ETS-Lindgren 94456 User Manual

Model 94456

Archived 6/1/10

Current Probe

MANUAL

© EMC TEST SYSTEMS, L.P. – MARCH 2002 REV B – PN 399265

94456-5

MODEL 94456 CURRENT PROBES

Archived 6/1/10

EMC Test Systems, L.P. reserves the right to make changes to any product described herein in order to
improve function, design or for any other reason. Nothing contained herein shall constitute EMC Test
Systems, L.P. assuming any liability whatsoever arising out of the application or use of any product or
circuit described herein. EMC Test Systems, L.P. does not convey any license under its patent rights or the
rights of others.

© Copyright 2002 by EMC Test Systems, L.P. All Rights Reserved.

No part of this document may be copied by any means

without written permission from EMC Test Systems, L.P.

E-MAIL & INTERNET

[e-mail]
http://www.ets-lindgren.com

USA

1301 Arrow Point Dr., Cedar Park, TX 78613
P.O. Box 80589, Austin, TX 78708-0589
Tel [phone] Fax [phone]

FINLAND

Euroshield OY
Mekannikontie 1
27510, Eura, Finland
Tel [phone]
Fax [phone]

SINGAPORE

Lindgren RF Enclosures Asia-Pacific
87 Beach Road
#06-02 Chye Sing Building
Singapore 189695
Tel [phone] Fax [phone]

© EMC TEST SYSTEMS, L.P. – MARCH 2002
REV B – PN 399265

MODEL 94456 CURRENT PROBES

Archived 6/1/10

Table of Contents

INTRODUCTION.........................................................................................................1

PRINCIPLES OF OPERATION..................................................................................2

CIRCUIT.......................................................................................................................2

SENSITIVITY.................................................................................................................3

CORE SATURATION AND INTERMODULATION ................................................................3

TRANSFER IMPEDANCE.................................................................................................4

INSTALLATION..........................................................................................................5

EQUIPMENT SETUP .......................................................................................................5

INSTALLATION .............................................................................................................6

TYPICAL TEST CONFIGURATION.........................................................................7

PRECAUTIONARY MEASURES...............................................................................8

OPERATION................................................................................................................9

SIGNAL MEASUREMENT ...............................................................................................9

Oscilloscope Use – In terms of RF Amperes ............................................................9

In Terms of dB Above One Microampere at Meter Input (CW Conducted

Measurements)........................................................................................................9

In Terms of dB Above One Microampere per Megahertz at Meter Input (Broadband

Interference Measurement)....................................................................................10

In Terms of Microampere in Test Sample Lead (CW Conducted Measurements)....11

In Terms of Microampere per Megahertz in Test Sample Lead (Broadband

Interference Measurement)....................................................................................12

SPECIFICATIONS.....................................................................................................13

MAINTENANCE........................................................................................................15

WARRANTY STATEMENT .....................................................................................16

© EMC TEST SYSTEMS, L.P. – MARCH 2002
REV B – PN 399265

MODEL 94456 CURRENT PROBES

Archived 6/1/10

© EMC TEST SYSTEMS, L.P. – MARCH 2002
REV B – PN 399265

MODEL 94456 CURRENT PROBES Introduction

Archived 6/1/10

INTRODUCTION

The ETS-Lindgren EMCO brand Model 94456 RF Current
Probe is a clamp-on RF current transformer designed for
use with Electromagnetic Interference (EMI) Test
Receivers/Spectrum Analyzers, or with any similar
instrument having a 50 Ohm input impedance, to determine
the intensity of RF current present in an electrical
conductor or group of conductors.

The Current Probe provides a means of accurately
measuring net (common mode) radio frequency current
flowing on a wire or bundle of wires without requiring a
direct connection to the conductor(s) of interest. The Model
94456 Current Probe is simply clamped around the test
conductor which then becomes a one turn primary winding,
with the current probe forming the core and secondary
winding of an RF transformer. Measurements can be made
on single and multi-conductor cables, grounding and
bonding straps, outer conductors of shielding conduits and
coaxial cables, etc.

