IIIHHHHHHHHHHIII

USOO51 149A
United States Patent (19) 11) Patent Number: 5,111,149
Lebesch 45) Date of Patent: May 5, 1992
(54) METHOD AND APPARATUS FOR OTHER PUBLICATIONS
AUTOMATICALLY CALCULATING THE
INTEGRITY OF AN ELECTRICAL COL ECG Co., Ltd., ECG Advanced Impulse Winding Tes
ter, Jun.-Sep., 1986.
75 Inventor: Jeffrey D. Lebesch, Fort Collins, Author: P. A. Sanghavi et al., Title: "Turn-to-turn
Colo. testing improves coil life", pp. 44, 45; date: Dec. 1972.
Author: R. Malewski et al., Title: "Impulse testing of
(73 Assignee: Baker Electrical Instrument power transformers using the transfer function
Company, Fort Collins, Colo. method", pp. 476-489; Apr. 1988.
Author: R. LaFevre, Title: "Test methods for electrical
21 Appl. No.: 317,274 windings and their applications in the field", pp. 12-16;
Jun. 1-5, 1987.
22 Filed: Feb. 28, 1989 Author: D. M. Santos et al., Title: "Industrial applica
tions of Mini, Micro & Personal Computers', pp.
(51 Int. Cl.5 .... ... G01R 31/02; G01R 31/06 870-872; Sep. 29-Oct. 3, 1986.
52 U.S. C. .................................... ...; Primary Examiner-Jack B. Harvey
58 Field of Search ................. "...g., Attorney, Agent, or Firm-Luke Santangelo
324/654, 655; 361/35; 364/482, 483,486, 487 57 ABSTRACT
s Method and apparatus for automatically testing an elec
(56) References Cited trical coil through a surge tester. Comparison to a
U.S. PATENT DOCUMENTS stored waveform through error area ratio computation
is achieved by use of digital computer data processing
As Era. a -a - a - - - - - - - - - -- : techniques. A uniform threshold of acceptability is dis
3,508,143 4/1970 Kuroda ................... 324/s closed which is not dependent on voltage or type of coil
3,526,830 9/970 Azuma ..........., 324/51 tested. Statistical analysis may be programmed or hard
3,659,197 4/1972 Alley et al. ..... . . 324/51 wired into an embodiment to yield easily discernable
3,731,85 5/1973 Pittman ........... ... 324/54 manufacturing or field test information. Optimization of
3,742,349 6/1973 Richardson ........................... 324/54 the entire process and the testing steps may also be
3,753,087 8/1973 Tan ................. 324/546 X achieved through an apparatus which may provide a
3,869,664 3/1975 Safer et al....... ... 324/5 variety of different output possibilities and which may
:
ww f
3,A1975
1975 Safer et al. ..
Safer et al. ..
...... 324/5
324/5 be customized to the user's situation. Update and
A.
stor
a
3,932,806 l/1976 Kawada ....., ... 324/5 age of test results is included as well as correlation with
4,287,547 9/1981 Vitins .................. 36/8 manufacturing data.
4,694,402 9/1987 McEachern et al. ............... 364/487
4,746,869 5/1988 Schrag et al........................ 324/546 50 Claims, 6 Drawing Sheets
20
U.S. Patent May 5, 1992 Sheet 1 of 6 5,111,149

PRIOR ART
U.S. Patent May 5, 1992 Sheet 2 of 6 5,111, 149

Fig. 4
U.S. Patent May 5, 1992 Sheet 3 of 6 5,111,149
U.S. Patent May 5, 1992 Sheet 4 of 6 5,111,149

INPUT
PRODUCT
INFORMATION

NEW INPUT
PRODUCT? TEST STDS
& TEST INFO

SELECT TEST
STDS & INFO

CONDUCT
COL
RESISTANCE
TEST

CONDUCT
CO
HIGH
POTENTIAL
TEST

CONDUCT
SURGE
TEST
(SUBROUTINE)
RETURN TO
NITALIZE

Fig. 6A
U.S. Patent May 5, 1992 Sheet 5 of 6 5,111,149

START
SUBROUTINE

DISPLAY SAFETY
"HAZARD" CLOSED?
YES
READ
TEST STDS

APPLY
SURGE

DIGITIZE
RESPONSE

CALC AREA
8 RATO

ASSESS
TYPE SET SURGE
=1

NCREMENT
SURGE V

STORE
DISPLAY RESULTS
RESULTS
YES
STORE
RETURN TO RESULTS
NITALIZE
DISPLAY
RESULTS

Gue) Fig. 6B
U.S. Patent May 5, 1992 Sheet 6 of 6 5,111,149

15 JAN 88 15.42
SOURCE ST112E 0.04LF LOAD TEST STATOR GOOD POS:
INTEGRATION SAMPLES 256 COMPARED TO LOW
ERROR AREA = 399 DOTS AMPLITUDE SHOT
ACCEPTANCE RANGE 1.0% REFERENCE AREA = 4,452 DOTS
- - -PASS- - - \ ERROR AREA RATO = 8%
2O
) 18 {9

