Method and apparatus for automatically calculating the integrity of an electrical coil

Method and apparatus for automatically testing an electrical coil through a surge tester. Comparison to a stored waveform through error area ratio computation is achieved by use of digital computer data processing techniques. A uniform threshold of acceptability is disclosed which is not dependent on voltage or type of coil tested. Statistical analysis may be programmed or hardwired into an embodiment to yield easily discernable manufacturing or field test information. Optimization of the entire process and the testing steps may also be achieved through an apparatus which may provide a variety of different output possibilities and which may be customized to the user's situation. Update and storage of test results is included as well as correlation with manufacturing data.

A. BACKGROUND OF THE INVENTION 
Generally, the present invention relates to the field of surge test 
equipment. More specifically it relates to methods and apparatus to 
automatically determine the existence and extent of a fault in an 
electrical coil from a surge test. 
The invention focuses on several needs of users of surge test equipment. 
These users include both manufacturers--who test their products before 
shipping--and users--who test their equipment in the field as part of 
maintenance procedures. From an understanding of both of these 
perspectives, the present invention addresses the needs of these persons 
and addresses limitations found in existing surge test equipment. One such 
need is the desire of those performing the test to rapidly ascertain the 
integrity of the item being tested. This is of particular concern in the 
surge test environment because production line testing may need to be 
accomplished very quickly. Another limitation of existing surge test 
apparatus is the inherent difficulty in accurately assessing the existence 
of a fault in the equipment being tested. Because traditional techniques 
often have been based upon a visual comparison of waveforms which are the 
reaction of the equipment to the surge, such visual comparison has been 
difficult to adapt for an automatic determination. This difficulty has 
perhaps been underscored by the fact that in spite of increasingly 
sophisticated analysis means becoming available, the vast majority of 
surge test equipment is still based on visual analysis by an operator. 
Since unacceptable fault levels in the equipment being tested are 
sometimes hard to detect visually, the operators would ideally have some 
degree of skill in analyzing the surge test response waveforms. This is 
inconsistent, however, with the need to have such waveforms reviewed in a 
highly repetitive fashion on an assembly line as frequently as every few 
seconds. Naturally such a method also introduces the possibility of human 
error and its associated limitations. While smaller and smaller tolerances 
have been demanded, the practical limitations inherent to a visual 
technique have been difficult to overcome. Although several efforts have 
been made to automate the determination of the existence of a fault in the 
equipment being tested, these efforts have met with varying degrees of 
success and have often proved not to provide as accurate a result as even 
the visual testing traditionally done. The present invention not only 
addresses each of these needs but several others. 
Two of the additional aspects focused on in the present invention are 
particularly noteworthy. First, the nature of a surge test is such that 
the surge imposed upon the equipment to be tested actually weakens or, in 
extreme cases, can create a fault in that equipment. Although this aspect 
has been well known, traditional surge testing has not automatically 
limited the stress to which the equipment is subjected. In fact, through 
the existence of industry standards such as National Equipment 
Manufacturers Association Standard 1-12.05, repetitive surge testing has 
been widely supported. The present invention addresses this aspect by 
providing methods and test apparatus which automatically minimize the 
stress to which the equipment is subjected. Second, traditional surge 
testing has been through simultaneous comparison of the tested coil with a 
coil which is assumed to be acceptable--that is, a standard coil. In 
traditional techniques this usually has involved repeatedly subjecting the 
standard coil to identical surges as each different test item is analyzed. 
Not only does this weaken the standard coil but it is attended with other 
practical and power consumption concerns. Since the traditional technique 
of comparison testing is not an exact science, it has also been necessary 
to experimentally ascertain the threshold amount of change in the response 
to the surge at which a "fault" condition is determined to exist. This has 
been done through intentionally faulting an acceptable coil in the 
smallest possible way and observing the amount of change so induced. 
Obviously this technique has several undesirable features. The present 
invention addresses each of these aspects and the aforementioned aspects 
in one invention. 
