Note: Descriptions are shown in the official language in which they were submitted.
CA 02959448 2017-02-27
Cable tester and method for testing an n-pole cable
The subject invention relates to a cable tester having a first tester unit
with a first control unit
and a second tester unit with a second control unit, wherein, in the first
tester unit, a first se-
lection circuit controlled by the first control unit is provided, which is
connected to a first con-
nector at the first tester unit, and, in the second tester unit, a second
selection circuit con-
trolled by the second control unit is provided, which is connected to a second
connector at
the second tester unit. Moreover, the invention relates to a method for
performing a func-
tional test on an n-pole cable having a number of individual conductors using
a cable tester
having a first tester unit with a first control unit and a second tester unit
with a second control
unit, wherein a first selection circuit in the first tester unit is controlled
by the first control unit
and a second selection circuit in the second tester unit is controlled by the
second control
unit, wherein a cable to be tested is connected with one end to a first
connector of the first
tester unit connected to the first selection circuit and with the other end to
a second connec-
tor of the second tester unit connected to the second selection circuit, and,
to perform the
test, an individual conductor of the cable is connected through by the first
selection circuit
and the second selection circuit.
So far, to test an n-pole cable, the cable has been disconnected at both ends
and the individ-
ual conductors of the n-pole cable have been tested individually using a
multimeter, for ex-
ample, by measuring resistance. Understandably, this procedure is time-
consuming and
prone to error, especially when it comes to multipole cables with very many
individual con-
ductors. An improvement may be achieved with cable testers where both ends of
the cable
are inserted into connectors provided at the cable tester. The cable tester
then tests the indi-
vidual conductors in an automated manner. However, in both cases, the cable
must be dis-
connected and the system in which the cable is used in normal operation must
be interrupted
for this purpose. Moreover, this is only possible for small cable lengths.
CN 102520308 A describes a cable tester having a master and a slave portion to
which the
ends of the cable to be tested are respectively connected. Controlled by the
master, the indi-
vidual conductors are individually tested through a relay circuit in the
master and slave in an
automated manner. By separating the cable tester into a master and a slave,
long cables can
also be tested. Here too, however, the cable must be disconnected to be able
to perform the
test.
One object of the subject invention now is to provide a cable tester and a
method for testing
a cable which enables testing cables of almost any length even during normal
cable opera-
tion.
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This object is achieved for the apparatus by the first tester unit and the
second tester unit be-
ing interconnected by at least one tester cable, wherein the tester cable
comprises at least
one line for a separate test ground that differs from the ground of the cable
tester, and a
measuring unit is provided in at least one of the first tester unit or the
second tester unit,
measuring an electrical variable relating to the test ground, in particular an
electric voltage or
an electric current, which the cable tester assesses to perform a test.
Similarly, the method
according to the invention is characterized by the individual conductor to be
tested being
connected to a separate test ground that differs from the ground of the cable
tester, and an
electrical variable relating to the test ground, in particular an electric
voltage or an electric
current, being measured in the first tester unit or the second tester unit and
assessed to per-
form the test. By using a separate test ground that differs from the ground of
the cable tester,
it is possible to carry out a measurement of an electrical variable on the
individual conductor
independently of any other system voltage or system current applied to the
individual con-
ductor. At the same time, this procedure does in no way influence the cable in
normal opera-
tion and thus an electrical connection of system components through the cable.
Therefore, it
is not only possible to test the cable when not in operation, but also during
normal cable op-
eration. This also ensures a very flexible field of application for the cable
tester. Due to the
separation of the cable tester into a first tester unit and a second tester
unit and the connec-
tion thereof by a dedicated tester cable, the possible length of the cable to
be tested essen-
tially only depends on the length of the tester cable, thereby also allowing
even very long
cables to be tested.
If the tester cable comprises a communication link, or a wireless
communication link is pro-
vided between the first control unit and second control unit through which the
first control unit
and the second control unit communicate, a master/slave operation of the cable
tester may
be implemented in a very advantageous manner. This means that a tester unit
(the master
unit) controls the other tester unit (the slave unit) through the
communication link. Similarly,
this can also be used to implement a master/master operation, wherein both
tester units ex-
change data over the communication link.
