IEFERENCE

UTED STATES WMENT OF MMERCE

PLICATION

''4TIlO»'

NBS TECHNICAL NOTE 731

\oo

U5753

no. 731

H70.

U.S.

PARTMENT

OF

COMMERCE

National

Bureau

of

Standards

Calibration of

Secondary Standard

Magnetic Tape Cassettes

(Computer Amplitude Reference)

Phase I
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 divisions and offices: Engineering Standards Services—Weights and Measures—Invention and

Innovation—Product Evaluation Technology—Building Research—Electronic Technology—Technical Analysis—Measurement Engineering—Office of Fire Programs.

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 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.
Bureau of Standards

8 1974

Y& Calibration of Secondary

1^1 Standard Magnetic Tape Cassettes

(Computer Amplitude Reference] Phase I

Sidney B. Geller and Paul A. Mantek

Information Processing Technology Division

Center for Computer Sciences and Technology

(^ t S • National Bureau of Standards " ' *" Washington, D.C. 20234

lu JUL. O

\

*£

v -V Jjif/

U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretory

NATIONAL BUREAU OF STANDARDS, Lawrence M. Kushner, Acting Director

Issued July 1972
National Bureau of Standards Technical Note 731

Nat. Bur. Stand. (U.S.), Tech. Note 731, 60 pages (July 1972) CODEN: NBTNAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.46.-731). Price 60 cents.
TABLE OF CONTENTS

PAGE

1. INTRODUCTION 1

2. DIGITAL MAGNETIC TAPE CASSETTES 4 2.1 Digital Cassette Applications 4 2.2 Digital Cassette Construction 5

2.3 Digital Cassette Transports 8

3. EXPERIMENTAL DESIGN FACTORS IN THE REFERENCE

CASSETTE PROGRAM 9

3.1 Development of Cassette Groups 9

3.2 Statistical Considerations 9

3.3 Development of Transducer Groups 10

3.4 Summary 13

4. THEORY OF OPERATION OF THE NBS CASSETTE SIGNAL

AMPLITUDE MEASUREMENT SYSTEM 14

4.1 System Components 14

4.2 Description of the System Operation 17

4.3 Description of the OA-4 Circuit 24

5. EXPERIMENTAL RESULTS 2 6

5.1 Case Histories of Submitted Cassette

Transports ^ 26

5.2 Cassette Transports Used for Measurements. . 26

5.3 Experimental Measurement Data 30

6. COMPONENT LIST 52

7. APPENDIX 53

7.1 Digital Cassette Standardization Progress. . 53

7.2 Tape and Leader Dimensions 53

8. REFERENCES . 55

LIST OF FIGURES

Figure

Number

1 Physical details of a digital magnetic tape

cassette 7

2 Block diagram of the interim NBS signal

amplitude measurement system 15

in
LIST OP FIGURES (Continued)

Figure

Number Page

3 Block diagram of the interim NBS read

channel measurement system 18

4 Read system input circuits. (LD-1C,

AT-1C) 19

5 Read system preamplifier (WPR-1) 20

6 Read system peak detect-sample-and-hold

system (PD-SH-1, OA-2, OA-3) 21

7 Read system output circuits (OA-4, OA-9,

OA-10 22

8 Cassette transport speed measurement

curves 38

9 Cassette transport speed measurement

curves 39

10 Tape tension test curves 40

11 Tape tension test curves 4l

12 Cassette torque test curves 43

13 Signal amplitude histogram for runs 1 to 15 . 44

14 Signal amplitude histogram for runs 1 to 6. . 45

15 Signal amplitude histogram for runs 7 to 12 . 46

16 Signal amplitude histogram for runs 13 to 15. 47

17 Six track chart recorder output curves. ... 49

18 Six track chart recorder output curves. ... 50

19 (J)-H loops for four cassettes 51

IV
CALIBRATION OP SECONDARY STANDARD MAGNETIC TAPE

CASSETTES (COMPUTER AMPLITUDE REFERENCE) PHASE I.

Sidney B. Geller and Paul A. Mantek

This Technical Note discusses a method for developing and maintaining a reference system which will

produce NBS Secondary Standard Magnetic Tape Cassettes (Computer Amplitude Reference). It describes both centerline tape search procedures and

an interim signal amplitude measurement system for

the reference magnetic tape cassette candidates.

The results of the initial experiments with cassette tapes and transports are given.

Key words: Cassette tapes; cassette transport;

computer amplitude reference; magnetic tape cassette; secondary standard; standard reference

material; unrecorded references.

1. INTRODUCTION

At the request of industrial users of computer cassette

tapes, Government procurement agencies, producers of magnetic

computer tapes, and producers of cassette tape handling equipment, the National Bureau of Standards is developing a signal

amplitude measurement system and will eventually supply

unrecorded Secondary Standard Magnetic Tape Cassettes (Computer Amplitude Reference) through the NBS Office of Standard

Reference Materials.

This Technical Note describes the activities in the signal amplitude reference magnetic tape cassette program which

is being performed in the NBS Center for Computer Sciences

and Technology. The methods that were used for developing

the continuing NBS signal amplitude computer reference tape

(reel-to-reel) program are briefly described and are being

used as a guide for the cassette program.

An actual reel of magnetic tape or a magnetic tape cassette is the only practical tool that is presently available

for adjusting and calibrating the signal amplitude response

of a magnetic tape or cassette recording system. The performance of one of these particular reels or cassettes must

typify the performance of the tapes in its own category in

order that maximum interchangeability of such storage media

can be achieved.

Once a system has been calibrated with a reference

cassette then:
(1) The manufacturer of cassettes can maintain production controls by comparing the output signal level from his

newly made tape cassettes to the pre-set reference signal

level as they are run and measured on a system which has

been calibrated with the reference cassette. For example,

a manufacturer can adjust his fabrication processes to

produce tapes with a signal level variation of at most + 10$

from the reference signal level that he has pre-set with his

reference tape.

(2) The manufacturer of tape handling equipment can

design his transducers, guidance systems and electronics

to perform in an optimum fashion with the reference signal

levels

.

(3) The tape user can assume with some confidence that

most tapes in the same category as the reference tape will

operate within given margins in his calibrated tape system,

i.e., good tape interchangeability can be achieved. This

would be especially valid if all of the industry reference

tapes were originally calibrated with respect to the same

primary reference tape group.

NBS is presently calibrating and issuing the unrecorded

signal amplitude reference tape reels which' are officially

described as "NBS Secondary Standard Magnetic Tape - (Computer Amplitude Reference) SRM-3200. In order to qualify in

this category, each tape reel undergoes a screening process

to determine its signal amplitude uniformity at all recording

densities as well as its signal output level relative to that

obtained from a particular tape described as the "NBS Master

Standard Magnetic Tape - (Computer Amplitude Reference).

The NBS computer reference magnetic tape program has

been accomplished in the following four major phases which

will be duplicated in the reference cassette program:

Phase 1: The development of a signal amplitude measurement system for reference tapes [l] 1 [2],

Phase 2(a) The determination of the unrecorded NBS

Primary Master Standard Magnetic Tape - (Computer Amplitude

Reference) group and its utilization and maintenance in

repository,

Figures in brackets indicate the literature references on

page 56.
Phase 2(b) The determination of the unrecorded NBS

Secondary Standard Magnetic Tapes - (Computer Amplitude

Reference) group and its utilization and maintenance in

repository. These secondary group tapes are not the SRM

3200's.

Phase 2(c) The determination and production on a continuing basis of "Working" signal amplitude reference tapes

to be used during the SRM 3200 calibration runs.

Phase 2(d) The determination of both a reference read/

write transducer group to remain in repository and a "Working"

read/write transducer group for use in performing calibration

runs. The "Working" transducers are sought on a continuing

basis

.

Phase 3: The industry and government evaluation and

acceptance of the NBS results of the two preceding phases.

Phase 4: Calibration and issuance of the SRM-3200

unrecorded signal amplitude reference tapes. This includes

all associated information such as a certificate, measurement charts and descriptive literature such as the NBS

Special Publication 260-29 [2].

The application of the same program phases to the

cassette program will now be discussed:

Phase 1: This has been partially fulfilled through

the design of some new circuits which operate in conjunction

with modified sections of the reference tape signal amplitude

measurement system described in [2], This is described in

section 4. Initial measurement results are described in

section 5.

Phase 2: There are critical differences in the cassette

program options for accomplishing Phase 2(a). This will be

the area of greatest difficulty because, while the SRM-3200

program was based upon existent de facto industry standard

reference tapes, none exist in the tape cassette field.

Possible approaches to the problem in the absence of similar

de facto standard cassettes are outlined in section 3. The

completion of Phase 2(a) in conjunction with Phase 2(d)

should lead to the certain completion of Phases 2(b) and

2(c).

Phase 3: This phase will probably take the form of a round-robin test procedure similar to that performed with

the reel tape. These SRM-3200 tests and their results were

as follows
After the NBS tape laboratory obtained the NBS primary

Standard Magnetic Tape - (Computer Amplitude Reference)

Group a number of candidate reels of tapes were calibrated

with respect to it on the amplitude measurement system.

