Abstract:
A test apparatus and method of electrical testing especially useful for verifying normal performance of essential functions in an aircraft atmospheric pressure responsive auxiliary altimeter under either of flight line or maintenance shop conditions. The tester provides electrical power and control signals needed to energize each of three functions in the considered altimeter instrument including instrument face illumination, altimeter stiction-limiting mechanical vibration generation, aircraft output signal generating potentiometer function and enables electrical current and voltage monitoring relating to the instrument functions being tested. Replacement of individual test instruments and other informal test apparatus with a convenient and probably more electrical accident-free integrated tester is contemplated.

Description:
RIGHTS OF THE GOVERNMENT 
   The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. 

   BACKGROUND OF THE INVENTION 
   Accurate knowledge of operating altitude is so critical to aircraft use and safety that it is common practice in many aircraft of either the military or the civilian types to include more than a single altitude indicating instrument in the airframe. Moreover, in an extension of this redundancy philosophy, it is often deemed wise to have these parallel instruments be of differing operating principle in order that a failure event or an accuracy jeopardizing event in one instrument can be recognized and tolerated with minimum impact on flight operation. 
   Thoughts of this type have resulted in the inclusion of an atmospheric pressure responsive standby auxiliary altimeter instrument in presently used military aircraft including the F-15E aircraft. This instrument is usually mounted in the instrument panel of the aircraft where it provides a visually discernable indication of altitude to the aircraft pilot or crewmembers and also can also provide an electrical signal representative of measured altitude to an automatic pilot or a computer or similar apparatus. Altimeters of this type, although simple and reliable in their atmospheric pressure responsive operating principle, are found to need periodic testing, calibration, maintenance and overhaul in order to function with needed accuracy and dependability. Work of this type may be accomplished with aid of the present invention while the altimeter is yet within the instrument panel of the aircraft or may be accomplished while the instrument is removed from the aircraft and undergoing bench examination or repair. 
   Heretofore it has been common practice to employ a collection of equipment in order to verify the satisfactory function of the atmospheric pressure responsive standby auxiliary altimeter instrument. In addition to a source of controllable pressure for changing the altitude indicated by the instrument under test, it is, for example, common to use three power supplies, two digital multimeters and a group of fourteen individual test leads in order to access the three active functions included in such altimeters. In the instance of the standby pressure altimeter instrument, for example, these functions include an electrical potentiometer controlled as to wiper arm position by the pressure responsive element of the altimeter, a mechanical vibration generating element used for reducing the effects of mechanical “stiction” in the linkage of the instrument and an assembly of electric lamps used for lighting the instrument face. In the F-15E standby pressure altimeter instrument, each of these functions happens to require a different operating voltage in order to function properly. 
   SUMMARY OF THE INVENTION 
   The present invention provides a testing apparatus and a testing method for verifying the performance of plural functions in an aircraft altimeter. 
   It is therefore an object of the present invention to provide a convenient integrated tester for a standby pressure operated aircraft altimeter. 
   It is another object of the invention to provide a tester for the instrument lighting, the stiction reducing vibration and the electrical output potentiometer functions of a pressure operated aircraft altimeter. 
   It is another object of the invention to reduce the clutter and confusion associated with the use of fundamental equipment in performing an aircraft altimeter test. 
   It is another object of the invention to provide a portable aircraft altimeter testing apparatus that may be used in either aircraft flight line or aircraft maintenance settings. 
   It is another object of the invention to provide an aircraft altimeter test apparatus in which an operator may select a desired altimeter test from a plurality of available tests. 
   It is another object of the invention to provide an aircraft altimeter test set in which the environmental conditions encountered by an altimeter in aircraft use may be conveniently duplicated. 
   These and other objects of the invention will become apparent as the description of the representative embodiments proceeds. 