As background to surge testing in general, it should be understood that the 
technique of subjecting an electrical coil to a voltage surge is well 
known having been disclosed at least by 1943 in an article by C. M. Faust 
and N. Rohats entitled "Insulation Testing of Electrical Windings" (Trans. 
AIEE Vol. 62, pp. 203-06). Basically the technique involves subjecting an 
electrical coil, such as is frequently found in an electrical motor, to a 
sharp, high voltage pulse and then allowing this pulse to oscillate or 
"ring" within the coil. This ringing produces decaying oscillations which 
may vary in several ways if there is any fault within the winding. One 
such type of fault is a breakdown in the insulation between adjacent 
coils--a turn-to-turn fault. Such a fault would change the inductance and 
capacitance characteristics of the coil and would thus be seen in the 
resulting waveform. Of particular importance is the need to subject the 
coil to one or more high voltage pulses in order to detect an incipient 
fault in such insulation. The fact that small breakdowns may not be 
visible until several surges have been accomplished is one reason for 
using repetitive surges for testing. The basic techniques involved are 
well known and have been the subject of numerous inventive efforts. An 
example of the types of waveforms occurring for the various possible fault 
scenarios is contained in several articles by the assignee including: 
"Winding Fault Diagnosis by Surge Comparison" presented at the Fourteenth 
Electrical/Electronic Insulation Conference and "Surge Test Methods for 
Rotating Machines" as published by the IEEE. 
While several inventive efforts have been directed to automating the 
technique of surge test analysis, most all of the automatic testers have 
been based upon the technique of comparing voltage levels of the test with 
those of a standard coil. Although envelope decay rate has also been used, 
it is almost always implemented in conjunction with voltage levels. The 
voltage level criterion has met with varying degrees of success and has 
not always resulted in more accurate determinations than were visually 
possible. U.S. Pat. No. 3,659,197 as assigned to General Electric 
Corporation presents an automatic testing device based on voltage 
comparisons which also allows visual analysis capabilities. That General 
Electric patent--through providing one technique for visual analysis and 
another technique for automatic analysis--also alludes to the inherent 
difficulties those skilled in the art have faced in attempting to develop 
a technique acceptable for automatic analysis. Another example of the 
prevalence of the use of voltage difference determinations as the 
criterion, is shown in U.S. Pat. No. 3,869,664 as assigned to Avtron 
Manufacturing, Inc., and its related patents. Although digital techniques 
have been available for some time, the focus by those skilled in the art 
on absolute voltage level criteria has become an impediment to the 
adaptation of automated techniques to the surge testing field. Even though 
absolute voltage criterion can be readily adapted to digital analysis, the 
potential for bad data points and its resulting in false indications has 
been undesirable. 
Since the present invention, in its preferred embodiment, is based upon 
well known computer integration and sampling techniques, at first glance 
it would seem that those skilled in the art would have had no trouble 
implementing these techniques to their field. This would seem especially 
true because there has been a long-felt need for accurate and reliable and 
automatic assessment of surge test results. The limitation that those 
skilled in art faced was that they simply failed to realize that the 
problem lay in properly choosing the detection criterion. They did not 
appreciate that the voltage difference criterion was at the root of the 
problem. Although the variety of patents in the field of automatic surge 
test equipment and the broad range of dates of these inventive efforts 
show that substantial attempts were made to automate the equipment, the 
fact that the traditional technique of visually detecting a fault still 
remains as the preferred technique shows that those attempts did not fill 
the need of surge test users. They simply did not understand that the 
effort necessary in this regard was not in refinement of the systems 
involved but rather was in development of a proper detection criterion. 
The broad acceptance of a voltage difference criterion by those skilled in 
the art of producing automated surge test apparatus basically led by 
teachings away from the technical direction of the present invention. It 
is also noteworthy that it was even a surprise to the inventor that the 
development of an area-based analysis resulted in not only one standard 
which was consistent across a broad range of motor types and 
characteristics, but also that utilization of such a technique lent itself 
so well to the data analysis capabilities described herein. 