Those tapes that fell within the certified signal uniformity

and level specifications were designated as NBS Secondary

Standard Magnetic Tapes - (Computer Amplitude Reference).

Eighteen of these tapes were submitted for evaluation to

industrial organizations including of both tape producers

and tape equipment manufacturers who used them to calibrate

their tape handling systems. These calibrated systems were

then used to compare the signal amplitude from the NBS tapes

relative to their "own" in-house reference and control tapes.

The results of the survey were gratifying in as much as the

NBS reference signal levels were well situated in a scatter

plot that showed the relationship of the industry reference

levels to the NBS level. However, some of the tape manufacturers felt that the deviation in their reference levels

from the NBS level was due mainly to the variations in the

different read/write head signal amplitude responses. This

difference commonly occurs even among heads of the same

type produced in the same plant. It is felt by both industry

and the NBS laboratory that it is very important to investigate both head-to-tape interaction effects and the problems

and causes of the variation in response from head-to-head.

This concern also exists for cassette transducers and it is

felt that solutions for the overall magnetic transducer

problem should be given high priority. This would be an

important step towards the design of a "standard" head. It

is also felt that the head problems will be compounded by

the various types of pressure pads in the cassettes that do

not exist in the reel-to-reel tapes.

Phase 4: This phase is dependent upon industry negotiated

requirements that will eventually be specified on the certificate which accompanies each reference cassette tape. For

example, the SRM-3200 is calibrated at the bit densities of

3200, 1600, 800 and 200 frpi. The present cassette specifications call for testing at 1600 frpi - saturated recording.

2. DIGITAL MAGNETIC TAPE CASSETTES

2.1 Digital Cassette Applications

There are three principal applications for digital cassettes: (1) data terminals, (2) data acquisition systems,

and (3) minicomputers. In data terminals the digital

cassette performs the task of data loading and storage; in

many cases this is done at remote terminals. The cassette

is also used to receive and transmit data over telephone

lines. Data acquisition systems usually involve keyboard

4
entry of information on an incremental basis into a lowcost cassette system. These applications include the use

of such instruments as typewriters, cash registers, or

accounting machines. In minicomputers the cassette is

used for input, output, and auxiliary storage in the same

way that magnetic tape is used in large scale computer tape

transports. Cassettes are also replacing punched paper

tape and punched cards in industrial processing systems

and numerically controlled machines

.

2.2 Digital Cassette Construction

(Philips Type)

The Philip's type of audio cassette which is referred

to as the "compact cassette" was developed by Philips

Electrologica of Eindhoven, Holland. This is the most prevalent type of cassette that is used for digital applications

and is produced under a cost-free license by a large number

of companies

.

Physical details of the Philip's type cassette are as

follows :

In most cases, the outside shell of the cassette is

made of a noninflammable , high impact polystyrene plastic.

One model is available with a metal shell. The shell consists of two pieces which are joined together either with

screws near the four corners or by ultrasonic welding.

The welded cassette cannot be opened without destroying

the shell.

The front edge of the cassette shown in Figure la has

5 holes which serve the following functions : holes A and

E are for pinch rollers (usually solenoid activated) which

enter the cassette and engage capstans which are directed

into holes A' and E' (figure lb

)

> when the cassette is inserted into the transport; holes B and/or D are used for BOT/EOT

optical sensing and hole B for an erase head when one is

used; hole C is used for the record and/or read head. The

side view (figure lb) shows the location of the pressure

pad F. There Is no general agreement about the need for a pressure pad; some transports require a pad, while others

are unable to use a cassette with a pad.

The back edge of the cassette (figure lc) has two Ushaped cuts in the shell which enclose areas that can be

punched out to allow read only operation. A write enable

plug can be inserted into these areas when a write operation

is desired. The use of this write enable plug has not been

entirely satisfactory because it is small in size and is

easily lost. One cassette manufacturer covers the hole with

5
a metal plate Inside of the cassette so that it can be

"read-only" or "write enabled" by rotating a small disc that

is built into the side of the cassette. This controls the

opening or closing of the hole when the write enable sensing

pin in the transport engages the metal plate. The dotted

square to the left of center (figure lc) is a hole which is

specified in the ECMA standard and is used to identify the

A and B sides of the cassette. At the present time, the

American manufacturers are avoiding this means of identification and instead prefer to label the A side of the cassette

in the area reserved for labels. Area H (figure lb) contains

a transparent window on both sides of the cassette to enable

the user to view the tape on both hubs.

The tape is wound on 2 flangeless hubs within the cassette. These hubs are loosely fit in order to allow for

the easy engagement of the tape supply and take-up drive

shafts. One manufacturer has used precision mounted ball

bearing tape hubs in the cassette shell. A hub usually has

provisions for fastening the tape leader to its outer surface.

Rollers are provided at position J (figure lb) for tape guidance. There are several configurations for these rollers.

In one model they are spring loaded in order to fix their

position in the cassette and the tape contacting surface is

convex shaped to keep the tape centered on this roller surface.

In another case, the rollers are free to move between the

cassette shells and the important tape guidance is performed

closer to the head.

The inside surfaces of the large sides of the cassette

shell contain a liner which is called a "slip sheet". These

are usually made of a plastic material which provides a low

friction surface for the tape pack to slide and rotate against.

One model has convex ribs onto the slip sheet which causes

the tape to be forced gently into a uniform pack on the hub.

It is also claimed that this design will reduce dynamic skew.

This is accomplished with an Increase In friction which must

be overcome by the driving source.

Since cassette tape is not held taut between the hubs

when a cassette is removed from the transport, the outer

tape layers tend to loosen from the pack due to handling.

Therefore, there is an abnormal space between the hub and

slip sheet, the outer layer may slide into this space and

cause a tape jam-up. Provisions are usually made in digital

cassette containers to prevent the loosening of the tape

pack during storage. This is accomplished with 2 fixed

posts in the container which engages the hub centers.
C A [b] C [d] E )

1 vl '

'

' ' /

a. Front Edge

(T. "Q""i

\

\ ^ v

\ /

*/ ' —*\

D

B'

X

\

\

\

D

D

"O jO

/

/ /

; (o H ov

\

// /

/

>

«

O

b. Side View

c u

» ~l

< 1

1 1

1 ~^

' n

c. Back view

Figure 1. Physical details of a digital magnetic tape cassette
2.3 Digital Cassette Transports

There is considerable activity in the area of compact

cassette digital transport development and manufacture.

Most of the companies either did not exist until recently

or are new to the digital transport field. It is also

interesting to note that to date no major digital computer

manufacturer has produced a compact cassette transport for

the commercial market, although some have submitted proposa

for a cassette with a wider and thicker tape. „

The lack of digital cassette standards has allowed transport manufacturers to proceed into different directions

with their designs. Some of the transports were designed

and built to operate with a specific system while many from

both this group and othershave been made available to the

OEM market with a large number of options. In many cases

the mechanical transport unit is available with a head, read

and/or write electronics, servo speed control, choice of

speed, incremental and/or continuous operation and other

options. Transports with heads and electronics are available

for the following operations: (1) read only, (2) write

only, (3) write pass then read pass, and (4) read-whilewrite pass. Many of the heads that are now in use were

originally designed for audio operation, but some are now

available that were designed specifically for digital use.

There is a variety of available operating characteristics

in digital transports. For example: Tape "slow-forward"

speed can be obtained from 1-7/8 to 15 inches per second with

5 to 6 inches per second being typical. Some units have the

same "slow-forward" and "reverse" speed, others have only a "high speed reverse" and still others also have a "high

speed forward". Tape movement in the "slow- forward" and

"reverse" speeds is usually performed with 2 pinch rollers

and capstans; in some transports this is done with one capstan and one pinch roller in which the capstan rotation is

reversed. In at least one unit both pinch rollers are activated to move the tape while in another unit the capstans

have been eliminated and tape motion is controlled entirely

by the reel motors. Incrementally operated transports are

also available and in some cases the transport is able to

operate in either the continuous or the incremental mode.

Section 5 discusses the specific digital cassette

transports that were used in the signal amplitude experiments

in this first program phase.
3. EXPERIMENTAL DESIGN FACTORS IN THE

REFERENCE CASSETTE PROGRAM

3.1 Development of Cassette Groups

The reference digital cassette program is proceeding

along lines which are similar to those of the SRM-3200 program as outlined in the introduction. The major activity

will consist of the development of the primary and secondary

reference cassette groups by conducting a statistical search

for industry "centerline" signal level. The statistical

search is required because there is no de facto reference

cassette. The physical embodiment of the "centerline"

signal level will eventually be in the primary reference

cassette group. One tape in this group will be designated

as the NBS Master Standard Cassette (Computer Amplitude

Reference) on the basis of factors such as its position in

the primary group signal level distribution, and its signal

amplitude stability and uniformity characteristics. Once

the NBS Primary Standard Cassette (Computer Amplitude Reference) Group has been developed it will be used to calibrate

the NBS measurement system in order to develop the secondary

and "working" reference cassette groups. Classically, a secondary reference group is used as a comparison medium

for monitoring the stability of the primary group in repository and is usually constructed from different materials.

