Agilent 6050A Operations Guide

Operating Manual

Electronic Load Mainframes

HP Models 6050A and 6051A

HP Part No. 5959-3368

For instruments with Serial Numbers:

HP6050A-2908A-00101 and Above
HP6051A-2927A-00101 and Above

Microfiche Part No. 5959-3369 Printed in USA: October, 1997

CERTIFICATION

Hewlett-Packard Company certifies that this product met its published specifications at time of shipment from the factory.
Hewlett-Packard further certifies that its calibration measurements are traceable to the United States National Bureau of
Standards, to the extent allowed by the Bureau's calibration facility, and to the calibration facilities of other
International Standards Organization members.

WARRANTY

This Hewlett-Packard hardware product is warranted against defects in material and workmanship for a period of three
years from date of delivery. HP software and firmware products, which are designated by HP for use with a hardware
product and when properly installed on that hardware product, are warranted not to fail to execute their programming
instructions due to defects in material and workmanship for a period of 90 days from date of delivery. During the warranty
period Hewlett-Packard Company will, at its option, either repair or replace products which prove to be defective. HP does
not warrant that the operation of the software, firmware, or hardware shall be uninterrupted or error free.

For warranty service, with the exception of warranty options, this product must be returned to a service facility designated
by HP. Customer shall prepay shipping charges by (and shall pay all duty and taxes) for products returned to HP for
warranty service. Except for products returned to Customer from another country, HP shall pay for return of products to
Customer.

Warranty services outside the country of initial purchase are included in HP's product price, only if Customer pays HP
international prices (defined as destination local currency price, or U.S. or Geneva Export price).

If HP is unable, within a reasonable time to repair or replace any product to condition as warranted, the Customer shall be
entitled to a refund of the purchase price upon return of the product to HP.

LIMITATION OF WARRANTY

The foregoing warranty shall not apply to defects resulting from improper or inadequate maintenance by the Customer,
Customer-supplied software or interfacing, unauthorized modification or misuse, operation outside of the environmental
specifications for the product, or improper site preparation and maintenance. NO OTHER WARRANTY IS EXPRESSED
OR IMPLIED. HP SPECIFICALLY DISCLAIMS THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE.

EXCLUSIVE REMEDIES

THE REMEDIES PROVIDED HEREIN ARE THE CUSTOMER'S SOLE AND EXCLUSIVE REMEDIES. HP SHALL
NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
WHETHER BASED ON CONTRACT, TORT, OR ANY OTHER LEGAL THEORY.

ASSISTANCE

The above statements apply only to the standard product warranty. Warranty options, extended support contracts,
product maintenance agreements and customer assistance agreements are also available. Contact your nearest Hewlett­Packard Sales and Service office for further information on HP's full line of Support Programs.

2

SAFETY SUMMARY

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. Hewlett-Packard Company assumes no liability for
the customer's failure to comply with these requirements.

BEFORE APPLYING POWER.

Verify that the product is set to match the available line voltage and the correct fuse is installed.

GROUND THE INSTRUMENT.

This product is a Safety Class 1 instrument (provided with a protective earth terminal). To minimize shock hazard, the instrument
chassis and cabinet must be connected to an electrical ground. The instrument must be connected to the ac power supply mains through
a three-conductor power cable, with the third wire firmly connected to an electrical ground (safety ground) at the power outlet. For
instruments designed to be hard-wired to the ac power lines (supply mains), connect the protective earth terminal to a protective
conductor before any other connection is made. Any interruption of the protective (grounding) conductor or disconnection of the
protective earth terminal will cause a potential shock hazard that could result in personal injury. If the instrument is to be energized via
an external autotransformer for voltage reduction, be certain that the autotransformer common terminal is connected to the neutral
(earthed pole) of the ac power lines (supply mains).

FUSES.

Only fuses with the required rated current, voltage, and specified type (normal blow, time delay, etc.) should be used. Do not use
repaired fuses or short circuited fuseholders. To do so could cause a shock or fire hazard.

DO NOT OPERATE IN AN EXPLOSIVE ATMOSPHERE.

Do not operate the instrument in the presence of flammable gases or fumes.

KEEP AWAY FROM LIVE CIRCUITS.

Operating personnel must not remove instrument covers. Component replacement and internal adjustments must be made by qualified
service personnel. Do not replace components with power cable connected. Under certain conditions, dangerous voltages may exist
even with the power cable removed. To avoid injuries, always disconnect power, discharge circuits and remove external voltage
sources before touching components.

DO NOT SERVICE OR ADJUST ALONE.

Do not attempt internal service or adjustment unless another person, capable of rendering first aid and resuscitation, is present.

DO NOT EXCEED INPUT RATINGS.

This instrument may be equipped with a line filter to reduce electromagnetic interference and must be connected to a properly
grounded receptacle to minimize electric shock hazard. Operation at line voltages or frequencies in excess of those stated on the data
plate may cause leakage currents in excess of 5.0 mA peak.

SAFETY SYMBOLS.

Instruction manual symbol: the product will be marked with this symbol when it is necessary for the user to refer to the
instruction manual (refer to Table of Contents) .

Indicates hazardous voltages.
Indicate earth (ground) terminal.

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

The CAUTION sign denotes a hazard. It calls attention to an operating procedure, or the like, which, if not
correctly performed or adhered to, could result in damage to or destruction of part or all of the product. Do not
proceed beyond a CAUTION sign until the indicated conditions are fully understood and met.

3

DO NOT SUBSTITUTE PARTS OR MODIFY INSTRUMENT.

Because of the danger of introducing additional hazards, do not install substitute parts or perform any unauthorized modification to the
instrument. Return the instrument to a Hewlett-Packard Sales and Service Office for service and repair to ensure that safety features
are maintained.

Instruments which appear damaged or defective should be made inoperative and secured against unintended operation until they can
be repaired by qualified service personnel.

4

SAFETY SUMMARY (continued)

GENERAL

Any LEDs used in this product are Class 1 LEDs as per IEC 825-l.

ENVIRONMENTAL CONDITIONS

This instruments is intended for indoor use in an installation category II, pollution degree 2 environment. It is designed to
operate at a maximum relative humidity of 95% and at altitudes of up to 2000 meters. Refer to the specifications tables for
the ac mains voltage requirements and ambient operating temperature range.

SAFETY SYMBOL DEFINITIONS

Symbol Description Symbol Description

Direct current Terminal for Line conductor on permanently

installed equipment

Alternating current Caution, risk of electric shock

Both direct and alternating current Caution, hot surface

Three-phase alternating current Caution (refer to accompanying documents)

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

Protective earth (ground) terminal Out position of a bi-stable push control
Frame or chassis terminal On (supply)

Terminal for Neutral conductor on
permanently installed equipment
Terminal is at earth potential(Used for
measurement and control circuits designed to
be operated with one terminal at earth
potential.)

Herstellerbescheinigung

Diese Information steht im Zusammenhang mit den Anforderungen der Maschinenläminformationsverordnung vom 18
Januar 1991.

* Schalldruckpegel Lp <70 dB(A) * Am Arbeitsplatz * Normaler Betrieb * Nach EN 27779 (Typprufung).

Manufacturer's Declaration

This statement is provided to comply with the requirements of the German Sound Emission Directive, from 18 January

1991.

