Omega Products HHM81 Installation Manual

Where Do I Find Everything I Need for

s

Process Measurement and Control?

OMEGA ... Of Course!

TEMPERATURE

3

o Thermocouple, RTD & Thermistor Probes, Connectors, Panels & Assemblies
o Wire: Thermocouple, RTD & Thermistor

3

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3

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3
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3

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M-3481/0899 99-MAN 100181

UserÕ

ON OL

!

INPUT:

0-4.5 A DC / AC peak

• 1 mV/mA

• OFF

HHM81

DC/AC MICROPROBE

CAT III300 V

®

http:/www.omeg

a.com

HEATERS

3

o Heating Cable
o Cartridge & Strip Heaters

3

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3

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3

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3

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3

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3

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3

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3

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3
3

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Model HHM81
Model HHM82

AC/DC Current Probes

WARRANTY/DISCLAIMER

.

h

t

t

OMEGA ENGINEERING, INC. warrants this unit to be free of defects in materials and workmanship for a
period of 13 months from date of purchase. OMEGA Warranty adds an additional one (1) month grace period
to the normal one (1) year product warranty to cover handling and shipping time. This ensures that
OMEGA's customers receive maximum coverage on each product.

If the unit should malfunction, it must be returned to the factory for evaluation. OMEGA's Customer Service
Department will issue an Authorized Return (AR) number immediately upon phone or written request. Upon
examination by OMEGA, if the unit is found to be defective it will be repaired or replaced at no charge.
OMEGA's WARRANTY does not apply to defects resulting from any action of the purchaser, including but not
limited to mishandling, improper interfacing, operation outside of design limits, improper repair, or
unauthorized modification. This WARRANTY is VOID if the unit shows evidence of having been tampered with
or shows evidence of being damaged as a result of excessive corrosion; or current, heat, moisture or
vibration; improper specification; misapplication; misuse or other operating conditions outside of OMEGA's
control. Components which wear are not warranted, including but not limited to contact points, fuses, and
triacs.

OMEGA is pleased to offer suggestions on the use of its various products. However, OMEGA neither
assumes responsibility for any omissions or errors nor assumes liability for any damages that result
from the use of its products in accordance with information provided by OMEGA, either verbal or
written. OMEGA warrants only that the parts manufactured by it will be as specified and free of
defects. OMEGA MAKES NO OTHER WARRANTIES OR REPRESENTATIONS OF ANY KIND
WHATSOEVER, EXPRESSED OR IMPLIED, EXCEPT THAT OF TITLE, AND ALL IMPLIED WARRANTIES
INCLUDING ANY WARRANTY OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE HEREBY DISCLAIMED. LIMITATION OF LIABILITY: The remedies of purchaser set forth herein are
exclusive and the total liability of OMEGA with respect to this order, whether based on contract,
warranty, negligence, indemnification, strict liability or otherwise, shall not exceed the purchase price
of the component upon which liability is based. In no event shall OMEGA be liable for consequential,
incidental or special damages.

CONDITIONS: Equipment sold by OMEGA is not intended to be used, nor shall it be used: (1) as a "Basic
Component" under 10 CFR 21 (NRC), used in or with any nuclear installation or activity; or (2) in medical
applications or used on humans. Should any Product(s) be used in or with any nuclear installation or activity,
medical application, used on humans, or misused in any way, OMEGA assumes no responsibility as set forth
in our basic WARRANTY/DISCLAIMER language, and additionally, purchaser will indemnify OMEGA and hold
OMEGA harmless from any liability or damage whatsoever arising out of the use of the Product(s) in such a
manner.

RETURN REQUESTS/ INQUIRIES

Direct all warranty and repair requests/inquiries to the OMEGA Customer Service Department. BEFORE
RETURNING ANY PRODUCT(S) TO OMEGA, PURCHASER MUST OBTAIN AN AUTHORIZED RETURN
(AR) NUMBER FROM OMEGA'S CUSTOMER SERVICE DEPARTMENT (IN ORDER TO AVOID
PROCESSING DELAYS). The assigned AR number should then be marked on the outside of the return
package and on any correspondence.

The purchaser is responsible for shipping charges, freight, insurance and proper packaging to prevent
breakage in transit.

FOR WARRANTY RETURNS, please have the following
information available BEFORE contacting OMEGA:

1. P.O. number under which the product was
PURCHASED,

2. Model and serial number of the product under
warranty, and

3. Repair instructions and/or specific problems
relative to the product.

OMEGA's policy is to make running changes, not model changes, whenever an improvement is possible. This
affords our customers the latest in technology and engineering.

