Note: Descriptions are shown in the official language in which they were submitted.
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. The invention relates to electrical circuit test
deYices for detecting the presence and polarity of an
~'ectric potential or performing a continuity test, the
de~ice comprising two test pro~es connected by a cable.
The German Patent Specification No. 2,060,884
describes a test device ~or indicating the polarity and
the phase state of electric potentials relative to a given
reference potential, whexein two luminescence diodes
are connected in parallel with opposite polarities, and a
series current limiting resistor is provided. The two
luminescent diodes are disposed by a protective
wlndow in a pencil-like housing of a test probe which
also contains the series current limiting re.~istor and has
a metal point at one end. The two luminescen~e diodes
are connected via the current limiting resistor between
the metal point and a test }ine which leads out of the
pencil-like hous~ng~ When testing the presence o~ a d.c.
~oltage causes one or the other of the lumine~cence diodes
to be illuminated, in accordance with the polarity, whereas
~0 when an a.c. voltage 15 present then both luminescence
diodes are illuminated.
T the current limiting resis or is in the form o~ a
ceramic cold conductor thermistor which, as is known,
may consist of ferro-electric material on a base of n~doped
and/or p-doped barium titanate, and has a temperature
dependence such that in the ragion of the Curie temperature
it exhibits a sudden increase ln its eIectrical xesistance
by approximately 4 powers of ten, this device can be used
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to check voltages ~rom approximately 2 V up to 500 V. The
ceramic cold conductor exexts a protective function for
~he luminescence diodes~ as it limits the current if
current flow causes self heating to a value above the
Curie temperature, with the consequent considerable increase
in resis~ancP.
However, in many cases it is not only necessary to
determine whether a device is connected to a current source,
i.e. to detect wheth~r a voltage is present and ascertain
the nature of the polarity thereo~, but it is also desirable
to be able to check whether there is continuity of an elec~ric
conductor path, so that it can be ascertained whether an
electric component, an electric assembly or the like load
circuit may be traversed by current when connected to a
lS source. Th~s chec~ing of con~inuity for the passage of
current i~ often of particulax ~nterest, and may be desired
when it is not necessary to check voltages.
Current continu~ty path checking devices operate in
accordance with the principle that a current is supplied
2~ ~rom a test voltage source to ~low through tha electrical
conductor path which is to be checked, and-an son~tic or
optical signal is normally provided to indicate whether
there ls a pa~sage of current or not.
The U.S. Patent Specification NoO 3,870,950 describes
an input protection circuit for electric current path
continuity che~king devi~e which contains a separate current
source and a current flow indicator fbr testing voltage-
free circuits, wi~h protection from al~en voltages which
could jeopardise the current flow indicator, a semiconductor
switch and a cold~conductor thermistor being connected in series,
with the free-ends of probe pins serving as connecting terminals,
the current source and the current flow indicator being connect-
ed in series between the free ends, one free end being connected
via the semiconductor switch and the other via the cold conduct-
or thermistor.
One object of the present invention is to provide a
voltage test device of a type known per se for detecting any
electric voltage and/or the polarity thereof with further
capabilities so that it can readily be used as a continuity test
device by the passage of current through an electric conductor
path, with adequate protection functions provided to increase
the reliability of the device.
According to the invention there is provided a test
device for .indicating an electrical voltage and/or the polarity
thereof, as well as the passage of current through an electrical
conductor, comprising two handles, which are connected by means
of a cable and are provided with contact tips, and one of the
handles contains two luminous diodes connected antiparallelly
and preconnected to a ceramic cold conductor as a current limit-
ing resistor and for testing for passage of current through an
electrical conductor, the following features are present:
a~ a battery connected in series with a protective
diode mounted in one of the handles, in which said cold conduc-
tor and the luminous diodes are housed;
b) a keying switch and a Zener diode connected in
parallel and mounted in said handle;
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c) the series connection of the battery and protective
diode connected to a normally open contact of a keying switch,
which is normally connected with a switch contact connected to
a parallel line, which bridges -the battery and the protective
diode;
d) the keying switch, Zener diode, battery and pro-
tective diode connected in series with the antiparallel connect-
ion of the luminous diodes;
e) the battery is housed with positive and negative
terminals in a removablehousing which, by means of projections
in the inserted state, engage the handle and is removeable only
to an extent such that the opening of the recess in the handle
remains closed.
Preferably the keying switch is arranged in front of a
guard ring.
Preferably the keying switch is connected in parallel
with a 2ener diode.
Advantageously, one handle may contain all the com-
ponents and the second handle simply serves as a contact point
probe.
The invention will now be described with reference to
the drawings, in which:
Figure 1 schematically illustrates constructional
details of one exemplary embodiment of the test device;
Figure 2 is a schematic circuit diagram of one
exemplary embodiment of the invention;
Figure 3 is a schematic circuit diagram of a further
exemplary embodiment of the invention;
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Figure 4 schematically illustrates constructional
details of another embodiment of the test device;
Figure 5 schematically illustrates details of yet
another exemplary embodiment of the test device;
Figure 6 shows details of a preferred form of battery
housing for use in embodiments of the invention; and
Figure 7 is a section along the line IV-IV of Figure 5
showing the battery housing in the extracted position.