CH1. 5V A 50puS -2.73. V CH1

Fig. 7
 5,111,149
1. 2
multaneous comparison of the tested coil with a coil
METHOD AND APPARATUS FOR which is assumed to be acceptable-that is, a standard
AUTOMATICALLY CALCULATING THE coil. In traditional techniques this usually has involved
INTEGRITY OF AN ELECTRICAL COIL repeatedly subjecting the standard coil to identical
surges as each different test item is analyzed. Not only
A. BACKGROUND OF THE INVENTION does this weaken the standard coil but it is attended
Generally, the present invention relates to the field of with other practical and power consumption concerns.
surge test equipment. More specifically it relates to Since the traditional technique of comparison testing is
methods and apparatus to automatically determine the not an exact science, it has also been necessary to exper
existence and extent of a fault in an electrical coil from O imentally ascertain the threshold amount of change in
a surge test. the response to the surge at which a "fault' condition is
The invention focuses on several needs of users of determined to exist. This has been done through inten
surge test equipment. These users include both manu tionally faulting an acceptable coil in the smallest possi
facturers-who test their products before shipping 15 ble way and observing the amount of change so in
-and users-who test their equipment in the field as duced. Obviously this technique has several undesirable
part of maintenance procedures. From an understand features. The present invention addresses each of these
ing of both of these perspectives, the present invention aspects and the aforementioned aspects in one inven
addresses the needs of these persons and addresses limi tion.
tations found in existing surge test equipment. One such As background to surge testing in general, it should
need is the desire of those performing the test to rapidly be understood that the technique of subjecting an elec
ascertain the integrity of the item being tested. This is of trical coil to a voltage surge is well known having been
particular concern in the surge test environment be disclosed at least by 1943 in an article by C. M. Faust
cause production line testing may need to be accom and N. Rohats entitled "Insulation Testing of Electrical
plished very quickly. Another limitation of existing Windings' (Trans. AIEE Vol. 62, pp. 203-06). Basi
surge test apparatus is the inherent difficulty in accu 25 cally the technique involves subjecting an electrical
rately assessing the existence of a fault in the equipment coil, such as is frequently found in an electrical motor,
being tested. Because traditional techniques often have to a sharp, high voltage pulse and then allowing this
been based upon a visual comparison of waveforms pulse to oscillate or "ring" within the coil. This ringing
which are the reaction of the equipment to the surge, produces decaying oscillations which may vary in sev
such visual comparison has been difficult to adapt for an 30 eral ways if there is any fault within the winding. One
automatic determination. This difficulty has perhaps such type of fault is a breakdown in the insulation be
been underscored by the fact that in spite of increas tween adjacent coils-a turn-to-turn fault. Such a fault
ingly sophisticated analysis means becoming available, would change the inductance and capacitance charac
the vast majority of surge test equipment is still based on teristics of the coil and would thus be seen in the result
visual analysis by an operator. Since unacceptable fault 35 ing waveform. Of particular importance is the need to
levels in the equipment being tested are sometimes hard subject the coil to one or more high voltage pulses in
to detect visually, the operators would ideally have
some degree of skill in analyzing the surge test response order to detect an incipient fault in such insulation. The
waveforms. This is inconsistent, however, with the fact that small breakdowns may not be visible until
need to have such waveforms reviewed in a highly 40 several surges have been accomplished is one reason for
repetitive fashion on an assembly line as frequently as using repetitive surges for testing. The basic techniques
every few seconds. Naturally such a method also intro involved are well known and have been the subject of
duces the possibility of human error and its associated numerous inventive efforts. An example of the types of
limitations. While smaller and smaller tolerances have waveforms occurring for the various possible fault sce
been demanded, the practical limitations inherent to a 45 narios is contained in several articles by the assignee
visual technique have been difficult to overcome. Al including: "Winding Fault Diagnosis by Surge Compar
though several efforts have been made to automate the ison' presented at the Fourteenth Electrical/Electronic
determination of the existence of a fault in the equip Insulation Conference and "Surge Test Methods for
ment being tested, these efforts have met with varying Rotating Machines" as published by the IEEE.
degrees of success and have often proved not to provide 50 While several inventive efforts have been directed to
as accurate a result as even the visual testing tradition automating the technique of surge test analysis, most all
ally done. The present invention not only addresses of the automatic testers have been based upon the tech
each of these needs but several others. nique of comparing voltage levels of the test with those
Two of the additional aspects focused on in the pres of a standard coil. Although envelope decay rate has
ent invention are particularly noteworthy. First, the 55 also been used, it is almost always implemented in con
nature of a surge test is such that the surge imposed junction with voltage levels. The voltage level criterion
upon the equipment to be tested actually weakens or, in has met with varying degrees of success and has not
extreme cases, can create a fault in that equipment. always resulted in more accurate determinations than
Although this aspect has been well known, traditional were visually possible. U.S. Pat. No. 3,659,197 as as
surge testing has not automatically limited the stress to signed to General Electric Corporation presents an
which the equipment is subjected. In fact, through the automatic testing device based on voltage comparisons
existence of industry standards such as National Equip which also allows visual analysis capabilities. That Gen
ment Manufacturers Association Standard 1-12.05, re eral Electric patent-through providing one technique
petitive surge testing has been widely supported. The for visual analysis and another technique for automatic
present invention addresses this aspect by providing 65 analysis--also alludes to the inherent difficulties those
methods and test apparatus which automatically mini skilled in the art have faced in attempting to develop a
mize the stress to which the equipment is subjected. technique acceptable for automatic analysis. Another
Second, traditional surge testing has been through si example of the prevalence of the use of voltage differ
 5,111,149
3 4.
ence determinations as the criterion, is shown in U.S. ular user, the particular uses, and the varying applica
Pat. No. 3,869,664 as assigned to Avtron Manufactur tion environments of surge test equipment.
ing, Inc., and its related patents. Although digital tech It is also an object of the present invention to present
niques have been available for some time, the focus by methods through which acceptability of a coil may be
those skilled in the art on absolute voltage level criteria 5 determined without reference to a threshold dependent
has become an impediment to the adaptation of auto on a particular coil. In accordance with this purpose it
nated techniques to the surge testing field. Even is an object to provide the ability to generate a standard
though absolute voltage criterion can be readily which does not directly depend on the results of any
