Keysight U3401A User And Service Manual

Keysight U3401A 4 1/2 Digit
Dual Display Multimeter

User’s and
Service Guide

Notices

CAUTION

WARNING

Copyright Notice

© Keysight Technologies 2009 - 2017
No part of this manual may be

reproduced in any form or by any
means (including electronic storage
and retrieval or translation into a
foreign language) without prior
agreement and written consent from
Keysight Technologies as governed by
United States and international
copyright laws.

Manual Part Number

U3401-90001

Edition

Edition 14, November 1, 2017

Printed in:

Printed in Malaysia

Published by:

Keysight Technologies
Bayan Lepas Free Industrial Zone,
11900 Penang, Malaysia

Technology Licenses

The hardware and/or software
described in this document are
furnished under a license and may be
used or copied only in accordance with
the terms of such license.

Declaration of Conformity

Declarations of Conformity for this
product and for other Keysight
products may be downloaded from the
Web. Go to http://www.keysight.com/

go/conformity. You can then search by

product number to find the latest
Declaration of Conformity.

U.S. Government Rights

The Software is “commercial computer
software,” as defined by Federal
Acquisition Regulation (“FAR”) 2.101.
Pursuant to FAR 12.212 and 27.405-3
and Department of Defense FAR
Supplement (“DFARS”) 227.7202, the
U.S. government acquires commercial
computer software under the same
terms by which the software is
customarily provided to the public.
Accordingly, Keysight provides the
Software to U.S. government
customers under its standard
commercial license, which is embodied
in its End User License Agreement
(EULA), a copy of which can be found at

http://www.keysight.com/find/sweula.

The license set forth in the EULA
represents the exclusive authority by
which the U.S. government may use,
modify, distribute, or disclose the
Software. The EULA and the license set
forth therein, does not require or
permit, among other things, that
Keysight: (1) Furnish technical
information related to commercial
computer software or commercial
computer software documentation that
is not customarily provided to the
public; or (2) Relinquish to, or
otherwise provide, the government
rights in excess of these rights
customarily provided to the public to
use, modify, reproduce, release,
perform, display, or disclose
commercial computer software or
commercial computer software
documentation. No additional
government requirements beyond
those set forth in the EULA shall apply,
except to the extent that those terms,
rights, or licenses are explicitly required
from all providers of commercial
computer software pursuant to the FAR
and the DFARS and are set forth
specifically in writing elsewhere in the
EULA. Keysight shall be under no
obligation to update, revise or
otherwise modify the Software. With
respect to any technical data as
defined by FAR 2.101, pursuant to FAR

12.211 and 27.404.2 and DFARS

227.7102, the U.S. government
acquires no greater than Limited Rights
as defined in FAR 27.401 or DFAR

227.7103-5 (c), as applicable in any
technical data.

Warranty

THE MATERIAL CONTAINED IN THIS
DOCUMENT IS PROVIDED “AS IS,”
AND IS SUBJECT TO BEING
CHANGED, WITHOUT NOTICE, IN
FUTURE EDITIONS. FURTHER, TO THE
MAXIMUM EXTENT PERMITTED BY
APPLICABLE LAW, KEYSIGHT
DISCLAIMS ALL WARRANTIES, EITHER
EXPRESS OR IMPLIED, WITH REGARD
TO THIS MANUAL AND ANY
INFORMATION CONTAINED HEREIN,
INCLUDING BUT NOT LIMITED TO THE
IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE. KEYSIGHT
SHALL NOT BE LIABLE FOR ERRORS
OR FOR INCIDENTAL OR
CONSEQUENTIAL DAMAGES IN
CONNECTION WITH THE
FURNISHING, USE, OR
PERFORMANCE OF THIS DOCUMENT
OR OF ANY INFORMATION
CONTAINED HEREIN. SHOULD
KEYSIGHT AND THE USER HAVE A
SEPARATE WRITTEN AGREEMENT
WITH WARRANTY TERMS COVERING
THE MATERIAL IN THIS DOCUMENT
THAT CONFLICT WITH THESE TERMS,
THE WARRANTY TERMS IN THE
SEPARATE AGREEMENT SHALL
CONTROL.

Safety Information

A CAUTION notice denotes a hazard. It
calls attention to an operating
procedure, practice, or the like that, if
not correctly performed or adhered to,
could result in damage to the product
or loss of important data. Do not
proceed beyond a CAUTION notice
until the indicated conditions are fully
understood and met.

A WARNING notice denotes a hazard. It
calls attention to an operating
procedure, practice, or the like that, if
not correctly performed or adhered to,
could result in personal injury or death.
Do not proceed beyond a WARNING
notice until the indicated conditions are
fully understood and met.

2 Keysight U3401A User’s and Service Guide

Safety Symbols

CAT II
300 V

The following symbols on the instrument and in the documentation indicate
precautions which must be taken to maintain safe operation of the instrument.

Direct current (DC) Caution, risk of electric shock

Alternating current (AC)

Both direct and alternating current Out position of a bi-stable push control

Earth (ground) terminal In position of a bi-stable push control

Protective earth (ground) terminal Frame or chassis (ground) terminal

IEC Measurement Category II.
Measurement performed on circuits
that are directly connected to the low
voltage installation (up to 300 VAC)
under Category II overvoltage
conditions

Caution, risk of danger (refer to this
manual for specific Warning or Caution
information)

Keysight U3401A User’s and Service Guide 3

General Safety Information

WARNING

The following general safety precautions must be observed during all phases of
operation, service, and repair of this instrument. Failure to comply with these
precautions or with specific warnings elsewhere in this manual violates safety
standards of design, manufacture, and intended use of the instrument. Keysight
Technologies assumes no liability for the customer’s failure to comply with these
requirements.

– Do not exceed any of the measurement limits defined in the specifications

to avoid instrument damage and the risk of electric shock.

– Do not defeat power cord safety ground feature. Plug in to a grounded

(earthed) outlet.

– Do not use multimeter in any manner that is not specified by the

manufacturer.

– Double-check the multimeter’s operation by measuring a known voltage.

– For current measurement, turn off circuit power before connecting the

multimeter to the circuit. Always place the multimeter in series with the
circuit.

– When connecting probes, always connect the common test probe first.

When disconnecting probes, always disconnect the live test probe first.

– Do not measure more than the rated voltage (as marked on the

multimeter) between terminals, or between terminal and earth ground.

– Do not use repaired fuses or short-circuited fuse-holders. For continued

protection against fire, replace the line fuses only with fuses of the same
voltage and current rating and recommended type.

– Do not service or perform adjustments alone. Under certain conditions,

hazardous voltages may exist, even with the multimeter switched off. To
avoid dangerous electric shock, service personnel must not attempt
internal service or adjustment unless another person, capable of
rendering resuscitation or first aid, is present.

4 Keysight U3401A User’s and Service Guide

WARNING

– Do not substitute parts or modify multimeter to avoid the danger of

CAUTION

introducing add itional hazards. Return the product to Keysight
Technologies Sales and Service Office for service and repair to ensure the
safety features are maintained.

– Do not operate damaged equipment as the safety protection features

built into this multimeter may have been impaired, either through
physical damage, excessive moisture, or any other reason. Remove power
and do not use the product until safe operation can be verified by
service-trained personnel. If necessary, return the product to Keysight
Technologies Sales and Service Office for service and repair to ensure the
safety features are maintained.

– Turn off circuit power and discharge all high-voltage capacitors in the

circuit before you perform resistance, continuity, diodes, or capacitance
tests.

– Use the correct terminals, functions, and range for your instruments.

– Do not measure voltage when current measurement is selected.

– Use the multimeter with the cables provided.

– Repair or service that is not covered in this manual should only be

performed by qualified personnels.

Keysight U3401A User’s and Service Guide 5

Environmental Conditions

NOTE

This multimeter is designed for indoor use only. The table below shows the
general environmental requirements for the multimeter.

Environmental conditions Requirements

Operating temperature Full accuracy from 0 °C to 50°C (Operating)

Operating humidity

Storage temperature –20 °C to 60 °C (Non-operating)

Altitude Operating up to 2,000 metres (6,562 feet)

Pollution degree Pollution Degree 2

The Keysight U3401A dual display complies with the following EMC
requirements:

– IEC 61010-1:2001/EN61010-1:2001 (2nd Ed ition)

– Canada: CAN/CSA-C22.2 No. 61010-1-04

– USA: ANSI/UL 61010-1:2004

– IEC 61326-1:2005/EN61326-1:2006

– Canada: ICES/NMB-001: Issue 4, June 2006

Full accuracy up to 80% R.H. (Relative humidity) for
temperature up to 28°C

– Australia/New Zealand: AS/NZS CISPR11:2004

6 Keysight U3401A User’s and Service Guide

Regulatory Markings

The CE mark is a registered trademark
of the European Community. This CE
mark shows that the product complies
with all the relevant European Legal
Directives.

ICES/NMB-001 indicates that this ISM
device complies with the
Canadian ICES-001.
Cet appareil ISM est conforme a la
norme NMB-001 du Canada.

The CSA mark is a registered
trademark of the Canadian
Standards Association.

The RCM mark is a registered
trademark of the Spectrum
Management Agency of Australia.
This signifies compliance with the
Australia EMC Framework regulations
under the terms of the Radio
Communication Act of 1992.

This instrument complies with the
WEEE Directive (2002/96/EC) marking
requirement. This affixed product label
indicates that you must not discard
this electrical or electronic product in
domestic household waste.

