Clonal Bureau of Standam

library, Ml BWj. JUL I*®*

NBS SPECIAL PUBLICATION 260-29

Standard Reference Materials:

CALIBRATION OF NBS

SECONDARY STANDARD MAGNETIC TAPE

(COMPUTER AMPLITUDE REFERENCE)

SRM 3200

USING THE REFERENCE TAPE

AMPLITUDE MEASUREMENT "PROCESS A"

MODEL II
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3,

1 901 . The Bureau's overall goal is to strengthen and advance the Nation's science and

technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Center for Computer Sciences and

Technology, and the Office for Information Programs. THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consistent system of physical measurement; coordinates

that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics—Electricity—Heat—Mechanics—Optical Physics—Linac

Radiation2—Nuclear Radiation2—Applied Radiation2—Quantum Electronics3—

Electromagnetics3—Time and Frequency3—Laboratory Astrophysics3—Cryogenics3

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research lead- ing to improved methods of measurement, standards, and data on the properties of

well-characterized materials needed by industry, commerce, educational institutions, and

Government; provides advisory and research services to other Government agencies; and develops, produces, and distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Reactor

Radiation—Physical Chemistry. THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to pro- mote the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Institute also monitors NBS engineering standards activities and

provides liaison between NBS and national and international engineering standards

bodies. The Institute consists of the following technical divisions and offices: Engineering Standards Services—Weights and Measures—Flammable Fabrics

Invention and Innovation—Vehicle Systems Research—Product Evaluation Technology—Building Research—Electronic Technology—Technical Analysis

Measurement Engineering. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition, and effective utilization of automatic data processing equipment; and serves as the principal focus within the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center

consists of the following offices and divisions: Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing Technology. THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and accessibility of scientific information generated within NBS and other agencies of

the Federal Government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader

aspects of the National Measurement System; provides appropriate services to ensure

that the NBS staff has optimum accessibility to the scientific information of the world, and directs the public information activities of the Bureau. The Office consists of the following organizational units: Office of Standard Reference Data—Office of Technical Information and

Publications—Library—Office of Public Information—Office of International

Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.
UNITED STATES DEPARTMENT OF COMMERCE • Maurice H. Stans, Secretary NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

Standard Reference Materials:

Calibration of NBS Secondary Standard Magnetic Tape

(Computer Amplitude Reference) SRM 3200

Using the Reference Tape Amplitude Measurement

"Process A" Model II

Sidney B. Geller Information Processing Technology Division Center for Computer Sciences and Technology

National Bureau of Standards Washington, D.C 20234

-6, National Bureau of Standards Special Publication 260-29

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-29 , 57 pages (June 1971) CODEN: XNBSA

Issued June 1971

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 03.10:260-29). Price 60 cents. Stock Number 0303-0860

PREFACE

Standard Reference Materials (SRM's) as defined by the

National Bureau of Standards are "well-characterized materials, produced in quantity, that calibrate a measurement

system to assure compatability of measurement in the nation."

SRM's are widely used as primary standards in many diverse

fields in science, industry, and technology, both within the

United States and throughout the world. In many industries

traceability of their quality control process to the national

measurement system is carried out through the mechanism and

use of SRM's. For many 'of the nation's scientists and technologists it is therefore of more than passing interest to know the details of the measurements made at NBS in arriving

at the certified values of the SRM's produced. An NBS series

of papers, of which this publication is a member, called the

NBS Special Publication - 260 Series is reserved for this

purpose

.

This 260 Series is dedicated to the dissemination of

information on all phases of the preparation, measurement,

and certification of NBS-SRM's. In general, much more detail will be found in these papers than is generally allowed,

or desirable, in scientific journal articles. This enables

the user to assess the validity and accuracy of the measurement processes employed, to judge the statistical analysis,

and to learn details of techniques and methods utilized for

work entailing the greatest care and accuracy. It is also

hoped that these papers will provide sufficient additional

information not found on the certificate so that new applications in diverse fields not foreseen at the time the SRM

was originally issued will be sought and found.

Inquiries concerning the technical content of this

paper should be directed to the author(s). Other questions

concerned with the availability, delivery, price, and so forth will receive prompt attention from:

Office of Standard Reference Materials

National Bureau of Standards

Washington, D.C. 20234

J. Paul Cali, Chief

Office of Standard Reference Materials

iii
OTHER NBS PUBLICATIONS IN THIS SERIES

NBS Spec. Publ. 260 3 Catalog of Standard Reference Materials,

July 1970. 75 cents.* (Supersedes NBS Misc. Publ. 260,

January 1968 and NBS Misc. Publ. 241, March 1962.)

NBS Misc. Publ. 260-1, Standard Reference Materials:

Preparation of NBS White Cast Iron Spect rochemical

Standards, June 1964. 30 cents.*

NBS Misc. Publ. 260-2, Standard Reference Materials:

Preparation of NBS Copper-Base Spectrochemical

Standards, October 1964. 35 cents.*

NBS Misc. Publ. 260-3, Standard Reference Materials:

Metallographic Characterization of an NBS Spectrometric

Low-Alloy Steel Standard, October 1964. 20 cents.*

NBS Misc. Publ. 260-4, Standard Reference Materials:

Sources of Information on Standard Reference Materials,

February 1965- 20 cents.*

NBS Misc. Publ. 260-5, Standard Reference Materials:

Accuracy of Solution X-Ray Spectrometric Analysis of

Copper-Base Alloys, March 1965 • 25 cents.*

NBS Misc. Publ. 260-6, Standard Reference Materials:

Methods for the Chemical Analysis of White Cast Iron

Standards, July 1965. ^5 cents.*

NBS Misc. Publ. 260-7, Standard Reference Materials:

Methods for the Chemical Analysis of NBS Copper-Base

Spectrochemical Standards, October 1965- 60 cents.*

NBS Misc. Publ. 260-8, Standard Reference Materials:

Analysis of Uranium Concentrates at the National

Bureau of Standards, December 1965. 60 cents.*

NBS Misc. Publ. 260-9, Standard Reference Materials:

Half Lives of Materials Used in the Preparation of

Standard Reference Materials of Nineteen Radioactive

Nuclides Issued by the National Bureau of Standards,

November 1965- 15 cents.*

NBS Misc. Publ. 260-10, Standard Reference Materials:

Homogeneity Characterization on NBS Spectrometric

Standards II: Cartridge Brass and Low-Alloy Steel,

December 1965. 30 cents.*

iv
NBS Misc. Publ. 260-11, Standard Reference Materials:

Viscosity of a Standard Lead-Silica Glass, November

1966. 25 cents.*

NBS Misc. Publ. 260-12, Standard Reference Materials:

Homogeneity Characterization of NBS Spect rometric

Standards III: White Cast Iron and Stainless Steel

Powder Compact, September 1966. 20 cents.*

NBS Misc. Publ. 260-13, Standard Reference Materials:

Mossbauer Spectroscopy Standard for the Chemical Shift

of Iron Compounds, July 1967. ^0 cents.*

NBS Misc. Publ. 260-14, Standard Reference Materials:

Determination of Oxygen In Ferrous Materials —

SRM 1090, 1091, and 1092, September 1966. 30 cents.*

NBS Misc. Publ. 260-15, Standard Reference Materials:

Recommended Method of Use of Standard Light-Sensit ive

Paper for Calibrating Carbon Arcs Used in Testing

Textiles for Colorfastness to Light, June 1967.

