Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With rotor
Reexamination Certificate
2002-12-18
2004-11-30
Nguyen, Vinh P. (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With rotor
Reexamination Certificate
active
06825653
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for and a method of making very accurate non-invasive measurements of electrical current flowing from a power source to a device under test (DUT).
2. Description of the Related Art
In testing of electronic devices, voltage and current waveforms are often measured during various modes of operation of the electronic device as an indicator of proper device functionality. In order to make waveform measurements, the power source which is used for supplying power to the electronic device under test (DUT) must be separated from the DUT to allow for addition of measurement instruments. Referring to
FIG. 1
, ideally, power is supplied from a voltage source
103
to a device under test
102
and no additional series impedance is encountered between the voltage source
103
and the device under test
102
. Therefore, the open circuit voltage at the DUT is equal to V
S
and the DC source impedance of the voltage source
103
is equal to R
S
. In order to make the necessary current measurements a measurement system and wiring are added to the circuit, which introduces non-desirable impedances.
In a conventional measurement system shown in
FIG. 2
, a device under test
102
is supplied from a power source
103
through wire impedances which are indicated as lumped parameters Z
A
and Z
C
. A current is sensed by a non-contact measuring probe
104
, such as for example, a current transformer or a hall effect sensor, and a representation of the current is displayed on an oscilloscope
105
. However, in such a measuring system, a transient voltage dip and overshoot results due to the additional insertion impedances of the probe, as well as from Z
A
and Z
C
. This voltage transient can overvoltage or undervoltage the DUT, potentially terminating the intended test or damaging the DUT.
Another conventional measuring system is shown in
FIG. 3. A
current measurement shunt R
M
is inserted in series with the voltage source
103
and the device under test
102
. An additional voltage drop will be realized due to the measurement shunt R
M
and the wire impedances, represented by the lumped parameters Z
A
, Z
B
and Z
C
.
Yet another conventional measuring system is shown in FIG.
4
. Using a dc power supply
106
with conventional two-wire sense, in a pass through mode where the supply is set to zero volts, current from the voltage source
103
can be measured. By using inputs sense (−) and sense (+), the power supply
106
compensates for voltage drops across the measurement system
106
and the impedances Z
A
and Z
B
but not for a voltage drop across the impedance Z
C
.
SUMMARY OF THE INVENTION
In the present invention, a second set of sense leads is provided for the power supply. This allows the supply to compensate for the additional voltage drop across impedance Z
C
within the bandwidth limitations of the power supply. By setting the power supply to zero volts a total of the errors introduced by the measurement system, Z
A
, Z
B
, and Z
C
is reduced nearly to zero within the bandwidth limits of the power supply. As a result, the open circuit voltage and source impedance at the DUT equals V
S
and R
S
respectively. Thus the required current measurements may be taken in a non-invasive manner.
REFERENCES:
patent: 5578932 (1996-11-01), Adamian
patent: 6040689 (2000-03-01), Gluszek
Benes Michael Joseph
Clegg Russell A.
Medunick James R.
Agilent Technologie,s Inc.
Nguyen Vinh P.
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