This symbol indicates the time period
during which no hazardous or toxic
substance elements are expected to
leak or deteriorate during normal use.
Forty years is the expected useful life
of the product.

Keysight U3401A User’s and Service Guide 7

Waste Electrical and Electronic Equipment (WEEE) Directive 2002/ 96/EC

This instrument complies with the WEEE Directive (2002/96/EC) marking
requirement. This affixed product label indicates that you must not discard this
electrical or electronic product in domestic household waste.

Product category

With reference to the equipment types in the WEEE directive Annex 1, this
instrument is classified as a “Monitoring and Control Instrument” product.

The affixed product label is as shown below.

Do not dispose in domestic household waste.

To return this unwanted instrument, contact your nearest Keysight Service Center,
or visit http://about.keysight.com/en/companyinfo/environment/takeback.shtml
for more information.

Sales and Technical Support

To contact Keysight for sales and technical support, refer to the support links on
the following Keysight websites:

– www.keysight.com/find/low-cost-dmm

(product-specific information and support, software and documentation
updates)

– www.keysight.com/find/assist

(worldwide contact information for repair and service)

8 Keysight U3401A User’s and Service Guide

Table of Contents

Safety Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

General Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Regulatory Markings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Waste Electrical and Electronic Equipment (WEEE) Directive

2002/96/EC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Product category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Sales and Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

1 Getting Started

Introducing the Keysight U3401A Dual Display Multimeter . . . . . . . . .18

Checking the shipping contents . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Connecting power to the instrument . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Stacking the U3401A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Adjusting the Handle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Product at a Glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Product dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

The front panel at a glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

The display at a glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

The keypad at a glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

The terminals at a glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

The rear panel at a glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Making measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Performing voltage measurements . . . . . . . . . . . . . . . . . . . . . . . . . .35

Performing current measurements . . . . . . . . . . . . . . . . . . . . . . . . . .37

Performing frequency measurements . . . . . . . . . . . . . . . . . . . . . . . .39

Performing resistance/continuity measurements . . . . . . . . . . . . . . .40

Performing diode and continuity test . . . . . . . . . . . . . . . . . . . . . . . .41

Selecting a Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

Keysight U3401A User’s and Service Guide 9

2Operations and Features

Operating Math Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

dBm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Rel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

MinMax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Comp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Hold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Percentage (%) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Using the Secondary Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Using the setup menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Changing the configurable settings . . . . . . . . . . . . . . . . . . . . . . . . . 60

Trigger mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

3 Application Tutorial

Applications for Using Dual Display . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Dual Display Operation Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Measure DC Voltage and AC Ripple on a Rectification Circuit . . . . 65

Measure AC and DC Current on a Rectification Circuit . . . . . . . . . . 66

Measure AC Voltage and Frequency on an AC Circuit . . . . . . . . . . . 67

Measure Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Measure True RMS AC + DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

4Performance Test

Calibration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Keysight Technologies calibration services . . . . . . . . . . . . . . . . . . . 72

Calibration interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Recommended Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Test Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Performance Verification Tests Overview . . . . . . . . . . . . . . . . . . . . . . . 75

Performance verification tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

5 Disassembly and Repair

Operating Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

Types of Service Available . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

10 Keysight U3401A User’s and Service Guide

Repackaging for shipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

To replace the power line fuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

To replace a current input fuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88

Electrostatic Discharge (ESD) precautions . . . . . . . . . . . . . . . . . . . .88

Mechanical Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89

Replaceable Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95

To order replaceable parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95

6 Characteristics and Specifications

Keysight U3401A User’s and Service Guide 11

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12 Keysight U3401A User’s and Service Guide

List of Figures

Figure 1-1 Stacking the U3401A . . . . . . . . . . . . . . . . . . . . . . . . . .21

Figure 1-2 Type of handle position . . . . . . . . . . . . . . . . . . . . . . . .22

Figure 1-3 Attaching and detaching the handle . . . . . . . . . . . . . .22

Figure 1-4 U3401A dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Figure 1-5 Front panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Figure 1-6 VFD full display with all segments illuminated . . . . . .25

Figure 1-7 Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Figure 1-8 Input terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

Figure 1-9 Rear panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Figure 1-10 ACV terminal connection and display . . . . . . . . . . . . .35

Figure 1-11 DCV terminal connection and display . . . . . . . . . . . . .36

Figure 1-12 ACI RMS or DCI (mA) terminal connection and

Figure 1-13 ACI RMS or DCI (10A) terminal connection and

Figure 1-14 Frequency terminal connection and display . . . . . . . .39

Figure 1-15 Resistance /continuity terminal connection and

Figure 1-16 Forward-biased diode/continuity test terminal

Figure 1-17 Reverse-biased diode/continuity terminal

Figure 2-1 Typical dBm operation display . . . . . . . . . . . . . . . . . . .47

Figure 2-2 Typical Rel operation display . . . . . . . . . . . . . . . . . . . .48

Figure 2-3 Typical Max operation display . . . . . . . . . . . . . . . . . . .49

Figure 2-4 Typical Min operation display . . . . . . . . . . . . . . . . . . .49

Figure 2-5 Typical Comp operation display . . . . . . . . . . . . . . . . . .51

Figure 2-6 Typical Hold operation display . . . . . . . . . . . . . . . . . . .53

Figure 2-7 Typical refresh hold operation display . . . . . . . . . . . . .54

Figure 2-8 Typical percentage (%) operation display . . . . . . . . . .55

Figure 2-9 Secondary display . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

Figure 2-10 Typical trigger mode display . . . . . . . . . . . . . . . . . . . .61

Figure 3-1 Connection terminal when measuring DC voltage

display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

connection and display . . . . . . . . . . . . . . . . . . . . . .42

connection and display . . . . . . . . . . . . . . . . . . . . . .42

and AC ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65

Keysight U3401A User’s and Service Guide 13

Figure 3-2 Connection terminal when using DC current and

AC ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Figure 3-3 Connection terminal when measuring AC Voltage

and Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Figure 3-4 Connection terminal when measuring Resistance . . . 68

14 Keysight U3401A User’s and Service Guide

List of Tables

Table 1-1 Display annunciators . . . . . . . . . . . . . . . . . . . . . . . . . .25

Table 1-2 Keypad functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Table 1-3 Input terminal for different functions . . . . . . . . . . . . . .32

Table 1-4 Range scale value . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Table 2-1 Math operations for different measurement functions 46

Table 2-2 Description for dual display combination . . . . . . . . . .58

Table 2-3 Setup menu and communications parameters . . . . . .59

Table 3-1 Typical combinations and applications when using

dual display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Table 4-1 Recommended test equipments . . . . . . . . . . . . . . . . .73

Table 4-2 DC voltage verification test . . . . . . . . . . . . . . . . . . . . .76

Table 4-3 DC current verification test . . . . . . . . . . . . . . . . . . . . . 77

Table 4-4 2-wire Ω verification test . . . . . . . . . . . . . . . . . . . . . . .78

Table 4-5 Diode verification test . . . . . . . . . . . . . . . . . . . . . . . . .79

Table 4-6 Frequency verification test . . . . . . . . . . . . . . . . . . . . . . 79

Table 4-7 AC volts verification test . . . . . . . . . . . . . . . . . . . . . . .80

Table 4-8 AC current verification test . . . . . . . . . . . . . . . . . . . . .81

Table 5-1 Type of supplied fuse (according to country of

destination) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

Table 5-2 Type of current input fuse . . . . . . . . . . . . . . . . . . . . . .88

Keysight U3401A User’s and Service Guide 15

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16 Keysight U3401A User’s and Service Guide

Keysight U3401A 4 ½ Digit Dual Display Multimeter
User’s and Service Guide

1 Getting Started

Introducing the Keysight U3401A Dual Display Multimeter 18
Connecting power to the instrument 20
Stacking the U3401A 21
Adjusting the Handle 22
Product at a Glance 23
Making measurements 34
Selecting a Range 43

This chapter provides an introduction to the U3401A digital multimeter and a
tutorial showing how to use the front panel in order to make measurements.

17

1 Getting Started

Introducing the Keysight U3401A Dual Display Multimeter

The key features of the U3401A dual display multimeter are:

– 4 ½-digit dual display measurement

– Ten measurement functions:

–AC voltage

–DC voltage

– AC current

– DC current

–AC + DC voltage

– AC + DC current

– Resistance

– Frequency

– Continuity test

–Diode test

– Six math operations:

–dBm

–Min/Max

–Hold

– Relative (Rel)

– Compare (Comp)

– Percentage (%)

– 50,000 count dual display.

– AC and DC current measurements to 10 A.

– Resistance measurement up to 50 MΩ, 10 mΩ resolution.

– Frequency measurement up to 500 kHz with 0.01 Hz resolution.

– Measurement of dBm with variable reference impedance from 2 Ω to 8000 Ω.

18 Keysight U3401A User’s and Service Guide

Checking the shipping contents

NOTE

Verify that you have received the following items with your multimeter:

–Power cord

–Standard test lead kit

– Quick start guide

– Product reference CD

–Test report

– Certificate of calibration

Inspect the shipping container for damage. Signs of damage may include a
dented or torn shipping container or cushioning material that shows signs of
unusual stress or compacting.

Carefully remove the contents from the shipping container and verify that any
options ordered are included with the shipment by checking the packing list
included with the shipment.

If anything is missing, contact your nearest Keysight Sales Office.

Getting Started 1

– If the shipping container or packaging material is damaged, it should be kept

until the contents have been checked mechanically and electrically. If there is
mechanical damage, notify the nearest Keysight Technologies office. Keep
the damaged shipping materials (if any) for inspection by the carrier and
Keysight representative. If required, you can find a list of Keysight Sales and
Service Offices on the last page of this guide.