20 cents.*

NBS Spec. Publ. 260-16, Standard Reference Materials:

Homogeneity Characterization of NBS Spectrometric

Standards IV: Preparation and Microprobe Characterization

of W-20$ Mo Alloy Fabricated by Powder Metallurgical

Methods, January 1969. 35 cents.*

NBS Spec. Publ. 260-17, Standard Reference Materials:

Boric Acid; Isotopic and Assay Standard Reference

Materials, February 1970. 65 cents.*

NBS Spec. Publ. 260-18, Standard Reference Materials:

Calibration of NBS Secondary Standard Magnetic Tape

(Computer Amplitude Reference) Using the Reference

Tape Amplitude Measurement "Process A", November 1969

.

50 cents.*

NBS Spec. Publ. 260-19, Standard Reference Materials:

Analysis of Interlaboratory Measurements on the

Vapor Pressure of Gold (Certification of Standard

Reference Material 7^5), January 1970. 30 cents.*

NBS Spec. Publ. 260-20, Standard ' Reference Materials:

Preparation and Analysis of Trace Element Glass

Standards. (In preparation)

NBS Spec. Publ. 260-21, Standard Reference Materials:

Analysis of Interlaboratory Measurements on the Vapor

Pressures of Cadmium and Silver, January 1971. 35 cents.*

v
NBS Spec. Publ. 260-22, Standard Reference Materials:

Homogeneity Characterization of Fe-3Si Alloy,

February 1971. 35 cents.*

NBS Spec. Publ. 260-23, Standard Reference Materials:

Viscosity of a Standard Borosilicate Glass, December 1970.

25 cents.*

NBS Spec. Publ. 260-24, Standard Reference Materials:

Comparison of Redox Standards. (In preparation)

NBS Spec. Publ. 260-25, Standard Reference Materials:

A Standard Reference Material Containing Nominally Four

Percent Austenite, February 1971. 30 cents.*

NBS Spec. Publ. 260-26, Standard Reference Materials:

National Bureau of Standards-U . S . Steel Corporation

Joint Program for Determining Oxygen and Nitrogen in

Steel, February 1971. 50 cents.*

NBS Spec. Publ. 260-27, Standard Reference Materials:

Uranium Isotopic Standard Reference Materials,

April 1971. $1.25.*

NBS Spec. Publ. 260-28, Standard Reference Materials:

Preparation and Evaluation of SRM's 481 and 482 Gold-Silver

and Gold-Copper Alloys for Microanalysis. (In preparation)

*Send order with remittance to: Superintendent of Documents,

U.S. Government Printing Office, Washington, D.C. 20402.

Remittance from foreign countries should include an additional one-fourth of the purchase price for postage.

vi
TABLE OP CONTENTS

PAGE

1. Introduction 2 2. Theory of Operation of the NBS Measurement

System (Model II) 4 A. System Components 4 1. Signal Amplitude Read Channel

Components 4 2. Write Channel Components 5 3. Auxiliary Components and Systems .... 5 B. Description of System Operation 5 1. Signal Amplitude Read Channel

Operation 5 2. Write Channel Operation 8 C. Switching System 10

1. Signal Amplitude Read System 10

2. Write System 11

3. Calibration and Operation of the Model II System 12

A. Dc Calibration Procedures 15

B. Ac Calibration Procedures 15

C. Master Gain Calibration and Operation of

the Model II System 17

1. Output Voltage e {%) versus Write

Current I Curves 18 w

2. ABC Chart Measurements 19

3. Candidate Tape Calibration Procedures . 21

4. Additional System Checking and

Calibrating Techniques 21 vii
4. Notes to Reference Tape Users 24

5. Component List 28

6. Acknowledgements 33

LIST OP FIGURES

PAGE

Figure No.

1. NBS Model II Measurement System 34

2. Signal Amplitude Read Channel Block

Diagram 35 3.-7- Signal Amplitude Read Channel Circuit

Diagrams 36-40

8. Write Channel Block Diagrams 4l 9.-11. Write Channel Circuit Diagrams 42-44

12. Switching System for the Read Channel ... 45

13. Switching System for the Write Channel . . 46

14. Front Panel Layout for the Model II System. 47

15. e (%) versus I Curve 48

o w

16. ABC Chart Recording 49

viii
CALIBRATION OF NBS SECONDARY STANDARD MAGNETIC TAPE

(COMPUTER AMPLITUDE REFERENCE) SRM 3200

USING THE REFERENCE TAPE AMPLITUDE MEASUREMENT "PROCESS A" MODEL II Sidney B. Geller

Information Processing Technology Division

Center for Computer Sciences and Technology

National Bureau of Standards

Washington, D.C. 2023^

This publication describes the design, operation and

calibration of the NBS signal amplitude measuring system

(Process A - Model II) that is used for calibrating

unrecorded Secondary Standard Magnetic Tapes (Computer

Amplitude Reference) SRM 3200. This system supercedes

the measurement system that was described in the NBS

Special Publication 260-18 (November 1969). The signal

level calibration is made with respect to a reference

signal level derived from the NBS Master Standard Magnetic

Tape (Computer Amplitude Reference) that is kept in

repository at NBS. The techniques for measuring and

recording the data that accompany each Secondary Standard

Magnetic Tape in the form of strip chart recordings and

saturation curves are described.

Key words: Average signal peak level; computer amplitude

reference; magnetic tape; master standard;

saturation curves; secondary standard; signal

level calibration; standard reference materials; unrecorded reference.

1
1. Introduction

The characteristics of present day magnetic computer

tapes are the result of long term research and development

by the magnetic tape industry. Technological developments

in related fields and transducer-tape interplay have

stimulated continuing improvement of the tape media and

their performance. This has often led to differences in

tape characteristics and to marginal operation when tapes

are interchanged between systems. The only tapes previously

available for quality assurance purposes have been industry

supplied standards

.

At the request of industrial users of computer tape,

Government procurement agencies, producers of magnetic

computer tapes, and producers of tape handling equipment

the National Bureau of Standards has developed a tape

measurement system and is supplying unrecorded Secondary

Standard Magnetic Tapes (Computer Amplitude Reference)

through the NBS Office of Standard Reference Materials.