The "working" groups are used for the day-to-day system

calibration procedures.

3.2 Statistical Considerations

In order to develop a properly randomized sample of

digital cassettes, it is necessary to consider questions

such as the following:

The size of the required sample is a function of the

signal level variability of the individual cassette tapes.

What is this variability and can it be determined other

than by extensive measurements and experimentation? In

order to have a valid statistical experiment with properly

randomized data, we must know a number of things about

every tape cassette under investigation. For example,

who manufactured it? Are the lot numbers different for

cassettes purchased from a particular manufacturer? Has

the tape been manufactured by still current techniques or

is it obsolete? Is it possible that some cassettes are

the result of a momentary loss of quality control? Is

it a special reel or an off-the-shelf item? How much

does the tape vary in output along its length and across

its width? Since the same output is not obtained from the

tape after each pass, what is the pass criterion? Should
the data be weighted according to company sales volume? If

so, what is that volume? Does this tape come from the primary source or has it been channeled through a secondary

source which has altered it in some way?

The following are three possible approaches for obtaining the sample cassettes from which the statistical signal

level data can be measured:

(1) Purchase through various external sources possibly

located in different geographical areas) groups of say, 20

each of every magnetic tape cassette which is commercially

marketed in a particular category from every manufacturer

of that particular category. If possible, each cassette

should be derived from a different production run (note the

lot numbers). Also the history of each cassette should be

known including the production date, the plant location and

if the tape has been subjected to any unusual secondary postprocessing.

(2) Or, directly contact all cassette manufacturers in

the category of interest and see if they will submit samples

to NBS of groups of tapes which represent the average and

upper and lower limits in each cassette category.

(3) Or, purchase groups of all the available company

reference tapes in each category of interest. This option

may be a very effective approach particularly if the reference tapes do in fact represent production average tapes.

Probably a combination of A and C or A and B would be most

efficient. For example, in making measurements in each

tape category it is possible to use the corresponding reference tape to calibrate the electronics and transport before

measuring each of the associated cassettes.

3.3 Development of Transducer Groups

The "centerline" search cannot proceed without a

simultaneous search for the reference transucers, i.e.

the read/write heads. The head-to-tape interaction effects

do not permit either the tape or the head to be characterized or completely analyzed independently of the other.

That is, the relative signal amplitudes that are read from

a group of recorded tapes can vary significantly from head

to head. The state-of-the-art of magnetic tape transducer

design has not yet produced an acceptable "standard" read/

write head. That is, the tape head industry is not able to

construct a head that is reproducible, stable, compatible

with existent commercial equipment and understood analytically

For this reason, it is likely that the interim reference

10
cassette transducer groups will consist of commercially available read/write heads. The first series of tests that are

reported in section 5 were made with such commercially available heads. The introduction of a head-to-tape pressure pad

into the digital cassette adds another complicating factor.

It has been found that both the absolute pad pressure and

the pad material will affect the signal response of the

cassettes

.

The following are the type of criteria that must be

applied in order to develop the commercialy available transducer group:

(1) Locate the individual head type (or types) which

tend to show maximum signal amplitude reproducibility among

the same cassettes. That is, there should be a reasonable

probability that heads with similar characteristics are

available in the market place and are not one-of-a-kind

items. This can only be ascertained by random sampling

and measurement.

(2) The break-in time criteria must be investigated;

i.e., the length of time that is required for the head response to stabilize. For example, in the SRM-3200 program

the average heads were run in for approximately 15 to 25

hours before being used for calibration purposes.

(3) The end-of-life criteria must be developed; that

is the point at which the usefulness of a head as a calibrating device must be known. This depends upon factors such

as:

(a) The changes in the original relative signal

level response of the head which becomes apparent when

the measurements performed on a group of test cassettes

become different as the head wears. In order to check the

stability of the test cassettes themselves, it is necessary

to maintain a test head that is seldom used. In this way

any changes in the response of the test cassettes can be

detected by re-measuring them with this test head periodically

(b) Changes in the reproduced signal smoothness:

for example, this is manifested by a "hashy" appearance In

the signal peak trace as shown in Figure 18.

(c) Unusual increase in absolute output signal

amplitude: This may indicate that the depth of the head

at the gap has narrowed significantly.

After the digital cassette samples and interim transducers have been obtained, the following experimental decisions must be made:

11
(1) The form of the information which is written onto

these cassette tapes: For example, mode: NRZI or phase

encoding; bit density; write current level; write current

shape; continuous pulse train or information blocks, ac

,

dc or bulk erase prior to recording,

(2) The method of extracting the recording information

and its form: For example, peak or average peak value;

peak-to-peak or average peak-to-peak value; read-while-write;

read-after-write (which pass?),

(3) There is a wide range of available cassette transport speeds, therefore, the same bit density can result in

a number of different output signal frequencies. This

affects the transducer and electronics design factors. The

decisions for the first experimental program phase were

as follows:

(a) The writing density and mode: 1600 frpi (NRZI).

(b) The write current levels were the fixed design

values determined by the cassette transport that was used.

(c) The write currents were square wave driven

without an initial step current.

(d) Continuous pulse train recording (All "l's").

(e) The cassette tapes are ac bulk erased before

recording.

(f) The peak and average peak; the peak-to-peak

and average peak-to-peak information are all measured

simultaneously and recorded on a 6 track chart recorder.

(g) The fourth or greater read-after-write passes

are measured.

(h) Six cassette transports were used with speeds

ranging from 4 to 12 inches per second. This results in

operating frequencies from 3.2 kHz to 9.6 kHz.

The background for these initial decisions is based

upon the experience gained in the SRM-3200 program and

upon existing digital cassette specifications and industry

trends. It is possible, however, that some of these

conditions will be changed as more experimental data

are accumulated.

12
3. ^ Summary

(1) Establish a reservoir of digital cassette tapes

that can be used as a random sample source.

(2) Obtain a number of available digital cassette

transports - at least 10 if possible.

(3) In addition to the read/write heads that normally

accompany each cassette transport, obtain additional replacement heads for each model.

(4) Develop a signal amplitude measurement system whose

gain-frequency characteristics are compatible with the above

digital cassettes and cassette transports.

(5) Now apply the operating conditions described in

the previous paragraph to measure the signal amplitude response of the cassette samples.

(6) Calibrate the measurement system so that the

range and the relative signal amplitude of the cassettes can

be conveniently charted. The charts information can then

be organized into statistical form.

(7) From the statistical data locate a group of cassettes that is central to the distribution from a modal

and median point of view.

(8) Reorganize the descriptive statistical data into

a form which displays the centrally located signal amplitude as the 100% reference level and all others levels

dispersed about it in their relative positions on a percentage basis.

(9) Repeat steps 5 through 8 with each transport

and replacement heads. Set aside those units that show

similar, reproducible and uniform results for use as possible interim references.

(10) Study the measurement data that are derived from

all the preceding runs and determine that group of 5 digital

cassettes which appears most often in the center of a signal

amplitude distribution. Place this group into repository

as the interim primary cassette group. This group now sets

the 100% signal level for its entire category.

13
4. THEORY OP OPERATION OF THE NBS CASSETTE SIGNAL

AMPLITUDE MEASUREMENT SYSTEM

The system which is used for making the cassette signal

amplitude measurements consists of both circuit modifications

and newly designed additions to the NBS reference tape signal

amplitude measuring system [2]. This new configuration measures and simultaneously charts the following output signal

amplitude data on a 6 track chart recorder: [See figures 17

and 18]

.

(1) Negative peak amplitude (Track 1).

(2) Average negative peak amplitude (Track 2).

(3) Positive peak amplitude (Track 3).

(4) Average positive peak amplitude (Track 4).

(5) Peak-to-peak signal amplitude (Track 5).

(6) Average peak-to-peak signal amplitude (Track 6).

This variety of output data will be useful for making

experimental decisions. Eventually, one data format will

prevail as the industry standard. The present trend appears

to favor the peak-to-peak measurements because they reduce

the effects of asymmetry in the writing process. That is,

the method of erasure and the write head current balance

causes less reproduce error in a peak-to-peak than in a zero-to-peak measurement. Peak-to-peak measurements also

tend to reduce the effects of loose experimental control,

particularly in recorded tape tests.

4.1 System Components

Figure 2 shows the organization of the initial system

that will be used for measuring and calibrating the unrecorded NBS Secondary Standard Magnetic Cassette Tapes (Computer Amplitude Reference). The system consists of a signal

amplitude read channel, a supply voltage section which 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.

This first phase report does not include a write circuit because one cannot be designed until an interim reference head or group of heads has been chosen. At that time,

it will be designed as a continuous write current controlled

system which is capable of producing sets of saturation

Ik
5 JO °y9 > < UJ

or

a i i j , o2 5

5Py to — >

5co

CO1 i I- " ' I ' i "o

'' gco £ 21 - D 1 n % < g 3 5 ? 2 CO 1 u _i

CO <

Ob ' 2 » ' CO

UJ

RITE ANNE

SIGNAL READ

(FIG

a > |5 i i L.