adapted to digital analysis, the potential for bad data one coil tested. A further object of this general goal is to
points and its resulting in false indications has been O establish a threshold of acceptability which is consistent
undesirable. for the varying other types of coils tested, for varying
Since the present invention, in its preferred embodi voltages, or for varying other characteristics.
ment, is based upon well known computer integration It is a further object of the present invention to pro
and sampling techniques, at first glance it would seem vide methods and apparatus which allow more accurate
that those skilled in the art would have had no trouble 15 surge testing of electrical coils. In this regard it is de
implementing these techniques to their field. This sired to overcome the limitations imposed by the visual
would seem especially true because there has been a techniques traditionally used in surge test determina
long-felt need for accurate and reliable and automatic tions.
assessment of surge test results. The limitation that Broadly stated, a general object of the present inven
those skilled in art faced was that they simply failed to tion is to automate the surge test process. In keeping
realize that the problem lay in properly choosing the with this general goal, it is an object of the present
detection criterion. They did not appreciate that the invention to achieve many objects through automatic
voltage difference criterion was at the root of the prob means including: automatically assessing the acceptabil
lem. Although the variety of patents in the field of 25 ity of the coil being tested, automatically warning of
automatic surge test equipment and the broad range of changes in typical production variations for a variety of
dates of these inventive efforts show that substantial parameters, automatically stepping through several
attempts were made to automate the equipment, the fact different tests at one point in both the manufacturing
that the traditional technique of visually detecting a process and in the field testing, and automatically stop
fault still remains as the preferred technique shows that ping subjecting the coil being tested to electrical surges
those attempts did not fill the need of surge test users. upon detection of a fault.
They simply did not understand that the effort neces Another broadly stated object of the present inven
sary in this regard was not in refinement of the systems tion is to incorporate statistical analysis into the surge
involved but rather was in development of a proper test process and to specifically incorporate such analysis
detection criterion. The broad acceptance of a voltage 35 into the surge test equipment. An object of this gener
difference criterion by those skilled in the art of produc ally stated goal is to minimize and to optimize the num
ing automated surge test apparatus basically led by ber of times which a coil being tested must be subjected
teachings away from the technical direction of the pres to a voltage surge. Another more specifically stated
ent invention. It is also noteworthy that it was even a object of such statistical analysis is to optimize the pro
surprise to the inventor that the development of an cess, levels, and standards which are utilized in deter
area-based analysis resulted in not only one standard mining the existence of a fault.
which was consistent across a broad range of motor It is also an object of the present invention to present
types and characteristics, but also that utilization of a method of analyzing the response of the coil being
such a technique lent itself so well to the data analysis tested to a surge test. An object of this goal is to present
capabilities described herein. 45 a method which is accurate and suitable for digital ap
The present invention recognizes and addresses each plications. An object of the present invention is to intro
of these concerns and overcomes the limitations per duce the use of area analysis to surge test operations.
ceived by those skilled in the art by presenting methods Naturally further objects of the invention are dis
and apparatus which, among other aspects, allow for closed throughout other areas of the specification and
digital processing and which overcome the difficulties 50 claims.
in implementing such processing to the surge test field. C. BRIEF DESCRIPTION OF ORAWINGS
The techniques and devices utilized in the present in
vention result in more accurate testing, in automatic FIG. 1 is a graphic representation of a traditional
testing and in testing which is more suitable from both simultaneous surge test of a standard coil and a faulted
the user's and manufacturer's perspectives. 55 coil superimposing both responses on one plot.
B. SUMMARY OF THE INVENTION FIG. 2 is a graphic representation of responses not
unlike those shown in FIG. 1 with the area which is the
Accordingly it is an object of the present invention to difference between the two response shaded.
minimize the use of a standard coil in surge testing of FIG. 3 is a graphic representation of a standard wave
equipment. Certainly an aspect of this goal is to avoid 60 form with the area under a standard waveform shaded.
the need to impose a fault in an acceptable coil in order - FIG. 4 is a graphic representation of the response of
to determine the minimum threshold at which a coil is an acceptable test coil with an anomalous data point
determined to contain a fault. included.
Another object of the present invention is to integrate FIG. 5 is a block diagram of the preferred embodi
a multipurpose, fully programmable computer into 65 ment of the present invention.
surge test techniques and equipment. An object of this is FIG. 6a is a flow chart of the overall steps which may
to present a system which allows sufficient variation in be programmed to be performed by the embodiment
technique, programming and analyses to suit the partic shown in FIG. 5.
 5,111,149
5 6
FIG. 6b is a flow chart of the surge test subroutine presented a practical expedient. However, voltage dif
which may be programmed to be performed as part of ference criterion has not been able to completely re
the flow chart shown in FIG. 6a. place the visual detection techniques in many circum
FIG. 7 is one possible output of the preferred embodi stances. In addition, it should be understood that other
ment of the present invention. types of area analyses are possible and would fall within
D. DETAILED DESCRIPTION OF THE
the scope and spirit of the present invention.
PREFERRED EMBODIMENT Referring to FIG. 4, one example of the limitation of
voltage differences as a detection criterion can be seen.
As can be readily understood from the steps set forth FIG. 4 shows an acceptable test waveform in which one
in the claims, the basic concepts of the present invention O anomalous data point (6) is included. Anomalous data
may be embodied in many different ways. Although the point (6) is intended to represent a bad data point which
field of surge testing is well understood, FIG. 1 shows is not due to the coil itself but is rather due to noise or
a display encountered whenever the traditional tech the like. Although the coil tested to produce the re
nique of visually ascertaining the existence of a fault is sponse shown in FIG. 4 should be acceptable, tradi
utilized. Such a display would usually appear on a dual 15 tional voltage difference criteria would reject the coil
channel oscilloscope. Referring to FIG. 1, in which the due to the fact that anomalous data point (6) would
vertical axis is voltage and the horizontal axis is time, exceed the set level of voltage difference determined to
the general technique of surge testing can be readily be acceptable when compared to standard waveform
understood. At time A a voltage pulse is imposed on the (1). Since visually an operator would question the test
coil being tested. This results in the rapid rise in the 20 waveform shown in FIG. 4 and would conclude accept