– Ensure you read and understand the preceding safety information before

proceeding.

Original packaging

Containers and materials identical to those used in the factory packaging are
available through Keysight Technologies office. If the multimeter is being returned
to Keysight Technologies for servicing, attach a tag indicating the type of service
required, return address, model number, and serial number. Also mark the
container FRAGILE to assure careful handling. In any correspondence, refer to the
multimeter by model number and serial number.

Keysight U3401A User’s and Service Guide 19

1 Getting Started

NOTE

CAUTION

Connecting power to the instrument

Connect the power cord and press the power switch to turn on the multimeter.

The front panel display illuminates while the multimeter performs its power-on
self-test. (If the multimeter does not power-on, refer “Operating Checklist” on

page 84). During the power-on session, press to hold the full display. Press
any key to resume the power-on self-test.

The multimeter powers up in the DC voltage function with autoranging enabled.
If self-test is successful, the multimeter goes to normal operation. If the self-test
fails, either a full annunciator or a blank display is displayed without entering the
normal operation. If the self-test repeatedly fails, contact your nearest Keysight
Sales and Service Office.

The multimeter will operate at any line voltage between 90 VAC and 264 VAC
when the line voltage selector is set properly with frequency range 50 Hz or 60 Hz.

– Before turning on the multimeter, make sure the line voltage selector is

set to the correct position for the applied line voltage to the power line
cord connector.

– Do not apply a line voltage that exceeds the specified range of the line

cord connector.

20 Keysight U3401A User’s and Service Guide

Stacking the U3401A

The U3401A is shipped with specially designed anti-slip protective bumpers on
the front and rear panel. The multimeters will not slide off when stacked on top of
each other.

To be able to stack the U3401A multimeters, ensure the attached bumpers are in
correct orientation. See Figure 1-1.

Getting Started 1

Figure 1-1 Stacking the U3401A

Keysight U3401A User’s and Service Guide 21

1 Getting Started

Carrying position

Handle removal position

Adjusting the Handle

To adjust the handle, grasp the handle by the side and pull outward. Then, rotate
the handle to the desired position. Figure 1-2 below shows the possible handle
positions.

Benchtop
position

Figure 1-2 Type of handle position

To attach or detach the handle, rotate the handle upright and pull it out from the
sides of the multimeter. Refer to Figure 1-3.

Figure 1-3 Attaching and detaching the handle

22 Keysight U3401A User’s and Service Guide

Product at a Glance

226.0 mm

105.0 mm

305.0 mm

Product dimensions

Front view

Side view

Getting Started 1

Figure 1-4 U3401A dimensions

Keysight U3401A User’s and Service Guide 23

1 Getting Started

Measurement
function
keypads

Math
operation
keypads

Primary display

Secondary display

Autoranging,
manual range,
and comparator
operation

Shift

Power
on/off
switch

Input terminals
and current fuse

The front panel at a glance

Figure 1-5 Front panel

24 Keysight U3401A User’s and Service Guide

The display at a glance

Figure 1-6 VFD full display with all segments illuminated

The highly visible vacuum fluorescent display (VFD) annunciators are described in

Table 1-1.

Tab le 1-1 Display annunciators

Annunciator Description

Primary display

Getting Started 1

S Reading rate: Slow. Not applicable for the U3401A.

M Reading rate: Medium. Not applicable for the U3401A.

F Reading rate: Fast. Not applicable for the U3401A.

PEAK Peak measurement. Not applicable for the U3401A.

HOLD Data hold

MIN MinMax math operation: Minimum value shown on the primary display

MAX MinMax math operation: Maximum value shown on the primary display

REL Relative value

dBm Decibel unit relative to 1 mW

4 2 W 4-wire/2-wire resistance. Not applicable for the U3401A.

Diode test

Audible continuity test for resistance

AUTO Autoranging

Keysight U3401A User’s and Service Guide 25

1 Getting Started

Tab le 1-1 Display annunciators (continued)

Annunciator Description

DC Direct current

AC Alternating current

DCAC AC + DC

Polarity, digits, and decimal points for primary display

°C Celcius temperature unit. Not applicable for the U3401A.

°F Fahrenheit temperature unit. Not applicable for the U3401A.

mV Voltage unit: mV, V

μmA Current unit: μA, mA, A

μmnF Capacitance unit: μF, nF, mF

MkΩ Resistance unit: Ω, kΩ, MΩ

MkHz Frequency unit: Hz, kHz, MHz

Secondary d isplay

Polarity, digits, and decimal points for secondary display

μmnF Capacitance unit: μF, nF, mF

°C Celcius temperature unit. Not applicable for the U3401A.

°F Fahrenheit temperature unit. Not applicable for the U3401A.

% Duty cycle measurement

mV Voltage unit: mV, V

μmA Current unit: μA, mA, A

S Shift mode

MkΩ Resistance unit: Ω, kΩ, MΩ

2ND Secondary display is enabled. Not applicable for the U3401A.

AUTO Autoranging

DC Direct current

AC Alternating current

26 Keysight U3401A User’s and Service Guide

Tab le 1-1 Display annunciators (continued)

Annunciator Description

DCAC AC + DC

COMP Compare operation

dBm Decibel unit relative to 1 mW

CAL Calibration mode

EXT External. Not applicable for the U3401A.

TRIG Trigger mode

REMOTE Remote interface control. For calibration use only.

LOCAL Local mode

STO Store instrument state. Not applicable for the U3401A.

RCL Recall stored instrument state. Not applicable for the U3401A.

Getting Started 1

Keysight U3401A User’s and Service Guide 27

1 Getting Started

The keypad at a glance

The operation for each key is shown on Tab l e 1 - 2. Pressing a key changes the
current key operation, illuminates the related symbol on the display and emits a
beep.

Figure 1-7 Keypad

Tab le 1-2 Keypad functions

Key Description

System related operation

Press to power-on or power-off the U3401A multimeter.

Press to select Shift.

Press to return the multimeter to front panel operation when it is in remote state.

Press to step through the Setup menu. See “Using the setup menu” on page 59 for more

+

information.

Press to enable the secondary display.

28 Keysight U3401A User’s and Service Guide

Tab le 1-2 Keypad functions (continued)

Key Description

Measurement related operation

Press to disable the secondary display.

+

Press to select the DC voltage measurement.

Press to select the AC voltage measurement.

Press to select the DC current measurement.

Press to select the AC current measurement.

Press to select the AC + DC voltage measurement.

+

Getting Started 1

Press to select AC + DC current measurement.

+

Press to select the frequency measurement.

Press to toggle between the diode and continuity measurement.

Press to toggle between resistance or resistance continuity.

– Press to select dBm measurement.

+

– Press to select the reference impedance for dBm measurement.

Press to toggle between manual ranging and autoranging.

Press to select a higher range and disable autoranging. See “Selecting a Range” on page 43 for
more information.

Keysight U3401A User’s and Service Guide 29

1 Getting Started

Tab le 1-2 Keypad functions (continued)

Key Description

Measurement related operation

Press to select a lower range and disable autoranigng. See “Selecting a Range” on page 43 for
more information.

Press to select Compare math operation.

+

Press to select and set the high limit for Compare math operation.

+

Press to select and set the low limit for Compare math operation.

+

Press to enable Hold math operation. See “Hold” on page 53 on for more information.

Press to enable the MinMax math operation.

Press to select the Relative math operation.

Press to select the Percentage operation.

+

30 Keysight U3401A User’s and Service Guide

The terminals at a glance

CAUTION

NOTE

To avoid damaging this multimeter, do not exceed the rated input limit.

Getting Started 1

Figure 1-8 Input terminals

Voltages above 300 VAC may be measured only in circuits that are isolated from
mains. However, transient overvoltages are also present on circuits that are
isolated from mains. The Keysight U3401A is designed to safely withstand
occasional transient overvoltages up to 2500 V PEAK. Do not use this
multimeter to measure circuits where transient overvoltages could exceed this
level.

Keysight U3401A User’s and Service Guide 31

1 Getting Started

Tab le 1-3 Input terminal for different functions

Measurement function Input terminal Overload protection

DC voltage (VDC)

1000 VDC

750 VAC RMS, 1100 V PEAK,

7

AC voltage (VAC), frequency (Hz)

Miliampere (mA), frequency (Hz) mA 500 mADC or AC RMS

COM

10 A, frequency (Hz) 10 A

Resistance (Ω)

Diode test, continuity test

V-Hz normal mode, or

2x10

6

V-Hz common mode

1x10

10 ADC or AC RMS continuous, and
>10 A DC RMS for 20 seconds maximum

500 VDC or AC RMS

500 VDC or AC RMS

All functions Any terminal to earth 1000 VDC or AC PEAK

32 Keysight U3401A User’s and Service Guide

The rear panel at a glance

AC line
voltage selector

Line voltage fuse
selection table

AC power
connector

AC line fuse Chassis

ground lug

RS232 interface connector
(For calibration use only)

Getting Started 1

Figure 1-9 Rear panel

Keysight U3401A User’s and Service Guide 33

1 Getting Started

NOTE

Making measurements

The following pages show you how to make measurement connections and how
to select measurement functions from the front panel for each of the
measurement functions.

