U.S. patent application number 15/592700 was filed with the patent office on 2017-08-31 for compensation current sensor arrangement.
The applicant listed for this patent is Vacuumschmelze GmbH & Co. KG. Invention is credited to Friedrich LENHARD.
Application Number | 20170248636 15/592700 |
Document ID | / |
Family ID | 51628962 |
Filed Date | 2017-08-31 |
United States Patent
Application |
20170248636 |
Kind Code |
A1 |
LENHARD; Friedrich |
August 31, 2017 |
COMPENSATION CURRENT SENSOR ARRANGEMENT
Abstract
The current sensor arrangement according to the compensation
principle has a primary conductor, designed to generate a primary
magnetic field dependent on a current to be measured flowing
through it, a first secondary winding, designed to generate a first
secondary magnetic field dependent on a first compensation current
flowing through said winding, a second secondary winding designed
to generate a second secondary magnetic field dependent on a second
compensation current flowing through said winding, a magnetic field
sensor designed to generate a measurement signal that represents a
magnetic field detected by it; a magnetic core of soft magnetic
material designed and arranged to magnetically interconnect a
primary conductor, a first seconding winding, a second secondary
winding, and a magnetic field sensor; a first evaluation circuit;
and a second evaluation circuit.
Inventors: |
LENHARD; Friedrich; (Hanau,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Vacuumschmelze GmbH & Co. KG |
Hanau |
|
DE |
|
|
Family ID: |
51628962 |
Appl. No.: |
15/592700 |
Filed: |
May 11, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14258217 |
Apr 22, 2014 |
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15592700 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 33/02 20130101;
G01R 15/185 20130101; G01R 19/0092 20130101 |
International
Class: |
G01R 19/00 20060101
G01R019/00; G01R 33/02 20060101 G01R033/02; G01R 15/18 20060101
G01R015/18 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2013 |
DE |
10 2013 207 277.5 |
Claims
1. A current sensor arrangement according to the compensation
principle comprising: a primary conductor that is designed to
generate a primary magnetic field dependent on a current to be
measured flowing through it, a first secondary winding that is
designed to generate a first secondary magnetic field dependent on
a first compensation current flowing through it, a second secondary
winding that is designed to generate a second secondary magnetic
field dependent on a second compensation current flowing through
it, a magnetic field sensor that is designed to generate a
measurement signal that represents a magnetic field detected by it,
a magnetic core of soft magnetic material that is designed and
arranged to connect a primary conductor, a first secondary winding,
a second secondary winding, and a magnetic field sensor to each
other, a first evaluation circuit, downstream from the magnetic
field sensor and upstream from the first secondary winding, that is
designed to generate a first compensation current corresponding to
the measurement signal of the magnetic field sensor and thus feed
the first secondary winding, and a second evaluation circuit,
upstream from the second winding, that is designed to generate a
second compensation current corresponding to the first compensation
current, and thereby feed the second secondary winding, wherein:
the magnetic field detected by the magnetic field sensor is the
magnetic field in the magnetic core resulting from the
superposition of the primary magnetic field, a first secondary
magnetic field, and the second secondary magnetic field, the first
compensation current and the second compensation current are set by
the first evaluation circuit and the second evaluation circuit in
such a manner that the resulting magnetic field detected by the
magnetic field sensor becomes zero, the second compensation current
is greater or smaller than the first compensation current and the
first or second compensation current represents the current to be
measured flowing in the primary conductor.
2. The current sensor arrangement according to claim 1, wherein the
second evaluation circuit comprises a mechanism that evaluates the
first compensation current and adjusts the second compensation
current proportionally to the measured first compensation
current.
3. The current sensor arrangement according to claim 2, wherein the
output signal, which represents the current to be measured flowing
the in the primary conductor, is generated from the first or second
compensation current.
4. The current sensor arrangement according to claim 2, wherein the
first compensation winding and second compensation winding have
wires with wire diameters that are measured in such a manner that
the current densities are identical in each when the first
compensation current or the second compensation current flow
through them respectively.
5. The current sensor arrangement according to claim 1, wherein the
first secondary winding and second secondary winding have different
turn numbers.
