Hp 333a Service manual

OPERATING AND SERVICE MANUAL

HEWLETT

PACKARD

L

@CopyrightHewlett-PackardCompany 1966

P.O.

Box

301,

Loveland, Colorado, 80537

U.S.A.

Reproduced with Permission, Courtesy

of

Agilent Technologies, Inc.

MODEL 333A/334A

DISTORTION

ANALYZER

Serial Numbers:

333A: 1137A03146and greater

334A: 1140A05641

and

greater

Appendix

C,

Manual Backdating Changes, adapts this manual

to

lower serial numbers.

WARNING

I

To

help minimize thepossibility of electricalfire

or

shock hazards,

do

not expose thisinstrument

to rain

or

excessive moisture.

Manual

Part

NO.

00333-90008

Microfiche

Part

No.

00333-90058

prlnttd:

October

1975,1985

HEWLETT

Pa

PACKARD

CERTIFICATION

Hewlett-Packard Company certifies that

this

product met itspublishedspecifcations at thetime

of

shipment

from

the

factory. Hewlett-Packard further certifies that its calibration measurements are traceable to the United States

Na-

tional Bureau

of

Standards, to the extent allowed by the Bureau’s calibrationfacility, and to thecalibrationfacilities

of

other International Standards Organization members.

WARRANTY

This Hewlett-Packard product is warranted against defects in material and workmanship for a period of one year

from date of shipment [,except that in the case of certain components listed in Section

I

of this manual, the warranty

shall be

for

the specified period] .During the warranty period, Hewlett-Packard Company will, at

its

option, either

repair

or

replace products which prove to be defective.

For

warranty service

or

repair, this product must be returned to a service facility designated by -hp. Buyer shall

prepay shipping charges

to

-hp- and -hp- shall pay shipping charges to return the product to Buyer. However, Buyer

shall

pay

all shipping charges, duties, and taxes for products returned to -hp- from another country.

Hewlett-Packard warrants that its software and firmwaredesignated by -hp- for use with an instrument will execute its

programming instructions when properly installed on that instrument. Hewlett-Packard does not warrant that the

operation

of

the instrument,

or

software,

or

firmware will be uninterrupted

or

error free.

LIMITATION

OF

WARRANTY

The foregoing warranty shall not apply to defects resulting from improper

or

inadequate maintenance by Buyer,

Buyer-supplied software

or

interfacing, unauthorized modification

or

misuse, operation outside of the environmental

specifications for the product,

or

improper site preparation

or

maintenance.

DISCLAIMSTHE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

PURPOSE.

NO OTHER WARRANTY

IS

EXPRESSED OR IMPLIED. HEWLETT-PACKARD SPECIFICALLY

EXCLUSIVE REMEDIES

THE REMEDIES PROVIDED HEREIN ARE BUYER’S SOLE AND EXCLUSIVE REMEDIES. HEWLETT-

PACKARD SHALL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSE-

QUENTIAL DAMAGES, WHETHER BASED ON CONTRACT, TORT, OR ANY OTHER LEGAL THEORY.

ASSISTANCE

Product maintenance agreements and other customer assistance agreements are available

for

Hewlett-Packad products.

For

any assistance, contact

your

nearest Hewlett-Packard Sales and Service Office.

Addnsscr

areprovided at the back

of

this manual.

HEWLETT

PACKARD

SAFETY

SUMMARY

Tho following

ganorol

ufotypneoutionrmurt

bo

oburvodduring

all

phrmof oporotior,

urviw,

and nprir

of

thir

inrtrumont friluro

to

comply

with

thaw

procautions

or

with rprcific

warnings

oluwhon

in

thir

manual

violotw

rrfoty rtandrrdrof dosign, mrnufrcturo, and intondod

uu

of tho inrtrumontHowlott-PieLordCompany

assume8

no

liabilityfor tho curtomar'r foiluro

to

comply

with thou roquinmont8.

This

is

I

Srfoty

Class

1

inrtrumont

GROUND

THE

INSTRUMENT

To minimize shock hazard, the instrument chassis and cabinet must be connected to an elec-

trical ground. The instrument is equipped with a three-conductor ac power cable. The power

cable must either be plugged into an approved three-contact electrical outlet

or

used with a

three-contact to two-contact adapter with the grounding wire (green) firmly connected to an

electrical ground (safetyground) at the power outlet. The power jack and mating

plug

of the

power cable meet International Electrotechnical Commission (IEC) safety standards.

DO

NOT

OPERATE

IN

AN

EXPLOSIVE

ATMOSPHERE

Do

not operate the instrument

in

the presence of flammable gases

or

fumes. Operation of any

electrical instrument

in

such an environment constitutesa definite safety hazard.

KEEP

AWAY

FROM

LIVE

CIRCUITS

Operating personnel must not remove instrument covers. Component replacement and internal

adjustments must be made by qualified maintenance personnel.

Do

not replace components

with powercable connected. Under certain conditions, dangerous voltages mayexisteven with

the power cable removed. To avoid injuries, always disconnect power and discharge circuits

before touching them.

DO

NOT

SERVICE

OR

ADJUST

ALONE

Do

notattempt internal service

or

adjustment unless another person, capable of rendering first

aid

and resuscitation, is present.

DO

NOT

SUBSTITUTE

PARTS

OR

MODIFY INSTRUMENT

Because of the danger of introducing additional hazards, do not install substitute parts

or

per-

form 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 main-

tained.

DANGEROUS

PROCEDURE

WARNINGS

Warnings, such as the example below, precede potentially dangerous procedures throughout

this manual. Instructions containe#

in

the warnings must be followed.

WARNING

I

Dongarour

voltagu,

wprbla of wuring drth,

on

prwont

in

thir inrtrumont Uso

ox.

tnmo

wution whon handling, twting,

and

rdjurting.

A

Instruction manual symbol: the product

will

be marked with this

symbol when

it

is necessary for the user to refer

to

the instruction

manual in order

to

protect against damage

to

the instrument.

A

Indicates dangerous voltage (terminals fed from the interior by

voltage exceeding

lo00

volts must be

so

marked).

/s

Protective conductor terminal. For protection against electrical

shock in case

of

a

fault.

Used with field wiring terminals

to

in-

dicate the terminal which must be connected

to

ground before

4

-

OR@

operating equipment.

Low-noise

or

noiseless, clean ground (earth) terminal. Used for

a

signal common, as well as providing protection against electrical

shock in case of a

fault.

A terminal marked with this symbol must

.beconnected to ground in the manner described in the installation

(operating) manual, and before operating the equipment.

D

,

Frame or chassis terminal. A connection to the frame (chassis) of

/f;r

OR

1,

the equipment which normally includes

all

exposed metal struc-

tures.

Alternating current (power line).

-

--

-

Direct current (power line).

Alternating or direct current (power line).

The WARNING sign denotes

a

hazard.

It

calls attention

to

a

pro-

cedure, practice, condition

or

the like, which,

if

not correctly per-

0

formed or adhered to, could result in injury or death

to

personnel.

WARNING

SAFETY

SYMBOLS

General Definitions of Safety Symbols

Used

On Equipment

or

In Manuals.

The CAUTION sign denotes

a

hazard.

It

calls attention

to

an

operating procedure, practice, condition

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.

CAUTION

The NOTE sign denotes important information.

It

calls attention

to

procedure, practice, condition or the like, which is essential

to

highlight.

E

'

Model 333A/334A

TABLE

OF

CONTENTS

Table

of

Contents

Section Page

I

GENERAL INFORMATION

........

1-3

1.1

. Description

............

1-3

1.6

.

Accessory Features

........

1-3

1.8

.

Option

...............

1-3

1.10

.

Instrument Identification

.....

1-3

Section

11

INSTALLATION

..............

2

.

1

. Introduction

............

2.3

.

Inspection

.............

2.5

.

Power Requirements

.......

2.7

.

Three-Conductor Power Cable

..

2

.

10

.

Installation

............

2.12

.

Bench Installation

.......

2.14 . Rack Installation

........

2.16

.

Repackaging For Shipment

....

page

2-1

Section

-ge

III

OPERATINGINSTRUCTIONS

......