voltage displayed. After the pulse, which has a short ability, and since tranditional voltage difference criteria
rise time (typically about one microsecond), the voltage would not lead to such a conclusion, automatic determi
then begins to decay and effects a ringing within the nation would be unacceptable in this case. The present
coil. This ringing is characteristic of a specific combina invention avoids this difficulty through the use of area
tion of capacitance, inductance, and resistance in the 25 analysis. This is because anomalous data point (6) would
coil being tested. As can be seen in FIG. 1, a standard result in only a small addition to error area (4). This
waveform-that is the response to the pulse by an ac small variation would not result in failure of the test by
ceptable coil-results in a voltage response which is the coil.
characteristic of that coil. Standard waveform (1) FIG. 5 shows a block diagram of an apparatus de
would of course vary whenever a different type of coil 30 signed to practice the present invention. Electrical coil
were used. This is the time-honored reason for compar (7) is connected for testing to the automated test appara
ing two simultaneous pulses and lead those skilled in the tus (9) through leads (8). The coil (7) represents any
art to presuppose the need for coil-dependent thresh type of coil which is currently tested by surge test
olds. Superimposed on this waveform is a simultaneous techniques such as a coil found in an electrical motor.
waveform of a coil being tested. As can be seen, this test 35 These types of coils typically involve numerous wind
waveform (2) displays different characteristics-that is ings of an electrical conductor separated by thin insula
a different time dependency and different voltage lev tion. Leads (8) serve to allow connection of coil (7) to a
els. It is these differences which allow detection of surge generator (12) and to some sensing means. Surge
faults in the coil being tested. The variation between the generator (12) is basically a device as currently used by
two is due to a difference in the combination of induc 40 those skilled in the art of surge testing. It is designed to
tance, capacitance and resistance with respect to the release a sharp voltage pulse into coil (7). This pulse
two coils. This difference is due to a fault in the coil then oscillates in a decaying fashion or "rings' within
being tested. This faulr can be any number of types of coil (7). This oscillation is characteristic of the integrity
faults as is well known to those accomplished at surge of the winding of the coil and thus can yield information
testing. An example would be a breakdown in the insu 45 to allow detection of a fault in a coil. While typical
lation between adjacent windings of the coil, a turn-to surge testers usually involve a sensing means and a
turn insulation defect. display means, in FIG. 5 the sensing means and the
Referring to FIG. 2, the technique of the present display means are shown separate from surge generator
invention can be easily understood. While in the prior (12). In addition, surge generator is designed and specif
art the majority of automatic test equipment has easily 50 ically configured to allow control through a computer
utilized a voltage difference (3) at any point along the (16). Interconnection between surge generator (12) and
two plots, this traditional voltage difference criteria has computer (16) may be accomplished through surge
limits as herein discussed. Rather than utilizing such an generator control line (13). Surge generator control line
analysis technique, the present invention analyzes the (13) may be either one or a series of electrical connec
area between standard waveform (1) and test waveform 55 tions or may represent an optical interconnection. An
(2), shown as shaded area in FIG. 2. This error area (4) optical connection would be useful specifically to aid in
provides a more accurate measurement of the degree of electrically isolating computer (16) from surge genera
fault contained in the test coil. tor (12) as surge generator is designed to produce high
Referring to FIG. 3, it can be understood that a refer voltage and operate in an electrical environment which
ence area (5) can be easily computed by measuring the 60 could be detrimental to computer (16).
area "under" standard waveform (1), shown as shaded In order to sense the response of coil (7) to the volt
area in FIG. 3. By "under' it is meant that the absolute age surge, a sensing means is used. As shown in FIG. 5,
value of the standard waveform would be utilized. A the sensor is basically analog-to-digital (A/D) con
dimensionless ratio of error area (4) to reference area (5) verter (14). A/D converter (14) serves to transform the
can thus be easily computed. Since the technique of 65 analog signal of the voltage response of coil (7) into a
surge testing electrical coils is still being developed on a digital representation. A/D converter (14) then pro
theoretical basis, it is true that prior to the present in vides this information to computer (16) through digital
vention the use of traditional voltage difference criteria transmission line (15). Again, digital transmission line
 5, 111,149
7 8
(15) may represent one or more electrical wires or may existing surge testers-a dual channel oscilloscope.
be accomplished through the use of optical interconnec Since such an oscilloscope represents a substantial por
tion. This would serve to isolate the high voltage re tion of the cost and componentry of traditional surge
sponse of coil (7) from computer (16) for the purposes testers, the separation of this component from surge
described above. Since the response of coil (7) is rela generator (12) allows greater variability and potentially
tively short-lived, sampling rate of A/D converter (14) less cost. This would be specifically true of a hardwired
must be sufficiently fast to permit adequate resolution in embodiment of the present invention designed to ac
the digital representation of test waveform (2), complish a narrow purpose for one specific application
With respect to computer (16), it should be under in a manufacturing line. Certainly surge generator (12)
stood that a variety of configurations are possible. O and computer (16) need some power source (20). Al
While the preferred embodiment utilizes a multipur though shown as a single source, power source (20)
pose, fully programmable computer such as an IBM XT might actual be several sources, one for computer (16)
compatible computer, certainly other computers or data and a separate one for surge generator (12). This separa
analysis means are possible. Computer (16) might in tion of power source would assist in electrically isolat
clude a more specialized computer, might include a 15 ing the various components.
specifically-wired data processer, or might even be a Referring to FIGS. 6a and 6b, it can be understood
permanently hardwired arrangement. The only essen that computer (16) could be programmed to perform a
tial aspects of computer (16) would be the ability to variety of functions. Although the preferred embodi
process the response of coil (7) to the surge in either an ment shows general functions described in the flow
analog or digital fashion and to compare that response 20 charts of FIGS. 6a and 6b, a large variety of variation is
to a standard waveform. Since area analysis is a basic possible. This is especially true when computer (16)
technique of othe preferred embodiment, computer (16) represents a multi-purpose, fully programmable com
should also be capable of either summing to obtain the puter. In addition, due to the variety in types of comput
areas involved or integrating an analog signal. Each of ers of programmable data processors available, the spe
these techniques would be readily available to those 25 cific steps representing the program may also vary
skilled in the art and could be accomplished without widely. Since implementation of the functions shown in
undue experimentation. Thus, both hardware, firm the flow chart could be readily accomplished by those