OMEGA is a registered trademark of OMEGA ENGINEERING, INC.
© Copyright 1996 OMEGA ENGINEERING, INC. All rights reserved. This document may not be copied,

photocopied, reproduced, translated, or reduced to any electronic medium or machine-readable form, in whole
or in part, without prior written consent of OMEGA ENGINEERING, INC.

FOR NON-WARRANTY REPAIRS, consult
OMEGA for current repair charges. Have the
following information available BEFORE
contacting OMEGA:

1. P.O. number to cover the COST of the repair,

2. Model and serial number of product, and

3. Repair instructions and/or specific problems
relative to the product.

OMEGAnetSM On-Line Service:

http://www.omega.com

Internet e-mail: [e-mail]

Servicing North America:

USA: One Omega Drive, Box 4047

ISO 9001 Certified Stamford, CT 06907-0047

Tel: [phone] FAX: [phone]
e-mail: [e-mail]

Canada: 976 Bergar

Laval (Quebec) H7L 5A1
Tel: [phone] FAX: [phone]
e-mail: [e-mail]

For Immediate Technical or Application Assistance:

USA and Canada: Sales Service: 1-800-826-6342 1-800-TC-OMEGA

Customer Service: 1-800-622-2378 / 1-800-622-BEST
Engineering Service: 1-800-872-9436 / 1-800-USA-WHEN
TELEX: 996404 EASYLINK 62968934 CABLE: OMEGA

Mexico and Tel: (95) 800-TC-OMEGA

SM

FAX: [phone]

Latin America: En Espanol: [phone] ext: 2203

e-mail: [e-mail]

SM

SM

SM

Servicing Europe:

Benelux: Postbus 8034,1180 LA Amstelveen, The Netherlands

Czech Republic: Ostravska 767, 733 01 Karvina

France: 9, rue Denis Papin, 78190 Trappes

Germany/Austria: Daimlerstrasse 26, D-75392 Deckenpfronn, Germany

United Kingdom: 25 Swannington Road, P.O. Box 7, Omega Drive,

150 9002 Certified Broughton Astley, Leicestershire, Irlam, Manchester,

It is the policy of OMEGA to comply with all worldwide safety and EMC/EMI regulations that apply
OMEGA is constantly pursuing certification of its products to the European New Approac
Directives. OMEGA will add the CE mark to every appropriate device upon certification.

The information contained in this document is believed to be correct but OMEGA Engineering, Inc
accepts no liability for any errors it contains, and reserves the right to alter specifications withou
notice.

WARNING: These products are not designed for use in, and should not be used for, patien
connected a

lications.

Tel: [phone] FAX: [phone]
Toll Free in Benelux: 06 0993344 e-mail: [e-mail]

Tel: [phone] FAX: [phone]
e-mail: [e-mail]

Tel: [phone] FAX: [phone]
Toll Free/France: 0800-4-06342 e-mail: [e-mail]

Tel: [phone] FAX: [phone]
Toll Free in Germany: 0130 11 21 66
e-mail: [e-mail]

LE9 6TU, England M44 5EX, England
Tel: [phone] Tel: [phone]
FAX: [phone] FAX: [phone]

Toll Free in England: 0800-488-488

e-mail: [e-mail]

Maintenance

War ni ng

For maintenance use only specified replacement parts.

· To avoid electrical shock, do not attempt to perform any servicing unless
you are qualified to do so.

· To avoid electrical shock and/or damage to the instrument, do not get
water or other foreign agents into the case. Turn the Model
HHM81/HHM82 OFF and disconnect the unit from all circuits before
opening the case.

· Also see warning on page 2.

Bat tery Repl acement

· Remove probe from any conductor and place it away from any active
conductors, circuitry, etc.

· Unplug electronic module from display device (e.g., DMM, oscilloscope).

· Remove the screws from the bottom cover of the electronic module.

· Replace battery with a new 9 V alkaline type.

· Replace bottom cover and re-attach with screws.

Cleaning

To ensure optimum performance, it is important to keep the probe jaw mating
surfaces clean at all times. Failure to do so may result in increased earth's
field susceptibility and overall errors in readings. The following is the
recommended procedure for cleaning the probe sensor:

1. Apply a few drops of isopropyl alcohol to an ordinary sheet of white

photocopy paper.