—

— 1 —

i 1 i 1

UJ £

-WRIT

EAD

iETTE

NSPOl o r <"<

UJ ** l~

cr <-> 1 B

CD PM

>>

CO

-pG

<DB

!h

COcd

cuS

a;

-P•H

rHae

cti C

hO

•Hw

CO

Sh

(D PC

•H

cu .ap

<poB

cti inhO

cti •H

-aoo

rH

CM

cu

bO

•H

Ph

15
curves. These curves relate the read head output voltage

versus the write head current as described in reference [2].

The write current circuits will eventually be automated and

externally controlled. In the absence of these circuits

the series of tests that are described in section 5 were

accomplished by recording the cassettes with the write

current levels already found in the test cassette transports.

These are fixed current values that were set by the manufacturers . The following descriptive material lists the components

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

the figures 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) Cassette Signal Amplitude Read Channel Components

( figures 3 to 7)

.

(a) A read/write head and associated cassette transport, a line driver LD-1C, a termination network TE-1C,

and attenuator circuit AT-1C and a wideband preamplifier

WPR-1 with internal and external gain potentiometers R_

and R|, and amplifier OA-1.

(b) Peak detect-sample-and-hold circuit PD-SH-1

that contains comparator IC-1, transistors T,- through

T,|., and diodes D_ through Dl.

(c) Level shifting, inverting range setting and

summing circuits containing operational amplifiers OA-2

through OA-5, OA-8 through OA-10.

(d) External 10-turn potentiometers R,- for setting

the "MASTER GAIN" of the system. 5

(e) Passive R-C signal peak averaging circuits.

(2) Auxiliary Components and Systems

(a) Pour precision voltage sources (+6.0, +14.0,

+30.0 volts) and a dividing network for providing dc calibration voltages. One precision digital voltage source.

(b) A function switching system.

(c) Read-out devices: a 6-track chart recorder, a digital panel meter DPM-1 and a digital voltmeter DVM-1.

An X-Y recorder will be added when the write circuits are

designed.

16
4.2 Description of the System Operation

(1) Cassette Signal Amplitude Read Channel Operation

(figures 3 to 7)

.

(a) The signal which has been reproduced during a read-after-write operation from a test cassette is passed

through the unity gain, line driving amplifier LD-1C which

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

incoming signals so that the input to the WPR-1 preamplifier

will fall within a reduced range of amplitudes for the different recording densities. AT-1C is adjusted with Rj and

R2

. Thus far, typical values of output signal from LD-1C

have been found to lie in the range of 6.0-12.5 mV p/p at

1600 frpi. This variation in head output voltage is caused

by both the differences in read head design and the greater

than 2:1 variation in transport speeds.

The preamplifier was adjusted with Ro so as to produce

an average output voltage of approximately 6.0 volts p/p when the input was read from the interim "master" cassette.

This is a convenient starting value which produces good

linear response from the system. The principal deviation

from the operating philosophy of the computer tape signal

amplitude measuring system is as follows: (See figures 3

and 5 )

.

In the original system 3 WPR-1 wide-band preamplifier

stages were used to amplify the output signals from three

read head tracks while in the cassette system only one WPR-1

is required. In the original system each of the WPR-1 '

s

drove a separate sample-and-hold circuit which in turn fed

its respective signal into individual level shifting amplifier OA-2 and summing amplifier OA-4. The adaptations for

the cassette signal amplitude measurement system are as

follows: The signal from the WPR-1 is fed simultaneously

into the sample-and-hold circuit PD-SH-1A and into the unity

gain inverter OA-8 whose output is then fed into PD-SH-1B.

In this way both the positive and negative signal peaks

are each passed through their own channels. PD-SH-1B processes the positive peaks and the PD-SH-1A processes the

negative peaks. The two peak-detect sample-and-hold circuits

convert their ac input 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 circuits PD-SH-1 in

^igure 6 operates as follows:

17
CO 5 - o

Q>

1—oo

cr

com o o

(0

CO1 ID r

CO o>

LL.

a

CD -pw

>swpC

CDS

(UinM

cd

CDCC

cd Co

T3

cti cu

!h CO6

•H

Ph

<D Pc

•H

CD P

CmOIM

hO

cd HOOH

ffl

en

CDM

hD

•H
QCa

5

cc

u

I<

orI

=>2

-AA/v-e

£C?

o

—AAA/

a: * AAA/-

IT) AAA ||i

>

1 CJ

1 '« O l°<

/ w\h

c3

> o

^ o

o

| _ ,A A A «

1

Mi 1

15

| ZOO

' VVV ' M

'u

+ 5 '

1 LlJ ^

1^-

LL. 2 4.

19

o

H

I Eh<

O

rH

I Q

CO -p

•HO

IH •HO

P

ftc

•H

CD -P

CO>3

ra

ctf (U K

CDU

hO

•H

Ph
,i V^/V-

—AA/V

o

2 L> o -

H

I K

CD H

(in •H

rHa

6

(U

CD -p

ra

ra

cd

CD PC

LO

CD

hO

•H

20
V

enl <O

CMI <OI 00I Q

PM

CD -P

CO>>

CO

-aHoi t3C

cdI CD HaS

cd

raI -po

0) p>

CD

cd

CDa

CD -p

CO>3

CO

cd

CD

CD

faO •H

21
a.

CO

<^? ,r—WV-*-| ( 1||,

o

H

I <

O

I <

o

I <

o

to -p

•Ho

in •HO

-P

P"a

-po

CD p

to

CD

Ph

•H

CC I Q

** " U 0. OB

m X CO 5 z in in

c? i ° <

u. <j a o

22
The hold capacitor C^ 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

integrated 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 Co before driving the upper gating circuits consisting

of Tg 9 T7 and Tg . This integration stretches the signal

peak voltage hold time across Ct, 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 T12 - T13 current switching

circuit and a strobe pulse is generated by T13 which drives

the gate terminal of T]_i| (PET) during the stretched signal

level interval. A dc level now appears across C2 and is

held there until another strobe pulse is initiated by the

next signal cycle.

(b) The input circuits of the 0A-2s are adjusted by R^

and Rio so that the dc levels from the PD-SH-ls will track

their incoming signal peak values. Now see figure 7.

(c) The output signal from each C2 is then fed into

the OA-3's. The outputs from the QA-3's are injected into

their respective "MASTER GAIN" or "MG" branches of the final

summing amplifiers OA-4. The MG potentiometers R5 are the

principal calibration devices of the system. The signal

is offset by the OA-4 "% RANGE" branch voltage in order to

attain the desired chart recorder percentage values.

(d) The output signal from each OA-4 then is passed

simultaneously to their respective chart recorder channels

and to the second peak-to-peak summer amplifiers OA-9 where

the outputs from each OA-4 are added together and then divided by 2.

(e) The output from OA-9 is inverted by the unity

gain amplifier OA-10. The output from OA-10 which represents the peak-to-peak signal level is fed into channels

#5 and #6 of the chart recorder.

(f) A passive R-C averaging circuit is used to

average the output signal from each OA-4 and OA-10. The

voltage across the capacitor C. is applied to the chart

recorder track that is adjacent to the signal peak track that

it is averaging. The upper track of each pair on the chart

is the average signal peak or average signal peak-to-peak

track.

23
4.3 Description of the OA-4 Circuit

The output summing amplifiers OA-4 circuits are

very important ones in the measurement system. They have

the following input lines which can be individually activated

either by formalized switching system or by patch-cords

(See figure 7 )

(1) "MASTER GAIN" (MG) R^

(2) "AC CALIBRATE" (AC) Rg

(3) "SET CHART" (SC) R

y

(4) "% RANGE" (SO R

Q

R5, Ry , and R8 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:

(1) The "MASTER GAIN" potentiometer R^ adjustment sets

the final gain of the positive and negative peak reading

channels so that they will produce the desired reference

output level as provided by the NBS master cassette. The

NBS secondary standard cassette tapes will then be calibrated

with respect to this level. The "MG" Input branch to OA-4

functions during the normal operating mode.

(2) The "AC CALIBRATE" input to OA-4 switches in a

simulating ac signal to test the stability and adjustment

of the system at any time.

(3) The "SET CHART" input to OA-4 is switched in

during the "SET CHART" mode of operation. In this mode

3.000 volts dc is injected into OA-4 and produces the output voltage level of 1.25 volts dc which is used when setting the chart recording devices into their 100% reference

states prior to recording and calibration.

(4) 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]_2 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 50% to 150% of the

total signal amplitude is charted on a strip chart recorder

24
by offsetting the lower 50$ of the output signal and then

selecting that chart recorder range that will encompass

the next 100$ of the total signal level over its limits.

An NBS chart recorder track has a useful width of 10

major linear divisions as shown in figure 17. When the

recorder sensitivity is set to 0.50 v/div then full chart

deflection is obtained with 5.000 volts dc . If the chart

centerline is chosen and "SET" as the 100$ reference level

then 1.250 volts dc output from OA-4 or OA-10 will produce

a trace at this level as previously indicated. Since 3.000

volts dc into OA-4 represents the 100$ signal 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 then represents the 50$ signal level

and the top of the chart represents the 150$ signal level.