Off (supply)

Standby (supply)
Units with this symbol are not completely
disconnected from ac mains when this switch
is off. To completely disconnect the unit from
ac mains, either disconnect the power cord or
have a qualified electrician install an external
switch.

* Sound Pressure Lp <70 dB(A) *At Operator Position * Normal Operation * According to EN 27779 (Type Test).

5

DECLARATION OF CONFORMITY

according to ISO/IEC Guide 22 and EN 45014

Manufacturer’s Name: Hewlett-Packard Co.
Manufacturer’s Address: New Jersey Division

150 Green Pond Road
Rockaway, NJ 07866 U.S.A.

declares that the product

Product Name: Load mainframe and modules
Model Number(s): HP 6050A, 6051A mainframes with modules

HP 60501A/B, 60502A/B, 60503A/B, 60504A/B, 60507A/B

conform(s) to the following Product Specifications:

Safety: IEC 348:1978 / HD401 S1:1981

1

EMC: CISPR 11:1990 / EN 55011:1991 Group 1, Class B

IEC 801-2:1991 / EN 50082-1:1992 4kV CD, 8 kV AD
IEC 801-3:1984 / EN 50082-1:1992 3 V/m
IEC 801-4:1988 / EN 50082-1:1992 0.5 kV Sig. Lines, 1 kV Power Lines

Supplementary Information:

The product herewith complies with the requirements of the Low Voltage Directive 73/23/EEC and the EMC
Directive 89/336/EEC and carries the CE-marking accordingly.

Note 1: The product family was introduced prior to 12/93

--------------------------------------------------------

New Jersey, January 1997 Bruce Krueger / Quality Manager

European Contact: Your local Hewlett-Packard Sales and Service Office or Hewlett-Packard GmbH,
Department TRE, Herrenberger Strasse 130, D-71034 Boeblingen (FAX:[phone])

Printing History

The current edition of this guide is indicated below. Reprints of this guide containing minor corrections and updates may
have the same printing date. New editions are identified by a new printing date and, in some cases, by a new part
number. A new edition incorporates all new or corrected material since the previous edition. Changes to the guide
occurring between editions are covered by change sheets shipped with the guide. Also, if the serial number prefix of your
power module is higher than those listed on the title page of this guide, then it may or may not include a change sheet.
That is because even though the higher serial prefix indicates a design change, that change may not affect the content of
the guide.

Edition 3 May, 1993  Copyright 1993 Hewlett-Packard Company.

.................... October, 1997

This document contains proprietary information protected by copyright. All rights are reserved. No part of this document
may be photocopied, reproduced, or translated into another language without the prior consent of Hewlett-Packard
Company. The information contained in this document is subject to change without notice.

6

If you are a first-time user, start with this manual, paying particular attention to Chapter 2. After installation (Chapter 3),
read Chapter 4 to learn front-panel operation. Programming users should then read Chapter 5 before going to the

Programming Reference Guide. Experienced programming users will probably refer only to the Programming Reference
Guide.

HP 6050A/6051A Operating Manual
HP Part No. 5959-3368
(this manual)

Specifications
System Overview
Installation Procedures
Front-Panel Operation Remote
Programming Introduction
Calibration Procedures

Module-Specific Pages

HP Models 60501A/B, 60502A/B, 60503A/B,

60504A/B, 60507B

Specifications
Programming Ranges
Factory Default Settings
Calibration Information

Hewlett-Packard Electronic Load Family

Programming Reference Guide
HP Part No. 06060-90005

Introduction to HP-SL
Introduction to Programming
Language Dictionary
Status Reporting

HP 6050A/605L4 Service Manual

Module Service Manuals

* Supplied with HP 6050A/6051A Electronic Load Mainframe.
** Supplied with individual load modules.
*** Available for purchase. Supplied with instrument if ordered as Option 910.

7

Table of Contents

1. General Information

What’s in this Manual .........................................................................................................................11

Options................................................................................................................................................11

Safety Requirements ............................................................................................................................12

Specifications ......................................................................................................................................12

2. Operation Overview

Introduction.........................................................................................................................................15

Front Panel Description.......................................................................................................................16

Remote Programming..........................................................................................................................16

Local/Remote Control..........................................................................................................................16

Extended Power Operation...................................................................................................................17

Programmable Features .......................................................................................................................17

Modes of Operation ..........................................................................................................................17

Constant Current CC (Mode)............................................................................................................18

Ranges..............................................................................................................................................18

Immediate Current Level..................................................................................................................18

Triggered Current Level ...................................................................................................................18

Transient Current Level....................................................................................................................19

Software Current Limit.....................................................................................................................19

Slew Rate..........................................................................................................................................19

Constant Resistance (CR) Mode........................................................................................................19

Ranges..............................................................................................................................................20

Immediate Resistance Level..............................................................................................................20

Triggered Resistance Level...............................................................................................................20

Transient Resistance Level................................................................................................................20

Slew Rate..........................................................................................................................................20

Constant Voltage (CV) Mode............................................................................................................20

Range...............................................................................................................................................20

Immediate Voltage Level..................................................................................................................21

Triggered Voltage Level ...................................................................................................................21

Transient Voltage Level....................................................................................................................21

Slew Rate..........................................................................................................................................21

Transient Operation..........................................................................................................................21

Continuous Transient Operation.......................................................................................................22

Pulsed Transient Operation...............................................................................................................22

Toggled Transient Operation............................................................................................................23

Triggered Operation .........................................................................................................................24

Slew Rate and Minimum Transition Time ........................................................................................25

Input Current, Voltage, and Power Measurement..............................................................................26

Short On/Off.....................................................................................................................................26

Input On/off......................................................................................................................................27

Saving and Recalling Settings...........................................................................................................27

Reading Remote Programming Errors...............................................................................................27

Status Reporting ...............................................................................................................................28

Protection Features ..............................................................................................................................28

Resetting Latched Protection.............................................................................................................28

Overvoltage ......................................................................................................................................29

8

Overcurrent ......................................................................................................................................29

Overpower........................................................................................................................................29

Overtemperature...............................................................................................................................30

Reverse Voltage................................................................................................................................30

Control Connector ...............................................................................................................................30

Remote Sensing................................................................................................................................30

Monitor Outputs ...............................................................................................................................30

External Programming Input ............................................................................................................31

Fault.................................................................................................................................................31

Port On/Off.......................................................................................................................................31

3. Installation

Introduction.........................................................................................................................................33

Inspection............................................................................................................................................33

Installing The Modules........................................................................................................................33

Procedure..........................................................................................................................................34

Channel Number ..............................................................................................................................35

Installing The Mainframes...................................................................................................................35

Cooling.............................................................................................................................................36

Rack Mounting.................................................................................................................................36

Turn-On Checkout...............................................................................................................................36

Changing Line Voltage.....................................................................................................................37

Turn-On/Selftest...............................................................................................................................38

Power Test........................................................................................................................................39

Controller Connection .........................................................................................................................39

HP-IB Address..................................................................................................................................40

Rear Panel Connectors and Switches....................................................................................................40

Input Binding Posts ..........................................................................................................................40

Control Connector ............................................................................................................................41

Sense Switch.....................................................................................................................................41

Trigger Connector ............................................................................................................................43

Application Connections......................................................................................................................43

Wiring Considerations......................................................................................................................43

Local Sense Connections ..................................................................................................................44

Remote Sense Connections ...............................................................................................................44