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Principles of Operation MODEL 94456 CURRENT PROBES

Secondary Winding

Noise Currents

Primary (Test Sample Lead)

Archived 6/1/10

PRINCIPLES OF OPERATION

The RF Current Probe, Model 94456 is an inserted-primary
type of radio frequency current transformer. When the
probe is clamped over the conductor or cable in which
current is to be measured, the conductor forms the primary
winding. The clamp-on feature of this probe enables easy
placement around any conductor or cable.

CIRCUIT

The circuit is that of a radio frequency transformer as

Electrostatic
Shield (Case)

illustrated below:

Output to Coaxial Cable
50 Ohms Impedance

Figure 1. Basic RF Transformer

Since the current probe is intended for “clamp on”
operation, the primary shown in Figure 1 is actually the
electrical conductor in which interference currents are to be
measured. This primary is considered as one turn since it is

2 © EMC TEST SYSTEMS, L.P. – MARCH 2002
REV B – PN 399265

assumed that the noise currents flow through the conductor
and return to the source via a “ground” conductor such as a
frame, common ground plane, or earth. On some current
probe models the secondary output terminals are resistively

MODEL 94456 CURRENT PROBES Principles of Operation

Archived 6/1/10

loaded internally to provide substantially constant transfer
impedance over a wide frequency range.

SENSITIVITY

Probe sensitivity in microamperes is dependant upon the
sensitivity in microvolts of the receiving equipment with
which it is used. The following table shows the relationship
of receiving sensitivity in microvolts to the overall
sensitivity of the probe and receiver in microamperes. This
data is based on the transfer impedance of each model.

Test Equipment Sensitivity in

microvolts

5 830
2 332
1 166

0.1 16.6

Table 1. Model 94456 Series Typical Sensitivity

94456-5

ZT = 0.006 ΩΩ

CORE SATURATION AND
INTERMODULATION

The magnetizing effects of a primary conductor carrying
large currents at power line frequencies can saturate the
current probe core material. Core saturation produces non­linear transforming action and can result in (a) a decrease in
the current probe RF output for a given RF current input,
and (b) modulation of the RF output by the power line
frequency.

The specified pulse duty cycle should not be exceeded or
the current probe internal load resistor (if applicable) may

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Principles of Operation MODEL 94456 CURRENT PROBES

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be subject to damage. The load resistor must also be
protected from excessive line currents.

The influence of intermodulation on the current probe
output as measured with the EMI test equipment is
negligible for primary conductor power frequency currents
under 300 Amperes. For primary power currents above 300
Amperes, measurements taken by the EMI test equipment
generally will not be affected by intermodulation because
of its “averaging” characteristics for the Quasi Peak and
Peak functions, the readings will increase with current.

TRANSFER IMPEDANCE

The RF current (IP) in microamps in the conductor under
test is determined from the reading of the current probe
output in microvolts (ES) divided by the current probe
transfer impedance (ZT).

IP = ES/ZT

Or, in dB

IP(dBµµA) = ES(dBµµV) – ZT(dB)

The typical transfer impedance of the current probe
throughout the frequency range is determined by passing a
known RF current (IP) through the primary test conductor
and noting the voltage, ES, developed across a 50 Ohm

4 © EMC TEST SYSTEMS, L.P. – MARCH 2002
REV B – PN 399265

load. Then,

ZT = ES/IP

MODEL 94456 CURRENT PROBES Installation

Archived 6/1/10

INSTALLATION

This section describes methods for setting up the current
probe and associated measuring equipment. Operating
procedures are contained in the Operation section.

EQUIPMENT SETUP

In measuring the RF current in a single conductor, the
probe jaws are placed around the conductor so that the
conductor passes through the center opening and then the
jaws are locked together. In the case of a two-conductor
cable, the probe can be used to evaluate the common mode
component of the noise current (the net effect of the
currents leaving and returning) by placing the probe over
both conductors at the same time, or the interference
current in either conductor can be measured separately by
placing the probe over each wire individually.

In a more complex case of multi-conductor cables, the
probe will measure the net external effects of all the
currents in the conductors that pass through the center of
the probe.