ware, and software embodiments are intended to fall skilled in the art, the specific programming sequences
within the letter and spirit of the present invention. are not included. Those skilled in the art could make
Computer (16) may also include a digital processor 30 and use the present invention from the disclosure with
such as a microprocesser chip, and both data and pro out undue experimentation. The programming could be
gram memory. With respect to program memory, it is readily accomplished once the methods herein are un
intended that the program would be stored in order to derstood as the steps involved are the basis of imple
operate the automated test apparatus (9) in a variety of mentation.
ways. Certainly the program contained in the program 35 FIG. 6a represents the overall flow chart of the meth
memory should be written to allow for not only the ods as they might be implemented through program
functions described, but also for easy variation by a ming. As can be seen, several tests have been per
user. Menu-driven software also would be highly desir formed. Each of these tests may require subroutines as
able as the users many not be sophisticated computer could be easily developed. The surge test subroutine is
programmers. The data memory used by computer (16) 40 shown in FIG. 6b, With respect to FIG. 6a the step of
should be substantial enough to contain both a variety inputting the appropriate test standards would include
and considerable quantities of data. This is necessary not only the proper parameters for each of the tests but
because sufficient resolution on both standard wave also the proper standard waveform for comparison
form (1) and test waveform (2) may require a number of purposes. The input of such a waveform could be by
data points. These data points would be generated by a 45 recall from memory, through a statistical generation, or
relatively fast A/D converter (14) as the pulse rises in by actually conducting a test of an acceptable coil.
less than a microsecond and the response of coil (7) lasts FIG. 6b is the subroutine for the surge test portion of
for no more than one second. In accordance with the the overall flow chart. As can be seen provision is made
statistical abilities of the present invention, it may also for counting the number of surges at any given voltage
be highly desirable to allow for data smoothing and 50 and for incrementing the voltage until a fault is de
retention of the resultant waveforms for later use. As to tected. Through storing results after the completion of
the latter, the data memory may thus include not only a any test, the results are then available for statistical
dynamic memory within computer (16) but also tape or analysis as discussed later. Displays are provided
disk memory for long term storage. throughout the flow chart and may be provided as
Computer (16) also incorporates an input component 55 appropriate to the particular output component (11).
(10) and an output component (11). Each of these could Certainly the display could include not only an indica
represent a variety of techniques readily available. In tion to the operator, but also some type of printout
the preferred embodiment input component (10) in which might accompany the failed coil so that those
volves both a keyboard input and a bar code reader as repairing it would have the benefit of the test results as
is described below. Output component (11) would in 60 well.
volve a cathode ray tube (CRT) display and a printer. In the preferred embodiment output component (11)
Since manufacturing environments often involve one or represents both a CRT display and a printer capable of
more control computers, both input and output could producing a hardcopy. As an example, FIG. 7 shows
involve some interface with another computer. Again, the hardcopy output produced by an embodiment of the
such variations are easily accomplished by those skilled present invention. Although the variety of display pos
in the art and thus fall within the letter and spirit of the sibilities may be limitless, the display shown in FIG. 7
present invention. It should be noted that output com contains many valuable features. The display shows the
ponent (11) replaces the typical output utilized by many acceptance threshold (18). One of the unique-and per
 5,111,149
9 10
haps surprising-features of the present invention is that tical analyses are possible, three different aspects are
it presents a technique in which acceptance threshold particularly noteworthy.
(18) is relatively independent of the type of coil, the First, statistical analysis of failure data is possible.
level of voltage or the configuration involved. It has This would include comparisons of the percentage of
been found by the present inventor that the acceptance failures, comparisons of different manufacturing
threshold (18) varies little for the current surge tests batches, comparisons of different supplier lines, and
conducted. This is quite significant as it allows easy comparisons of different production lines. For this rea
comparison across a variety of manufacturing lines, son product-specific manufacturing information may be
products and test conditions. While currently it is be incorporated in the methods described and represents a
lieved that an acceptance threshold of 10% represents O unique addition to the field of surge test equipment.
an optimal acceptance threshold, it is believed that a Such information might include batch information, in
range may be necessary when various configurations of formation with respect to the specific shift producing
automated test apparatus (9) are developed. As data the coils, information with respect to the production
sampling techniques are refined, it is believed that ac line when more than one line produces the same coils,
ceptance threshold (18) may be reduced to as low as 15 and the like. Product serial numbers or other identifying
2%. Certainly in some applications the acceptance the information might also be input. As a means of inputting
shold (18) might be reduced even with existing sam such information, it may be useful to incorporate a bar
pling techniques. In addition, there may exist conditions code reader as part of input component (10). By having
where the acceptance threshold might be raised to as such information stored within computer (16), com
high as 25%. With slower sampling rates, reduced stan puter (16) could be programmed to automatically ana
dards, analog integration, or other implementation as lyze and correlate the information. In the event of any
pects a broad range is thus necessitated. Certainly the deviation from acceptable standards, an automatic
threshold might even be set automatically based on warning might be provided. Such would be extremely
statistical analysis of the data sampled. useful in instances where assembly line techniques are
The actual value of error area ratio (19) also allows 25 involved. In this fashion if any change were made in the
determination of the type of fault present. It has been assembly line which caused the rate of failure to exceed
found that ratios ranging from 10% to 40% indicate a either a running average or a predetermined rate, man
turn-to-turn fault; ratios ranging from 40% to 80% agers might be immediately or even automatically noti
indicate either a coil-to-coil or a phase-to-phase fault; fied. Also, slow decays in the manufacturing process
and ratios ranging from 80% and above indicate a 30 might be sensed.
ground fault or an open connection. In this fashion the Another important aspect of these statistical analyses
techniques of the present invention allow automatic possible is the generation of the standard to which all
assessment of the type of fault existing. It should be coils are compared. As mentioned in the background of
understood that each of these ranges are only approxi the invention, present techniques involve testing some