6. The current sensor arrangement according to claim 1, wherein the
first evaluation circuit and the second evaluation circuit each
have a driver circuit, which generates the first compensation
current and the second compensation current in the first
compensation winding and the second compensation winding
respectively.
7. The current sensor arrangement according to claim 6, wherein at
least one of the driver circuits has an output-side half-bridge
circuit.
8. The current sensor arrangement according to claim 6, wherein at
least one of the driver circuits has an output-side full-bridge
circuit.
9. The current sensor arrangement according to claim 6, wherein at
least one of the driver circuits is a linear driver circuit.
10. The current sensor arrangement according to claim 6, wherein at
least one of the driver circuits is a pulse width-modulated driver
circuit.
11. The current sensor arrangement according to claim 6, wherein at
least one of the driver circuits is a driver circuit supplied with
bipolar supply voltages.
12. The current sensor arrangement according to claim 6, wherein at
least one of the driver circuits behaves on its output side like a
current source.
13. The current sensor arrangement according to claim 1, wherein
the magnetic core is a round, enclosed, ring-shaped magnetic core
with at least an air gap or a probe case.
14. The current sensor arrangement according to claim 1, wherein
the magnetic core is a rectangular or polygonal, enclosed,
ring-shaped magnetic core with at least four arms and at least an
air gap or a probe case.
15. The current sensor arrangement according to claim 14, wherein
the ampere-turns number is equal on each of the wrapped arms.
16. The current sensor arrangement according to claim 13, wherein
the first compensation winding and the second compensation winding
are wrapped in symmetrically arranged sections.
17. The current sensor arrangement according to claim 13, wherein
the magnetic core is wrapped by the first compensation winding and
the second compensation winding in an equally distributed manner
over the entire magnetic core.
18. The current sensor arrangement according to claim 16, wherein
the first compensation winding and the second compensation winding
are wrapped in each other.
19. The current sensor arrangement according to claim 16, wherein
the first compensation winding and the second compensation winding
are wrapped over each other.
20. The current sensor arrangement according to claim 1, wherein
the second compensation current is at least 20 percent smaller than
the first compensation current.
Description
[0001] This U.S. continuation application claims the benefit of
U.S. application Ser. No. 14/258,217, filed Apr. 22, 2014, which
claims benefit of the filing date of DE 10 2013 207 277.5, filed 22
Apr. 2013, the entire contents of which are incorporated herein by
reference for all purpose.
BACKGROUND
[0002] 1. Field
[0003] Disclosed herein is a current sensor arrangement according
to the compensation principle.
[0004] 2. Description of Related Art
[0005] Current sensor arrangements serve to determine the electric
current strength of a current to be measured and are special
instrument transformers that are operated according to various
principles. Current sensor arrangements operating according to the
compensation principle, also known as compensation current sensor
arrangements or compensation current sensors for short, generally
have a magnet core of a soft magnetic material, which encloses a
primary conductor carrying the current to be measured. The current
to be measured flows through the primary conductor and generates a
(primary) magnetic field in the magnetic core, which is compensated
by a (secondary) magnetic field generated by a compensating current
in a secondary winding wrapped around the core. To this end, the
magnetic flux in the magnetic core is measured by means of a
magnetic field sensor and adjusted to zero using an evaluation
circuit, whereby a suitable compensation current is fed into the
compensation winding, which, when the resulting magnetic flux in
the magnetic core is zero, is proportional to the primary current
to be measured.
SUMMARY
[0006] However, during the operation of such compensation current
sensors, brief peak currents may occur that are significantly above
the rated current (continuous current). In conventional
compensation current sensors, the ratio of permissible peak current
to rated current is less than two. However, often a ratio greater
than two, frequently also greater than three is advantageous.
However, in doing so and to have minimum power loss, the turn ratio
is to be high, for example 1:5,000. A corresponding improvement of
known compensation current sensors is therefore desirable.
[0007] This is achieved by means a current sensor arrangement
according to the compensation principle. The arrangement has a
primary conductor that is designed to generate a primary magnetic
field dependent on a current to be measured flowing through it.
