U.S. patent application number 11/430385 was filed with the patent office on 2007-11-08 for current probing system.
Invention is credited to Jonathan S. Dandy, Michael J. Mende, Thomas J. Sharp, Kerry A. Stevens.
Application Number | 20070257657 11/430385 |
Document ID | / |
Family ID | 38624422 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070257657 |
Kind Code |
A1 |
Stevens; Kerry A. ; et
al. |
November 8, 2007 |
CURRENT PROBING SYSTEM
Abstract
A current probing system has a current probe and a detachable
adapter. The current probe has a probe body with electrically
conductive contacts that mate with electrically conductive contacts
on the adapter. Leads extend from the adapter for coupling to a
current carrying conductor. The leads can connect to a plug that is
coupled to a current diverting device for coupling a current signal
to the current probe. The adapter may also include a switch that
selectively couples the current signal to the current probe when
the adapter is mated with the current probe. The contacts of the
current probe are coupled to a current sensing circuit which
generates a voltage output representative of the current signal.
The voltage output is coupled to an oscilloscope via an electrical
cable.
Inventors: |
Stevens; Kerry A.;
(Beaverton, OR) ; Mende; Michael J.; (Portland,
OR) ; Dandy; Jonathan S.; (Beaverton, OR) ;
Sharp; Thomas J.; (Tigard, OR) |
Correspondence
Address: |
WILLIAM K. BUCHER;TEKTRONIX, INC.
14150 S.W. KARL BRAUN DRIVE
P.O. BOX 500, MS 50-LAW
BEAVERTON
OR
97077
US
|
Family ID: |
38624422 |
Appl. No.: |
11/430385 |
Filed: |
May 8, 2006 |
Current U.S.
Class: |
324/72.5 |
Current CPC
Class: |
G01R 15/202 20130101;
G01R 1/06788 20130101 |
Class at
Publication: |
324/072.5 |
International
Class: |
G01R 31/02 20060101
G01R031/02 |
Claims
1. A current probing system for use with an oscilloscope for
acquiring a current signal from a current carrying conductor
disposed on a device under test comprising: a current probe having
a probe body and first and second electrically conductive contacts
disposed in one end of the probe body with the first and second
electrically conductive contacts adapted for coupling in series
with the current carrying conductor disposed on the device under
test; a current sensing circuit disposed in the probe body and
coupled to the first and second electrically conductive contacts
for generating an output signal representative of the current
flowing in the current carrying conductor disposed on the device
under test; and an electrically conductive cable extending from the
other end of the probe body coupled to receive the output signal
from the current sensing device and for coupling to the
oscilloscope; and an adapter having a housing adapted for mounting
on the probe body having first and second electrically conductive
leads extending from the housing with each of the first and second
electrically conductive leads having a first electrical contact for
coupling to the current carrying conductor disposed on the device
under test and a second electrical contact disposed within the
housing for coupling with one of the first and second electrically
conductive contacts of the current probe.
2. The current probing system as recited in claim 1 wherein the
first electrical contacts of the first and second electrically
conductive leads are coupled to a plug adapted for engaging
electrically conductive contacts acting as switch elements in a
current diverting device electrically coupled to the current
carrying conductor disposed on the device under test wherein the
current diverting device couples the current signal through the
current carrying conductor in a first position and couples the
current signal through the current probe in a second position
resulting from downward pressure of the plug on at least one of the
electrically conductive contacts of the current diverting device
causing the electrically conductive contacts of the current
diverting device to disengage in a second current diverting device
position.
3. The current probing system as recited in claim 1 wherein the
adapter further comprises a switch disposed within the adapter
housing having a first terminal electrically coupled to one of the
second electrical contacts of the first and second electrically
conductive leads and selectively coupled to one of the first and
second electrically conductive contacts of the current probe and a
second terminal coupled to the other of the second electrical
contacts of the first and second electrically conductive leads and
selectively coupled to the other of the first and second
electrically conductive contacts of the current probe and a
armature for selectively coupling the first and second terminals
together, wherein the switch has a first switch position wherein
the armature electrically couples the first and second electrically
conductive leads together when the adapter housing is separated
from the probe body and a second switch position wherein the
armature de-couples the first and second electrically conductive
leads from each other when the adapter housing is mounted on the
probe body, the first and second electrically conductive contacts
of the current probe being electrically coupled to the first and
second terminals of the switch when the adapter housing is mounted
on the probe body.
4. The current probing system as recited in claim 3 wherein the
current carrying conductor disposed on the device under test has
square pins mounted thereon on either side of a non-conductive gap
in the current carrying conductor and each of the first electrical
contacts of the first and second electrically conductive leads
further comprises an electrically conductive sockets having a bore
therein for mating with the square pin connectors mounted on the
current carrying conductor.