In the embodiment shown in Figure 1, the test device
consists of two probes in the form of handles 1 and 2 which
house the electrical components and electrical connection
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paths.
The handle 1 contains two luminescence diodes 11 and 12,
whi~h are visi~le from the exterior. A guard ring 13 surrounds
the handle 1 to serve as a protection against a user's
finger slipping cnto a voltage source when a test is being
carried out. ~ metal point l4 at one end of the handle 1
serves as a contact element tb connect the ~est devlce to a
line, component or circuit point which is to be checked.
A contact point 15 is provided o-, the handle 2, and the
two handles are connected together ~y a cable 16.
The handle 2 has a continuous guard rin~ 17 for
protection, similar to the ring 13 of the handle 1. ~
keying switch 5 is arxanged between the metal point 15 and
the ring 17. The handle 2 accommodates a battery 3 and a
protective diode 4, and the circuit elements are wired
together in accordance with the circuit diasram sho-~n i
~igure 2.
The battery, the pro~ctlve diode and the ~eying switch
5 can all be accommodated in the handle l, so that
the handle 2 is a simple test probe, as shown in the
embodimen~s illustra~ed in Figure 4 and 5.
In the circuit diagram shown in Figure 2, the terminal
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points 14 and 15 correspond t~ the metal contact polnts
of the test device. The ceramic cold conductor thermistor
18 is connected in series with the parallel arrangement of the
oppositely poled luminescence diodes 11 and 12 to the
keying switch 5, which in the rest position 9 is co~nected to
a direct connection line leading ~o ~he metal contact point
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15. The keying switch S is ~ring-loaded, and is depressed
manually to effect a continuity check so that contact is
made with a switch terminal 8.to bring a battery 3 into
circuit in series with a protective diode 4. The ~attery
3 has a positive pole 7 and a negative pole 6, and the diode
4 is poled to conduct current from the battery if there
is a continuous conductive path present when making a
continuity check.
The operation o the device is as follows. For a
voltage check, the keying switch is left in its rest
position, so that any voltage difference presented to.
the metal contact points flows via the thermistor and
one of the luminescence diodes, to c~use it to glow, the
particular diode indicating the polarity of the po~ential.
If an a.c. potential is present, then both diode~ glow. An
excessively high potential wi:Ll cause the thermistor to be
heated above its Curie temperilture so that its resistance
rises rapidly~ and so protect~i the diodes from damage.
For a contlnuity chec~, the metal contact points are
~0 positioned on the path to be chec~ed, and the keying
switch 5 is depre~sed so that current can flow from the
battery 3 if th~re is continuity, and diode will glow. If
an a.c. voltage or d.c. voltage is erroneously connected
~ia the circuit under test duriny a continuity check, this
will be fed in via the metal points 14 and 15 and if of one
polarity could produce a charging current and thus a gas
discharge in the hattery, which ~ould lea~ to its destruction
if it ls o~ encased design. The ceramic coId conductor
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thermistor provided for the protection o~ the luminescence
diodes also serves to protect the battery, and thus has a
combined effect which virtually eliminates the danger of
destr~ction J but as the cold conductor requires a specific
length o~ time in order to ~ecome high-ohmic ~y
self heatiny the protective diode 4 is incorporated into the
protective circuit to hIock excessi~e c~rren~ flow until
the thermistor comes into operation.
The battery 3 may ~e a primary cell structure or a
secondaxy cell structure, e.g. a 12 V monocell. In place of
a pxotective diode~ it is also possible to use another
semiconductor circuit element, for example a transistor or
a triac arranged to provide a similar protective function.
In the modified circuit sh~wn in Figure 3, which may
lS be used in place of the c.trcult illu~trated ln Figure
2 is expanded by the addition of a Zener diode l9 connected
ac~oss the keying switch 5 to link the bridglng parallel
line 10 to the adjacent ~unction of the parallel diode
comblna~ion.
In practice the Zener diode 19 provldes three further
pxotecti~e functions. Pirst~y, the keylng swltch 5 is
protected from high voltages. Secondly, duriny the
- tes~ing of high voltages, mistaken actuation of the keying
switch 5 is prevented from leading to breakdown o~ the
battery 3 and/or the protecti~e diode 4. Thixdly, pxovision
i5 made for the event in which there is no battery 3
inserted, or in which the battery is discharged, so that
misunderstandings by mistake~ act~atio~ of the keyi~g switsch
5 in positio~ for co~tinuity testing are elimlnatedO
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The ~orwards voltage o~ the Zener diode 19 should be
selected in accordance wlth the voltage of the battery 3.