Also provided are a first secondary winding that is designed to
generate a first secondary magnetic field dependent on a first
compensating current flowing through said winding and a second
secondary winding that is designed to generate a second secondary
magnetic field dependent on a second compensation current flowing
through said winding. The arrangement also has: a magnetic field
sensor that is designed to generate a measurement signal that
represents a magnetic field measured by it; a magnetic core of a
soft magnetic material that is designed and arranged to
magnetically interconnect a primary conductor, a first secondary
winding, a second secondary winding, and a magnetic field sensor; a
first evaluation circuit downstream from the magnetic field sensor
and upstream from the first secondary winding, said circuit being
designed to generate a first compensation current corresponding to
the measurement signal of the magnetic field sensor and thereby
feed the first secondary winding; and a second evaluation circuit
upstream from the second secondary winding, said circuit being
designed to generate a second compensation current corresponding to
the first compensation current and thereby feed the second
secondary winding. In doing so, the magnetic field measured by the
magnetic field sensor is the magnetic field resulting from the
superposition of the primary magnetic field, first secondary
magnetic field and the second secondary magnetic field in the
magnetic core. The first compensation current and the second
compensation current are adjusted by the first evaluation circuit
and the second evaluation circuit in such a manner that the
resulting magnetic field recorded by the magnetic field sensor
becomes zero. The second compensation current is greater or smaller
than the first compensation current and represents the current to
be measured flowing in the primary conductor.
BRIEF DESCRIPTION OF DRAWINGS
[0008] Embodiments of the invention are explained in further detail
below using the embodiments depicted in the figures of the drawing,
wherein identical elements are furnished with the same reference
signs.
[0009] FIG. 1 depicts a simplified schematic illustration of the
mechanical structure and the electrical wiring of a compensation
current sensor with two improved compensation windings for example
purposes.
[0010] FIG. 2 depicts in a wiring diagram a first sample design of
the compensation current sensor according to FIG. 1 with one driver
for each of the compensation windings.
[0011] FIG. 3 depicts in a wiring diagram a second sample design of
the compensation current sensor according to FIG. 1 with two
drivers in a full bridge circuit and two measurement resistors in
series to the two secondary windings.
[0012] FIG. 4 depicts in a wiring diagram a third sample design of
the compensation current sensor according to FIG. 1 with two
drivers in a full bridge circuit and two measurement resistors each
switched between two partial windings of the two secondary
windings.
[0013] FIG. 5 depicts in a wiring diagram a fourth sample design of
the compensation current sensor according to FIG. 1 with two
drivers in a full bridge circuit and four measurement resistors
leading to a ground and each switched in pairs between two partial
windings of the two secondary windings.
[0014] FIG. 6 depicts in a wiring diagram a sample linear driver
that generates a linear output voltage depending on the input
voltage.
[0015] FIG. 7 depicts in a wring diagram a sample pulsed driver
that generates a pulse width-modulated output voltage dependent on
the input voltage.
[0016] FIG. 8 depicts in a wiring diagram a sample linear driver
that generates a linear output current dependent on the input
voltage.
[0017] FIG. 9 depicts in a schematic illustration a ring-shaped
magnetic core for use in the compensation current sensor depicted
in FIG. 1.
[0018] FIG. 10 depicts in a wiring diagram a fifth sample design of
the compensation current sensor according to FIG. 1 with a driver
in a full bridge circuit and two measurement resistors leading to a
ground and each switched in pairs between two partial windings of
the first secondary winding and a half-bridge with a measurement
resistor for the second compensation winding.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0019] FIG. 1 depicts in a schematic illustration an example of an
improved compensation current sensor. The compensation current
sensor has four windings 1, 2, 3, and 4, which are wound on an
enclosed magnetic core 5 of soft magnetic material such as iron or
an iron alloy. In the present case, magnetic core 5 has the shape
of a ring core of a rectangular basic structure and a rectangular
cross-section (not apparent from FIG. 1). Magnetic core 5 has due
to its rectangular basic structure four arms of which two opposing
arms are equipped with two of the windings 1, 2, 3, and 4.