5. The current probing system as recited in claim 3 wherein the
current carrying conductor disposed on the device under test has a
non-conductive gap therein and each of the first electrical
contacts of the first and second electrically conductive leads
further comprises a contact pad connected to each of the first and
second electrically conductive leads and fixedly secured to the
current carrying conductor on either side of the non-conductive
gap.
6. The current probing system as recited in claim 3 wherein the
adapter further comprising first and second voltage clamps disposed
between the first and second terminals of the switch for minimizing
arcing across the contact terminal caused by inducive
kick-back.
7. The current probing system as recited in claim 6 wherein the
voltage clamps comprises diodes.
8. The current probing system as recited in claim 1 wherein the
electrically conductive contacts disposed in the probe body are
formed from an array of contact disposed in a receptacle with a
first portion of the array of contacts electrically coupled
together to form the first electrically conductive contact in the
probe body and a second portion of the array of contacts coupled
together to form the second electrically conductive contact in the
probe body and the first and second electrically conductive
contacts disposed in the adapter housing further comprise an array
of contact disposed in a receptacle with a first portion of the
array of contacts electrically coupled together to form the first
electrically conductive contact and a second portion of the array
of contacts coupled together to form the second electrically
conductive contacts, the receptacles in the probe body and adapter
housing mating for coupling the first and second electrically
conductive contacts in the probe body with the first and second
electrically conductive contacts in the adapter housing.
9. The current probing system as recited in claim 1 wherein the
current sensing circuit further comprises a magnetic sensor coupled
to the first and second electrically conductive contacts for
sensing the magnetic flux of the current signal and coupled to
amplifier circuitry for generating the output signal representative
of the current flowing in the current carrying conductor disposed
on the device under test.
10. The current probing system as recited in claim 9 wherein the
magnetic sensor further comprises a transformer having primary and
secondary windings and a magnetic core with the primary winding
coupled to the first and second electrically conductive contacts
for receiving the current signal from the current carry conductor
disposed on the device under test and inducing a magnetic flux
within the magnetic core and the secondary winding for generating a
current signal output in the secondary winding that is coupled to
amplifier circuitry.
11. The current probing system as recited in claim 10 wherein the
magnetic core of the transformer is ring-shaped and defines an
aperture with primary winding disposed around a portion of the
ring-shaped magnetic core of the transformer.
12. The current probing system as recited in claim 10 wherein the
transformer further comprises a magneto-electric converter disposed
in the magnetic core of the transformer and interacting with the
magnetic flux within the magnetic core for generating a voltage
signal representative of DC to low frequency current signals on the
current carrying conductor disposed on the device under test with
the voltage signal being coupled to the amplifier circuitry.
13. The current probing system as recited in claim 9 wherein the
magnetic sensor further comprises a flux gate.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to current probes
and more particularly to a current probe system for use with an
oscilloscope for acquiring a current signal from a current carrying
conductor.
[0002] Current probes used with oscilloscopes apply transformer
technology to measure current flowing in a conductor. The
transformer has a ring-shaped magnetic core defining an aperture
and may be solid or closed core or an open or split core where one
side of the magnetic core is movable relative to the other sides.
This allows the current carrying conductor to be passed through the
aperture of the transformer without having to disconnect the
current carrying conductor from a circuit. The current carrying
conductor is passed through the aperture in the magnetic core and
acts as the primary winding of the transformer. A secondary winding
is wrapped around one side of the magnetic core. The current
flowing in the current carrying conductor induces a magnetic flux
that is linked to the magnetic core and the secondary winding. The
magnetic flux causes a current to be generated in the secondary
winding that produces a magnetic flux that is opposite to that
generated by the current flowing in the current carrying conductor.
In a passive current probe, the alternating current generated by
the secondary winding is dropped across a transformer termination
resistor which generates an AC voltage output. The voltage output
is coupled via an electrical cable to an input channel of the
oscilloscope. The oscilloscope processes the voltage signal for
displaying a representation of the current signal.
[0003] Since transformers are AC signal coupling devices, the
passband of the transformer cut-off frequency is above the DC
level. To allow the current probe to sense DC and low frequency
current signals, an active current probe includes a Hall effect
device in the magnetic core of the transformer. The Hall effect
device is a semi-conductor positioned in the magnetic core such
that the magnetic flux in the magnetic core is substantially
perpendicular to the Hall plate. A bias is applied to the Hall
plate and the resulting voltage generated by the Hall effect due to
the flux in the magnetic core is coupled to the input of a
differential amplifier. The single ended output of the amplifier
may be coupled to a power amplifier which generates a current
output proportional to the current generated by the Hall effect
device. The output of the Hall device amplifier or alternately the
power amplifier is coupled to the secondary winding of the
transformer such that the output current from the amplifier flowing
through the secondary winding produces a flux that opposes the
input magnetic flux over the frequency passband of the Hall effect
device. In one implementation, the output of the Hall effect or
power amplifier is coupled to one side of the secondary winding
with the other side of the winding coupled to the transformer
termination resistor and amplifier circuitry. In another
implementation, the output of the Hall effect amplifier is coupled
via a resistor to the same side of the secondary as the amplifier
circuitry. A capacitor is coupled to the input of a wideband
amplifier in the amplifier circuitry for blocking the current from
the Hall effect amplifier. The output of the Hall effect amplifier
and the output of the wideband amplifier are summed at the input of
a operational amplifier having a feedback resistor that provides a
voltage output proportional to the combined current in the
secondary winding of the transformer. The voltage output of the
operational amplifier is a measure of the AC and DC components of
the magnetic core flux. The output of the operational amplifier is
coupled via an electrical cable to an input channel of the
oscilloscope. Generally, active current probes are of the
split-ring transformer type. U.S. Pat. Nos. 3,525,041, 5,477,135
and 5,493,211 describe the above current sensing circuits.