3-1

3-

1

.

Introduction

............

3

.

1

3.4

.

Controls and Indicators

......

3-1

3.6

.

General Operating Information

.

. 3-1

3.7 . Input Connections

.......

3-1

3.9 . Voltmeter Characteristic$

.

3-1

3.12

.

Output Terminals

.......

3-2

3.14

.

Operating Procedures.

......

3-2

3.15 . Instrument Turn.On

......

3-2

3.16

.

Adjustment of Meter

Mechanical Zero

.......

3-2

3.18

.

DistortionMeasurement

...

3-2

3.21

.

RF Carriers (334A only)

...

3-3

3.22

.

Voltage Measurement

.....

3-3

3.23

.

Meter

Indication

.......

3-4

3.27

.

Use

of

Output

Terminals ... 3-4

3.30 . 333A1334A with Option 01 .. 3-4

3.32

.

Manual Nulling

........

3-4

Section

Page

IV THEORY OF OPERATION

........

4-1

4.1

.

Overall Description

........

4-1

4.3

.

Block Diagram Description

....

4-1

4.4

.

Distortion Measuring

4.8 . Carriers.

..........

4-1

4.10 . Voltmeter Operation

.....

4-1

4.12

.

Detailed Circuit Description

...

4-1

4.13

.

Impedance Converter Circuit

.

4-1

4.17

.

Rejection Amplifier Circuit

.

4-2

4.39

.

High Pass

Filter

.......

4-5

4.41

.

Meter Amplifier

.......

4-5

4.49

.

Power Supply Circuit

.....

4-7

4.54

.

RF Detector Circuit(334Aonly) 4-7

Section Page

5.1

.

Introduction

............

5-1

5.3

.

Required Test Equipment

.....

5-1

Distortion Measurement

of

AM

Operation

..........

4

.

1

Distortion Measurement in

AM

V

MAINTENANCE

.............

5-1

Section Page

V

MAINTENANCE (Cont’d)

.........

5-1

5.5 . Performance Checks

.......

5-1

5.9 . FundamentalRejection Check . 5-1

5.10

.

Second Harmonic Accuracy .

.

5-2

5.11

.

Instrument Induced

Distortion Check

.......

5-2

5.12 . Frequency CalibrationAccuracy

Check

.............

5-3

5.13

.

Automatic Nulling Mode Check 5-4

5.14

.

Input Impedance Check

....

5-4

5.17 . Minimum Input Level Check.

.

5-5

5.18 . DC Isolation Check

......

5-5

5.19 . Voltmeter Accuracy and

Frequency Response Check 5-6

5.20

.

High

Pass

Filter

Check

....

5-7

5.21

.

Residual Noise Check ..... 5-7

5.22 . AM Detector Check (Model

5.23 .Adjustment and Calibration

Procedure

............

5-8

5.26

.

Adjustments

.........

5-8

5.27

.

Voltmeter Gain Adjustments . 5-8

5.28

.

Voltmeter Frequency Response

Adjustment

.........

5-10

5.29

.

Bridge Balance Adjustment

.

. 5-10

5.30 . Sensitivity SwitchCalibration

.

5-11

5.31

.

Components

.........

5-11

334Aonly)

..........

5-7

Power Supply and Bias

Adjustment of Factory Selected

5.33 . Troubleshooting Procedure

....

5-11

5

.38

.

Troubleshooting Voltmeter

Function

...........

5

.

12

5.40

.

Troubleshooting Distortion

Function

...........

5-14

5.45

.

Photoresistor Check and

Adjustment (A6V1thruA6V5)

.

5-15

5.49

.

Servicing Etched Circuit

Boards

...........

5-16

5.52 . Servicing Rotary Switches

...

5-16

5-54

*

Converter

........

5-16

Section Page

VI REPLACEABLE PARTS

.........

6-1

6.1

.

Introduction

............

6-1

6.4

.

Ordering Information

.......

6-1

6.6

.

Non-Listed

Parts

.........

6-1

Isolating the Impedance

Section Page

M

CIRCUITDIAGRAMS

...........

7-1

7-

1

.

Introduction

............

7-1

APpen&

A

CODE

LIST

OF

MANUFACTURERS

B SALES AND SERVICE OFFICES

C MANUAL BACKDATING CHANGES

iii

Table of Contents

LIST

OF

TABLES

Model

333A1334A

Page

1-

1

.

Specifications

..............

1

.

1

5.5

.

Power Supply and

Bias

Adjustments

..

5-8

Measurements

............

3-1 5.7

.

Factory Selected Components

.....

5-12

5.2

.

Second Harmonic Accuracy Check

...

5-2 5.8

.

Troubleshooting Aid

..........

5-13

Number Page Number

3.1

. Effect of Harmonics on Voltage

5.6

.

Sensitivity Switch Calibration

.....

5-12

5.1

. RequiredTestEquipment

........

5-0

5.3

. Frequency Calibration Accuracy Check

5-4 5.9

.

Photoresistor Check

..........

5-15

5.4

.

Voltmeter Frequency Response Check .

5-6 6.1

.

Replaceable Parts

...........

6-6

LIST

OF

ILLUSTRATIONS

Number Page Number Page

1.1

.

3.1

.

3.2

.

3.3

.

4.1

.

4.2

.

4.3

.

4.4

.

4.5

.

4.6

.

4.7

.

4.8

.

5.1

.

5.2

.

5.3

.

Model

333A

Distortion Analyzer

....

Front and Rear Panel Description

...

Manual Nulling Test Setup

Impedance Correction Graph

......

Block

Diagram

.............

Bridge Waveforms

...........

Wien Bridge Circuit and Rejection

Characteristics

...........

Auto Control Loop Detector

.......

Reference and Error Phase

Relationship

.............

Rejection Amplifier Block Diagram and

Typical Frequency Rejection

Characteristic

............

Bandwidth Versus

Null

Depth

......

Simplified Metering Circuit

.......

Fundamental Rejection Check

.....

Instrument Induced Distortion Check

..

Frequency Calibration Accuracy Check

111

5.4

.

3

-0

3-

5 5.5

.

3-5 5.6

.

4-0

4-2 5.7

.

5.8

.

4-3 6.1

.

4-3 6.2

.

6.3

.

4-4 7.1

.

7.2

.

4-5

7.3

.

4-6

4-7 7.4

.

5-1 7.5

.

5-2

5-3

7.6

.

Capacitance Check

...........

5-5

DC

Isolation Check

...........

5-6

Voltmeter Accuracy and Frequency

Response Check

...........

5-7

Shielded Load Assembly

........

5-8

Adjustment and Chassis Mounted

Component Location

..........

5-9

Mechanical

Parts

...........

6-2

Modular Cabinet

Parts

.........

6-4

Frequency Tuning Assembly

......

6-5

Impedance Converter (P/O

A2)

and RF

RejectionAmplifier (A3). Bridge Balance

(P/OA6) andH h

Pass

Filter

(A7)

7-7/7-8

Meter AmplifiervP/O

A2)

......

7-9/7-10

Control Circuit

(A5)

andBridge

Power Supply

(Al)

.........

7-13/7-14

Internal Wiring

Data

.........

74/74

Detector

(A4)

...........

7-5/74

Balance (P/O A6)

........

7-11/7-12

lv

Model 333A/334A

RANGE

100%-0.3%

0.1%

Section

I

*3%

*ts%

*12%

1MHz

3MHz

10

HZ

10H~

30

Hz

20

Hz

10 Hz

300

kHz

500

Wz

1.2

MHz

SECTION

I

GENERAL INFORMATION

1-1.

DESCRIPTION.

1-2.

The Hewlett-Packard Models 333A

and

334A

Distortion

Analyzers axe solid

state

instrumentsfor

measuring distortion on ac voltages. The

Models

333A and 334A include

two

control loops

that

auto-

maticdy

tune

both

legs of

a

bridge

circuitwhich

re-

jects the fundamental when the rejection circuit

is

initially

set

within the

range

of

the loops. The 334A

has

a

high

impedance detector which operates from

550

Mz

to

greater

than

65

MHz and provides the ca-

pability

of

monitoring the distortion of the amplitude

modulation on an

rf

carrier.