When an actual cassette signal produces 1.250 v dc output from an OA-4 stage, then the recorder channel which is

driven by that stage will produce a trace at the 100$ chart

centerline. As previously stated, recorder tracks #1 through

#4 display the zero-to-peak signal level responses and their

average values.

(5) The peak-to-peak chart recording is produced by

the output from the OA-9 - OA-10 combination. In "SET

CHART" operation each OA-4 feeds 1.25 v dc into the summer

OA-9. Since each input of OA-9 is adjusted for a gain of

G = 0.50, therefore, its output is also equal to 1.250 v

dc. Unity gain inverter OA-10 then drives channels 5 and

6 to their centerline (100$) position. The same situation

now obtains when the OA-4's are driven by a signal which

is repi-oduced from a cassette. An example of the actual

cassette measurement operation of the system after it has

been ac and dc calibrated is as follows:

(a) The NBS master cassette is run on the measurement

system and since the positive and negative peaks (zero-topeak) are assumed to be 100$ values when derived from the

master tape, the "MASTER GAIN" controls are set to produce

1.250 v dc output from each of the two OA-4's. This will

produce a trace at the centerline of each of the six chart

recorder tracks.

(b) The candidate cassettes are now run on the calibrated system and their relative zero-to-peak and peak-topeak percentages will be charted. For example, if a candidate tape cassette charts 100$ positive peak amplitudes on

channels #3 and #4 and 50$ negative peak amplitudes on

25
channels #1 and #2 it will chart peak-to-peak amplitude at

the 75% level on channels #5 and #6. In other words the

candidate cassette has a peak-to-peak signal amplitude which

is 150 or 75% relative to the "master" reference level.

200

5. EXPERIMENTAL RESULTS

5.1 Case Histories of Submitted Cassette Transports

The field of digital cassette transport design is relatively new and many of the manufacturers have little background in the development of this type of product. This

makes it difficult to find reference cassette transports at

the present state-of-the-art. All of the data which are

presented in section 5 were produced from 6 transports that

could be put into operation.

Some of the typical problems which were encountered

among the test cassette transports were as follows:

(a) Guidance defects which led to tape damage.

(b) Defects in the speed control systems which caused

instability

.

(c) Electronic system defects resulting in burnt

components and blown fuses.

(d) Mechanical defects in the driving motors.

5.2 Cassette Transports Used for Test Measurements

(1) Only 6 of the 8 cassette recorders which were

tested were used to produce the data which are described in

this section. These are recorders numbered 1, 4, 5, 6, 7

and 8. Although there are numerous options available with

each recorder, the following information relates only to the

models that were used by NBS

Unit #1 (Dual Capstan)

(a) Capstan motor: One printed circuit dc motor for

(b) Reel motor: all functions (4 belts).

In some instances the defects were able to be corrected and

the transports were used for the tests described in section

5.3.

26
(c) Motor speed: Slow 6 ips (forward and reverse)

Past 80 ips (forward and reverse)

(d) Speed stability: Company claims: 3% S.T.; 2% L.T.*

MBS measurements: see figure 8.

(e) Head: Single track - dual gap.

(f) Miscellaneous: Has write circuits (phase encode)

which needs external driving source.

Read amplifier outputs are analog.

Read-while-write capability.

Produced for OEM and in-house use.

Unit #4 (Dual Capstan)

Capstan motor: one dc with Hall generator feedback

control

.

Reel motors : two dc with Hall generator feedback

control.

Motor speed: Slow 7.5 ips (forward and reverse)

Fast 40-400 ips (forward and reverse)

Speed stability: company claims 4% S.T.; +2.5% L.T.

NBS measurement: see figure 8.

Head: 2 track - single gap (standard)**

Miscellaneous: No read or write circuit with NBS

unit. Produced for OEM use.

(Single Capstan)

Capstan motor: one ac synchronous

Reel motor: two dc servo controlled (belt drive)

Motor speed: Slow 5 ips (forward and reverse)

Past 120 ips (forward and reverse)

(d Speed stability: No company information.

NBS measurements: see figure

*"S.T." and "L.T." mean "short term" and "long term" speed

variations respectively.

**A "standard" head indicates that both gaps are of equal

width.

27
(e) Head: 2 track - single gap (non-standard: different track widths

)

(f) Miscellaneous: Has write circuits (phase encode)

which need external driving source.

Has analog output read amplifiers.

Produced for OEM and in-house use.

Unit #6 (Dual Capstan)

(a) Capstan motor: one dc servo controlled.

(b) Reel motor: two dc torque.

(c) Motor speed: Slow 7.5 ips (forward and reverse).

Fast 90 ips (reverse).

(d) Speed stability: Company claims: 3% S.T., + 3% L.T.

NBS measurements: see figure 9.

(e) Head: 2 track - dual gap (standard). Write

current 8. mA.

(f) Miscellaneous: Has write circuits (phase encode)

which needs external driving source.

Has analog output read amplifiers.

Produced for OEM use. Read-whilewrite capability.

Unit #7 (Single Capstan Type)

(a) Capstan motor: one bidirectional servo controlled.

(b) Reel motors: two dc torque (direct drive).

(c) Motor speed: Slow 12.5 ips (forward and reverse)

Past 120 ips (forward and reverse)

(d) Speed stability: No company information

NBS measurements: see figure 9.

(e) Head: 2 track - single gap (standard). Write

current 5.0 mA.

(f) Miscellaneous: Has write circuits (phase encode)

which need external drive source.

Has analog output read amplifiers.

Produced for OEM and in-house use.

Needs separarate external generator

for servo loop control
Unit #8 (Dual Capstan)

(a) Capstan motor: Two hysteresis synchronous.

(b) Reel motors: Two dc torque (direct drive).

(c) Motor speed: Slow 8 ips (forward and reverse).

(d) Speed stability: Company claims k% S.T., 0.5% L.T.

NBS measurement: see figure 9.

(e) Head: 2 track - single gap (standard). Write

current 5.25 mA

.

(f) Miscellaneous: Has write circuits (phase encode)

which needs external driving source

Read amplifier outputs are analog

or shaped. Produced for OEM use.

(2) The cassette recorder speed stability data in figures 8 and 9 were all produced with a test tape which was

accurately recorded at 1600 frpi. The signal frequency output from the recorder was measured on a frequency counter and

was plotted as a function of the "Time in Minutes from the

BOT" . Note that the machine speed can be determined from:

Machine speed ( in /s) = Measured frequency

oUU

For example the speed of cassette transport #4 is equal to:

Measured frequency 6000 „ r in , , . v 800 " = ~W0 = 7 ' 5 /s (lps)

This is the rated machine speed for this #4 transport; it is

achieved only for a small time interval at approximately 0.7

minutes from the BOT. At all other times, the machine speed

deviates from this nominal value. Note that the curves in

figures 8 and 9 terminate at different times due to the

variation in the average recorder speeds.

Figures 10 and 11 display the tension which is exerted

on the cassette tape by the take-up reels of the recorders

in the figures. Recorder #6 is not shown in the figures

which are drawn in terms of the "Tape Tension in Grams versus

the Time in Minutes from the BOT". The measurements were

performed on an ITC M-100 Tension Monitor with the tapes

running in the forward direction.

29
5.3 Experimental Measurement Data

The six cassette transports which were described in the

previous paragraph were used to perform a series of signal

amplitude measurements on a sample of 20 tape cassettes.

These cassettes were chosen from a pool of 44 tapes which were

obtained from 9 sources and are identified in the tables with

a letter and number designation.

(1) Table 1 gives the base and oxide coating thickness

dimensions for the 20 test cassettes.

(2) Table 2 gives the pressure pad dimensions and. the

pad materials used in the 20 test cassettes.

(3) Table 3 gives the coercitivity H c

, the residual

flux <J> r and the squareness ratio of the test cassette tapes.

Figure 19 shows the hysteresis loops for four of the cassettes;

C9, C13, PI and G3. C9 is chromium dioxide tape whose output was above 150% of the average level and was not included

in the 20 tape samples.

(4) Tables 4a and 4B give the 300 signal amplitude

measurement results relative to the 100% level set by the

interim "master level" tape C13. The histograms in figures

12 to 15 are derived from these tabulated data.

(5) Table 5 gives the average, the median, the mode

and the standard deviation of the 300 signal amplitude

measurements. The data is broken down into groups of runs:

1-6, 7-12, and 13-15 as well as the full run of 1-15.

(6) Table 6 denotes which cassette transport was used

for recording and reproducing the signal during each of the

15 runs.

Figure 12 is a group of curves which show the results

of a cassette torque test which was performed on the 20 test

cassettes using the ITC M-200 Torque Tester. Although all

of the cassettes are not displayed in these curves the upper

and lower limit curves are shown. Note that 8 g-cm of holdback torque was applied during the tests.

The signal amplitude test procedures were as follows:

(1) The 20 test cassettes were ac (60 Hz) bulk erased.

