Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Reexamination Certificate
2002-04-04
2004-11-30
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
C324S1540PB
Reexamination Certificate
active
06825649
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a detection probe respectively used in a method and a device for measuring an AC voltage applied to a conductor insulated by insulation, such as a vinyl insulated electrical wire, without contacting the conductor.
2. Description of the Prior Art
Conventionally, an AC voltmeter is generally used in the measurement of a voltage of a commercial AC current (supply) being applied to an insulated electrical wire.
However, with a method using a conventional AC voltmeter, since it is necessary to bring one measurement electrode into contact with a conductor, it was necessary to cut away part of the insulation of the insulated electrical wire, or to provide a terminal for measurement in advance.
The applicant of the present application has previously proposed a non-contact voltage measurement method and a device that operates at low voltage and is portable (Japanese Patent No. 3158063).
FIG. 13
is a block diagram showing the structure of a non-contact voltage measurement device
80
of the related art, and
FIG. 14
is an equivalent circuit of essential parts of the voltage measurement device
80
.
In
FIG. 13
, the voltage measurement device
80
comprises a detection resistor R
1
, a detection probe
11
, an oscillator
12
, a current detection section
13
j
, a band pass filter
21
, a rectifier
22
, a capacitance calculation section
23
, a floating capacitance detection section
24
, a switch
25
, a low pass filter
26
, an integrator
27
and a divider
28
.
The detection probe
11
is provided with a detection electrode
111
for electrostatically shielding part of a conductor CD, by covering part of the surface of insulation SL of an electrical wire WR from the outside, and a shield electrode
112
for electrostatically shielding the detection electrode
111
from the outside. Impedance Zw between the detection electrode
111
and the conductor CD is measured using the detection probe
11
. In practice, reactance XC
1
, namely capacitance C
1
, is measured in place of the impedance Zw.
Composite capacitance due to capacitance between the probe electrode
111
and the shield electrode
112
, floating capacitance due to wiring to the detection resistor R
1
, and other floating capacitance, is made C
0
, and reactance due to this is made XC
0
. Capacitance C
0
is sometimes referred to as “floating capacitance C
0
”.
Electric current flowing from the oscillator
12
through the detection resistor R
1
into the detection electrode
111
is Is, and electric current discharged from the detection electrode
111
towards the oscillator
12
is Ix. Within current Is, there is current Is
0
flowing through the floating capacitance C
0
to a ground terminal, and a current Is
1
flowing through the capacitance C
1
and the conductor CD to the ground terminal.
The oscillator
12
outputs, for example, a 5 KHz sine wave signal of a certain voltage Es. The current detection section
13
j
detects current flowing into the detection electrode
111
and current discharged from the detection electrode
111
, and outputs a signal S
1
.
Within the signal S
1
output from the current detection section
13
j
, the band pass filter
21
allows only a component due to the signal Es of the oscillator
12
to pass. The floating capacitance detection section
24
measures and stores floating capacitance C
0
with the detection probe
11
separated from the electrical wire WR. The capacitance calculation section
23
calculates capacitance C
1
based on a signal S
3
output from the rectifier
22
with the surface of the insulation SL covered by the detection probe
11
, and the floating capacitance C
0
stored in the floating capacitance detection section
24
. The obtained capacitance C
1
is output to the divider
28
as a signal S
4
.
Within the signal S
1
output from the current detection section
13
j
, the low pass filter
26
allows only a component due to the voltage Ex applied to the conductor CD to pass. The integrator
27
integrates a signal S
5
output from the low pass filter
26
. In this way, phase compensation of the signal waveform is carried out. The divider
28
obtains a voltage Ex by dividing the signal S
6
(Erx) output from the integrator
27
by the signal S
4
(capacitance C
1
) output from the capacitance calculation section
23
.
