1、The Engineering Society For Advancing Mobility Land Sea Air and SpaceI N T E R N A T I O N A L400 Commonwealth Drive, Warrendale, PA 15096-0001AEROSPACESTANDARDCopyright 1996 Society of Automotive Engineers, Inc.All rights reserved.Printed in U.S.A.SAE Technical Standards Board Rules provide that: “
2、This report is published by SAE to advance the state of technical andengineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use ,including any patent infringement arising therefrom, is the sole responsibility of the user.”SAE revi
3、ews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invit esyour written comments and suggestions.Submitted for recognition as an American National StandardIssued 1971-06Revised 1996-09REV.AAS942PRESSURE ALTIMETER SYSTEMMINIMUM SAFE PERF
4、ORMANCE STANDARDFOREWORDChanges in the revision are format/editorial only.SECTION I1 . SCOPE:The instrument system specified shall accept an input of static pressure and in some equipment other inputs that contribute altitude information to provide a visual indication of pressure altitude. If equipp
5、ed with an automatic correction mechanism, it shall indicate by a positive means when the automatic correction mechanism is not in use. If the static source pressure error compensating mechanism is operational it shall be functional throughout the required operating envelope of the particular aircra
6、ft. Each aircraft type has its own static source error data which shall be obtained from the airframe manufacturers certified data. When a Central Air Data Computer is used in the altimeter system, the CADC shall be certified to its own governing document and the altimeter system (CADC and display)
7、shall comply with the requirements of this document.NOTE: The instrument system specified herein does not include the aircraft pressure lines and pressure sources.1.1 Purpose:The purpose of Section I of this document is to specify the requirements for minimum safe performance of an altimeter system
8、in its normal mode of operation on subsonic aircraft. Compliance with this section is a means of assuring that the altimeter system will satisfactorily perform its intended function when exposed to conditions encountered in routine aeronautical operations (normal operation).SAE AS942 Revision A- 2 -
9、2. APPLICABLE DOCUMENTS:Altitude Reference - U.S. Standard Atmosphere, 1962.Airspeed Reference - NASA TN-D822 Tables.Both of the above references are available from the Superintendent of Documents, U.S. Government Printing Office.Environmental Conditions and Test Procedures - RTCA Document No. DO-13
10、8, June 27, 1968, by Radio Technical Commission for Aeronautics, 2000 K Street, N.W., Washington, DC 20006.3. GENERAL REQUIREMENTS:3.1 Materials:Materials shall be of a quality which experience and/or tests have demonstrated to be suitable and dependable for use in aircraft instruments.3.2 Workmansh
11、ip:Workmanship shall be consistent with high grade aircraft instrument manufacturing practice.3.3 Identification:The following information shall be legibly and permanently marked on the instrument or nameplate attached thereto:a. Name of Instrumentb. Manufacturers Part Numberc. Manufacturers Serial
12、Number or date of manufacture and/or modificationd. Manufacturers Name and addresse. Rangef. Normal operating environment. See code in RTCA DO-138, Appendix B.g. Aircraft identification (if applicable)h. TSO or other means of certification3.4 Aircraft Installation:When instruments have a correction
13、mechanism that is unique to a particular aircraft, means shall be provided to prevent installation in the incorrect aircraft type.NOTE:Paragraph (3.3 g) may be used as a means of identification.3.5 Compatibility:If components are individually acceptable, but require matching for proper operation, th
14、ey shall be identified in a manner that will assure performance to the requirements of this standard.SAE AS942 Revision A- 3 -3.6 Barometric System:3.6.1 Barometric Setting System: The barometric setting system shall permit the altimeter to be set to any ambient barometric pressure throughout a mini
15、mum range of 28.1 to 31.0 inches of mercury (951.5 to 1050.0 millibars). A safety feature shall be provided which will prevent an incorrect indication of the barometric pressure scale when the setting mechanism exceeds its intended barometric pressure limits.3.6.2 Interaction: Means shall be incorpo
16、rated to prevent the barometric setting system adjustment from causing the additional requirement for adjustment of other coupled systems or outputs.3.7 Multiple Mode Indications:Where an instrument has more than one mode of operation, means shall be provided to indicate other than normal mode of op
17、eration.NOTE:When an instrument has more than one mode of operation the “normal mode” is the usual operating condition.3.8 Environmental Conditions:The instrument shall be capable of its intended function throughout the environmental conditions set forth, and the conditions selected shall be declare