(2) A pulse train consisting of all l's was then recorded on each of the test tape cassettes at 1600 flux reversals

per inch. Only 3 of the six test transports were used for

recording purposes: transports numbered 6, 7 and 8. These

30
Table 1. Test cassette tape dimensions

TAPE BASE THICKNESS COATING THICKNESS

ym pink ym yin

A4 12.4 490 6.85 270

Bl 13.8 545 5.71-5.84 225-230

B3 14.1 555 5.20-5.58 205-220

CI 12.4 490 6.59-6.85 260-270

C2 12.2 480 6.59-6.73 260-265

C3 12.2 480 7.10 280

C8 12.7 500 6.09-6.22 240-245

CI 3 14.0 550 5.32-5.84 210-230

D6 11.2 440 6.73 265

D8 10. 7 420 6.59-7.36 260-290

E6 12.4 490 ~ 5.46-5.84 215-230

E7 12.6 495 5.46 215

Fl 11.2 440 5.58-5.87 220-230

F8 12.9 510 5. 84-6.59 230-260

P9 12.4 490 6.59 260

PI 5 12.9 510 6.59 260

G3 11.4 450 6.87-7.36 270-290

G4 11.9 470 6.59-6.85 260-270

Jl 12.3 485 5.46-5.71 215-225

SI 11.2 440 4.69-5.07 184-200

In tables 1, 2 and 3 the data are given in terms

of the SI units followed by the equivalent English

units in the column to the right.

yin = micromches

ym = micrometer (1 ym=39.4 yin)

31
Table 2. Test cassettes pressure pad dimensions and materials

PAD MATERIALS

Pelt on Foam Rubber

Pelt on Spring

Pelt on Spring

Pelt on Spring

Felt on Spring

Felt on Spring

Felt on Foam Rubber

Cloth on Foam Rubber

Felt on Spring

Pelt on Spring

Plastic Sheet on Foam Rubbc

Plastic Sheet on Foam Rubbt

Pelt on Spring

Felt on Foam Rubber

Felt on Foam Rubber

Felt on Foam Rubber

Felt on Spring

Felt on Spring

Felt on Spring

Felt on Spring

PAD LENGTH PAD WIDTH

TAPE mm in mm in

A4 5.33 0.21 7.62 0.30

Bl 3.81 0.15 5.59 0.22

B3 3.81 0.15 5.59 0.22

CI 4.32 0.17 6.10 0.24

C2 4.32 0.17 6.86 0.27

C3 4.32 0.17 6.86 0.27

C8 5.84 0.23 9.40 0.37

C13 6.86 0.27 9.40 0.37

D6 3.30 0.13 5.33 0.21

D8 3.30 0.13 5.33 0.21

E6 8.64 0.34 8.38 0.33

E7 8.64 0.34 8.38 0.33

Fl 4.32 0.17 5.84 0.23

F8 6.10 0.24 8.64 0.34

F9 6.10 0.24 8.89 0.35

F15 6.10 0.24 8.89 0.35

G3 6.60 0.26 5.59 0.22

G4 6.60 0.26 5.59 0.22

Jl 7.87 0.31 7.87 0.31

SI 4.32 0.17 5.59 0.22

32
Table 3. Magnetic characteristics of test cassette tapes

TAPE

He

A/m

24,670

(oe)

310

<J>r Wb

See Note C

(mx) b

0.313

Squareness

Ratio

A4 0.86

Bl 21,490 270 0.231 0.90

B3 21,490 270 0.231 0.90

CI 23,080 290 0.263 0.91

C2 23,080 290 0.269 0.89

C3 23,080 290 0.275 0. 90

C8 23,080 290 0.244 0.91

CI 3 21,490 270 0.244 0.93

D6 24,670 310 0.313 0.86

D8 24,670 310 0.313 0.88

E6 21,490 270 0.231 0.90

E7 21,490 270

• 0.231 0.90

Fl 36,607 460 0.244 0.91

P8 21,490 270 0.269 0.90

F9 21,490 270 0.263 0.89

F15 21,490 270 0.269 0.90

G3 22,280 280 0.313 0.88

G4 22,280 280 0.300 0.87

Jl 26,260 330 0.269 0.89

SI 24,670 310 0.269 0.89

A/m = Amperes per meter Wb = Mx x 10

oe = Oersteds

b Wb = Weber

Mx = maxwells

33
Table 4a. Signal amplitude response of the 20 test cassettes

\ Run \ No.

Tapes.

No.\ 1

101

2

101.3

3

93.5 96.5

5

101.8

6

Bl 95

B3 99 100 100 99.5 98.5 98.5

CI 106 104 112.5 105.5 98.5 99

C2 98 99 101.5 98.5 100 102

C3 100 102 109.5 103 95.5 102.5

C8 101.5 99 105.5 98.5 96.5 92

C13 a 100 100 100 100 100 100

D6 131 129 133 127.5 126.5 131

D8

E6

126

97

124

96

125.5

106.5

127.5

97.5

119

97.5

131.5

97

E7 94 94 94.5 94.5 94.5 85

PI 128 129 130.5 121.5 122.5 122

P8 89 90 95 91.5 87.5 89

F9 94 97 108.5 100.5 96.5 94

PI 5 97 95 104 86 93.5 89

G3 103 102 105.5 101.5 101.5 104

G4 101.3 102 103.5 103.5 102.5 100

Jl 127 126 137.5 125.5 125.5 131

J2 125 124 131.5 121.5 126.5 128.5

SI 129 128 131.5 129.5 127.5 134

a C13 is the "master" tape.

34
Table 4b. Signal amplitude response of the 20 test cassettes

\ Run

\ No.

Tape\

No\ 7 8 9 10 11 12 13 m 15

Bl 98 100 98 103 99 98 98 100 97

B2 97.5 100 96.5 104 100.5 107.5 99 100 97

CI 98 99 99.5 100 100 112 99 102 99

C2 107 104 102 98 102 100 101 102 100. 5 C3 97 100 100.5 100 103.5 108 102 100 102.5

C8 965 96 101.5 107 102 106 102 102.5 99.5

C13 100 100 100 100 100 100 100 100 100

D6 121 126 121.5 125 124.5 125.5 124 122 127.5

D8 121 123 121.5 117 128.0 124 125 120 120.5

E6 102 100 101.5 99 104 118 96 94 99.5

E7 98 100 99.5 100 100 111.5 96 98 98.5

PI 101.5 108 110.5 103.5 103 110 100 99 103.5

F8 99 96 91.5 105 107 117 102 102 99

F9 90 98 97.5 108 110.5 121.5 102 103 101.5

PI 5 97.5 92.5 95.5 110 108 100 102 104 89.5

G3 105 102 106 112 112 120.5 108 110 110.5

G4 110 112 109.5 116 112 121 110 112 113.5

Jl 125 126 120.5 125 131 140.5 124 120.5 124.5

J2 125 125.5 121.5 129 121 136.5 121 122.5 122.5

SI 127 127.5 128.5 123 129 143 125 122 124

35
Table 5. Cassette transports used for each run

Test

Run No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Recorded on Transport No,

1st Recorded

Pass

2nd Recorded

Pass

3rd Recorded

Pass

Reproduced on Transport No.

5

6

4

36
Table 6. Statistical data derived from the 15 runs

AVERAGE MEDIAN ABSOLUTE STANDARD

RUNS VALUES VALUES MODES DEVIATION

1-6 (LOW) 98.7 99.3 100.0 5.11

1-6 (HIGH) 127.6 127.5 x

a 3.90

1-6 (ALL) 107.3 101.5 100.0 X

7-12 ( LOW

)

102.1 100.0 100.0 5.05

7-12 (HIGH) 124.9 124.8 X 5.82

7-12 (ALL) 108.9 104.5 100.0 X

13-15 (LOW) 101.3 100.0 102.0 4.54

13-15 (HIGH) 123.0 122.5 ~ 124 2.03

13-15 (ALL) 106.7 102.0 100.0 X

1-15 (LOW) 100.6 100 100 5.2

1-15 (HIGH) 125.7 125.0 125.0 4.88

1-15 (ALL) 107.9 102.0 100.0 X

= didn't calculate

"Computed standard deviation". Data processed by William

B. Truitt

37
7000 —

6000 —

5000

FREQUENCY

IN HERTZ

4000 —

3000

Signal Frequency Output

vs Time for Cassette

Transports 1,4, and 5

2 4 6 8

TIME IN MINUTES FROM BOT MARKER

Figure 8. Cassette transport speed measurement curves

38
1000

10000

FREOUENCY

IN HERTZ

7000

6000

Signal Frequency Output

vs Time for Cossette

Transports 6, 7 and 8

#7

#8

#6

2 4 6 8

TIME IN MINUTES FROM BOT MARKER

10

Figure 9. Cassette transport speed measurement curves

39
60 1—

GRAMS

12 3 4

TIME IN MINUTES FROM BOT MARKER

Figure 10. Tape tension test curves

40
Tope Tension Tests for Cassette Transports I and 8

GRAMS

30

20

#8

10

12 3 4

TIME IN MINUTES FROM BOT MARKER

Figure 11. Tape tension test curves

41
were the only units which were received with operative write

circuits. The continuously controlled NBS write system has

not yet been developed since the reference transducers have

not been determined at this time.