mate and can include substantial overlap in some situa 35 coil which is assumed to be a standard, acceptable coil.
tions. Also the ranges unlike the base threshold, do vary This standard coil responds to the pulse by producing a
with winding design, number of windings, and the like. standard waveform (1). Standard waveform (1) may
The display shown in FIG. 7 also shows an error area either be reproduced simultaneously with test wave
ratio (19). This represents the ratio of the error area (4) form (2) or may be recalled from memory for the com
shown in FIG. 2 to the referenced area (5) shown in 40 parison. Since there is some degree of variation in the
FIG. 3. As can be seen from the waveforms in FIG. 7, responses of even acceptable coils, it may be useful to
some variation is acceptable. Certainly the printout of generate standard waveform (1). Such generation could
FIG. 7 shows graphically that visual detection tech be from a theoretical basis or more practically and as
niques are of limited accuracy as tighter tolerances are used in the preferred embodiment, may be stored from
demanded. The present invention overcomes these lim 45 a test of a known, acceptable coil. This standard wave
its thus paving the way for more accurate testing. form (1) could then be updated through statistical tech
In addition, the display shown in FIG. 7 shows a final niques based upon tests of other acceptable coils. Cer
test determination (20). This final test determination tainly different weights could be ascribed to test wave
represents either a "pass' or "fail' conclusion which forms as is well known for such statistical efforts. Natu
may be made by comparison of error area ratio (19) to 50 rally the standard waveform could be automatically
acceptance threshold (18). The display also shows a updated each time a coil passes a test. Again, by use of
dual trace display (21) as a graphic indication of the test. digital techniques such methods could be accomplished
Dual trace display (21) is identical to what would be without undue experimentation and so are not discussed
shown by a dual channel oscilloscope as used in tradi in extreme detail. When such generation of a standard
tional techniques. It serves the added advantage of al 55 waveform is utilized, it would be possible to reassess the
lowing quick confirmation to those accustomed to exist threshold levels at which the acceptability determina
ing techniques and also shows the actual position of tion is made. Certainly, with respect to error area ratio
error area (4). (19), the threshold could be varied depending upon the
The techniques of the present invention also lend size of sample utilized for the generated standard wave
themselves to statistical analysis. By saving waveforms 60 form or dependent upon the failure rate deemed accept
in digital form and by summarizing the variation of the able by the manufacturer. As discussed earlier, one of
test waveforms through area analysis, the integrity of the suprising results of the area calculation techniques is
the coil being tested can be automatically calculated. that the threshold is relatively independent of the type
While there are many different techniques for automatic of coil involved, the voltages involved, or the frequen
calculation, use of some type of area computation al 65 cies inherent to the coils. Variations in the threshold
lows appropriate comparison of coils. Even more sim may thus be accomplished independent of any tests of
ply, the specific error area ratio for each coil can be the particular coil involved. The considerable advan
easily analyzed. Although many different types of statis tages of this were discussed earlier.
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A third statistical technique is the possibility of opti each are designed to yield information with respect to
mizing the number of pulses to which the coil is sub the acceptability of test coil (7). Even when coil (7) fails
jected. As is known in the art of surge testing, an incipi one of these tests, a surge test might still be completed
ent fault is frequently not detectable by a single pulse to assist those in repairing coil (7). Naturally automation
alone. Rather, the prevalent technique of repetitive 5 with respect to all of these tests may lend itself to more
surge testing has developed. Although repetition of the accurate testing. For instance a resistance test might be
surges is desirable for the detection of minor faults, temperature-varied automatically to yield more accu
repetition is also undesirable because it unduly stresses rate information. The simple inclusion of the multipur
the insulation of good coils. By statistically analyzing pose computer allows these new variations to be auto
the results of tests using more than one surge at a given 10 matic.
voltage, the present invention could statistically deter I claim:
mine the number of pulses necessary to reach the de 1. A method for automatically calculating the integ
sired detection accuracy. The maximum number of rity of an electrical coil comprising the steps of sequen
pulses to any given voltage could also be set by the tially:
operator. Again, although those skilled in the art recog- 15 (a) connecting an electrical coil to test equipment;
nize the undesirability of unduly stressing the insulation (b) subjecting said coil to at least one electrical surge;
of the windings of a coil, little effort has been made to (b) subjecting said coil to at least one electrical surge;
automatically minimize the stresses. The facilitation of (c) reading the reaction of said coil to the electrical
an area-based analysis makes implementation of this surge through operation of said test equipment;
aspect straightforward. 20 (d) automatically calculating the integrity of said coil;
Although the methods of the present invention are and
relatively self-explanatory to those skilled in the art, (e) automatically determining the acceptability of the
certain aspects are so significant that they deserve fur integrity by comparing said calculation of integrity
ther explanation. As mentioned, a basic aspect of the to a limit wherein said limit is set without faulting
present invention is the ability to conduct surge testing 25 a representative coil and wherein said limit is a
where a limit is set without testing a standard coil. This dimensionless error representing a deviation from a
avoids the need to intentionally fault an otherwise resonance established by an impedance in the tester
acceptable coil and also allows for easy comparison and an impedance of the coil.
among different coil types. Without this aspect the sta 2. A method for automatically calculating the integ
tistical analysis mentioned earlier would be more in- 30 rity of an eletrical coil as described in claim 1 wherein
volved. Another aspect is that a variety of standards said reaction is a test waveform and wherein said step of
might be utilized very easily. This is of particular impor automatically calculating the integrity further con
tance when production line testing involves more than prises the steps of:
one coil such as when one motor has more than one
type of coil. When the traditional technique (of compar-35 (a) computing the area under a standard waveform;
ison testing through a simultaneous test of a standard . (b) comparing the test waveform to the standard
coil) was used, operators simply had to connect numer waveform;
ous coils to the test apparatus. In the present invention, (c) computing the area of the difference between said
only the type of coil needs to be entered, perhaps auto waveform and said standard waveform; and
matically through a bar code reader. The program con- 40 (d) ascertaining the ratio of said area of the difference
trolling the equipment would then simply compare the to said area under the standard waveform.
result with the appropriate stored standard waveform. 3. A method for automatically calculating the integ
These methods also facilitate the use of multiple test rity of an electrical coil as described in claim 2 and