1-3.

Distortion levels

of

0.1% to 100%fullscale

are

measured in seven rangesforanyfundamentalfrequen-

cy of

5

Hz

to

600

Wz.

Harmonics are indicated upto

3

MHz.

The high sensitivity of these instruments re-

quires only 0.3V rms for the 100%set level reference.

The distortion characteristics can

be

monitored atthe

OUTPUT connectors with an oscilloscope,

a

true rms

voltmeter, or

a

wave analyzer. The instruments are

capable of an isolation voltage of 400 volts above

chassis ground.

1-4. The voltmeter can

be

used separatelyforgeneral

purpose voltage and gain measurements.

It

has

a

frequency range of

5

Hz

to 3

MHz

(20

Hz

to

500

Mz

for 300 pV

range)

and

a

voltage range of 300pV to

300

V

rms full scale.

1-5. The

AM

detector included in the Model 334A

is

a

broadband dc restoring peak detector consisting of

a

semiconductor diode and

filter

circuit.

AM

distor-

tion levels

as

low

as

0.3% can be measured on

a

3

V

to

8

V

rms

carrier modulated 30% in the standard

broadcast band. Distortion less than

1%

can

be

measured

at

the 8amelevelof the carrier up to

65

Mc.

1-6. ACCESSORY FEATURES.

1-7. The accessory available with the 333Aand334A

Distortion Analyzers

is

a

voltage divider probe, -hp-

Model No. 10001A. The features

of

the probe are:

a.

10 megohms shunted

by

10 pF, giving

1O:l

b.

c.

2%

division accuracy.

d.

600Vpeakinput.

e.

5

ns rise-time.

attenuation.

DC

to 30 MHz bandwidth.

1-8.

OPTION.

1-9. Option 01

is

a

standard -hp- Model333A

or

334A

with

a

special meter and meter amplifier, compen-

sated to permit response to

W

(volume

units)

characteristic

8.

1-10

INSTRUMENT IDENTICATION.

1-11.

Hewlett-Packard uses

a

two-section

serial

number. The first section (prefix) identifies

a

series

of instruments. The

last

section (suffjx) identifies

a

particular instrument within the series.

If

a letter

is

included with the serial number, it identifies the coun-

try in which the instrument

was

manufactured.

If

the

serial prefix of

your

instrument differs from the one

on the title page of this manual,

a

change sheet

will

be

supplied to make this manual cornpatable

with

new-

erinstruments

or

the backdating information in Appen-

dix

C will

adapt this manual to earlier instruments.

All correspondence with Hewlett-Packard should in-

clude the complete serial number.

Table

1-1.

Specifications

MODEL 333A Fundamental

Input

Greater Than 30

V

DISTORTION MEASUREMENT RANGE

Any fundamental frequency,

5

Hz to

600

kHz.

Distortion levels of

0.

1%-100%are measured

full scale

in

7

ranges.

Harmonic measurement accuracy

(full

scale)

Fundamental Input Less Than 30

V

DISTORTION MEASUREMENT

ACCURACY

RANGE

I

*3%

1

*6%

I

*12%

50 Hz

Elimination Characteristics:

Fundamental Rejection

>

80

dB

Second Harmonic Accuracy for

a

fundamental

of:

5

Hz

to 20 Hz: better than

+1

dB

20 Hz to 20

Wz:

better than

4.6

dB

20

kHz

to 100

kHz:

better

than

-1

dB

100

Wz

to 300

kHz:

better than -2 dB

300

kHz

to

600

kHz:

better

than -3 dB

1-1

Model

333A/334A

Section

I

300

pv

1

mV-30 V

100

V-300 V

Table

1-1.

Specifications (Cont'd)

30

HZ-300

IrHz

20

HE-~OO~HZ

10

He-1

MHe

5

Hz-3

MHe

10 HE-300

~HZ

5

He-500

kHz

Distortion Introduced

by

Instrument:

>

-70

dB

from

5

He

to 200

kHz

>

-64

dB

from 200 kHz to

600

kHz

Meter

indication

is

proportional to the aver-

age

value

of

a

waveform.

FREQUENCY CALIBRATION ACCURACY

Better

than

*5%

from

Better

than

f

10%

from

300

kHz

to

600

kHz

5

Hz

to 300 kHz

INPUT IMPEDANCE

Distortion

Mode:

1

MS1

*5%

shunted

by

<70

pF.

Voltmeter Mode:

1

Mi2

15%

shunted

by

40

pF (333A

only),

1

Mi2

*5%

shunted by

45

F

(334A

only),

1

to

300

V

ranges;

1

MS1

*5

4l

shunted

by<70

pF,

300

pV to

0.3

V

ranges.

INPUT LEVEL

FORDISl?ORTIONMEASOaEMENTS

0.3

V

rrns for

100%

set

level (up to

300

V

may

be

attenuated to

set

level reference). The

minimum measurable distortion

for

floating

operation on the

X1

frequency

range

L

50dB

below the fundamental.

DC ISOLATION

Signal

ground may

be

rl00

Vdc from external

chassis.

VOLTMETER RANGE

300

pV

to

300

V

rrns

full scale

(13

ranges),

10

dB

per

range.

5

Hz

to

3

MHz

(300

pV

range:

20

Hz-500

Hie).

VOLTMETER FREQUENCY RANGE

VOLTMETER ACCURACY:

RANGE

I

*2%

I

*5%

I

NOISE MEASUREMENTS

Voltmeter

residual

noise on

the

300

pV

range:

<

25

pV

rms terminated

in

shielded

60OQ

<30

pV

rrns

terminated in shielded

100

kS1.

OUTPUT

For input frequencies from

20

Hz

to 600

kRz,

0.1

V

rma

*

0.01

V

open circuit

for

full

scale

meter deflection;

0.05

V

rms

f

0.005

V

into

2

kS2

for

full scale meter deflection.

AUTOMATIC

NULLWG

MODE

Set

Level:

At

least

0.2

V

rms.

Frequency Ranges:

X1,

manual null tuned to

less

than

3%

of

set

level; total frequency hold-in

io.

5%

about

true manual

null.

X10

through

X10

K,

manual

null

tuned

to

less

than

10%

of

set

level;

total

frequency

hold-in

1

1%

about

true manuaX null.

AUTOMATIC NULL ACCURACY

5

Hz

to

100

Iiz:

Meter reading within

0

to

+3

dB

of manual null.

100 Hz

to

600

kHz:

Meter reading within0 to

+l.

5

dB

of manual null.

HIGH-PASS FILTER

3

dB point

at

400

Hz

with

18

dB

per

octave

roll

off.

60

Hz

rejection

>

40

dB.

Normally used

only

with fundamental frequencies greater than

1

BHZ.

POWER SUPPLY

100

V/120 V/220 V/240

V

+

5%

-

108,

48

-

66

Hz,

approximately 4

watts.

-

MODEL 334A

1.6

MHz

to

65

MHz:

Distortion introduced

by

detector

is

c

1%

for

3

to

8

volts rms carriers

modulated

30%.

Same

as

Model 333A except

as

indicated below:

AM

DETECTOR

High

impedance dc restoring

peak

detector with

semi-conductor

diode

operates from

550kHz

to

greater than

65

MHz.

Broadband input.

Maximum

input;

40

V

p-p

ac

or

40

V

peak

transient.

CARRIER

FREQUENCY

550kHzto

1.6

MHz:

Distortion introduced

by

detector

is

c

0.3%

for

3

to

8

volt carriers

modulated

30%.

NOTE

Distortion measurement

at

carrier levels

as

low

as

1

volt may

be

made with reduced

accuracy.

OPTION

01

Indicating meter

has

W

characteristics con-

forming to FCC Requirements for

AM,

FM,

and TV broadcasting.

1-2

Model 333A/334A

StCTION

II

INSTALLATION

Section

XI

2-1.

I

NTR ODUCTION.

2-2.