First of all, the floating capacitance C
0
is measured with the detection probe
11
in an open state. The impedance Z
0
seen from the oscillator
12
side is:
Z
0
=
R
1
+
j XCx
0
but since the detection resistor R
1
can be ignored compared to the reactance XC
0
, the impedance Z
0
becomes:
Z
0
=XC
0
Accordingly, current Is
0
flowing into the floating capacitance C
0
due to the signal Es output from the oscillator
12
is:
Is
0
=
Es
/
Z0
=
Es
/
XC0
(
1
)
while a voltage Er across the two ends of the detection resistor R
1
due to this current is:
&AutoLeftMatch;
Er
=
Is
0
×
R1
=
(
Es
×
R1
)
/
XC0
(
2
)
and therefore:
XC
0
=(
Es×R
1
)/
Er
C
0
=(
Es×
R
1
)/
&ohgr;s·Er
(3)
A value of floating capacitance Co obtained from this equation (3) is stored in the floating capacitance detection section
24
. Next, capacitance C
1
is measured with the detection probe
11
closed.
The capacitance C
1
is increased by the fact that the detection electrode
111
covers the electrical wire WR. Accordingly, impedance Zw seen from the oscillator
12
is:
Zw=R
1
+j XCc
(4)
provided that, Cc=C
0
+C
1
Since the detection resistor R
1
is small compared to reactance XCc, and can be ignored,
Zw=XCc
Accordingly, current Is flowing into the detection resistor R
1
due to the signal Es output from the oscillator
12
is:
Is
=
Es
/
Zw
=
Es
/
XCc
(
5
)
while a voltage Er developed across the two ends of the detection resistor R
1
by this current is:
Er
=
Is
×
R1
=
(
Es
×
R1
)
/
XCc
(
6
)
Accordingly, since:
XCc=
(
Es×R
1
)
/Er
and XCc is &ohgr;s (C
0
+C
1
),
C
0
+
C
1
=(
Es×R
1
)
/&ohgr;s ·Er
(7)
A value of capacitance (C
0
+C
1
) obtained from this equation (7) is input to the capacitance calculation section
23
as a signal S
3
. In the capacitance calculation section
23
, capacitance C
1
is obtained by subtracting the value of floating capacitance C
0
stored in the floating capacitance detection section
24
from the input value of capacitance (C
0
+C
1
), and this is output to the divider
28
.
Next, a voltage Er developed across the two ends of the detection resistor R
1
attributable to the voltage Ex applied to the conductor CD is obtained with the detection probe
11
closed.
Impedance Zx of the circuit through the detection resistor R
1
seen from the conductor CD side is:
Zx=R
1
+j XC
1
(8)
Since the detection resistor R
1
is small compared to reactance XC
1
, and can be ignored,
Zx=XC
1
Accordingly, current Ix flowing into the detection resistor R
1
due to the voltage Ex applied to the conductor CD is:
Ix
=
Ex
/
Zx
=
Ex
/
XC1
(
9
)
A voltage Er developed across the two ends of the detection resistor R
1
by this current is:
Er
=
Ix
×
R1
=
(
E
×
XR1
)
/
XC1
=
ω
×
XC1
×
(
Ex
×
R1
)
(
10
)
A value of voltage Er (Ers) obtained from this equation (10) is input to the divider
28
as a signal S
6
. The voltage Ex is obtained by the divider
28
, by dividing the input voltage Er by a coefficient containing the capacitance C
1
output from the capacitance calculation section
23
. That is,
Ex=Er
/(
&ohgr;x×C
1
×
R
1
) (11)
is obtained.
However, if the above described voltage measurement device
80
of the related art is used, there is influence from floating capacitance between the detection electrode
111
and the shield electrode
112
, and from floating capacitance due to the wiring. For this reason, it is necessary to measure the floating capacitance C
0
with the detection probe
11
Cuneo Kamand
Hokuto Electronics Incorporated
LandOfFree
Non-contact voltage measurement method and device, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-contact voltage measurement method and device, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-contact voltage measurement method and device, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3316480