   These and other objects of the invention are achieved by the method of testing illumination operation, mechanical stiction-reducing vibration generation and electrical output signal communication functions in an atmospheric pressure responsive aircraft standby auxiliary altimeter instrument, said method comprising the steps of: 
   collecting an assembly of electrical, electronic and electromechanical components enabling of said testing into a portable enclosure having a plurality of test controls, audible and visual operator communicating transducers and electrical measurement connections received on an external portion thereof; 
   connecting said assembly of electrical, electronic and electromechanical components with a source of aircraft compatible direct current electrical energy and with an aircraft standby auxiliary altimeter instrument under test by way of tethering electrical conductors; 
   configuring said portable enclosure assembly of electrical, electronic and electromechanical components into a circuit network suited to energizing a selected first one of said illumination operation, mechanical stiction reducing vibration generation and electrical output signal communication functions in said aircraft standby auxiliary altimeter instrument; using selected of said plurality of test controls; 
   heeding a plurality of indications, warnings and suggestions communicated by said audible and visual operator communicating transducers during said configuring step; 
   holding said selected first one of said illumination operation, mechanical stiction reducing vibration generation and electrical output signal communication functions of said altimeter instrument in a standby state of non-energization until completion of said configuring and heeding steps; 
   verifying normal operation of said selected illumination operation, mechanical stiction-reducing vibration generation and electrical output signal communication functions in said aircraft altimeter instrument in response to a manually initiated termination of said holding step; 
   repeating said configuring, observing, holding and verifying steps for a second selected one of said illumination operation, mechanical stiction reducing vibration generation and electrical output signal communication functions in said pressure responsive altimeter instrument; 
   re-accomplishing said configuring, observing, holding and verifying steps for a remaining third selected one of said illumination operation, mechanical stiction reducing vibration generation and electrical output signal communication functions in said pressure responsive altimeter instrument. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present invention and together with the description serve to explain the principles of the invention. 
       FIG. 1  shows an electrical schematic diagram of components in an atmospheric pressure responsive standby auxiliary altimeter instrument subject to analysis with use of the present invention. 
       FIG. 2  shows an electrical schematic diagram of an altimeter test apparatus according to the present invention. 
       FIG. 3  shows details of the operator control panel of an altimeter test apparatus according to the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  in the drawings shows an electrical schematic diagram of essential components in an aircraft atmospheric pressure responsive or barometric standby auxiliary altimeter instrument  100  subject to analysis with use of the present invention. Generally the  FIG. 1  altimeter components include a mechanical vibration generating apparatus  101 , an electrical potentiometer  102  mechanically connected with the atmospheric pressure responsive element of the altimeter, an array of altimeter instrument face-illuminating lamps  104 , a plurality of electrical conductor leads  106  and an electrical connector  120 . These components are also referred to herein as altimeter function components.  FIG. 1  also shows at  122  a representation of the three voltage source power supplies needed to operate the altimeter  100 . 
   In the  FIG. 1  drawing it may be observed that the altimeter vibration source  101  includes a vibrator component  110 , a component that is of the electromechanical and electromagnetic type, and also an electrically coupled a-stable multivibrator electronic driving circuit  108  that may be of the integrated circuit type. More precisely, the electronic driving circuit  108  may be embodied as a type LM 555 integrated circuit as is available, for example, from the integrated circuit supplier Motorola Incorporated. The driving circuit  108  is attended by externally mounted capacitive and resistive electrical components as are generally indicated in the  FIG. 1  drawing, and as may be better appreciated with reference to LM 555 application literature supplied by the manufacturer. 
   It is also notable in the  FIG. 1  drawing that the illustrated array  112 ,  114 ,  116  and  118  of altimeter instrument face-illuminating lamps  104  are connected in electrical parallel and are therefore somewhat limited as to simple input lead continuity or no continuity electrical examination for normal operating conditions. The indicated pins of the electrical connector are used to convey the three differing altimeter-energizing voltages at  122  to the respective of the  FIG. 1  components and also used to convey an electrical signal output or wiper arm output of the potentiometer  102  on pin  2  of the connector. The ccw indication adjacent the potentiometer  102  indicates of course the counter clockwise end of potentiometer rotation. 