This section contains information

and

instruc-

tions necessaryforthe installation

and

shipping

of

the

Models 333A/334A Distortion Analyzers. Included

areinitial inspectionprocedures, power and grounding

requirements, installation information,

and

instruc-

tions for repackaging for shipment.

2-3.

INSPECTION.

2-4.

This instrument

was

carefully inspected both

mechanically

and

electrically before shipment.

It

shouldbe physically

free

of mms

or

scratches

and

in

perfect electrical order upon receipt. To confirm

this,

the instrument should

be

inspected for physical

damage

in

transit. Also checkforsuppliedaccessories,

and

test

the electricalperformance of

the

instrument

using the procedure outlined

in

Paragraph 5-5.

If

thereisdamageordeficiency,

see

the warranty on

the

inside front cover

of

this manual.

2-5.

POWER REQUIREMENTS.

2-6. The

Model

333A/334A can

be

operated from any

ac source

of

100 V/120 V/220 V/240

V

+

5%

-

10%

48

-

66

Hz. With the instrument disconnected from

the ac power source, move the slide (located on the

rear panel) until the desired line voltage appears.

Power dissipation

ie

approximately 4

watts.

2-7.

THREE-CONDUCTOR POWER

CABLE.

2-8. To protect operating personnel, the National

ElectricalManufacturers'

Association (NEMA) recom-

mendsthat

the

instrumentpanelandcabinet

be

grounded.

All

Hewlett-Packard instruments are equipped with

a

three-conductor power cable, which, when plugged in-

toanappropriate receptacle, grounds the instrument.

Theoffsetpinon the power cable three-prong connec-

tor

is

the

ground

wire.

2-9

.INSTALLATION.

2-10. The Model 333A/334A

is

fully transistorized;

therefore, no special cooling

is

required. However,

the instrument should not

be

PerateBwhere the am-

bient

temperature exceeds 55

C

(131

F).

2-11.

BENCH mSTALLATION,

2-12.

The

Model

333A/334A

is

shipped with plastic

feet and tilt

stand

in place, ready for use

as

a

bench

instrument

.

2-13.

RACK

INSTALLATION,

2-14. The Model 333A/334A may

be

rack mounted

by

usingthe 5"RackMount Kit (-hp- Part No. 5060-0775).

Instructions for the conversion are included with the

kit. The rack mount for

the

Model 333A/334A

ie

an

EIA standard width of

19

inches. When mounted in

a

rack using

the

rack mount

kit,

additional support

at

the rearof theinstrument should be provided

if

vibra-

tion

or

similar

stress

is

likely.

2-15.

REPACKAGING FOR SHIPMENT.

2-16. The following paragraphs contain

a

general

guide

for

repackaging

of

the instrument

for

shipment.

Refer

to Paragraph 2-17

if

the

original

container

is

to

be

used; 2-18

if

it

ia

not.

If

you

have any questions, con-

tact your

local

-

hp

-

Sales and Service Office. (See

Appendix

B

for

&ice locations.)

NOTE

If

the instrument

is

to

be

shippedsto

Hewlett-Packardfor service

or

repair,

attachatag to the instrument identify-

ing the owner and indicate the service

or

repairto be accomplished. Include

themodelnumber and

full

serial

num-

ber

of

the instrument.

In

any corres-

pondence, identify the instrument

by

model number, serial number, and

serial number prefix.

2-17.

a

able.

If

original

container

is

to

be

used, proceed

as

follows:

Place instrument in

original

container

if

avail-

If

original

container

is

not available,

a

suitable

one can

be

-purchased from your nearest -hp-

Sales

and Service Office.

b.

Ensure that container

is

well sealed with strong

tape

or

metal

bands.

2-18.

If

original

container

is

not to

be

used, proceed

as follows:

a.

Wrap

instrument in heavy paper

or

plastic

be-

fore placing in an inner container.

b.

Place packing material around

all

sides of in-

strumentandprotectpanel facewith cardboard strips.

c. Place instrument andinner container in

a

heavy

carton or wooden box

and

seal

with strong

tape

or

metal bands.

d. Mark shipping container with "DELICATE

INSTRUMENT,

I'

"FRAGILE,

I'

etc.

2-1

Section

TII

Model

333A/334A

@LINE switch turns instrument ac power on.

Pilot lamp glows when instrument

is

turned

ON.

@Meter indicates distortion

or

voltage level of

input.

@MODE switch selects MAIUUAL

or

AUTOMATIC

bridge tuning operation.

@FREQUENCY RANGE switch selects frequency

range which corresponds

to

fundamental of input

@COARSE BALANCE control provides coarse

ad-

justment for balancing the

Wien

bridge circuit.

6

FINE BALANCE control provides

a

vernier

ad-

'justment forbalancing the Wien bridge circuit.

7

Frequency

dial

tunes

the

Wien

bridge

circuit to

'fundamental

of

input signal.

@HJGH PASS FILTER switch inserts

or

bypasses

HIGH

PASS

FILTER

in

SET LEVEL and

DIS-

TORTION function. When inserted, filter pro-

vides

>

40

dB attenuation

to

50

-

60

Hz hum

components but no attenuation

to

frequencies

over

1

kHz.

@OUTPUT

connectors provide means of monitor-

ing output of meter circuit.

@Frequency vernier provides

fine

adjustment of

frequency dial.

@METER RANGE switch selects

full

scale range

of meter

in

percent,

dB

and rms volts.

Signal.

OSENSITMTY selector provides

r)

-

50

dB

atteau-

@SENSITIVITY VERNIER control provides fine

@Mechanical zero adjust provides mechanical

OFUNCTION switch selects type of operation

of

@Shorting

bar

connects circuit ground

to

chassis

@INPUT terminalsprovide connections for input

ation of input signal

in

10

dB

steps

in

SET LEVEL

and

DISTORTION functions.

adjustment of sensitivity setting.

zero adjustment of meter.

instrument.

ground.

stgnal.

@RF

INPUT

connector (Model

334A

only) provides

input connection for

AM

RF carrier input signal.

20

FUSE provides current overloadprotection for

0

instrument circuits.

21

Line voltage switch sets inrrtrument to

'operate

from

100

V/120

V/220

V/240

V.

@)