– After measuring a high voltage measurement of up to 1000 VDC, you are

recommended to wait for approximate two minutes before measuring a
low-level measurement with 1 to 10 μV resolutions

– After measuring a high current measurement using the A input terminal, you

are recommended to wait for approximate ten minutes before measuring a
low-level DC measurements of volts, amperes, or ohms; to achieve accurate
measurement. This is due to the thermal voltages generated during the high
current measurements that may cause errors when measuring the low-level
measurements.

34 Keysight U3401A User’s and Service Guide

Performing voltage measurements

WARNING

CAUTION

+

–

ACV
voltage
source

Exceeding the crest factor limit may result in an incorrect or a lower reading.
Do not exceed the crest factor limit to avoid instrument damage and the risk
of electric shock.

Ensure that the terminal connections are connected correctly before making
any measurement. To avoid damaging the multimeter, do not exceed the
rated input limit.

AC vol tage

– Five ranges: 500.00 mV, 5.00 V, 50.00 V, 500.00 V, 750.00 V
– Measurement method: AC coupled true RMS—measure the AC component

with up to 400 VDC bias on any range
– Crest factor: Maximum 3:1 at full scale
– Input impedance: 1 MΩ±2% parallel with capacitance <100 pF on all ranges
– Input protection: 750 V RMS on all ranges

Getting Started 1

1 Press .

2 Connect the red and black test leads to the respective input terminals as

shown in Figure 1-10.
3 Probe the test points and read the display. In autoranging mode, the multimeter

automatically selects the appropriate range and the measurement is displayed.

Figure 1-10 ACV terminal connection and display

Keysight U3401A User’s and Service Guide 35

1 Getting Started

+

DCV
voltage
source

–

DC Voltage

– Five ranges: 500.00 mV, 5.00 V, 50.00 V, 500.00 V, 1000.00 V

–Measurement method: Sigma Delta A-to-D converter

– Input impedance: 10 MΩ±2% range (typical)

– Input protection: 1000 V on all ranges

1 Press .

2 Connect the red and black test leads to the respective input terminals as

3 Probe the test points and read the display. In autoranging mode, the

shown in Figure 1-11.

multimeter automatically selects the appropriate range and the measurement
is displayed.

Figure 1-11 DCV terminal connection and display

36 Keysight U3401A User’s and Service Guide

Performing current measurements

ACI or DCI

current source

+

–

Measuring AC (RMS) or DC Current in mA

– Measurement ranges: 500.00 μA, 5.00 mA, 50.00 mA, 500.00 mA

– Shunt resistance: 0.01 Ω to 100 Ω for 500 μA to 10 A ranges

– Input protection: Internal 25 A, 440 V FH fuse for one terminal

1 Press or .

2 Power off the measured circuit.

3 Connect the red and black test leads to mA input terminal as shown in

Figure 1-12.

4 Probe the test points in series with the circuit.

5 Power on the measured circuit and read the display.

Getting Started 1

Figure 1-12 ACI

RMS or DCI (mA) terminal connection and display

Keysight U3401A User’s and Service Guide 37

1 Getting Started

+

–

ACI or DCI

current source

Measuring AC (RMS) or DC Current up to 10 A

– Measurement ranges:

– Shunt resistance: 0.01 Ω to 100 Ω for 500 μA to 10 A ranges

– Input protection: Internal 25 A, 440 V fuse for 10A terminal,

1 Press or .

2 Press or to select the measurement range.

3 Power off the measured circuit.

4 Connect the red and black test leads to the A input terminal as shown in

5 Probe the test points in series with the circuit.

6 Power on the measured circuit and read the display.

– 5.000 A, 10.000 A for DC or AC RMS continuous

– 12.000 A DC or AC RMS for maximum 30 seconds

Figure 1-13.

Figure 1-13 ACI RMS or DCI (10A) terminal connection and display

38 Keysight U3401A User’s and Service Guide

Performing frequency measurements

WARNING

Frequency
source

+

–

Use the frequency counter for low voltage applications. Do not use the
frequency counter on AC power line systems.

– Five ranges:

– 500.00 mV, 5.0000 V, 50.000 V, 500.000 V, 750.000 V

– Range is based on the voltage level of the signal, not frequency

– Measurement method: Reciprocal counting technique. AC coupled input using

AC voltage function

– Signal level: 10% of range to full scale input on all ranges

– Gate time: 0.1 s or 1 period of the input signal, whichever is longer

– Input protection: 1000 V RMS on all ranges

1 Press .

2 Connect the red and black test leads to the input terminal as shown in

Figure 1-14.

3 Probe the test points and read the display. In autoranging mode, the multimeter

automatically selects the appropriate range and the measurement is displayed.

Getting Started 1

Keysight U3401A User’s and Service Guide 39

Figure 1-14 Frequency terminal connection and display

1 Getting Started

CAUTION

+

–

Test current

Resistance

Performing resistance/continuity measurements

Disconnect circuit power and discharge all high-voltage capacitors before
measuring resistance, or testing circuit continuity, to avoid damaging the
multimeter or the device under test.

– Six ranges: 500.00 Ω, 5.0000 kΩ, 50.000 kΩ, 500.00 kΩ, 5.000 MΩ, 50.000 MΩ,

– Measurement method: Two-wire ohms, open-circuit voltage limited to < +9 V

– Input protection: 500 V on all ranges

1 Press .

2 Connect the red and black test leads to the input terminal as shown in

3 Probe the test points (by shunting the resistor) and read the display.

Figure 1-15.

In autoranging mode, the multimeter automatically selects the appropriate
range and the measurement is displayed.

Figure 1-15 Resistance /continuity terminal connection and display

40 Keysight U3401A User’s and Service Guide

Performing diode and continuity test

CAUTION

NOTE

The diode test measures the forward voltage of a semiconductor junction of
approximately 0.5 mA. The beeper will emit a single beep tone when the input
voltage is below +0.7 V (approximately 1.4 kΩ) and emits a continuos beep tone
when the input voltage is below 50 mV (approximately 100 Ω).

Disconnect circuit power and discharge all high-voltage capacitors before
testing diodes to avoid damaging the multimeter.

– Measurement method: 0.5 mA ± 0.2% constant current source, open-circuit

voltage limited to < +9 V

– Continuity threshold: 10 Ω fixed

– Input protection: 500 V DC or AC RMS

To test a diode, switch the circuit power off, and remove the diode from the circuit.
Then proceed as follows:

Getting Started 1

1 Press to toggle the diode and continuity function. The default function

is diode measurement.

2 Connect the red and black test leads to the input terminal as shown in

Figure 1-16 on page 42.

3 Connect the red test lead to the positive terminal (anode) of the diode and the

black test lead to the negative terminal (cathode). Refer to Figure 1-16 on

page 42.

4 Read the display.

The cathode of a diode is indicated with a band.

5 Reverse the probes and measure the voltage across the diode again as shown

in Figure 1-17. Assess the diode according to the following guidelines:

– A diode is considered good if the multimeter displays OL in reverse bias

mode.

Keysight U3401A User’s and Service Guide 41

1 Getting Started

Test current

Forward
bias

+

–

+

–

Reverse
bias

Test current

– A diode is considered shorted if the multimeter displays approximately

0 V in both forward and reverse bias modes, and the multimeter beeps
continuously.

– A diode is considered open if the multimeter displays OL in both forward

and reverse bias modes.

Figure 1-16 Forward-biased diode/continuity test terminal connection and

display

Figure 1-17 Reverse-biased diode/continuity terminal connection and

42 Keysight U3401A User’s and Service Guide

display

Selecting a Range

You can allow the multimeter to select the range automatically by using
autoranging, or you can select a fixed range using manual ranging. Autoranging is
convenient because the multimeter automatically selects the appropriate range
for sensing and displaying each measurement. However, manual ranging results
in better performance, since multimeter does not have to determine which range
to use for each measurement.

– The range setting is synchronous for dual display for current or voltage

measurement. In autoranging mode, the range setting for both the primary

and secondary display are corresponding to the higher range of two displays.

Getting Started 1

Selects autoranging and disable manual ranging. Press to toggle
in and out of the manual ranging and autoranging.

Selects a higher range and disable autoranging.

Selects a lower range and disable autoranging.

– Manual ranging — If the input signal is greater than can be measured on the

selected range, the multimeter will display an overload indication, OL on the

primary or secondary display front panel.

– The multimeter remembers the selected ranging method (auto or manual) and

the selected manual range for each measurement function.

– Autorange thresholds - The multimeter shifts ranges as follows:

– Down range at < 5% of current range.

– Up range at > full scale of current range.

– Table 1-4 shows the summary of range scale values respectively.

Keysight U3401A User’s and Service Guide 43

1 Getting Started

Tab le 1-4 Range scale value

Measurement function Range Auto ranging

DCV 500.000 mV, 5.000 V, 50.000 V, 500.000 V, 1000.00 V 

ACV , DCV + ACV 500.000 mV, 5.000 V, 50.000 V, 500.000 V, 750.000 V 

DCI , ACI , DCI + ACI 500.000 μA, 5.000 mA, 50.000 mA, 500.000 mA 

DCI, ACI , DCI + ACI 5.000 A, 10.000 A

Frequency 500.000 Hz, 5.000 kHz, 500.000 kHz, 500.000 kHz 



[a]

Resistance

500.000 Ω, 5.000 kΩ, 50.000 kΩ, 500.000 kΩ, 5.000 MΩ,

50.000 MΩ



Diode test 2.3000 V Fixed range

Continuity

Notes:

[a] You are required to select the range manually when a signal is applied to the A terminal.

