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Current Probe: Parts List

This document describes the design and operation of a current probe for safely measuring alternating currents. The probe uses two transformers with a 1:32 turns ratio cascaded to provide a total current step-down ratio of 1:1,000. This allows measurement of currents up to 15A or 20A at 50Hz with relative errors less than 1.5% or 5% respectively. The output current is converted to a voltage by an opamp circuit for measurement on an oscilloscope. Test data shows the probe has a frequency range of 50Hz to 100kHz or 30Hz to 1MHz with errors less than 1.5% or 5%.

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Tariq Zuhluf
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157 views1 page

Current Probe: Parts List

This document describes the design and operation of a current probe for safely measuring alternating currents. The probe uses two transformers with a 1:32 turns ratio cascaded to provide a total current step-down ratio of 1:1,000. This allows measurement of currents up to 15A or 20A at 50Hz with relative errors less than 1.5% or 5% respectively. The output current is converted to a voltage by an opamp circuit for measurement on an oscilloscope. Test data shows the probe has a frequency range of 50Hz to 100kHz or 30Hz to 1MHz with errors less than 1.5% or 5%.

Uploaded by

Tariq Zuhluf
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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CURRENT PROBE

hen it comes to mea- length is60.1 rnm. The core ma-


W suring alternating CUf-
rents in a safe manner, CUf-
terial 1S 3C 11. The secondary
windings consist of 32 turns
ICl = AD847JN
01,02 = lN4151

rent probes have a number of of 1 mm dta. (20 SWG) enarn-


signtficant advantages over elled copper wire: the prnnary K1
*
T,1 *
T<2
sertes resrstors. Ta begtri wtth, windings of one turn of the
the measuring ctrcutt is elec- same wire. For proper insu-
trically iso la ted from the a.c. Iatton. the primary of Tri ts
su pply line whtch carries the best made from solid, irrsu-
current to be measured. lated. wire. The PCB connec-
Secondly, tho a.c. supply Iine tion via terminal block K! must 1:321:32
need not be broken to insert notbe used at a.c.unevoltages *see text
a sertes reststor, or a cluster greater than 42 V, or currents
of sertes resistors with an as- greaterthan5A.ln those cases. 944093-11
sociated range switch. Thirdly, the measuremenl wire must
voltage lass caused by the the be run through the core of Tr j .
current probe is neghgtble. Finally, some testdata ob-
Current probes are based tained with a prototype ofthe
on mductrve coupling only, current probe:
and usually have a transformer
at the Input to couple on to the frequency range:
a.c. supply line. Ta ensure 50 Hz to 100 KHz (relativeerror
that the current which flows <1.5%)
through the a.c. supply ltne is 30 Hz to 1 MHz (relative error
transformed down to a safe <5%)
level.which can be handled by current range at 50 Hz:
an opamp. the input trans- lmax= 15A (relativeerror c 1.5%)
Iormer usually has a turns Imax = 20 A (relative error <5%)
ratio of 1: 1,000 01' so. In prac-
ttce. that means that the prt- Parts list
malY of the transformer has
one turn, and the secondary. Resistors:
1,000. Rl ~ 102 Q, 1%
Here. two transformers wtth PI = 10 kQ multiturn preset
a turns ratrc of 1:32 are cas-
caded to obtain a total cur- Capacitors:
rent step-down ratio of 1:1.000 Cl, C2 ~ 100 nF
(1:322). Thiswasdonemainly C3, C4 = 100 )lF, 10 V, ra-
to avoid the tedium ofhaving
to wind 1,000 turns of wire
dial IC1 = A0847JN
on to a ferrite ring core. Dcsprte Semiconductors: 01,02 = 1N4151
the fact that two trans formers Dl. D2 = IN4151
are used instead ofone, the cur-
rent probe still has an im- Integrated circuits:
K1
pressive frequency and curren t
range.
ICI = AD847JN *
Tr1 *
Tr2

Trl and Tr2 lower tbe cur'- Miscellaneous: D1 D2


rent carried on the a.c. line Kl = PCB terminal block.
bya factor of Szß. The output pitch 7.5mm
current is applied to a cur- Tr j • Tr2 = ferrite ring core
rent-to-voltage converter based RCC26/l0-3C11
on an AD84 7 oparnp. Resistor (Philips Components
R1 gtves the opamp a conver- order code 4330 030)
ston factor of about 0.1. An 1 : 32 1 : 32
off-setadjustment, Pj , is pro- Design: H. Bonekamp
vided to keep the oscilloscope (9440931 *see text
'in the ptcture' without havtng
to swttch tt to a.c. Input mode.
The transformers are wound 944093-11
using ferrite ring cores type
RCC26/1O-3Cll (order code
43300303752) from Phi!ips
Components. The inductance
conversion factor. AL. of this
core is quttc high at 5)lH per
turn. The cross-sectional area
ts 55.9 mmä, and the effectlve

ELEKTOR ELECTRONICS DECEMBER 1994

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