A test apparatus is described for locating electrical shorts that is especially suited for use while an electrical circuit is being fabricated or assembled. A ring counter derives input pulses from a square wave oscillator. The outputs of the counter are fed through transistors to an array of light emitting diodes. Each diode is connected to an electrical conductor, such as a bus bar, that is to be tested. In the absence of a short between the electrical conductors the diodes are sequentially illuminated. When a short occurs, a comparator/multivibrator circuit triggers an alarm and stops the oscillator and the sequential energization of the diodes. The two diodes that remain illuminated identify the electrical conductors that are shorted

Deboo, G. J.

Devine, D. L.

English

NASA Technical Reports Server

United States Patent [191 
Deboo et al. 
[54] TEST APPARATUS FOR LOCATING 
SHORTS DURING ASSEMBLY OF 
ELECTRICAL BUSES 
[75] Inventors: Gordon J. Deboo, Sunnyvale; David 
[73] Assignee: The United States of America as 
J. Devine, San Jose, both of Calif. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 69,485 
[22] Filed: Aug. 24, 1979 
[51] Int. Cl.3 ............................................. GOlR 31/02 
[52] U.S. C1. ......................................... 324/51; 324/52 
[58] Field of Search ................... 324/51, 52, 66, 73 R; 
340/651, 652; 29/739, 741, 755, 624, 628, 630 
R, 630 A 
t561 References Cited 
U.S. PATENT DOCUMENTS 
2,814,774 11/1957 Wong ..................................... 324/51 
3,103,808 9/1963 Eichelberger ..................... 324/51 X 
3,495,172 2/1970 Davis ..................................... 324/51 
3,546,581 12/1970 Herrendeen et al. .................. 324/54 
3,699,432 10/1972 Brown .................................... 324/51 
3,480,856 11/1969 Scott ...................................... 324/51 
3,713,019 VI973 Van Bosse ............................. 324/51 
3,795,860 3/1974 Sylvan ............................... 324/51 X 
4,013,947 3/1977 Arai ........................................ 324/51 
4,015,200 3/1977 Strandh .................................. 324/5 1 
4,019,129 4/1977 Grau .................................. 324/51 X 
Primary Examiner-Gerard R. Strecker . 
Attorney, Agent, or Firm-Darrell G. Brekke; John R. 
Manning 
1571 ABSTRACT 
A test apparatus for locating electrical shorts that is 
especially suited for use while an electrical circuit is 
being fabricated or assembled. A ring counter derives 
input pulses from a squarewave oscillator. The outputs 
of the counter are fed through transistors to an array of 
light emitting diodes. Each diode is connected to an 
electrical conductor, such as a bus bar, that is to be 
tested. In the absence of a short between two electrical 
conductors the diodes are sequentially illuminated. 
When a short occurs, a comparator/multivibrator cir- 
cuit triggers an alarm and stops the oscillator and the 
sequential energization of the diodes. The two diodes 
that remain illuminated identify the electrical conduc- 
tors that are shorted. 
3 Claims, 2 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19820016544 2020-03-21T16:42:13+00:00Z
U.S. Patent Aug. 4,1981 Sheet 1 of 2 
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4,282,479 
U.S. Patent Aug. 4, 1981 Sheet 2 of 2 4,282,479 
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4,282,479 
1 2 
When a short occurs, the voltage drop sensed across the 
resistor triggers a sonic alarm and stops the sequential 
activation of the light emitting diodes. The diodes cor- 
responding to the shorted bus bars remain illuminated 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a schematic diagram of an electrical short 
locator circuit in accordance with the principles of the 
invention. 
FIG. 2 is a perspective view of a bus bar assembly 
that may be tested with the electrical short locator. 
TEST APPARATUS FOR LOCATING SHORTS 
DURING ASSEMBLY OF ELECTRICAL' BUSES 
DESCRIPTION 5 until the short is removed. 
ORIGIN OF THE INVENTION 
The invention described herein was made by an em- 
PloYee of the United States G ~ e r n m e n t  and may be 
manufactured and used by or for the Government for 
