructions for field modification:

1. Remove the 4 screws, lockwashers and cover plate. Do not remove the D-Sub serial data connector.

2. Remove and discard the C1 capacitor network (refer to figure 1 below.) The network may be removed
using a pair of pliers to slowly rock the network back and forth until it breaks away.

3. Replace the cover plate, 4 lockwashers and screws.

4. A modification label is located on the side of the altitude digitizer. Using an indelible ink pen, place an
"X" in the box identifying modification 1 as complete.

Figure 1
15 Pin D-Subminiature Connector

C1 Capacitor Network

13
Encoder Interconnections

The following encoder/transponder interconnections are provided as a quick reference only, and though they
are correct to the best of our knowledge, always consult the latest installation, operation, and service bulletins
from the equipment manufacturer.

Table I

SSD120 SSD120 KT76/78 King KT-76A/78A King KXP

15 pin
conn. Function Pin Number Pin Number Pin Number
1 D4 ** ** V
2 A1 6 M G
3 A2 7 K H
4 A4 9 J J
5 B1 4 E K
9 B2 1 C L
10 B4 2 B M
11 C1 3 D P
13 C2 8 L R
12 C4 10 H S
6 Output Connect to aircraft Connect to aircraft Connect to aircraft
Enable ground. ground. ground.
8 or 14 to Connect to aircraft=s Connect to aircraft=s Connect to aircraft=s
14* 28VDC avionics buss avionics buss protected avionics buss protected
Input. protected by a fuse by a fuse or circuit by a fuse or circuit
or circuit breaker. breaker. breaker.
15 Ground Connect to aircraft Connect to aircraft Connect to aircraft
ground. ground. ground.

*Pins 8 and 14 are connected together internally.

**Data for this connection is not available at this time.

14
 Table II

Cessna RT359A, Narco AT-150

RT459A, AT-50, Narco AT6A Garmin
SSD120 RT859A AT-50A AT-5 AT-6 GTX 327
15 pin
Conn. Function Pin Number Pin Number Pin Number Pin Number
1 D4 10 ** ** 18
2 A1 14 7 2 3
3 A2 13 6 4 5
4 A4 15 8 8 6
5 B1 19 12 9 9
9 B2 17 10 10 11
10 B4 16 9 11 12
11 C1 21 14 1 10
13 C2 18 11 3 4
12 C4 20 13 5 7
6 Output 11 5 12 13 or 25 or
Enable aircraft ground.
*8 14 to 9 18 13 14 to 28VDC
or 28VDC Input
14 Input

15 Ground Connect to Connect to 14 Connect to

aircraft aircraft ground. aircraft ground.
ground.

*Pins 8 and 14 are connected together internally.

**Data for this connection is not available at this time.
***Narco transponders see page 12 for modification requirements.

15
 Table III

SSD120
Edo-Air Genave Radair Becker Avionic
15 Pin RT-777 Beta 5000 250 Systems
Conn. Function Pin Number Pin Number Pin Number ATC3401
ATC2000
1 D4 15 0 15 23
2 A1 7 4 7 16
3 A2 5 5 6 15
4 A4 3 6 13 14
5 B1 12 7 9 17
9 B2 13 8 10 19
10 B4 14 9 11 18
11 C1 8 10 14 22
13 C2 6 11 16 21
12 C4 4 12 12 20
6 Output 2 3 19 24
Enable
8 or 14 to Connect to 2 22 6
14 28VDC aircraft=s
* Input avionics buss
protected by a
fuse or circuit
breaker.
15 Ground 2 Connect to Connect to 24
aircraft aircraft
ground. ground.

*Pins 8 and 14 are connected together internally.

**Data for this connection is not available at this time.

16
 Table IV

SSD120
Bendix Bendix Wilcox UPS AT
15 Pin TPR-2060 TR641A/B 1014A Apollo SL70
Conn. Function Pin Number Pin Number Pin Number Pin Number
1 D4 ** N C 35
2 A1 4 A k 13
3 A2 6 B c 31
4 A4 8 C W 12
5 B1 9 D T 33
9 B2 10 E L 14
10 B4 11 F D 32
11 C1 3 H P 16
13 C2 5 J f 34
12 C4 7 K Z 15
6 Output Connect to Connect to Connect to aircraft Connect to aircraft
Enable aircraft ground. aircraft ground. ground. ground.

8 or 14 to Connect to Connect to Connect to Connect to

14 28VDC aircraft=s avionics aircraft=s aircraft=s avionics aircraft=s avionics
buss protected by avionics buss buss protected by a buss protected by a
* Input a fuse or circuit protected by a fuse or circuit fuse or circuit
breaker. fuse or circuit breaker. breaker.
breaker.

15 Ground Connect to Connect to Connect to aircraft Connect to aircraft

aircraft ground. aircraft ground. ground. ground.

*Pins 8 and 14 are connected together internally.

**Data for this connection is not available at this time.

17
 Table V

Bendix/King Bendix/King This column This column left

SSD120
KGP 560 KMH 870 left blank blank
15 Pin
Conn. intentionally. intentionally.
Function EGPWS IHAS Processor
1 D4 No connection 18
2 A1 12 11
3 A2 52 10
4 A4 33 9
5 B1 14 14
9 B2 34 13
10 B4 73 12
11 C1 32 17
13 C2 13 16
12 C4 72 15
6 Output Connect to Connect to aircraft
Enable aircraft ground. ground.

8 or 14 to Connect to Connect to avionics

14 28VDC avionics buss via buss via circuit
circuit breaker. breaker.
* Input
15 Ground Connect to Connect to aircraft
aircraft ground. ground.

*Pins 8 and 14 are connected together internally.

18
 WARRANTY REGISTRATION
Trans-Cal Industries warrants each Model SSD120-(XX)A(E) Solid State digitizer / serializer to be
free of defects in workmanship and materials for a period of 42 months after purchase. This warranty
applies to the original purchaser of the instrument.

Trans-Cal’s obligation under this warranty is limited to repairing or replacing any unit returned to
Trans-Cal during the life of this warranty provided:
(1) The defective unit is returned to us, transportation pre-paid.
(2) Prior approval is obtained from Trans-Cal.
(3) The unit has not been damaged by misuse, neglect, improper operation, accident alteration or
improper installation.

Trans-Cal DOES NOT reimburse labor costs on warranty repairs. Trans-Cal Industries will be the sole
judge as to the cause of the malfunction and wherein the responsibility lies. No other obligation or liability
is expressed or implied.

For the above warranty to become effective, the attached registration card must be completed
and returned to Trans-Cal Industries, properly filled out and signed by the dealer selling or installing this
equipment.

Mail to: Trans-Cal Ind., Inc., 16141 Cohasset St., Van Nuys, CA 91406
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - cut here - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

MODEL: SSD120-( )A(E) SERIAL NO: A-___________________

AIRCRAFT:______________________ NUMBER:__________________________

OWNER:___________________________________________________________

ADDRESS:_________________________________________________________

CITY:_________________________________ STATE:_______ZIP:___________

DEALER:__________________________________________________________

INSTALLED BY:____________________________________________________

LICENSE NO:______________________________________________________

INSTALLATION DATE:_______________________________________________

I hereby certify the above instrument was installed in accordance with the instructions of
Trans-Cal Industries, and the installation was done to industry standards. I further certify
the instrument was properly working on the above date.

SIGNED:___________________________________________________________
PRINT NAME:_____________________________________________________________

19