Using a tester cable with a test line connected to both the first selection
circuit and the sec-
and selection circuit, a functional test of the cable tester can be readily
implemented. Simi-
larly, the resistance of the line can also be easily estimated for the test
ground in the tester
cable to render the measurement of the electrical variable relating to the
test ground and/or
the subsequent assessment thereof more accurate and/or reliable.
If an electrical power source is provided in at least one of the first tester
unit or the second
tester unit which is connected to the output of the associated first or second
selection circuit
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and is connected to the test ground, a second test case can be implemented in
the form of a
current measurement.
Here, it is particularly advantageous if the electrical power source is
executed as a current
source and the measuring unit measures a voltage relating to the test ground,
since a single
measuring unit will then be sufficient for measuring a voltage.
In a first test case, to perform a voltage measurement on the individual
conductor connected
through, the voltage relating to the test ground is measured and compared to a
threshold
value, and a fault in the individual conductor is detected if the measured
value is greater or
less than the threshold value.
In a second test case, to perform a current measurement, the individual
conductor connected
through is switched to an electrical power source relating to the test ground,
and the electri-
cal variable produced thereby relating to the test ground is measured. Here,
the electrical
power source may either be executed as a current source or as a voltage
source.
In a very particularly advantageous embodiment of the invention, a first end
of the cable to
be tested is simultaneously connected to a first system unit and a first
tester unit and the
other end of the cable to be tested is simultaneously connected to a second
system unit and
a second tester. Thereby, a test of the cable in normal cable operation is
implemented with-
out disrupting normal operation.
The subject invention will now be explained in greater detail with reference
to figures 1
through 6, schematically showing advantageous embodiments of the invention in
an exem-
plary and non-limiting manner. Thereof,
Fig. 1 shows the configuration of a cable tester according to the invention,
Fig. 2 shows the configuration of a cable tester according to the invention
with a cable
in normal operation,
Fig. 3 shows the performance of a voltage measurement using the cable tester,
Fig. 4 shows the performance of a voltage measurement with a fault in the
cable,
Fig. 5 shows the performance of a current measurement using the cable tester,
and
Fig. 6 shows the performance of a current measurement with a fault in the
cable.
Cable tester 1 of the invention, as exemplified in fig. 1, consists of a first
first tester unit 2 and
a second measuring unit 3 and a tester cable 4 connecting the two measuring
units 2, 3. The
first measuring unit 2 and the second tester unit 3 each have a connector 5, 6
to which the
cable 7 to be tested having a number n 1 of individual conductors 10 (n-pole
cables 7) may
be connected using connectors 8, 9 thereof.
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Tester cable 4 comprises a communication link 11, a line for supply voltage
VCC and a line
of the ground GND of cable tester 1. In addition, tester cable 4 also
comprises an additional
line for a separate test ground TGND, the function of which will be described
in detail below.
The ground GND and test ground TGND are not directly interconnected in cable
tester 1.
Tester cable 4 may also comprise a test line TL which will also be described
in detail below.
It is understood that tester cable 4 may also consist of several individual
cables and does not
have to be configured as one cable. Similarly, communication link 11 may also
be imple-
mented wirelessly, for example, as a Bluetooth or WLAN connection.
With this separation of cable tester 1 into a first measuring unit 2 and a
second measuring
unit 3 connected thereto by a tester cable 4, almost any length of cable 7 may
be tested. The
length of cable 7 is essentially only limited by the possible length of tester
cable 4 and/or an
acceptable distance in the case of a wireless connection.
The first tester unit 2 comprises a voltage supply 12 providing supply voltage
VCC of cable
tester 1. Voltage supply 12 may also be implemented as a galvanically isolated
voltage sup-
ply, as indicated by the dashed line in the first tester unit 2. The galvanic
isolation may in-
crease the safety of cable tester 1. Preferably, the ground of the voltage
supply coincides
with ground GND of cable tester 1.
Moreover, a first control unit 13 is provided in the first tester unit 2, e.g.
in the form of a mi-
crocontroller or a programmable memory device. The first control unit 13 may
have an ana-
log-to-digital converter (ADC) 14 to digitize a measuring variable for further
processing in the
first control unit 13. It is understood, that the first tester unit 2 could
also be implemented
completely analogously.