governmental purposes without the Payment of any 
royalties thereon or therefor. 
TECHNICAL FIELD 
finding instrument and more Particularly to one suited 
for locating shorts as they occur while an electrical 
system is being fabricated. 
BACKGROUNDART 
systems 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Referring to the drawings, the electrical short locator 
is shown at 1 and a typical bus bar assembly on which 
the locator may be employed is depicted at 2 (FIG. 2). 
Bus bars 3u, 36, 3c, 3n are separated from eaach other by 
20 electrical insulators 4. Pin-like terminals 6 are affixed to 
each of the bus bars, and electrical leads 7 are connected 
The present invention relates to an electrical short 15 
In as computers it is 
common to power and grounding bus bars or rails. 
Often these bus bars have hundreds or even thousands 
to the terminals by conventional solder or wire-wrap 
techniques. ~~~h bus bar 3u-3n has a plug 8. These of wires connected thereto. After the wires are attached plugs typically are used to connect bus bars to remote to the bus bars and the circuits are inspected, shorts are 25 circuits such as power sources, Socket (shown in FIG. 
invariably discovered, especially when the terminals are 1) mates with plugs and it enables the electrical short closely spaced. It is very difficult and time consuming locator 1 to be brought into electrical communication to detect these wiring errors. If the system is energized with the bus bars 3u-3n. before shorts are removed, components in the system The bases of bipolar transistors 12u, 12b, 12c and 12n can be damaged. 
ducted after the electrical equipment was completed, 13', 13bi 13' and 13'. Ring counter l1 may for 
meter was used to hunt for shorts. The collectors of the transistors are commonly joined 
some test instruments have been designed to detect between one fixed terminal of potentiometer PO and 
shorts in assembled cables, They require a connector for 35 SPST switch 16. The other terminal of switch 16 is 
each end of the cable under test and they utilize com- connected to a d-c Power SUPPlY 5. The emitters ofthe 
$ex circuits, slow unreliable mechanical switching de- NPN transistors 1% 126, 12c, 12n are connected to the 
vices, or high voltages. Representative cable testing anodes of light emitting diodes, LED's, lk, 146, 1&, 
devices are disclosed in U.S. Pat. Nos. 2,814,774; 14n, respectively. Resistors 16u, 166, 16c, 16n, are con- 
3,480,856; and 4,015,200. 40 nected between the cathodes of the LED's and node 17. 
In the past, searches for shorts were normally con- 30 are connected to the Outputs Of ring counter l1 by leads 
not during the actual assembly process. Often an ohm- example, or cascaded CMOS 4017's or 4022's* 
US. Pat. No. 3,713,019 describes an apparatus for 
sequentially examining points in an electrical matrix so 
as to detect failures in components such astransistors. A 
transformer is required at every sensing station and the 
switching is accomplished with relays. 
DISCLOSURE OF INVENTION 
Inasmuch as it is cost effective to locate electrical 
shorts as they occur during the assembly process of 
complex bus bar circuits, it is an object of the subject 
invention to provide an instrument that generates an 
audible warning as soon as a shorting-type wiring error 
is made. 
It is another object of this invention to provide a 
visual indication of the actual bus bars that have errone- 
ously been brought together in electrical contact. 
It is still a further object of the instant invention to 
provide a real time electrical short locator that can 
quickly and reliably scan many bus bars and operate 
from a lowvoltage battery power supply. 
Briefly, the electrical short locator in accordance 
with the above objects requires only a single connection 
to the bus bar or conductor under test. A light emitting 
diode is provided for h bus bar, rail or electrical 
conductor to be tested. Each diode is serially connected 
istor and the transistors are normally 
ated. The current through the transis- 
tors and diodes passes through a common resistor. 
Resistor 18 is coupled between node 17 and ground. 
Conductors or leads 19u, 196, 19c, 19n extend from the 
