NAT L INST. OF STAND & TECH R.I.C.

NiST

PUBLICATIONS

NIST SPECIAL PUBLICATION 260-115

U.S. DEPARTMENT OF COMMERCE/National Institute of Standards and Technology

Standard Reference Materials:

Calibration of NIST Standard

Reference Material 3201 for

0.5 Inch (12.65 mm) Serial

Serpentine Magnetic Tape

Cartridge

QC

100

U57 Williamson, Natalie E. Willman, and Dana S. Grubb

260-115

1991

C.2

Standard Reference Materials:

Calibration of NIST Standard

Reference Material 3201 for

0.5 Inch (12.65 mm) Serial

Serpentine Magnetic Tape

Cartridge

Mark P. Williamson, Natalie E. Willman,

and Dana S. Grubb

Advanced Systems Division

National Computer Systems Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE, Robert A. Mosbacher, Secretary

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, John W. Lyons, Director

Issued February 1991
National Institute of Standards and Technology Special Publication 260-115

Natl. Inst. Stand. Technol. Spec. Publ. 260-115, 39 pages (Feb. 1991)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1991

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
Table of Contents

1. INTRODUCTION 1

2. TESTING METHODOLOGY 3

2.1 Self-Correcting Calibration System 3

2.2 Saturation Test 4

2.3 Overwrite Test 5

2.4 Resolution Test 5

2.5 Peak Shift Test 6

3. INTRODUCTION TO SYSTEM HARDWARE 6

3.1 Commercially Available Instruments 7

3.2 Tester Assembly 8

3.3 TK70 Tape Drive Modifications 9

3.4 TD70-B Controller 10

3.5 Peak Shift Ring Counter 10

3.6 Peak Shift Output Circuit 10

3.7 Peak-to-Peak Detector 10

3.8 Offset Adjustment of Peak-to-Peak Detector.... 11

3.9 Alternatives to the Use of Peak-to-Peak

Detector 12

3.10 Head Degaussing 12

4. INTRODUCTION TO SYSTEM SOFTWARE 12

4.1 Development Environment 13

4.2 Software Structure 13

4.3 #Define Statements 14

4.4 System Files 15

4.4.1 Parameters File 15

4.4.2. Current Source File 17

4.4.3. Correction Factors File 17

4.5 Test Result File Naming Conventions 17

4.6 Saturation File 18

4.7 Other Parameters File 18

4.8 Test Results Logging Procedure 19

5. PROCEDURE FOR THE USE OF AN SRM 3201 TAPE 20

5.1 Stabilization of the Test System 20

5.2 Procedure for the Calibration of the Test

System 2 0

5.3 Procedure for Calibrating a Tertiary Tape 21

6 . REFERENCES 2 3

List of Figures

1. SRM 3201 Saturation Curve and Data 24

2. System 3 Setup for SRM 3201 25

3. DEC Tester Assembly for SRM 3201 26

4. Tape Drive Modifications 27

5. Tape Drive Modifications 28

6. NIST Ring Counter for Peak Shift Pattern 29

7. Peak Shift Output Circuit 3 0

8. Peak-to-Peak Detector Circuit 31

9. Peak-to-Peak Detector Op Amp Connections 32

10. Saturation Curve on User's Test System 3 3

iii

Calibration of NIST

Standard Reference Material 3201

for

0.5 Inch (12.65 mm) Serial Serpentine

Magnetic Tape Cartridge

22 track, 6667 ftpi (262 ftpmm) and

48 track, 10000 ftpi (394 ftpmm)

by

Mark P. Williamson, Natalie E. Willman, and Dana S. Grubb

Abstract

This publication describes the test system design and

operation for the calibration of the NIST Standard Reference

Material (SRM) 3201 Secondary Standard Reference tape for 0.5

inch (12.65 mm) 22 and 48 track serial serpentine magnetic

tape cartridges. The importance of producing a Standard

Reference Material for this magnetic tape cartridge is to

promote the ability to interchange data both within and among

various computer installations. Reliable interchange

requires that the media be designed and manufactured on the

basis of a comparison to a known and accepted standard

reference media.

Key words: digital magnetic tape, Master Standard

Reference tape, overwrite, peak shift,

Secondary Standard Reference, signal

amplitude, Standard Reference Material

1 . INTRODUCTION

Standard Reference Material (SRM) 3201 is produced in support

of American National Standard (ANSI) X3.197-199X for

unrecorded media and X3. 181-1990 for recorded media.

Magnetic tape standards are essential to the development of a community of vendors with interchangeable products. With

several vendors building drives and media to voluntary

standards, users can be assured of both competitive

development of the products and a reasonable product

lifetime. The latter is essential for archival storage,

since archival data is useless without the drives and

subsystems capable of reading it.

1
NIST's role in the development of magnetic tape standards

goes far beyond active participation in Technical Committee

X3B5, Digital Magnetic Tape, and other regional and

international standards development committees. Several of

the properties essential to the interchange of the new high

density magnetic tapes cannot be directly measured from the

media. The output signal amplitude, the typical write

current, frequency rolloff, the ability to overwrite old

data, and peak shift all require dynamic measurements

relative to a master tape. All of the new and proposed

magnetic tape standards specify several parameters requiring

such dynamic measurements.

Vendors and users of several important digital magnetic tape

technologies depend upon NIST as the world source for

Secondary Standard Reference tapes calibrated against Master

Standard Reference tapes held in repository at NIST. In

addition to Standard Reference Materials (SRMs) for open reel

0.5 inch (12.65 mm) computer tape, two 0.2 5 inch (6.30 mm)

tape cartridges and a cassette tape, NIST is completing work

on three SRMs for newer high density tape cartridges. (The

Physikalisch-Technische Bundesanstalt in Germany provides a

similar service for flexible disks cartridges.)

Earlier SRMs developed by NIST include SRM 3200 and SRM 6250

(open reel tape) , SRM 1600 (1600 ftpi cassettes) , and SRM

3216 (3200 ftpi cartridges) . These SRMs are produced on a

system which is entirely manual in operation. The system

uses a ramp generator for the write current and direct

plotting on an analog recorder.

SRM 3217 (6400 and 10,000 ftpi cartridges) is produced on a second system that is partially computer-controlled and has a

digital plotter.