When placed over shielding conduit, coaxial cable, or
ignition shielding, the probe measures the current flowing
on the external surface of the shield. The probe can thus be

© EMC TEST SYSTEMS, L.P. – MARCH 2002 5
REV B – PN 399265

used to evaluate the shielding effectiveness.

NOTE: Standing waves can exist on the test conductor
under test at or near its resonant frequency. Under these

Installation MODEL 94456 CURRENT PROBES

Archived 6/1/10

conditions, several measurements taken along the line will
provide a complete picture of the RF current distribution
and amplitude.

INSTALLATION

The window (aperture) of the probe will accommodate
cables up to a maximum outside diameter of 4.0 inches.

After placing the probe around the conductor(s) to be
measured, the probe jaws should be carefully locked. If this
is not done, inadequate shielding or incorrect air gap will
result and the measurement will not be accurate.

The connecting cable used between the current probe and
the EMI test equipment must have a 50 Ohm characteristic
impedance and matching cable connectors. The current
probe is calibrated for use only with a 50 Ohm load.
Therefore, the EMI test equipment must have a 50 Ohm
input impedance. Precautions regarding minimum bending
radius should be observed when installing and using the
cable. For long cables and at high frequencies, cable loss
may also be a factor. Care should be taken to use low loss
cables and to perform cable loss corrections if necessary.

The probe rejection of any external pickup from conductors
not passing through the window is better that 60 dB. The
presence of very strong magnetic fields will likely have an

6 © EMC TEST SYSTEMS, L.P. – MARCH 2002
REV B – PN 399265

effect on probe sensitivity. Care must be taken not to place
the unit close to permanent magnets or the magnetic field
structures of motors or generators.

MODEL 94456 CURRENT PROBES Typical Test Configuration

5 cm

Archived 6/1/10

For greatest accuracy, the conductor under measurement
should be centered in the window of the current probe.

TYPICAL TEST CONFIGURATION

LISN

EUT

MEASUREMENT

RECEIVER

DATA

RECORDER

© EMC TEST SYSTEMS, L.P. – MARCH 2002 7
REV B – PN 399265

Precautionary Measures MODEL 94456 CURRENT PROBES

Archived 6/1/10

PRECAUTIONARY MEASURES

When measuring uninsulated conductors use extreme care
when installing the current probe and taking measurements.
If possible, de-energize the test sample during assembly
and disassembly of the setup. Also, arrange to center the
test conductor in the current probe window for additional
voltage breakdown protection.

Do not permit the uninsulated current probe connector and
cable connectors to come in contact with the ground plane
or other nearby conductors. This will prevent possible
measurement error due to ground loops, and will avoid
danger from high voltages.

Ensure that the 50 Ohm load is capable of safely dissipating
the incurred power. Should the load become disconnected,
the developed voltage will be come much greater and may
be very dangerous.

8 © EMC TEST SYSTEMS, L.P. – MARCH 2002
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MODEL 94456 CURRENT PROBES Operation

Archived 6/1/10

OPERATION

The RF current probe is a broadband RF transformer for
use with EMI test equipment. Radio frequency currents can
be measured in cables without physically disturbing the
circuit.

SIGNAL MEASUREMENT

Oscilloscope Use – In terms of RF Amperes

1. Standardize the gain of the oscilloscope to read
correctly the voltage (ES) applied to its input terminals.

2. Divide ES in volts by the average current probe transfer
impedance ZT in Ohms. The result is the value of the
RF signal in terms of Amperes in the test conductor.

Example:
Assume an oscilloscope peak voltage measurement of 5
Volts and the average ZT to be 1.06 Ohms. Then: 5/1.06 =

4.71 Amperes in the test conductor. The example is valid

providing that the oscilloscope rise time (T = 0.3/BW) is
shorter than RF signal pulse duration. This also applies to
the current probe which has a rise time of about 3
nanoseconds based on a 100 megahertz bandwidth.

In Terms of dB Above One Microampere at Meter
Input (CW Conducted Measurements)

© EMC TEST SYSTEMS, L.P. – MARCH 2002 9
REV B – PN 399265

1. Adjust the EMI test equipment for standard gain and
make a measurement of the CW signal (voltage output
from the current probe) in terms of dB above one

Operation MODEL 94456 CURRENT PROBES

Archived 6/1/10

microvolt. Use procedures outlined in the EMI test
equipment instruction manual.