emitters of transistors 12u-12n to socket 9. The conduc- 
tors are so arranged within the socket so that when 
45 socket 9 is connected with plugs 8, conductor 19u 
makes electrical contact with the uppermost plug, con- 
ductor 19b makes contact with the second-from-the-top 
plug, and so forth. Conductors 19u-19n need not termi- 
nate in a socket. If desired, each conductor may termi- 
50 nate in a test clip such as an alligator clip. The clips may 
be fastened to a terminal on the bus bar or to the bus bar 
itself. 
A comparator 21 has a first input 22 coupled to wiper 
23 of potentiometer 10 by means of lead 24. The second 
55 input 25 of comparator 21 is connected to node 17 via 
lead 20. 
NOR gates 26 and 27 are interconnected with resis- 
tors 28,29 and capacitor 30 so as to form a squarewave 
oscillator 31. For example, a waveform with a fre- 
6o quency of 1 Hz is generated when resistors 28 and 29 
are 1 M a  and 390 K a ,  respectively, and capacitor 30 
has a value of 0.22 pF. The clock pulses for ring 
counter 11 are provided by oscillator 31 and carried to 
the counter on conductor 15. Alarm 32 is coupled to a 
65 one-shot multivibrator 35 by means of lead 33. When a 
pulse, preferable with a period of at least five seconds, 
is released from one-shot multivibrator 35, sound is 
produced from alarm 32 for the duration of the pulse. 
4,282,479 
3 4 
Alarm 32 may be a bell, a buzzer, or a piezoelectric nated, and the test circuit will once again be ready to 
sounder such as the Sonalert manufactured by Mallory. detect an inadvertent short. 
The output of comparator 21 is coupled to the input of Transistors 12u-1211 serve two useful functions. They 
multivibrator 35 and one input of NOR gate 26 by amplify the LED currents and they protect the ring 
conductor 36. Power for the entire electrical short 5 counter when a short occurs. Specifically, under a short 
locator is supplied by power supply 5. 
The subject electrical short locator is highly suited to 
detecting shorts at the time they are made, that is, dur- 
ing the process of adding leads 7 to terminals 6. In oper- 
ation, the assembler connects conductors 19a-19n to 
bus bars 3a-3n, respectively, by connecting socket 9 to 
plugs 8, and closes power switch 16. When the power is 
on, a train of positive pulses is fed to ring counter 11. 
Each time a pulse enters counter 11, a positive pulse of 
equal duration is generated on a different counter out- 
put lead. Leads 13a-13n receive the positive output 
pulses in sequential order. At any given time all counter 
outDut leads 13a-13n are grounded except one. The 
circuit condition the transistors isolate a high-level 
counter output from a low-level output. Stating it an- 
other way, the transistors prevent the grounding of the 
counter output with the positive voltage. 
While one specific embodiment of the invention has 
been described in detail above, it is to be understood 
that various modifications may be made from the spe- 
cific details described without departing from the spirit 
and scope of the invention. The invention is applicable 
5 to any electrical system involving complex wiring 
wherein it is desired to achieve real time discovery of 
wiring errors. When the number of busses or conduc- 
tors is very large, the scanning rate can be increased by 
changing the values of resistors 28, 29 and capacitor 30 
0 
positive output pulses are channeled to the transistor - -  
bases and thus the transistors are sequentially biased 2o so as to increase the oscillator frequency* 
into conduction and likewise the LEDs are sequentially 
biased into conduction. That is, when a positive pulse 
emanates from counter 11 on lead 13a, transistor 12u 
and LED 14a simultaneouslv conduct for the duration _ _  
We 
1. Test apparatus for locating shorts between electri- 
cal buses in a bus system having n buses, said apparatus 
comprising: 
25 of the positive pulse. As soon as these semiconductors 
stop conducting, semiconductors 12b and 14b and con- 
duct, and so forth. If oscillator 31 has a frequency of 1 
Hz, the LED’s will sequentially glow and each will 
glow for a period of 0.5 seconds. 
The wiper 23 of potentiometer 10 is adjusted so that 