[0004] To measure the current passing through a conductor, the
current probe must be coupled in series with the conductor. This
proves difficult when the current carrying conductor is fixed to a
substrate, such as a circuit trace on a circuit board. The general
procedure for measuring the current in a current trace is to break
the trace and solder a length of wire between the trace break. The
wire is passed through the aperture in the transformer of the
current probe where the wire acts as the primary winding of the
transformer. Another procedure is to manufacture the circuit board
with gaps in the traces and install square pins on either side of
the gaps. A conductive jumper is coupled to the square pins during
normal testing of the circuit board. When a current measurement is
required the jumper is removed and a length of wire is connected
between the square pins. As before, the wire is used as the primary
winding of the transformer in the current probe.
[0005] Transformer based current probes have a number of
limitations in measuring currents through circuit traces on a
circuit board. The sensitivity and accuracy of the resulting
current measurement is limited by the repeatability of placing the
wire in the same position within the magnetic core of the
transformer and the repeatability of the split core being exactly
aligned in the same position when it is opened and closed. What is
needed is a current probing system that eliminates the use of a
loop of wire as the primary winding of a current probe.
Additionally, the current probing system should provide flexibility
in connecting the current probe to the current carrying conductor.
Further, the current probing system should provide greater
repeatability in the sensitivity and accuracy of the current
measurement.
SUMMARY OF THE INVENTION
[0006] Accordingly, a current probing system for use with an
oscilloscope for acquiring a current signal from a current carrying
conductor that meets the above described needs has a current probe
and an adapter mountable on the current probe. The current probe
has a probe body and first and second electrically conductive
contacts disposed in one end of the probe body. The first and
second electrically conductive contacts are adapted for coupling in
series with the current carrying conductor. The first and second
electrically conductive contacts are coupled to a current sensing
circuit for generating an output signal representative of the
current flowing in the current carrying conductor. The output
signal from the current sensing circuit is coupled to the
oscilloscope via an electrically conductive cable extending from
the other end of the probe body. An adapter has a housing adapted
for mounting on the probe body and has first and second
electrically conductive leads extending from the housing. Each of
the leads has a first electrical contact for coupling to the
current carrying conductor and a second electrical contact disposed
within the housing for coupling with one of the first and second
electrically conductive contacts of the current probe.
[0007] The first electrical contacts of the first and second
electrically conductive leads may be coupled to a plug adapted for
engaging electrically conductive contacts acting as switch elements
in a current diverting device electrically coupled to the current
carrying conductor. The current diverting device couples the
current signal through the current carrying conductor in a first
position and couples the current signal through the current probe
in a second position resulting from downward pressure of the plug
on at least one of the electrically conductive contacts of the
current diverting device. The downward pressure causes the
electrically conductive contacts of the current diverting device to
disengage in a second current diverting device position.
[0008] Each of the first electrical contacts of the electrically
conductive leads may also be formed of an electrically conductive
sockets having a bore therein for mating with square pin connectors
mounted on either side of a non-conductive gap in the current
carrying conductor. Each of the first electrical contacts of the
first and second electrically conductive leads may further be
formed as a contact pad that are fixedly secured to the current
carrying conductor on either side of the non-conductive gap. Where
the leads of the adapter are coupled across a non-conductive gap in
the current carrying conductor, a switch disposed within the
adapter housing having a first terminal electrically coupled to one
electrically conductive leads and selectively coupled to one of the
current probe contacts and a second terminal coupled to the other
electrically conductive lead and selectively coupled to the other
current probe contact. A switch armature selectively couples the
first and second terminals together. The switch has a first
position where the switch armature electrically couple the
electrically conductive leads together when the adapter housing is
separated from the probe body and a second position where the
switch armature de-couples the leads from each other when the
adapter housing is mounted on the probe body. The current probe
contacts are electrically coupled to the first and second terminals
of the switch when the adapter housing is mounted on the probe
body. The adapter may also include first and second voltage clamps,
preferably in the form of diodes, disposed between the first and
second terminals of the switch for minimizing arcing across the
contact terminal caused by inductive kick-back.