SRM 32 01 is the first SRM produced on a new generation of

computer-controlled systems developed at NIST. All

instruments in the test system are commercially available.

The software and the peak-to-peak detector, as well as

several specialized digital circuits, were developed by NIST.

This new system uses a computer-controlled current source to

provide the write current. Other computer-controlled

instruments are used to measure the write current and the

peak-to-peak read voltage, and to provide the write

frequency. Tape drive motion is controlled via an RS-232

interface and a TD70-B controller. In addition, digital

output lines from the write current instrument are used to

reset various circuits. Files for each tape tested are

stored by the computer on magnetic media.

The 0.5 inch (12.65 mm) serial serpentine magnetic tape

cartridge has 48 tracks recorded when used in high density

drives and a physical recording density of 10,000 flux

transitions per inch (ftpi) (394 ftpmm) . When used in low

2
density drives, 22 tracks are recorded at a physical

recording density of 6,667 ftpi (262 ftpmm)

The SRM consists of a digital magnetic tape in its cartridge

and documentation of the tape's performance relative to the

Master Standard Reference tape's performance, on the

following tests:

saturation: to make a plot of the average signal

amplitude as a function of the write

current.

overwrite: to determine the ratio of the average

signal amplitude of the residual of the IF

recording frequency (half the maximum

frequency) , after being overwritten by the

2F recording frequency (maximum frequency)

to the average signal amplitude of the

original IF recording frequency.

resolution: to determine the ratio of the average

signal amplitude at the 2F (maximum)

physical recording density to that at IF

(half the maximum) physical recording

density

peak shift: to measure the time displacement of

adjacent read back signal peaks from the

corresponding written timing.

The following sections explain the testing methodology, the

system hardware and the system software of SRM 3201.

Note: Manufacturer's names and model numbers are cited

solely to identify the hardware, software, and equipment used

and do not imply a recommendation.

2. TESTING METHODOLOGY

2.1 Self-Correcting Calibration System

SRM 3201 Secondary Standard Reference tapes are calibrated

using an optional self-correcting calibration system. This

scheme is fully documented in an article cited in

reference 1.

In this self-correcting scheme, there is a Master Standard

Reference tape, from which several working tapes are

calibrated against. The data is stored in table form on

magnetic disk and a magnetic disk backup medium.

3
The Secondary Standard Reference tapes will be calibrated at

some later date, and subsequent batches calibrated over a

period of years. At the time of the calibration of the

secondary tapes, one of the working tapes is run and a

correction factor table is determined, which is defined as

the differences between the working tape data when it was

first run, and the current working tape data. If significant

differences are found, this "correction factor" table may

then be added to the data gained when the Secondary Standard

Reference tapes are run. This will correct the system's gain

adjustments which may have drifted since the Master Standard

Reference tape was selected.

2.2 Saturation Test

The saturation test is defined as a plot of the average

signal amplitude as a function of the write current. The

tape is written with an incrementing current, and the average

signal amplitude produced by each current setting is read

from the tape and stored in a table. These values are then

plotted with average signal amplitude on the y axis and write

current on the x axis.

Certain values are derived from the saturation test. For all

tapes, the following values are calculated:

Peak amplitude (Ap) - The maximum average signal

amplitude.

Peak current (Ip) - The write current corresponding to

the peak amplitude.

Typical amplitude (At) - 95 percent of the peak amplitude

(Ap) . Typical current (It) - The write current which produced the

typical amplitude (At)

When a Master Standard Reference tape is chosen and a

saturation test is performed on it, the following data are

calculated:

Standard reference

current (Ir) - the typical current of the Master

Standard Reference tape.

Standard measurement

current (Im) - 1.5 times the standard reference

current (Ir) as defined in the

standard for the unrecorded media.

4
Standard reference

amplitude - the average signal amplitude from

the Master Standard Reference tape

when it is recorded with the

standard measurement current (Im)

When a Secondary Standard Reference tape is calibrated, the

following data are collected for both physical recording

densities

- Standard reference current (Master Tape)

- Standard measurement current (Master Tape)

- Typical current (Test Tape)

- Ratio of It to Ir

- Ratio of the test tape's

average signal amplitude at

the standard measurement

current to the standard

reference amplitude.

Figure 1 shows an SRM 3201 saturation (SAT) curve produced by

this system. The x axis is write current in milliamperes and

the y axis is the read output voltage in amplitude units.

(Amplitude units are normalized to 40 units for the Master

Standard Reference tape.)

2 . 3 Overwrite Test

Overwrite is defined as the ratio of the average signal

amplitude of the residual of the IF (half the maximum)

recording frequency, after being overwritten by the 2F

(maximum) recording frequency, to the average signal

amplitude of the original IF recording frequency.

A tape "is recorded at the IF physical recording density at

the standard measurement current (Im) . The average signal

amplitude of the IF pattern is read from the tape. The tape

is then recorded at the 2F physical recording density at the

standard measurement current. The average signal amplitude of

the IF pattern is read from the tape.

The ratio of the overwritten IF pattern's average signal

amplitude and the original IF pattern's average signal

amplitude is then calculated.

2.4 Resolution Test

Resolution is defined as the ratio of the average signal

amplitude at the 2F (maximum) physical recording density to

that at the IF (half the maximum) physical recording density.

5
A tape is recorded at the IF physical recording density at

the standard measurement current, and the average signal

amplitude is recorded.

The tape is AC bulk erased and recorded at the 2F physical

recording density at the standard measurement current. The

average signal amplitude is recorded.

The ratio of the average signal amplitude at the 2F physical

recording density to the average signal amplitude at the IF

physical recording density is then calculated.

2.5 Peak Shift Test

Peak shift is defined as the time displacement of adjacent

readback signal peaks from the corresponding written data.

The tape is written with a pattern of 110110110 using the

standard measurement current for the selected physical

recording density.

The time between adjacent peaks in the ONE-ONE interval is

denoted at Tl. The time between the last ONE in the ONE-ONE

interval to the last ONE in the following ONE-ONE interval is

denoted as TO.

The time interval measurement is defined in the unrecorded

media standard as the average of 2 50 recorded patterns taken

at a sampling rate of 96 x the 2F frequency.

