Apparatus for and method of testing hydraulic/pneumatic apparatus using computer controlled test equipment

Automatic test equipment for testing hydraulic/pneumatic devices which devices are included within the test system as well as those which may be attached to the test system. Object oriented programming preferably using C++ language is utilized. Abstract classes representative of characteristics of a group of devices to be tested are provided. Also provided are subclasses characteristic of types of units to be tested. Upon declaration of a specific instance of a type of unit to be tested, the abstract class is inherited into a subclass which in turn is incorporated into the unique characteristics for the declared unit to be tested. A test program is activated for the specific unit to be tested. The test program is also constructed by utilizing abstract and subclasses of information characteristic to the unit to be tested. As the test is being conducted, additional tests or devices within the system are addressed to permit utilization of the information so addressed or alternatively, communication with devices contained within the test system as required for conducting and completing the test on the unit under test.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to the testing of hydraulic/pneumatic 
apparatus and more specifically to an apparatus and a method for testing 
such apparatus utilizing computer controlled automatic test equipment. 
2. Prior art 
It has been common practice in the art to test hydraulic/pneumatic 
component subsystems and systems (devices) subsequent to their assembly to 
ascertain whether such devices are operating in accordance with the 
specifications set forth for them. Such testing may occur at the time of 
manufacture of the device or subsequently during maintenance thereof. For 
example, it is typical to connect a hydraulic actuator to a test stand and 
determine its frequency response, external and internal leakage, proof 
pressure, ram travel and velocity, damping, hysteresis and the like. 
In such prior art test stands, the device may be connected to dedicated 
ports for application of fluid under pressure and/or return thereto, or 
alternatively, connected arbitrarily to ports which can then be controlled 
by a computer through a manifold so that the desired pressure and return 
is then applied to the ports to which the device has been connected. One 
example of such a structure is that shown and described in U.S. Pat. No. 
4,480,464, which is incorporated herein by reference. Subsequent to 
connection of the device, the system steps through a series of tests to 
ascertain whether or not the device is functioning according to its 
predetermined specifications. The tests may be performed in accordance 
with selections made by an operator's input or alternatively, in a manner 
controlled automatically by a computer controlled system. Examples of such 
computer controlled automatic testing systems are as shown and described 
in U.S. Pat. No. 4,782,292, which is incorporated herein by reference. In 
such systems, a computer control system automatically sequences through a 
plurality of tests specific to the device being tested, determines whether 
the device falls within the predetermined tolerances programmed within the 
system and thus, whether it has met the predetermined specifications or 
not. 
A similar automatic testing structure is that as shown and described in 
U.S. Pat. No. 4,916,641 which is incorporated herein by reference. Such a 
system receives and stores a plurality of tables of data. Each such table 
contains data which is characteristic to the specific device being tested. 
Additional tables of data are also stored with each such additional table 
containing data which is characteristic of each transducer, amplifier or 
other component relating to the device to be tested. The table of 
characteristic data for each such transducer, amplifier or other component 
can then in effect be used by incorporating it into other definition 
tables. Thus for each such transducer, amplifier or other component there 
is developed a specific set of characteristic data which is then 
automatically referenced or used when desired and as controlled by the 
computer control system to test a particular device. Thus, when a specific 
device to be tested is identified, the computer will search out the tables 
containing the set of data characteristic to the device, to the 
transducers, the amplifiers and the other components as they use those 
data to test the device. 
Although the prior art systems have worked quite well for the applications 
intended, it is evident that if there is any change in the hardware, 
either in the test stand or the device, then each of the tables of 
characteristic data must be changed to accommodate the same. Those skilled 
in the art will recognize that such changes can effect the overall 
operation of the system in that they must be incorporated into a plurality 
of different tables of characteristic data resulting in necessary changes 
in the system software. Such changes necessarily add to the expense for 
maintenance and operation of the system as well as introducing problems of 
reliability. 
SUMMARY OF THE INVENTION 
A method for automatically testing hydraulic/pneumatic devices which 
includes defining a plurality of characteristics common to all of a 
plurality of such devices and storing such characteristics; defining a 
plurality of characteristics which are specific to a single predetermined 
device and storing such specific characteristics; declaring said specific 
device for testing; retrieving from storage said specific characteristics 
for said specific device and also retrieving said common characteristics 
from storage; combining said common characteristics and said specific 
characteristics; activating a test program including said common and 
specific characteristics and testing said specific device; measuring the 
results of said test; comparing the results of said test with said 
specific and common characteristics and reporting whether said test 
results fall within said specific and common characteristics. 
In accordance with a more specific aspect of the present invention, there 
is provided a test station which includes an electronic console 
interconnected with a hydraulic console with appropriate interconnections 
between the two for allowing the electronics control console through the 
utilization of the computer contained therein to control the hydraulic 
console for the purpose of configuring the same to perform tests both upon 
the electronic and hydraulic devices in the test station as well as upon 
devices to be tested which are connected to the test station. In 
conducting the tests upon the devices, the common characteristics 
applicable to an entire class of such devices are combined with the 
specific characteristics identifiable for a specific device to provide a 
test program for the specific device. The device is tested and the results 
of the test are provided at the electronic control console either visually 
or by way of hard copy printout or both as may be required in any specific 
instance.

DETAILED DESCRIPTION 
The automatic test equipment system of the present invention includes both 
hardware and software which together provide the ability to automatically 
test, through utilization of a computer, various hydraulic/pneumatic 
components, subsystems and systems. The automatic test equipment provides 
the capability of testing such parameters as flow control, pressure 
control, sensor excitation, frequency response, external and internal 
leakage, proof pressure, hysteresis, ram travel, velocity, damping, and 
others well known to those skilled in the art. 
The system provides the capability of accommodating hardware changes in 
either the test equipment or the devices to be tested without a major 
redesign of the software utilized to accomplish the test. This is 
accomplished by partitioning the software into a hierarchy of classes 
associated with a group of devices (units under test and the automatic 
test equipment) which are to be tested. The hierarchy is based upon the 
most general characteristics of the devices which are applicable to all 
the devices within the group (abstract base class) followed by further 
classifications of a less general nature (sub classes) descending to those 
characteristics specific to only one particular device (a class). When the 
operator then makes the decision to test a specific device and identifies 
it (an instance of the class or object), a test for that specific device 
is formulated by inheriting all of the characteristics relating to that 
device found in the hierarchy of classes of characteristics ascending to 
the most general such classification. It can thus be seen that where there 
are a large number of specific devices to be tested, there is no need or 
requirement to have provided a full list of characteristics attributable 
to each such specific device. Rather by identifying a specific device as 
falling within the overall group for which the hierarchy of 
classifications of characteristics has been established, one need only 
then inherit from all of the higher order of classes of characteristics 
into those characteristics which are specific to the identified device to 
accomplish the testing. Also, if a new device is to be added to the system 
for testing, only those characteristics unique to that specific device and 
not found in any of the higher order classifications of characteristics 
need be added and identified for that specific device. 
To accomplish the foregoing, object-oriented design was chosen since it is 
a method which leads to software architectures based on the objects the 
system or subsystem manipulates (rather than the function it is meant to 
perform). Object-oriented design is the construction of software systems 
as structured collections of abstract data type implementations. For a 
more detailed discussion, reference is hereby made to "Object-Oriented 
Software Construction" by Bertrand Meyer, published by Prentice Hall 1988. 