[0009] In the preferred embodiment, the electrically conductive
contacts disposed in the probe body and the adapter housing are
formed from an array of contact disposed in respective receptacles.
Each receptacle has a first and second portions of the array of
contacts electrically coupled together to form the first and second
electrically conductive contact in the probe body and the first and
second electrically conductive contacts in the adapter housing. The
receptacles in the probe body and adapter housing mate together for
coupling the first and second electrically conductive contacts in
the probe body with the first and second electrically conductive
contacts in the adapter housing.
[0010] The current sensing circuit may be implemented as a magnetic
sensor coupled to the first and second electrically conductive
contacts for sensing the magnetic flux of the current signal and
coupled to amplifier circuitry for generating the output signal
representative of the current flowing in the current carrying
conductor. The magnetic sensor may take the form of a transformer
or a flux gate. The transformer has a magnetic core with primary
and secondary windings wrapped around the magnetic core. The
primary winding is coupled to the first and second electrically
conductive contacts for receiving the current signal from the
current carry conductor and induces a magnetic flux within the
magnetic core and the secondary winding for generating a current
signal output in the secondary winding that is coupled to amplifier
circuitry. The transformer may further include a magneto-electric
converter disposed in the magnetic core that interacts with the
magnetic flux within the magnetic core for generating a voltage
signal representative of DC to low frequency current signals on the
current carrying conductor with the voltage signal being coupled to
the amplifier circuitry.
[0011] The objects, advantages and novel features of the present
invention are apparent from the following detailed description when
read in conjunction with appended claims and attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective view of the current probing system
according to the present invention.
[0013] FIG. 2 illustrates various adapters for the current probing
system.
[0014] FIG. 3 is an exploded perspective view of the adapter for
the current probing system.
[0015] FIG. 4 is a schematic representation of the circuitry in the
adapter for the current probing system.
[0016] FIG. 5 is a perspective view of the adapter usable with a
current diverting device mounted on a current carrying
conductor.
[0017] FIG. 6 is a schematic representation of a current sensing
circuit in the current probing system.
[0018] FIG. 7 is a schematic representation of another current
sensing circuit in the current probing system.
[0019] FIG. 8 is a schematic representation of a further current
sensing circuit in the current probing system.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIG. 1 is a perspective view of current probing system 10
for use with an oscilloscope 12 for acquiring a current signal from
a current carrying conductor 14. The current probing system 10 has
a current probe 16 having a probe body 18 in which is disposed a
current sensing circuit. The current sensing circuit is
electrically coupled to first and second electrically conductive
contacts disposed in one end of the probe body 18. An adapter 20 is
selectively attached to the probe body 16. The adapter 20 has a
housing 22 from which extends first and second electrically
conductive leads 24 and 26. Extending from the other end of the
probe body 18 is a conductive cable 28 for coupling an output
signal from the current sensing circuit to the oscilloscope 12 and
providing electrical power to the current probe 16. The conductive
cable 28 is preferably coupled to a current probe control box 30
that is coupled to one of a number of input signal channel 32 of
the oscilloscope 12. Each input signal channels 32 has a receptacle
interface 34 with each interface having electrically conductive
contacts and a coaxial signal jack. The current probe control box
30 has an plug interface 36 that mates with the receptacle
interfaces 34 and has electrical contacts and a coaxial signal jack
that interface with the corresponding electrical contacts and
coaxial signal jack in receptacle interfaces 34. The interfaces 34
and 36 provide electrical power to the current probe 16 as well as
providing communications between the current probe 16 and the
oscilloscope 12. The interfaces 34 and 36 also provide a signal
path between the current probe 16 and the oscilloscope 12.
[0021] Various types of electrical contacts 38, 40 are provided on
the first and second electrically conductive leads 24 and 26 of the
current probe adapter 20 which will be described in greater detail
below. The electrical contacts are adapted for electrically
coupling to one of a number of electrical connectors 42, 44 mounted
on a current carrying conductor 14, such as a circuit trace formed
on a circuit board 46 or the like. The electrical connectors 42, 44
are positioned on the current carrying conductor 14 across a
non-conductive gap 48 in the current carrying conductor 14. The
electrical connector 42 has square pins 50 mounted on either side
of the non-conductive gap 48 which are electrically coupled to the
current carrying conductor 14. An electrical jumper 52 is
positioned in the square pins 50 for coupling the current signal
across the non-conductive gap 48 when the current probe adapter 20
is not coupled into the current carrying conductor 14. The
electrical connector 44 is a coaxial receptacle 54 mating with a
coaxial plug to be described in greater detail below. Contacts pads
56 may also be formed on the current carrying conductor 14 on
either side of the non-conductive gap 48. A removable electrical
conductive foil 58 is secured to the contact pads for coupling the
current signal across the non-conductive gap 48. The electrically
conductive foil 58 is removed from the current carrying conductor
14 when the current probe adapter 20 is coupled to the current
carrying conductor 14.