The present invention recognizes and addresses each of these concerns and 
overcomes the limitations perceived by those skilled in the art by 
presenting methods and apparatus which, among other aspects, allow for 
digital processing and which overcome the difficulties in implementing 
such processing to the surge test field. The techniques and devices 
utilized in the present invention result in more accurate testing, in 
automatic testing and in testing which is more suitable from both the 
user's and manufacturer's perspectives. 
B. SUMMARY OF THE INVENTION 
Accordingly it is an object of the present invention to minimize the use of 
a standard coil in surge testing of equipment. Certainly an aspect of this 
goal is to avoid the need to impose a fault in an acceptable coil in order 
to determine the minimum threshold at which a coil is determined to 
contain a fault. 
Another object of the present invention is to integrate a multipurpose, 
fully programmable computer into surge test techniques and equipment. An 
object of this is to present a system which allows sufficient variation in 
technique, programming and analyses to suit the particular user, the 
particular uses, and the varying application environments of surge test 
equipment. 
It is also an object of the present invention to present methods through 
which acceptability of a coil may be determined without reference to a 
threshold dependent on a particular coil. In accordance with this purpose 
it is an object to provide the ability to generate a standard which does 
not directly depend on the results of any one coil tested. A further 
object of this general goal is to establish a threshold of acceptability 
which is consistent for the varying other types of coils tested, for 
varying voltages, or for varying other characteristics. 
It is a further object of the present invention to provide methods and 
apparatus which allow more accurate surge testing of electrical coils. In 
this regard it is desired to overcome the limitations imposed by the 
visual techniques traditionally used in surge test determinations. 
Broadly stated, a general object of the present invention is to automate 
the surge test process. In keeping with this general goal, it is an object 
of the present invention to achieve many objects through automatic means 
including: automatically assessing the acceptability of the coil being 
tested, automatically warning of changes in typical production variations 
for a variety of parameters, automatically stepping through several 
different tests at one point in both the manufacturing process and in the 
field testing, and automatically stopping subjecting the coil being tested 
to electrical surges upon detection of a fault. 
Another broadly stated object of the present invention is to incorporate 
statistical analysis into the surge test process and to specifically 
incorporate such analysis into the surge test equipment. An object of this 
generally stated goal is to minimize and to optimize the number of times 
which a coil being tested must be subjected to a voltage surge. Another 
more specifically stated object of such statistical analysis is to 
optimize the process, levels, and standards which are utilized in 
determining the existence of a fault. 
It is also an object of the present invention to present a method of 
analyzing the response of the coil being tested to a surge test. An object 
of this goal is to present a method which is accurate and suitable for 
digital applications. An object of the present invention is to introduce 
the use of area analysis to surge test operations. 
Naturally further objects of the invention are disclosed throughout other 
areas of the specification and claims.

D. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As can be readily understood from the steps set forth in the claims, the 
basic concepts of the present invention may be embodied in many different 
ways. Although the field of surge testing is well understood, FIG. 1 shows 
a display encountered whenever the traditional technique of visually 
ascertaining the existence of a fault is utilized. Such a display would 
usually appear on a dual channel oscilloscope. Referring to FIG. 1, in 
which the vertical axis is voltage and the horizontal axis is time, the 
general technique of surge testing can be readily understood. At time A a 
voltage pulse is imposed on the coil being tested. This results in the 
rapid rise in the voltage displayed. After the pulse, which has a short 
rise time (typically about one microsecond), the voltage then begins to 
decay and effects a ringing within the coil. This ringing is 
characteristic of a specific combination of capacitance, inductance, and 
resistance in the coil being tested. As can be seen in FIG. 1, a standard 
waveform--that is the response to the pulse by an acceptable coil--results 
in a voltage response which is characteristic of that coil. Standard 
waveform (1) would of course vary whenever a different type of coil were 
used. This is the time-honored reason for comparing two simultaneous 
pulses and lead those skilled in the art to presuppose the need for 
coil-dependent thresholds. Superimposed on this waveform is a simultaneous 
waveform of a coil being tested. As can be seen, this test waveform (2) 
displays different characteristics--that is a different time dependency 
and different voltage levels. It is these differences which allow 
detection of faults in the coil being tested. The variation between the 
two is due to a difference in the combination of inductance, capacitance 
and resistance with respect to the two coils. This difference is due to a 
fault in the coil being tested. This faulr can be any number of types of 
faults as is well known to those accomplished at surge testing. An example 
would be a breakdown in the insulation between adjacent windings of the 
coil, a turn-to-turn insulation defect. 