Peak shift is calculated using the following formula:

3T1-T0

peak shift = x 100 percent.

2T0

3. INTRODUCTION TO SYSTEM HARDWARE

Manufacturer's names and model numbers are cited solely to

identify the equipment used and do not imply a

recommendation. Such identification is essential, since the

system software must be written using the control/status

codes and data formats specified for the particular

equipment. Alternative equipment may be used, but some

modification of the system software will be necessary. As

the instruments are set up by the software, those interested

in the instruments' settings should consult the software

listings for the instrument drivers. (Source code is

available on magnetic media from NIST.)

Figure 2 shows the system interconnection. It is essential

that the 50 ohm terminators be used as shown. (The

6
terminators are available from Hewlett-Packard.) The output

of the current source is connected using a triax to coax

converter (available from Keithley) . The connections to DVM1

(HP 3456A) are floating measurements; the coax shields on the

two inputs are connected together and to the instrument 1 s ground input. The 1 Mfl input of the HP3585A is used.

3.1 Commercially Available Instruments

The computer is an IBM PC AT with a 30 Mbyte hard disk, two

floppy disks drives, math co-processor, and the PC DOS 3.2

operating system. A computer that is software compatible and

has similar or better performance could be used instead. An

RS-232 output is used to control the TK70-B tester.

The interface to the instruments is via the IEEE-488

interface board. The board selected is the National

Instruments GPIB-PC2A (IEEE-488) interface board. This GPIB

was purchased with its PC DOS handler and Turbo C language

interface object code. (The manufacturer has interface

object code available for several other compilers.)

A Hewlett-Packard 3325A frequency synthesizer/function

generator is used for the write frequency and a Hewlett-Packard 5334A universal counter is used to check the

write frequency. However, use of the counter is not

essential, since it is only used as a check on the

calibration of the generator. The synthesizer provides a square wave pattern via a gate circuit in the peak shift ring

counter unit to the tape drive for all measurements except

peak shift. For peak shift, the square wave is used as an

input to the peak shift ring counter for generating the

proper peak shift test pattern.

A Stanford Research SR620 time interval counter is used to

make the peak shift measurements.

A Keithley 224/2243 programmable current source with triax to

BNC adapter is used to provide the write current. This

instrument has a relatively lengthy 2 3 ms. switching/

settling delay for the small current increments used in

making saturation tables. (This delay is compensated by a software delay in the dcslwr() function.) Range changes are

avoided by setting the range in the PA (parameters) file high

enough for the largest write current to be used. This

instrument also has a 4-bit digital output that is used for

software generated resets to the system. Bits 0, 1, and 2

(Pins 7, 8, and 9) are used to reset the peak shift ring

counter, the TK70-B controller, and the E13 write flip-flop,

respectively.

A Hewlett-Packard 3456A digital multimeter is used to measure

the write current. The guarded input circuit is important

when making floating measurements of the write circuit. (If

7
when making floating measurements of the write circuit. (If

an alternative instrument is considered, its suitability for

such measurements should be closely examined.) The write

current measurement is not essential, since it is used only

as a proof that the write current was close to that intended.

A NIST-designed peak-to-peak detector circuit (described

elsewhere in this document) is used to measure the read

amplifier output amplitude. A Hewlett-Packard 3457A digital

multimeter is used to measure the dc output level of the

peak-to-peak detector. (Alternatively, an HP3456A could have

been used instead with its driver software instead of the

HP3457A.

)

A Hewlett-Packard HP3585A spectrum analyzer is used to make

the overwrite measurements. A Hewlett-Packard HP3586C

selective level meter would have provided more precise

measurements, except that its maximum bandwidth is less than

required by the speed variations of the tape drive.

Consequently, the signal would drift in and out of band and

provide unacceptable results. A Hewlett-Packard 7550A

graphics plotter with IEEE-488 bus interface is used to plot

the SRM saturation curve charts.

3.2 Tester Assembly

Figure 3 shows the Digital Equipment Corporation (Digital)

tester assembly provided by Digital. It is a clear plastic

box with mountings for various components, connectors on the

rear and a clear plastic dust cover.

The assembly contains a modified Digital TK70 tape drive, a

TD70-B (modified TD50-B) controller and a NIST-designed peak

shift measurement circuit. These components are described

subsequently.

The connector assignments at the rear of the Digital tester

assembly are:

Coaxial connectors:

Port 1 - Output signal (E31-17) to peak-to-peak detector

Port 2 - Output signal (E31-16) to peak-to-peak detector

Port 3 - Peak shift signal to SR620

Port 4 - Write frequency from peak shift ring counter

unit

Port 5 - Current source from Keithley 224

Port 6 - Write current measurement high to HP3456A

Port 7 - Write current measurement low to HP3456A

8
RS-232 cable from IBM PC AT to TD70-B controller.

Twisted pair wires from Keithley 224 digital output pins:

Pin 8 (Bit 1) of Keithley 224 to TD70-B controller reset

Pit 9 (Bit 2) of Keithley 224 to TK70 drive reset

3.3 TK70 Tape Drive Modifications

The TK70 tape drive must be modified to permit control and

measurement of the write current, control of the write

frequency, resetting of the write frequency flip-flop,

crippling of the automatic gain control, and access to the

read signals. All connections except the reset are made

using coaxial cable. Tape drive motion is controlled by the

TD70-B controller unit. Logical track 02 (physical track 26)

near the middle of the tape is used for all tests as

specified in ANSI X3.197-199X and X3. 181-1990.

The write current source circuitry is modified by cutting the

connection to the tape drive's current source at R47 and

inserting a connection to the external current source

(Keithley 224/2243) at the emitter of E30 (see fig. 4) . The

coax shield is grounded at both ends. A 1000 ohm 2 watt

resistor is connected in series with the current source and

mounted in the drive near E3 0, which tends to improve the

time constant for the circuit by reducing the effect of

circuit inductance. The write pulse wave shape is very close

to that of the unaltered drive.

The write pulse current value is checked by measuring the

voltage across a precision 10 ohm resistor inserted in the

write head center tap circuit. This is done by inserting the

resistor in the output of E25 pin 8. The voltage drop across

the resistor is measured with the HP3456A digital multimeter.