This material, which is designated as the NBS Standard

Reference Material No. 3200 (SRM 3200), consists of a 600-

foot or greater length of secondary reference tape accom- panied by applicable test and calibration data, and a description of the equipment and procedures employed for

measurement of the tape. At least 600 continuous feet

on each tape must meet all of the requirements that are described on the accompanying SRM 3200 certificate. The

remaining tape footage will also be calibrated but may

or may not meet the certificate requirements. The calibration data charts will physically locate the 600 foot

region of interest on each reel. The secondary tapes are

1/2 inch wide unrecorded magnetic computer tapes wound on 8-1/2 inch diameter precision reels.

Each SRM 3200 is calibrated in terms of a 100$ signal

level that is derived from the NBS Master Standard Magnetic

2
Tape (Computer Amplitude Reference) which is kept in

repository at NBS. This signal level calibration is done

at recording densities of 200, 800, 1600 and 3200 flux

reversals per inch. Information in the form of signal

output strip charts accompanies each secondary tape. These

are recorded on the first read-while-write pass from 3 head tracks; one near each tape edge and one at the tape

center and are referred to as ABC charts . A set of X-Y recorder curves relating the reproduce head output voltage

to the write current on the first read-while-write pass at each bit density of both the NBS master and each secondary

tape also accompanies the SRM 3200. These are referred to

as e {%) versus I curves or X-Y curves,

o w Presently, the main criteria for the selection of

unrecorded amplitude reference tapes for calibration as secondaries are signal amplitude uniformity and proximity

of read-while-write output voltage to that of the master.

The instantaneous track-to-track variation in the average

signal peak amplitude is limited to a maximum of 3% among

the outputs from the NBS test tracks 2, 5 and 8. The

location of these tracks is defined in USASI Document

X3 . 22-1967. The maximum variation in the longitudinal

average signal peak amplitude along each test track is

limited to 4% over the documented 600 foot length of tape.

The value of the average signal peak amplitude measured

from each test track is within 10% of the signal level

derived from the NBS Master Standard Magnetic Tape (Computer

Amplitude Reference.) These criteria are applied for peak

signal recording on degaussed (fully ac erased) tape when

measured on the NBS system in the manner described in this

publication

.

3
2. Theory of Operation of the NBS

Measurement System (Model II)

A. System Components

Figure 1 shows the organization of the Model II system used for measuring and calibrating the unrecorded

NBS Secondary Standard Magnetic Tapes (Computer Amplitude

Reference) SRM 3200. The system consists of a write

channel (NRZI mode), three identical signal amplitude read

channels (Channels A, B and C), a supply voltage section

that includes a precision voltage dividing network and a switching system for use in both the operation and the

calibration of the system. Various readout instruments

are also included in the system.

The following descriptive material lists the components

that appear in each of the sections or channels. One of

the figures that is given with each channel contains the

block diagram of the channel functions and the other figures consist of the circuit realizations of the block

functions. Note that within most of the individual blocks

a figure number is inscribed which identifies the circuit

diagram that corresponds to that block.

1. Signal Amplitude Read Channel Components (figures

2-7)

a. A slotted read-write head (IBM Assembly No. 5417960, Part No. 2510730 or equivalent), a line driver LD-1, a termination network TE-1B,

and attenuator circuit AT-1 and a wideband

preamplifier WPR-1 with internal and external

gain potentiometers R^ and R^ and amplifier

OA-1.

b. A peak level detect-sample-and-hold circuit

PD-SH-1 that contains comparator IC-1,

transistors Tg through T-^s and diodes

through .

4
c. Level shifting, range setting and summing

circuits containing operational amplifiers

OA-2 through OA-5

d. External 10-turn potentiometers R,- for setting the "MASTER GAIN" of the system.

e. A passive R-C signal peak averaging circuit.

2. Write Channel Components (figures 8-11)

a. A variable frequency square wave generator

G-l whose frequency ranges from at least

22.5 kHz to 360.0 kHz, a pulse counter, a binary counter circuit BC-1 and pulse level

shifting circuits LS-1.

b. A slotted read-write head (IBM Assembly No. 5417960, Part No. 2510730 or equivalent), a write head current driver circuit WD-1 and a motorized write current amplitude control circuit CC-1.

3. Auxiliary Components and Systems

a. Pour precision voltage sources (±6.0, ±14.0,

±14.0, +30.0 volts) and a dividing network

DV-1 for providing dc calibration voltages

Operational amplifiers OA-6 and OA-7. One

precision digital voltage source.

b. A function switching system containing 9 wafer

switch assemblies, 2 pushbutton switches, 1 lever and 1 toggle switch (figures 12-13).

c. A modified IBM-2401-VI Tape Transport.

d. Read-out devices: a 6-track ABC chart re- corder, an X-Y recorder, a digital panel

meter DPM-1 and a digital voltmeter DVM-1.

Description of the System Operation

1. Signal Amplitude Read Channel Operation (figures

2-7)

The signal amplitude measurements are performed

at all bit densities on candidate tapes that
have been initially degaussed and then recorded

with all "ones" in the NRZI mode.

a. The signal which has been reproduced by a read-while-write operation from a candidate

tape is passed through a unity gain, line

driving amplifier LD-1 which is physically

located at the read head. The line is terminated by TE-1B and network AT-1. AT-1

attenuates the incoming signals so that the

inputs to the WPR-1 preamplifiers will fall

within a reduced range of amplitudes for the

different recording densities. AT-1 is adjusted with R

1 and R

2

. Typical values of

output signal from LD-1 have been found to lie in the range of 12.0-14.0 mV p/p at 3200

frpi and 17.0-22.0 mV p/p between the densities of 1600 to 200 frpi. The WPR-1 ' s are adjusted with R^ to operate at gains of 470

with R^ set at its mid-value of 500 ohms.

b. The amplified signals from the WPR-1 's are then fed into the peak-detect-sample-andhold PD-SH-1 circuits via OA-1. PD-SH-1

converts the ac signals into dc levels that

are equal to their peak values. 3-000 volts

dc represents the 100$ level for the measuring system and all output levels are described in terms of their value as a percentage

of 3.000 volts.

The peak detect-sample-and-hold circuit

PD-SH-1 in figure 5 operates as follows:

The hold capacitor is charged to the

positive signal peak value through diode D^. Simultaneously, the output signal from OA-1

is fed into the high-speed comparator inte6
grated circuit IC-1. The output from IC-1

is a 4.0 volt p/p pulse train whose widths are determined by the zero cross-over points of

the signal. This pulse train is fed into the

two network branches that are tied to the output of IC-1 at terminal 7. The pulses are integrated by capacitor before driving the

upper gating circuits consisting of Tg, T^, and

Tg . This integration stretches the signal peak

voltage hold time across C-^, and therefore produces a sampling time margin. The sampling

is initiated when the IC-1 output pulse signal

level falls from +4.0 volts towards ground

and is differentiated at the input to T^.