A zener diode for 15 V is particularly suitable in the case
of battery voltages of less than 15 V, e.g. 12 V~
In the further embodiment shown in Figure 4, the test
device again consists of two handles 1 and 2~ but ~he handle
2 contains no circuit components, and merely has the
function of ~earlng the contact poin~ lS, and is provided
with a guard ring 17, whereas the handle 1 connected to
the handle 2 ~ia the line 16 contains all the components
of the circuit illustrated in Figuxe 2 or Figure 3.
The luminescent diodes ll and 12 are arranged between
the contact poin~ 1`4 and the guard ring 13, so that
they are easily visible. They may be mutually aligned parallel
to the longitudinal axls, or t:ransverse thereto.
The handle 1 also pos~esses the keying switch 5, which
ls positioned on that side of the guard ring 13 opposite the
luminescence diodes 11 and 12, i.e. on that side o~ the
handle.l which is enclosed ~y the operators hand, when in
use.
Within the handle l there is arranged the bat~ery 3,
which lies with its poles 6 and 7 engaged between clamping
cont~ct springs 20 and 21. The batte~y 3 i5 accommodated in a
battery container 22 which ~tself is provided with an :
2S openiny 23 matched to the size of the battery.
A projection 24 ser~es to allow the extr2ctable housing
22 to be positiveIy engaged with the wall of the housing 1
when in the inserted state.
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In order to extract the battery 3 from the recess 23 of
the container 22, the wall thereof is partially removed at
one end 25 so that fxee areas are formed on ~oth sides of
the ba~tery ~nd through which the battery can be gripped.
When the container 22 has ~ee~ extracted, an opening
is provided through which the protective components, i.e.
the cold conductor 18~ protecti~e diode 4, and the Zener diode
19 if proYide~, are all accessi~le fro~-the exterior, ~or
xepair or replacement.
In th~ alternative embodiment s~o~n ln Figure 5, the
test device again consists of two handles l and 2 very
similar to the embodiment shown in Figure 4.
Figure 6 lllustrates details of the battery container
22 with the cylindrical cavity 23 in which the battery 3
can be accommodated. The cavity 23 i~ partially closed at the
left-hand end 30, as drawn, ~n such manner that only the
positlve pole 7 o~ the battery passes through opening 31.
At the other end, the opening of the cavity 23 corresponds
to the crDss-section o the battery 3. The lenyth of
the cavlty 23 between the ends 30 and 32 corresponds exactly
to the length of the battery less its positive pole 7, so that
i~ the battery ls incoxrectly inserted into the recess 23,
the positive pole 7 project~ towards the right. If the
housing 22 wer then impressed into the opening 26 (Figure
5) o~ the handle l, the positi~e pole 7 would prevent
complete insertion, ~ecause ~t projects beyond the outer
dimensions o the container 220
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As shown in the cross~section shown in Figure 7, the
container 22 can be fully removed ~rom the handle 1, for
example, when the device requires to be serviced. However,
the contalner cannot ~e readily extracted during nonmal
use, because this is prevented by the projections 27 (Fig. 6).
In place of ~he projections 27 it ls also possible to provide
a bead 28 which extends along the entire length of the
conta~ner 22. Since, when the container 22 is in this
limited state of extractlon, in accordance with Figure 7,
the opening 26 reamins closed to prevent arcess to the
interior, so that lt is not normally possible to touch
the contact 20 or the contact 21. The projections serve
to lock the container 22 in the fully inserted state.
It is most advantageous to install the container ~2 into
the handle 1 when this handle is itsel assembled. The
handle 1 in this embodiment consists of two halves 33 and
34, as indicated in Figure ~ a:nd Figure 7, which are
screwed together o~ flrmly ~lu,ed to one another in a plane
35. Prior to this assembly, t!he handle half 33 can be
elastically deformed ln the region o~ the opening 26 to such
an extent that the battery container can be insertedO The
glu~ing of.the two.handle halves 33 and 34 along the lin~
35 cancels this elasticity, so that the container 22 can
no longer be rPadily extracted if the handle halves are not
simultaneously dlsassembled.
Naturally, it is also possible to bevel the projactions
as indicated by the line 36 in ~igure 7, so that the
projections act, as it were~ as barbs. In this case the
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hatter~ container can be installed following. the assembly o~
the handle 1 by force~ul pressure, but cannot be full~
extracted without the use of a sulta~le tool.
This embodiment o~ the invention ensures that when
S the test device is used to indicate a voltage, then in
the event of any misactuation of the keying switch 5, and
pos~ibly a breakdown Gf the protective diode 19 which
bridges this keying switch 5, two possible dangers are
avoided~ namely the touching of the contacts 20 and 21
or the possibillty that due to the misinsertion o~ the
battery into the cavity 23 the negative pole 6 of the
battery 3 lie~ in the recess in such manner that it
incorractly touches the contact 21 and doe~ not as is
correct - touch the contact 20. Naturally the touchin~
o~ the contacts 20 and 21 by a user in the e~ent of
misactuation of the key 5 during ~he display of a
voltage could be a serious and dangerous condit~on.
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