Accordingly, windings 1 and 2 are wound around one of these two
arms, while windings 3 and 4 are wound around the other of these
two arms. To this end, windings 1 or 3 are initially applied on the
two arms in question, on which then windings 2 or 4 are wound on
top of these. Windings 1 and 3 are electrically switched in series
and together form a first secondary winding 21. Accordingly,
windings 2 and 4 are electrically switched in series and together
form a second secondary winding 22.
[0020] Instead of magnetic core 5 with a rectangular basic
structure and a rectangular cross-section, any shapes can be used
for the basic structure and cross-section, such as round (cf. FIG.
9), oval, square, or polygonal basic structures and cross-sections,
as long as the basic structure of magnetic core 5 is a closed form
with a central opening. A closed basic structure means that the
central opening completely encloses the small gap relative to the
circumference of the central opening or encloses it to a narrow air
gap relative to the total circumference of the magnetic core.
Accordingly, any combinations of various basic structures and
cross-sections of magnetic core 5 are possible. In addition,
instead of windings 1 and 2 or 3 and 4 wound on top of each other
respectively, windings wound into each other or along the magnetic
core circumference in alternating sections may be provided.
[0021] Through the central opening of magnetic core 5, a primary
conductor 6 is guided essentially in a linear manner, in which a
current to be measured, hereinafter referred to as primary current
ip, flows. Instead of guiding primary conductor 6 in a more or less
linear manner through the central opening, it can also be wound as
an additional winding, in other words as primary winding, around
magnetic core 5.
[0022] In addition, a magnetic field sensor 7 is provided, which in
the present case is housed in a recess closed on almost all sides
in magnetic core 5 under winding 1. As a magnetic field sensor 7,
one can use for example electromagnetically functioning sensors,
which in the simplest case themselves only consist of a winding, or
semiconductor sensors using the so-called Hall effect. Magnetic
field sensor 7 can alternatively also be arranged on magnetic core
5 on an outwardly opening indentation or if an air gap is present
in it.
[0023] Downstream from magnetic field sensor 7 is a first
evaluation circuit 8, which prepares a measurement signal delivered
by magnetic field sensor 7 and provides a current corresponding to
it. This current represents compensation current is1 and is
controlled by magnetic field sensor 7 in connection with the first
evaluation circuit 8 in such a manner that the resulting magnetic
flux in magnetic core 5 is almost zero and is thus proportional to
primary current ip. Compensation current is1 is led through the
electrical series circuit of winding 1 and winding 3 (first
secondary winding 21) and the input circuit of a second evaluation
circuit 10 to ground G (reference potential). Evaluation circuit 10
thereby measures the first compensation current is1 and generates
proportional to the first compensation current is1 a second
compensation current is2, which is led through the electrical
series circuit of winding 2 and winding 4 (second secondary winding
22) and an ohmic resistor 9 switched in series to ground G. The
second compensation current is2 is proportional to the first
compensation current is1 and is smaller than it. Based on the
proportionality to the first compensation current is1, it also
represents the current to be measured flowing in the primary
conductor, the primary current ip. Consequently via resistor 9, a
voltage Um can be tapped that is proportional to the second
compensation current is2, which is in turn proportional to the
first compensation current is1 and thus proportional to the primary
current ip to be measured.
[0024] The turn number w21 of the first secondary winding 21 is
thereby higher than turn number w22 of the second secondary winding
22 (w21>w22). Since in the present example, first and second
secondary windings 21, 22 are each formed from two identical
(partial) windings 1, 3 and 2, 4 respectively, it is provided that
windings 1 and 3 have among each other the same turn numbers
w1=w3=0.5w21 and windings 2 and 4 have among each other the same
turn numbers w2=w4=0.5w22. The turn direction of windings 1 to 4 is
thereby of such a type that in connection with the currents flowing
through them, they generate rectified magnetic fluxes in magnetic
core 5. In addition, the wire thicknesses of the two secondary
windings 21 and 22 may each be selected in such a manner that the
current densities in both are (approximately) equal.