The frequency of the tape drive is controlled by connecting

the output of the HP3325A frequency synthesizer (via the gate

circuit in the peak shift ring counter to the input of the

write frequency flip-flop in the drive. This is done by

breaking the connection at E13 pin 3 and attaching the

frequency input at that point. Since the flip-flop divides

the frequency in half, the synthesizer must be set to double

the frequency (see fig. 4)

The write frequency flip-flop is externally reset by cutting

the connection to E13 pin 1 and attaching a twisted pair to

Bit 2 of the Keithley 224 current source. This allows the

software to reset the flip-flop as necessary.

The AGC (automatic gain control) is crippled by cutting the

connections from resistors R106 and R107 to E6 pin 9, and by

9
cutting the pin 2 side of R84 and the pin 13 output of E19

(see fig. 5)

The read signal for the saturation curve, resolution and

overwrite measurements is obtained using the outputs from E31

pins 17 and 16. The read signal for the peak shift

measurements is obtained using the output from E31 pin 10

(see fig. 5)

3.4 TD70-B Controller

The TD70-B is a Digital TD50-B controller (tester) with a

modified PROM (programmable read-only memory) and an

NIST-installed connection for external resetting. The

modified PROM is available from Digital at a reasonable cost.

(The Digital representative on Technical Committee X3B5 would

be the contact person.) The reset connection is made by

cutting the connection to E10 pin 9 of the Controller and

attaching a coaxial cable to that point.

3.5 Peak Shift Ring Counter

Figure 6 shows the NIST-designed peak shift ring counter.

This circuit provides the peak shift write pattern which is

modified by the flip-flop in the tape drive to produce a

"110110" pattern on tape. The software prompts the operator

to put the switch in the bypass position for all tests except

peak shift. In the case of peak shift, the switch is used to

write the normal all l's pattern during the calibrate cycle

and the peak shift pattern thereafter. The output of the

ring counter uses a 50 ohm line driver. It is therefore

necessary to hard wire a 50 ohm termination on the write

frequency input (Port 4) of the Digital tester assembly. The

Counter is reset by Bit 0 from the Keithley 224.

3.6 Peak Shift Output Circuit

Figure 7 shows the NIST-designed peak shift output circuit.

This circuit is needed to convert the narrow peak shift

pulses from the tape drive into full width pulses for the

SR62 0 time interval counter. (It is adapted from the circuit

specified in ANSI X3. 137-1988 for 90 mm floppy disk.) The

circuit has a 50 ohm line driver as its output. The SR620 is

set to 50 ohm termination by the software.

3.7 Peak-to-Peak Detector

Figures 8 and 9 show the NIST-designed peak-to-peak detector

circuit. The peak-to-peak detector is used for the read

signal because a peak-to-peak reading is specified by the

standard. (A base-to-peak detector has potential baseline

shift problems and an rms detector would be valid only if the

10
read signal was a pure sinusoid with no harmonics.) With the

integrator on the output of the detector, it will measure

over the minimum length of tape specified by the standard.

The peak-to-peak detector provides a low-noise dc output for

measurement by the digital voltmeter.

The input to this circuit is a differential signal from the

TK7 0 drive that has some odd harmonics content. The output

of the first stage is used to drive two base-to-peak

detectors of opposite polarity. The two base-to-peak values

are summed in the output stage.

The standard reguires that the measurements be averaged over

at least one inch (25.4 mm) of tape. This is done by the

integrator on the output. The integrator is designed for

about three time constants for the one inch of tape at the

100 ips (inches per second) of the drive. This has been

found empirically to provide about the ideal amount of

integration.

The detector's response is linear within 1 percent from 350

to 1350 mV and from 250 kHz to 500 Hz, the ranges of interest

for this SRM. (The detector is also linear within 2 percent

from 100 kHz to 2 MHz.) The circuit design relies on the use

of a particular type of operational amplifier (Comlinear

CLC-400) , Polypropylene or similar specification capacitors

and other selected components. While the operational

amplifiers are quite stable, the offsets should be adjusted

prior to calibrating tapes.

The detector also has an output from the first stage that is

used for converting the differential read signal into a

single-ended output for the HP3585A spectrum analyzer.

3.8 Offset Adjustment of Peak-to-Peak Detector

The peak-to-peak detector is quite stable, but the offsets

should be periodically readjusted. Following is a list of

steps to adjust the detector:

1) Turn the power on and let the detector warm up for

at least 1 hour.

2) Ground the two differential inputs to the detector

using BNC connectors with shorting wires.

3) Using an oscilloscope with a high gain preamplifier

capable of at least 10 mV/division sensitivity,

adjust the differential amplifier. Place the scope

probe on the output of the amplifier (Ul pin 6) and

adjust R7 for ground level on the oscilloscope.

4) Repeat step three for the linear halfwave

rectifiers. Place the probe on U2 pin 6 and adjust

R15, then place the probe on U3 pin 6 and adjust

11
R21. As U2 and U3 are subject to noise, adjust the

outputs for an average level of zero.

5) Use a high input impedance voltmeter capable of

reading to 1 mV to adjust the offset of the

inverting summing amplifier. Place the probe on U4

pin 6 and adjust R23 for an average reading of zero.

Each amplifier will drift approximately +5 mV for output

levels in the 500 mV and higher range, this means an error of

less than 1 percent even when the detector has not been used

for a while.

3.9 Alternatives to the Use of a Peak-to-Peak Detector

Some drive and media manufacturers use a spectrum analyzer,

a selective level meter, or an rms reading digital voltmeter

for their testing. A spectrum analyzer does not measure over

the length of tape specified by the standards. Also, a

spectrum analyzer has a lot of noise even at the minimum

bandwidth permitted by tape speed variations. Hence, the

precision is too limited. A selective level meter is

excellent when used with a tape drive having precise speed

control (e.g., a Honeywell 96 instrumentation drive) and when

no significant harmonics are present. However, it has too

narrow a bandwidth for the tape speed variations found in

production tape drives. Also, there are significant

harmonics present with this media. Since the amount of

harmonic content varies with write current, this would

introduce an unnecessary error in the measurements. Some

digital voltmeters read rms. However, the conversion from

rms to peak-to-peak is known only if there is no significant

harmonic content. Also, most digital voltmeters do not have

good precision at these frequencies.