The differentiated signal triggers the T^^ - T^^ current switching circuit and a strobe

pulse is generated by T-^ which drives the

gate terminal of T.^ (FET) during the stretched

signal level interval. A dc level now appears

across C^ and is held there until another

strobe pulse is initiated by the next signal

cycle

.

The input circuit of OA-2 is adjusted by R^ and R

1Q so that the dc levels from PD-SH-1

will track the incoming signal peak values.

The output signal from C^ is then fed into

OA-3. The output from OA-3 is injected into

the "MASTER GAIN" or "MG" branch of the final

summing amplifier OA-4 . The MG potentiometer

R^ is the principal calibration device of the

system. The signal is offset by the OA-4 "% RANGE" branch voltage in order to attain the

desired ABC chart percentage values . The output signal from OA-4 then is passed to the ABC

and X-Y recording devices

.

7
e. A passive R-C averaging circuit with a time

constant of = 0.30 seconds is used to average the output signal from each OA-4 . As seen in figure 6 , R

A

= 100KX2 and C A= 3-0 yfd.

The voltage across the capacitor C A

is applied

to the ABC chart recorder track that is adjacent to the signal peak track that it is av- eraging. The upper track of each pair on the

ABC chart is the average signal peak track.

(See figure 16)

2. Write Channel Operation (figures 8-11)

The NBS signal amplitude read channel operates independently of the system from which the

head-tape signal is derived, however the NBS write

channel is designed to operate specifically with

the IBM 2401-VI transport. This channel is not shown in detail because many different transports

will be used with the SRM 3200 tapes in the field.

Only the current control circuit CC-1, the binary

counter circuit BC-1 s the level shifter LS-1 and

a simplified version of the write driver circuit

WD-1 are shown (figures 9-11). WD-1 and the current source for WD-1 are both on the IBM 2401-VI

"PHW" card. Additional level shifting beyond LS-1

is supplied by the "EPY" and "PAN" cards.

The following steps were taken to convert the IBM 2401-VI tape transport for continuous current

and frequency control by the NBS system. These

steps should be applied to any system for which

similar control is desired:

a. Disable the internal bit rate generator and

connect an external generator G-l . The pulse

frequencies that are supplied by G-l are as follows: 200 frpi - 22.5 kHz; 800 frpi -

8
90.0 kHz; 1600 frpi - 180.0 kHz; and 3200

frpi - 360.0 kHz.

b. Since these frequencies produce double the

desired bit rate they are used to trigger

BC-1 which (1) halves the bit rate and (2)

produces a constant amplitude square wave.

c. The signal levels from BC-1 are then made

compatible for driving the write head with

level shifting circuits such as LS-1.

d. Disable any step write current circuit if one exists.

e. Disable or alter any circuits that are necessary in order to make it possible to re- cord all "ones" in the NRZI mode.

f. The current control circuit CC-1 consisting

of T

22 , T

23 , and T^ (figure 11) is used to control the output from a continuously variable current source circuit over a range of

0.0 to 50.0 mA dc of write head current. The

total write head current is controlled with

the potentiometer R^,_ . R-^ is operated in

the "MANUAL" mode (in conjunction with vernier

control R-j_6^ when the ABC chart recordings are made and in the "AUTOMATIC" mode when producing the X-Y curves . R^,_ is motor driven

through one turn in 10 seconds during automatic

operation. The head current I is measured

w and displayed' with the digital panel meter

DPM-1.

Any existent circuits that impede the

current source from attaining its full range

of values should be disabled or removed.

g. T^^ and T^^ form a constant current switch

with matched circuit components so that equal

values of write current will flow through each
winding of the write head during each half of

the operating cycle. The switched head current is equal to the output from the current

source and the switching rate is controlled by

the level shifted pulse train that is applied

to the base of . The direction of current

in the write head depends upon the instantaneous

"on" and "off" states of and T 26<

C. Switching System (figures 12-14)

The NBS IV :>del II measuring system has a switching network that permits rapid dc, ac and "MASTER GAIN" calibration. However, these procedures could be performed with

patch-cords or any other device that allows the user to

cut into the circuitry.

The NBS measuring system contains 11 switches in the

signal amplitude read section and 2 switches in the write

section. The switches are shown in the simplified switching

diagrams of figures 12 and 13- They are shown in their

actual panel positions on the NBS Model II unit in figure

14. Figure 12 shows only the required switching sections

for a single read channel. The other two read channels

are controlled in an identical fashion by additional wafer

sections that are stacked onto and are mechanically coupled

to the same switch assemblies. The functions of the individual switches will now be described. Switch markings on the panel are in quotation marks:

1. Signal Amplitude Read System (See figure 12)

Switch SI: "3200, 1600-200". Bit density switch.

"nooses AT-1 output line according to the

operating bit density range.

Switch S2: (Sections A, B, C): "OPERATE, SET CHART,

AC CALIBRATE." Main function switch for

the signal amplitude read channels.

10
Switch S3: "Set X-Y . " Pushbutton switch. Sets the

100$ reference level on the X-Y recorder

when depressed and the 0% level when released. The 100$ level is equal to 5.000

volts dc.

Switch S4: (Sections A to E) : "ABC - X-Y." Chooses

the measuring mode and the output recording

device

Switch S5: "OPERATE, EXTERNAL INPUT, DC CALIBRATE."

External high level signals or dc calibration volts can be injected into the system

under the control of S5- Switch S6: "2-3-4-5": Routes "DC CALIBRATE" volts to

S5 from DV-1.

Switch S7: "OP, % 3 AC, MG : (Not shown in detail in

figure 12.) S7 is used to both open and/or

to cut into the individual inputs of OA-4

for calibration and system check purposes.

Switches S8

and S9 : These switches are used for metering purposes

only. All supply voltages and the outputs

from OA-3 and OA-4 are measured by a digital

voltmeter (DVM-1) via S8 and S9

Switch S10A: "GROUND T 13C

" Toggle switch on circuit card.

Used during "DC CALIBRATE".

Switch S10B: "GROUND DVM" . Pushbutton switch. This is

used to check the DVM or oscilloscope ground

level

2. Write System (See figure 13)

Switch Sll: "OFF, LOCAL, MAIN FRAME." Main write current

control switch. Reduces write current to zero in "OFF" or gives control of the write

current to the NBS measurement system in

"LOCAL". Sll can also be wired to return

11
current control to the transport main frame

if desired.

Switch S12: "AUTO-MANUAL." Lever Switch. Chooses the

mode of write current control. The automatic

mode is used for X-Y recording and the manual

mode is used for setting the reference current level for ABC charts. S12 also controls

the X-Y recorder pen drop circuit and activates the potentiometer motor during X-Y re- cording. Note that there are 4 SPDT sections

on S12. The normally open sets of points are designated by "N.O."