Connector 5 of the first tester unit 2, and thus also the individual
conductors 10 of n-pole ca-
ble 7, is connected to a first selection circuit 15, e.g. in the form of a
multiplexer or a relay
circuit, connecting exactly one individual conductor 10 of cable 7 to be
tested through to an
output 24 of the first selection circuit 15. The first selection circuit 15
and/or output 24 thereof
is also connected to an electrical power source 16 also supplied by the
voltage supply, which
may be activated or deactivated via a switch 18. However, the electrical power
source 16 is
connected to test ground TGND rather than to ground GND of voltage supply 12.
Thus, in a
test case, as explained in greater detail below, the electrical power source
16 is incorporated
into a closed circuit with test ground TGND as the ground. The first selection
circuit 15 and
switch 18 are controlled by the first control unit 13, as indicated in fig. 1.
The electrical power
source 16 may be configured as a current source, as shown in the figures, or
as a voltage
source.
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A measuring unit 19 measures an electrical variable, current IT or voltage
Upoc, depending on
the configuration of the electrical power source 16, between output 24 of the
first selection
circuit 15, at which an individual conductor 10 is connected through, and test
ground TGND.
A current source and a voltage measurement are shown throughout the figures.
As an equiv-
alent, however, cable tester 1 of the invention may also be configured with a
voltage source
and a current measurement as the measuring unit 19. What is essential for the
invention is
that the electrical variable, current or voltage, is measured against test
ground TGND and
that test ground TGND differs from ground GND of cable tester 1. This measured
electrical
variable, here voltage UADC, is transmitted to ADC 14 and thus to the first
control unit 13 as a
measuring variable and can be assessed to perform a test on a cable 7, as will
be explained
in greater detail below.
The first tester unit 2 may further comprise an input/output unit 17 to
control the sequence of
a test of cable 7 and/or display the result of the test. The first tester unit
2 may, of course,
also have an interface with a data network, e.g. a LAN, WAN, WLAN or the like,
to control
the first tester unit 2 from a remote computing unit.
In the second tester unit 3, a second control unit 20 is provided, e.g. in the
form of a micro-
controller or a programmable memory device, which is connected to the first
control unit 13
via communication link 11 of tester cable 4, e.g. a serial interface or data
bus. The second
control unit 20 and the first control unit 13 may exchange data and commands
via communi-
cation link 11. In particular, the second control unit 20 may be controlled by
the first control
unit 13 via communication link 11.
Moreover, in the second tester unit 3, a second selection circuit 21 is
provided, e.g. in the
form of a multiplexer or a relay circuit, which is controlled by the second
control unit 20. The
second selection circuit 21 is connected to connector 6 of the second tester
unit 3 and thus
to the individual conductors 10 of cable 7, on the one hand, and by output 25
thereof to test
ground TGND, on the other hand.
The first tester unit 2 and the second tester unit 3 may also have an
identical hardware setup
and be configured correspondingly for use as a master or slave. However, a
configuration as
master and master is also conceivable.
To perform a test on cable 7, an individual conductor 10 of cable 7 is
connected through via
the first selection circuit 15 by the first control unit 13. Via communication
link 11, the second
tester unit 3 is caused by the second control unit 20 and the second selection
circuit 21 to
connect through the same individual conductor 10 of cable 7. In this way, a
respective one of
the individual conductors 10 is selected for the test and connected to test
ground TGND. The
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individual conductors 10 may therefore be tested individually and successively
in an auto-
mated manner. Testing cable 7 will now be described in detail with reference
to figures 2
through 6 taking an n-pole cable 7 in normal operation as an example.
