NBSIR 74-552

Technical Manual for Phosphor

Standards Calibrator

M. L. Greenough

Electronic-Optical Development Section

Measurement Engineering Division

and

H. K. Hammond, III

Laboratory Performance Section

Engineering and Product Standards Division

Institute for Applied Technology

August 12, 1974

Technical Report to U. S. Postal Service

Equipment Development Division

Office of Letter Mail Systems Development

Planning and New Development Department

Letter Agreement 72-2-02701

NBSIR 74-552

TECHNICAL MANUAL FOR PHOSPHOR

STANDARDS CALIBRATOR

M. L. Greenough

Electronic-Optical Development Section

Measurement Engineering Division

and

H. K. Hammond, III

Laboratory Performance Section

Engineering and Product Standards Division

Institute for Applied Technology

August 12, 1974

Technical Report to U. S. Postal Service

Equipment Development Division

Office of Letter Mail Systems Development

Planning and New Development Department

Letter Agreement 72-2-02701

U. S. DEPARTMENT OF COMMERCE. Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director

Preface

This report is in the Torn of a technical nanual coverinp;

the theory and operation of an instrument for measuring the

lumiinescent activity of the reference phosphor standards employed

in the US Postal Service Model 'lA Phosphornet ers . The general

design of the instrument follows that outlined in the final

report on a prior project entitled "Development of phosphormeter

standards, measurement techniques, and specification of solar

cell characteristics, IIBS Report 10 i^SC" , This technical manual

together with the companion report, "Preparation and calibration

of phosphormeter standards, MBS Report 7H 553", ^nd the Drawing

Package, constitute the final report on the project sponsored

by the Postal Service, Luminescence Calibration Equipment and

Standards

.

In addition to the listed authors, many others have made

contributions to the v;ork on the project. Especially among

tliese should be mentioned Herbert D. Cook, v/ho was responsible

for developing the basic calibration teclinique. Credit should

also he given for the work of L. F. Leach in the shop fabrication

of the instrument.