3. Calibration and Operation of the Model II System

The calibration and operation of the read system is accomplished in the following sequence

:

A. Dc Calibration

B. Ac Calibration

C. "MASTER GAIN" Calibration and System Operation.

The calibration of the Model II system proceeds from

the output of OA-4 back toward the input circuitry. The

first adjustments are made on the output summing amplifier

OA-4 which has the following input lines: (See figure 6)

a. "MASTER GAIN" (MG) R

5 b. "AC CALIBRATE" (AC) Rg

c. "SET CHART" (SC) R 7

( d. "% RANGE" (%) Rg

Rg, R^, and Rg are adjusted so that the gain of OA-4

relative to dc inputs on these lines is equal to G = 1.667-

This gain converts the input signal amplitudes to output

values that yield a direct relationship between the chart

divisions and the percentage value of the signal under

test

.

The functions of these OA-4 inputs and adjustments are

as follows

:

12
The "MASTER GAIN" potentiometer R^ adjustment

sets the final gain of each read channel so that it will produce the desired reference

output level as provided by the NBS master

tape. The NBS secondary standard magnetic

tapes are then calibrated with respect to this level. The "MG" input branch to OA-4 is functional during the normal "OPERATE" (S2)

mode . The "AC CALIBRATE" input to OA-4 is used in the

"AC CALIBRATE" (S2) mode of operation. This

mode uses a simulating ac signal to test the

stability and adjustment of the system.

The "SET CHART" input to OA-4 is used in the

"SET CHART" (S2) mode of operation. In this

mode 3-000 volts dc is injected into OA-4 and

produces the output voltage level which is used

to set the X-Y and ABC recording devices into

their 100% reference states prior to recording.

The "%" input to OA-4 affects each of the preceding modes by providing a controlled offset

voltage. This offset voltage is adjusted with

the calibrated 10 turn potentiometer R^ so that the signal output from OA-4 will consist of a desired percentage of the total

signal range. For example, a range consisting of from 75% to 125$ of the total signal

amplitude is charted on a strip chart re- corder by offsetting the lower 75% of the

output signal and then selecting that chart

recorder range that will encompass the next

50% of the total signal level over Its limits.

An NBS ABC chart recorder track has a useful width of 10 major linear divisions as shown

in figure 16. When the recorder sensitivity is

m
set to 250mV/div then full chart deflection is obtained with 2.500 volts dc . If the chart

centerline is chosen as the 100% reference

level then 1.250 volts dc output from OA-4 is equal to 100%. Since 3.000 volts dc into OA-4

represents the 100% level for the system, it is necessary to offset this by inserting 2.250

volts dc onto the "%" line. This results in an OA-4 output equal to 0.750 volts times the OA-4

gain of G = 1.667 or 1.250 volts during the

"SET CHART" (S2) mode of operation. The bottom

of the chart represents the 75% signal level

and the top of the chart represents the 125%

signal level. The NBS system is designed so that the lowest percentage values on the 250

mV/div chart can be calculated from:

Lowest f.

" % RANGE " input^oltage x 100

On the 250 mV/div scale setting the highest chart

percentage is 50% above this lowest value.

NOTE: This same "%" offset capability can be used to com- pare relative signal peak values and to measure the

distribution of incoming signal peaks on a high

sensitivity range of an oscilloscope. This measurement, however, does not require prior peak

detection and sample-and-holding of the signal,

i.e., the signal is passed directly from WPR-1 to OA-4. When the oscilloscope sweep rate is set to display only one half or less (positive or negative)

of one signal cycle per trace then a broad arched

band of light appears on the screen. The broadness

of the band is a function of the scope sensitivity

and of the distribution of the signal peak amplitudes read from the tape. The intensity of the

14
light band varies across its height with the brightest level appearing at the amplitude related to the

most prevalent signal peak value.

A. Dc Calibration Procedures (figures 4 to 6, 12)

1. The "AC", "SC" and "%" inputs of the 0A-4's in

figure 6 are set for gains of G = 1.667 by injecting 3.000 volts dc from the precision digital

voltage source into each of these inputs via

switch S7 and adjusting trimmers R^, , and Rg

for an output of 5.000 volts dc from OA-4 as measured on DVM-1. This can be done on an individual

basis via S7 with all inputs held at zero volts

except for the one being adjusted.

2. After the QA-4 inputs have been adjusted then the

peak detect sample-and-hold PD-SH-1 system is dc

calibrated as follows

:

a. Open the input to OA-1 at point A of R^ (via

Sj-) and set R^ to its mid-point value of 500 ft. R^l is an external 10 turn potentiometer with

a calibrated dial. (figure 4)

b. Short the collector of to ground (via S10A

in figure 5 ) • c. Inject 2.000, 3-000, 4.000 and 5.000 volts dc

sequentially into R^ from the precision voltage

divider source DV-1 (figure 7). This is done

with switch S5 and S6.

d. Adjust R^ and R

1Q at the OA-2 inputs (figure 6)

until the dc outputs from OA-3 track these

voltages within an accuracy of at least 0.25$.

This completes the dc calibration and all

switches or connections are returned to normal.

B. Ac Calibration Procedures (figures 3, 4)

1. This is accomplished in two steps when the system

is ac calibrated for the first time after the dc

calibration has been completed:

15
Step (1) - An external sine wave signal is shunted

around AT-1 and is injected directly into

the connector to the input capacitors of

each of the WPR-1 preamplifiers with S2

in "AC CAL" (figure 3). It has been

found that an input signal amplitude of

12.7 mV p/p is a good value to use as the

nominal operating signal level. The

internal WPR-1 gain trimmers are then

adjusted in each of the 3 read channels

so that the output from each OA-3 is equal to 3-000 volts dc . This corresponds

to an output of 6.0 volts peak to peak

from WPR-1. The frequencies of the injected signals are 180 kHz, 90 kHz, 45 kHz, and 11.25 kHz for 3200, 1600, 800

and 200 frpi, respectively.

Step (2) - After each WPR-1 has been set for an equal gain of 470 the external sine wave

signal is then injected into the input

of attenuator AT-1 at point A (figure 3)

with S2 in "OPERATE". For 3200 frpi the

input signal level is set to 14.2 mV peak

to peak at 180 kHz and the trimmer R^ is

adjusted so that the output from OA-3

is again 3-000 volts dc. The input

signal is then set to 22.5 mV p/p at

45 kHz and the trimmer R^ is set so that the output from OA-3 is again

3.000 volts dc. Trimmers and R

2 are now permanently secured and never re- adjusted. In operation switch SI (figure 3) is used to activate the

trimmer circuit at 3200 frpi and the

R

2 trimmer circuit at 1600 to 200 frpi

16
so that the WPR-l's will be able to operate over a reduced range of gains

for all densities. The ac calibration

is now completed and if desired only

step (2) need be performed for checking the dynamic response of each of

the three read channels and the output recorders

.