Parallel Connections.........................................................................................................................44

Zero-Volt Loading Connections........................................................................................................45

Table of Contents (continued)

4. Local Operation

Introduction.........................................................................................................................................49

Local Control Overview.......................................................................................................................52

Using The CHAN Keys........................................................................................................................53

Selecting the Channel.......................................................................................................................54

Identifying the Selected Channel.......................................................................................................54

Using The Function Keys.....................................................................................................................54

Turning the Input On/Off .................................................................................................................54

Setting the Mode of Operation..........................................................................................................56

Setting CC Values ............................................................................................................................56

Programming Ranges .......................................................................................................................56

9

Examples..........................................................................................................................................56

Setting CR Values ............................................................................................................................57

Programming Ranges .......................................................................................................................57

Examples.............. ...........................................................................................................................58

Setting CV Values............................................................................................................................59

Programming Range.........................................................................................................................59

Examples..........................................................................................................................................59

Transient Operation..........................................................................................................................60

Shorting the Input.............................................................................................................................61

Resetting Latched Protection.............................................................................................................61

Using The System Keys .......................................................................................................................62

Setting the HP-IB Address................................................................................................................62

Displaying Error Codes.....................................................................................................................62

Saving and Recalling Settings...........................................................................................................62

Changing "Wake-up" Settings ..........................................................................................................63

Recalling the Factory Default Values................................................................................................63

5. Remote Operation

Introduction.........................................................................................................................................65

Enter/Output Statements......................................................................................................................65

HP-IB Address.....................................................................................................................................65

Sending A Remote Command..............................................................................................................66

Selecting A Channel............................................................................................................................66

Getting Data Back ...............................................................................................................................66

Remote Programming Commands........................................................................................................67

CC Mode Example ...........................................................................................................................68

CV Mode Example ...........................................................................................................................68

CR Mode Example............................................................................................................................71

Continuous Transient Operation Example.........................................................................................71

Pulsed Transient Operation Example................................................................................................72

Synchronous Toggled Transient Operation Example.........................................................................72

Table of Contents (continued)

6. Calibration

Introduction.........................................................................................................................................75

Equipment Required............................................................................................................................75

Calibration Commands........................................................................................................................76

Calibration Flowcharts.........................................................................................................................77

Example Programs...............................................................................................................................77

A. Considerations for Operating in Constant Resistance Mode ...................................................91

Index......................................................................................................................................................93

HP Sales and Support Office................................................................................................................97

10

1

General Information

What's In This Manual

This manual applies to both the HP 6050A and HP 6051A Electronic Load mainframes. The two mainframes are
functionally identical, but the HP 6051A is a half-rack width unit, with only two slots for load modules. Most of the
information given in this manual applies to both mainframes. Where differences occur, information specific just to the
HP 6051A is given in parentheses following information that applies only to the HP 6050A, for example: ... a total of
1800
(600) watts...

This chapter contains specifications that apply to the HP 6050A and HP 6051A Electronic Load mainframes, as well as
information concerning options and safety requirements. The remaining chapters in this manual contain instructions for
installing, operating, programming, and calibrating the Electronic Load as follows

Chapter 2 "Operation Overview": describes all of the Electronic Load's functions and briefly describes how they can be

controlled locally at the front panel and/or remotely via an HP-IB controller.

Chapter 3 "Installation": provides instructions for installing load modules in the mainframe, controller and

application connections, and turn-on checkout procedures.

Chapter 4 "Local Operation": describes in detail how to operate the Electronic Load at the front panel.

Chapter 5 "Remote Operation": provides an introduction to remote programming.

Chapter 6 "Calibration": contains calibration procedures for the Electronic Load and gives sample calibration

programs. Yearly calibration intervals are recommended.

Specifications and other information pertinent to a specific load module are given in the module-specific pages provided
with each load module.

Options

Unless one of the following line voltage options is ordered, the unit is shipped from the factory set for 120 Vac, 48-63 Hz
ac input power. If Option 100, 220, or 240 is ordered, the unit will be factory set for the appropriate line voltage.
For information about changing the line voltage setting, see "Turn-On Checkout" in Chapter 3.

100: Input Power, 100 Vac, 48-63 Hz
220: Input Power, 220 Vac, 48-63 Hz
240: Input Power, 240 Vac, 48-63 Hz

Additional options are:

800: One rack mount kit for two half-rack units side by side (HP 6051A only)*
908: One rack mount kit*
909: One rack mount kit with handles (HP 6050A only)*
910: One service manual with extra Operating Manual and Programming Reference Guide

*Support rails are required for Options 800, 908, and 909.

General Information 11

Safety Requirements

This product is a Safety Class 1 instrument, which means that it is provided with a protective earth ground terminal. This
terminal must be connected to an ac source that has a 3-wire ground receptacle. Review the instrument rear panel and this
manual for safety markings and instructions before operating the instrument. Refer to the Safety Summary page at the
beginning of this manual for a summary of general safety information. Specific safety information is located at
appropriate places in this manual.

The Electronic Load is designed to comply with the following safety and environmental requirements:

• IEC 348-Safety requirements for electronic measuring apparatus.

• CSA 22.2 No. 231-Electronic instruments and scientific apparatus for special use and applications.

• UL 1244-Electrical and electronic measuring and testing equipment.

Specifications

Table 1-1 lists the specifications and supplemental characteristics for the HP 6050A/6051A Electronic Load mainframe.
All specifications apply over an operating range of 0 to +55°C for the mainframe. Specifications are guaranteed through
the warranty of the product. Supplemental characteristics are type-tested or typical values based on a product sample and,
while representative, are not guaranteed for all instruments.

Table 1-1. HP 6050A/6051A Specifications and Supplemental Characteristics
Specifications:
AC Input:

Three internal switches permit operation from 100, 120, 220, or 240 Vac lines.

Amplitude: -13% to +6% nominal line voltage
Frequency: 48 to 63 Hz

Supplemental Characteristics:
AC Input:

Fuse: The ac input is protected by internal fuses.
Maximum VA: 635

HP-IB Programming Command Processing Time (Time required for an HP-IB command processed by
the Electronic Load): 70 milliseconds (typical)

HP-IB Interface Capabilities:

SH1, AH1, T6, L4, SR1, RLI, DT1, DC1

Trigger Input:

Vlo = 0.9 V maximum at Ilo = -1 mA
Vhi = 3.15 V minimum (pull-up resistor on input)

Trigger Input:

Vlo = 0.72 V maximum at Ilo = 1 mA
Vhi = 4.4 V minimum at Ilo = -20 µA

12 General Information

Table 1-1. HP 6050A/6051A Specifications and Supplemental Characteristics (continued)

Weight:

Net (mainframe only): HP 6050A, 9.5 kg (21 lb.)

HP 6051A, 5.5 kg (12 lb.)

Shipping: HP 6050A, 14 kg (31 lb.)

HP 6051A, 7.5 kg (17 lb.)

Dimensions:

Width: HP 6050A, 425.5 mm (16.75 in.)

HP 6051A, 213 mm (8.4 in.)

Height: 178 mm (7 in.), add 10 mm (0.4 in.) for removable feet
Depth: 625 mm (24.6 in.), including input connectors on modules

General Information 13

2

Operation Overview

Introduction

The HP 6050A and HP 6051A Multiple Input Electronic Load Mainframes are used for design, manufacturing, and
evaluation of dc power supplies, batteries, and power components. Other applications include use as a power circuit
breaker or crowbar, high-current function or pulse generator, fuel-cell and photovoltaic cell test, and de-energizing
superconducting magnets.