Table of Contents

Pape

Frontispiece : Photo^'iraph of IIBS Phosphor 'standards Calibrator

1.0 Introduction 1

1.1 Function 1

1.2 Specifications 1

2.0 Theory of operation 2

2.1 General 2

2.1a Instrument design 2

2.1b Definition of efficacy ^4 2.1c Measurement process 5

2.2 Theory of operation, detailed 6

2.2a Measurement unit 6

2.2a(l) Housinp; 7

2.2a(2) Pulsed uv lamp and ancillary equipment . 7

2.2a(3) Sample holder 8

2.2a(^) Filter case 9

2.2a(5) Photomultiplier tube, mount, and slide

shutter 11

2.2a(6) Entrance port for Detector Calibrator . . 11

2.2b Detector Calibrator unit 11

2.2c Conversion to PMU values 12

2.2c(l) Phosphor ratio 15

2.2c(2) Detector ratio l6

2,2c(3) Irradiance ratio l6

2.2c(4) Reflectance of barium sulfate standard . 17

2.2c(5) Spectral response of PMT and filters . . 17

2.2c(6) Computation of efficacy 19

2. 2c (7) Conversion of efficacy to MBS-PMIJ values. 20

2.2c (8) Computation of working PMU values .... 21

2. 2d Electronic unit 21

2.2d(l) Oscillator 21

2.2d(2) Binary counter 22

2.2d(3) Lamp drive 23

2. 2d (^4) Sample delay 24

2.2d(5) Sample period 24

2.2d(6) Photomultiplier tube (PF-fT) 25

2.2d(7) PMT amplifier Al 25

2.2d(8) Integrator 25

2.2d(9) Meter amplifier A2 26

2.2d(10) Digital voltmeter 26

2.2d(ll) Power supplies 27

2.2e Adjustment of controls 27

2,2e(l) Frequency trim 27

2.2e(2) Delay trim 28

2.2e(3) Zero adjust 28

2.2e(4) Sample period 28
Pape

3.0 Operating procedure. Comparator mode 30

3.1 Comparator mode, phosphorescent standards 30

3.2 Comparator mode, fluorescent standards 33

H.O Operating procedure. Calibrator mode ... 36

^.1 Calibrator mode, phosphorescent standards 36

^.2 Calibrator mode, fluorescent standards 42

5.0 Components 47

5.1 Five-year spare parts list 47

5.2 Complete parts list 48

5.3 Drawings list 52

Illustrations

Mechanical drawings (separate package)
List of Illustrations

Figure No. JASJ:.^

1 NBS Phosphor Standards Calibrator

2 Overall plan, Phosphor Standards Instrumentation (Schematic)

3 Measurement unit, " " "

"

4 Measurement unit

5 Front view of Measurement unit, partially disassembled

6 Rear

7 Pulsed uv lamp and entrance port for Detector Calibrator

8 Sample holders

9 Filter case

10 Photoraultiplier housing and shutter with dark, slide

11 Detector Calibrator unit

12 Control panel. Electronics unit

13 Block diagram of Electronics unit

14 Diagram of Oscillator

15 Diagram of Binary Counter

16 Diagram of Lamp Drive

17 Diagram of Sample Delay and Sample Period

18 Diagram of PMT circuits

19 Diagram of power wiring

20 Test point list

21 Component location, Electronic chassis

22 " " Electronic circuit board

23 Sample data sheets
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1.0 Introduction

1 . 1 Function

The Phosphor Standards Calibrator Is desip;ned to measure

the luminescent activity of USPS Pliosphor Standards of the

phosphorescent and fluorescent types. It Is capable of

operation In either of two modes, which are:

Comparator- mode - Simplified operation v/hereby the

resultant Phosphormeter unit (PMU)

values are based upon direct comparison

with Immediately-available reference

standards;

Calibrator m.ode - Operation based upon determining;

a factor called efficacy for each

tested standard. Efficacy Is then

related to PFTI value by previouslydetermined conversion constants

based upon statistical evaluation

of designated phosphor standards

in prior use.

The difference betv/een the two modes Is that in the Calibrator

mode, the long-term calibration of luminescent activity is

referred to reproducible measurement of Irradlance in watts

per unit area at a given distance from ultraviolet and visible

radiant sources. This is in contrast to the Comparator mode,

which while more convenient, depends upon the measurement

and preservation of potentially non-permanent physical

standards. VJhenever possible, however, the Calibrator mode,

for v;hlch the instrument was primarily designed, is

recommended for operation.

1. 2 Specifications

Design range - 0.1 to 200 PMU nominal, extendable to 1000 PMU

Ultraviolet excitation - wavelength 253.7 nanom.etres (nm)

- duty cycle, Oil for 10 milliseconds (ms);

OFF for 90 m.s , repeated cyclically

Spectral region of luminescent measurement - ^50 to 650 nm

Measurement sample time - phosphorescence, 0.5 ms after

extinction

- fluorescence, 0.5 ms before extinction
Output Indication - analop; on cathode ray oscilloscope

- digital, on dipital panel meter 0.000 to

2.000 (volts)

Size of standards accepted - 3 x 4 x 7/1*^ inches

(7.^)2 X 10.16 X 1.11 cm)

Size, inches and (centimetres)

• ^ Overall bench space - 88w x 2^d (23^ x 6l cm)

T'^easurement unit - llw x 13. 5h x l8d (28 x 3^.3 x ^5.7 cm)

Detector Calibrator unit - ^t^w x 9h x 7d

(117 x 22.9 X 17.8 cm)

Power supply for Detector Calibrator - 10. 5v; x 6.5h x 15. 5d

(26.7 X 16.5 X 30.^) cm)

Electronics unit ~ 20. 5w x 31h x l8d (52 x 78. 8 x ^15.7 cm)

V/eight, approx, pounds and (kilop;rams)

Measurem.ent unit - 10 (^1.5 kp)

. Detector Calibrator unit - 15 (6.8 kp)

Power Supply for Det . Cal. - 30 (13.6 kg)

Electronics unit - 75 (3^ kg)

0 Theory of operation

2 . 1 General

This section includes a general outline of the calibration

system for phosphor standards, covering the overall layout and

operating principles. A photograph of the complete instrument

is shown in Figure 1.