[0022] FIG. 2 shows representative examples of the adapters 20 for
the current probing system 10. The probe body 18 of the current
probe 16 has a substantially rectangular shaped front section 60
that is recessed from the outer surface of the probe body 18. In
the preferred embodiment, the front section 60 has a receptacle 62
having an array of contacts forming the first and second
electrically conductive contacts of the current probe 16. One
portion of the array of contacts forms the first electrically
conductive contact and the other portion of the array of contacts
forms the second electrically conductive contact. The adapter
housing 22 mates with and is secured to the front section 60 of the
probe body 18 via latching elements 64 disposed on the extending
front portion 60. A release lever 66 is positioned on the probe
body 18 that when moved from a first to a second position
disengages the latching elements 64 from the adapter housing
22.
[0023] The housing 22 of the adapter 20 has an aperture 68 from
which extend a cable 70 containing the first and second
electrically conductive leads 24 and 26. One end of each of the
electrically conductive leads 24 and 26 are configured with
electrical contacts 38, 40 for electrically coupling to the current
carrying conductors 14 via one of the electrical connectors 42, 44
or the contact pads 56 on the current carrying conductor 14. In one
configuration, the electrical connectors are electrically
conductive sockets 72 attached to the electrically conductive leads
24, 26. The electrically conductive sockets 72 mate with the square
pins 50 on either side of the non-conductive gap 48 in the current
carrying conductor 14. In another configuration, the electrical
contacts 38, 40 are electrically conductive wires 74 extending from
end of the electrically conductive leads 24, 26. The electrically
conductive wires 74 may be the ends of the leads or they may be
formed as contact pads for securing to the contact pads 56 of the
current carrying conductor 14 on either side of the non-conductive
gap 48. In still a further configuration, the electrically
conductive leads 24, 26 are electrically coupled to a coaxial plug
76 that mates with the coaxial receptacle 54 mounted over the
non-conductive gap 48 in the current carrying conductor 14.
[0024] Referring to FIG. 3, there is shown an exploded perspective
view of the adapter 20. The adapter housing 22 is preferably formed
of housing halves 80 that are mated together to capture a circuit
board 82 therein. Extending through the aperture 68 in the adapter
housing 22 is the cable 70 containing the first and second
electrically conductive leads 24, 26. The electrically conductive
leads 24, 26 are electrically coupled to the circuit board 82. A
ground lead 84 also extends from the cable 70 and is connected to
an outer shielding conductor. A receptacle 86 is mounted on the
circuit board 82 that has an array of contacts similar to the array
of contacts in the receptacle 62 in the probe body 18. The
receptacles 62 and 86 are mating devices where the array of
contacts in one receptacle 62 mates with the array of contacts in
the other receptacle 86. A switch 88 is also mounted on the circuit
board 82. The switch 88 is used with the adapters 20 having the
contact pads 74 and electrically conductive sockets 72. The
electrically conductive leads 24, 26, the receptacle 86 and the
switch 88 are electrically coupled together through circuit traces
on the circuit board 82 as best shown by the schematic
representation of FIG. 4.
[0025] In the schematic of FIG. 4, the receptacles 62 and 86 show
the respective array of contact 90 and 91. First and second
portions 92 and 93 of the array of contacts 90 are ganged together
to form the first and second electrically conductive contacts 94
and 95 of the current probe 16 that are coupled to the current
sensing circuit 96. First and second portions 97 and 98 of the
array of contacts 91 are ganged together to form the first and
second electrically conductive contacts 99 and 100 of the adapter
20. The first electrically conductive contact 99 is electrically
coupled to a first terminal 101 of switch 88 and the second
electrically conductive contact 100 is electrically coupled to a
second terminal 102 of the switch 88. The first electrically
conductive lead 24 is also electrically coupled to switch terminal
102 and the second electrically conductive lead 26 is electrically
coupled to switch terminal 101. A switch armature 103 is
electrically coupled to switch terminal 102 and selectively coupled
to switch terminal 101. The switch armature 103 is mechanically
coupled to a plunger 104 extending from the switch 88. Clamping
diodes 105 and 106 are electrically coupled across the switch
terminals 101 and 102.
[0026] The switch armature 103 couples the switch contacts 101 and
102 together when the adapter 20 is not connected to the current
probe body 18. The resulting electrical switch connection couples
the first and second electrically conductive leads 24 and 26
together. This provides a current path across the non-conductive
gap 48 in the current carrying conductor 14 when the adapter 20 to
be connected to the current carrying conductor 14. Mating the
adapter 20 with the current probe body 18 first brings the array of
contacts 90 and 91 of the receptacles 62 and 82 into electrical
contact. Continued insertion of the adapter 20 onto the probe body
18 brings the switch plunger 104 into contact of the probe body 18.