Ac power connector provides input connectton

for ac power.

~~~

Figure

3-1.

Front and Rear Panel Description

3-

0

Model 333A/334A

100

100.5

102

112

100.5

102

112

Section

III

I

SECTION

111

OPERATING INSTRUCTIONS

3-1.

INTRODUCTION.

3-2. The Models 333A and 334A DistortionAnalyzers

measure

total

harmonic distortion

of

fundamentalfre-

quencies from 5

Hz

to

600

kHz;

harmonics upto3

MHc

are included. The sharp elimination characteristics

(

>80

dB),

the low level of instrument induced

dtstor-

tion, and the meter accuracy

of

theseinstrumentsre-

sult

in

highly accurate measurement of low level har-

monic distortion.

3-3.

An

rms

calibrated voltmeter

is

inherent in the

333A and

334A.

The voltmeter provides

a

full

scale

sensitivity

of

300

p

voltsrms(residualnoise

<25p

volts).

The voltmeter frequency range

is

from 5

HZ

to 3 MHz

except on the 0.0003 volt range, which

is

from 20

Hz

to 500

kHz.

3-4.

CONTROLS AND INDICATORS.

3-5. Figure 3-1

illustrates

anddescribesthefunction

of

all

front

and

rear

panel

controls, connectors, and

indicators.

keyed tothe drawing included within the

figure,

The description

of

each component

is

3-6.GENERAL OPERATING INFORMATION.

3-7.

INPUT

CONNECTIONS.

3-8. The

input

signal

can

be

connected to the 333A

and 334A through twisted pair

leads

or

a

shieldedcable

with banana plug connectors. Keep

all

test

leads

as

short

as

possible to avoid extraneous pickup from

stray

ac

fields. When measuring Low-level

signals,

ground loope may occur causing erroneous readings.

Ground loops may

be

avoided

by

connecting the 333A/

334A Distortion Analyzer toan appropriate isolation

transformer to break the chassis ground from power

supply ground. Connect

all

other

instruments

to one

power

strip

with the three-prong connectors

as

close

as

possible.

3-9. VOLTMETER CHARACTERISTICS.

3-10. The RMS VOLTS markmgs on the meter face

arebased ontheratiobetweentheaverageandeffective

(rms)values

of

a

pure

sine

wave, Theratioof average

to effective values in a true sine wave

is

approximately

0.9

to

1.

When the meter

is

used to measure complex

waves,

the voltage indicated may not

be

the rms value

of the

signal

applied. This deviation

of

meter indica-

tion exists because the ratios of average to effective

values are usually not the same in

a

complex wave

as

in

a

sine wave. The amount of deviation depends on

the magnitude and phase relation betweenthe harmonics

and fundamental frequency of the signal applied.

Table 3-1

lists

the deviation of the meter indication

of

a

sine wave

partly

distorted

by

harmonics.

As

in-

dicated in the table, harmonic content of less than

108

results

in

very small errors.

Table

3-1

Effect of Harmonics on Voltage Measurements

Input Voltage

Characteristics

Fundamental

=

100

Fundamental

+

10%

2nd harmonic

Fundamental

+

20%

2nd harmonic

Fundamental

+

50%

2nd harmonic

Fundamental

+

10%

3rd harmonic

Fundamental

+

208

3rd harmonic

Fundamental

+

50%

3rd harmonic

Meter

100

-

102

100

-

110

96

-

104

94

-

108

90

-

116

NOTE

This chart

is

universal in application

since these errors are inherent in

all

average-responding voltage-measuring

instruments.

3

-11.

When making distortion measurements where

tne fundamental frequency

is

suppressed and the re

-

mainder of the

signal

is

measured, the reading ob-

tained on an average responding meter may deviate

from the true total rms value. When the residual

wave contains many inharmonically related sinusoids,

the maximum error

in

the distortion reading

is

about

11

%

(11

%

of the measured distortion) low for dis-

tortion levels below 10

%.

EXAMPLE

:

Measured Maximum Error Total

Distortion In Meter Indication Distortion

2.5%

+O.

llx0.025= 0.025+0.0027=

0.00027 0.0277

or

2.8%

This example representsthe maximumpossible

error,

and in most cases the error

is

less. In distortion

measurements, the reading

of

an

average-responding

meter

is

sufficiently close to the rms value to

be

satisfactory for most applications.

3-12.

OUTPUT

TERMINALS.

3-13. The

OUTPUT

terminals provide

a

0.1

V

rms

open circuit

output

for

full

scale meter deflection.

These terminals can

be

used to monitor the output

signal

with

an

oscilloscope,

a

true rms voltmeter,

or

a wave analyzer. The combination

of

the distortion

meter and oscilloscope provides more significant in-

3-1

Section

IIf

Model

333A/334A

formation about the device under test than the

expression of distortion magnitude alone. Information

obtained from the oscilloscope pattern

is

specific

and

reveals

the

nature

of distortion which sometimes

occurs

at

such low levels that

it

is

difficult to detect

in

the presence

of

hum and

noise.

The impedance

at

the

OUTPUT terminals

is

2000

ohms,

therefore, ca-

pacitive loads greater than

50

pF should

be

avoided

to

maintain the accuracy

of

meter readings.

3-14.

OPERATING PROCEDURES.

3-15.

INSTRUMEN"

TURN-ON.

a

Set the

115-230

VAC switch

to

coincide with the

line

voltage in

we.

Turn switch to ON position.

Pilot lamp

will

glow, indicating application

d

primary power.

3-16.

ADJUSTMENT OF METER MECHANICAL

ZERO.

3-17.

The meter

ia

properly zero-set when the

pointer rests over the zero calibration mark and the

instrument

ie

in

its

normal operating enivronment

and

is

turned

off,

Zero-set the meter

as

follows

to

obtain

maximum accuracy and mechanical stability:,

Turn instrument on and allow

it

to

operate

for

at

least

20

minutes, to let meter move-

ment reach normal operating temperature.

b.

Turn

instrument off and allow

30

seconde

for

all

capacitorsto discharge.

c. Rotate zero adjustment screw clockwise

un-

til

pointer

is

left

of

zero and moving upscale.

d.

Continue rotating screw clockwise; stopwhen

pointer

ia

exactly

at

zero.

e.

When

pointer

is

exactly over zero, rotate

adjustment screw

slightly

counterclockwise

to

relieve

tension on pointer suspension.

If

pointer moves

aff

zero, repeatstepsc

through

e,

but make counterclockwise

rotation

lese.

a.

3-18.

DISTORTION

MEASUREMENT.

e

DO

NOT EXCEED THE INPUT VOLT-

DAMAGING COMPONENTS

ON

A2

BOARD.

AGES

LISTED

BELOW

ro

PREVENT

VOLTMETER FUNCTION

-lV

RANGE AND BELOW, AND

DISTORTIONANALYZER

FUNCTION

-

MAXIMUM

SENSITIVITY.

1.

300

VABOVE

100

HE

2.

50

VABOVE

1

kHz

3-19.

MANUAL MODE.

a.

Turn

instrument on and mechanically

zero

meter according to procedure in

Paragraphs

3-15

and

3-16.

b.

C.

d.

e.

f.

g.

h.

k.

1.

m.

Set NORM-R.

F.

DET. switch to NORM.

Set FUNCTION switch to SET

LEVEL.

Set MODE switch to MANUAL.

If

fundamentalfrequency

is

1

kHz

or

greater,

set

HIGH

PASS FILTER switch to

IN.

Set SENSITIVITYselector to

MIN.

position,

and rotate VERNIER control maximum

counterclockwise.

NOTE

The bandwidth of the SENSI-

TMTY selector

is

reduced

in

the

two

extreme

CCW

positions (positions used with

an input

signal

greaterthan

30

V).

Set METER RANGE switch to SET

LEVEL,

and

set

BALANCE

COARSE

and

FINE

con-

trols to center position.

Connect

signal

to

be

measuredto333A/334A

INPUT terminals.

I

WARNING

1

REMOVE SHORTING

STRAP

BETWEEN

FRAME GROUND

(A

)

AND

CHASSIS

GROUND (

)

TERMINALSON

FRONT

PANEL INPUT TERMINALS WHEN

MEASURING DISTORTION BETWEEN

TWOPOINTSWHICHAFEDCOFFSET

FROM GROUND POTENTIAL.

Set

SENSITIVITY selector to

obtain

meter

indication greater than

1/3

full

scale.

Adjust SENSITIVITY VERNIERfor

full

scale

meterindication

if

making

distortion

measure-

ment in percent;

if

makingdistortionmeasure-

ment

in

dB

adjust SENSITMTY

VERNIER

for

0

dB

meter indication.

NOTE

If

unable to adjust for full scale

or

OdB

indication, (whichindicates

input

signal

is

below

0.3

volts),

set METER RANGE selectordown-

scale.

Use

this

new

setting

as