In normal operation, n-pole cable 7 connects a first system unit 30 to a
second system unit
31. System voltages Us(t) that are different or vary over time from a system
ground GNDs
may be applied to the individual conductors 10 of cable 7, as exemplified in
fig. 2 by the first
individual conductor 10. System ground GNDs differs from test ground TGND. At
the same
time, cable 7 is connected to cable tester 1 as described above. For this
purpose, the cable
ends of cable 7 may each be provided with a Y-adapter 22, 23 (indicated in
fig. 2), which
makes it possible to connect cable 7 to both the first and second system units
30, 31 and the
first and second tester units 2, 3. Of course, instead of an advantageous Y-
adapter 22, 23,
other connection options may also be provided, such as alligator clips, pins,
etc. Therefore,
cable tester 1 may also be connected to cable 7 only if needed, without
disrupting normal
operation. Thus, for the cable test, cable 7 does not need to be disconnected
from the first
and second system units 30, 31. However, it is understood, that is also
possible to test a
cable 7 not in operation by connecting it, as in fig. 1, by connectors 8, 9
thereof to cable
tester 1.
Fig. 3 shows a voltage measurement as a first test case, only including the
parts of cable
tester 1 which are relevant for this test. As described above, an individual
conductor 10 of n-
pole cable 7 to be tested is connected through for the test. Electrical power
source 16 is
switched off. Measuring unit 19 measures the voltage Upoc dropping between the
first selec-
tion circuit 15 and/or output 24 thereof and the second selection circuit 21
and/or output 25
thereof connected to test ground TGND, i.e. a voltage potential relative to
test ground TGND.
Substantially disregarding any other line resistance, the voltage drop is
thereby measured at
individual conductor 10 of cable 7 to be tested. Due to the measurement
against test ground
TGND, this voltage drop is completely independent of the system voltages Us
and a system
current Is across individual conductor 10. This voltage drop UADc will be very
small with a
faultless individual conductor 10, usually in the range of >OV to <1V. Once
the electrical
properties of cable 7, such as line resistance, are known or can at least be
estimated, the
expected voltage drop UADcset may also be estimated in advance and compared to
the mea-
sured voltage drop UADc as a setpoint value. The comparison of the measured
voltage drop
UADc with a threshold value UTs, e.g. in the form of the expected voltage drop
UADcset or a
predetermined voltage value, allows to determine whether individual conductor
10 is dam-
aged, in particular broken, or not. This fault case is shown in fig. 4. Due to
a fault F in individ-
ual conductor 10, here a break, system voltage Us is essentially measured,
i.e. UADc¨Us,
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which is usually much higher than the normal voltage drop across an undamaged
individual
conductor 10. The result of the test may be displayed on input-/output unit
17.
Fig. 5 shows a current measurement as a second test case, only including the
parts of cable
tester 1 which are relevant for this test. As described above, an individual
conductor 10 of
cable 7 to be tested is connected through for the test. Electrical power
source 16 is switched
on (and/or switch 18 closed) for the current measurement such that a test
current IT flows.
Depending on the system, test current IT may be in the kA range for high-
voltage operation or
in the mA range for small control lines.
When using a current source as the electrical power source 16, measuring unit
19 measures
the voltage UADc dropping between the first selection circuit 15 and the
second selection cir-
cuit 21 which is connected to test ground TGND, i.e. again a voltage potential
relative to test
ground TGND. In the event a voltage source is used as the electrical power
source 16, mea-
suring unit 19 would measure the test current IT flowing in the circuit formed
by test ground
TGND and individual conductor 10. However, use of a current source is
preferred, since
measuring unit 19 then measures a voltage for both test cases.
Test current IT flows via the first tester unit 2 to the individual conductor
10 to be tested and
connected through cable 7 to be tested. There, system current Is, flowing
across cable 7 dur-
ing normal operation, and test current IT overlap. At the opposite end of
cable 7, test current
IT flows to the second tester unit 3 and from there via test ground TGND back
to the first
tester unit 2. Since system ground GNDs and test ground TGND are electrically
isolated,
system current Is and test current IT can be clearly separated and test
current IT does in no
way influence the first or second system unit 30, 31. In the illustrated
exemplary embodi-
ment, voltage measuring unit 19 again measures voltage IJADc (and/or test
current IT when
using"a voltage source) dropping between the first selection circuit 15 and
the second selec-
tion circuit 21 which is connected to test ground TGND, i.e. a voltage
potential relative to test
ground TGND. Due to the measurement against test ground TGND, this voltage
drop is com-
pletely independent of system voltages Us and a system current Is across
individual conduc-
tor 10. The measured voltage Upnc essentially results from the resistance Rw
of individual
conductor 10, the resistance RK of the return line of test ground TGND in
tester cable 4 and
the test current IT with UADc = (Rw RK) * IT. The same applies analogously if
a voltage
source having a nominal voltage UADc is used as the electrical power source
16. Once the
electrical properties of cable 7 and tester cable 4, such as line resistance,
are known or can
at least be estimated, the expected voltage drop UADcset (and/or expected test
current ITset)
may also be estimated in advance and compared to the measured voltage drop
Uppc (and/or
test current IT) as a setpoint value. The comparison of the measured value
with a threshold
value UTs (and/or Irs), e.g. in the form of the expected voltage drop UAocset
or a predeter-
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mined voltage value, allows to determine whether individual conductor 10 is
damaged, in
particular broken, or not. This fault case is shown in fig. 6.