Continued insertion of the adapter 20 onto the probe body 18
depresses the plunger 104 causing the switch armature 103 to
disengage from the switch contact 101. This opens the short across
the switch contacts 100 and 101 and couples the current carrying
conductor 14 in series with the current sensing circuit 96 via the
electrically conductive leads 24 and 26. The configuration of the
switch 88 and the receptacle 86 on the circuit board 82 provides
for a make before break contact of the array of contacts 90 and 91
of the receptacles 86 and 62 prior to the switch armature 103
breaking contact with the switch terminal 101. The clamping diodes
105 and 106 mounted on the circuit board 82 are provided for
minimizing arcing across the switch terminal 101 and contact
terminal 10 caused by inductive kick-back.
[0027] FIG. 5 is a perspective view of adapter 20 with the
electrically conductive leads electrically coupled to the coaxial
plug 76. One of the electrically conductive leads 24, 26 is
electrically coupled to a center electrical conductor in the
coaxial plug 76 and the other lead electrically is coupled to the
electrically conductive outer body of the plug 76. The center
electrical conductor and the electrically conductive outer body of
the coaxial plug 76 are insulated from each other. The electrical
connector 44 is a current diverting device having a coaxial
receptacle 54 with a central bore 108 insulated from an outer
electrically conductive sleeve 109. Extend in opposite direction
from the coaxial receptacle are electrically conductive contacts
110 that are fixedly secured to the current carrying conductor 14
on either side of the non-conductive gap 48 using solder,
electrically conductive adhesive or the like. The electrically
conductive contacts 110 extend into the coaxial receptacle 54 with
one of the electrically conductive contacts extending across the
central bore 108 to overlap the other electrically conductive
contact 110 to act as switch elements. One of the electrically
conductive contacts 110 is electrically coupled to the electrically
conductive sleeve 109 via electrically conductive leads 111
extending from the coaxial receptacle 54 in a direction
perpendicular to the other electrically conductive contacts 110 and
electrically coupled to the current carrying conductor 14 on the
other side of the non-conductive gap 48 via contact pads 112 formed
on the circuit board 46. The electrically conductive contacts 110
couple the current signal across the non-conductive gap 48 in the
current carrying conductor 14 in the first current diverting device
position.
[0028] The coaxial plug 76 is secured to the coaxial receptacle 54
with the electrically conductive outer body of the coaxial plug 76
electrically coupled to the outer electrically conductive sleeve
109 of the coaxial receptacle 54. The central electrical conductor
of the coaxial plug 76 extends into the central bore 108 of the
coaxial receptacle 54 and engages the electrically conductive
contact 110 extending into the bore 108. The central electrical
conductor of the coaxial plug 76 exerts downward pressure on the
electrically conductive contact 110 causing the contact 110 to
disengage from the other electrically conductive contact 110. The
current signal is diverted from the current carrying conductor 14
through the current sensing circuit of the current probe 16 and
back to the current carrying conductor 14 via one of the
electrically conductive contacts 110 coupled to the central
conductor of the coaxial plug 76 and to the current probe 16 via
one of the electrically conductive leads 24, 26 and the other
electrically conductive contact 110 coupled to the outer
electrically conductive sleeve 109 of the coaxial receptacle 54 and
the electrically conductive outer body of the coaxial plug 76 and
to the current probe 16 via the other of the electrically
conductive leads 24, 26. The mating of the coaxial plug 76 with the
coaxial receptacle 54 couples the current probe 16 in series with
the current carrying conductor 14 and is the second current
diverting device position. Removal of the coaxial plug 76 from the
current diverting device 54 releases the downward pressure on the
electrically conducive contact 110 which causes the contacts 110 to
re-engage each other. The above described coaxial receptacle 54 and
mating coaxial plug 76 are manufactured and sold by Amphenol,
Corp., Wallingford, Conn., as a RF-Switch and RF-Probe under
respective Part Nos. MCH-201 and MCH203.