Referring to FIG. 2, the technique of the present invention can be easily 
understood. While in the prior art the majority of automatic test 
equipment has easily utilized a voltage difference (3) at any point along 
the two plots, this traditional voltage difference criteria has limits as 
herein discussed. Rather than utilizing such an analysis technique, the 
present invention analyzes the area between standard waveform (1) and test 
waveform (2), shown as shaded area in FIG. 2. This error area (4) provides 
a more accurate measurement of the degree of fault contained in the test 
coil. 
Referring to FIG. 3, it can be understood that a reference area (5) can be 
easily computed by measuring the area "under" standard waveform (1), shown 
as shaded area in FIG. 3. By "under" it is meant that the absolute value 
of the standard waveform would be utilized. A dimensionless ratio of error 
area (4) to reference area (5) can thus be easily computed. Since the 
technique of surge testing electrical coils is still being developed on a 
theoretical basis, it is true that prior to the present invention the use 
of traditional voltage difference criteria presented a practical 
expedient. However, voltage difference criterion has not been able to 
completely replace the visual detection techniques in many circumstances. 
In addition, it should be understood that other types of area analyses are 
possible and would fall within the scope and spirit of the present 
invention. 
Referring to FIG. 4, one example of the limitation of voltage differences 
as a detection criterion can be seen. FIG. 4 shows an acceptable test 
waveform in which one anomalous data point (6) is included. Anomalous data 
point (6) is intended to represent a bad data point which is not due to 
the coil itself but is rather due to noise or the like. Although the coil 
tested to produce the response shown in FIG. 4 should be acceptable, 
traditional voltage difference criteria would reject the coil due to the 
fact that anomalous data point (6) would exceed the set level of voltage 
difference determined to be acceptable when compared to standard waveform 
(1). Since visually an operator would question the test waveform shown in 
FIG. 4 and would conclude acceptability, and since tranditional voltage 
difference criteria would not lead to such a conclusion, automatic 
determination would be unacceptable in this case. The present invention 
avoids this difficulty through the use of area analysis. This is because 
anomalous data point (6) would result in only a small addition to error 
area (4). This small variation would not result in failure of the test by 
the coil. 
FIG. 5 shows a block diagram of an apparatus designed to practice the 
present invention. Electrical coil (7) is connected for testing to the 
automated test apparatus (9) through leads (8). The coil (7) represents 
any type of coil wh ich is currently tested by surge test techniques such 
as a coil found in an electrical motor. These types of coils typically 
involve numerous windings of an electrical conductor separated by thin 
insulation. Leads (8) serve to allow connection of coil (7) to a surge 
generator (12) and to some sensing means. Surge generator (12) is 
basically a device as currently used by those skilled in the art of surge 
testing. It is designed to release a sharp voltage pulse into coil (7). 