18、d as operating limitations.4.PERFORMANCE:4.1 Individual Requirements:4.1.1 Electrical Insulation: The instrument shall withstand voltage applications that are consistent with good engineering practice.4.1.2 Case Pressure (Pressure Operated Instruments): The instrument case shall withstand a positive
19、 external differential pressure of 26 inch Hg.4.1.3 Case Leakage (Pressure Operated Instruments): The static and total (if applicable) pressure systems shall not exceed the allowable leak, in 1 minute, as specified in Table 2.4.1.4 Scale Error: The instrument shall meet the tolerance specified in Ta
20、ble 3 which includes the following conditions: decreasing and increasing pressure for the test pressure ranges specified in Table 3, or these pressures plus the static defect correction pressures (if specified) for the applicable aircraft as supplied by the airframe manufacturer.4.1.5 Balance Error:
21、 Balance errors shall not exceed those specified in Table 4 for a change in indication from the normal operating position.SAE AS942 Revision A- 4 -4.1.6 Barometric Setting Scale: The barometric setting scale shall not introduce an error in the altimeter system greater than 20 ft at any altitude betw
22、een -1000 and 18,000 feet.4.1.7 Friction: Friction errors shall not exceed those specified for dynamic friction in Table 6 and static friction in Table 7.4.1.8 Minimum Operating Rate: The instrument shall be capable of a slew rate of 20,000 feet/minute.4.1.9 Threshold and Resolution: The instrument
23、shall be capable of discerning a change equivalent to 10 ft of pressure altitude from -1000 to 18,000 ft and 20 ft above 18,000 feet.4.1.10 Power Loss: When electrical power is required for the instrument operation, the instrument shall provide for an indication of loss of power.4.1.11 Servo Perform
24、ance (Electrical Instruments): The damping ratio specified shall be indicative of adequate response and stable operation of linear servos. Where performance requirements dictate use of nonlinear servos, the damping ratio may vary from that specified, provided comparable response and stability is mai
25、ntained.4.1.12 Scale Error - High or Low Temperature: A change in ambient test temperature of 25 C shall not cause the scale error in the altimeter system to exceed the sum of the room (25 C) temperature tolerance and 1% of the room tolerance per degree C temperature change from the room temperature
26、. The high or low temperature that is to be applied shall be determined by the manufacturer and be consistent with the environmental condition specified in the applicable category of RTCA DO-138.4.2 Qualification Requirements:4.2.1 Drift and After Effect: The instrument when subjected to 80% of the
27、operating pressure range for 6 hours shall meet the tolerances specified in Table 8 for drift and after effect.4.2.2 Temperature Extremes: The instrument tolerance, when tested within the specified temperature limits for the environmental condition specified shall not exceed the sum of the room temp
28、erature tolerance plus 2% of the room temperature tolerance per degree C of temperature change from the room temperature.4.2.3 Vibration: The instrument shall be subjected to the applicable vibration characteristics in accordance with the aircraft types and locations as specified in the Standard Vib
29、ration Environment of RTC DO-138.4.2.4 Humidity: The instrument shall withstand relative humidity up to 100% without affecting performance and there shall be no evidence of corrosion following this test.SAE AS942 Revision A- 5 -4.2.5 Fogging (Hermetically Sealed Instruments): The instrument, while o
30、perating, shall be exposed to a 70 C ambient temperature for a minimum of 30 minutes. While at this temperature, the external face of the coverages shall be reduced to a temperature of 20 C or less. No moisture or other material shall be deposited on the internal face of the cover glass as a result
31、of this test.4.2.6 Thermal Shock (Hermetically Sealed Instruments): The instruments shall be subjected to four cycles of exposure to water at 85 C 5 C and 4 3 C without evidence of moisture penetration or damage to enclosure.4.2.7 Power Variation: The instrument shall function with 15% variation in
32、DC and/or 10% variation in AC voltage, and 5% variation in frequency.4.2.8 Magnetic Effect: The magnetic effect of the instrument shall not cause the indication of an aircraft compass to change by more than 5 degrees when held 12 inches from the center of the magnet.4.2.9 Radio Interference: The ins
33、trument shall not be a source of objectionable electrical interference under operating conditions.SECTION II5. PURPOSE:The purpose of Section II of this document is to specify test procedures, for an altimeter system, in order to determine compliance with the minimum safe performance requirements sp