The mainframe contains six (two) slots for load modules. Load modules occupy either 1 or 2 slots, depending on the
power rating of the module. The mainframe can dissipate up to 300 watts per slot, to a total of 1800 (600) watts for a
fully loaded mainframe. An individual module may have either 1 or 2 channels, each of which has its own channel
number. Each module contains its own input connectors. The mainframe contains a processor, HP-IB connector and
interface circuits, trigger circuits, front-panel keypad and display, and other circuits common to all the load modules.

Each module can operate independently in constant current (CC) mode, constant voltage (CV) mode , or constant
resistance (CR) mode. In addition, each input can be turned on or off (open circuit) or short circuited.

Features include built-in HP-IB interface and built-in pulse generator, both standard. Pulse mode allows dynamic testing
of power supplies and components, without giving the device under test time to heat up. The flexible pulse mode provides
six triggering methods, allowing synchronization with a wide variety of events. A Save/Recall feature allows you to save
up to 7 complete instrument setups, one of which can be saved in non-volatile memory so that it is recalled automatically
at power-on. Also standard is HP-IB readback of actual input voltage and current, and extensive protection and status
reporting capability.

The mainframe contains two (one) cooling fans whose speed automatically increases or decreases as the module
temperatures rise and fall. This feature reduces overall noise level because the fans do not run at maximum speed at all
times.

The input power rating curve for each module is shown in the module-specific pages. See the extended power paragraphs
in this section for a description of the power rating curves. Note that regardless of a module's power rating, input current
is derated linearly from 2 volts down to 0 volts.

Each load module can be individually controlled either via HP-IB or locally via the front panel. Once a channel is
selected or addressed, all subsequent commands go to that channel until another channel is selected or addressed.
Operation of all models is similar, regardless of power ratings. Therefore, the operating instructions given in this manual
are generic, and apply to all modules. The module-specific pages provided with each module include specifications and
other information pertinent just to a particular model. Some examples described here may use values that are not
appropriate for your module, but the example is valid. Some descriptions refer to ranges, limits, full-scale values, and
similar terms (for example, low range and high range). Refer to the module-specific pages provided with each module for
the actual values.

Programs written for the HP 6060 series of single Electronic Loads can be used with the multiple loads, easing program
development for applications using various members of the HP Electronic Load family. (Triggering via the ac line
frequency or the load's internal timer is available only in the multiple load mainframe.)

If your application requires a greater power or current capacity than one module can provide, load modules can be
connected in parallel in CC or CR mode.

Operation Overview 15

Front Panel Description

The front panel includes a 12-character alphanumeric display, 11 status indicators, and four groups of keypads.
Ordinarily the alphanumeric display shows the number of the channel presently under front-panel control, and the input
voltage and current of that channel. By using the key you can sequentially display input power, programming
error codes, and protection-circuit status. If any protection circuits are active, that status will be displayed first when you
use the
channel. Then you can key through the display in the normal sequence. The alphanumeric display also shows what
function is being performed when you use the keypads.

The display also includes 11 annunciators that point to the 11 status labels printed on the front panel. The Constant
Current, Constant Resistance, Constant Voltage, Transient, and Unregulated status annunciators are specific to the
channel displayed. The Protection, Error, Shift, Remote, Address, and Service ReQuest status annunciators are channel
independent.

Four of the keys perform two functions, with the alternative function labeled in blue above the key. The alternative
function is selected by first pressing the blue (shift) key, which turns on the Shift annunciator and enables the alternative
function.

Note that the front-panel display operates independently from the HP-IB CHANNEL command. In other words, you can
select a channel locally (front panel) for which the display will show the input voltage and current, and the controller can
subsequently send commands to other channels without changing the channel being displayed.

key. If you change channels via the front panel, any fault information will be displayed first for the new

Remote Programming

Commands sent to the Electronic Load via HP-IB are decoded by the mainframe microprocessor, which detects syntax and
range errors. The mainframe processor also prescales data sent to the modules, and maintains status registers for each
module. Three commands have aliases for compatibility with other HPSL instruments. MODE can also be called
FUNCtion, INPut can also be called OUTPut, and CHANnel can also be called INSTrument. OUTPut and INSTrument
would typically be used if you want your program to refer to the load modules in terms of the device or instrument under
test. Be careful if using INSTrument for CHANnel in systems that have more than one Electronic Load mainframe;
someone looking at the listing in the future may be misled.

Local/Remote Control

Local (front panel) control is in effect immediately after power is applied. The front panel keypad and display allow
manual control of each individual module when the Electronic Load is used in bench test applications. Remote
(computer) control goes into effect (front panel Rmt annunciator is on) as soon as the mainframe receives a command via
the HP-IB. A built-in HP-IB interface and HPSL compatible commands allow control and readback of all functions when
the Electronic Load is used in computer controlled applications.

With remote control in effect, only the computer can control the Electronic Load; the front panel keypad has no effect.
You can, however, still use the front panel display to view the input voltage and current readings. You can return the
Electronic Load to local control from remote control by pressing . This will return the Electronic Load to local
control, unless the local-lockout command has been received from the HP-IB computer.

Most of the functions that can be performed remotely over the HP-IB can also be performed locally at the front panel. The
names on the keys reflect the HPSL commands that are used to program the various functions. Consequently, learning to
operate the Electronic Load from the front panel will aid you when you start to write computer programs.

16 Operation Overview

Details of local operation are covered in Chapter 4 - Local Operation and fundamentals of remote programming are given
in Chapter 5 - Remote Operation. Complete HPSL programming details are given in the HP Electronic Loads
Programming Reference Guide. The remaining paragraphs in this chapter describe the operating modes, transient
operation, protection features, and other operating features of the Electronic Load.

Extended Power Operation

Note: Extended power operation is not available on "B " load modules (HP Models 60501B-60507B). In

addition, this feature may not be present in "A" modules produced after 1989.

The extended power feature allows a module to dissipate considerably more than its nominal power rating in many cases.
The primary factor limiting the amount of power that can be dissipated is the temperature of the current-control pass
transistors, as sensed at the heatsink. A module's nominal power rating is specified for continuous power at high ambient
temperature, but in many applications average power is less than 100%, and ambient temperature is considerably lower
than the highest specified full-power temperature. In these less-than-extreme applications, each load module can safely
dissipate as much as one third more power than its nominal power rating for a limited time.

In effect, each module has two power-limit curves, as shown in Figure 2-1. Whether the module is operating with the
nominal power-limit curve or the extended power-limit curve is determined by heatsink temperature. The module turns
on with extended power available and extended power continues to be available unless and until the internal temperature
rises beyond a safe operating point for extended power. At the point, the module automatically reduces the power-limit
curve to the module's nominal power rating, and sets the Extended Power Unavailable (EPU) bit in the status registers.
Extended power is available any time the EPU bit (bit 9) is not set. A graph provided in the module-specific
specifications under DC Input Rating shows the typical time that a module can operate at full extended power after
having stabilized at a given average power before extended power becomes unavailable.