This pulse then oscillates in a decaying fashion or "rings" within coil 
(7). This oscillation is characteristic of the integrity of the winding of 
the coil and thus can yield information to allow detection of a fault in a 
coil. While typical surge testers usually involve a sensing means and a 
display means, in FIG. 5 the sensing means and the display means are shown 
separate from surge generator (12). In addition, surge generator is 
designed and specifically configured to allow control through a computer 
(16). Interconnection between surge generator (12) and computer (16) may 
be accomplished through surge generator control line (13). Surge generator 
control line (13) may be either one or a series of electrical connections 
or may represent an optical interconnection. An optical connection would 
be useful specifically to aid in electrically isolating computer (16) from 
surge generator (12) as surge generator is designed to produce high 
voltage and operate in an electrical environment which could be 
detrimental to computer (16). 
In order to sense the response of coil (7) to the voltage surge, a sensing 
means is used. As shown in FIG. 5, the sensor is basically 
analog-to-digital (A/D) converter (14). A/D converter (14) serves to 
transform the analog signal of the voltage response of coil (7) into a 
digital representation. A/D converter (14) then provides this information 
to computer (16) through digital transmission line (15). Again, digital 
transmission line (15) may represent one or more electrical wires or may 
be accomplished through the use of optical interconnection. This would 
serve to isolate the high voltage response of coil (7) from computer (16) 
for the purposes described above. Since the response of coil (7) is 
relatively short-lived, sampling rate of A/D converter (14) must be 
sufficiently fast to permit adequate resolution in the digital 
representation of test waveform (2). 
With respect to computer (16), it should be understood that a variety of 
configurations are possible. While the preferred embodiment utilizes a 
multipurpose, fully programmable computer such as an IBM XT compatible 
computer, certainly other computers or data analysis means are possible. 
Computer (16) might include a more specialized computer, might include a 
specifically-wired data processer, or might even be a permanently 
hardwired arrangement. The only essential aspects of computer (16) would 
be the ability to process the response of coil (7) to the surge in either 
an analog or digital fashion and to compare that response to a standard 
waveform. Since area analysis is a basic technique of othe preferred 
embodiment, computer (16) should also be capable of either summing to 
obtain the areas involved or integrating an analog signal. Each of these 
techniques would be readily available to those skilled in the art and 
could be accomplished without undue experimentation. Thus, both hardware, 
firmware, and software embodiments are intended to fall within the letter 
and spirit of the present invention. 
Computer (16) may also include a digital processor such as a microprocesser 
chip, and both data and program memory. With respect to program memory, it 
is intended that the program would be stored in order to operate the 
automated test apparatus (9) in a variety of ways. Certainly the program 
contained in the program memory should be written to allow for not only 
the functions described, but also for easy variation by a user. 
Menu-driven software also would be highly desirable as the users many not 
be sophisticated computer programmers. The data memory used by computer 
(16) should be substantial enough to contain both a variety and 
considerable quantities of data. This is necessary because sufficient 
resolution on both standard waveform (1) and test waveform (2) may require 
a number of data points. These data points would be generated by a 
relatively fast A/D converter (14) as the pulse rises in less than a 
microsecond and the response of coil (7) lasts for no more than one 
second. In accordance with the statistical abilities of the present 
invention, it may also be highly desirable to allow for data smoothing and 
retention of the resultant waveforms for later use. As to the latter, the 
data memory may thus include not only a dynamic memory within computer 
(16) but also tape or disk memory for long term storage. 
Computer (16) also incorporates an input component (10) and an output 
component (11). Each of these could represent a variety of techniques 
readily available. In the preferred embodiment input component (10) 
involves both a keyboard input and a bar code reader as is described 
below. Output component (11) would involve a cathode ray tube (CRT) 
display and a printer. Since manufacturing environments often involve one 
or more control computers, both input and output could involve some 
interface with another computer. Again, such variations are easily 
accomplished by those skilled in the art and thus fall within the letter 
and spirit of the present invention. It should be noted that output 
component (11) replaces the typical output utilized by many existing surge 
testers--a dual channel oscilloscope. Since such an oscilloscope 
represents a substantial portion of the cost and componentry of 
traditional surge testers, the separation of this component from surge 
generator (12) allows greater variability and potentially less cost. This 
would be specifically true of a hardwired embodiment of the present 
invention designed to accomplish a narrow purpose for one specific 
application in a manufacturing line. Certainly surge generator (12) and 
computer (16) need some power source (20). Although shown as a single 
source, power source (20) might actual be several sources, one for 
computer (16) and a separate one for surge generator (12). This separation 
of power source would assist in electrically isolating the various 
components. 