channels or leads to conduct even faster testing. further comprising the step of automatically assessing
Another aspect of the methods disclosed is the poten- 45 the type of fault existing in an unacceptable coil.
tial to step up the voltage of a test and stop as soon as a 4. A method for automatically calculating the integ
fault is detected. Since some applications may require rity of an electrical coil as described in claim 3 wherein
different levels of acceptability and may subject the said step of automatically determining the acceptability
coils to different levels of stress, it may be useful to test comprises the step of comparing said ratio of said areas
a coil and to record the level at which a fault is first 50 to a threshold value.
detected. While this level could also be analyzed statisti 5. A method for automatically calculating the integ
cally, it may allow groupings which are appropriate rity of an electrical coil as described in claim 4 wherein
depending upon the ultimate uses of the coils. By not said threshold value is from 0.02 to 0.25.
subjecting all coils to the highest level of voltage de 6. A method for automatically calculating the integ
sired, the stress induced in such coils, especially those 55 rity of an electrical coil as described in claim 4 wherein
which display a fault early on, might be minimized. said threshold value is 0.10.
Finally, it should be noted that the automated surge 7. A method for automatically calculating the integ
testing equipment proposed may also include automa rity of an electrical coil as described in claim 6 wherein
tion of a variety of tests. As an example, resistance and said step of automatically assessing the type os fault
high potential testing as are well known to those skilled 60 comprises the step of comparing the value of said ratio
in the art could also be incorporated. Through inclusion to a range of values.
of the appropriate test apparatus and allowing such 8. A method for automatically calculating the integ
apparatus to be controlled by computer (16), automated rity of an electrical coil as described in claim 7 and
test apparatus (9) might step through a variety of tests in further comprising the steps of:
sequence. It would be particularly efficient to combine 65 (a) obtaining a standard waveform; and then
surge testing with resistance and high potential testing (b) storing said standard waveform.
because each of these three tests are possible at roughly 9. A method for automatically calculating the integ
the same point in a manufacturing process and because rity of an electrical coil as described in claim 8 wherein
 5,111,149
13 14
the step of obtaining a standard waveform comprises Said step of automatically sequencing comprises the
the step of testing an acceptable coil. steps of:
10. A method for automatically calculating the integ (a) performing a resistance test on said electrical coil;
rity of an electrical coil as described in claim 9 wherein then
said step of subjecting said coil to at least one electrical (b) performing a high potential test on said electrical
surge comprises the step of automatically optimizing coil; and then
the number of surges to which said electrical coil is (c) subjecting said coil to at least one electrical curge.
subjected at any given voltage. 22. A method for automatically calculating the integ
11. A method for automatically calculating the integ rity of an electrical coil as described in claim 1, 3, or 9
rity of an electrical coil as described in claim 8 wherein O and further comprising the step of automatically se
the step of obtaining a standard waveform comprises quencing through more than one test.
the step of generating said standard waveform. 23. A method for automatically calculating the integ
12. A method of automatically calculating the integ rity of an electrical coil comprising the steps of sequen
rity of an electrical coil as described in claim 11 wherein tially:
the step of generating said standard waveform con 15 (a) connecting an electrical coil to test equipment;
prises the steps of: (b) subjecting said coil to at least one electrical surge
(a) creating a sample of similar electrical coils; and having a voltage level;
then (c) reading the reaction of said coil to the electrical
(b) statistically calculating the standard waveform. surge through operation of said test equipment;
13. A method for automatically calculating the integ 20 (d) automatically calculating the integrity of said coil;
rity of an electrical coil as described in claim 12 wherein and
said step of generating a standard waveform further (e) automatically determining the acceptability of the
comprises the step of automatically updating said san integrity wherein said determination is independent
ple each time a similar coil is determined to be accept of said voltage level.
able. 25 24. A method for automatically calculating the integ
14. A method for automatically calculating the integ rity of an electrical coil as described in claim 23 wherein
rity of electrical coil as described in claim 13 wherein said reaction is a test waveform and wherein said test
said threshold is dependent on the sample of similar step of automatically calculating the integrity further
electrical coils. comprises the steps of:
15. A method for automatically calculating the integ 30 (a) computing the area under a standard waveform;
rity of an electrical coil as described in claim 1, 3, or 9 (b) comparing the test waveform to the standard
wherein said surge is a voltage surge and wherein said waveform;
step of subjecting said coil to at least one electrical (c) computing the area of the difference between said
surge comprises the steps of automatically: test waveform and said standard waveform; and
(a) subjecting the coil to at least one surge having a 35 (d) ascertaining the ratio of said area of the difference
relatively low voltage; then to said area under the standard waveform.
(b) subjecting the coil to additional surges having 25. A method for automatically calculating the integ
increasingly higher voltages; and rity of an electrical coil as described in claim 24 and
(c) stopping the surges at the lesser of either the low further comprising the step of automatically assessing
est voltage at which a fault is detected, or a prede 40 the type of fault existing in an unacceptable coil and
termined maximum voltage. wherein said step of automatically determining the ac
16. A method for automatically calculating the integ ceptability comprises the step of comparing said ratio of
rity of an electrical coil as described in claim 15 and said areas to a threshold value.
further comprising the steps of: 26. A method for automatically calculating the integ
(a) inputting product-specific manufacturing informa 45 rity of an electrical coil as described in claim 25 wherein
tion into the test equipment; and then, said threshold value is 0.10, and wherein said step of
(b) automatically coordinating said information with automatically assessing the type of fault comprises the
the test results for that product. step of considering the value of said ratio.
17. A method for automatically calculating the integ 27. A method for automatically calculating the integ
rity of an electrical coil as described in claim 16 wherein SO rity of an electrical coil as described in claim 24 and
said step of inputting the product manufacturing infor further comprising the step of automatically assessing
mation comprises the step of using a bar code reader. the type of fault existing in an unacceptable coil.
18. A method for automatically calculating the integ 28. A method for automatically calculating the integ
rity of an electrical coil as described in claim 16 and rity of an electrical coil as described in claim 23 or 21
further comprising the step of statistically comparing 55 wherein said surge is a voltage surge and wherein said
said product manufacturing information and said test step of subjecting said coil to at least one electrical
results. surge comprises the steps of automatically:
19. A method for automatically calculating the integ (a) subjecting the coil to at least one surge having a
rity of an electrical coil as described in claim 18 and relatively low voltage; then
further comprising the step of automatically warning of 60 (b) subjecting the coil to additional surges having
any deviation in said test results from an acceptable increasingly higher voltages; and
failure rate. (c) stopping the surges at the lesser of either the low
20. A method for automatically calculating the integ est voltage at which a fault is detected, or a prede
rity of an electrical coil as described in claim 19 and termined maximum voltage.
further comprising the step of automatically sequencing 65 29. A method for automatically calculating the integ
through more than one test. rity of an electrical coil as described in claim 1 or 23
21. A method for automatically calculating the integ wherein said reaction is a test wavefrom and wherein
rity of an electrical coil as described in claim 20 wherein said step of automatically calculating the integrity com
 5,111,149
15 16
prises the setp of making an area computation involving 40. An apparatus for automatically calculating the
the test waveform. integrity of an electrical coil as described in claim 39
30. A method for automatically calculating the integ wherein said data processor is programmed to update
rity of an electrical coil as described in claim 1 or 23 and said sample each time a similar coil is determined to be
further comprising the step of automatically assessing acceptable.
the type of fault existing in an unacceptable coil. 41. An apparatus for automatically calculating the
31. An apparatus for automatically calculating the integrity of an electrical coil as described in claim 38 or
integrity of an electrical coil comprising: 40 wherein said data processor is programmed to opti
(a) a surge generator for subjecting said electrical coil mize the number surges to which said electrical coil is
to at least one electrical surge; O subjected at any given voltage.
(b) a means for sensing the response of the coil to said 42. An apparatus for automatically calculating the
electrical surge; integrity of an electrical coil as described in claim 41
(c) a means for calculating the integrity of the coil; wherein said data processor is programmed to:
and (a) accept the input of product-specific manufactur
(d) a means for determining the acceptability of the 5 ing information;
integrity by comparing said calculation of integrity (b) coordinate said information with the test results
to a limit wherein said limit is set without faulting for that product; and
a representative coil, and wherein said limit is a (c) statistically compare said product manufacturing
dimensionless error representing a deviation from a information and said test results.
resonance established by an impedance in the tester 43. A surge tester for determining the integrity of an
and an impedance of the coil. electrical coil comprising;
32. An apparatus for automatically calculating the (a) an electrical surge generator;
integrity of an electrical coil as described in claim 31 (b) a multi-purpose, fully programmable computer;
wherein the response is a test waveform and wherein (c) a means for sensing the response of the coil to said
said means for calculating the integrity of the coil com 25 electrical surge, wherein said means for sensing
prises a means for making an area computation involv comprises an analog to digital converter and
ing said test waveform. wherein said fully programmable computer com
33. An apparatus for automatically calculating the prises:
integrity of an electrical coil as described in claim 32 (i) a digital processor;
wherein said means for sensing comprises an analog to 30 (ii) a data memory;
a digital converter. (iii) a program memory;
34. An apparatus for automatically calculating the (iv) a means for displaying output of said computer;
integrity of an electrical coil as described in claim 31 (v) an input component for entering and revising
wherein said means for calculating and said means for the program memory by the user of the surge
determining comprise a programmable means which 35 tester; and
further comprises a data processor. (vi) an output component; and
35. An apparatus for automatically calculating the (d) wherein said response is a test wave form and
integrity of an electrical coil as described in claim 34 wherein said program memory controls said digital
wherein said response is a test waveform and wherein processor to make an area computation involving
said data processor is programmed to make an area 40 the test wave form.
computation involving the test waveform. 44. A surge tester for determining the integrity of an
36. An apparatus for automatically calculating the electrical coil as described in claim 43 wherein said
integrity of an electrical coil as described in claim 35 program memory controls said digital processor to:
wherein said data processor is programmed to: (a) compute the area under an acceptable response
(a) compute the area under an acceptable response 45 having a standard waveform;
having a standard waveform; (b) compare the test waveform to the standard wave
(b) compare the test waveform to the standard wave form; and
form; (c) ascertain the ratio of said area of the difference to
(c) compute the area of the difference between said said area under the standard waveform.
test waveform and said standard waveform; and 50 45. A surge tester for determining the integrity of an
(d) ascertain the ratio of said area of the difference electrical coil as described in claim 44 wherein said
between said test waveform and said standard program memory controls said digital processor to
waveform to said area under said standard wave assess the type of fault existing in an unacceptable coil.
form. 46. A surge tester for determining the integrity of an
37. An apparatus for automatically calculating the 55 electrical coil as described in claim 45 wherein said
integrity of an electrical coil as described in claim 36 program memory controls said digital processor to
wherein said data processor is programmed to assess the compare said ratio of said areas to a threshold value.
type of fault existing in an unacceptable coil. 47. A surge tester for determining the integrity of an
38. An apparatus for automatically calculating the electrical coil as described in claim 46 wherein said
integrity of an electrical coil as described in claim 37 program memory controls said digital processor to:
wherein said data processor is programmed to compare (a) create a sample from tests of similar electrical
said ratio of said areas to a threshold value. coils; and then
39. An apparatus for automatically calculating the (b) statistically calculate the standard waveform.
integrity of an electrical coil as described in claim 38 48. A surge testor for determining the integrity of an
wherein said data processor is programmed to: 65 electrical coil as described in claim 47 wherein said
(a) create a sample from tests of similar electrical program memory controls said digital processor to
coils; and then update said sample each time a similar coil is determined
(b) statistically calculate the standard waveform. to be acceptable.
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electrical coil as described in claim 49 wherein said
49. A surge tester for determining the integrity of an program memory controls said digital processor to:
electrical coil as described in claim 43 of 48 wherein (a) accept the input of product-specific manufactur
said program memory controls said digital processor to 5 ing information:
(b) coordinate said information with the test results
optimize the number of surges to which said electrical for that product; and
coil is subjected at any given voltage. (c) statistically compare said product manufacturing
information and said test results.
50. A surge tester for determining the integrity of an k
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