The language chosen to implement the object-oriented design, is C++. For a 
more detailed discussion of the C++ language, reference is hereby made to 
the "Annotated C++ Reference Manual" by Margaret A. Ellis and Bjarne 
Stroustrup, published by Addison Wesley 1990. The object-oriented design 
along with the C++ language requires modularization based upon data. Prior 
art modularization was based upon function and this, in turn, caused 
similar data to be scattered throughout many parts or modules of the 
system. 
Through the utilization of such a technique, automatic computer controlled 
testing of hydraulic/pneumatic devices can be accomplished much quicker 
and in a more reliable and less expensive way than has heretofore been 
possible in the prior art. 
By reference now to FIGS. 1-3, there is shown an automatic test equipment 
test stand constructed in accordance with the principals of the present 
invention. The test stand includes an electronic control console 10 and a 
hydraulic console 12. The two consoles are electronically interconnected 
to provide communications therebetween so that the electronic control 
console can, upon appropriate instructions from an operator, activate the 
hydraulic console and carry out the steps required to test a device which 
is connected to the hydraulic console. As is typical in devices of this 
type, the electronic control console includes a programmable alternating 
current power supply 34 having a voltage meter 32, an operating interface 
panel 14, a microcomputer 16, a printer 18 and a pair of drawers 20 and 22 
which contain appropriate printed wiring based assemblies (PWBA), i.e. 
printed circuit cards, for the instrument and control interface and the 
flight control electronic interface when the system is utilized to test 
flight control electrohydraulic/pneumatic flight control components, 
subsystems and systems. The various components of the electronic control 
console are removably mounted in a rack 24 which in turn may be positioned 
within an appropriate overall test station assembly by utilization of a 
locking device 26. 
As is well known to those skilled in the art, the operating interface panel 
includes a cathode ray tube output device 28 and a keypad 30. 
The hydraulic console 12 contains the appropriate electrical control panels 
32 which communicate electronically with the electronic console and in 
turn interface with the various portions of hardware contained within the 
hydraulic console to provide the test. The hydraulic console contains such 
hydraulic and electromechanical devices as the solenoid valves, 
servovalves, pumps, motors, pressure and flow transducers, a sink, 
manifolds, and the fixtures that hold, instrument control and apply loads 
to the devices that are being tested during the testing process. For 
example, as shown more specifically in FIG. 3, a fixture 34 is provided to 
receive a linear actuator 36 which can be caused to move through various 
steps during the testing process under control of a test program activated 
and sequenced by the electronic control console. As the actuator 36 is 
placed through its test, signals are generated at the hydraulic console 
indicative of the test results. These signals are then transmitted back to 
the electronic control console for appropriate comparison and recording as 
the case may be. There is also provided on the hydraulic console 12, a 
fixture 38 which receives a rotary servoactuator which may be tested in a 
similar manner. Appropriate hydraulic ports 42 are provided for 
interconnection between the hydraulic fluid source and the devices such as 
36 during the test. Appropriate manifolds and control devices are housed 
within the hydraulic console 12 which, under control of the electronic 
control console and the panel 32 on the hydraulic console, provide the 
various transducers, pumps and the like and their operation to provide the 
desired fluid under pressure to the devices such as 36 being tested. This 
is more fully explained in U.S. Pat. No. 4,480,464 to which reference is 
hereby made for a complete understanding by those skilled in the art. 
Referring now more particularly to FIG. 4, there is disclosed a generalized 
block diagram illustrative of the overall automatic test equipment system 
and the interconnections between the electronic control console and the 
hydraulic console. As is therein shown, the electronic control console 10 
includes a computer 50 which is utilized to control the overall automatic 
test equipment system. The computer is utilized to automatically test 
various types of hydraulic/pneumatic component subsystems and systems, for 
example, such as the flight control actuators on modern military and 
commercial aircraft including both rotary and linear actuators. The 
testing can be directed to the unit under test (UUT), a self test of the 
automatic test equipment or calibration tests on the automatic test 
equipment. Diagnostic tests can also be conducted on the UUT and on the 
automatic test equipment in the event of a failure. The computer controls 
a source of electrical power such as the programmable power supplies 52 
which are then utilized to apply the appropriate level of voltage and 
current through the various components throughout the system as may be 
required. Appropriate interfaces between the electronic control console 
and the hydraulic control console such as the instrumentation and control 
interface 54 and the flight control electronics interface 56 are provided. 
Within the hydraulic console 12 there is contained the drive load system 58 
which is utilized to apply an appropriate load to the unit under test as 
may be desired. The supply pressure control system 60 is utilized to 
provide the appropriate fluids such as hydraulic fluid at the desired 
pressures and flow rates to the unit under test 62. The return pressure 
control system 64 is utilized to provide the appropriate pressure for the 
return flow from the unit under test. A cylinder assembly control system 
66 is utilized for controlling application of tests to one type of UUT 
which includes a cylinder assembly. Appropriate fixtures 68 are utilized 
upon which the UUT is mounted to provide support for the UUT during tests. 
The mechanical interconnection between the UUT 62 and the fixture 68 is 
shown by the dash line 70 therebetween. 
As is indicated by the paths 72 and 74, there is appropriate communication 
between the electronic control console and the hydraulic console so that 
appropriate commands for conducting the tests on the UUT or on the 
hydraulic console can be communicated from the computer through the 
appropriate interfaces to the hydraulic console and in turn, data and 
information concerning the hydraulic console and the UUT can be 
transmitted back to the computer for appropriate operations such as 
comparisons, logging, printout and the like. As can be seen by the 
interconnections, the instrumentation and control interface 54 through the 
appropriate path 72 controls the hydraulic console while the flight 
control electronics interface 56 through the path 74 controls the UUT. 
By reference now more specifically to FIGS. 5(a)-(f), more detailed block 
diagrams of the system as shown in FIG. 4 is provided. As is therein 
shown, the electronic control console 10 is interconnected to the 
hydraulic console 12 through the utilization of the input/output connector 
panel 80 which also provides interconnection to the UUT 62. As was noted 
in conjunction with the description of FIG. 1, the electronic control 
console includes the operator interface panel 14, the microcomputer system 
16, the printer 18, the instrumentation and control interface 20 and the 
flight control electronics interface 22. 
The operator interface panel 14 contains the typical control switches such 
as a power switch 82, a system reset switch 84 and an emergency stop 
switch 86. Also is provided a manual pump control switch to energize or 
de-energize the hydraulic pump in the hydraulic console should such be 
desired. An appropriate operator keypad 90 is utilized to allow the 
operator to input instructions, orders, data, or other commands to the 
computer as may be desired. The key input encoder printed wiring board 
assembly (PWBA) 92 is used for communicating between the operator 
interface panel and the microcomputer system 16. Also located in the 
operator interface panel 14, is the cathode ray tube 94 which is utilized 
to display information to the operator, such as the test being run, the 
status of the test, the results of the test, and the like. An appropriate 
cathode ray tube controller PWBA, is utilized to communicate between the 
computer and the operator interface panel. 
A printer assembly 18 is connected to the computer system and is utilized 
to provide a hard copy of the test results on an appropriate UUT, when 
such is desired or commanded by the operator or automatically commanded by 
a particular test. 
The microcomputer 16 is a standard state-of-the-art microcomputer system. 