(3) After each of the 20 cassettes had been recorded

on one of these 3 machines their recorded signal amplitudes

were measured (after the fourth or later pass) on the

system as described in section 4. This resulted in 120

measurements for each of the first two recorded passes and

for 60 measurements on the third recorded pass for a total

of 300 signal amplitude measurements.

(4) There was no de facto signal amplitude "master"

cassette available for calibrating the measurement system on

the first run; therefore the system was set up close to its

operating center and was gradually readjusted until the general dispersion of signal amplitudes were all contained

within the chart recorder range: in this case from 50% to

150J6.

After this first coarse measurement run was completed,

the numerical data were organized and evaluated. Cassette

C13 was found to be centrally located and was assigned the

position of temporary "master level" cassette. As such, it

was used during each run to calibrate the measurement system

to the "100% level" as described in section 4.

The results of the 300 signal level measurements are

compiled in Tables 4a and 4b in terms of percentages relative

to the "100% level" established by C13 and the histograms in

figures 13 to 16 were based on the data in these tables.

The abscissae of these histograms are plotted in terms of

the "% variations from the 100% master level". For example,

+5% is equivalent to a 105% signal amplitude level relative

to the 100% master level. The histogram in figure 13 shows

the distribution of signal amplitudes for the accumulated

results of all 3 recording runs consisting of a total of

300 samples. The histograms in figure 14 to 16 are the

results of the individual recording runs, i.e., figure 14

shows the signal amplitude distribution which results from

120 measurements made on the 6 test transports after the 20

cassettes had been recorded on transport No. 6. Figure

15 and 16 shows the histograms which resulted from the runs

which were based upon the recordings made on transports

numbered 8 and 7 respectively. Note that in every instance

the absolute modal value is at "0% deviation from the 100%

master level" while relative modal values occur 20 to 25%

above this level. That is, there is a trend towards relative

signal amplitude classes which are approximately 25% apart.

42
70

TORQUE

IN GM-CMS

Cassette Torque Test using

8 GM'CM Holdback Torque

I 2 3

TIME IN MINUTES FROM BOT MARKER

Figure 12. Cassette torque test curves

43
Q.3Oworooio

Ifo H K>+ o

-p

m

H

CJ+ COG3

-i Ih m o >

CM Ul ?H + _l

orUJ o

Cm

l- S

in </) cd TM < M + 2 bO

s8

O

-P o Og

CO •H + 2O a

CC 0) U. •d

tn 3

U) z p + o •H H H < a

oc S < cd o >

5?

H

cd

mI

faO •H

CO

ro

CDMH

O

oo o o

ID om o o O

S3TdlNVS dO a38wriN

44
o

+

(0

o

Q.

c/> c

o

12u

ou

— </>v£> _

a> <u c l*° °

-1 E

"°

ai en S? £ wo

a.oo

x:r

Q.3oo

5o

IT) to+

o 8

-p +

CO

U*) 3

CM M

+

_j Sh ui O > Cm o UJ CM+

_i

orUJ M

in+

1-

c/) <2

bOO

-Pw

i5 •H O .c O CD o n

+ 2

O

u.

3

-p•H

CO a

z S m o ctf + »-

<I H

or<

> hO o

8* •H00

in

1 i—

I

cuM

3

O hO

I •H

in

l

o

to

tf) CM io o

S3HdWVS JO id38wnN

to

^5
—ou

CDO

a.o

1- O

_ tn CM

at at

— ^ I" 5 _ cr cr

a.3Oa*o

in

*•+o*+

in

to+

C\J H o

to

•4-

OP m

<M

M + £ _iUJ> 2

•4

-i in o

CM+

crUJ

iO

<4H

m+ <5O 1

hOO

O -Pm o 2O

•H + or

CD

CO 3 z -P

in o •H + 1- H < a

ce e < cd > o iH 8s cti

hO

•H

in1

CO o

to

m

C\J oCM

jo o «n

S3"ldWVS JO d39Wf1N

LC\

CDU

hO

•H

ft

46
touou

0) (O > o> <u _

-I Q. w E

0)

g

ti #> ° O 5 vo o

Q.

in c

*- -0

K>

at "O 3 01 a: oc

Q.3Oo

a.oOso

IT) +o+m

to+oto

in

CM+m

UJ>

UJZOO o 2 * 2zo

in

10 o m

CM o(M

m

inoP

ro

COCm

inO

CmS

cdM

bOO

-Pm

•H

<u

-P

•HHa6

cd < H

or cd < C > hC

s?

H

CO• m1 H

(I) M3

hO

•H

m1 O1

S31dWVS dO M38wnN

47
Note that the histograms were drawn on the basis of the

complete data derived during each specified group of runs

and that the "low-high" division about the 115$ signal level

naturally appeared from the full set of data without prior

separation.

(5) The data in Tables 4a and 4b were extracted from

6 track chart recordings such as that shown in figures 17 and

18. The data is the peak-to-peak signal amplitude shown on

the bottom track (#6). Figure 17 shows the 6 track chart

recording derived from the C13 interim "master level" tape.

Each track is set to the 100$ chart level with the "Master

Gain" adjustment that was discussed in section 4. Figure 18

shows the measurement chart derived from cassette B3 after

the system was calibrated by C13. Note that figure 17 shows

the chart recorder set for a 2$ variation per small division

and figure 18 shows the chart recorder set for 1$ variation

per small division.

(6) The output voltages were measured directly at the

read heads of some of the transports in response to the

recorded interim "master level" cassette C13. There was no

observed correlation among the absolute output voltage

levels from different heads at different transport speeds in

response to this as well as other recorded tapes. For example,

for C13 on transport #4 the head output voltage was 1.87 mv

rms at 6.057 kHz; on transport #7 the head output voltage

was 3.55 mv rms at 10.31 kHz and on transport #1 the head

output voltage was 2.43 mv rms at 4.98 kHz. Therefore, it will

be necessary to make all output measurements on a relative

basis until such time that a "standard reference" read/write

head is available.

(7) The data in tables 4a and 4b were inspected to

see if any of the test transports seemed to yield amplitude

results which correlated with any of the others. Transport

Nos. 1 and 4 seemed to be the most out of line, therefore,

they were removed from further consideration as possible

reference units: only the measurements made with transports

5, 6, 7 and 8 were considered. It was found that for runs 1

through 6 that the maximum variation in relative amplitude

for a tape which was run on these 4 transports was less than

10$ from transport to transport after each had been first

calibrated to the 100$ level by C13. For runs 7-12 with

the exceptions of tapes F8, F9 and F15 the maximum variation

in relative amplitude was also approximately 10$. Since

transports 1 and 4 were used in runs 13-15 no maximum variation was computed.

48
Ur* d>*

/iO"> *y&

/

\

\Ca~l &ra-t

r*K*r± ck.A C«y-)

1

! \ i

TXH #g Ck: * (.pe**-)

n

- V V

i •pt A

,~*. Chart -3D&xt «"*/*

.

00

Cr\ 9

*""' r*?«* ¥ CA./3 (Pco,k)

nitiuifiiihniiiiiiiiiiiiiiiiiMu

::;

i

T*K *3" (*v% • Pee.*-** - Peak)

1

T/?/< *C ( Pe«.«-6c-Pe«X.)

Figure 17. Six track chart recorder output curves

49
w*.

.. Urt m

,

6 o */i J***'

Ck..4 (Avf>)

fcijnyiiiii<iiaili<MiMmiimn«Mmutam>nM*i«iniifti>< iatiMUtftttii

Ck /! (Pea.*.J

f

•* -» ft

'::..

/ <Z%

ISvo si.

i;

T<'<-e~ « " '" ok. 8 (Ay.)

1 3

C^k,. 8 (Pe*.k)

i'iiiii!iimiiiiiiliiiii'imilrMfilimiliiiiiiiMii l iimliiiiiiiim ! iMii IIUI ! MIITl|llllil!llkllllt

4ft ^Y "1

, V i

Peedi-ib-Pe*k. Cbtf .)

i " TM

{'«tK -tv- F<ft. <

Figure 18. Six track chart recorder output curves

50
Cassette: G3 Cassette: Fl

Cassette: C13 Cassette: C9

Horizontal Scale 16,000 A/m per division

200 Oe. per division

Vertical Scale 0. 25 (10-8) wb per div.

0. 125 mx per division

Figure 19. G'-H Curves for Cassette Tapes

Figure 19. (f^-H loops for four cassettes

51
(8) Additional Observations:

(a) Some cassettes had difficulty in running properly on some transports; however, cassettes which were produced by the manufacturer of the transport invariably ran

well on that transport.

(b) Some cassettes which produced clean smooth

chart traces on one pass would become highly erratic on an

ensuing pass.

(c) The signal amplitude on the tapes would become

stable by the 4th or 5th pass : the signal amplitude from

the 1st to the 5th pass was found to decrease by approximately

5% on the average for the test cassettes.