C. "MASTER GAIN" (MG) Calibration and Operation of the

Model II System

After the dc and ac calibrations are completed the

system is ready for its final working adjustment using

either the NBS master or a working reference tape. This

step is accomplished at each density by running either

one of these reference tapes and adjusting the three ex- ternal MG potentiometers . The sequence of operations

are as follows

:

1. Produce an uncalibrated e {%) versus I curve

o w using the master or working reference tape and

determine the reference write current level at the initial signal peak.

2. Produce an ABC strip chart recording of the signal outputs from 3 head tracks using the reference write current level. Adjust the MG potentiometers to achieve the correct percentage values

on the ABC chart as determined by the master or working reference tape.

3. Now produce the calibrated e (%) versus I o w curves and ABC charts for the NBS master tape

and for each candidate tape.

4. Record the MG numbers or voltages and make a "master template". Each one of these operations

must be repeated for each of the 4 bit densities.

The following is a detailed description of steps

1 to 4: 17
Output Voltage e Q (%) versus Write Current 1^ Curves

(figure 15)

(a) In order to determine the reference write current

levels at which the ABC strip charts for the can- didate tape are to be produced, it is first nec- essary to make an e Q (%) versus 1^ curve for the

master tape or a working reference tape at each

operating density. This reference level is the

"initial" saturation write current and is defined

as the minimum write current level that produces

the maximum value of output read head voltage as plotted on the X-Y chart. The output voltage e Q {%) is always obtained during a read-while-write

pass on a previously bulk erased tape. The e Q {%) versus I curves are measured from the output of w

" the center track (track #5) of the 9-track read

head and are produced over a section of tape which

lies approximately 100 'feet past the beginning mark

of the calibrated 600 foot section of the reference

tape

(b) The e (,%) versus I curves are plotted on an X-Y

o w recorder whose X axis is driven by a voltage that

is derived from the voltage drop across the 10 ohm resistor in series with the center tap of the

write head (figure 11). These voltage drops are converted by an X axis gain adjustment into chart

abscissae values that represent the write head

current in milliamperes . The range of the write

current in the system is continuously controlled

from 0 to 50.0 mA by CC-1 and the motorized potentiometer unit R, ,- . The write current is read

15 from DPM-1.

(c) The Y axis of the X-Y recorder is driven directly

by the output signal voltage from OA-4. The Y axis gain is calibrated so that 5.000 volts dc will

18
drive the recorder pen to the line that has been

chosen as the 100$ level on the e

Q ($) versus 1^

chart. These 5.000 volts dc are derived from OA-4

in the "SET CHART" (S2) - "X-Y") (S4) mode of

operation by depressing pushbutton S3,

(d) The operating procedure is as follows:

(1) The NBS master or working reference tape is threaded onto the tape transport.

(2) The system is switched into "OPERATE" (S2) "X-Y" (S4).

(3) The current control switch Sll is placed into

"LOCAL"

.

(4) S12 is depressed into "AUTO" and the tape

transport is started.

(5) The motorized potentiometer R^,- varies the

write current from zero to 50.0 mA and the

e (%) versus I curve is plotted.

o w

(6) During step (5) the external "MASTER GAIN"

potentiometer for the center channel (channel

B-track #5) is adjusted to bring the e

Q {%)

signal peak value to within 5$ of the 100$ X-Y chart level that was set in step (c) above.

This may require several passes over the same chart as the tape is running.

2. ABC Chart Measurements (See figure 16)

These measurements are made after the initial saturation write current level has been determined from the

e ($) versus I chart as follows:

o w f (a) The system is switched into the "ABC" (S4) - "SET

CHART" (S2) mode of operation and the ABC strip

chart recorder tracks are adjusted or "set" to their 100$ level. For example, the chart centerline is used as the 100$ level if the "$ RANGE"

voltage is set equal to 2.250 volts dc with

and the recorder sensitivity set to 250 mV/div.

19
(b) After the ABC chart is "set", the write head current is adjusted to the initial saturation current

level previously determined using the CC-1 write

current control potentiometers R^^ and R.^ with

S12 in the ^'MANUAL" position. The system is then

switched into the "ABC" (S4) "OPERATE" (S2) mode

of operation and the ABC chart recorder and tape

transport are activated.

(c) (1) The ABC chart speed is set at 1 mm/s

(2) The IBM 2401 - VI tape transport speed is 112.5 in/s.

(3) Each major horizontal chart division (5 mm)

represents the passage of 47 feet of tape.

(4) The 6 ABC tracks consist alternately of the

signal peak outputs and the average of these

signal peak outputs as derived from 3 head

tracks (tracks #2, #5 and #8).

(d) If the NBS master tape is being run on the transport, then the three external "MASTER GAIN" potentiometers Rp- are adjusted so that the signals

on all of the ABC chart recorder tracks fall ex- actly at the pre-set 100$ level. If a working

reference tape is used instead of the master

tape, then each MG potentiometer R,_ is set so that the signal level on each ABC track will

fall at the predetermined relative percentage

values for the working tape outputs. For example,

for a particular working tape the MG potentiometers

Rt- may have to be set to produce: track A = 98$

level, track B = 95$ level and track C = 97$

level relative to the 100$ master tape level. The

system is now completely calibrated.

20
3. Candidate Tape Calibration Procedures

(a) When the "MASTER GAIN" potentiometers have been

adjusted as described above then calibrated e

Q (%) versus I curves are produced for all of the

w candidate tapes and the master tape by repeating

the procedures in Section 3, C, 1, d, but omitting

step 6 in this section.

(b) The reference current values that will now be used

to produce the final ABC charts are marked on each

of the calibrated X-Y curves that accompany the

SRM 3200' s as shown in figure 15. An e Q {%) versus

I chart that was derived from the NBS master tape

wwill also be marked and included in the package.

Since the system is completely calibrated

the peak output voltage e

Q (%) from the NBS master

tape at each recording density will now fall at the

100$ level on its X-Y chart and the peak voltage

outputs from the candidate secondary tapes will

appear directly in terms of their relative percentage values to the master tape. For example,

if the peak output voltage e Q {%) for an NBS can- didate secondary tape is reached at the 9%% chart

level, then that tape has been measured on the

NBS calibration system as having a peak output

voltage that is 2% less than the peak output voltage derived from the NBS master tape.

(c) The steps in Section 3, C, 2, a, through 3, C, 2, c, are now repeated for all candidate secondary

reference tapes at each bit density. These procedures will result in calibrated ABC charts for

these tapes. The candidates are now completely

calibrated

.