Such for example, as an Intel multi-bus II. However, a ruggedized IBM-AT 
compatible system may preferably be substituted. As is illustrated in 
FIGS. 5(a) and (b), the computer 16 includes a bus 96 for communication 
between the various portions of the system. As is illustrated, there are 
provided a serial communications PWBA 98, a central services module PWBA 
100, a single board computer PWBA 102 and a peripheral controlled PWBA 
104. The peripheral controller in turn communicates with a 40 megabyte 
hard disc drive 106 as well as a 60 megabyte tape drive memory backup 108. 
A microcomputer bus interface (PWBA 110) is interconnected by the ECC 
system bus 112 to the instrumentation control bus interface PWBA 114 as 
well as the flight control electronics bus interface PWBA 116. 
The instrumentation and control interface assembly (ICI) 20 is a drawer as 
shown in FIG. 1 which contains a plurality of printed wiring board 
assemblies (PWBA) such as illustrated in FIGS. 5(a), (b) and (d-f). In one 
specific application, the PWBA in the ICI drawer 20 would be a switch 
monitor 118, a solenoid command 120, an analog data acquisition 122, a 
plurality of servoamplifier PWBA 124, a plurality of bridge transducer 
conditioner PWBA 126, and a plurality of pulse train conditioner PWBA 128. 
Each of these communicates through the ICI bus interface PWBA with the ICI 
bus 130 so that appropriate commands can be received from the computer 
system 16 for application to the desired components within the ICI. 
As is illustrated particularly in FIGS. 5(a)-(f), the ICI 20 functions to 
control the hydraulic console 12 and the various components contained 
therein, the connection being through the I/O connector panel 80. As is 
illustrated, the switch monitor PWBA 118 communicates with the 
limit/pressure switches 132 in the hydraulic console 12. The solenoid 
command PWBA 120 communicates through a solid state relay assembly 134 
with solenoid valves 136. The solid state relay assembly 134 also 
communicates with the analog data acquisition PWBA 122 to provide 
information as to the state of the solenoid valves 136. The pressure 
electrohydraulic valves 138, which control the pressure of the fluid to be 
applied to the UUT, communicate with the servoamplifier PWBA 124, as do 
the flow electrohydraulic valves 140 which control the flow of fluid to 
the UUT. 
There are numerous transducers which are of the analog direct current type 
shown at 142 in the hydraulic console 12. These analog d.c. transducers 
142 communicate with the bridge transducer conditioner PWBA 126 which in 
turn communicate with the servo amplifier PWBA and the analog data 
acquisition PWBA to provide the appropriate controls to the pressure and 
flow valves 138 and 140 as well as the desired information concerning the 
status of the transducers for application to the microcomputer system 16. 
Additional transducers of the digital pulse type as shown at 144, 
communicate with the pulse train PWBA 128 so that appropriate information 
may be provided to the computer system 16. 
The flight control electronics interface assembly (FCEI) 22 as is shown in 
FIG. 1, is again a drawer similar to the ICI drawer 20 which contains a 
plurality of PWBA. The PWBA communicate with the FCEI bus interface PWBA 
116 through the FCEI bus 146. As is illustrated on FIGS. 5(a)-(f), the 
FCEI controls the UUT which is coupled to the automatic test equipment 
through the I/O connector panel 80. As is more clearly illustrated and 
discussed with regard to FIG. 3 above, the UUT will be mounted on a 
fixture disposed within the hydraulic control console 12 with appropriate 
hydraulic and electrical connections made to the UUT so that it may be 
caused to sequence through a plurality of tests controlled by the computer 
16 to determine whether or not the UUT is functional. 
Disposed within the FCEI drawer 22 is a switch monitor PWBA 148 which 
communicates with limit pressure switches 150 in the UUT. Solenoids 152 in 
the UUT communicate with a UUT solenoid valve controller PWBA 154 in the 
FCEI. A programmable source of direct current 156 is connected to the UUT 
solenoid valve controller PWBA 154 to provide the appropriate energization 
to the solenoids 152 in the UUT 62. The UUT solenoid valve controller PWBA 
154 also provides information to the analog data acquisition PWBA 158 to 
communicate the status of the solenoids to the computer system 16. Also 
provided is a frequency response analyzer PWBA 160 which communicates with 
the command generator PWBA 162, the direct drive servocontrol PWBA 164 and 
the servocontrol PWBA 166. In addition, the oscillator PWBA 168 
communicate with a programmable source of alternating current 170. 
Depending upon the particular UUT which is connected to the hydraulic 
console for testing, there may be LVDT position transducers which are 
typically associated with linear servoactuators. There may also be direct 
drive servovalves which have appropriate feed back position indicators 
associated therewith and there may also be torque motor servovalves 176 
which also have appropriate feedback position indicators associated 
therewith. As is illustrated, the direct drive servocontrol PWBA 164 
communicate with the direct drive servovalve 74, the servocontrol PWBA 166 
communicate with the torque motor servovalves 176 as well as the LVDT 
position transducers 172. As will also be noted, in the event that the 
direct drive servoactuator also includes LVDT, the position transducers 
would be associated as needed with the oscillator PWBA as well as the 
servocontrol PWBA. 
From the foregoing, it will be understood by those skilled in the art that 
the automatic test equipment constructed in accordance with the principles 
of the present invention, may communicate directly from the microcomputer 
system through the appropriate busses, the ICI and FCEI, to the hydraulic 
console and the UUT to automatically sequence through a series of 
preprogrammed tests to determine the functionality of the UUT. The 
particular tests to be initiated and sequenced are chosen by the operator 
through the utilization of the operator interface panel through 
identification of the particular UUT that is to be tested. As will become 
more apparent hereinafter, the operator may choose the type of test as 
well as the presentation of the results of the test and the like. 
As will also be apparent to those skilled in the art, there is also 
provided access to electrical power to power the equipment contained in 
the automatic test equipment as is illustrated schematically at 178. As is 
therein shown, the alternating current power is applied to the alternating 
current distribution assembly 180 which in turn applies power to the 
cooling/filter assembly 182, the power supply assembly 184 and the voltage 
reference assembly 186 all as will be clearly understood by those skilled 
in the art. 
The hydraulic control system contained within the hydraulic console is 
shown in block diagram form in FIG. 6 to which reference is hereby made. 
Generally, the hydraulic supply system for utilization in the console and 
for connection to a UUT includes a source of hydraulic fluid under 
pressure which is supplied to a master manifold which through appropriate 
controls can be used to supply to output ports hydraulic fluid of the 
desired pressure and at a desired flow rate depending upon the particular 
UUT being tested. The system as shown in FIGS. 6(a) and (b) presumes a 
self-contained source of hydraulic fluid under pressure. It will be 
understood by those skilled in the art that the self-contained source may 
be eliminated and a source of fluid under pressure provided at the 
facility wherein the test equipment is housed, may be used. Under these 
circumstances, the facility hydraulic supply would be connected to the 
master manifold assembly and the return to the facility hydraulic supply 
would be connected from the master manifold assembly to the facility 
hydraulic supply return. 