500.000, 5.000 k, 50.000 k, 500.000 k, 5.000 M, 50.000 MΩ
(Continuity Mode)



44 Keysight U3401A User’s and Service Guide

Keysight U3401A 4 ½ Digit Dual Display Multimeter
User’s and Service Guide

2 Operations and Features

Operating Math Functions 46

Using the Secondary Display 57

This chapter explains the various functions and features available on the U3401A
digital multimeter.

45

2 Operations and Features

Operating Math Functions

Table 2-1 presents a summary of the math operations that can be used with each

measurement function.

Tab le 2-1 Math operations for different measurement functions

Measurement function

DCV 

DCI

Resistance

ACV 

ACI

Frequency

Diode/Continuity

dBm Rel Min Max Comp Hold %

—



——

—

—





——

Allowed math operations





– All math operations can be toggled on and off by selecting the same math

operation.

– Only one math operation can be turned-on at a time. When selecting another

math operation when one is already on, you are required to turn off the first
operation and then turn-on the second math operation.

– All math operations are automatically turned-off when changing the

measurement functions.

– Range changing is allowed for all math operations.

46 Keysight U3401A User’s and Service Guide

dBm

Operations and Features 2

The logarithmic dBm (decibels relative to one milliwatt) scale is often used in RF
signal measurements. The multimeter’s dBm operation takes a measurement and
calculates the power delivered to a reference impedance (typically 50, 75 or 600 Ω).
The formula used for conversion from the voltage reading is:

dBm = 10 x Log

Figure 2-1 Typical dBm operation display

The default reference impedance value is 600 Ω.. You can select the following
21 reference impedance values:

2 Ω, 4 Ω, 8 Ω, 16 Ω, 50 Ω, 75 Ω, 93 Ω, 110 Ω, 124 Ω, 125 Ω, 135 Ω, 150 Ω, 250 Ω,
300 Ω, 500 Ω, 600 Ω, 800 Ω, 900 Ω, 1000 Ω, 1200 Ω, 8000 Ω.

The dBm operation can be applied to DCV, ACV and DCV + ACV measurement
functions only. The multimeter displays the dBm modifier on the primary display
and displays the reference impedance selection on the secondary display.

[1000 x (Reading2 / reference impedance)]

10

Procedure 1

1 Press to enable the dBm modifier mode and dBm operation.

2 Use and to select the desired reference impedance.

Keysight U3401A User’s and Service Guide 47

2 Operations and Features

Rel

When making Rel (relative) measurements, each reading is the difference
between a stored relative value and the input signal. For example, this feature can
be used to make more accurate resistance measurements by nulling the test lead
resistance.

After you enable the Rel operation, the multimeter stores the next reading as
a Rel # (reference value) and immediately displays on the primary display:

Primary Display = Reading – Rel #

When the Rel operation is enabled in autoranging mode, enabling the Comp or
Percentage operation will disable the Rel operation.

Procedure

1 Press to exit the relative mode.

Figure 2-2 Typical Rel operation display

48 Keysight U3401A User’s and Service Guide

MinMax

Elapsed time

Elapsed time

Operations and Features 2

The MinMax (Minimum/Maximum) operation stores the minimum and maximum
values of reading during a series of measurements.

When enabled, the MinMax operation turns on the MINMAX annunciator and
begins accumulating various statistics of the readings being displayed.

Figure 2-3 Typical Max operation display

Figure 2-4 Typical Min operation display

Each time a new minimum or maximum value is stored, the multimeter beeps
once (if the beeper is enabled) and briefly turns on the appropriate MAX or MIN
annunciator.

Accumulated statistics are:

– MAX—maximum reading since MinMax was enabled

– MIN—minimum reading since MinMax was enabled

– MINMAX—actual readings

Keysight U3401A User’s and Service Guide 49

2 Operations and Features

The elapsed time is recorded when the MinMax operation is selected. The elapsed
time is shown on the secondary display with HH.MM.SS.

– HH is 0-19 hours

– MM is 0-59 minutes

– SS is 0-59 seconds

Procedure

1 Press to enable MinMax operation.

2 Press continuously until the desired operation appear. The MinMax

operation will display MINMAX > MAX > MIN > MINMAX in sequence when
this key is press continuously.

3 Press to disable the MinMax operation.

50 Keysight U3401A User’s and Service Guide

Comp

Operations and Features 2

The Comp (compare) operation allows you to perform pass/fail testing against
specified upper and lower limits. You can set the upper and lower limits to any
value between 0 and ±100% of the highest range for the present operation.

Figure 2-5 Typical Comp operation display

When enabled, the actual readings are shown in primary display and the
comparison results such as HI, LO or PASS is shown in secondary display.

– You should specify the upper limit to always be a more positive number than

the lower limit. The initial factory setting for each limit is 0.

– The secondary display shows PASS when readings are within the specified

limits. The secondary display shows HI when the reading is outside the high

limit and LO when the reading is outside the low limit.

– When the beeper is ON (see “Using the setup menu” on page 59), the beeper

beeps three tones on the transition from PASS to HI or LO. When transitioning

from HI or LO to PASS, it will only beep once.

– Press to enable Comp operation.

Keysight U3401A User’s and Service Guide 51

2 Operations and Features

Procedure

1 Press to enter the upper limit setup mode. The upper limit is

shown on primary display while the HI annunciator is shown on secondary
display.

2 Use , , , and to modify the upper limit.

3 Press to store the specified HI limit value.

4 Press to enter the lower limit setup mode.

The lower limit is shown on primary display while the LO annunciator is shown
on secondary display.

5 Use , , , and to modify the lower limit.

6 Press to store the specified LO limit value.

52 Keysight U3401A User’s and Service Guide

Hold

Operations and Features 2

The reading hold feature allows you to capture and hold a reading on the front
panel display. When enabled, the Hold operation turns on the HOLD annunciator
and hold the reading.

Procedure

1 Press to hold the reading on the display.

Figure 2-6 Typical Hold operation display

Refresh Hold

The refresh hold operation allows you to take measurement in dangerous or
difficult measuring field and you could not look at the display. This operation will
update the hold value with a new measurement value automatically, and thus
reminds you with a beep.

Procedure

1 Press to access to the Setup menu.

2 Use and to select the rHold.

3 Press to enter the second tier menu. Use and to set the

state to ON.

Keysight U3401A User’s and Service Guide 53

2 Operations and Features

NOTE

4 Press to confirm.

5 Press twice quit the Setup menu.

6 Press to select refresh hold mode. The present value will be held and the

HOLD will be lit. The multimeter is now ready to hold a new measurement

value once the variation of measuring value exceeds the setting of the
variation count. The HOLD annunciator will be blinking continuously.

7 When the refresh hold is not in use, repeat step 1 to step 4 to turn off the

refresh hold’s state.

Figure 2-7 Typical refresh hold operation display

– For voltage and current measurements, the held value will not be updated

when the reading is below 500 counts.

– For resistance and diode measurements, the held value will not be updated

when the reading is at OL or open state.

54 Keysight U3401A User’s and Service Guide

Percentage (%)

This operation allows you to transfer the measurement value with a proportional
percentage display. You can set the upper limit (HI) and lower limit (LO) to any
value between 0 and ±100% of the highest range for the present function.

The percentage operation calculates and display the measurement value using
the equation below:

Percentage (%) = [Measurement value – LO/(HI-LO)] x 100%]

When the HI limit is equal to LO limit, the percentage operation will use the
equation as below:

Percentage (%) = [(Measurement value – HI)/HI] x 100%]

Figure 2-8 Typical percentage (%) operation display

Operations and Features 2

When enabled, the actual readings are shown in primary display and the
percentage’s result is shown in secondary display.

– The secondary display shows OL when readings exceed the maximum display

of 999.99%.

– When autoranging is enabled, this operation will be used to lock the current

range.

Keysight U3401A User’s and Service Guide 55

2 Operations and Features

Procedure

1 Press to enter the upper limit setup mode. The upper limit is

shown on primary display while the HI annunciator is shown on secondary
display.

2 Use , , , and to modify the upper limit.

3 Press to store the specified HI limit value.

4 Press to enter the lower limit setup mode.

The lower limit is shown on primary display while the LO annunciator is shown
on secondary display.

5 Use , , , and to modify the lower limit.

6 Press to store the specified LO limit value.

7 Press to enable percentage operation.

8 Press to disable percentage operation.

56 Keysight U3401A User’s and Service Guide

Using the Secondary Display

Secondary
display

Figure 2-9 Secondary display

To enable the secondary d isplay mode:

Repeatedly pressing cycles through the secondary display choices for the
present math operation as shown in Table 2-2 on page 58.

To disable the secondary d isplay mode:

Operations and Features 2

Press . The display will remain in primary display mode.

Keysight U3401A User’s and Service Guide 57

2 Operations and Features

Tab le 2-2 Description for dual display combination

Secondary display

Primary display

DCV Frequency

ACV Frequency

ACV + DCV Frequency

Defaul t
secondary
display

Press secondary
display once

[b]

ACV

[b]

DCV

[b]

ACV

Press secondary
display twice

dBm —

dBm —

[b]

DCV

dBm ACV DVC ACV+DCV —

DCI Frequency

ACI Frequency

ACI + DCI Frequency

Frequency

[a]

ACV ACI — —

ACI

DCI

ACI

[b]

[b]

[b]

——

——

[b]

DCI

COMP (Measuring Value) HI, LO, PASS — — —

Percentage (Measuring Value) %— — —

Notes:

[a] The Frequency reading is corresponding to the current or voltage input signal respectively. The Frequency measurement is always working

on autoranging mode. The Buttons of AUTO, UP and DOWN are used to select the range of measuring signal. If the current measurement is
set before selecting Hz function, the default will show ACI first, else show ACV.