6. 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

equivalent devices. There is considerable latitude in the

choice of semi-conductor components, potentiometers, recording, reproducing and measuring devices. The following is a tabulation of some of the devices that are used in the NBS

cassette measurement system:

Transistors T( Numbers in Figures) Type

2N3646

2N3638

2N916

2N3821

2N4222A

7-10, 27, 28

6, 11, 12, 13

1-3

K 5

14

NPN Switching

PNP Switching

NPN High Frequency

Amplifier

NPN High Speed Switch

N-Channel FET

Diodes D( Numbers in Figures) Type

1N276

1N916 2,

1

3, 4

Ge Switch

Si Switch

Amplifiers (Numbers in Figures) Type

PP45U OA-l-to 10 Operational Amplifier

(Solid State)

52
Integrated

Circuits (Number in Figures) Type

yA710C IC-1 Differential Comparator

7. APPENDIX

7.1 Digital Cassette Standardization Progress

Most of the effort in standardization work to date for

the Philip's type of cassette has been carried out in Europe

Since the cassette was initially designed for audio applications, the first standards appeared in the IEC TC60 Audio

Group. Document 94 from this group detailed, among other

items, the physical specifications of the cassette. This

was followed by Addition 1 which relaxed many of the tolerances of the original document. Around December 1969 ECMA

began work on a digital cassette standard when it became

apparent that manufacturers were going in many different

directions and requested guidelines in the design of transports and choice of recording methods. With Addition 1 as

the basis, ECMA produced a draft proposal which was accepted

with minor modifications by ISO TC97/SC4/WG1 as a First

Draft Proposal. The U.S. ANSI Task Group X3B1 has had

three meetings devoted toward the development of an ANSI

digital cassette standard and is basing their work on the

ECMA document. In the meantime, proposals for a 1/4 inch

digital tape cassette standard have been submitted in the

U.S. and in Europe. None of the 1/4 inch digital tape

cassettes have been made available as yet for evaluation.

7.2 Tape and Leader Dimensions

The following specifications for the tape and leader

have been taken from the most recent ECMA document on the

compact cassette:

Tape Width: 3.8l to -0.05 mm (0.150 to -0.002 in)

Total Tape Thickness: 19 ym (750 y in) maximum

Coating Thickness: 5 + 1 ym (200 + 40 y in)

Tape Length: 86 *

|j m (282 * ^ ft)

Leader Thickness: 38 ym (1500 y in) maximum

53
Leader Length: 500 + 50 mm (20 + 2 in)

Measured from the cassette face to

beginning of the magnetic tape (measured perpendicular to the cassette

face)

.

BOT/EOT Markers Shall be circular holes having a

diameter of 0.6 + 0.05 mm (0.0237

+ 0.002 in). The distance of the

marker centers from the physical

beginning and of the magnetic tape

(for BOT and EOT respectively) shall

be 450 + 30 mm (17.7 + 1.2 in).

With respect to read signal output amplitude, manufacturers of cassettes appear to have separated into two groups

whose signal output differs by about 30%. (This was observed

in the NBS laboratory as described in section 5). The lower

signal output tapes are usually produced by the 1/2 inch

computer tape manufacturers who would like to keep the outputs

of the cassette and computer tapes similar.

Although a digital cassette standard is well under way

in the U.S.A. at the present time, quite a bit of work still

remains before digital cassettes will be interchangeable

both from a mechanical and information point of view. The

quality of digital cassettes has improved to where drop-out

free certified cassettes are now available. Due to the lack

of a standard, however, there are quite a variety of recording techniques, control systems, track configurations, BOT/

EOT sensing techniques, etc., now available and most of these

differences will have to be resolved if information interchange between different systems is to be achieved. ANSIX3B1 recognized that digital cassettes would be subjected

to a wide variety of applications and included consideration

of the applications in their program of work on cassettes.

54
8. REFERENCES

[1] Geller, S.B., Mantek, P. A., Cleveland, N.G., Calibration

of NBS Secondary Standard Magnetic Tape (Computer Amplitude Reference) SRM-3200 Using the Reference Tape Amplitude Measurement "Process A"; NBS Special Publication

260-18, November 1969.

[2] Geller, S.B., Calibration of NBS Secondary Standard

Magnetic Tape (Computer Amplitude Reference) SRM-3200

Using the Reference Tape Amplitude Measurement "Process

A" Model II; NBS Special Publication 260-29, June 1971.

55
FORM NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBS TN-731

2. Gov't Accession No.3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Calibration of Secondary Standard Magnetic Tape

Cassettes (Computer Amplitude Reference) Phase I

5. Publication Date July 1972

6. Performing Organization Code

7. AUTHOR(S)

Sidney B. Geller and Paul A. Mantek

8. Performing Organization

10. Project/Task/Work Unit No. 9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Same as No. 9<

13. Type of Report & Period Coveted

Final

14. Sponsoring Agency Code

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.) This Technical Note discusses a method for developing and maintaining

a reference system which will produce NBS Secondary Standard Magnetic

Tape Cassettes (Computer Amplitude Reference). It describes both

centerline tape search procedures and an interim signal amplitude

measurement system for the reference magnetic tape cassette candidates

The results of the initial experiments with cassette tapes and

transports are given.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Cassette tapes; cassette transport; computer amplitude reference;

magnetic tape cassette; secondary standard; standard reference material

18. AVAILABILITY STATEMENT a" x ««««-«led references.

|X~] UNLIMITED.

I I FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

6o

22. Price

60 cents

USCOMM-DC 66244-P
NBS TECHNICAL PUBLICATIONS

PERIODICALS

L JOURNAL OF RESEARCH reports National

Bureau of Standards research and development in

J physics, mathematics, and chemistry. Comprehensive

it scientific papers give complete details of the work,

I including laboratory data, experimental procedures,

I and theoretical and mathematical analyses. Illustrated with photographs, drawings, and charts. Includes

I listings of other NBS papers as issued.

! Published in two sections, available separately:

• Physics and Chemistry

Papers of interest primarily to scientists working in these fields. This section covers a broad range of

I physical and chemical research, with major emphasis

I on standards of physical measurement, fundamental

if- constants, and properties of matter. Issued six times

la year. Annual subscription: Domestic, $9.50; $2.25

I additional for foreign mailing.

• Mathematical Sciences

Studies and compilations designed mainly for the

' mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design,

: numerical analysis, theoretical physics and chemistry, logical design and programming of computers

and computer systems. Short numerical tables. Issued

quarterly. Annual subscription: Domestic, $5.00;

'$1.25 additional for foreign mailing.

I TECHNICAL NEWS BULLETIN

The best single source of information concerning the

1 Bureau's measurement, research, developmental, co- operative, and publication activities, this monthly

publication is designed for the industry-oriented

individual whose daily work involves intimate contact with science and technology

for engineers, chemists,

physicists, research managers, product-development

managers, and company executives. Includes listing of

all NBS papers as issued. Annual subscription: Domestic, $3.00; $1.00 additional for foreign mailing.

Bibliographic Subscription Services

The following current-awareness and literature- survey bibliographies are issued periodically by

the Bureau: Cryogenic Data Center Current

Awareness Service (weekly), Liquefied Natural

Gas (quarterly), Superconducting Devices and

Materials (quarterly), and Electromagnetic

Metrology Current Awareness Service (monthly) . Available only from NBS Boulder Laboratories. Ordering and cost information may be

obtained from the Program Information Office,

National Bureau of Standards, Boulder, Colorado 80302.

NONPERIODICALS Applied Mathematics Series. Mathematical tables, manuals, and studies. Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) de- veloped in cooperation with interested industries,

professional organizations, and regulatory bodies. Special Publications. Proceedings of NBS conferences, bibliographies, annual reports, wall charts,

pamphlets, etc. Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities. National Standard Reference Data Series.

NSRDS provides quantitative data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality, and methods for testing various industrial products. These standards are developed co- operatively with interested Government and industry

groups and provide the basis for common understanding of product characteristics for both buyers and

sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other-agency and

NBS-sponsored work) of limited or transitory interest. Federal Information Processing Standards

Publications. This series is the official publication

within the Federal Government for information on

standards adopted and promulgated under the Public

Law 89-306, and Bureau of the Budget Circular A—86

entitled, Standardization of Data Elements and Codes

in Data Systems.

Consumer Information Series. Practical information, based on NBS research and experience, cover- ing areas of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's tech- nological marketplace.

CATALOGS OF NBS PUBLICATIONS NBS Special Publication 305, Publications of

the NBS. 1966-1967. When ordering, include

Catalog No. CI 3. 10: 305. Price $2.00; 50 cents additional for foreign mailing.

NBS Special Publication 305, Supplement 1, Publications of the NBS, 1968-1969. When ordering, include Catalog No. C13.10:305/Suppl. 1. Price

$4.50; $1.25 additional for foreign mailing.

NBS Special Publication 305, Supplement 2,

Publications of the NBS, 1970. When ordering, include Catalog No. C13.10:305/Suppl. 2. Price $3.25; 85 cents additional for foreign mailing.

Order NBS publications (except Bibliographic Subscription Services)

from : Superintendent of Documents, Government Printing Office, Washington, D.C. 20402.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, D.C. 20234

OFFICIAL BUSINESS

Penalty for Private Use, $300

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE

215