[0025] FIG. 2 depicts in a wiring diagram for example purposes a
possible electrical wiring advancement of the compensation current
sensor according to FIG. 1. Accordingly, primary current ip to be
measured is led through primary conductor 6 that is depicted as a
primary winding in the example shown in FIG. 2. With primary
conductor 6, the first secondary winding 21 and the second
secondary winding 22 are magnetically coupled to each other via the
magnetic core 5. The magnetic flux in magnetic core 5 is measured
by magnetic field sensor 7 and evaluated by means of the first
evaluation circuit 8, which, depending on that, generates the first
compensation current is1. It is then passed through the first
secondary winding 21 to the second evaluation circuit 10, which
from that as explained above generates the second compensation
current is2. The second compensation current is2 is passed through
the second secondary winding 22 as well as resistor 9 placed in
series thereto. The voltage drop Um caused by the second
compensation current is2 at resistor 9 then forms the output
variable, i.e., the variable representing primary current ip.
[0026] In the present example, the evaluation circuit is formed by
a differential input stage 13, which is downstream from magnetic
field probe 7 and generates from the floating output signal of
magnetic field probe 7 a corresponding output signal--in this case
an output voltage--relative to ground G. Input stage 13 is designed
in a conventional manner corresponding to the respectively used
magnetic field sensor type (for example a Hall sensor or magnetic
sensor) so that their design will not be addressed in further
detail herein. However, input stage 13 is distinctive in that it
emits a signal, particularly a proportional one, representing a
magnetic flux appearing at it. This can for example be a voltage
proportional to the magnetic flux as is established for further
considerations; however any other suitable variable can be used,
such as current, frequency, duty cycle, or also correspondingly
coded digital signals such as binary words.
[0027] The output signal of differential input stage 13 is supplied
to a driver amplifier 14, which, depending on the design, generates
an output voltage sufficient for actuating the first secondary
winding 21 or an output current sufficient to do so. The example
according to FIG. 2 pertains to a voltage-voltage amplifier,
however a voltage-current amplifier can be used in the same manner.
Driver amplifier 14 may supply a unipolar output voltage or a
unipolar output current or a bipolar output voltage or a bipolar
output current, depending on the application. A unipolar output
voltage or a unipolar output current thus only have one polarity,
while a bipolar output voltage or a bipolar output current may have
two opposite polarities.
[0028] Driver amplifier 10 comprises an ohmic resistor 11 connected
to ground G as well as a driver amplifier 12 controlled by the
voltage via resistor 11. In this case, driver amplifier 12 is
designed as a voltage-current amplifier; however a correspondingly
dimensioned voltage-voltage amplifier can be used in the same way.
Driver amplifier 14 may supply a unipolar output voltage or a
unipolar output current or a bipolar output voltage or a bipolar
output current, depending on the application. In the depicted
situation, the first compensation current is1 is transformed by
means of resistor 11 into a voltage proportional hereto and this
voltage is in turn transformed by driver amplifier 12 into a
proportional current, the second compensation current is2. Resistor
11 and driver amplifier 12 together form a current-controlled power
source (with an amplification less than one), such as a
current-current amplifier or a current mirror, in which the output
current and input current are in a certain ratio to each other.
Since in this case, the output current of such a current-current
amplifier or current mirror is equal to the second compensation
current is2 and its input current is equal to the first
compensation current is1, wherein the first compensation current
is1 is greater than the second compensation current is2, the
following correlation results:
is1=xis2, [0029] where x>1. [0030] Accordingly, x>1.2, or
x>1.5 or x>2.
[0031] When using a voltage-voltage amplifier instead of the
depicted voltage-current amplifier, it and resistor 11 shall be
dimensioned in such a manner that the second compensation current
is2 is smaller than the first compensation current is1. This can
take place in a simple manner for example by the corresponding
dimensioning of resistor 11. Instead of the voltage across resistor
11, the voltage at the output of driver amplifier 14 could also be
used to control driver amplifier 12.
[0032] When using driver amplifiers 12 and 14 supplied from bipolar
supply voltage sources, i.e., out of two voltage sources switched
in series with opposing polarities, driver amplifiers 12 and 14 can
be operated inversely to each other to somewhat evenly load the
supply voltage sources with opposing polarities so that the second
compensation current is2 is always drawn from the supply voltage
source with the polarity opposite to that which is supplied by the
first compensation current is1.