[b] In autoranging mode, the ranges setting of both the primary and secondary display are corresponding to the higher range of two displays.

Whereas in manual range, the ranges of secondary display are the same as the primary display.

Press
secondary display
three times

dBm

—

58 Keysight U3401A User’s and Service Guide

Using the setup menu

The Setup menu allows you to customize a number of non-volatile instrument
configurations. The content of the Setup menu are shown in Table 2-3.

.

Tab le 2-3 Setup menu and communications parameters

Operations and Features 2

First tier
menu

rS232

Ref Ω

bEEP Beeper selection

rHold Refresh hold

Notes:

[a] For calibration use only.

[b] Variation count is used to recognize new value will be updated once the variation of measuring value is esceeded the setting value.

Description

RS232 interface

[a]

parameters

Reference
impedance

Second tier
menu

bAUd

PArtY

dAtA

StoP Stop bit. 1 1 or 2

Echo

Print

bEEP Enable or disable beep operation. ON ON or OFF

bEEPF Beep frequency. 4096 Hz 4096, 2048, 1024 8192 Hz

StAtE State. OFF ON or OFF

Count

Description

Baud rate for remote
communication with a PC (remote
control).

Parity bit for remote
communication with a PC.

Data bit length for remote
communication with a PC.

ECHO. Return a character to PC in
remote communication.

Printer-Only. Print measured data
to a PC in remote communication.

Variation count.

[b]

Defaul t
factory
setting

9600

None None, odd or even

8 7 or 8

OFF ON or OFF

OFF ON or OFF

600 Ω

300

Available settings

9600, 4800, 2400, 1200,
600 and 300

8000 Ω, 1200 Ω, 1000 Ω,
900 Ω, 800 Ω, 600 Ω,
500 Ω, 300 Ω, 250 Ω,
150 Ω, 135 Ω, 125 Ω,
124 Ω, 110 Ω, 93 Ω, 75 Ω,
50 Ω, 16 Ω, 8 Ω, 4 Ω, 2 Ω

100, 200, 300, 400, 500,
600, 700, 800, 900, 1000.

Keysight U3401A User’s and Service Guide 59

2 Operations and Features

Changing the configurable settings

The parameters in the Setup Menu can be configured by using the following
procedures:

1 Press to access to the Setup Menu.

2 Press and to select the desired configurable items in the first tier

menu.

3 Press to enter second tier menu. The original parameter is indicated in

primary display.

4 Use or to select the desired parameter.

5 Press to confirm the selected parameter or press to quit from the

tier menu without saving the changes.

6 After saving the changes, press to quit from the tier menu.

7 Press again to quit from the setup menu.

8 The configuration settings is saved and main display is displayed.

60 Keysight U3401A User’s and Service Guide

Trigger mode

This multimeter has two types of trigger mode.

– Internal — triggers measurements continuously.

– External — triggers a measurement only when a direction is given.

The external trigger is used with a delay settling that has been set by the
multimeter automatically. The amount of trigger delay varies depending on
different function. When external trigger is enabled, the multimeter determines
the range for the primary display based on the input at that time.

Autoranging response time is required before a reading is displayed when you
change the input after a trigger is received.

Procedure

1 Press to enter trigger mode and standby condition. The TRIG

annunciator will be lit and display is indicated with “–––––”.

2 Press to get a new value. After a measurement, the result will be

indicated and held on the display.

Operations and Features 2

3 Press to get a new value again.

4 Press , or to select autoranging or manual range as

necessary.

5 Press to disable external trigger operation mode.

Figure 2-10 Typical trigger mode display

Keysight U3401A User’s and Service Guide 61

2 Operations and Features

NOTE

– All math operations will be disabled when external trigger is enabled.

– Press may also disable external trigger.

– Both the primary and secondary display will only appear when frequency

operation is selected in trigger mode.

62 Keysight U3401A User’s and Service Guide

Keysight U3401A 4 ½ Digit Dual Display Multimeter
User’s and Service Guide

3 Application Tutorial

Applications for Using Dual Display 64

Dual Display Operation Examples 65

This chapter describes the advanced features and the possible applications for
effective operation of the multimeter.

63

3 Application Tutorial

Applications for Using Dual Display

The dual display feature in the multimeter can be used to enhance test and
measurement capabilities. See Tab le 3-1 for the available combinations and
application when using dual display.

Tab le 3-1 Typical combinations and applications when using dual display

No. Primary d isplay Secondary display Applications

1 DCV ACV – Test DC to AC or AC to DC converter circuit.

2 ACV + DCV DCV

3 ACV Frequency – Measuring AC frequency response of amplifier circuit.

4ACI Frequency

5 DCI ACI – Measuring AC ripple and DC current of power supply.

6 ACI + DCI DCI

7dBm Reference Ω – Setting dB reference impedance and show dBm.

8 dBm DCV – Indicating DC voltage and dBm.

– Measure DC level and AC ripple of power supply.

– Adjusting AC motor control.

– Measuring current dissipation for power supply analysis.

9 dBm ACV – Indicating AC voltage and dBm.

64 Keysight U3401A User’s and Service Guide

Dual Display Operation Examples

NOTE

This section describes some practical operations when using dual display feature.

Measure DC Voltage and AC Ripple on a Rectification Circuit

A single measurement for both DC voltage and AC ripple can be displayed
through both displays while testing a rectifier circuit.

1 Connect the red and black test leads to the input terminal and probe the test

points as shown in Figure 3-1.

+

AC/DC v olta ge

source

–

Application Tutorial 3

Figure 3-1 Connection terminal when measuring DC voltage and AC ripple

2 Press to select DC voltage measurement in primary display.

3 Press to select AC voltage measurement for secondary display.

4 Press . Use and to select autoranging or manual range for

secondary display.

– Press to disable the secondary display.

– Press to select the suitable range if DCV+ACV ripple is above the scale

of the current range.

Keysight U3401A User’s and Service Guide 65

3 Application Tutorial

WARNING

NOTE

Measure AC and DC Current on a Rectification Circuit

A single measurement for both AC current and DC current can be displayed
through both displays while testing a rectifier circuit.

– Make sure you select the correct input terminal according to the input

range used.

– Do not apply current exceeding specified range to input terminals of mA

or A.

1 Connect the red and black test leads to the input terminal and probe the test

points as shown in Figure 3-2.

+

AC/DC current

source

–

Figure 3-2 Connection terminal when using DC current and AC ripple

2 Press to select AC current measurement for primary display.

3 Press to enable the DC current measurement for secondary display.

4 Press , or to select autoranging or manual range for

secondary display.

Press to disable the secondary display.

66 Keysight U3401A User’s and Service Guide

Measure AC Voltage and Frequency on an AC Circuit

NOTE

A single measurement for both AC voltage and frequency can be displayed
through both displays while testing a rectifier circuit.

1 Connect the red and black test leads to the input terminal and probe the test

points as shown in Figure 3-3.

+

AC vol tage

source

–

Figure 3-3 Connection terminal when measuring AC Voltage and

Frequency

Application Tutorial 3

2 Press to select AC voltage measurement for primary display.

3 Press to select frequency measurement for secondary display.

4 Press , or to select autoranging or manual range for

secondary display.

Press to disable the secondary display.

Keysight U3401A User’s and Service Guide 67

3 Application Tutorial

WARNING

Measure Resistance

Do not apply voltage exceeding 500 V PEAK between and COM
input terminals.

1 Connect a resistor under test to and LO input terminals as shown in

Figure 3-4.

+

Resistance

–

Figure 3-4 Connection terminal when measuring Resistance

2 Press to select resistance measurement.

3 Press . Use and to select autoranging or manual range for

primary display.

68 Keysight U3401A User’s and Service Guide

Measure True RMS AC + DC

NOTE

The multimeter can measure the true RMS of AC voltage and AC current.

1 Press , and or and simultaneously. The

multimeter will measure the DC and AC signals alternatively, calculate and

display the AC+DC RMS value using the quation below:

AC+DC (RMS) = DC

When AC+DC voltage measurement is selected, the DCV input impedance is
paralleled with the AC coupled 1.1 MΩ AC divider.

2

+ AC

Application Tutorial 3

2

Keysight U3401A User’s and Service Guide 69

3 Application Tutorial

THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK.

70 Keysight U3401A User’s and Service Guide

Keysight U3401A 4 ½ Digit Dual Display Multimeter

WARNING

User’s and Service Guide

4 Performance Test

Calibration Overview 72

Recommended Test Equipment 73

Test Considerations 74

Performance Verification Tests Overview 75

This chapter contains performance test procedures and calibration procedures.
The performance tests procedures allow you to verify that the multimeter is
operating within its published specifications.

– Shock hazard. Only service-trained personnel who are aware of the

hazards involved should perform the procedures in this chapter. To avoid

electrical shock and personal injury, make sure to read and follow all test

equipment safety instructions.

– Use only completely electrically insulated test lead sets with connectors

that prevent contact with test voltages.

71

4 Performance Test

NOTE

Calibration Overview

Make sure you have read “Test Considerations” on page 74 before calibrating the
instrument.

Keysight Technologies calibration services

When your instrument is due for calibration, contact your local Keysight Service
Center. The U3401A is supported on automated calibration systems at Keysight
service centres only.