a reference voltage is produced on input 22 that is 
slightly greater than the voltage across resistor 18 (and 
at comparator input 25) when no bus bar short is pres- 
ent. 
When two bus bars become shorted, the LED’s stop 
conducting in sequence and the two particular LEDs 
associated with the shorted bus bars continue to provide 
a visual indication until the short is removed or power 
switch 16 is opened. For example, when end 38 of lead 40 
7 touches bus bar 3b and causes bus bar 3a to be shorted 
to bus bar 36, the anode of LED 14b is connected to the 
anode of LED 14a. Consequently, when a positive pulse 
reaches the base of transistor 12a after the short occurs, 
LED’s 14a and 14b both conduct and generate a visual 45 
indication. The current through resistors 16a and 166 
also flows through resistor 18. With LED’s 14a and 146 
both conducting, the resulting current through resistor 
18 produces a voltage drop across the resistor which 
exceeds the reference voltage on input 22 of comparator 50 
21. The output of comparator 21 goes from ground 
potential to a positive potential and performs two tasks. 
It stop oscillator 31 (by switching the output of NOR 
gate 18a to ground potential) and it triggers one-shot 
multivibrator 35. The pulse from the multivibrator turns 55 
on alarm 32 for the duration of the pulse. Thus, as soon 
as the assembler hears alarm 32, he knows that a short 
has been created. By observing that LEDs 14a and 14b 
are illuminated, the assembler knows that the short 
occurs between bus bar 3a and bus bar 36. Without 60 
pulses from oscillator 31, the positive pulse originally 
30 
35 
means for generating pulses at a predetermined rate; 
means having n outputs and an input coupled to said 
pulse generating means for sequentially emitting 
pulses at said n outputs at said predetermined rate; 
a resistor having first and second terminals, said first 
terminal being grounded; 
n indicator circuits each including an electric lamp 
coupled between said resistor second terminal and 
a different output of said pulse emitting means, said 
output pulses from said pulse emitting means caus- 
ing said lamps to be sequentially energized at said 
predetermined rate and a maximum voltage V to be 
produced across said resistor when no buses are 
shorted together; 
a single conductor linking each indicator circuit lamp 
to a different bus; 
a comparator having first and second inputs and an 
output, said first input being connected to said 
second terminal of said resistor; 
means for producing a fixed voltage slightly greater 
than V and applying it to said second input of said 
comparator; 
a sonic alarm; 
means coupled to said output of said comparator for 
turning on said alarm for a predetermined period 
and switching off said means for generating pulses 
when said voltage at said first comparator input 
exceeds said voltage at said second comparator 
input; 
a short condition between two of said buses causing: 
said voltage across said resistor to exceed said volt- 
age applied to said second comparator input; said 
means for generating pulses to stop generating 
pulses; and said electric lamps associated with said 
shorted buses to remain illuminated until said short 
condition is removed. 
2. Test apparatus as set forth in claim 1 wherein said 
applied to the base of transistor 12a by ring counter 11 
will be extended indefinitely. Consequently, LEDs 141 
and 14b will remain illuminated until the short is discov- 
ered and removed. As soon as the short is removed, the 65 
current through resistor 18 will drop, the comparator 
output will swing to ground potential, oscillator 31 will 
means for sequentially emitting pulses is a ring counter 
and said means for turning on said alarm for a predeter- 
mined period is a one-shot multivibrator. 
3. Test apparatus as claimed in claim 2 wherein each 
indicator circuit includes a transistor switch controlled 
by said pulses emitted from said ring counter. 
start up, the LED’s will again be sequentially illumi- * * * * *  


Test apparatus for locating shorts during assembly of electrical buses

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