     FIG. 2  in the drawings shows an electrical schematic diagram of an altimeter test apparatus according to the present invention, a test apparatus suitable for energizing the  FIG. 1  altimeter, for example. The  FIG. 2  test apparatus  200  may be considered to include the five inter-related electrical circuit areas identified with the bracket numbers  202 ,  204 ,  206 ,  208  and  210 ; each of these circuit areas is described in an ensuing paragraph herein. In considering these circuit areas, it is well to appreciate that the altimeter shown at  100  in  FIG. 1  has need for the three different sources of electrical energy shown at  122  in  FIG. 1 , however, the altimeter does not require the simultaneous presence of these energy sources for testing purposes, as might be implied from the  FIG. 1  drawing. Stated in other words, the identified illumination operation, mechanical stiction-reducing vibration generation and electrical output signal communication functions in altimeter  100  can be individually considered and need not be simultaneously operating for present test purposes. 
   One of the more significant circuit areas in the  FIG. 2  test apparatus resides in the circuits indicated at  206  in the  FIG. 2  drawing, i.e., in the variable voltage regulator circuit identified as U 4  in the  FIG. 2  schematic diagram. This voltage regulator may be embodied in the form of the indicated LM117 integrated circuit and if so embodied, makes use of the circuit pin numbers indicated in the  FIG. 2  drawing for output and control purposes. In these pins, pin  3  serves as an input energy supply and is energized from the 28-volt direct current energy of the employed aircraft bus-compatible energy supply connected to the J 1  connector in the circuit area  202  of  FIG. 2 . Enabling of this pin  3  energy source is achieved by way of the K 1  relay in the  FIG. 2  circuit area  204 , as is described subsequently herein. Control of the output voltage level of the regulator U 4  is achieved by way of the rheostat-connected potentiometer R 12 . This control allows the voltage supplied to the altimeter  100  to be set at each of the levels identified at  122  in  FIG. 1  during a particular part of the present invention altimeter test. Feedback frequency rolloff and output filtering of the voltages supplied by the regulator U 4  is provided by the capacitor C 6  in the circuit area  206 . 
   Another significant circuit area in the  FIG. 2  drawing resides in the flip-flop U 2 A and relay K 1  in the circuit area  204  of  FIG. 2 . These components are used to allow delayed precision operator control of energization of altimeter components from a present invention tester that is residing in an energized standby state. By way of operator actuation of the momentary switch SW 2  in the  FIG. 2  circuit area  204  the flip-flop circuit U 2 A is placed in a “set” condition and the relay K 1  closed to energize the selected portion of the tested altimeter during a particular test. Both the set and reset or the Q and /Q outputs of the flip-flop U 2 A feed 2N2222A junction transistor emitter follower amplifier circuits to enable driving loads that are beyond the capability of the 74HC74 flip-flop integrated circuit itself. 
   Setting of the flip-flop U 2 A also causes energization of the operator warning signal provided by the light emitting diode LD 2  in circuit area  204  and at the top of the  FIG. 2  drawing. A U 2 A setting also causes energization of the audible signal provided by the buzzer B 1  located in the lower circuit area  208  of  FIG. 2 . The buzzer B 1  is intermittently operated for increased operator attention gathering by way of the a-stable multivibrator composed of the cross-connected inverter circuits U 3 A and U 3 B in the circuit area  208  of  FIG. 2 . The period of this operator attention-gathering warning is controlled by way of the electrical size selected for the capacitors C 3  and C 4  in circuit area  208 . The 0.412 microfarad capacitors as shown at C 3  and C 4  in the  FIG. 2  drawing provide a 153 millisecond period for the a-stable multivibrator. 
   A regulated source of electrical energy for energization of the electronic circuits shown in the  FIG. 2  drawing is provided by the additional LM117 integrated circuit regulator shown at U 1  in the lower part of the circuit area  202  of  FIG. 2 . This regulator is disposed to provide a fixed rather than adjustable output voltage set at  5 . 0  volts by way of the resistor divider composed of R 2  and R 3  in circuit area  202 . A tester control panel “active” visual flag warning is provided to the operator by way of the light emitting diode LD 1  and associated Zener diodes Zr 1  and Zr 2  in the circuit area  202  of  FIG. 2 . 
   Measurement of the voltage applied to an altimeter function circuit and measurement of the current flowing to this circuit is afforded by the volts and amperes terminals provided in the circuit area  210  of  FIG. 2 . The switch SW 3  in this area provides bypassing of the current measuring instrument for measuring instrument safety and measuring instrument-absent tester operations. Digital volt ohm milliamperes (VOM) instruments or equivalents may be used for these measurements. The P 5  connector shown in  FIG. 2  mates with the similar connector shown in the  FIG. 1  drawing to effect tether connection of the present invention tester with an altimeter under test. 