2. Open probe to expose the mating surfaces of the sensor and insert the

sheet of paper into the jaws. Allow the jaws to close.

3. With the jaws closed, pull free the end of the paper through the jaws until

it releases.

4. Repeat step (3) several times, using a new (dry) section of paper each

time.

5. Open probe and inspect mating surfaces. They should be free of dust

particles or any other contamination. Otherwise, repeat the cleaning
process starting again at step (1).

Table of Contents

Warning................................................................................................... 2

International Electrical Symbols.............................................................2

Receiving Your Shipment....................................................................... 3

Packaging ...............................................................................................3

Description .............................................................................................. 3

Specifications..........................................................................................5

Typical Frequency Response................................................................. 7

Operating Procedure .............................................................................. 8

Making Measurements with the Models HHM81/HHM82................ 8

Indicator Lights .................................................................................. 8

Operation Examples ............................................................................... 9

DC Current Measurement ................................................................. 9

DC Current Measurement - Current Reversed ................................9

Two-Wire Sum-of-Currents ............................................................. 10

Two-Wire Current Differential .........................................................10

Oscilloscope Measurement (HHM81)............................................. 11

Maximum Step Discontinuity........................................................... 11

Measuring the DC Component of an (AC+DC) Waveform............ 12

Measuring the AC Component of an (AC+DC) Waveform ............ 12

Oscilloscope Measurement (HHM82)............................................. 13

Tips for Making Precise Measurements ......................................... 14

Residual Readings Following Severe Overloads...........................15

Maintenance .........................................................................................16

Warning .......................................................................................... 16

Battery Replacement ..................................................................... 16

Cleaning ......................................................................................... 16

16

Warning

These safety warnings are provided to ensure the safety of
personnel and proper operation of the instrument.

· Read the instruction manual completely and follow all the
safety information before attempting to use or service this
instrument.

· Use caution on any circuit: Potentially high voltages and
currents may be present and may pose a shock hazard.

· Read the Safety Specifications section prior to using the probe.
Never exceed the maximum voltage ratings given.

· Safety is the responsibility of the operator.

· NEVER open the back of the instrument while connected to

any circuit or input.

· ALWAYS connect the adapter to the display device before
clamping the probe onto the sample being tested.

· ALWAYS inspect the instrument, probe, probe cable, and
output terminals prior to use. Replace any defective parts
immediately.

· NEVER use the probe on electrical conductors rated above

300 V in overvoltage category II (CAT II).

International Electrical Symbols

This symbol signifies that the probes are protected by double or
reinforced insulation. Use only specified replacement parts when
servicing the instrument.

This symbol signifies CAUTION! and requests that the user refer to
the user manual before using the instrument.

2 15

· Make sure that probe jaw mating surfaces are free of dust and
contamination. Contaminants cause air gaps between sensor halves,
making the Model HHM81/HHM82 susceptible to external magnetic
fields which can contribute to measurement errors. See page 16 for
cleaning procedure.

· Do not allow probe jaws to abruptly snap closed from the open state.
This can lead to residual readings. If this happens, the probes will
need to be rezeroed.

· Beware of short-circuit currents. Large in-rush currents (which can
occur when power is first applied in a circuit) and large high-current
transients may cause varying degrees of residual readings. If in
doubt of a particular reading, remove the probe from the conductor
under test and check to see that the display device returns zero. If
not, it will be necessary to rezero the Models HHM81 and HHM82.

· When using the probes to measure AC currents, keep in mind the
maximum current ratings and the frequency response curves shown
in the electrical specifications section. Dynamic currents that contain
large step discontinuities and/or frequency constituents near or
beyond the measurement passband are subject to measurements
errors and waveform distortion (oscilloscope display). If the red LED
comes on during measurement, the output signal may be in error.

· Many DVMs provide null (relative) measurement capability. A DVM
placed in the null mode displays the difference between a stored null
value and the input signal.

· You can use a DVMÕs null function in place of the external DC zero
control to cancel any DC offset from the Models HHM81/HHM82.
The DVM null function should be enabled with the probe removed
from the conductor immediately before measurement.

· You can use a DVMÕs null function to display changes in measured
current from a fixed (constant) level. In this application, the DVM null
function is enabled with the probe connected to the conductor.

· When making null (relative) measurements, the probe aperture
current (not displayed current) must not exceed the maximum ratings
set forth in the specifications section.