[0033] Furthermore, it can be provided that the wire thicknesses of
both compensation windings 21 and 22 are each configured in such a
way that the current densities in both compensation windings 21 and
22 are approximately equal during operation. Even though it is
possible in a similar manner to tap the output voltage Um via
resistor 11 in the electric circuit of the first compensation
current is1, in the depicted ones it is tapped via resistor 9 in
the electric circuit of the second compensation current is2. In
this way, a virtual turns ratio can be generated that is
significantly smaller than the nominal turns ratio. The nominal
turns ratio results from turn number wp of the primary winding as
well as turn numbers w1, w2, w3, and w4 of the secondary (partial)
windings 1, 2, 3, and 4 as follows:
N=wp/(w1+w2+w3+w4)>Nv,
[0034] Whereas the virtual turns ration Nv still undergoes a
reduction, which is definitively determined by the ratio of the
first compensation current is1 to the second compensation current
is2. In doing so, the primary-side ampere turn number and the sum
of the secondary-side ampere turn numbers compensate each
other:
ipwp=is1(w1+w3)+is2(w2+w4).
[0035] The circuit depicted in FIG. 2, including all variation
possibilities described above, can furthermore also be implemented
with full bridge circuits, instead of half-bridge circuits as they
are frequently used in connection with bipolar-supplied driver
amplifiers. A corresponding example is depicted in FIG. 3. Compared
to the circuit depicted in FIG. 2, there is downstream from driver
amplifier 14 via inverter 15 a driver amplifier 16 identical to
driver amplifier 14. Instead of the combination of inverter 15 and
driver amplifier 16, one could also similarly use an inverting
driver amplifier. Due to the interposition of inverter 15, there
are at the outputs of driver amplifiers 14 and 15 inverse, i.e.,
counter-phase, output signals. If now the first secondary winding
21 is switched (full bridge circuit) between the outputs of driver
amplifiers 14 and 15, then the voltage present at it doubles in
relation to a half-bridge circuit (as in the circuit according to
FIG. 2) and consequently, assuming a constant load, also the
current generated thereby.
[0036] However, the series circuit of a first secondary winding 21
and resistor 11 is no longer referenced to ground G, but "hangs" in
a floating manner between the outputs of the driver circuits 14 and
16. To this end in the example depicted in FIG. 3, resistor 11 is
connected directly to the output of driver amplifier 16 and, upon
interposition of the first secondary winding 21, connected to the
output of driver amplifier 14. In the example depicted in FIG. 4,
partial winding 3 is connected directly to the output of driver
amplifier 16 and partial winding 1 is connected directly to the
output of driver amplifier 14. The two partial windings 1 and 3 are
connected to each other via resistor 11. In the examples according
to FIGS. 3 and 4, the floating voltage across resistor 11 is
detected by a differential input stage 17 and supplied as a hereto
corresponding output voltage referenced to ground G to a driver
amplifier 18. There is downstream from driver amplifier 14 via
inverter 15 a driver amplifier 16 identical to driver amplifier
14.
[0037] In the present case, all driver amplifiers 14, 16, 18, and
20 are designed identically; however, other combinations, up to and
including four different driver amplifiers are similarly possible.
In the example depicted in FIG. 3, resistor 9 is connected directly
to the output of driver amplifier 20 and, upon the interposition of
the second secondary winding 22, connected to the output of driver
amplifier 18. In the example depicted in FIG. 4, partial winding 4
of the second secondary winding 22 is connected directly to the
output of driver amplifier 20 and partial winding 2 is connected
directly to the output of driver amplifier 18. Both partial
windings 2 and 4 are connected to each other via resistor 9. In
both examples according to FIGS. 3 and 4, voltage Um is tapped in a
floating manner across resistor 9.
[0038] In the example according to FIG. 4, the turn direction of
both partial windings 2 and 4 is reversed in relation to partial
windings 1 and 3, since the actuation of partial windings 2 and 4
is reversed in relation to partial windings 1 and 3, i.e., partial
windings 2 and 4 are actuated with inverse voltages in relation to
the example according to FIG. 3. One shall note the deviating
circuitry of the outputs of driver amplifiers 18 and 20 to the
second compensation winding 22.