As is shown more in detail in FIG. 6, there is provided a reservoir 200 
containing hydraulic fluid. Connected to the reservoir is a pump 202 which 
is driven by a motor 204 which has applied to it appropriate electrical 
energy from a source 206 through a motor controller 208. The pump 202 
functions in a normal manner to draw fluid from the reservoir 200 and 
supply the same under pressure through an appropriate conduit 210 to a 
master manifold assembly 212. Fluid is returned to the reservoir through a 
return conduit 214. Also connected to the reservoir 200 is a high pressure 
pump 216 which is driven by a hydraulic motor 218 that is connected to the 
master manifold assembly. The function of the high pressure pump 216 is to 
provide hydraulic pressure to predetermined UUT's at a pressure higher 
than that normally available from the normal supply pump 202. 
Through appropriate commands received from the computer system and applied 
to the ICI and from there through the appropriate connector panel 80 to 
the hydraulic control system, various of the sub-manifolds may be 
activated. Such activation causes the hydraulic fluid at the pressure and 
flow rate needed for a particular test to be applied through the master 
manifold assembly 212 to the ports 42. For example, the filtration 
manifold 220 would be activated so that the fluid provided from the pump 
202 is appropriately filtered both at the supply and return to remove any 
unwanted contaminants from the fluid. The drive load manifold 222 would be 
activated and controlled in order to supply fluid under pressure through 
the appropriate port to drive or manipulate the UUT connected to that 
particular port. The high pressure control manifold 224 is utilized to 
control the application of high pressure fluid through the high pressure 
pump 216 to the master manifold assembly. The supply pressure control 
manifold 226 is utilized to control the application of fluid under 
pressure at the normal supply pressure to the master manifold assembly. 
The return for the low and high flow manifold assemblies 228 and 230, 
respectively, are utilized to control the return to the reservoir from 
either a low flow or high flow condition depending upon the UUT. The 
cylinder assembly control manifold 232 is utilized to apply the 
appropriate flow of fluid to the desired port which is connected to a 
cylinder UUT. As is noted, the output ports 42 are connected to a 
hydraulic distribution manifold 234 through appropriate conduits 236. 
It will be understood by those skilled in the art that through the 
appropriate interconnections, both electrical and hydraulic, within the 
hydraulic control system and to the ICI and the computer control system 
that various of the control ports 42 can have applied to them a desired 
flow of hydraulic fluid at the desired pressure for application to a UUT 
which is to undergo tests. With such controls, the operator can connect 
the UUT to any of the ports desired and thereafter have the fluid applied 
to the UUT under control of the hydraulic control system without 
additional difficulty or interaction with the system. 
For the automatic test equipment constructed in accordance with the 
principals of the present invention to properly operate, there is provided 
software. The software consists basically of four major parts; the system 
software, the UUT test software, the self-test and maintenance software, 
and calibration software. The system software provides an interface for 
all other high level software to access the automatic test equipment's 
electronic and hydraulic functional capabilities. The UUT test software 
includes the commands which control the automatic test equipment and the 
UUT through the test sequences as required by the UUT's specifications. 
The self-test and maintenance software provide a suite of automatic tests 
necessary to maintain or troubleshoot the automatic test equipment. The 
calibration software provides automated calibration procedures that 
calibrate the automatic test equipment's internal instruments with 
acceptable external standards. 
The system software may be visualized as a plurality of layers enabling 
communication between a test program manager and the system hardware in 
order to sequence through a series of test steps (a test program) 
necessary to test the functionality of a UUT. This is illustrated in FIG. 
7 to which reference is hereby made. As is therein illustrated, a test 
program manager 250 controls a plurality of tests 252 by communication as 
illustrated by the communication path 254 between the tests 252 and the 
input/output system 256 as well as between the tests 252 and the devices 
258 as shown by the path 260. The input/output system (or channels) 256 
communicates with the system hardware 262 to in turn run the test through 
the UUT 264 and provide results back to the test program manager. As 
shown, there is two-way communication between the various portions of the 
system software. 
More specifically, the input/output system (channels) as illustrated in 
FIG. 7 is shown in greater detail in FIG. 8. The input/output (I/O) 
channel, as indicated above, provides the communication objects that 
interface the upper layers of software to the system hardware. The I/O 
channel as shown in FIG. 8 is the principal class involved in this layer. 
FIG. 8 shown the inheritance structure of the I/O channel. Channels are 
either of the proportional or the discrete type depending upon the 
communication hardware. Proportional channels are used for parameters such 
as hydraulic flow, pressures and the like which vary proportionally 
throughout the range of the device. Discrete channels are used for state 
oriented controls such as controlling a solenoid valve to the open state 
or the closed state. The system software contains a plurality of such 
channel declarations which define the hardware/software interface. In 
addition, the I/O system includes other classes which operate on channels 
to generate dynamic commands, record test system parameters against time 
and detect test system events, respectively. 
For any particular channel, the information which is common is the name of 
the channel, the type of channel, the address of the channel, the range 
between high and low of the characteristics of the channel and the built 
in test (BIT) mask, i.e. where, in the word being received, will the 
desired information reside. The capabilities for the particular channel 
class insofar as functionality is concerned, is to read, raw read (read 
unscaled data), write, raw write (write unscaled data), initialize (check 
the data read falls within the specified range) and to get information. 
The characteristics and the functionality for the channel class would be 
common to all of the channels in the automatic test equipment. A subclass 
of the base or abstract class, channel, is the proportional channel class. 
The proportional channel class inherits all of the characteristics and the 
functionality from the channel abstract class and, in addition thereto, 
also includes the additional characteristics of resolution, the particular 
units in which measurement controls communicate in the parameter name and 
the scaling line. The functionality of the proportional channel includes 
scaling, unscaling, ramping (which means to cause the particular 
characteristic being controlled to increase or decrease at some specified 
rate), to stop ramping, to wait for the ramp and to check the range. It 
may thus be seen that when a proportional I/O channel is defined and a 
specific instance thereof is declared (named), the characteristics for 
that instance are defined utilizing the information and functionality 
inherited from the abstract channel class as well as the more specific 
information from the proportional class. 
The discrete channel class is an additional subclass in an I/O channel. 
These devices are those which have a particular state such as on/off 
devices, for example solenoids, or the like. The discrete channel class 
provides a means to read from and write to an automatic test equipment 
communications port for such a discreet on/off data device. When the 
discrete channel class is declared, it, like the proportional channel 
class, inherits from the abstract channel class as above identified, both 
as to characteristics and functionality. In addition thereto, the 
characteristics include, for the discrete channel class, state name array 
(which associates a name with each possible value), initial state, and the 
functions, to get the state name and get the state value. 
As specific examples of some of the channels which may be available in any 
particular automatic test equipment, the following is provided. 
CHANNEL 1--Facility Pressure Select--3,000 psi 
CHANNEL 2--Facility Pressure Select--4,500 psi 
CHANNEL 3/4--Leakage Flowmeter Select 
CHANNEL 5--RI Leakage Meter Select 
CHANNEL 6--RII Leakage Meter Select 
CHANNEL 9/10--SVD OUT O/OUT 1 
CHANNEL 11--Supply Filter 
CHANNEL 12--Return Filter 
CHANNEL 13--High Pressure Supply Filter 
CHANNEL 14--Return Shutoff Valve 
CHANNEL 15--Rotary Coupler Engaged 
CHANNEL 16--Rotary Coupler Disengaged 
CHANNEL 17--ECC Interlock Switch 
CHANNEL 18--Test Bed Safety Doors 
CHANNEL 19--Linear Encoder Conditioner Alarm Indicator 
CHANNELS 1-6 are each discrete read/write solenoids which are visible to 
the operator, while CHANNELS 9-19 are discrete devices which are read only 
and are visible to the operator. As can be seen, each of the devices has a 
state of being on or off and thus is discrete. 