Programmable Features

Modes of Operation

The three modes of operation are:

• constant current (CC)

• constant voltage (CV)

• constant resistance (CR)

Figure 2-1. Power Limit Curves

Operation Overview 17

When programmed to a mode, a module remains in that mode until the mode is changed or until a fault condition, such as
an overpower or overtemperature, occurs. When changing modes, the module's input is momentarily disabled (non­conducting state) before the new mode is enabled. This insures that there will be minimum overshoots when changing
modes.

The current, resistance, and voltage mode parameters described in subsequent paragraphs can be programmed whether or
not the mode is presently selected. When a mode is selected via the front panel or via the HP-IB, most of the associated
parameters will take effect at the input (exceptions are noted in the mode descriptions).

Constant Current CC (Mode)

In this mode, the module will sink a current in accordance with the programmed value regardless of the input voltage (see
Figure 2-2). The CC mode can be set with front panel keys( , , and ) or via the HP-IB
(MODE:CURR command). The CC mode parameters are discussed in the following paragraphs.

Figure 2-2. Constant Current Mode

Ranges

Current may be programmed in either of two overlapping ranges, a low range and a high range. The low range provides
better resolution at low current settings. The range can be set at the front panel ( and ENTRY keys) or via the
HP-IB (CURR:RANG command). Any value in the low range selects the low range. Any value above the maximum of
the low range selects the high range. Changing the range affects the module in the same manner as changing modes; i.e.,
it causes the input to go through a non-conducting state. Note that the values of the present current settings may be
automatically adjusted to fit the new range. For example, if 10 A is the present setting and the 0 to 6 A range is then
programmed, the current setting will automatically be changed to 6 A; see Chapter 4 - Local Operation.

Immediate Current Level

The current level can be set at the front panel ( and ENTRY keys) or via the HP-IB (CURR command). If the CC
mode is the active mode, the new setting immediately changes the input at a rate determined by the slew setting (described
below). If the module is not in the CC mode, the new setting is saved for use when the mode is changed to CC.

Triggered Current Level

The current level can be preset (stored in the Electronic Load) allowing the input to be updated when a trigger is received
instead of immediately as described above. The current level can only be preset via the HP-IB (CURR:TRIG command).
The preset capability is not available at the front panel.

If the CC mode is the active mode, the preset current level will become the actual value and the input will be updated
when a trigger occurs. If the CC mode is not the active mode, the preset current level will become the actual value when a

18 Operation Overview

trigger occurs but there will be no effect on the input until the CC mode becomes active. Once a level is triggered,
subsequent triggers will have no effect on the input unless another CURR:TRIG command is sent. The trigger sources
available to the Electronic Load are described later in this chapter. The Electronic Load has a status reporting capability
to keep track of pending triggers and other operating conditions. The status reporting capability is described in detail in
the HP Electronic Loads Programming Reference Guide.

Transient Current Level

The transient current level can be set at the front panel ( , and ENTRY keys) or via the HP-IB
(CURR:TLEV command). The transient current level determines the higher current level when transient operation
(described later in this chapter) is turned on. The module input will switch between the main level and the transient level
when transient operation is turned on.

Software Current Limit

The Electronic Load allows the user to set a current limit (0 to 102% of full scale) for each module via the HP-IB
(CURR:PROT command) which will shut down the input if the current limit is exceeded beyond a programmable time
delay. Note that the software current limit is in effect for any mode of operation (not just the CC mode). The software
current limit feature is described later in this chapter under Protection Features.

Slew Rate

Slew rate determines the rate at which the current input to a module changes to a new programmed value. Slew rate can
be set at the front panel ( , and ENTRY keys) or via the HP-IB (CURR:SLEW command). This slew rate
remains in effect for the immediate, triggered, and transient level changes previously described.

There are 12 discrete current slew rates within each slewrate range. Any slew rate value can be sent to a module (there
are no upper and lower limits that would cause an error), and a module will automatically select one of the 12 rates that is
closest to the programmed value. The slew rate is rescaled to the closest fit in the 1-of-12 discrete steps if the
current range is changed.

Constant Resistance (CR) Mode

In this mode, the module will sink a current linearly proportional to the input voltage in accordance with the programmed
resistance (see Figure 2-3). The CR mode can be set at the front panel ( , and keys) or via the HP­IB (MODE:RES command). The CR mode parameters are described in the following paragraphs (see also Appendix A).

Figure 2-3. Constant Resistance Mode

Operation Overview 19

Ranges

Resistance may be programmed in any of three overlapping ranges (low, middle, high). The range can be set at the front
panel ( , , and ENTRY keys) or via the HP-IB (RES:RANG command). Any value in the low range
selects the low range. Any value that is within the middle range and above the maximum low-range value selects the
middle range. Any value that is within the high range and above the maximum middle-range value selects the high
range. Note that the values of the present resistance settings may be automatically adjusted to fit within the new range.

Immediate Resistance Level

The resistance level can be set at the front panel ( and ENTRY keys) or via the HP-IB (RES command). If the CR
mode is the active mode, the new setting immediately changes the input at a rate determined by the voltage or current
slew setting (see description below). If the module is not in the CR mode, the new setting is saved for use when the mode
is changed to CR.

Triggered Resistance Level

The resistance level can be preset (stored in the Electronic Load) allowing the input to be updated when a trigger is
received instead of immediately as described above. The resistance level can only be preset via the HP-IB (RES:TRIG
command). The preset capability is not available at the front panel.

If the CR mode is the active mode, the preset resistance level will become the actual value and the input will be updated
when a trigger occurs. If the CR mode is not the active mode, the preset resistance level will become the actual value
when a trigger occurs but there will be no effect on the input until the CR mode becomes active. Once a level is triggered,
subsequent triggers will have no effect on the input unless another CURR:TRIG command is sent.

Transient Resistance Level

The transient resistance level can be set at the front panel ( , and ENTRY keys) or via the HP-IB
(RES:TLEV command). The transient level and the main level are used in transient operation, which is described later in
this chapter. In the low resistance range, the transient level must be set to a higher resistance value than the main level.
However, in the middle and high resistance ranges, the transient level must be set to a lower resistance value than the
main level.

Slew Rate

Slew rate in resistance mode is not programmed in ohms/second. In the low resistance range, slew rate is programmed in
volts/second. Whatever value is programmed for the voltage slew rate is also used for the low resistance range.

In the middle and high resistance ranges, slew rate is programmed in amps/second. Whatever value is programmed for
the current slew rate is also used for the middle or high resistance ranges.

Constant Voltage (CV) Mode

In this mode, the module will attempt to sink enough current to control the source voltage to the programmed value (see
Figure 2-4). The module acts as a shunt voltage regulator when operating in the CV mode. The CV mode can be set
at the front panel ( , and keys) or via the HP-IB (MODE:VOLT command). The CV mode
parameters are described in the following paragraphs.

Range

Voltage mode has only one range

20 Operation Overview

Immediate Voltage Level

Figure 2-4. Constant Voltage Mode

The voltage level can be set at the front panel (
mode is the active mode, the new setting immediately changes the input at a rate determined by the voltage slew setting.
If the module is not in the CV mode, the new setting is saved for use when the mode is changed to CV.

Triggered Voltage Level

The voltage level can be preset (stored in the Electronic Load) allowing the input to be updated when a trigger is received
instead of immediately as described above. The voltage level can only be preset via the HP-IB (VOLT:TRIG) command.