[0029] Referring to FIG. 6, there is shown a schematic
representation of a current sensing circuit 96 usable in the
current probe 16 of the current probing system 10. The current
sensing circuit 96 has a ring-shaped core 120 of magnetic material
defining an aperture. The current carrying conductor 14 is coupled
via the first and second electrically conductive contacts 94 and 95
of the current probe 16 to a primary winding 122 that is coupled in
series with the current carrying conductor 14. The current carrying
conductor 14 is coupled in a flux linking relationship with
ring-shaped magnetic core 120 via the primary winding 122. The
current to be measured in the current carrying conductor 14
produces a magnetic flux in the magnetic core 122 and is linked to
a secondary winding 124. One terminal of the secondary winding 124
is coupled to ground with the other terminal being coupled to the
inverting input terminal of a transimpedance amplifier 126. The
inverting input terminal of the transimpedance amplifier 126 is
coupled to the output terminal of the amplifier 126 via a current
signal path 128 having a transimpedance resistor 130. Thus the
primary winding 122, the magnetic core 120 and the secondary
winding 124 function as a transformer 132. A magneto-electric
converter 134 is disposed within the magnetic core 120
substantially perpendicular to the lines of flux in the magnetic
core 120. The magneto-electric converter 134 is preferably a thin
film semiconductor Hall effect device having a first pair of
terminals coupled to a bias source 136 and a second pair of
terminals connected to differential inputs of amplifier 138. The
amplifier 138 is preferably a high gain differential amplifier
having low noise and high common mode rejection The single ended
output of the differential amplifier 138 is coupled to the
non-inverting input of the transimpedance amplifier 126. Offset
control signals resulting from the degaussing of the current
sensing circuit may also be applied to the differential amplifier
138 via an offset voltage line 140.
[0030] The current in the primary winding 122 produces a magnetic
flux in the magnetic core 120 of the transformer 132 that is linked
to the secondary winding 124 and the Hall effect device 134. DC or
low frequency components of the current flowing the in the primary
winding 122 generate a potential difference between the second pair
of terminals of the Hall effect device 134. The voltage output of
the Hall effect device 134 is coupled to the differential inputs of
the amplifier 138. The output of amplifier 138 is coupled to the
non-inverting input of the transimpedance amplifier 126. The
changing signal level on the non-inverting input of the
transimpedance amplifier 126 caused by the voltage generated by the
Hall effect device 134 produces a corresponding change in the
output voltage level of the transimpedance amplifier 126. The
voltage at the output of the transimpedance amplifier 126 results
in a current being generated in the current signal path 128 that is
coupled to the secondary winding 124 of the transformer 132. The
current flowing in the secondary winding 124 is opposite the
current flowing in the primary winding 122 producing a magnetic
flux in the magnetic core 120 that nulls the magnetic flux produced
by the current flowing in the primary winding 122. This DC to low
frequency feedback loop maintains an opposing current through the
current signal path 128 that is equal to the DC or low current
signal in the primary winding 122 of the transformer 132.
[0031] The high frequency components of the current flowing in the
primary winding 122 results in a current being induced in the
secondary winding 124 in a direction such as to produce a magnetic
field in the magnetic core 120 that is opposite to the field
created by the current in the primary winding 122. The current
induced in the secondary winding 124 is coupled to the inverting
input of the transimpedance amplifier 126. Since the inverting
input is a virtual ground, the current in the secondary winding 124
is coupled via the current signal path 128 through the
transimpedance resistor 130 to the output of the transimpedance
amplifier 126 resulting in an amplified voltage output
representative of the high frequency components of the current
flowing in the primary winding 122. The transimpedance amplifier
126 functions as both a power amplifier for generating a bucking
current for nulling the magnetic flux in the magnetic core 120 at
DC to low current frequencies and as a transimpedance amplifier for
higher frequencies. The output of the transimpedance amplifier 126
is to the oscilloscope 12 via the conductive cable 28.
[0032] FIG. 7 is a schematic representation of another current
sensing circuit 96. Like elements from the previously are labeled
the same in FIG. 7. The current sensing circuit 96 has a
ring-shaped core 120 of magnetic material defining an aperture. The
current carrying conductor 14 is coupled via the first and second
electrically conductive contacts 94 and 95 of the current probe 16
to a primary winding 122 that is coupled in series with the current
carrying conductor 14. The current carrying conductor 14 is coupled
in a flux linking relationship with ring-shaped magnetic core 120
via the primary winding 122. The current to be measured in the
current carrying conductor 14 produces a magnetic flux in the
magnetic core 122 and is linked to a secondary winding 124. Thus
the primary winding 122, the magnetic core 120 and the secondary
winding 124 function as a transformer 132. A magneto-electric
converter 134 is disposed within the magnetic core 120
substantially perpendicular to the lines of flux in the magnetic
core 120. The magneto-electric converter 134 is preferably a thin
film semiconductor Hall effect device having a first pair of
terminals coupled between a bias source 136 and ground and a second
pair of terminals connected to differential inputs of amplifier
138. The amplifier 138 is preferably a high gain differential
amplifier having low noise and high common mode rejection. The
single ended output of the differential amplifier 138 is coupled to
a power amplifier 150 whose output is coupled to one end of the
secondary winding 124. The other end of the secondary winding 124
is coupled to the input of a voltage gain amplifier 152 via a
transformer termination resistor 154 summing node.