Residual Readings Foll owi ng Severe Over loads

· Large short-circuit and transient currents outside the operating

range of the probe may cause large residual readings. In extreme
cases they will not zero. If this happens:

- Remove the probe from the test conductor.

- Open the probe and release, allowing the jaws to snap back.
Repeat this step several times.

- Rezero the instrument before making successive measurements.

Tips For Maki ng Pr ecise Measur ements

· The Models HHM81 and HHM82 are capable of making
measurements of DC and low frequency currents over a wide range.
Here are some key considerations for getting the most accuracy from
your displaying instrument:

· When using the probes with a meter, it is important to select the range
that provides the best resolution. Failure to do this may result in
measurement errors. The following examples use an ordinary 3-1/2
digit DMM with the probes, to measure 16.7 mA DC:

Resolution: 10 mV

Display Error: 19.8%

Resolution: 1 mV

Display Error: 1.8%

Resolution: 100µV

Display Error: 0%

Receiving Your Shipment

Upon receiving your shipment, make sure that the contents are
consistent with the packing list. Notify Omega of any missing items. If the
equipment appears to be damaged, file a claim immediately with the
carrier and notify Omega at once, giving a detailed description of any
damage.

Packaging

The Models HHM81 and HHM82 include a electronic plug-in module
with an attached current probe, 9 V battery, and user manual.

Model

HHM81

Model

HHM82

.02

V

V

2

2

0

V

0

0

m

2

PUSH

DC Zero

V

Resolution: 10 mV

Display Error: 1.8%

.17V

V

2

2

V

0

2

PUSH
DC Zero

Description

These microprobes are low current measurement instruments that
feature a compact, high sensitivity current probe. Unlike other

V

0

2

.017

2

V

V

2

0

0

m

V

16.7

V

0

2

M

V

V

2

2

0

0

m

V

instruments, the Model HHM81 exhibits a wide dynamic operating range,
which extends from below 100µA to ± 4.5 A peak, from DC to 2.0 kHz*,

PUSH

DC Zero

PUSH

DC Zero

without the need for ranging. The HHM82 has an operating range of
100µA to ± 450 mA Peak, from DC to 1500 Hz.

This series is designed to be operated in conjunction with a digital
multimeter, oscilloscope or recording device. The microProbe outputs the

16.7 mA

current measured in the form of a voltage that is the image of the current,
in shape and amplitude. The Model HHM81 outputs 1 mV per mA of

Figure 10

measured current. The Model HHM82 outputs 10 mV per mA of
measured current. To take advantage of the Model HHM82Õs high
sensitivity, best results are obtained through 4-1/2 digit (or more) DMM

Resolution: 1 mV

Display Error: 0%

Resolution: 100µV

Display Error: 0%

with a relative zero function. The Model HHM82 was designed to provide
the operator with enhanced low current linearity and accuracy, but is
limited to 450 mA Peak current.

.167V

V

2

0

0

m

V

2

0

0

V

m

0

2

V

167.0MV

V

2

2

V

0

2

The microprobes always output a signal proportional to the total current

0

0

m

V

(AC+DC) in the conductor under test. This has proven to be the most
versatile signal output format, and allows the user to isolate and measure
DC and AC components of measured current separately, if so desired.

PUSH
DC Zero

PUSH
DC Zero

Typical applications include 4 to 20 mA loop measurements, automotive
current applications, benchtop electronic current consumption in circuits,
and other applications requiring very low current measurements in
crowded areas.

16.7 mA

Figure 11

14 3

1

Oscil loscope Measur ement Exampl e ( HHM82)

· Conductor carrying a 0.2 A peak AC waveform

2

7

· Model HHM82 connected to oscilloscope

To Oscilloscope

2.0 V

3

0

4

ON OL

INPUT:

5

DC/AC MICROPROBE

!

CAT III300 V

0-4.5 A DC / AC peak

• 1 mV/mA

• OFF

HHM81

-2.0 V

Oscilloscope

Output

!