[0039] Based on the example shown in FIG. 3, the circuit of the
compensation current sensor depicted in FIG. 5 is changed to the
effect that resistors 9 and 11 are each designed as resistor pairs
with the pair-wise identical resistors 9a, 9b and 11a, 11b
respectively, which are all led on the one hand to ground G and on
the other are each connected to a connection of windings 2 and 4 or
windings 1 and 3. The other connection of winding 1 is connected to
the output of driver amplifier 14, the other connection of winding
3 is connected to the output of driver amplifier 16, the other
connection of winding 4 is connected to the output of driver
amplifier 18, and the other connection of winding 2 is connected to
the output of driver amplifier 20. The connections wired to
resistors 9a, 9b and 11, 11b are the connections facing each other
of windings 1 and 3, and 2 and 4 respectively, so that here the
wiring of the first and second compensation windings 21, 22 is
similar to the wiring shown in FIG. 4, with the exception that
resistors 9 and 11 are equipped so to say with a tap placed at
ground G. The tap here is formed in each case by the nodal point of
resistors 9a and 9b, and 11a and 11b respectively. Accordingly, the
corresponding voltages are each taken via the series circuits of
resistors 9a and 9b, and 11a and 11b respectively.
[0040] FIG. 6 depicts in a wiring diagram an example of a linear
driver amplifier that can be used for example as driver amplifier
14, 16, 18, and 20. The core of the linear driver amplifier
depicted there forms an operational amplifier 23 that is supplied
via a resistor 24 by the positive supply voltage Vp and via a
resistor 25 by the negative supply voltage Vn. The output of
operational amplifier 23 is connected via a resistor 26 to the
positive supply voltage Vp and via a resistor 27 to the negative
supply voltage Vn. Serving as an output stage are a pnp bipolar
transistor 28 and a npn bipolar transistor 29, whose collectors are
connected to each other and to the output OUT of the driver
amplifier. Transistor 28 is connected by means of its emitter to
the positive supply voltage Vp and connected by means of its base
to the node of resistor 25 and operational amplifier 23. Output OUT
is protected against incorrectly poled voltages appearing at it by
means of two diodes 30 and 31, which lead from output OUT to
positive supply voltage Vp and to the negative supply voltage Vn
respectively. Operational amplifier 23 is counter-coupled by a
voltage divider, having two resistors 32 and 33, which is switched
between the output of operational amplifier 23 and ground G, by the
tap of the voltage divider, i.e., the nodal point between resistors
32 and 33, being connected to the inverting input of operations
amplifier 23. The non-inverting input of operational amplifier 23
forms the input IN of the driver amplifier. Instead of bipolar
transistors, (MOS) field effect transistors can be used in a
similar manner.
[0041] Alternatively to a linear driver amplifier described above
in relation to FIG. 6, a pulsed driver amplifier can also be used,
whose output voltage can be changed by pulse width modulation for
example. From the pulsed voltage and using a low pass, which is
formed in this case by an RL element comprising the inductivity of
the respective compensation winding 21 or 22, and their respective
resistors 9 or 11, is implemented into linear voltage changes. An
example of such a pulse width-modulated driver amplifier is
depicted in FIG. 7. The core of the pulse width-modulated driver
amplifier shown there is formed by a comparator 34 (for example
with hysteresis), which is supplied via a resistor 36 from the
positive supply voltage Vp and via a resistor 36 from the negative
supply voltage Vn. The output of comparator 34 is connected via a
resistor 37 to the positive supply voltage Vp and via a resistor 28
to the negative supply voltage Vn. Serving as output stages are a
pnp bipolar transistor 39 and an npn bipolar transistor 40, whose
collectors are connected to each other as well as with the output
OUT of the driver amplifier. Transistor 39 has its emitter
connected to the positive supply voltage Vp and has its base
connected to the junction point of resistor 35 and comparator 34.