Transient Voltage Level

The transient voltage level can be set at the front panel ( , and ENTRY keys) or via the HP-IB
(VOLT:TLEV + command). The module input will switch between the main level and the transient level when transient
operation is turned on. The transient voltage level determines the higher voltage level.

Slew Rate

Slew rate determines the rate at which the voltage changes to a new programmed setting. Slew rate can be set at the front
panel ( , , and ENTRY keys) or via the HP-IB (VOLT:SLEW command). This slew rate remains in effect
for the immediate, triggered and transient voltage level changes described above.

There are 12 discrete slew rates that can be programmed for CV Mode slew rate. Any slew-rate value can be sent to a
module (there are no upper and lower limits that would cause an error). The module will automatically select one of the
12 rates that is closest to the programmed value. It is important to note that the fastest slew rates cannot be achieved
because of bandwidth limitations. The module-specific pages list the usable slew rates.

and ENTRY keys) or via the HP-IB (VOLT command). If the CV

Transient Operation

Transient operation enables the module to periodically switch between two load levels, as might be required for testing
power supplies. A power supply's regulation and transient characteristics can be evaluated by monitoring the supply's
output voltage under varying combinations of load levels, frequency, duty cycle, and slew rate. Transient operation can be
turned on and off at the front panel (
you turn on transient operation, you should set the desired mode of operation as well as all of the parameters associated
with transient operation. Transient operation may be used in the CC, CR, or CV modes and can be continuous, pulsed, or
toggled. Note that the pulsed or toggled operation cannot be programmed from the front panel.

key) or via the HP-IB (TRAN ON and TRAN OFF commands). Before

Operation Overview 21

Continuous Transient Operation

In continuous operation, a repetitive pulse train switches between two load levels. Continuous transient operation is
selected via the HP-IB using the TRAN:MODE CONT command. For front panel operation, continuous transient
operation is automatically selected when transient operation is turned on( key).

The two load levels in the transient operation are the previously described main level (immediate or triggered) and
transient level for current, resistance, or voltage. The rate at which the level changes is determined by the slew rate (see
slew rate descriptions for CV, CR, or CV mode as applicable). In addition, the frequency and duty cycle of the continuous
pulse train are programmable. The frequency can be set from 0.25 to 10000 Hz at the front panel (
keys) or via the HP-IB (TRAN:FREQ command) The duty cycle can be set from 3% to 97% (0.25 Hz to 1 kHz) or from
6% to 94% (above 1 kHz) at the front panel( and ENTRY keys) or via the HP-IB (TRAN:DCYC command).

For example, assume that the CC mode is active, the slew rate is at the default setting (maximum rate), and the applicable
transient operation parameters have been set as follows:

and ENTRY

HPSL Command

TRAN:MODE CONT
CURR 5
CURR:TLEV 10
TRAN:FREQ 1000
TRAN:DCYC 40
TRAN ON

Figure 2-5 shows the waveform that would result in this example. The module input current will slew to and remain at 10
amps for 40% of the period (400 µs), then slew to and remain at 5 amps for the remaining 60% (600 µs) of that cycle.

The load module starts conduction at the main level (in this case 5 amps). When transient operation is turned on and at a
time specified by the frequency setting the input level starts increasing at a rate determined by the slew rate. When the
value specified by the transient level setting is reached, it stays there for the remainder of the time determined by the
frequency and duty cycle settings. After this time has elapsed, the input level decreases to the main level again at the rate
specified by the slew setting and stays there for the remainder of the period prescribed by the frequency setting.

Description

Sets continuous operation.
Sets main current level to 5 amps.
Sets transient current level to 10 amps.
Sets transient generator frequency to 1 kHz.
Sets transient generator duty cycle to 40%.
Turns on transient operation.

Figure 2-5. Continuous Transient Operation

Pulsed Transient Operation

Pulsed transient operation is similar to continuous operation with the following exceptions:

22 Operation Overview

a. In order to get a pulse, an explicit trigger is required. The trigger can be an external trigger signal received via

the TRIGGER input on the rear panel, the HP-IB GET function, the *TRG common HPSL command, the TRIG
subsystem HPSL command, or the ac line or internal timer signal.

b. One pulse results from each trigger. Therefore, frequency cannot be programmed. The main level, transient

level, and slew rate are programmed as described for continuous operation. The pulse width is programmable
from 0.00005 to 4 seconds via the HP-IB (TRAN:TWID command). Pulsed transient operation cannot be
programmed at the front panel.

c. The appearance of the pulse at each module's input may be delayed from the trigger signal. For pulse widths of

17 ms or greater, delay is less than 1.6% of the pulse width. For pulse widths of less than 17 ms, delay is less than
4% of the pulse width.

In this example, assume that the CC mode is active, the slew rate is at the factory default setting (maximum rate), an
external trigger input is connected to the Electronic Load's rear panel, and the applicable transient operation parameters
have been set as follows:

HPSL Command Description

TRIG:SOUR EXT Selects the external trigger input.
TRAN:MODE PULS Selects pulsed transient operation.
CURR 5 Sets main current level to 5 amps.
CURR:TLEV 10 Sets transient current level to 10 amps.
TRAN:TWID.001 Sets pulse width to 1 millisecond.
TRAN ON Turns on transient operation.

Figure 2-6 shows the waveform that would result in this pulsed transient operation example. The Electronic Load starts
conduction at the main current level setting (5 amps). When the transient mode is turned on and an external trigger
signal is received, the input level starts increasing at a rate determined by the slew rate. When the value specified by the
transient level setting (10 amps) is reached, it stays there for the remainder of the time determined by the pulse width
setting (1 millisecond). After this time has elapsed, the input level decreases to the main level again at the rate specified
by the slew setting and remains there until another trigger is received. Any triggers that occur during the time the
transient level is in effect will be ignored.

Figure 2-6. Pulsed Transient Operation

Toggled Transient Operation

Toggled transient operation causes the module input to alternate between two predefined levels as in continuous operation
except that the transient points are controlled by explicit triggers instead of the internal transient generator. As in pulsed
transient operation, the trigger signal can be an external trigger signal, the HP-IB GET function, the *TRG command,
the TRIG command, or the ac line or internal timer signals. Note that toggled transient operation can only be
programmed via the HP-IB (TRAN:TOGG command); it cannot be programmed at the front panel.

Operation Overview 23

In this example, assume that the CC mode is active, the slew rate is at the factory default setting (maximum rate), an
external trigger input signal is connected to the Electronic Load's rear panel, and the applicable transient operation
parameters have been set as follows:

HPSL Command Description

TRIG:SOUR EXT Selects the external trigger input source.
TRAN:MODE TOGG Selects toggled operation.
CURR 5 Sets main current level to 5 amps.
CURR:TLEV 10 Sets transient current level to 10 amps.
TRAN ON Turns on transient operation.

Figure 2-7 shows the waveform that would result for this toggled transient operation example. Operation is similar to that
described for continuous and pulse operation, except that each time a trigger is received the input alternates between the
main and transient current levels.