3.10 Head Degaussing

It is essential to periodically degauss the write/read head

in the TK7 0 drive. Carefully remove the head and degauss it.

Replace the head and test the system using a control tape to

ensure that the head has been properly mounted.

4. INTRODUCTION TO SYSTEM SOFTWARE

The software is public domain, and source code is available

on floppy disks to interested parties.

The system software is menu-driven with computer control of

all aspects of the tape testing. The operator is asked to

key in answers to necessary questions, such as: the type of

tape to be tested and the type of test to be performed.

12
4 . 1 Development Environment

The program is written in C language, which allows low-level

control of the hardware. In addition, C can be compiled to

efficient object code, is portable with little modification

between widely varying computers (e.g., IBM PC AT and VAX

11/780) , and is designed for writing structured programs.

Software maintenance for a program written in C is much

easier than that of a program written in BASIC.

The software was written using an IBM PC AT computer with DOS

3.2. Early development was begun on a VAX 11/780 under VMS

and transferred to an IBM PC XT and then to an IBM PC AT.

Since the instruments needed for the system are all designed

with very different commands, responses and formats, the

source code is unique for each instrument. (Even very similar

instruments from the same manufacturer, such as the HP3456A

and HP3457A digital multimeters, are designed with totally

different commands and responses.) Therefore, the

substitution of other instruments will necessitate a re-write

of the drivers.

The software should run properly on most IBM-compatible

personal computers having a hard disk and DOS Version 3.2 or

later. The graphics functions used for displaying the

saturation curves are specific to EGA monitors, and would

require slight modification if another monitor is used.

Computer speed should approximate that of an IBM PC AT or

better.

The program is compiled using Borland Turbo C Version 1.5,

although there are several other C compilers available that

would probably be satisfactory. However, the IEEE-488

interface board used in the system must come with object code

that works with the compiler. The compiler selected should

make use of the math co-processor chip and should produce

relatively fast object code.

The system program should compile properly with most

compilers, except for the graphics which use library

functions specific to Turbo C. Also, the input byte and

output byte functions are not specified in exactly the same

way by all compilers, so modification of how these functions

are specified would be needed. Segment addressing is not

used, since both the program and the data use less than 64

kbytes

4.2 Software Structure

The system software consists of two executable files, sat3201.exe for the saturation test, and orp-3201.exe for the

overwrite, resolution, and peak shift tests. These

13
linked together.

Sat-3201.exe Modules

- svar.h

- ovar.h

Orp-3201.exe Modules

- svar.h

- ovar.h

- smam.c - omain.c

- spec.c

- sgen.c

- s488.c

- ospec.c

- ogen.c

- 0488.

- s-3201.c

- slog.c

- tcibs.obj

- graphics. lib

- 0-3201.

- olog.c

- tcibs.obj

- graphics. lib

The smain.c and omain.c modules contain the main() function

and the highest level functions. The spec.c and ospec.c

modules contain the next lower level of functions which are

specialized to the test being performed. The sgen.c and

ogen.c modules contain all of the general purpose functions,

except those using the IEEE-488 bus. The s488.c and o488.c

modules contain all the IEEE-488 bus functions used to

control the various instruments. The s-3201.c and o-3201.c

modules contain all of the functions that are specific to SRM

3201. The slog.c and olog.c modules contain routines for

logging test data. The tcibs.obj module is provided by

National Instruments, the manufacturer of the IEEE-488 bus

interface board. The graphics library is provided with

Turbo C.

The #include files specified by the software modules, svar.h

and ovar.h, are provided with the software listing. Two

others, stdio.h and math.h, are supplied with the compiler.

The file svar.h and ovar.h contain C structures with

variables used by several functions.

4.3 #Def ine Statements

There are several #define statements that are essential to

proper functioning of the system. Those affected by the

choice of computer model or compiler used are described here.

The screen is cleared using a print function with the #define

statement "CLEARS." CLEARS is set to "\033[2J" for an IBM PC

AT. This declaration appears in several modules.

The function "delay" is used in several places to force

specific timing delays needed. The function is passed the

desired delay in milliseconds. Since this function uses

software to create the specified delay, the value for its

parameter DLY_CT must be set for the particular computer and

compiler used. If a different computer or compiler is used,

it is absolutely essential that the value of DLY_CT be

14
checked. DLY_CT appears at the beginning of the sgen.c and

ogen.c modules.

Several other #define statements are needed for the

particular instruments selected. Different instruments

would, in some cases, need different #define values.

4.4 System Files

The system uses several files that are stored on disk: the

parameters file, the current source files, and the correction

factors file. Each tape type has its own set of files with

each set identified by a single character for the tape type.

SRM 3201 uses the letter "d" for low density and the letter

"e" for high density.

4.4.1 Parameters File

Each tape type has a "parameters" file to specify such

parameters as srm number, tape speed, etc. The parameter

files for SRM 3201 are "dpa" and "epa."

Each parameter (pa) file contains the following parameter

values expressed as ASCII character strings:

- tape type

- SRM number

- length of tape in feet

- tape speed in inches per second

- tape density in flux transitions per inch

- flux transitions per sample

- read while write or read after write

- track number used

- the minimum write current in mA

- the maximum write current in mA

- increment of write current in mA

- array size

- the standard reference current factor (.95 for this SRM)

- the standard measurement current factor (1.5)

- whether the current source or the voltage source is

used (current source is used for this SRM)

- voltage drop in write head circuit (needed only for

voltage source)

- resistance in series with the write driver circuit that

is used to change the time constant by reducing the

effect of circuit inductance (called "wdr")

= resistance from write head center tap connection that is

used for measuring the write current (called

"DVMlres")

- range of the current source (or voltage source) used

(set high enough to avoid range changes during

operation)

15
- amount of tape in feet to skip before testing

- the initial delay (dlyl) prior to the first write

current

- the incremental delay (dly2) for each write current

increment

- the peak noise factor This value of this parameter is

determined empirically for eliminating the noise

spikes at the peak amplitude

- the amplitude unit scale factor for primary and master

originals (determined empirically to approximately

normalize data for the plotter)

The dlyl and dly2 values cited above are determined by the

response of the current/voltage source and the time constant

of the integrator on the output of the peak-to-peak detector.