Due to a fault F in individual conductor 10, here a break, test current IT can
no longer flow
across individual conductor 10 but flows via system ground GNDs and the second
system
unit 31 to the second tester unit 3, as shown in fig. 6. Therefore, the
voltage drop Utoc mea-
sured in the first tester unit 2 is considerably higher since additional
voltage is lost to internal
resistance R of the second system unit 31 and Rs of the first system unit 30.
When measur-
ing current, the measured test current IT would be smaller in the event of a
fault. Accordingly,
in the event of a fault, the measured voltage drop UADC is UADC = (RW RK R +
Rs)* IT. The
same applies analogously if a voltage source having a nominal voltage UADC is
used as the
electrical power source 16. Thus, a fault is clearly detectable when
performing a comparison
with a threshold value UTs and/or ITs. The result of the test may again be
displayed on input-
/output unit 17. The threshold values UTs and/or ITs of both test cases will
usually not have
the same values.
Test line TL of communication link 11 may also be used to estimate the
resistance of the
return line of test ground TGND in communication link 11. To this end, like
individual conduc-
tor 10, test line TL in the first tester unit 2 and second tester unit 3 is
connected to the first
selection circuit 15 and second selection circuit 21. Thus, test line TL can
be connected
through and a test current IT can be applied thereto and the resistance RK of
test line TL, ap-
proximately corresponding to the resistance of the return line of test ground
TGND, can be
inferred by measuring the resulting voltage drop UADC and applying Ohm's law.
However, test line TL may also be used for a simple functional check of cable
tester 1. If test
line TL is connected through and a test current IT or voltage UADC is applied,
a voltage drop
UADC or test current IT should be measured in the first tester unit 2. If this
is not the case,
there must be a fault, for example, in the communication between the first
tester unit 2 and
second tester unit 3.
For testing an n-pole cable 7, either the voltage measurement or current
measurement de-
scribed above or both can be used as a test case. In case of a voltage
measurement, system
voltage Us may be zero at the time of testing an individual conductor 10 (e.g.
with a logical 0
in a binary line). This means that, during a voltage measurement on cable 7 in
normal opera-
tion, an intact cable 7 or intact individual conductor 10 cannot be safely
assumed when mea-
suring a small voltage UADC. Since this low voltage UADC may also result from
individual con-
ductor 10 having a fault F, and system voltage would then be measured as Us ¨
0. In this
case, the voltage measurement should be supplemented with a current
measurement test
case, since a fault F can then be identified with certainty.
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In the above exemplary embodiments, the measurement of electrical variables
for the test is
always carried out in the first tester unit 2. However, it is understood, that
it is also contem-
plated to perform this measurement in the second tester unit 3. The above
explanations then
apply analogously. For this purpose, as with the first tester unit 2, a
measuring unit 19 and an
ADC 14 may be provided in the second tester unit 3. The measurement will again
be carried
out relative to test ground TGND. The measured value may also be transmitted
from the sec-
ond tester unit 3 via communication link 11 to the first tester unit 2 and/or
to the first control
unit 13 and be assessed therein. However, the assessment may also be performed
in the
second tester unit 3 and/or the second control unit 20. The results of a test
may also be dis-
played at the second tester unit 3 and/or at both tester units 2, 3.
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