2. Subtract the transfer impedance of the current probe in
dB at the test frequency from the dB measurement of
Step (1). The result is the value of the conducted CW
signal in terms of dB above one microamp at meter
input.1

Example:
Frequency is 10.0 kHz; Step (1) measurement is 52 dB
above one microvolt. For example, suppose the transfer
impedance of the current probe used in the example was

8.0 dB below one Ohm at 10.0 kHz. Then, as outlined in

Step (2); 52 dB + 8.0 dB = 60 dB above one microampere
at meter input.

In Terms of dB Above One Microampere per
Megahertz at Meter Input (Broadband Interference
Measurement)

1. Adjust the EMI test equipment for standard gain and
make a Peak measurement of the broadband
interference (voltage output from the current probe) in
terms of dB above one microvolt-per-megahertz. Use
procedures outlined in the EMI test equipment
instruction manual.

2. Subtract the transfer impedance of the current probe in
dB at the test frequency from the dB measurement of
Step (1). The result is the value of the broadband

1

The term “at meter input” as used in the MIL-I-26600 and MIL-I-6181D specifications refers to the

current in the test sample lead.

10 © EMC TEST SYSTEMS, L.P. – MARCH 2002
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MODEL 94456 CURRENT PROBES Operation

Archived 6/1/10

interference in terms of dB above one microamp-per­megahertz at meter input.*

Example:
Frequency is 100 kHz; Step (1) measurement is 41 dB
above one microvolt-per-megahertz. For example, suppose
the transfer impedance of the current probe was 8.0 dB
below one Ohm at 100 kHz. Then, as outlined in Step (2):
41 dB + 8.0 dB = 49 dB above one microamp-per­megahertz at meter input.2
This result is beyond the limit of 46.2 dB above one
microamp-per-megahertz .

In Terms of Microampere in Test Sample Lead
(CW Conducted Measurements)

1. Adjust the EMI test equipment for standard gain and
make a measurement of the CW signal (voltage output
from current probe) in terms of microvolts at meter
input. Use procedures outlined in the EMI test
equipment instruction manual.

2. Divide the microvolt measurement of Step (1) by the
transfer impedance in Ohms at the test frequency. The
result is the value of conducted CW signal in terms of
microamperes in the test sample lead.

Example:
Frequency is 3.0 kHz; Step (1) Measurement is 150
microvolts. For example, suppose the transfer impedance of

2

The term “at meter input” as used in the MIL-I-26600 and MIL-I-6181D specifications refers to the

current in the test sample lead.

© EMC TEST SYSTEMS, L.P. – MARCH 2002 11
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Operation MODEL 94456 CURRENT PROBES

Archived 6/1/10

the current probe was 0.34 Ohms. Then, as outlined in Step
(2), 150/0.34 = 441.1 microamperes in test sample lead.

In Terms of Microampere per Megahertz in Test
Sample Lead (Broadband Interference
Measurement)

1. Adjust the EMI test equipment for standard gain and
make a measurement of the broadband interference
(voltage output from current probe), in terms of
microvolts-per-megahertz at meter input. Use
procedures outlined in the EMI test equipment
instruction manual.

2. Divide the microvolt-per-megahertz measurement of
Step (1) by the transfer impedance in Ohms at the test
frequency. The result is the value of conducted
broadband interference in terms of microamps-per­megahertz in test sample lead.

Example:
Frequency is 10.0 kHz; Step (1) measurement is 8,000
microvolts-per-megahertz. For example, suppose the
transfer impedance of the current probe was 0.39 Ohms.
Then, as outlined in Step (2), 8000/0.39 = 20,513
microamps-per-megahertz in test sample lead.