The array size is the result of the difference between the

maximum and minimum write current, divided by the write

current increment. (Thus, the array size is redundant

information, but included to permit a software check that the

operator is specifying what is really desired.) Array size

is limited to 4 00 due to the memory addressing limitations of

the 80286 microprocessor used in the IBM PC AT class

computers. (If more than 16 address bits were available,

larger arrays would be permissible.)

The actual dpa and epa files are:

dpa file epa file

d type e type

3201 SRMNO 3201 SRMNO

0625 feet 0625 feet

100 ips 100 ips

006667 ftpi 010000 ftpi

006667 sample 010000 sample

w rww_raw w rww_raw

2 trackno. 2 trackno.

0006 minimum 0006 minimum

0021 maximum 0021 maximum

00.075 increment 00.075 increment

0200 size 0200 size

0.95 It&Irfactor 0.95 It&Irfactor

01.5 Imratio 01.5 Imratio

c current/voltage c current/voltage

0000 drop 0000 drop

1000 wdr 1000 wdr

0010 DVMlres 0010 DVMlres

9 range 9 range

0100 skip 0100 skip

1000 dlyl 1000 dlyl

0100 dly2 0100 dly2

16
0.9990 pnf

0.88 peakpov

0.9990 pnf

0.77 peakpov

4.4.2 Current Source File

The current source file is a table that is used to check the

write current. The first column is Id, the desired write

current. The values in this column are determined by the

parameters file entries for minimum and maximum write

current, and the incremental current. With some types of

media, the second column will be the source current setting

needed to obtain the desired write current. However, with

this type of media (SRM 3201) , this column is left identical

with the first column. The third column is la, the actual

write head current, as measured by the digital voltmeter. It

is provided as data in the event that there should ever be a

question regarding the precision of the current source.

4.4.3 Correction Factors File

The use of the correction factors file is a software option

for SRM 3201 when calibrating Secondary Standard Reference

tapes (see sec. 2.1.). It is intended to permit automatic

correction for gain drift in the system. However, the gain

stability is much better than the random errors inherent in

tape testing on production drives and it tends to add noise

rather than correct the very stable system gain. Therefore,

it will probably not be used.

The correction factors file is generated when a working tape

is run and compared against the data in the "working true"

saturation table, obtained when the same working tape was run

earlier. The correction file factors contain a table of the

differences for both the signal amplitude voltage, and for

the amplitude units. Unlike the saturation table files, this

file does not have header information and does not have

column headings. (It is a temporary file used only for

making the secondary corrected saturation tables on that

particular day and is not retained.) The first column is Id,

the desired write current; the second column is la, the

actual write current measured; the. third column is CFm, the

voltage correction factor; and the fourth column is CFa, the

amplitude units correction factor. A typical file might look

like this:

4.5 Test Result File Naming Conventions

The files for saturation, overwrite, resolution, and peak

shift data are named abbbcccc.def where:

5. 0000

5. 1000

4.9723

5. 0682

0. 0001

0. 0001

0. 0070

0. 0068

17
a is the tape manufacturer

bbb is the tape number

cccc is the pass number

d is the tape type (e.g., d for SRM 3201 low density)

e is the tape class (e.g. , Master True) where:

Test Tape = 0

Primary Original = 1

Master Original = 2

Master True = 3

Working True = 4

Sec. Corrected = 7

f is the tape test where:

sat curve = s other data = o (resolution, overwrite and peak shift)

rise data = r.

4.6 Saturation File

The saturation files have a format like that shown in the

following example. The column headings are Id, desired write

current; la, actual (measured) write current; Vm (signal

amplitude) ; and AUs (amplitude units, which are Vm normalized

by the Master True peak signal amplitude of 4 0 AUs)

a0211013.e4s filename

a0410000.e3s mtfilename

021690 monthdayyear

dsg operator

002 headnumber

0.686 Ap_for_test_tape

9.825 Ip_for_test_tape

0.651 At_for_test_tape

8.775 It_for_test_tape

8.850 Ir_for_master_true

13.275 Im_for_master_true

0 . 602 Am_for_test_tape_at_master_true 1 s_Im

Id la Vm AUs

6.0000 5.9751 0.3133 18.2180

6.0750 6.0267 0.3168 18.4184

6.1500 6.0752 0.3416 19.8583

4.7 Other Parameters File

The "other" files containing overwrite, resolution, and peak

shift data, have the following format:

a0211016.e4o filename

a0410000.e3o mtfilename

a0211014.e4s satfilename

021690 monthdayyear

dsg operator

002 headnumber

13.2750 Im_for_master_true

8.7000 It_for_test_tape

18
8.8500 Ir_for_master_true

0.9831 It_to_Ir

0.0343 overwrite_for_test_tape

0.0351 overwrite_for_master_true

0.9775 overwrite_test_to_master

0.5931 resol_for_test_tape

0.5955 resol_for_master_true

0.9959 resol_test_to_master

0.6770 fl_volts

0.02 3 2 f l_residual_volts

0.0000 f2_volts

1.0177 f3_volts

0.6036 f4_volts

19.2874 peakshift_for_test_tape

19 . 6900 peakshift_for_master_tape

-0 . 4026 peakshift_test_minus_master

4.8 Test Results Logging Procedure

Data from each run is kept in an automated log. The

following information is written to a temporary file which

will later be imported to a Lotus 1-2-3 spreadsheet:

All Tests

- tape number

pass number

file name for test results

date of test

head

operators initials

Sat Test

Master Standard Reference Tape's File Data

Peak Signal Amplitude

Peak Current

Typical Field

Typical Current

Standard Measurement Current

Signal Amplitude at Standard Measurement Current

Comments on the test

Rise Test

Peak Signal Amplitude

Peak Current

Percentage of Tilt

Comments on Run

Overwrite. Resolution, and Peak shift

Standard Reference Tape's File Data

Standard Measurement Current

Typical Current

- Standard Reference Current

Ratio of Typical Current to Standard Reference

Current

Overwrite value of tape under test

19
Overwrite value of Master Standard Reference Tape

Ratio of test tape 1 s and master tape ' s overwrite

value

Resolution value of tape under test

Resolution value of Master Standard reference Tape

- Ratio of test tape's and master tape's resolution

value

Fl value

Fl residue value

F2 value

F3 value

F4 value

Percentage of peak shift for test tape

- Percentage of peak shift for master tape

Difference between master tape's and tape under

test's percentage of peak shift

5. PROCEDURE FOR THE USE OF AN SRM 3201 TAPE

The Secondary Standard Reference tapes are sold to industry

to use for calibrating tertiary tapes for daily use.