Typical examples of proportional channels are provided as follows. 
CHANNEL 1--Linear Actuator Fixture Encoder 
CHANNEL 2--Manual Input Arm Fixture Encoder For Linear UUT's 
CHANNEL 3--Rotary Fixture Encoder 
CHANNEL 4--Drive/Load Actuator Control 
CHANNEL 5--Drive/Load Actuator Control With Rotary Actuator Positioned 
Feedback 
CHANNEL 6--Feedback Offset With Range Gain Of 0.25 
CHANNEL 7--Rotary UUT Manual Input Arm Actuator With Feedback Proportional 
CHANNEL 8--Large Flowmeter 
CHANNEL 9--Leakage Flowmeter 
CHANNEL 10--Load Fixture Torque Transducer 
CHANNEL 11--Linear Load Actuator Load Cell 
CHANNEL 12--Manual Input Arm Load Cell For Linear UUT 
CHANNEL 13--Manual Input Arm Load For Rotary UUT 
CHANNEL 15--System Supply Fluid Temperature 
CHANNEL 16--Hydraulic Console Cabinet Air Temperature 
CHANNEL 17--RI Port Fluid Temperature 
CHANNEL 18--RII Port Fluid Temperature 
As can be seen, each of these proportional channel devices are 
proportional, insofar as their characteristics are concerned, Channels 1 
through 7 are read/write while channels 8 through 18 are read only and are 
visible to the operator. Those skilled in the art will readily recognize 
that many additional I/O channels can be utilized depending upon the 
particular test equipment and the UUT's to be tested. 
By reference now to FIG. 9, there is illustrated schematically, in block 
diagram form, the hierarchy of classes as applied to servocontrol devices. 
The device 280 is an abstract class containing characteristics for all 
servodevices which characteristics are inherited into the lower classes of 
such devices as will be more fully explained hereinafter. The 
characteristics for the devices falling within the device abstract class 
would be such characteristics as get Device, get the Device list, stop all 
Devices, register Device clean up, and stop. For each servocontrol 282 
subclass, such characteristics as the electrical signal wave type 
(sinusoidal, sawtooth or the like), the duration of the wave, the maximum 
number of cycles, the amplitude, offset, frequency resolution and ramp 
rate may be utilized. In addition thereto, commands are provided from the 
test program manager, as will be described more fully hereinafter, to 
write, to read and to ramp insofar as the servocontrol device is 
concerned. 
As can be seen, there are specific servocontrols such as the flow 
servocontrol 284, the direct drive servocontrol 286 and the UUT 
servocontrol 288 which function as additional subclasses of the 
servocontrol. Under the flow servocontrol, there are specific devices 
identified as the linear actuator 290 and the rotary actuator 292. The 
flow servocontrol and the two instances of linear actuator and rotary 
actuator are utilized as part of the automatic test equipment system. It 
will thus be recognized by those skilled in the art that the particular 
tests which are conducted utilizing the automatic test equipment in 
accordance with the present invention, are applicable to those devices 
which exist within the automatic test equipment as well as to the devices 
which are units under test such as the UUT servocontrol 288. 
When a UUT servocontrol 288 is declared, the characteristics which exist 
with respect thereto are set the current gain, set the frequency 
component, enable the digital to analog converter (DAC) get the feedback 
type, determine whether the servo is on, get the total current and either 
open or close feedback loops as may be required. 
As will be noted, under the UUT servocontrol 288 there are two additional 
subclasses, the LVDT feedback servocontrol 294 and the encoder feedback 
servocontrol 296. The encoder feedback servocontrol would be a type of a 
specific servocylinder in which the characteristics would be to initialize 
the feedback by setting the position feedback offset and to then set the 
gain and range of the feedback stages. When the specific instance of the 
encoder feedback servocontrol 296 is declared, inheritance would occur 
from the characteristics for the UUT servocontrol 288, the servocontrol 
282 and the device 280 all of which would be included with the encoder 
feedback servocontrol 296 to provide the necessary information needed to 
conduct a test. On the other hand, if an LVDT feedback servocontrol 294 is 
declared, then the characteristics which would be utilized with respect 
thereto is the current gain, the frequency component and the cutoff 
frequency. Again the characteristics from the device 280, servocontrol 282 
and UUT servocontrol 288 would be inherited into the LVDT feedback 
servocontrol 294 for conducting the appropriate tests. In the event that a 
particular servocontrol device included multiple LVDT's, then that 
instance, as shown at 298, would be declared and the multiple LVDT paths 
would be enabled and the appropriate frequency components and read/write 
commands would be provided. In this manner, all of the previous 
characteristics from the device 280, servocontrol 282, UUT servocontrol 
288 and LVDT feedback servocontrol 294 would be inherited and included 
into the specific instance of the multi LVDT feedback servocontrol 298 to 
provide the control for such a device. 
It will be recognized by those skilled in the art that similar 
characteristics would be developed for each of the additional subclasses 
such as the flow servocontrol 284 and direct drive servocontrol 286 as 
well as the specific instances of the linear 290 and rotary 292 actuators 
in order to provide the required tests for such devices. 
The test program manager as shown in FIG. 7 is set forth in more detail 
schematically and in block diagram form in FIG. 10 to which reference is 
hereby made. The test program 300 contains components, test groups and 
tests and provides functions to add items to the test program, show the 
items which belong to the test program, run all of the tests or individual 
tests as may be desired, to perform fault isolation, generate test status 
reports and detailed test results reports, generate a fault isolation 
report, indicate whether it is valid to resume a test sequence and to 
provide additional miscellaneous functions to support these various tasks. 
The most important purpose of the test program is to provide a framework 
for running a sequence of tests. A particular test to be administered by 
the test program 300 can be determined as the UUT program 302, the 
self-test program 304 or the calibration program 306. The test 308 
sequences the test from the test program to the particular instance which 
has been declared, receives and stores the data generated during the test 
and conducts the diagnostics test when such is to be done as a result of a 
failure of the device being tested whether it be a UUT or a part of the 
automatic test equipment. 
A UUT test is defined when a specific instance of a specific type of UUT 
test has been declared. When such occurs, a specific instance of a UUT, 
for example an instance of a cylinder UUT 310, is specified to the UUT 
test. The UUT test can thereby utilize the services provided by the 
specified UUT object to perform the required testing procedure. The UUT 
object, for example an instance of a cylinder UUT 310, inherits the 
characteristics for the linear UUT 312 and UUT 314. The UUT test class 
adds an instance relationship which identifies what UUT a test object is 
testing. The UUT class provides functions that can be used by the UUT test 
objects to control the UUT. For example, the UUT class provides the 
ability to statically and dynamically command the UUT, control its 
solenoid valves, and provide functions for applying standard operating 
pressures, coupling or uncoupling the UUT from an external load, mounting 
a UUT into its fixture, and purging the air from a UUT, to name a few. In 
addition, the UUT objects defines how a specific UUT is connected to the 
automatic test equipment system. As a result, UUT tests can be designed to 
operate on various UUTs that are each connected to the automatic test 
equipment differently. For example, an LVDT test can be written to query 
the UUT object to determine how many LVDT channels it has and what 
automatic test equipment devices they are connected to. With this 
information, the same test class can be used for various types of UUTs 
that have one or many LVDTs. 