Referring to FIGS. 6a and 6b, it can be understood that computer (16) could 
be programmed to perform a variety of functions. Although the preferred 
embodiment shows general functions described in the flow charts of FIGS. 
6a and 6b, a large variety of variation is possible. This is especially 
true when computer (16) represents a multi-purpose, fully programmable 
computer. In addition, due to the variety in types of computers of 
programmable data processors available, the specific steps representing 
the program may also vary widely. Since implementation of the functions 
shown in the flow chart could be readily accomplished by those skilled in 
the art, the specific programming sequences are not included. Those 
skilled in the art could make and use the present invention from the 
disclosure without undue experimentation. The programming could be readily 
accomplished once the methods herein are understood as the steps involved 
are the basis of implementation. 
FIG. 6a represents the overall flow chart of the methods as they might be 
implemented through programming. As can be seen, several tests have been 
performed. Each of these tests may require subroutines as could be easily 
developed. The surge test subroutine is shown in FIG. 6b. With respect to 
FIG. 6a the step of inputting the appropriate test standards would include 
not only the proper parameters for each of the tests but also the proper 
standard waveform for comparison purposes. The input of such a waveform 
could be by recall from memory, through a statistical generation, or by 
actually conducting a test of an acceptable coil. 
FIG. 6b is the subroutine for the surge test portion of the overall flow 
chart. As can be seen provision is made for counting the number of surges 
at any given voltage and for incrementing the voltage until a fault is 
detected. Through storing results after the completion of any test, the 
results are then available for statistical analysis as discussed later. 
Displays are provided throughout the flow chart and may be provided as 
appropriate to the particular output component (11). Certainly the display 
could include not only an indication to the operator, but also some type 
of printout which might accompany the failed coil so that those repairing 
it would have the benefit of the test results as well. 
In the preferred embodiment output component (11) represents both a CRT 
display and a printer capable of producing a hardcopy. As an example, FIG. 
7 shows the hardcopy output produced by an embodiment of the present 
invention. Although the variety of display possibilities may be limitless, 
the display shown in FIG. 7 contains many valuable features. The display 
shows the acceptance threshold (18). One of the unique--and perhaps 
surprising--features of the present invention is that it presents a 
technique in which acceptance threshold (18) is relatively independent of 
the type of coil, the level of voltage or the configuration involved. It 
has been found by the present inventor that the acceptance threshold (18) 
varies little for the current surge tests conducted. This is quite 
significant as it allows easy comparison across a variety of manufacturing 
lines, products and test conditions. While currently it is believed that 
an acceptance threshold of 10% represents an optimal acceptance threshold, 
it is believed that a range may be necessary when various configurations 
of automated test apparatus (9) are developed. As data sampling techniques 
are refined, it is believed that acceptance threshold (18) may be reduced 
to as low as 2%. Certainly in some applications the acceptance theshold 
(18) might be reduced even with existing sampling techniques. In addition, 
there may exist conditions where the acceptance threshold might be raised 
to as high as 25%. With slower sampling rates, reduced standards, analog 
integration, or other implementation aspects a broad range is thus 
necessitated. Certainly the threshold might even be set automatically 
based on statistical analysis of the data sampled. 