Following is a list of steps to follow to use SRM 3201.

(This procedure is adapted from the procedure described in

ISO/IEC JTC 1/SC 11 N 1 014 Rev. for use with open reel 0.5

inch SRM tapes.)

5.1 Stabilization of the Test System

Switch on the test system and allow a minimum of 1 hour for

the temperature of the components to stabilize so that the

amplifier gains will remain stable during the following

operations.

The test system shall remain switched on until all operations

have been completed.

5.2 Procedure for the Calibration of the Test System

To minimize the use of the SRM tape and the risk of damage to

it, test the system for correct operation using a tape other

than the SRM tape.

Bulk erase and load the SRM tape and make one forward and one

reverse pass at normal speed to re-tension the tape.

Note: An SRM tape should never be wound at high speed.

Make a complete forward read-while-write pass with the SRM

tape and plot the saturation curve, that is, the curve of

average signal amplitude versus write current (see fig. 10)

Writing shall commence at 31 m (100 ft) after the BOT

(beginning of tape) . Note: Partial passes shall never be

made with an SRM tape.

20
Rewind the SRM tape at normal speed.

Determine the maximum average signal amplitude from the

saturation curve.

Determine II, the minimum write current required to give an

average signal amplitude equal to 95 percent of the maximum

average signal amplitude. II is the current required to

produce on the test system the typical field for the

particular SRM tape (see fig. 10)

Multiply II by the current calibration factor, Cc, provided

with the SRM tape, to obtain 12. Cc is ratio of the write

current required on the NIST system to produce the reference

field to the write current required on the NIST system to

produce the SRM tape's typical field. (See data at top of

fig. 1.)

12 is the write current required to produce on the test

system the reference field; it is the standard reference

current. The reference field is the typical field of the

Master Standard Reference tape.

Multiply 12 by 1.5 (the factor specified in X3.197-199X) to

obtain 13, the measurement current for the user's test

system.

Determine the average signal amplitude Al produced by the SRM

tape at the write current 13.

Multiply Al by the amplitude correction factor Ca, provided

with the SRM tape, to obtain A2 . Ca is the ratio of the

standard reference amplitude to the average signal amplitude

of the SRM tape at the standard measurement current on the

NIST system. (See data at top of fig. 1.)

A2 is the standard reference amplitude on the user's test

system.

The test system may now be calibrated for overwrite,

resolution and peak shift using write current 13 and the

relationships printed in the right hand column of the box at

the top of the saturation curve chart (see fig. 10)

5.3 Procedure for Calibrating a Tertiary Tape

Bulk erase and load the tertiary tape and make one forward

and one reverse pass at normal speed to re-tension the tape.

Note: since tapes tend gave a significant rise in the signal

amplitude with usage, additional forward and reverse passes

shall be made until the rise in signal amplitude per pass is

less than 0.05 percent. (Typically, 100 to 200 passes from

BOT to EOT to BOT should suffice.)

21
Make a complete forward read-while-write pass with the

tertiary tape, ignoring the first 31 m (100 ft) after BOT,

and plot the saturation curve.

Rewind the tertiary tape a normal speed.

Determine the maximum average signal amplitude.

Determine Itl, the minimum write current required to give an

average signal amplitude equal to 95 percent of the maximum

average signal amplitude.

The current calibration factor for the tertiary tape relative

to the Master Standard Reference tape shall be calculated

from the ratio:

12

Ctc = . Itl

Determine Atl, the average signal amplitude at the write

current 13.

The amplitude calibration factor for the tertiary tape

relative to the Master Standard Reference tape shall be

calculated from the ratio:

SRA

Cta = . Atl

Overwrite, resolution and peak shift may now be measured for

the tertiary tape using the write current 13.

Note: it may be desirable to rerun the SRM tape at the

conclusion of the above operations to verify the stability of

the test system. However, the SRM tape should not be run

more than necessary.

We wish to acknowledge Steven Boone, Michael O'Brien, James

Chu, and the Digital Equipment Corporation (Digital) for

providing information on how to make modifications to the

TK70 tape drive, developing a TD70-B controller (TD50-B with

custom firmware) , donating a tester assembly (housing) with

power supplies and fans, and various technical advice; Paul

Jahnke with the Minnesota Mining and Manufacturing Company

(3M) for technical advice; Matt Jacobs as a member of

Technical Committee X3B5 for obtaining instrument donations

for this SRM and for SRM 3202; Stanford Research Systems for

the donation of an SR62 0 time interval counter needed for the

22
peak shift measurements; and those member companies of

Technical Committee X3B5 (Digital Equipment Corporation,

Minnesota Mining and Manufacturing Company, Storage

Technology Corporation, Laser Magnetic Storage, Carlisle

Memory and Pericomp Corporation) who contributed financially

via the Computer Business Equipment Manufacturers Association

for the development of new SRMs.

6 . REFERENCES

[1] Podio, F. , "A New Computer-Based Self-Correcting

Calibration System for Computer Storage Media Standard

Reference Material," Computers and Standards: The

International Journal, Vol. 4, No. 4 (1985).

[2] American National Standard (ANSI) X3. 181-1990.

[3] American National Standard (ANSI) X3.197-199X.

23
Figure 1
Figure 2

System 3 Setup for SRM 3201

IBM PC AT

Nat. Inst.

GPIB-PC2A

RS-232

Freq. Synth.