the

100'KDor

OdB

SET LEVEL position,

thus making the next range

30%

or

-10

dB,

etc.

Set FREQUENCY RANGE switchandfrequency

dial

to fundamental frequency of input

signal.

Set FUNCTION switch to DISTORTION.

Adjust frequency

dial

vernier and BALANCE

COARSE and FINE controls for minimum

3-2

Model

333A/334A

Section

III

meter indication.

Set

METERRANGE

switch

down-scale

as

necessary to keep meter

in-

dication on scale.

n.

Repeat step

m

until

no further reduction

in

meter indication can

be

obtained.

0.

Observe distortion

either

in

percentage or

dB,

as

indicated

by

meter deflection and

METER RANGE

switchsetting.

For

example,

if

meter indicates

0.4

and

METER

RANGE

setting

is

18,

distortion measured

is

0.4%

of

fundamental. Similarly,

if

meter

indi-

cates

-6

dB

and

METER RANGE

setting

ie

-40

dB, distortion measured

is

-46

dB from

fundamental.

NOTE

In

MANUAL

mode

the

accuracy

of

distortion measurements

is

affected

by

frequency stability

of

the input

signal.

An

inaccuracy

in

distortion indications occurs

when

the

frequency

drift

of

the

input

signal

exceeds

the

bandwidth

of

the rejection curve.

p.

If

desired, rms voltage of

input

signalcan

be

measured

by

setting

FUNCTION

switch to

VOLTMETER,

and

setting

METER

RANGE

switch

to

obtain

an on-scale indication.

3-20. AUTOMATIC

MODE.

a

b.

C.

d.

e.

f.

Perform steps athroughlof Paragraph

3-19.

Adjust frequency

dial

vernier and

BALANCE

COARSE

and

FINE

control8for minimum

meter indication.

When meter indication

is

less than

10%

of

SET LEVEL

indication,

set

MODE

switch to

AUTOMATIC.

(If

fundamental cannot

be

manually

nulled below

10%

of

SET LEVEL

indication, automatic mode cannot

be

used).

Set

METER RANGE

switch down-scale to

obtain on-scale meter indication.

Observe distortion either in percentage

or

dB,

as

indicated

by

meter deflection and

METER RANGE

switch

setting.

Forexample,

if meter indicates

0.4

and

METER RANGE

setting

is

18,

distortion measured

is

0.4%

of

fundamental. Similarly,

if

meter indicates

-6

dB

and

METER RANGE

setting

is

-40

dB,

distortion measured

is

-46

dB from funda-

mental.

If

desired, rms voltage of input

signal

canbe

measured by setting

FUNCTION

switch to

VOLTMETER,

and

setting

METER RANGE

switch to obtain

an

on-scale indication.

3-21. DISTORTION MEASUREMENT OF

AM

RF

CARRIERS

(334A

only).

DO

NOT EXCEED

MAXIMUM

INPUT

VOLTAGES LISTEDON

REAR

PANEL.

a.

Turn instrument

on

and

mechanically zero

meter according toprocedure

in

Paragraphs

3-15

and

3-16.

b.

Set

NORM.-R

F.

DET.

switch to

R.

F.

DET.

c. Connectinput

signal

to

R

F.

INPUT

terminal

on rear panel.

Refer

to Paragraph

3-19

formanual distort-

ion measurement;

refer

to

Paragraph

3-20

for

automatic distortion measurement.

d.

NOTE

If

no

meter deflection can

be

obtained with

an

RF

input,

diode

A4CR1

should

be

checked.

A

spare diode

is

located on

the

outside

of

the

A4

shield.

3-22. VOLTAGE MEASUREMENT.

a.

Turn instrument on and mechanically zero

meteraccordingto procedure in Paragraphs

3-15

and

3-16.

b.

Set

NORM.-R.

F.

DET.

switch to

NORM.

c.

Set

FUNCTION

switch to

VOLTMETER.

6

Set

METER RANGE

switch to

a

range

exceeding amplitude

of

signal to

be

mea-

sured.

e. Connect

signal

to

be

measured to

INPUT

terminals.

f.

Set

METER RANGE

switch to give a reading

as

close to

full

scale

as

possible, and

ob-

serve meter indication.

g. The dB scale

of

the

333A/334A

is

calibrated

in

dBm, such

that

0

dBm =

1

milliwatt

dissi-

pated

by

600

ohms.

Therefore,

a

dBm mea-

surement must

be

made across

600

ohms.

However,

dB

measurements

across

other

impedances can

be

converted to dBm

by

use

of

the Impedance Correction Graph of

Fig-

ure

3-3.

For example: to convert

a

-30

dB

reading

across

200

ohms

to dBm, locate the

200

ohm

impedance line

at

the bottom

of

the

graph.

heavy

black

line, and

read

the

meter correc-

tion

at

that

point. The correction for

200

ohms

is

+5

dBm;

thus

the

corrected reading

is

-25

dBm.

3-3

Follow the impedance

line

to

the

Section

III

3-23. METER INDICATION.

3-24. The 333A/334A meter

is

calibrated to indicate

in

both dB and volts.

It

is

interesting to notethat the

METER RANGE markings differ from most ac volt-

meter range markings.

On

most

ac

voltmeters

(600

ohms)

0

dB

corresponds

to

the

1

volt

range.

This

is

not

true

inthecase

of

the333A/334A. Sincethe

instru-

ment

is

primarily

a

distortionanalyzer, measurements

are

in

dB (relative measurement) rather than

in

dBm

(absolute measurement). Zero dB on the 333A/334A

corresponds to0.3 volt range rather than

the

1

volt

range. This allows a10

dB

greater

dynamic

range

of

distortion measurements.

Model 333AI334A

3-30. 333A/334A

WT”H

OPTION 01.

3-25.

E

measurements

are

to

be

made in dBm, 10

dB

must

be

subtracted from the METER RANGE

setting.

Thus

0

dB

becomes the -10 dBm

range

for absolute

power measurements. Zero dBm

is

equal

to

1

milli-

watt dissipatedbyanyimpedance andinthis particular

case

is

800

ohms.

The +10 DECIBELS marking on the

meter

face

indicates

thatwhenvoltmetermeasurements

are

being made, the indication (METER RANGE plus

meter indication)

is

10

dB

greater

than when power

(dBm) measurements

are

being made.

3-26.

In

short, when distortion and voltage measure-

ments

are

being made, utilizethe instrumentMETER

RANGE and meter scale

as

they

exist.

For absolute

power measurements in dBm, simply subtract 10

dB

from the METER RANGE

setting.

3-27. USE OF OUTPUT TERMINALS.

3-28.

InVOLTMETERand SET LEVEL functions, the

333A/334A can

be

used

as

a

low distortion, wide-band

amplifier. A portion of the meter

input

(0.1

V

rms

open

circuit for

full

scale meterdeflection

is

provided

at

the

OUTPUT terminals.

3-29.

In

DISTORTION function, the distortion (0.1

V

rmsopen circuit forfull

scale

deflection)

is

provided

at

the OUTPUT terminals for monitoring purposes.

NOTE

The INPUT terminal and the

OUTPUT terminalshouldnot be

connected directly together when

making low level measurements.

These terminals

are

isolated from

each other

by

1

ohm which reduces

the

effects

of

commonmodevoltages.

3-31. Operating procedures for the 333A/334A with

Option01

are

the same asforthe standard instrument.

The onlydifference between the standard and optional

instrument

is

that the Option 01has

a

special

meter

and meter amplifier which

is

compensated to respond

to

W

(volume

unit)

characteristics.

3-32. MANUAL NULLING.

3-33. Since the frequency and balance controls

are

rather

sensitive in

the

MANUAL mode,

the

following

information

is

suppliedto

simplify

nulling the

333A/334A

in

the MANUAL mode. When nulling

the

333A/334A

in

the MANUAL mode, connect

the

equip-

ment

as

shown

below

and

adjust

the

333A/334A

fre-

quency

and

balance controls for the waveform shown

in

step

a

below. Additional waveforms

are

provided

to simplify nulling.

No harmonic

dietortion.

Frequency

and

balance adjustment correct.

Frequency and balance control

im-

properly adjusted.

Frequency approximately

correct;

balance

incorrect.

Balance

approximately correct;

fre-

quency incorrect.

Second harmonic predominant;

fre-

quency and balance adjusted.

Second harmonic predominant;

fre-

quency and balance

adjusted;

phase

changed.

Second harmonic predominant;

fre-

quency and balance

adjusted;

phase

changed.

Third harmonic predominant.

Balance incorrect; meter reading

&

scale.

Frequency incorrect; meter

readin(

off

scale.

3-4

Section

IV

Model

333A/334A

I

I3

If

I

13

jP

I

L

PI

I

-----

I

---A-

Y

m

0

W

lb

I

-

.-

I

1

I

1

Model 333A/334A Section IV

SECTION

IV

THEORY

OF

OPERATION

4-1.