Calibration interval

A one-year interval is adequate for most applications. Accuracy specifications are
warranted only if adjustment is made at regular calibration intervals. Accuracy
specifications are not warranted beyond the one-year calibration interval.
Keysight does not recommend extending calibration intervals beyond two years
for any application. When an adjustment is required, contact your local Keysight
Service Center.

72 Keysight U3401A User’s and Service Guide

Performance Test 4

Recommended Test Equipment

The test equipments recommended for the performance verification procedures
are listed below. If the exact instrument is not available, substitute calibration
standards of equivalent accuracy.

A suggested alternate method would be to use the Keysight 3458A 8½ -digit
digital multimeter to measure less accurate yet stable sources. The output value
measured from the source can be entered into the instrument as the target
calibration value.

Tab le 4-1 Recommended test equipments

Application Recommended equipment Recommended accuracy requirements

Zero calibration Shorting plug—Dual banana plug with copper wire short

between the two terminals

DC voltage Fluke 5520A < 1/5 instrument 1 year spec

DC current Fluke 5520A < 1/5 instrument 1 year spec

Resistance Fluke 5520A < 1/5 instrument 1 year spec

AC voltage Fluke 5520A < 1/5 instrument 1 year spec

AC current Fluke 5520A < 1/5 instrument 1 year spec

—

Frequency Fluke 5520A < 1/5 instrument 1 year spec

Diode Fluke 5520A < 1/5 instrument 1 year spec

Keysight U3401A User’s and Service Guide 73

4 Performance Test

NOTE

Test Considerations

For optimum performance, all procedures should comply with the following
recommendations:

– Ensure that the calibration ambient temperature is stable and between 18°C

and 28°C. Ideally the calibration should be performed at 23°C ±1°C.

– Ensure ambient relative humidity is less than 80%.

– Allow a 30 minutes warm-up period with a Shorting Plug connected to the Hi

and Lo input terminals.

– Use shielded twisted pair PTFE-insulated cables to reduce settling and noise

errors. Keep the input cables as short as possible.

– Connect the input cable shields to earth ground. Connect the calibrator Lo

source to earth ground at the calibrator except where noted in the procedures.
It is important that the Lo to earth ground connection be made at only one
place in the circuit to avoid ground loops.

Please ensure that the calibration standards and test procedures used do not
introduce add itional errors. Ideally, the standards used to verify and adjust the
instrument should be an order of magnitude more accurate than each
instrument range full-scale error specification.

74 Keysight U3401A User’s and Service Guide

Performance Verification Tests Overview

NOTE

Performance verification tests is an extensive set of tests that are recommended
as an acceptance test when you first receive the instrument.

Use the performance verification test to verify the measurement performance of
the instrument. The performance verification test uses the instrument’s
specifications listed in Chapter 6, “Characteristics and Specifications”.

Performance verification tests

The performance verification test is recommended as acceptance tests when you
first received the instrument. The acceptance test results should be compared
against the one-year test limits. After acceptance, you should repeat the
performance verification tests at every calibration interval.

If the instrument fails performance verification, adjustment or repair is required.
Contact your local Keysight Service Center for details.

Make sure you have read “Test Considerations” on page 74 before doing the
performance verification tests.

Performance Test 4

This test checks the full-scale reading accuracy of the instrument.

DC Voltage Verification Test

1 Connect the calibrator to the front panel Hi and Lo input terminals.

2 Select each function and range in the order shown in Table 4-2. Provide the

input shown in Table 4-2

3 Make a measurement and observe the result. Compare measurement results

to the appropriate test limits shown in the Tab le 4-2. (Be certain to allow for

appropriate source settling when using the Fluke 5520A).

Keysight U3401A User’s and Service Guide 75

4 Performance Test

CAUTION

Tab le 4-2 DC voltage verification test

Function Input Range Error from nominal one year

DC voltage 0.00 V 500 mV ±40 μV

0.0000 V 5 V ±0.4 mV

0.000 V 50 V ±4 mV

0.00 V 500 V ±40 mV

0.0 V 1000 V ±400 mV

450.00 mV 500 mV ±130 μV

4.5000 V 5 V ±1.3 mV

45.000 V 50 V ±13 mV

450.00 V 500 V ±130 mV

900.0 V 1000 V ±580 mV

Set the calibrator output to 0 V before disconnecting it from the multimeter
input terminals.

DC Current Verification Test

1 Connect the calibrator to the front panel Hi and Lo input connectors.

2 Select each function and range in the order shown in Table 4-3. Provide the

input shown in Table 4-3.

3 Make a measurement and observe the result. Compare measurement results

to the appropriate test limits shown in Tab le 4 - 3 . (Be certain to allow for
appropriate source settling when using the Fluke 5520A).

76 Keysight U3401A User’s and Service Guide

Performance Test 4

CAUTION

Tab le 4-3 DC current verification test

Function Input Range Error from nominal one year

DC current 0.00 μA 500 μA±0.05 μA

0.0000 mA 5 mA ±0.4 μA

0.000 mA 50 mA ±4 μA

0.00 mA 500 mA ±40 μA

450.00 μA 500 μA±0.27 μA

4.5000 mA 5 mA ±2.6 μA

45.000 mA 50 mA ±26 μA

450.00 mA 500 mA ±0.26 mA

0.0000 A 5 A ±0.5 mA

0.000 A 10 A ±5 mA

4.5000 A 5 A ±11.7 mA

9.000 A 10 A ±27 mA

Connect calibrator to multimeter’s A and Lo terminals before applying 10 A.

Keysight U3401A User’s and Service Guide 77

4 Performance Test

Resistance Verification Test

Configuration: 2-Wire Ω

1 Select the resistance function.

2 Select each range in the order shown in Table 4-4. Provide the resistance value

indicated. Compare measurement results to the appropriate test limits shown
in Table 4-4. (Be certain to allow for appropriate source settling).

Tab le 4-4 2-wire Ω verification test

Function Input Range Error from nominal one year

2-wire Ω

0.00 Ω 500 Ω

0.0000 kΩ 5 kΩ

0.000 kΩ 50 kΩ ±3 Ω

0.00 kΩ 500 kΩ ±30 Ω

0.0000 MΩ 5 MΩ ±300 Ω

0.000 MΩ 50 MΩ ±3 kΩ

450.00 Ω 500 Ω

4.5000 kΩ 5 kΩ

±50 mΩ

[a]

±0.3 Ω

±500 mΩ

[a]

±4.8 Ω

[a]

[a]

45.000 kΩ 50 kΩ ±48 Ω

450.00 kΩ 500 kΩ ±480 Ω

4.5000 MΩ 5 MΩ ±4.8 kΩ

30.000 MΩ 50 MΩ ±93 kΩ

Notes:

[a] Specifications are for 2-wire ohms function using the Rel operation enabled to eliminate lead resistance.

78 Keysight U3401A User’s and Service Guide

Performance Test 4

Diode Verification Test

Configuration: Diode

1 Connect the calibrator to the front panel Hi and Lo input terminals.

2 Select each function and range in the order shown in Table 4-5. Provide the

input shown in Table 4-5.

3 Make a measurement and observe the result. Compare measurement results

to the appropriate test limits shown in Table 4-5. (Be certain to allow for

appropriate source settling when using the Fluke 5520A).

Tab le 4-5 Diode verification test

Function Voltage Range Error from nominal one year

Diode 1.0000 V 2.3 V ±1 mV

2.0000 V 2.3 V ±1.5 mV

Frequency Verification Test

Configuration: Frequency

1 Select the frequency function.

2 Select each range in the order shown in Table 4-6. Provide the input voltage

and frequency indicated. Compare measurement results to the appropriate

test limits shown in Tab le 4-6. (Be certain to allow for appropriate source

settling).

Tab le 4-6 Frequency verification test

Function Vol tage Input frequency Range Error from nominal one year

Frequency 2 V 4.5 kHz 5 kHz ±0.7 Hz

Keysight U3401A User’s and Service Guide 79

4 Performance Test

CAUTION

AC Voltage Verification Test

Configuration: AC volts

1 Select the AC voltage function.

2 Select each range in the order shown in Tab l e 4-7. Provide the indicated input

voltage and frequency. Compare measurement results to the appropriate test
limits shown in Tab le 4 - 7 . (Be certain to allow for appropriate source settling).

Tab le 4-7 AC volts verification test

Function V RMS Input frequency Range Error from nominal one year

AC voltage 50.00 mV 1 kHz 500 mV ±650 μV

450.00 mV 1 kHz 500 mV ±2.65 mV

0.5000 V 1 kHz 5 V ±3.2 mV

4.5000 V 1 kHz 5 V ±17.2 mV

5.000 V 1 kHz 50 V ±32 mV

45.000 V 1 kHz 50 V ±172 mV

50.00 V 1 kHz 500 V ±400 mV

450.00 V 1 kHz 500 V ±2.4 V

75.0 V 1 kHz 750 V ±1.8 V

675.0 V 1 kHz 750 V ±4.8 V

Set the calibrator output to 0 V before disconnecting it from the multimeter
input terminals.

80 Keysight U3401A User’s and Service Guide

Performance Test 4

AC Current Verification Test

Configuration: AC current

1 Select the AC current function.

2 Select each range in the order shown in Table 4-8. Provide the input current

and frequency indicated. Compare measurement results to the appropriate test

limits shown in Table 4-8. (Be certain to allow for appropriate source settling).