The actual value of error area ratio (19) also allows determination of the 
type of fault present. It has been found that ratios ranging from 10% to 
40% indicate a turn-to-turn fault; ratios ranging from 40% to 80% indicate 
either a coil-to-coil or a phase-to-phase fault; and ratios ranging from 
80% and above indicate a ground fault or an open connection. In this 
fashion the techniques of the present invention allow automatic assessment 
of the type of fault existing. It should be understood that each of these 
ranges are only approximate and can include substantial overlap in some 
situations. Also the ranges unlike the base threshold, do vary with 
winding design, number of windings, and the like. 
The display shown in FIG. 7 also shows an error area ratio (19). This 
represents the ratio of the error area (4) shown in FIG. 2 to the 
referenced area (5) shown in FIG. 3. As can be seen from the waveforms in 
FIG. 7, some variation is acceptable. Certainly the printout of FIG. 7 
shows graphically that visual detection techniques are of limited accuracy 
as tighter tolerances are demanded. The present invention overcomes these 
limits thus paving the way for more accurate testing. 
In addition, the display shown in FIG. 7 shows a final test determination 
(20). This final test determination represents either a "pass" or "fail" 
conclusion which may be made by comparison of error area ratio (19) to 
acceptance threshold (18). The display also shows a dual trace display 
(21) as a graphic indication of the test. Dual trace display (21) is 
identical to what would be shown by a dual channel oscilloscope as used in 
traditional techniques. It serves the added advantage of allowing quick 
confirmation to those accustomed to existing techniques and also shows the 
actual position of error area (4). 
The techniques of the present invention also lend themselves to statistical 
analysis. By saving waveforms in digital form and by summarizing the 
variation of the test waveforms through area analysis, the integrity of 
the coil being tested can be automatically calculated. While there are 
many different techniques for automatic calculation, use of some type of 
area computation allows appropriate comparison of coils. Even more simply, 
the specific error area ratio for each coil can be easily analyzed. 
Although many different types of statistical analyses are possible, three 
different aspects are particularly noteworthy. 
First, statistical analysis of failure data is possible. This would include 
comparisons of the percentage of failures, comparisons of different 
manufacturing batches, comparisons of different supplier lines, and 
comparisons of different production lines. For this reason 
product-specific manufacturing information may be incorporated in the 
methods described and represents a unique addition to the field of surge 
test equipment. Such information might include batch information, 
information with respect to the specific shift producing the coils, 
information with respect to the production line when more than one line 
produces the same coils, and the like. Product serial numbers or other 
identifying information might also be input. As a means of inputting such 
information, it may be useful to incorporate a bar code reader as part of 
input component (10). By having such information stored within computer 
(16), computer (16) could be programmed to automatically analyze and 
correlate the information. In the event of any deviation from acceptable 
standards, an automatic warning might be provided. Such would be extremely 
useful in instances where assembly line techniques are involved. In this 
fashion if any change were made in the assembly line which caused the rate 
of failure to exceed either a running average or a predetermined rate, 
managers might be immediately or even automatically notified. Also, slow 
decays in the manufacturing process might be sensed. 
Another important aspect of these statistical analyses possible is the 
generation of the standard to which all coils are compared. As mentioned 
in the background of the invention, present techniques involve testing 
some coil which is assumed to be a standard, acceptable coil. This 
standard coil responds to the pulse by producing a standard waveform (1). 
Standard waveform (1) may either be reproduced simultaneously with test 
waveform (2) or may be recalled from memory for the comparison. Since 
there is some degree of variation in the responses of even acceptable 
coils, it may be useful to generate standard waveform (1). Such generation 
could be from a theoretical basis or more practically and as used in the 
preferred embodiment, may be stored from a test of a known, acceptable 
coil. This standard waveform (1) could then be updated through statistical 
techniques based upon tests of other acceptable coils. Certainly different 
weights could be ascribed to test waveforms as is well known for such 
statistical efforts. Naturally the standard waveform could be 
automatically updated each time a coil passes a test. Again, by use of 
digital techniques such methods could be accomplished without undue 
experimentation and so are not discussed in extreme detail. When such 
generation of a standard waveform is utilized, it would be possible to 
reassess the threshold levels at which the acceptability determination is 
made. Certainly, with respect to error area ratio (19), the threshold 
could be varied depending upon the size of sample utilized for the 
generated standard waveform or dependent upon the failure rate deemed 
acceptable by the manufacturer. As discussed earlier, one of the suprising 
results of the area calculation techniques is that the threshold is 
relatively independent of the type of coil involved, the voltages 
involved, or the frequencies inherent to the coils. Variations in the 
threshold may thus be accomplished independent of any tests of the 
particular coil involved. The considerable advantages of this were 
discussed earlier. 