The test base class 308 includes characteristics applicable to all test 
subclasses which includes data comparison operations, test result report 
generation, start time logging, temporary information and results storage, 
and the like. The functions would be such things as get the results, 
isolate, report the isolation information, report test details, run the 
tests, set the test status and the like. The UUT test 312 is an abstract 
class which defines characteristics which are used by each of the specific 
instances of UUT tests to be performed. 
In some cases, there are test classes which provide functionality specific 
to a particular testing procedure which are designed to be inherited by 
more specific test classes and applied as appropriate to a plurality of 
UUTs. These tests may be referred to as general purpose tests and are 
shown, for example, as frequency response 313. More specific tests are 
then defined, for example, F-15 stabilator frequency response 315 which 
inherits the services provided by the general purpose test and applied as 
appropriate to specific UUT testing applications. This is illustrative of 
the fact that tests may be designed to be performed with regard to a 
plurality of different instances of specific devices without a change in 
the test, that is the specific test such as EHVOPER 311 or stabilator 
frequency response 313 does not "know" what UUT it is being run on. In 
this manner, it can be seen that a specific detailed test procedure does 
not need to be designed for each and every instance of specific device be 
it UUT or self-test that is to be tested. 
The self-test and calibration test are the sequence of tests which are 
conducted directed to the automatic test equipment devices when the 
self-test program or the calibration program has been selected either 
automatically or by the operator. 
The self-test software is illustrated more specifically in FIG. 11 to which 
reference is hereby made. The self-test software contains a set of classes 
that model the types of tests required to adequately verify that the 
automatic test equipment is fully operational. Self-tests are developed by 
inheriting from the self-test base class 301 which in turn inherits from 
the test class 303. As is clearly shown in FIG. 11, the self-test includes 
a drawer card test, miscellaneous electronic tests and miscellaneous 
hydraulic tests applicable to the entire automatic test equipment. Set 
forth in each of the types of tests to be conducted is at least one 
instance of every class listed. Some classes have more than one instance 
such as the direct current conditioner test (DC Conditioner). As an 
example, the D.C. conditioner test tests the direct current conditioner 
cards in the automatic test equipment system. Since there are four of 
these cards contained in the drawers in the automatic test equipment, 
there are four individual D.C. conditioner test objects one for each of 
the cards. The test objects require parameters which characterize the test 
to be specified when the specific test is declared. In the case of the 
four D.C. conditioner test objects, the only difference between the four 
instances is the different I/O channels which are specified. Should the 
system be reconfigured to use more or less cards, or should the I/O 
channel assignments change, such can be accommodated by changing the 
parameters that define the D.C. conditioner test objects or by adding or 
deleting test instances. 
Referring now more specifically to FIGS. 14-17, there are shown a series of 
flow charts which are representative of the performance of tests utilizing 
the system and automatic test equipment of the present invention. These 
flow charts are merely representative of the diagnostic capability of the 
test program and test classes of the system. As is shown in FIG. 14, an 
internal leakage test is being conducted on a servoactuator which, for 
example, may be used as part of an aileron package on an aircraft. As is 
indicated at 400, the actuator has applied thereto a signal which causes 
the actuator to retract and the pressure to the actuator is reduced to 
2,200 psi with the return being at zero psi. Flow is caused to stabilize 
and the leakage is then measured. If the leakage is greater than 197 cubic 
centimeters per minute, the actuator has failed and a display and print 
will occur indicating that the main ram seals or the internal seals 
require replacement. If, however, the leakage is less than (LT) 197 cubic 
centimeters per minute in the retracted position, a command is given to 
the servoactuator to full extend after which the flow is stabilized and 
the leakage is again measured. Again, the leakage cannot exceed 197 cubic 
centimeters per minute, and if such does occur, then a no-go will be 
issued and there will be displayed and printed an indication that the 
fault lies in the overload relief valve, the main ram seals or the 
internal seals of the unit. If, however, the leakage is less than (LT) 197 
cubic centimeters per minute, then a command is given to the actuator to 
return to its null or neutral position. Thereafter, the flow is allowed to 
stabilize and the leakage is measured. The leakage at this point should be 
less than or equal to (LE) 787 cubic centimeters per minute. If the 
internal leakage is greater than 787 cubic centimeters, then there will be 
a no-go and the display and print will indicate that the internal seals 
need to be replaced in order to put the actuator into an operable 
condition. If, however, the leakage is less than or equal to 787 cubic 
centimeters per minute, a go is indicated and the test program 300 
automatically will sequence to the next test. 
FIG. 15 is a flow chart illustrative of an additional test subject directed 
to, for example, an elevator operator on a bypass door on an aircraft. As 
is shown at 406, 28 volts d.c. is applied to a solenoid and the solenoid 
current is then measured to determine if it is within limits. The upper 
limit (UL) is 650 milliamperes and the lower limit (LL) is 100 
milliamperes. If the current falls within these limits, then the test 
sequences to the solenoid diode at 408. At this step in the test sequence 
the 28 volts d.c. is removed from the diode and the back EMF voltage is 
measured. The upper limit (UL) is minus 10 volts, the lower limit is -43 
volts. If the measurement verifies that the back EMF voltage is within 
these limits, the sequence moves to the electrohydraulic valve command at 
410. At this position in the test sequence a command signal of 0.666 volts 
is applied and the current is then measured. The current should be greater 
than (GT) at 15 milliamperes. If such is the case, then the test is 
satisfactory and complete and the test program manager sequences to the 
next test. 
The flow chart as illustrated in FIG. 14 is also illustrative of the 
ability of the present system to isolate a fault which has been detected 
during the sequencing of the test program. When a test is being conducted, 
the test is sequenced through each step under control of the test program 
300 and test 308 as above described. When the test has been completed, 
then the test program returns and ascertains whether any of the limits 
have been exceeded, that is, asks the question of whether the failure has 
occurred. If a failure has occurred, the test program then sequences to 
that position in the test and defines in greater detail the failure and 
provides a diagnosis as to the probable cause of the failure. For example, 
if a failure has occurred in the solenoid current, at 406 there will be a 
no-go to determine whether the failure was low or high. If the failure was 
low, then a no-go will exist showing that the solenoid or solenoid diodes 
are defective as shown at 412. If the failure was high, then it indicates 
that the solenoid and wires which open to the solenoid exist and such 
would be displayed as is illustrated at 414. On the other hand, if the 
solenoid diode failed and was outside the upper and lower limits, there 
would be a no-go and it would be displayed and printed that the solenoid 
diodes had failed as shown at 413. If, however, the electrohydraulic valve 
command current was not as required, then there would be displayed and 
printed that the wires were open to the EHV as shown at 415. 
As is illustrated in FIG. 16, a test on a UUT including an LVDT is being 
conducted and as shown the first step in the sequence is a purge at 420 
which is accomplished by applying 1,100 psi supply slowly and cycling the 
input at least ten times. Thereafter, as shown at 422, the command to 
extend in a hard over condition is applied with the feedback loop open. 
That is, none of the feedback circuits as shown in FIG. 13 for the UUT 
servocontrol block diagram are enabled (ENB). Thereafter, the output 
position and the LVDT voltage are measured and the measurements are saved. 