HP 3325A

Counter

HP 5334A

Time Interval

Counter

SR 620

50

ohms

Current Source

Keithley 224

with 2243

option

Triax

to - Coax

Digital

Output

GND

DVM1

HP3456A

(floating measurement)

DVM2

HP3457A

Spectrum Analyzer

HP3 585A

Plotter

HP7550A

Motion

Control

signal

Input

A

Input

front

panel

NIST

P-P Det.

SRM3201

Version

(gain

setting)

P-P

Det

lr

50 ohms

Bit

0

11

out

NIST

Peak Shift

Ring Ctr.

Reset Ctr

Bit 1 Bit 2

Volts Hi

Volts Lo

Input Hi/Lo

1 Megohm Input

(front panel)

All rear panel connections

DEC

Tester

Assembly

TK7 0,

TD50,

etc.

PI

P2

P3

P4

50

bhms

P5

P6

P7

Peak

Shift

-TD50

Write

Freq.

-TD7 0B

-TK70

Current

-Source

DVM1

HI

DVM1

LO

25
Figure 3

DEC Tester Assembly

for

SRM 3201

Peak

Shift P3

To IBM

PC AT

To pin 8

Write

P4 Freq.

To pin 9

Current P5

Source

DVM1

HI P6

DVM1

LO P7

Read PI

Output P2

IN

RS-232

OUT

TK70-B

RS232

NIST Peak Shift Output Circuit

TD70-B Controller

Modified PROM

RS232

E10 Reset

Control

Cable

TK70 Drive

AGC crippled and other mods

Write Circuitry

E13-3 Write Frequency

E13-1 Reset Write FF

R55-2 Write Current

Source

E25-8 Across 10 ohm

0.1% write

current resister

Read Circuitry

E31-17

E31-16

Read Analog

Signal

E31-10 Read Data Pulse

26
Figure 4

Write Frequency x 2

P4

Reset

R12

+5v

Write Frequency Input

Current Source

P5

1000 ohms

2 watts

1%

Current Source Input

HP3456A High

P6 i-W^—

10 ohms

0.1 %

HP3456A Low

P7

Write Current Measurement

Tape Drive Modifications

27
Figure 5

10

E6

R84

C9

1

1 1 2

R106

R107

, A\AAr

i

R88

2 OK

1%

-AAA1

i

" C53 y

CRIPPLE AGC

Z3

El 9

13

4-

Read Amplitude High Disable

Read Signal

PI

Read Signal

P2

Read Data Pulse

P3

Signal Amplitude and Peak Shift

Data Output

Tape Drive Modifications

28
Figure 6

29
Figure 7

30
Figure 8

1

c

liamsc * s

on S o $

5 1

« 3 * i

k a!

i

5

5 2

o>

co If

ONm

ot=5

— >

O 3

u

ai u

Va

OS

0) a*oH

09

0) Ou

^ O V- IN O X

? =

WvA-1 SAAA

3

a.3O

U

5

a)>O

<-WV^-||l

m • - vO m asu

Ok • m u as u u

a . a •»

asu

» -

OS a u

c •

a) CM

-I OS >s U

a. » o —

u a u au «

o

Ou in n

iw co —' in 10s I • - N N

. 00 —

0 O *t in

1 ou a z u

<m o

cj to u

ai a

o a - •* » u a as

oaa

E4

ia

o

u

o

O 3 0 a ««

I "O O 0) J X

u o

eg

0) u

a. u

E <

1 V

a. u o f>

31
Figure 9

32
Figure 10

Saturation Curve on User 1 s Test System

NIST-114A

(REV. 3-89) U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

BIBLIOGRAPHIC DATA SHEET

1. PUBLICATION OR REPORT NUMBER

NIST/SP-260-115

2. PERFORMING ORGANIZATION REPORT NUMBER

3. PUBUCATION DATE February 1991

4. TITLE AND SUBTITLE Standard Reference Materials: Calibration of NIST Standard Reference Material

3201 for 0.5 Inch (12.65 mm) Serial Serpentine Magnetic Tape Cartridge

5. AUTHOR(S)

Mark P. Williamson, Natalie E. Willman, and Dana S. Grubb

6. PERFORMING ORGANIZATION (IF JOINT OR OTHER THAN NIST, SEE INSTRUCTIONS)

U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

GAITHERSBURG, MD 20899

7. CONTRACT/GRANT NUMBER

8. TYPE OF REPORT AND PERIOD COVERED

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (STREET, CITY, STATE, ZIP) NIST

Bldg. 225, Rm. A61

Gaithersburg, MD 20899

10. SUPPLEMENTARY NOTES

DOCUMENT DESCRIBES A COMPUTER PROGRAM; SF-185, FIPS SOFTWARE SUMMARY, IS ATTACHED.

11. ABSTRACT (A 200-WORD OR LESS FACTUAL SUMMARY OF MOST SIGNIFICANT INFORMATION. IF DOCUMENT INCLUDES A SIGNIFICANT BIBLIOGRAPHY OR

UTERATURE SURVEY, MENTION IT HERE.)

This publication describes the test system design and operation for the calibration

of the NIST secondary standard reference tapes SRM 3201 for 0.5 inch (12.65mm)

22 and 48 track serial serpentine magnetic tape cartridges. The importance of

producing a Standard Reference Material for this magnetic tape cartridge is

to promote the ability to interchange data both within and among various computer

installations. Reliable interchange is assured when the media is designed and

manufactured on the basis of a comparison to a known and accepted standard

reference media.

12. KEY WORDS (6 TO 12 ENTRIES; ALPHABETICAL ORDER; CAPITALIZE ONLY PROPER NAMES; AND SEPARATE KEY WORDS BY SEMICOLONS)

digital magnetic tape; Master Standard Reference tape; overwrite; peak shift;

Secondary Standard Reference; signal amplitude; Standard Reference Material

13. AVAILABILITY UNLIMITED FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE TO NATIONAL TECHNICAL INFORMATION SERVICE (NTIS). X

X

ORDER FROM SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT PRINTING OFFICE,

WASHINGTON, DC 20402. ORDER FROM NATIONAL TECHNICAL INFORMATION SERVICE (NTIS), SPRINGFIELD, VA 22161.

14. NUMBER OF PRINTED PAGES

39

15. PRICE

ELECTRONIC FORM *U.S.G.P.0: 1991 -281 -557: 40003

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