[0033] The current in the primary winding 122 produces a magnetic
flux in the magnetic core 120 of the transformer 132 that is linked
to the secondary winding 124 and the Hall effect device 134. DC or
low frequency components of the current flowing the in the primary
winding 122 generate a potential difference between the second pair
of terminals of the Hall effect device 134. The voltage output of
the Hall effect device 134 is coupled to the differential amplifier
138 whose output is coupled to the power amplifier 150. The power
amplifier 150 generates a current output that is coupled to the
secondary winding 124. The current flowing in the secondary winding
124 from the power amplifier 150 is opposite the current flowing in
the primary winding 122 producing a magnetic flux in the magnetic
core 120 that nulls the magnetic flux produced by the current
flowing in the primary winding 122. This opposing current through
secondary winding representing the DC or low current signal in the
primary winding 122 of the transformer 132 and is coupled to the
input of the voltage gain amplifier 152 via the transformer
termination resistor 154 summing node.
[0034] The high frequency components of the current flowing in the
primary winding 122 results in a current being induced in the
secondary winding 124 in a direction such as to produce a magnetic
field in the magnetic core 120 that is opposite to the field
created by the current in the primary winding 122. The current
induced in the secondary winding 124 is coupled to the input of
voltage gain amplifier 152 via transformer termination resistor 154
summing node. The current flowing in the secondary winding 124 from
the power amplifier 150 nulls the magnetic flux in the magnetic
core 120 for DC to low frequency current signals. The current
induced in the secondary winding 124 by the current flowing in the
primary winding 122 nulls the magnetic flux in the magnetic core
120 for high frequency current signals. The transition range
between the current flowing in the secondary winding 124 from the
power amplifier 150 and the current induced into the secondary
winding 124 at higher frequencies results in the currents from both
sources being summed at the transformer termination resistor 154
summing node. The voltage output of the voltage gain amplifier 152
is coupled to the oscilloscope 12 via the conductive cable 28.
[0035] FIG. 8 is a schematic drawing of a further current sensing
circuit 96. The current carrying conductor 14 is coupled via the
first and second electrically conductive contacts 94 and 95 of the
current probe 16 to an input winding 160 of a flux gate 162 that is
coupled in series with the current carrying conductor 14. The flux
gate 162 has a cylindrical magnetic core 164 around which the input
winding 160 is wrapped. A conductive bar 166 is disposed coaxially
through the cylindrical magnetic core 164 and is coupled to a
driver circuit 168 coupled to an oscillator 170. A detecting coil
172 is placed around the cylindrical magnetic core 164 for
detecting the magnetic flux of the current signal on the input
winding and the magnetic flux of a signal from the oscillator 170.
The detecting coil 172 is coupled to a detection circuit 174 having
a mixer 176 that receives a signal from the oscillator 170 that is
twice the frequency of the signal applied to the conductive bar
166. The mixer 176 is coupled to a low pass filter (LPF) 178 which
in turn is coupled to an output amplifier 180 via a termination
resistor 182.
[0036] The driver circuit 168 generates an oscillating drive
current that causes the magnetic core 164 to saturate at the peaks
of the drive current signal so that the magnetic flux leaves the
magnetic core 164 and is aligned with the conductive bar 166.
During these periods, the degree of magnetization of the core 164
in the longitudinal direction is decreasing. As the driving current
approaches the zero crossing points, the magnetic flux again passes
through the magnetic core 164. During these periods, the degree of
magnetization of the core 164 in the longitudinal direction is
increasing. The direction and density of the magnetic flux in the
magnetic core changes according to the changes in the driving
current. The voltage output induced into the detecting coil 172
with the current drive signal applied to the flux gate 162 has two
cycles for each cycle of the drive current. A current signal
applied to the input winding 160 modulates the magnetic flux in the
magnetic core producing a modulated voltage output at detecting
coil 172 representative of the current signal on the input winding.
The modulated output voltage on the detecting coil 172 is coupled
to the mixer 176. The mixer 176 multiplies the modulated output
voltage with the oscillator signal that is twice the frequency of
the drive current. The low pass filter 178 filters the output of
the mixer to provide a voltage proportional to the current flowing
the input winding 160. The output amplifier 180 receive the filter
signal and generates an amplified voltage output. The above
described current sensing circuits are by example only and
modifications to the above circuits may be made without departing
from the scope of the invention.
[0037] A current probing system had been described having a current
probe and a detachable adapter. The current probe has a probe body
and electrically conductive contacts that mate with electrically
conductive contacts on the adapter. Leads extend from the adapter
for coupling to a current carrying conductor. The leads can connect
to a plug that is coupled to a current diverting device for
coupling a current signal to the current probe. The adapter may
also include a switch that selectively couples the current signal
to the current probe when the adapter is mated with the current
probe. The contacts of the current probe are coupled to a current
sensing circuit which generates a voltage output representative of
the current signal. The voltage output is coupled to an
oscilloscope via an electrical cable.
[0038] It will be obvious to those having skill in the art that
many changes may be made to the details of the above-described
embodiments of this invention without departing from the underlying
principles thereof. The scope of the present invention should,
therefore, be determined only by the following claims.
* * * * *