34、ecified in Section I.NOTE: The test procedures specified herein apply specifically to analog type instruments. Digital instruments or automatic test instrumentation may require other test procedures. Such differing procedures shall be justified prior to use.SAE AS942 Revision A- 6 -6. CROSS REFERENC
35、E INDEXTABLE 17. TEST CONDITIONS:7.1 Atmospheric Conditions:Unless otherwise specified herein, all tests required herein shall be made at an atmospheric pressure of approximately 29.92 inches of mercury absolute, an ambient temperature of approximately 25 C and a relative humidity of not greater tha
36、n 85%. When tests are conducted with atmospheric pressure or temperature substantially different from these values, allowance shall be made for the variation from the specified conditions.Section IRequirementSection IITest4.1.1 Electrical Insulation4.1.2 Case Pressure4.1.3 Case Leak (Table 2)4.1.4 S
37、cale Error (Table 3)4.1.5 Balance Error (Table 4)4.1.6 Barometric Setting Scale (Table 5)4.1.7 Friction (Table 6, 7)4.1.8 Minimum Operating Rate4.1.9 Threshold4.1.10 Power Loss4.1.11 Servo Performance4.1.12 Scale Error (Low-High Temperature)4.2.1 Drift and After Effect (Table 8)4.2.2 Temperature Ext
38、reme4.2.3 Vibration4.2.4 Humidity4.2.5 Fogging4.2.6 Thermal Shock4.2.7 Power Variation4.2.8 Magnetic Effect4.2.9 Radio Interference8.1 Electrical Insulation8.2 Case Pressure8.3 Case Leak (Table 2)8.4 Scale Error (Table 3)8.5 Balance (Table 4)8.6 Bar-Set Scale (Table 5)8.7 Dynamic (Table 6)8.8 Static
39、 (Table 7)8.9 Slew Rate8.10 Threshold8.11 Power Loss8.12 Servo Performance8.13 Temperature Test9.1 Drift and After Effect (Table 8)9.2 Low Temperature9.3 High Temperature9.4 Extreme Temperature Exposure9.5 Vibration9.6 Humidity9.7 Fogging9.8 Thermal Shock9.9 Power Variation9.10 Magnetic Effect9.11 R
40、adio InterferenceSAE AS942 Revision A- 7 -7.2 Power Conditions:Unless otherwise specified herein, all tests shall be conducted at the power rating recommended by the manufacturer.7.3 Attitude:Unless otherwise specified herein, all tests shall be conducted with the instrument in its normal operating
41、attitude.7.4 Standard Pressures:7.4.1 Altitude pressures values shall be in accordance with U.S. Standard Atmosphere, 1962 (reference ICAO Standard Atmosphere Document 7488/2).7.4.2 Differential pressure values shall be in accordance with NASA Technical Note D-822, “Tables of Airspeed, Altitude and
42、Mach Number based on latest International Values for Atmospheric Properties”.7.4.3 Pressure Reference Standard: The reference standard for atmospheric pressure shall be a mercury barometer or equivalent. The reference barometer shall be maintained in such a manner as to assure that the reference bar
43、ometer, utilizing its calibration data, will have an accuracy of .005 inches of mercury when checked against the plant standard. The user shall maintain records to show that above conditions have been complied with at intervals of three months or less, dependent on usage.The plant standard shall be
44、a mercury barometer whose calibration is traceable, to the Reference Prime Standard as maintained by the National Bureau of Standards. Using calibration data, it shall have an accuracy of .003 inches of mercury. The user shall maintain records to show that above conditions for the plant standard hav
45、e been complied with, at intervals of one year.If used, a differential pressure manometer or equivalent, shall exhibit the same accuracy characteristics as those specified for the atmospheric pressure standard and shall be maintained accordingly.7.5 Vibration During Performance Tests:7.5.1 Instrumen
46、ts intended for installation in reciprocating powered aircraft and turbine powered helicopters, shall have external vibration applied while accomplishing the performance tests.7.5.2 Instruments intended for installation in turbine powered aircraft, except helicopters, shall not have external vibrati
47、on applied while accomplishing the performance tests unless otherwise specified herein.Where integral vibrators are provided for, they shall be activated throughout the performance tests unless otherwise specified.SAE AS942 Revision A- 8 -7.6 Barometric Setting Scale:When adjusting the barometric pr
48、essure scale to 29.92 inches of mercury (1013.2 millibars) prior to starting a performance test, the 29.92 (1013.2) setting shall always be approached from the low value end of the baro-scale.8. INDIVIDUAL TESTS:All instruments shall be tested in accordance with the following recommended test proced
49、ures to show specific compliance with this standard and any additional test recommended by the manufacturer.8.1 Electrical Insulation:Each instrument shall be tested by the method of inspection listed herein:8.1.1 Insulation Resistance: The insulation resistance measured at 200 volts DC for 5 seconds between all ungrounded electrical connector terminals connected together and the metallic case shall not be less than 20 megohms. Insulation resistance measurements shall not be made to circuits where the potential will appear across elements such as windings, resistors, ca