Accordingly, transistor 40 has its emitter connected to the
negative supply voltage Vn and its base connected to the node of
resistor 36 and comparator 34. Output OUT is protected by means of
two diodes 41 and 42, which lead from output OUT to positive supply
voltage Vp and negative supply voltage Vn respectively, against any
incorrectly poled voltages appearing at it.
[0042] Comparator 34 receives at its inverting input a
triangle-shaped reference voltage from reference voltage source 43
in relation to ground G. The non-inverting input of comparator 34
forms the input IN of the driver amplifier. Here too, (MOS) field
effect transistors can be used without problems instead of the
bipolar transistors.
[0043] The driver amplifiers depicted in conjunction with FIGS. 6
and 7 generate an output voltage dependent on the input voltage
(voltage-voltage amplifier). However, in the same way,
voltage-current amplifiers, in other words amplifiers whose output
current is dependent on the input voltage, can be used in a similar
manner. Such a driver amplifier is used for example as driver
amplifier 12 in the circuit depicted in FIG. 2; however, it can be
used in any of the other driver amplifiers 14, 16, 18, and 20
depicted in FIGS. 3, 4, and 5. An example of a driver amplifier
designed as a voltage-current amplifier is depicted in FIG. 8.
[0044] The driver amplifier illustrated in FIG. 8 comprises an
operations amplifier 44, which is supplied via a resistor 45 from
the positive supply voltage Vp and via a resistor 46 from the
negative supply voltage Vn. The output of operations amplifier 44
is on the one hand connected directly to its inverting input and on
the other via a resistor 47 to ground G. In addition, two
operations amplifiers 48 and 51 are provided whose non-inverting
input is connected to the nodal point between resistor 45 and
operations amplifier 44, and to the nodal point between resistor 46
operations amplifier 44. Operations amplifier 48 has its supply
lines directly connected to positive supply voltage Vp and ground
G, while operations amplifier 51 has its supply lines connected
directly to negative supply voltage Vn and ground G.
[0045] Connected to the output of operations amplifier 48 is the
base of a pnp bipolar transistor 49, whose emitter is connected
directly to the inverting input of the operations amplifier 48 and,
by the interposition of a resistor 50, is connected to positive
supply voltage Vp. Connected to the output of operations amplifier
51 is the base of a npn bipolar transistor 53, whose emitter is
connected directly to the inverting input of the operations
amplifier 51 and, by the interposition of a resistor 52, is
connected to negative supply voltage Vn. The collectors of
transistors 49 and 53 are interconnected and form output OUT of the
driver amplifier.
[0046] FIG. 9 depicts an example of a round, ring-shaped, enclosed
magnetic core 54, which can be used instead of the rectangular,
ring-shaped, enclosed magnetic core 5 used in the example according
to FIG. 1. Magnetic core 54 is completely wrapped by a first
compensation winding 55, on which is then wrapped also in its full
circumference a second compensating winding 56. Alternatively, the
two compensation windings 55 and 56 may also be wrapped into each
other or wrapped alternatingly in sections. Magnetic core 54 has a
recess 57, housing a magnetic field sensor 58, that is over-wrapped
by the two compensation windings 55 and 56 when magnetic field
sensor 58 is inserted in recess 57.
[0047] Based on the example depicted in FIG. 3, the circuit of the
compensation current sensor shown in FIG. 10 has been changed to
the effect that resistor 11 is designed as a resistor-pair with
identical resistors 11a, 11b, which are led on the one hand to
ground G and on the other are each connected to a connection of
windings 1 and 3. The other connection of winding 1 is connected to
the output of driver amplifier 14, the other connection of winding
3 is connected to the output of driver amplifier 16, the other
connection of winding 4 is connected to the output of driver
amplifier 18, and the other connection of winding 2 is connected to
resistor 9 that is also led to ground G. The connections wired with
resistors 11a, 11b are the facing connections of windings 1 and 3,
so that here the wiring of the first compensation winding 21 is
similar to the wiring shown in FIG. 4 except that resistors 11 are
so to say equipped with a tap placed at ground G. The tap is formed
primarily by the node point of resistors 11a and 11b respectively.
Accordingly, the corresponding voltages are taken across series
circuits of resistors 11a and 11b.
* * * * *