Figure 2-7. Toggled Transient Operation

Triggered Operation

The Electronic Load has various triggering modes to allow synchronization with other test equipment or events. The
triggering circuits are located in the mainframe, and all modules receive the trigger simultaneously (although each
module is programmed individually as to what operation, if any, will be triggered. As described previously, triggering can
be used for the following applications:

Triggering a preset level

Triggering a transient pulse

Toggling

Three triggering methods are available over the HP-IB: the GET function, the *TRG common HPSL command, and the
TRIG subsystem HPSL command (refer to HP Electronic Loads Programming Reference Guide). The HPSL TRIG

subsystem allows you to select either the ac line frequency, internal timer, or TRIG command as the trigger source.
There is also a TRIGGER connector on the rear panel for external trigger inputs. Triggering cannot be done via the
front panel.

*TRG and the TRIG command are both synchronous with other commands; that is, the modules are not triggered until
pending operations are completed. GET, external triggers, ac-line triggers, and internal-timer triggers are all
asynchronous; that is, the modules are triggered as soon as the trigger signal is received.

Transfers all pending preset levels to the actual level. For the presently active mode,
the new level appears at the input. For the modes which are not presently active, the
preset levels will not take effect at the input until the applicable mode becomes active.

Generates a transient pulse of programmable width when pulsed transient operation is
in effect.

Changes the input between the main level and the transient level when toggled
transient operation is in effect.

24 Operation Overview

If the ac line is selected via the HP-IB as the trigger source, triggers will be generated once for each cycle of ac input
power. An ac line frequency of 60 Hz produces a trigger period of 16.67 ms; 50 Hz line frequency produces a trigger
period of 20 ms.

The rear-panel TRIGGER connector also provides a trigger output signal. This signal is generated synchronously with
the trigger signal sent by the mainframe to the modules. The trigger output signal can be used to trigger an external
device such as an oscilloscope, DVM, or another Electronic Load mainframe.

The Electronic Load has a status reporting capability to keep track of trigger operations. Refer to 'Status Reporting' in the

HP Electronic Loads Programming Reference Guide.

Slew Rate And Minimum Transition Time

Slew rate is defined as the change in current or voltage over time. A programmable slew rate allows a controlled
transition from one load setting to another to minimize induced voltage drops on inductive power wiring, or to control
induced transients on a test device (such as would occur during power supply transient response testing).

In cases where the transition from one setting to another is large, the actual transition time can be calculated by dividing
the voltage or current transition by the slew rate. The actual transition time is defined as the time required for the input to
change from 10% to 90% or from 90% to 10% of the programmed excursion. In cases where the transition from one
setting to another is small, the small signal bandwidth of the load limits the minimum transition time for all
programmable slew rates. Because of this limitation, the actual transition time is longer than the expected time based on
the slew rate, as shown in Figure 2-8.

Figure 2-8. Risetime Transition Limitation

Therefore, both minimum transition time and slew rate must be considered when determining the actual transition time.
This is shown in Figure 2-9 for the twelve programmable slew rates in current mode operation. The actual transition time
will be either the total slew time (transition divided by slew rate), or the minimum transition time, whichever is longer.

In voltage mode, all minimum transition times are based on a low-capacitance current source. These transition times are
affected by capacitive loading of the inputs. For example, a capacitance of 2.2 microfarads increases the 85 microsecond
minimum transition time (shown in the specifications table) to 110 microseconds. Therefore, no graph is provided for
minimum transition time and slew rate in voltage mode operation.

In resistance mode, the low resistance range uses the slew rate that has been programmed for voltage mode. The middle
resistance range uses the slew rate that has been programmed for the high current range. The high resistance range uses
the slew rate that has been programmed for the low current range.

Operation Overview 25

Input Current, Voltage, and Power Measurement

Each module's input current, voltage, and power can be measured at the front panel ( key) or via the HP-IB (MEAS
command). With local (front panel) control in effect, pressing will continually step the display through voltage
and current input values, the computed power value, and various status conditions for the selected channel.

With remote control in effect, a module may be instructed to measure its dc input voltage, current, or power by sending
the appropriate query command (e.g. MEAS:CURR). The results will be read back when the Electronic Load is
addressed to talk. Voltage and current measurements are performed with approximately 12-bit resolution of full scale
ratings. Power is computed from this information.

Figure 2-9. Transition Times and Slew Rates

Short On/Off

A module can simulate a short circuit at its input by turning the load on with full-scale current. The short circuit can be
toggled on/off at the front panel key) or via the HP-IB (INPUT:SHORT ON|OFF command). The short
on/off change uses the slew rate setting of the active mode and range.

The actual value of the electronic short is dependent on the mode and range that are active when the short is turned on. In
CV mode it is equivalent to programming zero volts. In CC mode it is equivalent to programming full-scale current for
the present current range. In CR mode it is equivalent to programming the minimum resistance for the present resistance
range.

26 Operation Overview

Note that turning the short on in CV mode may cause the load to draw so much current that the software current limit
operates, which may turn the input off.

Turning the short circuit on does not affect the programmed settings, and the load input will return to the previously
programmed values when the short is turned off.

Pressing the Short On/Off key with certain user applications may cause damage to the equipment
being tested, which may result in personal injury. Contact your HP Sales and Service office if you
need to have the Short On/Off key disabled.

Input On/Off

A module's input can be toggled on/off at the front panel ( key) or via the HP-IB (INPUT ON|OFF
command). The input on/off change does not use the slew rate setting so the input will change at the maximum slew rate.

Turning the input off (zero current) does not affect the programmed settings. The input will return to the previously
programmed values when the input is turned on again. Note that the Input On/Off command supersedes the mode
commands and Short On/Off command.

Saving and Recalling Settings

The Electronic Load has internal registers in which settings (mode, current, voltage, resistance, slew, transient level, etc.)
for each module can be saved. By saving settings and recalling them later you can save programming time.

The present settings for all channels are saved in the specified register (0 to 6) at the front panel ( key) or via the
HP-IB (*SAV command). All of the settings are saved in the specified location in the mainframe's memory. Settings
saved in locations 1 through 6 will be lost when ac line power is cycled. However, the *SAV 0 command will cause the
settings to be stored in non-volatile memory; and, the next time the Electronic Load is turned on, these settings will
become the power-on settings.

You can recall the saved settings from the specified register (0 to 6) at the front panel ( key) or via the HP-IB
(*RCL command). All of the parameters for each module which were saved by the *SAV command are set to the saved
values. At power-on, the Electronic Load automatically executes a *RCL 0, which recalls the values saved in nonvolatile
memory.

You can recall the factory default settings at the front panel ( ) or via the HP-IB (*RST command).

Remember that Save and Recall operate on all channels, not just the presently addressed or selected channel.

Reading Remote Programming Errors

Remote programming errors can be read via the HP-IB (SYST:ERR? query) or at the front panel ( key). The Err
annunciator indicates when remote programming errors have occurred. The errors are negative numbers grouped into
blocks of 100 as follows:

-lxx Command errors

-2xx Execution errors

-3xx Device-specific errors

-4xx Query errors

The SYST:ERR? query (or key) reads back the errors in the order in which they occurred (the error queue can
hold up to 30 entries). Once the error is read back it is removed from the list. A value 0 indicates there is no error; and 0

Operation Overview 27

will be returned when all errors in the list have been read. Pressing the key displays just the error number. The
SYST:ERR? query returns the error number and a short description of the error to the computer. Refer to Chapter 6 in
the HP Electronic Loads Programming Reference Guide.

Local programming errors generated by front panel operations are not put into the error list, but are immediately put on
the Electronic Load's front panel display; e.g., 'OUT OF RANGE'.