2.1a Instrument design

The overall plan of the MBS phosphor calibration system is

shown in Figure 2. A more detailed view of the measurement

system is given in Figure 3. The basic design of the instrument

calls for irradiating the phosphor standard by a uv source

at an angle of ^5 degrees and detecting the emitted visible

radiation with a photomult iplier tube (PMT) on an axis normal

to the phosphor surface. Both the uv source and the PMT are

located about 5 inches (125 nm) from the phosphor standard

2
as it is held by the sample holder. Appropriate filters are

located at the uv source (to pass only the 25 ^-1 -nanometre

line of the low-pressure mercury lamp) and in front of the

PMT (to block the reflected uv radiation). At the PMT a dual

filter carriag-e arrangement is used, each carriace holding

two filter assemblies as needed. Filter requirements are

such that one carriage remains in the instrument while the

other is interchanged according to whether green or red

phosphorescence, or red or yellow fluorescence, is being

measured. This filter arrangement is designed to provide

rapid change of filters as needed in the measurement procedure.

On the other side of the PMT, also at ^5 degrees from the

normal to the standard, is a detector calibrator assembly

whose purpose is to allow in situ calibration of the relative

PMT sensitivity for ultraviolet and for visible radiation.

The function of the detector calibrator assembly is to

provide known irradiances at its exit port, both in the

ultraviolet and in the visible regions. Irradiance measurements on a stabilized mercury vapor lamp have been carried

out by the Optical Radiation Section of NBS. The lamp is

to be recalibrated at periodic intervals, by comparison with

an NBS standard of spectral irradiance, a 1000-watt quartzhalogen lamp. The PMT calibrator assembly is in a one-metre

tunnel designed to hold the uv visible source(s) and to permit

ready transference to the Optical Radiation laboratory.

The electronic portions of the system provide the waveform

to excite the pulsed uv lamp used in phosphor measurement.

This lamp is energized for 10 milliseconds and de-energized

for 90 milliseconds on a repetitive basis. Reliable firing

of the pulsed uv lamp is assured through the use of an

envelope heater at ^5°C and a nearby low-power, keep-alive

lamp.

The measurement circuitry consists of a signal sampler which

examines the PMT output current at the designated time, namely

0.5 millisecond after lamp extinction. Provision is made for

changing this sampling time if desired. The sampled signal

is further processed through peak-reading and electrical

filtering networks to provide averaging over approximately

30 lamp flashes. This averaged current is displayed on a

digital readout panel in illuminated numerals.

Physically the electronic components are located in a tablemounted rack cabinet which is located at the left of the

optical measurement unit.

3
2. lb Definition of efficacy

Efficacy Is the term applied to a dimensionless factor

derived from the NBS instrument which is indicative of

luminescent activity exhibited by phosphor standards. The

concept of efficacy is in some ways similar to that of reflectance, where the light reflected (emitted, in the case

of phosphors stimulated by ultraviolet radiation) from an

illuminated specimen is compared to that from a perfectly

diffusing surface. Thus efficacy may be regarded as reflectance with a wavelength shift, since the uv-lrradiated

specimen emits energy in the visible green or red portions

of the spectrum.

The measurement of efficacy is a process of determining the

ratio of two radiant power levels as received by a detector

which is responsive to both uv and visible radiant energy.

In the formula by which efficacy is calculated from observed

readings, the radiant power reaching the detector is computed

by dividing the measured detector current by its sensitivity

in the appropriate wavelength region. The numeric value of

efficacy can be expected to be rather small, since the emitted

phosphorescent power in the visible portion of the spectrum

is low compared to the diffusely reflected power in the uv

region.