     FIG. 3  in the drawings shows physical details of the housing, operator control panel and tether cables for a  FIG. 2  altimeter test apparatus  200  according to the present invention. The  FIG. 3  drawing also provides an identification of the controls for the test apparatus  200 ,  300  in terms of the control identities used in the  FIG. 2  schematic diagram description of the tester. In the  FIG. 3  drawing, for example, the  FIG. 2  tethering input power cord and connector J 1  appear at  304 , the safety ground lead and connector at  305  and the multi conductor cable and connector P 5  joining the tester to an altimeter at  306 . The tester housing connected safety ground at  305  in  FIG. 3  appears at  212  in the  FIG. 2  schematic diagram. 
   The tester control panel front surface also appears at  302  in the  FIG. 3  drawing. The additional set of control identity numbers as defined in the  FIG. 2  drawing are shown in various proximity locations with the controls in  FIG. 3  and are believed helpful in relating the  FIG. 2  depicted tester to the  FIG. 3  control panel and to the ensuing operational description of an altimeter test using the  FIG. 2  and  FIG. 3  tester. For completeness of the present description, it may be noted that the altimeter tested in the following operational description paragraphs is of the National Stock Number 6610013195039 type that is also identified with the catalog number of 86046A. Such auxiliary standby altimeters are manufactured by Aerosonic Corporation of Clearwater, Fla., www.aerosonic.com. This and related instruments are employed in several aircraft currently in operational usage by the U.S. Air Force. 
   A warning and altimeter power prevention circuit has been incorporated into the  FIG. 2  and  FIG. 3  tester in order to prevent one of the 9.75 volt, 5 volt and 28 volt testing voltages from being supplied to the altimeter pins  3 ,  7 , and  13  respectively until the operator activates the “Safety Run Switch”  310  in  FIG. 3 . Upon actuation of switch  310 , testing power is applied to the P 5  altimeter conductor that has been elected by the selector switch  314 . This warning and altimeter voltage prevention circuit does not preclude an incorrect application of altimeter test voltage, but is intended as a warning arrangement to remind the test operator to establish a correct test voltage using the control at  312 . Another feature of the  FIG. 2  and  FIG. 3  tester involves the  FIG. 3  manually operated circuit breaker  326 , a 500 milliamperes-rated device, connected in series with the tester input energy source. 
   Energization of an altimeter under test commences with connection of the tester connector  304  to a source of 28-volt direct current electrical energy and connection of the safety ground conductor and connector at  305 . The 28-volt source may be any of an aircraft electrical system, a battery or an electrical inverter of the static or rotary type. After connecting a 0 to 1 ampere scaled direct current ammeter and a 0 to 30 volt scaled direct current voltmeter to the terminals  318  and  320  respectively, the selector switch  322  is set to the “voltage test” position and selector switch  314  set to the position needed for operation of the altimeter component selected, i.e., to one of the lights test, vibrator test or potentiometer test positions. With these selections made, the power switch  308  can be closed. 
   With switch  308  closed, the audible warning device  324  is activated and the visual warning lamp at  330  is energized to call attention to the need for a correct voltage setting at  312  for the function being tested. Closure of the run switch at  310  deactivates these warning devices and energizes the selected altimeter function. Verification of normal operation by the selected altimeter function is made by vision and/or by manual sensing. The test start signal lamp at  328  illuminates to indicate testing initiation. 
   Operator depression of the switch  316  allows checking of the current flow magnitude to the tested altimeter function. In the case of the identified altimeter the current flow during functional test of the lights test, vibrator test and potentiometer test should be near to the magnitudes of 300, 98 and 10–162 milliamperes respectively. 
   The present invention therefore adds a notable degree of convenience, cost savings and safety to the functional testing of altimeters that have been heretofore tested with the use of individual instruments and other discrete testing components. The described testing apparatus and testing method are usable in a plurality of real-world testing conditions. 
   While the apparatus and method herein described constitute a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus or method and that changes may be made therein without departing from the scope of the invention, which is defined in the appended claims.