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MODEL 94456 CURRENT PROBES Specifications

17.46 cm

Archived 6/1/10

SPECIFICATIONS

PHYSICAL

Window Diameter 10.16 cm

4.0 in

Outside Diameter 17.46 cm

6.87 in

Width 5.71 cm

2.25 in

Weight 2.83 kg

6.25 lbs
Output Connector Type N
Input Impedance

50 Ω

© EMC TEST SYSTEMS, L.P. – MARCH 2002 13
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Specifications MODEL 94456 CURRENT PROBES

rents to 4000

Amps can be measured if the pulse duty

6 millivolts across a 50 Ohm load for a 1

Archived 6/1/10

SERIES SPECIFIC ELECTRICAL SPECIFICATIONS

Electrical

Specifications

Frequency Range

Transfer

Impedance

(Nominal)

RF Current Range

(RF CW)

RF Current Range

Maximum Power

Maximum Power

Sensitivity Under

Rated Load

(Pulse)

Current

Voltage

91197-1

10 kHz to 100 MHz

0.006 Ohms

0 to 40 Amps

Pulse signals with peak cur

cycle does not exceed:
(500 Amps IP) 0.0065 Duty
(1000 Amps IP) 0.0016 Duty
(2000 Amps IP) 0.0004 Duty
(3000 Amps IP) 0.00018 Duty
(4000 Amps IP) 0.0001 Duty
350 Amps at DC
250 Amps at 60 Hz
40 Amps at 400 Hz
No limitation, subject to adequate
conductor insulation.

ampere RF signal in the primary

14 © EMC TEST SYSTEMS, L.P. – MARCH 2002
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MODEL 94456 CURRENT PROBES Maintenance

Archived 6/1/10

MAINTENANCE

To ensure reliable and repeatable long term performance
annual recalibration of your current probe by
ETS-Lindgren’s experienced technicians is recommended.
Our staff can recalibrate almost any type or brand of
current probe. Please call to receive a Service Order
Number prior to sending a current probe to us for
calibration.

For more information about our calibration services or to
place an order for current probe calibration visit our
calibration website at http://www.antennacalibration.com/.

© EMC TEST SYSTEMS, L.P. – MARCH 2002 15
REV B – PN 399265

Warranty Statement MODEL 94456 CURRENT PROBES

Archived 6/1/10

WARRANTY STATEMENT

EMC Test Systems, L.P., hereinafter referred to as the Seller, warrants that standard EMCO
products are free from defect in materials and workmanship for a period of two (2) years from
date of shipment. Standard EMCO Products include the following:

v Antennas, Loops, Horns
v GTEM cells, TEM cells, Helmholtz Coils
v LISNs, PLISNs, Rejection cavities & Networks
v Towers, Turntables, Tripods & Controllers
v Field Probes, Current Probes, Injection Probes

If the Buyer notifies the Seller of a defect within the warranty period, the Seller will, at the Seller’s
option, either repair and/or replace those products that prove to be defective.

There will be no charge for warranty services performed at the location the Seller designates.
The Buyer must, however, prepay inbound shipping costs and any duties or taxes. The Seller will
pay outbound shipping cost for a carrier of the Seller’s choice, exclusive of any duties or taxes. If
the Seller determines that warranty service can only be performed at the Buyer’s location, the
Buyer will not be charged for the Seller’s travel related costs.

This warranty does not apply to:

v Normal wear and tear of materials
v Consumable items such as fuses, batteries, etc.
v Products that have been improperly installed, maintained or used
v Products which have been operated outside the specifications
v Products which have been modified without authorization
v Calibration of products, unless necessitated by defects

THIS WARRANTY IS EXCLUSIVE. NO OTHER WARRANTY, WRITTEN OR ORAL, IS
EXPRESSED OR IMPLIED, INCLUDING BUT NOT LMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE REMEDIES
PROVIDED BY THIS WARRANTY ARE THE BUYER’S SOLE AND EXCLUSIVE REMEDIES.
IN NO EVENT IS THE SELLER LIABLE FOR ANY DAMAGES WHATSOEVER, INCLUDING
BUT NOT LIMITED TO, DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
DAMAGES, WHETHER BASED ON CONTRACT, TORT, OR ANY OTHER LEGAL THEORY.

Note: Please contact the Seller’s sales department for a Return Materials Authorization (RMA)
number before shipping equipment to us.

16 © EMC TEST SYSTEMS, L.P. – MARCH 2002
REV B – PN 399265