ON OL

CAT III300 V

INPUT:

8

®

0-450 mA DC / AC peak

• 1 mV/mA

• OFF

HHM82

DC/AC MICROPROBE

®

Current Waveform

0.2 A

0

-0.2 A

Figure 9

6

1. Positive: Red banana plug (+)

2. Negative: Black banana plug (-)

3. Power ON indicator (green LED)

4. OVERLOAD indicator (red LED)

5. Power switch

6. Zero adjust knob (push in and turn to zero)

7. Probe window aperture

8. Probe handle

4 13

Measuri ng the DC Component of an ( AC+DC) Wavef or m
( HHM81)

· Conductor carrying 20.0 mA DC + 15.0 mA AC

· Voltmeter placed in DC Volts mode

· Voltmeter displays 20.0 mV

HHM81
Specifications

ELECTRICAL

Current Range:

0 to ± 4.5 A DC
0 to 3 Arms (sinusoidal)

HHM82
Specifications

ELECTRICAL

Current Range:

0 to ± 450 mA DC
0 to 300 mA rms

20.0

M

V

D

C

V

V

C

A

15 mA AC

+

20 mA DC

PUSH

DC Zero

Figure 7

Measuri ng the AC Component of an ( AC+DC) Wavef or m
( HHM81)

· Conductor carrying 20.0 mA DC + 15.0 mA AC

· Voltmeter placed in AC Volts mode

· Voltmeter displays 15.0 mV

15.0

M

V

D

C

V

V

C

A

15 mA AC

+

20 mA DC

Output (Vout): 1 mV/mA

Resolution:

DC: 50µA typical
AC: 100µA typical

Accuracy:

DC: 1% reading ± 200µA
AC: 2% reading ± 200µA

Output Noise:

< 100µV, DC to 5 kHz

Frequency Response:

DC to 2 kHz (@ -3 dB sine)

Zero Adjust:

Output (Vout): 10 mV/mA

Resolution:

DC: 50µA typical,
AC: 100µA typical

Accuracy:

DC: 0.5% reading ± 150µA
AC: 0.8% reading ± 200µA

Output Noise:

<100µV, DC to 5 kHz

Frequency Response:

DC to 1500 Hz (@ -3 dB sine)

Zero Adjust:

COMMON SPECIFICATIONS

ELECTRICAL

Rise Time: < 200µS, 10% to 90% Vout

Fall Time: < 200µS, 90% to 10% Vout

Output Impedance: 200W

Probe Inductance: <1µH

Influence of Adjacent Conductor: < 50µA/A

PUSH

DC Zero

Influence of Earth's Field: < 120µA, null to maximum

Figure 8

*Reference Conditions: Temperature 23¡C, 20 to 75% RH; battery voltage 9 V ±

0.1 V; earth's magnetic field < 40 A/m; absence of AC fields; input impedance of
display device ³ 1 MW/100 pF; DC or sinusoidal AC current 45 - 65 Hz.

12 5

Common Specifications (cont.)

MECHANICAL

Connectors: Two 4 mm banana jacks, standard 3/4" (19 mm) spacing

Maximum Conductor Diameter: 3/16Ó, 0.180" (4.5 mm)

Overload LED (Red): Indicates momentary or continuous overload

Power LED (Green): Indicates power ON and good battery

Battery: 9 V alkaline, NEDA 1604 or IEC 6 LF22

Dimensions (Probe): 4.4 x 0.6 x 1.0" (111 x 15 x 25 mm)

Dimensions (Electronic Module): 4.9 x 2.5 x 1.1" (124 x 64 x 28 mm)

Cable Length: 5 ft (1.5 m)

Oscil loscope Measur ement Exampl e ( HHM81)

To Oscilloscope

ON OL

INPUT:

0-4.5 A DC / AC peak

• 1 mV/mA

• OFF

HHM81

DC/AC MICROPROBE

2.0 V

0

-2.0 V

!

CAT III300 V

®

Oscilloscope

Output

Current Waveform

2.0 A

0

Weight: 9 oz (250 g)

Operating Temperature: -14¡ to 131¡F (-10¡ to 55¡C)

Storage Temperature: -40¡ to 176¡F (-40¡ to 80¡C)

Humidity: < 95% @ ³ 35¡C, 75% @ 55¡C

SAFETY SPECIFICATIONS

The MicroProbes are designed to be used in conjunction with a digital
multimeter or other instrument for the purpose of displaying measured
readings. The Models HHM81 and HHM82 are safety rated as voltage
probes. The user should ensure that they are connected to an instrument
properly rated to international safety standards and/or agency approvals.

Working Voltage: 300 V per IEC 1010-1 Cat. II

Immunity (EN 50082-1), IEC 1000-4-3 aptitude criteria A:

DC: 15mV @ 0, AC (60Hz): 2dB from 10 mA to 4.5A

Emmissivity (EN 50081-1): negligible

Drop Test: 1 m per IEC 1010

Shocks: 100 G per IEC 68-2-27

Vibrations: IEC 529

Figure 5

Maximum St ep Di scont inui t y Example ( HHM81)

· Conductor carrying non-sinusoidal AC

· Model HHM81 connected to oscilloscope

· Max allowable step-discontinuity 2 A

To Oscilloscope

!