If the output position of the actuator is greater than (GT) 25.85 inches, 
the position is appropriate as well as the LVDT voltage being greater than 
(GT) 2 volts rms. If either of these do not meet the requirements, then a 
no-go is issued. If, for example, the position of the ram is not as 
required, then there would be an automatic branching to the diagnostic 
test DT1 as shown in FIG. 17. 
As is shown at 424, the phase of the applied signal to which reference is 
hereby made is reversed and the output extended and measured to determine 
whether it is greater than (GT) 25.85 inches. If such occurs, then there 
would be a display and print showing that the wires are reversed to the 
EHV. If, however, it does not meet this standard, then there would be 
displayed and printed that the solenoid, the electrohydraulic valve and 
the main ram lock are improperly assembled and that the UUT is thus 
inoperative. 
If, however, the output position and the LVDT voltage is appropriate, as 
shown in the flow chart of FIG. 15, then a signal is applied to cause the 
actuator to retract at which time the position is measured along with the 
LVDT voltage. If the position is less than (LT) 19 inches and the LVDT 
voltage is less than (LT) 20 volts rms, then the actuator is within 
specifications and the test program manager would automatically step to 
the next test. If, however, either of these tests show that the position 
is improper or that the voltage is improper, a no-go would be issued and 
there would be displayed and printed to either disassemble the actuator 
and assemble it correctly as shown at 426 or that the LVDT is inoperative 
as shown at 428. 
Referring now to FIG. 12, there is illustrated a schematic diagram in block 
form for a flow servocontrol. The circuit as illustrated in FIG. 12 is the 
circuit which is controlled for the flow servocontrol 284 as shown in FIG. 
9 responding to a test as described in conjunction with FIG. 10. As is 
illustrated in FIG. 12, commands are provided from the appropriate test 
program through the data bus interface 315 to a digital to analog 
converter 316 and then to a summing junction 318. Appropriate coding, 
control address information and DAC timing functions are provided by the 
erasable programmable logic devices (EPLD) 317 and registers 319 as is 
well known to those skilled in the art. Feedback is provided from the 
rotary potentiometer 320 through an appropriate feedback select 322 and 
feedback gain select 324 and also to the summing junction 318. The current 
gain select determines the appropriate gain for the specific device. The 
output is then applied to the servovalve drive 328 which in turn provides 
the appropriate signal to drive the servovalve 329 in accordance with the 
test sequence. The particular structure, as just described, would be used 
in the event that a rotary actuator 292 (FIG. 9) has been declared as the 
specific instance. In the event a linear actuator is to be utilized, then 
the feedback from the digital encoder 330 would be utilized and passed 
through the appropriate decoder 332, shift register 334, digital to analog 
converter 336 and filter 338 to the feedback select 322 and then as above 
described. The particular information which has developed as a result of 
the test would be applied back through the busses to the data acquisition 
system (DAS) for appropriate comparisons and storage. As is shown, a 
second channel may be provided. 
By reference now to FIG. 13, there is shown a block diagram for a UUT 
servocontrol test circuit. Although there are three specific instances of 
UUT servocontrols, namely the LVDT 294, the multi LVDT 298 and the encoder 
feedback 296 as shown in FIG. 9, it will be recognized by those skilled in 
the art that the command digital to analog (DAC) converter 340, the 
summing junctions 342 and 344, the gain select 346 and the 
electrohydraulic valve (EHV) drive 348 are all common to anyone of the 
specific instances to be declared. In the event that a linear device, not 
utilizing an LVDT, such as the encoder feedback servocontrol 296, is 
declared, then the linear encoder 350, the position decoder 352, the 
digital to analog (DAC) converter 354, the appropriate filter 356 and the 
gain select 358 are enabled (ENB) by an appropriate command to apply a 
feedback signal to the summing junction 360 for application to the summing 
junction 342 and subsequently to the electrohydraulic valve drive 348. The 
additional feedback circuits utilizing LVDTS would not be activated but 
only the linear feedback circuit. 
It will, of course, be understood by those skilled in the art that similar 
to the circuit as shown in FIG. 12, appropriate control command and timing 
signals are provided over the various busses as illustrated to the command 
digital to analog converter 340 to sequence through the series of steps 
required to test the UUT servo. 
In the event a single LVDT is to be utilized, then the linear encoder 
section will be disabled and the LVDT feedback for UUT, LVDT 1 is enabled 
(ENB). Appropriate exitation is applied to the LVDT 1 362 which would in 
turn provide a signal to the input select 364, the differential amplifier 
366, the demodulator 368, the appropriate filter 370, the gain select 372 
and then to the summing junction 360 and ultimately to the 
electrohydraulic valve drive 348 as above described. Under these 
circumstances, the other feedback path for the UUT, LVDT 2 would not be 
enabled. If, however, a specific instance of a multi LVDT feedback 
servocontrol 298 is declared, then the UUT LVDT 2 feedback circuit is 
enabled along with the UUT LVDT 1 feedback circuit. The UUT LVDT 2 
feedback circuit utilizes the same reference numerals as the UUT LVDT 1 
except they are primed. 
It can thus be seen that for the UUT servocontrol, various portions of the 
circuit are activated or deactivated depending upon the specific instance 
of servocontrol device which is being declared for the particular test 
involved. During the sequencing of the test as applied to the specific 
device, appropriate information concerning the specific device is applied 
to the data acquisition system (DAS) for comparison with the 
characteristics applicable to that device, be they specific or inherited 
from a higher class, to determine the functionality of the specific device 
being tested. 
Similar types of circuits would be utilized for the direct drive 
servocontrol as will be readily recognized by those skilled in the art. 
Referring now more specifically to FIGS. 18 and 19, there are illustrated 
flow charts showing the use of the EHVOPER 311 test (FIG. 10) on two 
different instances. In FIG. 18 the EHVOPER test is used on a specific 
instance of a stabilator having a multi LVDT feedback whereas in FIG. 19 
the specific instance is a rotary rudder having a single LVDT feedback. 
The multi LVDT feedback servocontrol circuit is shown in FIG. 12, the UUT 
test 310 in FIG. 10 and the multi LVDT feedback servocontrol test 298 is 
shown in FIG. 9. These flow charts are illustrative of the fact that a 
specific test does not "know" what UUT or device it is being run with 
respect to. Rather, when a specific test is required for a UUT, that test 
is called out in the test program at the appropriate position and the test 
sequence is executed. 
As is shown in FIG. 18 at 430, the voltage is removed from the solenoid 
diode and the back EMF voltage is measured to determine whether or not it 
is within the limits upper (UL) of -10 volts and the lower (LL) of -43 
volts. If such is within those limits, then the test sequences to the next 
step as shown at 432 wherein a command voltage of 0.666V is applied to the 
electrohydraulic valve A (EHVA) and the current is measured. If the 
current is greater than (GT) 15 milliamperes as required, then the test 
sequences to its next step as shown at 434. At this step the 0.666V 
command signal is applied to the electrohydraulic valve B (EHVB) and the 
current is measured. If the measurement is correct at or greater than (GT) 
15 milliamperes the test is satisfactory and the test program manager 
sequences to the next test. If, however, the back EMF voltage is outside 
limits, a no-go is issued and it is displayed and printed that the 
solenoid B diodes are defective as shown at 436. If the electrohydraulic 
valve A current is improper, then a no-go is issued and there is displayed 
and printed as shown at 438, EHVA, wires open to EHVA. Additionally, if 
the voltage as EHVB is incorrect, then there will be displayed and printed 
as shown at 440 that the EHVB is inoperative and that wires are open to 
it. 