OVERALL DESCRIPTION.

4-2. Models 333A and 334A Distortion Analyzers in-

clude

an

impedance converter,

a

rejection amplifier,

a

metering circuit, and

a

power supply. The Model

334A also

contains

an

AM

detector. The impedance

converter provides a

low

noise input circuit with

a

highinput impedance independent

of

source impedance

placed

at

the INPUT terminals. The rejection ampli-

fier

rejects the fundamental frequency of the

input

signal

and

passes

the remaining frequency components

on to the metering circuit for measuring distortion.

The metering circuit provides visual indications of

distortion

and

voltage

levels

on the front panel meter,

M1. The

AM

detector (Model 334A only) detects the

modulating

signal

from the

RF

carrier

and

filters

all

RF

components from the modulating

signal

before

it

is

applied

to

the impedance converter circuit,

(Refer to Figure 4-1)

4-3.

BLOCK DIAGRAM DESCRIPTION.

level

applied to

the

metering circuit to

1

mV for full

scale deflection. Sensitivity

of

the metering circuit

is

increasedto 300

pV

for full scale deflection onthe

.0003

Vrange.

Themeteringcircuitprovides a visual

indication of the distortion level

of

the input signal.

In

addition totheindication provided

by

the

meter, the

OUTPUT terminals provide

a

means

of

monitoring

the distortion components.

4-8. DISTORTION MEASUREMENT

IN

AM

CARRIERS.

4-9. The

Model

334A DistortionAnalyzer contains an

AM

detector circuitformeasuringenvelope distortion

in

AM carriers. The input

signal

is appliedto the in-

pt

of

the AM detector circuit where the modulating

signal

is

recovered from

the

RF carrier. The sipal

is

then applied to the impedance converter circuit

through the one megohm attenuator and then through

the same circuits previously described in the distor-

tion measuring mode operation.

4-4. DISTORTION MEASURING OPERATION. 4-10. VOLTMETER OPERATION.

4-5. For distortion measurement, the input signalis

appliedto

the

impedance converter (Assembly

A2)

through the FUNCTION selector, S1, and the one

megohm attenuator. The one megohm attenuator

is

a

voltage

divider

network which provides 50 dB atten-

uation

in

10

dB

steps. The desiredlevelof attenuation

is

selected

by

the SENSITIVITY selector,

S2.

The

impedance

converterprovides impedance matching and

unity

gain between the INPUT terminals and the input

of the rejection amplifier.

4-6. Therejectionamplifierconsistsof

a

preamplifier,

a

Wien

bridge, andabridgeamplifier. TheSENSITIVITY

VERNER control,

at

the input

of

the preamplifier,

provides

a

set

level

signal

to

obtain

a

full scale read-

ing on the meter for any voltage level at the input

of

the

instrument.

With the FUNCTION switchintheSET

LEVEL position,

a

ground

is

applied to theWienbridge

circuit to allow

a

signal

reference level to be set up

on the meter.

With

the FUNCTION switch

in

theDIS-

TORTION position, the Wien bridge

is

used asan in-

terstage coupling network between the preamplifier

and bridge amplifier. The Wien bridge

is

then tuned

and balanced to reject the fundamental frequency

of

the

applied input

signal.

Two automatic control loops con-

sisting of

two

phase detectors, lamp drivers, lamps,

and photocells provide fine

tuning

and balance in the

AUTOMATIC MODE. The remaining frequency com-

ponents are appliedto the bridge amplifier and

are

measured

as

distortion by the metering circuit.

Nega-

tive feedback from the bridge amplifier to the preamp-

lifiernarrowstherejectionresponse of theWienbridge.

4-7. The output of the rejection amplifier

is

applied

to the metering circuit through the post-attenuator.

The post-attenuator

is

used to limit the input signal

4-11. In the voltmeter mode of operation, the input

signal

is

applied to the impedance converter circuit

through the

1:l

and

1OOO:l

attenuator. The

1:l

atten-

uation ratioisusedonthe0.0003 too.

3

VOLTSrangcs,

and the

1OOO:l

attenuationratiois used in the

1

to 300

VOLTS ranges.

With

the FUNCTION switch

in

the

VOLTMETER position, the output of

the

impedance

converter bypasses the rejection amplifier and

is

applied to the metering circuit through the

post-

attenuator (METER RANGE switch). Meteringcircuit

sensitivity

is

increased from

1

mV for full scale

deflection to

300

pV on the ,0003V range,

as

it was in

the distortion measuring operation. The function

of

the post-attenuator andmeteringcircuit

is

thesame

for

voltmeter operation as for the distortion measuring

operation.

4-12.

DETAILED CIRCUIT DESCRIPTION.

4-13. IMPEDANCE CONVERTER CIRCUIT.

;

4-14. The input

signal

is

applied to the impedance

converter circuitthroughthe

1:1

and 1000:

1

attenuator

S3R12

in voltmeter operation, and through the one

megohm attenuator S2R1through

S2R6

in distortion

operation. Capacitive dividers SC1through SC10

in

the attenuator keep

the

frequency response flat.

The impedance converter

is

a

low distortion, high

input impedance amplifier circuit with gain indepen-

dent of the source impedance placed at the INPUT

terminals.

4-15. Instrument induced distortion of the signal

being measured

is

minimized

hy

keeping the input

impedance and the gain of

the

impedance converter

4-1

Section IV Model 333AI334,

linear. The input impedance

is

kept linear

by

use of

local positive feedback from the source of A2Ql to

the gate of A2Ql and to the protective diodes A2CR2

and A2CR3. Thus signals with

a

large sourceimped-

ance can

be

measured accurately. Overall induced

distortion

is

further minimized

by

a high open loop

gain and 100%negative feedback. The high open loop

gain

is

achieved

by

local

positive feedback from the

emitter

of

A2Q3 to the collector

of

A2Q2. Overall

negative feedback from the emitter circuit

of

A2Q4

to the source of A2Ql results in unity gain from the

impedance converter.

4-16. Thebias

points

of thetransistors

in

the imped-

ance converter

are

selected to minimize instrument

induced distortion. A2Q1, an extremely low noise,

high impedance field

effect

transistor,

is

the major

component that makes linearity of the impedance con-

verter independent

of

the

signal

source impedance.

4-17. REJECTION AMPLIFIER CIRCUIT.

(Refer to

Figures

7-3

and

7-5)

4-18. The rejection amplifier circuit consists of the

preamplifier (A3Q1

thru

A3Q3), the Wien bridge

resistive leg and auto control loop (A5Q1 thru A5Q9

with associated lamp and photocell), the reactiveleg

and auto control loop (A5Q10 thru A5Q18 with associ-

ated lamp and photocell), and the bridge amplifier

(A3Q4 thru A3Q6).

4-19. PREAMPLIFIER CIRCUIT.

4-20. The signal from the impedance converter

is

applied tothe preamplifier, which

is

used during SET

LEVEL

and DISTORTION measuring operations.

Negative feedback from the junction of A3R10 and

A3Rll

is

applied to the junction of A3R2 and A3C2 to

establish the operating point for A3Q1. Negative

feedback from the emitter

of

A3Q3

is

applied to the

emitter

d

A3Q1 to stabilize the preamplifier. The

preamplifier, like the impedance converter,

is

designed for high open loop

gain

and low closed loop

gain

to minimize

instrument

induced distortion.

4-21. WIEN BRIDGE CIRCUIT.

4-22. In the distortion measuringoperationthe Wien

bridge

circuit

is

used as

a

rejection

filter

for the

fundamental frequency of the input

signal.

With the

FUNCTION selector, S1, inthe DISTORTION position,

the Wien brldqe

is

connected

as

an

interstagecoupling

network between the preamplifier circuit and the

bridge amplifier circuit. The bridge

is

tuned to the

fundamental frequency

of

the input signal by setting

the FREQUENCY RANGE selector,

S4,

for the appli-

cable frequency

range,

andtuning the capacitors C4A

through C4D. The bridge circuit

is

balanced by ad-

justing

the

COARSE balance control, R4, andtheFINE

balance control, R5.

In

the AUTOMATIC MODE fine