A third statistical technique is the possibility of optimizing the number 
of pulses to which the coil is subjected. As is known in the art of surge 
testing, an incipient fault is frequently not detectable by a single pulse 
alone. Rather, the prevalent technique of repetitive surge testing has 
developed. Although repetition of the surges is desirable for the 
detection of minor faults, repetition is also undesirable because it 
unduly stresses the insulation of good coils. By statistically analyzing 
the results of tests using more than one surge at a given voltage, the 
present invention could statistically determine the number of pulses 
necessary to reach the desired detection accuracy. The maximum number of 
pulses to any given voltage could also be set by the operator. Again, 
although those skilled in the art recognize the undesirability of unduly 
stressing the insulation of the windings of a coil, little effort has been 
made to automatically minimize the stresses. The facilitation of an 
area-based analysis makes implementation of this aspect straightforward. 
Although the methods of the present invention are relatively 
self-explanatory to those skilled in the art, certain aspects are so 
significant that they deserve further explanation. As mentioned, a basic 
aspect of the present invention is the ability to conduct surge testing 
where a limit is set without testing a standard coil. This avoids the need 
to intentionally fault an otherwise-acceptable coil and also allows for 
easy comparison among different coil types. Without this aspect the 
statistical analysis mentioned earlier would be more involved. Another 
aspect is that a variety of standards might be utilized very easily. This 
is of particular importance when production line testing involves more 
than one coil such as when one motor has more than one type of coil. When 
the traditional technique (of comparison testing through a simultaneous 
test of a standard coil) was used, operators simply had to connect 
numerous coils to the test apparatus. In the present invention, only the 
type of coil needs to be entered, perhaps automatically through a bar code 
reader. The program controlling the equipment would then simply compare 
the result with the appropriate stored standard waveform. These methods 
also facilitate the use of multiple test channels or leads to conduct even 
faster testing. 
Another aspect of the methods disclosed is the potential to step up the 
voltage of a test and stop as soon as a fault is detected. Since some 
applications may require different levels of acceptability and may subject 
the coils to different levels of stress, it may be useful to test a coil 
and to record the level at which a fault is first detected. While this 
level could also be analyzed statistically, it may allow groupings which 
are appropriate depending upon the ultimate uses of the coils. By not 
subjecting all coils to the highest level of voltage desired, the stress 
induced in such coils, especially those which display a fault early on, 
might be minimized. 
Finally, it should be noted that the automated surge testing equipment 
proposed may also include automation of a variety of tests. As an example, 
resistance and high potential testing as are well known to those skilled 
in the art could also be incorporated. Through inclusion of the 
appropriate test apparatus and allowing such apparatus to be controlled by 
computer (16), automated test apparatus (9) might step through a variety 
of tests in sequence. It would be particularly efficient to combine surge 
testing with resistance and high potential testing because each of these 
three tests are possible at roughly the same point in a manufacturing 
process and because each are designed to yield information with respect to 
the acceptability of test coil (7). Even when coil (7) fails one of these 
tests, a surge test might still be completed to assist those in repairing 
coil (7). Naturally automation with respect to all of these tests may lend 
itself to more accurate testing. For instance a resistance test might be 
temperature-varied automatically to yield more accurate information. The 
simple inclusion of the multipurpose computer allows these new variations 
to be automatic.