As shown in FIG. 19, there is a test directed to the rotary rudder on an 
aircraft and as shown at 442, a voltage of 8 volts d.c. is applied to the 
solenoid and the current is measured. If it is within the upper limit (UL) 
of 1.07 amps and the lower limit (LL) of 0.107 amps, the test sequences to 
the next step as shown at 444 where as with the stabilator test (FIG. 17) 
a command of 0.666 volts is applied to the electrohydraulic valve (EHV) 
and the current is verified. If the current is greater than (GT) 15 
milliamperes as required, the test is satisfactorily completed and the 
test program manager sequences to the next step. 
If, however, the solenoid current was outside the limits as specified, then 
the test is a no-go at this point and as shown at 446, if the failure was 
low, that is less than 0.107 amps, then there would be a display and print 
that the solenoid or the solenoid diode was defective and that there is 
possibly a short. If the failure was high, then there would be displayed 
and printed as shown at 450 that the solenoid failed and that it is 
probably open. 
By way of further clarification, a specific example will now be discussed 
setting forth the steps utilizing the computer controlled automatic test 
equipment of the present invention in conducting a test on a specific UUT. 
It will be assumed that the UUT to be tested is a stabilator for a 
specific aircraft and that the stabilator in this case has been identified 
as STAB-F 19. Other UUTs will be identified by specific titles as well. 
The specific UUT identified as the STAB-F 19 is installed on the hydraulic 
console fixture as shown at 36 in FIG. 3 with attachments being made by 
way of appropriate conduits between the UUT and the hydraulic ports 42 as 
well as the appropriate electrical connections. The operator then calls up 
on the CRT 28 screen a menu of all of the test programs available to 
conducted. Among those will be the STAB-F 19 test program. The operator 
then indicates to the system that the STAB-F 19 test program is to be 
conducted At this point there appears on the screen a list of tests that 
are applicable to the STAB-F 19 UUT. The operator at this point may elect 
to conduct any one of the tests set forth on the list, or alternatively, 
may elect to have the automatic test equipment sequentially conduct each 
of the tests in order as they appear on the list without further 
intervention by the operator. It is here assumed that the operator chooses 
to have all the tests run automatically. Assuming that the first test on 
the list of tests to be conducted for the STAB-F 19 is a frequency 
response test as shown at 313 in FIG. 13, there will be a pointer (an 
address) identifying where in memory that particular test sequence 
resides. Each item in the list will similarly contain a pointer to the 
specific address for that test sequence. The test sequence, as thus 
identified, will then be conducted automatically. 
When the frequency response 313 test is addressed, it will contain portions 
from the test 308, the UUT test 312 as well as the frequency response test 
313. The UUT test will include a pointer (an address) to the UUT which 
will in turn identify the STAB-F 19 as the UUT. The UUT STAB-F 19 will in 
turn contain a plurality of pointers (addresses) to various of the devices 
258 (FIG. 7) which are to be utilized with a UUT 264 (FIG. 7) such for 
example as the hydraulic ports 42 or the servocontrol devices as shown in 
FIG. 9, or the like. 
It will thus be seen that when the operator chooses the STAB-F 19 test 
program to be conducted on the STAB-F 19 UUT, the test program 300 
specifies the test sequence which in turn specifies the specific test for 
the STAB-F 19 stabilator which includes and inherits from the UUT test 312 
the frequency response general purpose test 313 and utilizes the specific 
instance definitions for the STAB-F 19. The UUT test will in turn include 
a pointer (an address) to the UUT 314 which will in turn include a pointer 
(an address) through the appropriate I/O 257 (FIG. 7) to specific 
hydraulic ports for connection with the STAB-F 19 UUT to be tested. 
When the UUT test for the STAB-F 19 is being conducted, as above referred 
to, the servocontrol will be identified as one of the devices to be used. 
Since the STAB-F 19 is the UUT, the multi LVDT feedback servocontrol 298 
(FIG. 9) is a device which will be utilized. As a result, there will be a 
pointer (an address) to the servocontrol device since the multi LVDT 
feedback servocontrol is included as a part of the STAB-F 19 test. Through 
the inheritance hierarchy, the test will include the device 280, the 
servocontrol 282, UUT servocontrol 288, LVDT feedback servocontrol 294, 
the multi LVDT feedback servocontrol 298 as well as the specific 
definitions for the instance of the STAB-F 19 stabilator. When the 
specific test and the specific devices, as above described, have been 
appropriately selected as a result of the various commands given in the 
sequencing of the test on the STAB-F 19 stabilator, then specific values 
are automatically assigned to each of the characteristics or parameters 
which definitions or values are unique to the STAB-F 19 stabilator. It is 
these specific values which provide the specific parameters against which 
the STAB-F 19 is tested, for example, as shown in the flow charts above 
described specifically with respect to FIGS. 18 and 19. 
Once the STAB-F 19 test program has been conducted on the specific 
stabilator which is attached to the hydraulic console and the test is 
fully completed, then the specific values for that particular test program 
are no longer needed and are automatically eliminated from the test 
program. It is, however, to be clearly understood that the various 
hierarchies for that test such as the test, UUT test, frequency response 
and the like or the device, servocontrol, UUT servocontrol, LVDT feedback 
and multiple LVDT feedback as above described, are not destroyed but 
remain in the system for use with regard to future testing when a specific 
instance of a UUT is declared by the operator's selection of the 
particular test for that UUT. 
There has thus been disclosed a plurality of tests which may be applied to 
both the automatic test equipment and to units under tests as desired for 
any particular point in the testing procedures. In each instance, there is 
developed an abstract class of characteristics and functions which are 
applicable to all devices which fall within the particular group under 
consideration. One or more subclasses of such characteristics and 
functions may also be provided which are applicable to some but not all of 
the devices under consideration. When a specific instance of a device is 
declared, such as a specific servoactuator, for example such as a 
stabilator on an aircraft, then the characteristics and functions 
previously defined for the abstract class and subclasses, are inherited 
into the specific instance as declared to thereby define the 
characteristics for the specific device which has been declared. The test 
program manager will then sequence a series of tests applicable to the 
specific instance as declared to determine whether or not the device as 
declared is operable. If the device fails at any specific level, the test 
may then sequence to a diagnostic test to ascertain the manner in which 
the particular test step failed along with a printout as to the probable 
cause of the failure. Other operations may also be suggested such as 
adjustments, disassembly and reassembly or the like depending upon the 
particular type of failure which has occurred. 
Those skilled in the art will recognize that through the utilization of the 
particular architecture of software as described herein, there is no 
requirement, as has been the case in the prior art, to list all of the 
characteristics and functions for each device which is to be tested in 
order to provide a means for testing the same in a computer controlled 
automatic test equipment. Rather, characteristics applicable to all 
devices within a group can be inherited into specific instances when they 
are declared to provide this information. When the test is completed, the 
specific instances containing definitions for the characteristics and 
functions for that instance are no longer needed and are "destroyed". 
However, the group characteristics are retained and can be used at a later 
time when tests are to be conducted on other devices.