tuningandbalancing

are

accomplished

by

photoelectric

cells which

are

in the resistive and reactive legs of

the Wien bridge. The error signals for driving the

photocells

are

derived by detecting the bridge output

using the input signal

as

a

reference,

4-23. When the Wien bridge

is

not tuned exactly to

the frequencytobe nulled, aportion of thefundamental

4

-2

INPUT TO BRIDGE

OUTPUT OF BRIDGE

IFRESISTIVE LEG

IS

UNBALANCED

OUTPUT

OF

BRIDGE

IF

REACTIVE LEG

IS DETUNEO

Figure

4-2. Bridge Waveforms

frequency will appear

at

the bridge output. The phase

of this

signal

depends

on

which leg

of

the bridge

is

nc

tuned,

or

on the relative errors in tuning

if

neither

if

set

correctly. The magnitude of the signal

is

propor

tional to the magnitude of the tuning error

of

either

0.

both legs of the bridge.

4-24.

Figure

4-2a shows

a

sinusoidinputtothe Wien

bridge.

If

the resistive leg of the bridge

is

slightly

unbalanced, the output of the bridge

is

very small,

but has the waveform shown

in

Figure 4-2b and

is

in

phase with the input.

As

the resistive leg

is

tuned,

the signal approaches zero amplitude at null and then

becomes larger, but 180° out of phase, if the

null

position

is

passed.

Whentheresistive leg

is

correctly

tuned and the reactive leg

is

tuned through null,

a

similar waveform

is

produced, Figure 4-2c. The

only difference

is

that the reactive signal

is

90°

out

of phase with the resistive

signal.

4-25. When

the

bridge output

is

detected using the

input signal

as

the

reference, the error

signals

in

phase

or

1800 out of phase with the reference develop

a voltage that is used to vary the resistance

in

the

resistive leg

of

the bridge, to tune it to the correct

null position. Signalsof theformin Figure4-2c donot

develop any voltage,

as

the resistive detector is in-

sensitivetoinputs differingfromthereferenceby

90°.

Model

333A/334A

Section IV

(5

E IN

0

~

TYPICAL WlEN

BRIDGE

I

Figure

4-3.

Wien Bridge Circuit and Rejection Characteristics

4-26.

In

an

independent, but similar, control loop,

the bridge input

signal

is

shifted

900

and used

as

the

reference

signal

for the detector. This detector

develops control voltages to null the reactive leg of

the bridge, but

is

insensitive to signals of the form

in

Figure

4-2b,

which

are

caused by small tuning

errors

of

the

resistive branch.

4-27.

The

result

is

that the two control loops derive

information from

a

common source and develop two

independent control signalsfornulling the two legs

of

the bridge. These control voltages are used to vary

the brilliance of lamps, which

in

turn cause resistance

changes

in

photocells

that

form part of

the

Wien bridge.

4-28.

When the bridge circuit

is

tuned and balanced,

the voltage and phase

of

the fundamental, which

appears

at

junction of the

series

reactive leg

(SQR1,

3, 5,

7,

or

9 and

C4A/B)

and the shunt reactive leg

(SQRll, 13, 15, 17,

or

19,

and

C4C/D),

is

the

same

as

at

the midpoint of the resistive leg

(A3R12

and

A3R14).

When

these

two

voltages

are

equal

and

in

phase, the fundamentalfrequency will not appear

at

the drain of the field effect transistor

A3Q4.

For

frequenciesother than the fundamental, the reactive

leg of the Wien bridge offers various degrees

of

attenuation and phase shift which cause a voltage at

the output points of the bridge. This difference volt-

age

betweenthe reactive leg and resistive leg

is

amp-

lified by

A3Q4, A3Q5,

and

A3Q6.

Figure

4-3

illus-

trates a typical Wien bridge circuit and the rejection

characteristics for

it.

4-29.

The Wien bridge circuit

is

designed

to

cover

a

continuous frequency range of over a decade for each

position of the

FREQUENCY

RANGE

selector

S4.

S4

provides coarse tuning

of

the

reactive leg by changing

the bridge circuit constants in five steps at

1

decade

per

step.

For

the automatic control loop, the refer-

ence voltage

is

taken from

R6

at the input to the re-

jection amplifier and applied to

the

buffer amplifier

A5Q7.

The reference voltage

is

amplified andclipped

by

A5Q8

and

A5Q9,

and coupled to the detector

A5Q4.

The output of the metering circuit, which contains the

fundamentalfrequency

if

either leg of the bridge

is

untuned,

is

applied to the

buffer

amplifier

A5Q1.

It

is

amplified by

A5Q2

and

A5Q3

and coupled to the

detector

A5Q4.

4-30.

RefertoFigure

4-4,

partial scheiiiatic

for

detector operation. The discussion

is

applicable

to both resistive and reactive detector circuits.

4-31.

The

signals

from the error amplifier,

(A5Q2

andA5Q3)

will

be

equal and of opposite phase, and

will

cancel out each other when

the

detector,

A5Q4,

is

off. However, when the positive half of the referencc

square wave gates

A5Q4

on,

the

signal from thc coll-

ector of

A5Q3

will

be shorted to ground. Thus the

signal from the collector

of

A5Q2

will

be

couplcd

through the filter network to the base of

A5Q5.

If

thc

signal from

A5Q2

is

in phase with the referencc, thc

positive half of the signal

will

be

passcd, and

if

it

is

out of phase, the negative half will

be

passed.

4-32.

The normal working voltage at

A5TP3

is

be-

tween0and

-1

volt. Thedcoutput of thefilter nctwork

causes the voltage

at

A5TP3

to go in

a

positive dircc-

tion (toward zero) for in phase error signals, and

in

a

negative direction (toward

-1

V)

for

out of phase

error

signals. The change in base voltage

is

then ampIificd

by

A5Q5

and lamp driver

A5Q6.

This

will

change thc

brilliance of lamp

A6DS1,

which

will

vary

theresist-

anceof

A6V1

inthe directionnecessaryto balance the

resistive leg of the bridge.

I

I I

I-1

I

Figure

4-4.

Auto

Control

Loop

Detector

4-3

Section

IV

Model

333A/334

4-33.

Refer

to

Figure

4-5

for the phase relationship

of

the

bridge

error

signal

andreferencevoltage

at

the

base

of

A5Q4.

The

shaded

portions of

the

error

sig-

nals

(bandc) indicate that

part

of the error

signal

which contributesto

the

dc

lamp control voltage.

As

indicatedind, any error

signal

that

ie

90°

outofphase

with

the

reference

does

not affect

the

dc lamp control

voltage, because

equal

amounts

of

the

positive and

negative

portions

are

passed.

4-34.

The operation

d

the reactive branch control

loop

ie

similar to

that

of

the

resistive branch. The

phase

delay

circuit,

A5Q15, A5Q16, S4AF

and

S4C1

through

S4C5,

shifts

the

reference voltagc

90°,

aa

shown

in

Figure

4-5f.

This makes the detector

A5Ql2

sensitive to components

of

the bridge error

signal

that are

900

out

of

phase

(g

and

h).

The outpui

of

the

lamp driver,

A5Q14,

controls the brilliance

of

A6DS2,

which varies the resietance

of

A6V2

through

A6V5

to

tune

the

branches

of

the

reactive leg. Deck

AR

of

the

FREQUENCY RANGE switch,

54,

switches

A5R56

in

parallel

with

A5R55

on

the

top

three

fre-

quency

ranges.

A6DS2

will

becomebrighter, andlower

the resistance

of

A6V2

through

A6V5,

makingvariatio

45'

135'

225'

315'

a

Ref. signalforResistive

Detector

(A564)

b

Resistive

Error

signal

in

phase

with

reference

at

bridge

Resptive

Error

signal

180

out

of

phase

d

Reactive

Error

signal

30

out

of

phase

(Results

in

no

output

from

Re-

sistive Detector)

e

Error

signal,

reactive

leg detuned, resistive

.eg unbalanced

f

Ref.

signal

for Reactive

Detector

(A5612

b

Reactive

Error

signal

in

phase with reference

at

bridge

Reactive

Error

out

of

phase

h

signal

i

Reptive

Error

signal

90

out of phase(Results

in

no output from

Re-

active Detector)

Error

signal,

Reactive

leg detuned, Resistive

leg unbalanced

45'

13s'

225'

316'

Figure

4-5.

Reference and

Error

Phase Relationship

4-4

HP 333A Service manual

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