Status Reporting

The Electronic Load incorporates a status reporting capability. Various status conditions within the Electronic Load can
be reported using this capability. The user determines which condition(s) will be reported. Chapter 5 of the HP
Electronic Loads Programming Reference Guide describes each of the status registers in the Electronic Load. (These
registers, including the channel status registers, are all maintained in the mainframe.) Notice that the same information is
available in both the channel status and questionable status registers, but the channel registers are organized by channel,
and the questionable registers are organized by fault. Therefore, depending on which channels and/or faults are most
critical in your application, you can use one branch to localize selected faults quickly, and use the other branch for broader
fault reporting. By knowing that only a particular fault (questionable branch) or a particular channel (channel branch) is
enabled to initiate a service request, you can eliminate the need to read one or more registers to locate a fault.

Protection Features

Each load module includes the following protection features:

• Overvoltage

• Overcurrent (hardware and software)

• Overpower (hardware and software)

• Overtemperature

• Reverse Voltage

The appropriate bit(s) in the mainframe's status registers are set when any of the above protection features are active.
Also, the Prot annunciator comes on and the front-panel alphanumeric display indicates which condition(s) have been
detected. For example, if an overtemperature (OT) condition has been detected causing a module's input to be turned off
(protection shutdown, PS), the display will indicate "PS OT".

Resetting Latched Protection

All of the protection features latch (remain set) when they are tripped, except for the hardware overcurrent and reverse
voltage. The latched protection features can be reset via the HP-IB (*RST or INP:PROT:CLE commands) or at the front
panel ( key). Of course, the condition that caused the protection feature to trip must be removed or it will trip
again as soon as it is reset.

To protect the Electronic Load from possible damage, the input voltage must not exceed the
maximum input voltage rating specified in the module-specific pages supplied with each module.
Never apply the ac line voltage to a module's input binding posts.

28 Operation Overview

Overvoltage

The overvoltage protection circuit is set at a predetermined voltage, which cannot be changed. If the overvoltage circuit
has tripped, the module will attempt to limit the voltage by drawing current from the DC source. The module limits the
value of current drawn such that the resulting power is within the power rating. The overvoltage (OV) and voltage fault
(VF) status register bits are set when the OV condition occurs, and will remain set until they are reset as previously
described.

An overvoltage condition does not cause the module's input to be turned off . However, a Fault signal output at the
module's rear-panel control connector will indicate when either an overvoltage condition or a reverse voltage condition
has occurred. The Fault signal is latched true (high TTL level) when the VF bit in the status register goes true. The
Fault output signal (see Chapter 3 - Installation) can be used to trip an external circuit breaker or control a relay (e.g., HP
59510A Relay Accessory) in order to disconnect the Electronic Load input from the source it is testing when an
overvoltage or a reverse voltage condition occurs.

Overcurrent

The Electronic Load includes both hardware and software overcurrent protection features.

Hardware. When operating in the CR or CV mode, it is possible for a module to attempt to sink more current than it is
rated for.

Under this condition, the load current will be limited by a current limit circuit, which is set at a value slightly above the
current rating of the module. It protects both the Electronic Load and the device under test from operating too far beyond
specified limits. The hardware current limit circuit does not turn the module's input off. The overcurrent (OC) bit in the
status register is set when an OC condition occurs, and is reset when the OC condition is removed.

Software. In addition to the hardware overcurrent protection circuit, the Electronic Load allows the user to define a
current protection limit in software which will shut down a module's input if the limit is exceeded. This feature can only
be programmed via the HP-IB. It is turned on/off using the CURR:PROT:STATE ON|OFF command. The software
current limit level (in amps) is set using the CURR:PROT command. A programmable delay (in seconds) before trip is
also provided with the CURR:PROT:DEL command. If the software overcurrent limit is exceeded and persists beyond
the specified delay time, the module is turned off. Also, for these conditions, the OC and PS (protection shutdown) status
register bits are set and will remain set until the OC condition is removed and the bits are reset as previously described.

Overpower

A load module's response to an overpower condition depends on whether the module was operating with the nominal
power limit or the extended power limit when the overpower condition occurred.

Nominal Power Limit. The nominal power-limit boundary is set by software that monitors the input current and voltage.
If the input power exceeds the nominal power limit, the load module sets the overpower status bit, which will reset if the
overpower condition ceases. If the overpower condition persists for 3 seconds, the load module's input circuit turns off,
and the OP and PS status bits are both latched on. The input circuit remains off, and the OP and PS status bits remain set,
until protection clear occurs. Of course, if the overpower condition is not corrected, the load will turn off again.

Extended Power Limit. The extended power-limit boundary is set by hardware circuits. This hardware power-limit
circuit can be activated by any of three conditions:

1. If an overpower condition occurs while the module is operating in the extended power area.

2. During certain large programmed changes

Operation Overview 29

3. If the nominal power limit is exceeded (the software limit sets the OP bit and starts the 3-second timer, but does
limit the input power)

If the hardware power-limit circuit becomes active, it attempts to limit power by limiting the current drawn by the load.

Once the power has been returned to the safe operating area, the protective circuit allows the current to rise again. This
protective sequence can turn on and off (approximately 5% of full scale peak-to-peak) at rates from 2 kHz to 12 kHz. It
will continue until the overpower condition ceases, or the module's heatsink temperature rises enough to cause the module
to impose the nominal power limit. With the nominal power limit in effect, the module's input circuit will open after the
3-second delay. Note that this oscillation is a design feature that protects your instrument while preventing nuisance
shutdowns caused by transient conditions.

Overtemperature

Each module has an overtemperature (OT) protection circuit which will turn off the input if the internal temperature
exceeds safe limits. If the OT circuit activates, the OT and PS status register bits are set and will remain set until they are
reset. If the OT condition still exists when the reset is executed, the module's input will remain off. You must wait until
the module cools down before you can reset the OT circuit. The fan(s) will continue to operate to cool the unit as quickly
as possible.

Reverse Voltage

This feature protects the load module in case the input dc voltage lines are connected with the wrong
polarity. If a reverse voltage (RV) condition is detected, turn off power to the dc source and the
Electronic Load and make the correct connections.

The Electronic Load conducts reverse current when the polarity of the DC source connection is incorrect. The maximum
safe reverse current is specified in the module-specific pages. The reverse voltage (RV) and voltage fault (VF) bits in the
status register are set when reverse voltage is applied. When the reverse voltage is removed the RV bit is cleared.
However, the VF bit remains set until it is reset. As previously described, the Fault output signal at the control connector
tracks the state of the VF bit. The Fault signal can be used to control an external relay in order to disconnect the module
from the dc source if an RV condition occurs.

Control Connector

Each module has a 10-pin connector mounted on its rear panel. These signals are described in the following paragraphs.
See Chapter 3 for connection details.

Remote Sensing

The remote sensing inputs, + S and - S, can be used in CV or CR modes. By eliminating the effect of the inevitable
voltage drop in the load leads, remote sensing provides greater accuracy by allowing the load to regulate directly at the
source's output terminals, as well as measure the voltage there.

Monitor Outputs

The IMON and VMON output signals indicate the input current and voltage. A 0-to-10V signal at the appropriate
output indicates the zero-to-full scale input current or voltage. An external DVM or oscilloscope can be connected to
monitor the input voltage and current.

30 Operation Overview