4. Additional System Checking and Calibrating Techniques

Techniques have been developed for checking and calibrating the NBS Model II measurement system which do not

21
require the constant use of a working reference tape. In each instance the method assures that the overall system

gain and the MG potentiometers R,- are maintaining their

original values

(a) "MASTER GAIN" Numbers and Voltages

The "MASTER GAIN" potentiometers R,_ are 10-turn

units with calibrated dials . After completing

Section 3, C, 2 3 d 3 the numbers on these MG dials

are recorded and can serve as future references.

That is, if the system is dc and ac calibrated

and the MG potentiometers R,- are reset to these

same dial numbers then the system is back in its

original operating condition. These MG numbers

are related only to the particular head that was used when they were derived. A more precise technique for resetting the MG potentiometers to their

original values is achieved in the NBS system by

injecting 3-000 volts dc into the calibrated "MG" inputs of the 0A-4's with all of the other inputs

at zero (switch S7 in "MG"). The output voltage

from the 0A-4's are then logged and the MG potentiometers can then be reset very precisely to these OA-4 output voltages when desired. This

approach eliminates the effects of mechanical dial errors in the MG number method.

(b) Master Template Technique:

An alternate technique for testing the stability

of the entire NBS measurement system as well as for recalibrating the system without the use of

a reference tape is with a "master template".

This template is produced as an ABC 6-track chart

recording immediately after the system has been

calibrated (after Section 3 3 C, 2, d) . It is done

by disconnecting the LD-1 line driver outputs and

producing the ABC chart by injecting a sine wave

22
signal into the input of the calibrated system

at AT-1. The frequencies and amplitudes of these

signals are the same as those discussed in the

Section 3, B. For example, at 3200 frpi a 180

kHz, 14.2 mV p/p signal is injected into AT-1.

Since the injected sine wave signal consists of

constant amplitude peaks the master template will

consist of smooth lines at a fixed level on each

ABC track. This template includes the effects of

the entire measuring system on the injected signal.

During an actual tape calibration run the system

can be rechecked regularly by producing new ABC

charts using the same injected sine wave signal

and comparing the levels on the new charts to the

levels on the original master templates. If necessary, amplifier gains can be adjusted with R^ or to bring these levels into line with the

master levels. A separate template is produced

at each bit density for .each calibrating head and

the set of templates is stored with that head when

it is removed from service

.

When the response of the measuring system is

recorded in this fashion, it is possible to observe

changes in the head-tape output signal with time.

These changes are due to variations in environmental and operating conditions as well as to the

mutual physical effects of the heads and tapes on each other,

(c) Ac Calibration Mode:

This mode of calibration is similar to the master

template mode with the exception that the reference

sine wave signal is switched via S2 directly into

the WPR-l's and the OA-4 input trimmers Rg ("AC

CAL") are set so that the 6-track chart recordings

all fall at the 100$ level in response to these

23
signals. The MG adjustment is assumed to be correct and no template is required. This mode offers

a rapid system check during a candidate tape calibration run but is not as complete as the master

template method. The sine wave generator can be

permanently connected into an "AC CAL" input jack

and the line drivers do not have to be disconnected

in this mode. Notes to Reference Tape Users

A. Important: The NBS Secondary Standard Magnetic

Tapes (Computer Amplitude Reference) SRM 3200

should be used sparingly so as to minimize physical changes to the tape and to assure continued

performances as near to the supplied calibrations

as possible.

It has been found that the best correlation

with the NBS measurement system results can be

produced under the following conditions

(1) The tape is bulk ac erased before writing.

(2) The dc erase head on the tape transport is not energized during the measurement process.

(3) A slotted read-write head (IBM Assembly No. 5417960 Part No. 2510730 or equivalent) is

used as the transducer.

(4) The curves are made during a first read-whilewrite pass.

(5) The characteristics of the tape transport such

as speed, tension and guidance should be similar to the IBM 2401-VI.

Departure from one or more of these con- ditions can result in variations from the calibrated results.

B. The NBS Secondary Standard Magnetic Tape (Computer

Amplitude Reference) SRM 3200 is packaged in lengths

of approximately 900 to 1200 feet of tape per reel.

24
At least 600 continuous feet of tape within this

length satisfy the requirements that are stated

on the accompanying certificate. However, the

full reel can be used for adjustment purposes

because calibration data for the entire length of

tape are included on the ABC charts. Originally

the SRM 3200' s were packaged in exact 600 foot

lengths. 'The decision to change to the 900 to 1200 foot format resulted from experimental evidence which indicated that the longer tape lengths

reduced the signal "rise" effect. It has been

noted that many different tapes display a rise in

signal amplitude as the tape is read from end to end, with the signal increasing most rapidly as the reel hub is approached. It is believed that

the increase in signal amplitude is caused by

effects of the pressure variation per unit length

of tape upon the tape surface after it has been

wound and stored. The longer tape length lowers

this pressure gradient and the percentage signal

amplitude variation over any continuous length

of tape is also reduced.

Figure 16 shows 2 out of 3 channels on a typical ABC chart recording with the principal

600 foot section lying between the two right

hand "marks". The length of tape between the

"Beginning of Tape" (BOT) marker to the 600 foot

starting "mark" is also shown on each ABC chart.

The time in seconds that is required to reach

this starting "mark" from the BOT mark is found

from

:

H )= length from BOT to starting "mark" (feet) seconds; speed of transport (feet/second)

25
Note that the length of tape between each horizontal ABC chart division is approximately 47 feet,

therefore in figure 16 the distance from the BOT

mark to the starting "mark" is 376 feet. As an example, if the transport speed is 112.5 inches

per second (9.38 ft/s) then the time required

to reach the starting "mark" from the BOT marker

is m 376 feet ,. n , T = 9.38 ft/s * 40 second s It is anticipated that SRM 3200 users will

devise other means for finding the starting "mark"

after it has been located by them for the first

time. For example, additional BOT and EOT ("End

of Tape") markers may be added to the tape according to the operational design of each particular

system. However, cutting the tape to different

lengths is not recommended since it will alter the

signal rise characteristics

.

e (%) versus I saturation curves for 3200, 1600,

o w

800 and 200 frpi will accompany the NBS Secondary

Standard Magnetic Tape (Computer Amplitude Reference) SRM 3200 from which they are derived. In addition, the four e {%) versus I saturation

o w curves that were obtained from the NBS Master

Standard Magnetic Tape (Computer Amplitude Reference) at these bit densities will also be included

in the package. The user will therefore be able

to use these curves in order to determine the re- lationships at different write current levels between the NBS master tape and the NBS secondary

tapes. The user should note that every e Q {%)

value on the NBS master tape X-Y curve can be

assumed to be the 100$ reference level and that

the secondary tape outputs are then considered in

26
terms of their percentage relationship to these

master levels at whatever write current has been

chosen. NBS has chosen the initial saturation current at the e Q {%) peak as the basic reference current level at which all of the ABC charts are produced. This level is marked on the X-Y curves

as shown in figure 15- The ABC chart shown in

figure 16 was produced at the current level that

was marked for the tape T-l in figure 15. It has been found at 3200 frpi that most

initial saturation write current levels lie between

13.0 to 16.0 mA and that between 200 and 1600 frpi

most values lie between 26.0 to 30.0 mA . These

results were obtained with a number of IBM slotted

read-write heads described in Section 2, A, 1, a, and with groups of various industry tapes chosen

at random.