Tab le 4-8 AC current verification test

Function Current Input frequency Range Error from nominal one year

AC current 50.00 μA 1 kHz 500 μA ±0.45 μA

450.00 μA 1 kHz 500 μA ±2.45 μA

0.5000 mA 1 kHz 5 mA ±4.5 μA

4.5000 mA 1 kHz 5 mA ±24.5 μA

5.000 mA 1 kHz 50 mA ±45 μA

45.000 mA 1 kHz 50 mA ±0.245 mA

50.00 mA 1 kHz 500 mA ±0.45 mA

450.00 mA 1 kHz 500 mA ±2.45 mA

0.5000 A 1 kHz 5 A ±5.5 mA

1.000 A 1 kHz 10 A ±35 mA

4.5000 A 1 kHz 5 A ±25.5 mA

9.000 A 1 kHz 10 A ±75 mA

Keysight U3401A User’s and Service Guide 81

4 Performance Test

THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK.

82 Keysight U3401A User’s and Service Guide

Keysight U3401A 4 ½ Digit Dual Display Multimeter
User’s and Service Guide

5 Disassembly and Repair

Operating Checklist 84

Types of Service Available 85

Mechanical Disassembly 89

Replaceable Parts 95

This chapter will help you troubleshoot a faulty multimeter. It describes how to
disassemble the multimeter, how to obtain repair services, and lists the
replaceable parts.

83

5 Disassembly and Repair

Operating Checklist

Before returning your multimeter to Keysight for service or repair check the
following items:

Is the multimeter inoperative?

Verify the power line voltage setting.

?

Verify the power line fuse is installed.

?

Check the power cord is connected to multimeter and to AC line power.

?

Verify the front panel power switch is depressed.

?

See page 86

Is the mutimeter’s current input inoperative?

Verify the current input fuse.

?

84 Keysight U3401A User’s and Service Guide

Types of Service Available

If your instrument fails during the warranty period, Keysight Technologies will
repair or replace it under the terms of your warranty. After your warranty expires,
Keysight offers repair services at competitive prices.

Extended service contracts

Many Keysight products are available with optional service contracts that extend
the covered period after the standard warranty expires. If you have such a service
contract and your instrument fails during the covered period, Keysight
Technologies will repair or replace it in accordance with the contract.

Obtaining repair service (worldwide)

To obtain service for your instrument (in-warranty, under service contract, or
post-warranty), contact your nearest Keysight Technologies Service Center. They
will arrange to have your instrument repaired or replaced, and can provide
warranty or repair-cost information where applicable.

To obtain warranty, service, or technical support information you can contact
Keysight Technologies at one of the following telephone numbers:

In the United States: (800) 829–4444

Disassembly and Repair 5

In Europe: 31 20 547 2111

In Japan: 0120–421–345

Or use our Web link for information on contacting Keysight worldwide:

www.keysight.com/find/assist

Or contact your Keysight Technologies representative.

Before shipping your instrument, ask the Keysight Technologies Service Center to
provide shipping instructions, including what components to ship. Keysight
recommends that you retain the original shipping carton for use in such
shipments.

Keysight U3401A User’s and Service Guide 85

5 Disassembly and Repair

Repackaging for shipment

If the instrument is to be shipped to Keysight for service or repair, be sure to:

– Attach a tag to the unit identifying the owner and indicating the required

service or repair. Include the model number and full serial number.

– Place the unit in its original container with appropriate packaging material for

shipping.

– Secure the container with strong tape or metal bands.

– If the original shipping container is not available, place your instrument in a

container which will ensure at least 4 inches of compressible packaging
material around all sides for the instrument. Use static-free packaging
materials to avoid additional damage to your instrument.

Keysight suggests that you always insure shipments.

Cleaning

Clean the outside of the multimeter with a soft, lint-free, slightly dampened cloth.
Do not use detergent. Disassembly is not required or recommended for cleaning.

86 Keysight U3401A User’s and Service Guide

Disassembly and Repair 5

2 Remove the line voltage selector from

fuse holder assembly.

1 Disconnect the power cord. Depress tab 1 and

2 and pull the fuse holder from rear panel.

1

2

4 Replace fuse holder assembly in

rear panel.

3 Rotate the line voltage selector and

reinstall it back, so that the correct voltage
appears in the fuse holder window.

To replace the power line fuse

The power line fuse is located within the multimeter’s fuse-holder assembly on
the rear panel. The multimeter is shipped from the factory with a power-line fuse
installed (according to country of destination). See Table 5-1. If you determine
that the fuse is faulty, replace it with one of the same size and rating.

Tab le 5-1 Type of supplied fuse (according to country of destination)

Type of fuse (time-lag, low breaking fuse) Input line vol tage Part number

0.25A, 250V, 5x20 mm 100 V to 120 V A02-62-25592-3U

0.125A, 250V, 5x20 mm 220 V to 240 V A02-62-25648-1U

Keysight U3401A User’s and Service Guide 87

5 Disassembly and Repair

To replace a current input fuse

Both the mA and the A current input terminals are fuse protected. The fuse for the
mA input terminal is located on the front panel (see page 32). The fuse is a 0.63 A,
500 V fuse (refer to Table 5-2). If you determine that the fuse is faulty, replace it
with one of the same size and rating.

The fuse for the A current input terminal is located inside the multimeter (see

page 93) and requires partial disasembly of the multimeter. The fuse is a 25 A,

440 V fast-acting fuse (refer to Table 5-2). If you determine that the fuse is faulty,
replace it with one of the same size and rating.

Tab le 5-2 Type of current input fuse

Type of fuse Part number

0.63 A, 500 V fuse 2110-1432

25 A, 440 V fast-acting fuse 2110-1431

Electrostatic Discharge (ESD) precautions

Almost all electrical components can be damaged by electrostatic discharge
(ESD) during handling. Component damage can occur at electrostatic discharge
voltages as low as 50 volts.

The following guidelines will help prevent ESD damage when servicing the
instrument or any electronic device.

– Disassemble instruments only in a static-free work area.

– Use a conductive work area to reduce static charges.

– Use a conductive wrist strap to reduce static charge accumulation.

– Minimize handling.

– Keep replacement parts in original static-free packaging.

– Remove all plastics, foam, vinyl, paper, and other static-generating materials

from the immediate work area.

– Use only anti-static solder suckers.

88 Keysight U3401A User’s and Service Guide

Mechanical Disassembly

WARNING

For procedures in this manual, the following tools are required for disassembly:

– T15 Torx driver

– T20 Torx driver (most disassembly)

– #2 Pozi-drive screw driver

Shock hazard. Only service–trained personnel who are aware of the hazards
involved should remove the instrument covers. To avoid electrical shock and
personal injury, make sure to disconnect the power cord from the instrument
before removing the covers. Some circuits are active and have power applied
even when the power switch is turned off.

General Disassembly

1 Remove power and all cables from the instrument.

2 Remove the carrying handle by rotating the handle upright and pulling out

from the sides of the instrument.

Disassembly and Repair 5

Keysight U3401A User’s and Service Guide 89

5 Disassembly and Repair

3 Remove the instrument bumpers. Pull from a corner and stretch the bumpers

off the instrument.

4 Remove the rear bezel. Loosen the two captive screws in the rear bezel and

remove the rear bezel.

90 Keysight U3401A User’s and Service Guide

Disassembly and Repair 5

5 Remove the cover. Remove the screw in the bottom of the cover and slide the

cover off the instrument.

Front Panel Removal

1 Remove on/off switch push rod. Gently move the power switch push rod

toward the front of the instrument to disengage it from the switch. Be careful

not to twist or bend the push rod.

Keysight U3401A User’s and Service Guide 91

5 Disassembly and Repair

2 Remove the screw holding the front panel.

3 Disconnect the two ribbon cable connectors from the front panel.

92 Keysight U3401A User’s and Service Guide

Disassembly and Repair 5

25 A current

fuse

4 Disconnect the individual front panel wires shown below.

5 There is now enough play to allow the side of the front panel to be pried from

the chassis and removed as an assembly.

Keysight U3401A User’s and Service Guide 93

5 Disassembly and Repair

Front Panel Disassembly

1 Remove the keyboard and display assembly. Remove the two screws holding

the circuit board. Lift the keyboard and display assembly from the plastic
housing.

a The rubber keypad can now be pulled from the plastic housing.

94 Keysight U3401A User’s and Service Guide

Replaceable Parts

This section contains information for ordering replacement parts for your
instrument. You can find the instrument support part list at Keysight’s
Test & Measurement Parts Catalog at http://www.keysight.com/find/parts.

This parts list includes a brief description of each part with applicable Keysight
part number.

To order replaceable parts

You can order replaceable parts from Keysight using the Keysight part number.
Note that not all parts listed are available as field-replaceable parts.

To order replaceable parts from Keysight, do the following:

1 Contact your nearest Keysight Sales Office or Service Center.

2 Identify the parts by the Keysight part number shown in the support parts list.

3 Provide the instrument model number and serial number.

Disassembly and Repair 5

Keysight U3401A User’s and Service Guide 95

5 Disassembly and Repair

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96 Keysight U3401A User’s and Service Guide

Keysight U3401A 4 ½ Digit Dual Display Multimeter
User’s and Service Guide

6 Characteristics and

Specifications

For the characteristics and specifications of the U3401A 4 ½ Digit Dual Display
Multimeter, refer to the datasheet at

http://literature.cdn.keysight.com/litweb/pdf/5990-3970EN.pdf.

97

6 Characteristics and Specifications

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98 Keysight U3401A User’s and Service Guide

This information is subject to change
without notice. Always refer to the
Keysight website for the latest
revision.

© Keysight Technologies 2009 - 2017
Edition 14, November 1, 2017

Printed in Malaysia

*U3401-90001*

U3401-90001

www.keysight.com