ON OL

CAT III300 V

INPUT:

0-4.5 A DC / AC peak

• 1 mV/mA

• OFF

HHM81

DC/AC MICROPROBE

®

Note: Step Discontinuities

2.0 V

0

-2.0 V

Oscilloscope

Output

Current Waveform

2A

0

-2A

Protection Index: IP 40 per IEC 529

Electromagnetic Compatibility: EN 50082-1 class A EN 50081-1

6

Figure 6

11

Two-Wir e Sum- of -Cur r ents Exampl e ( HHM81)

· Two conductors in probe aperture (note orientations)

· Voltmeter placed in DC Volts mode

· Voltmeter displays 18.0 Mv

18.0

M

V

D

C

V

C

A

V

7 mA DC 11 mA DC

PUSH

DC Zero

Figure 3

Two-Wir e Cur r ent Di f ferenti al Exampl e ( HHM81)

· Two conductors in probe aperture (note orientations)

· Voltmeter placed in DC Volts mode

· Voltmeter displays -4.0 mV

Typical Frequency Response

Model HHM81 Typical Frequency Response

Frequency (Hz)

400

200

50

0

-0.5

-1.0

-1.5

-2.0

Decibels (dB)

-2.5

-3.0

-3.5

-4.0

Model HHM82 Typical Frequency Response

600

800

1000

Frequency (Hz)

1800

1600

1400

1200

2200

2000

30 mA

3.0 A

-4.0MV

D

C

V

C

A

PUSH

DC Zero

400

200

0

0

-0.5

V

7 mA DC 11 mA DC

-1.0

-1.5

-2.0

Decibels (dB)

-2.5

-3.0

-3.5

-4.0

600

800

1000

1400

1200

1600

0 - 300 mA RMS

Figure 4

10 7

Operating Procedure

Operation Examples

Making Measur ements wi th the Model s HHM81/HHM82

· Remove any conductor from within the probe jaws.

· Plug the electronic module into the displaying device (e.g., DMM,

oscilloscope). Note the polarity of the module output banana plugs
(red = positive [+], black = negative [-]).

· Select the appropriate range on displaying device (e.g., DMM,
oscilloscope). Note that the module output is 1 mV/ mA for Model
HHM81 and 10 mV/A for Model HHM82.

· Turn displaying device power ON. Turn on the probe: the green
LED should be ON, and the red LED OFF.

· With the probe disconnected from test samples (no conductor in
probe jaw window), adjust the zero control (push in the knob and
turn) to read zero volts on the displaying device. In the unlikely
event where the zero point is unobtainable, refer to ÒResidual
Readings Following Severe OverloadsÓ section (pg. 15). The probe
may be temporarily magnetized.

· Clamp the probe around the conductor to be tested. The displaying
device should now display the measured conductor current. In DC,
a positive reading indicates current flowing in the direction of the
arrow on the probe. A negative reading indicates current flow in the
opposite direction of the arrow.

I ndicat or Li ght s - Green and Red LEDs

· The green LED indicates that the probe is ON and that the battery
is good. The green LED will not light under low battery conditions.
Replace the 9 V battery if the green LED is not lit.

· The red LED indicates a momentary or continuous overload of the

instrument. Readings taken while the red LED is ON or FLASHING
should be considered inaccurate. Momentary or continuous
currents exceeding ± 4.7 A for Model HHM81 and 470 mA for
Model HHM82, and dynamic currents with large step discontinuities
will cause the red LED to turn ON.

DC Curr ent Measur ement Exampl e (HHM81)

· Conductor carrying 20.0 mA DC in the direction of the arrow

· Voltmeter placed in DC Volts mode

· Voltmeter displays 20.0 mV

20.0

M

V

D

C

V

V

C

A

PUSH

DC Zero

Figure 1

20 mA DC

DC Curr ent Measur ement Exampl e - Cur r ent Rever sed ( HHM81)

· Conductor carrying 20.0 mA DC in opposite direction of arrow

· Voltmeter placed in DC Volts mode

· Voltmeter displays -20.0 mV

-

20.0

M

V

D

C

V

C

A

V

PUSH

DC Zero

Figure 2

8 9

20 mA DC