D. ABC strip charts derived from 3 head tracks at each

of the 4 bit densities accompany the NBS secondary

tapes from which they were derived. Data from each

read head are recorded on two adjacent pen tracks

with the signal peak amplitude appearing on the

lower track and the average peak amplitude of the

signal appearing on the upper pen track. Figure

16 shows tracks B, B, C and C as they appear on a typical ABC strip chart recording. The bar over

the track letter indicates the average peak value

track

.

(1) Chart track A corresponds to the signal

output from head track No. 2. (2) Chart track B corresponds to the signal

output from head track No. 5- (3) Chart track C corresponds to the signal

output from head track No. 8. The head tracks are numbered in accordance

27
with USA Standard Recorded Magnetic Tape for

Information Interchange (800 CPI, NRZI) - USASI X3. 22-1967.

E. Construction Notes

(1) Printed circuit layout figures for the plug-in

cards that are used in the NBS Model II system

will be made available upon request.

(2) The muffin fans are important for maintaining

the dc stability of the solid state devices

and should be used. They are positioned to move the air through the side of the SDS card

cage. The NBS laboratory is maintained at a temperature of 70° ± 1° P.

(3) Separate ± 14.0 volt supplies are used for the

low signal level circuits in WPR-1 and for the

high level signal circuits in PD-SH-1.

(4) Coaxial leads are used in the low signal level

input circuits and switches.

(5) The NBS system is designed so that all printed

circuit card adjustments are available from

the front of the machine. This includes all

Internal trimmer resistors.

(6) If the NBS circuit cards and the SDS Type MT-12

card cages are used it will be necessary to cut open the common pin No. 51 buss line on the SDS

cage etched circuit plate.

(7) The three read channels A, B and C do not interact, therefore, it is feasible to build a single channel read system if desired. Also,

if only ABC charts are desired then it is not necessary to build the NBS write control system.

5. Component List

The mention of specific equipments or components in any

portion of publication is not to be construed as an endorsement of these items by NBS to the exclusion of other equiv28
alent devices. There is considerable latitude in the choice

of semi-conductor components, potentiometers, recording, re- producing and measuring devices . The following is a tabulation of the devices that are used in the NBS measurement

system Model II

.

Note: The marking of a component or heading with an asterisk indicates that only one each of these

components or devices under the heading is used

in the entire system. All other components unless otherwise indicated are used one each per

channel, therefore, three of each are used in

this system.

Transistors T(Numbers in Figures) Type

2N3646 7-10, (17 -22)* 27, 28 NPN Switching

2N3638 6, 11, 12 , 13, 15*, 16* PNP Switching

2N916 1-3 NPN High Frequency

Amplifier

2N3831 4, 5, 25, 26 NPN High Speed Switch

2N1700 23*, 24* NPN Switching

2N4222A 14 N-Channel FET

Note : T to T

x and to T^g were unmarked transistors

that appeared on commercial circuit cards. They are replaceable with the types that are listed in the

table

.

Diodes

1N276

1N916

Operational

Amplifiers

PP45U

Integrated

Circuits

UA710C

D(Numbers in Figures)

12, 3, 4, (5-10)*

OA

Type

Ge Switch

Si Switch

(Numbers in Figs.)

1-7

IC

( Number in Figs .

)

1 29

Type

Philbrick Researches, Inc.

Differential comparator,

Fairchild semiconductor
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32
Power Supplies*

Dual Supplies

Single Supply

Digital Voltage Source

Miscellaneous

Card Cage*

Muffin Pans (3 per system)

10 turn dials (6 per system]

10 turn dials*

Transformer TR-1*

Voltage

±li».0(2ea. ), ±6.0

+28.0

0.0-99.999

Type

Kepco DTM 2x16-0

Kepco BKP 28-0 .6 SRC Model 3517

Type

SDS Type MT-12

Rotron 115 CFM, 115 vac. Bourns No. H-494-3

Beckman Instruments Duodial

Triad P-25X Filament Transformer

6. Acknowledgements

The assistance . of Mr. N. G. Cleveland (IBM Research

Associate, Boulder, Colorado) with the initial testing and

development of the system, of Mr. P. A. Mantek (Information

Processing Technology Division) with the conversion of the

IBM tape transport to local current control and Mr. A. W. Ericson (Information Processing Technology Division) with

the testing, construction and operation of the system is

gratefully acknowledged. The assistance of Miss Sharon

Michael (Information Processing Technology Division) in

the preparation of the manuscript is also gratefully ac- knowledged .

33
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Figure 16. ABC Chart Recording

49

FORM NBS-1MA (1-71) US DEPT OF COMM. PUBLICATION OR REPORT NO. 2# Gov't Accession BIBLIOGRAPHIC DATA NBS # SP260-29 No' SHEET 7

4. title and subtitle Calibration of NBS Secondary Standard

Magnetic Tape (Computer Amplitude Reference) SRM

3200 Using the Reference Tape Amplitude Measurement

"Process A" Model II June 1971

6« Performing Organization Code

7. AUTHOR(S) Sidney B. Geller

%0 Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

iu. project/ 1 ask/ work Unit INo. 3020585

11. Contract/Grant No.

12. Sponsoring Organization Name and Address 13. Type of Report & Period Final

14, Sponsoring Agency Codie

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) Thl g publication describes the design,

operation and calibration of the NBS signal amplitude measuring system

(Process A - Model II) that is used for calibrating unrecorded Secondary

Standard Magnetic Tapes (Computer Amplitude Reference) SRM 3200. This

system supercedes the measurement system that was described in the NBS

Special Publication 260-18 (November 1969). The signal level calibration

is made with respect to a reference signal level derived from the NBS

Master Standard Magnetic Tape (Computer Amplitude Reference) that is kept

in repository at NBS. The techniques for measuring and recording the

data that accompany each Secondary Standard Magnetic Tape in the form of

strip chart recordings and saturation curves are described.

17. key words (Alphabetical order, separated by semicolons) Average signal peak level; computer

amplitude reference; magnetic tape; master standard; saturation curves;

secondary standard; signal level calibration; standard reference materials ;

' <-> 18. availability statement unrecorded reference. 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES 23 UNLIMITED. UNCLASSIFIED 57

1 1 FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

20. SECURITY CLASS

(THIS PAGE) UNCLASSIFIED

22. Price 60 cents USCOMmVc 88244-P7I
!



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