Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
2002-03-28
2004-03-09
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S1540PB
Reexamination Certificate
active
06703822
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a circuit arrangement for detecting a current through a consumer, which is disposed between the outputs of two amplifiers, each of which, in order to be supplied with a unipolar operating voltage, has a supply voltage connection and a ground connection.
In order to measure currents, often circuit arrangements are used, which function according to the compensation principal. In this method, a value is detected, which is proportional to the current to be measured, and by producing the same value with an opposite polarity, the detected value is regulated to zero. The current required to regulate the value to zero represents a measure for the current to be measured. The advantage of this method lies in the fact that the measuring device does not cause interference in the electrical circuit in which the current is to be measured.
For example in order to measure a current drawn from or supplied to a battery in a motor vehicle, it is thus known to detect this current by means of a compensation current sensor. A corresponding circuit arrangement is schematically depicted in FIG.
1
.
As can be inferred from
FIG. 1
, a toroidal core
2
is disposed with an air gap around a supply line
1
, for example of a battery. In the air gap of the toroidal core
2
, an element
3
is provided for measuring the magnetic field intensity, which is generated by the current through the supply line
1
in the toroidal core
2
. The toroidal core
2
is also provided with a coil
6
, which can be used to produce a magnetic flux in the toroidal core
2
. If a current is sent through the coil
6
and the magnitude of the current is selected so that the magnetic field intensity in the air gap is zero, then the current through the coil
6
corresponds to the current through the supply line
1
; the number of windings of the coil
6
must be taken into account here.
In order to measure the current flowing through the coil
6
, an ohmic resistor
7
is connected in series with the coil
6
. The falling current at the ohmic resistor
7
is a measure for the current flowing through the coil
6
and is consequently a measure for the current flowing through the supply line
1
.
In order to be able to measure a current of alternating polarity, it must be possible to change the direction of the current flowing through the coil
6
. In order to be able to change the direction of the current flowing through the coil
6
, the coil
6
is connected between the outputs of two amplifiers
4
,
5
. The inputs of the amplifiers
4
,
5
are connected to the element
3
for detecting the magnetic field intensities in the air gap of the toroidal core
2
so that the field intensity in the air gap can be regulated to zero.
Although a current of alternating polarity can be in fact measured with the circuit arrangement shown, it still has the disadvantage that the falling voltage at the ohmic resistor
7
has no ground reference. This is disadvantageous particularly because as a rule, the voltage is processed in a microcontroller, whose integrated AD converter is only suited for measuring a voltage between zero volts and u
ref
. This requires a corresponding voltage adaptation, with the attendant costs and imprecisions.
This problem can in fact be eliminated through the use of an amplifier, which can supply a positive and a negative output voltage, but both a positive and a negative supply voltage are required to operate an amplifier of this kind. But since a positive and a negative supply voltage of the required magnitude are not available in a motor vehicle, a circuit arrangement of this kind cannot be used in a motor vehicle.
DE 195 49 181 A1 has disclosed a device for measuring a current flowing in a conductor, in which a magnetic field, which is generated by the current flowing through the conductor, is evaluated in order to determine the current. In the known device, the conductor is embodied so that it has two parts that are disposed parallel to each other and convey the current in different directions. Between the two parts of the conductor, a sensor is provided, which supplies an output signal that is dependent on the magnetic field generated and is representative of the intensity of the flowing current. The known device, however, gives no indication of the use in a compensation current arrangement and the problems associated with this.
SUMMARY OF THE INVENTION
The object of the invention is to embody a circuit arrangement mentioned at the beginning in such a way that it supplies a ground-referenced output signal when operated with a low supply voltage.
According to the invention, a circuit arrangement for detecting a current through a consumer, which is disposed between the outputs of two amplifiers that each have a supply voltage connection and a ground connection in order to be supplied with a unipolar operating voltage, characterized in that between the connection of the operating voltage source and the supply voltage connection and/or between the ground connection and ground, an ohmic resistor is provided, at which a voltage falls, which is proportional to the current to be measured.
Since an ohmic resistor, at which a voltage falls, which is proportional to the current to be measured, is connected between the connection of the operating voltage source and the supply voltage connection and/or between the ground connection and ground, then a ground potential-referenced voltage can easily be produced, which is proportional to the compensation current.
The invention takes advantage of the fact that the output voltage supplied by the amplifiers essentially corresponds to the current drawn from the operating voltage source to supply the amplifiers. In this connection, it is naturally important that the quadrature-axis current of the amplifiers is very low. In amplifiers of this kind, the current drawn from the operating current source flows almost entirely through the consumer so that the current flowing through the consumer does not have to be measured directly in the current path in which the consumer is disposed, but can be measured in the supply voltage supply line or supply voltage discharge line of the amplifiers.
In a particularly advantageous embodiment of the invention, the ground connections of the amplifiers are connected to each other and the ohmic resistor is disposed between the connected ground connections and ground. Since only one ohmic resistor is used in a circuit arrangement of this kind, the current can be detected very precisely, no matter which direction the current is flowing through the consumer. This is particularly due to the elimination of imprecision with regard to the component tolerances that can occur when several ohmic resistors are used to detect the current. In a particularly advantageous manner, the use of a single ohmic resistor produces a characteristic curve without a bend at the zero point.
In order to determine the current direction through the consumer, in the embodiment described above, the voltage drop at the consumer can be measured by means of an amplifier, where the output voltage of the consumer is used to determine the current direction, as is provided in another particular embodiment of the invention. It is particularly advantageous if the amplifier is embodied as a comparator. As a result, a voltage polarity, which corresponds to the flow direction through the consumer, can be picked up at the output of the amplifier or comparator.
If it is desirable to eliminate the amplifier for determining the current direction through the consumer, then a separate ohmic resistor can be provided between the ground connection of each amplifier and ground, as is provided in another particular embodiment of the invention. The magnitude of the falling voltage at an ohmic resistor corresponds to the magnitude of the current through the consumer. The direction of the current flowing through the consumer is a function of which ohmic resistor a voltage drop occurs at so that the direction of the current through the consumer is determine
Cuneo Kamand
Nguyen Trung Q.
Robert & Bosch GmbH
Striker Michael J.
LandOfFree
Circuit for detecting a current passing through a consumer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit for detecting a current passing through a consumer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit for detecting a current passing through a consumer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3287561