Efficacy as defined and measured by the MBS calibrator is

essentially independent of the technique of measurement, with

a single exception for phosphorescent (but not fluorescent)

standards. Because of the energy-storage characteristics of

phosphorescent materials, the magnitude of observed emission

depends upon the length of time during which the phosphor is

excited. Thus when a phosphor is excited, the luminescent

output builds up in an exponential manner, decaying in the

same manner when the excitation is removed. Hence the observed

emission is a function of the duration of excitation as well

as the interval between cessation of excitation to the time

of measurement.

In the NBS calibration system, the duration and delay Intervals

have been selected as approximations to service conditions

in the facer-cancelers and phosphormet ers . The NBS calibration

system uses a recurring excitation (duty cycle) of 10 milliseconds on and 90 milliseconds off, for a repetition rate of

10 per second. This allows the green phosphor to become very

nearly fully charged and discharged, the red phosphor to charge

to approximately 30 percent and to discharge almost completely.

4
The resultant is that the response to green phosphors is

about 80 percent of the maximum possible, while that for

the red is between 10 and 30 percent. Hence once the system

has been calibrated to determine the conversion factor

between measured efficacy and PMU, it is important to maintain the same duration of excitation and delay before measurement, as prevailed during the conversion process.

In contrast to measurements on phosphorescent standards,

efficacy for fluorescent standards does not exhibit the

time-dependent factor, provided certain conditions are met

regarding minimum delay times. Therefore duty cycle and

measurement times have virtually no effect upon the observed

values of efficacy for fluorescent standards.

2.1c Measurement process

As mentioned in the definition of efficacy in Section 2.1b

above, the measurement process is that of determining the

incident power reaching the photodetector , under the two

conditions of 1) visible emitted phosphorescence, and

2) uv reflection from a diffusing surface. These power

levels are determined by measuring the output current of

the detector and dividing it by the detector sensitivity

at the specific wavelength region of interest.

Sensitivity in turn is provided through additional measurements

of detector current when known levels of radiant power are

introduced into the instrument. Since only the relative

power levels (uv/visible) are involved in efficacy, many

factors, which would otherwise have influence on the numeric

value of efficacy are self-cancelling in the formula for

its computation. Some of the cancelling factors are those

relating to the angle of illumination (if it is identical

with that for the detector calibration), the intensity of the

pulsed uv lamp, the PMT gain, and the uv reflectance of the

diffusing surface.

The procedure by which efficacy values are obtained involves

four measurements under specified conditions, with prior

calibration of uv and visible irradiances at the exit port

of the detector calibrator, and of the reflectance in the

visible region of a reference diffuse reflector. These are

the basic factors involved in developing efficacy values

from the NBS instrument; to these must be applied a precomputed correction factor for the spectral response characteristic of the photomultiplier tube. The four measurements

concerned with each tested standard enter the formula for

efficacy as two ratios called Phosphor and Detector.

5
The Phosphor ratio is proportional to the phosphorescent

activity of the standard; it involves two peak-sampled

currents resulting from the use of the pulsed uv source

in the Measurement unit. A Phosphor ratio is computed

for every tested standard. The Detector ratio, which is

indicative of the relative uv/visible sensitivity of the

PMT, originates from the Detector Calibrator and involves

averaged currents. It is usually necessary to measure

the Detector ratio only once during a measurement session.

The manner in which these two ratios enter into the formula

for efficacy, which in turn is convertible into PMU

evaluations, is covered in Section 2.2c - Conversion to PMU

values. The general procedure is to determine the effective

PMU contribution which is proportional to efficacy, to which

a minor correction constant is added. The final result for

each phosphor standard is a working PMU value to which the

phosphormeters must be set for evaluation of stamps and other

luminescent materials.

2 . 2 Theory of operation, detailed

Specific details of design and operation are given in

this section covering

a) Measurement unit

b) Detector Calibrator unit

c) Conversion to PMU values

d) Electronics unit

Step-by-step operating procedures are contained In

Sections, 3 and ^ of this report,

2.2a Measurement unit

The major components of this unit are:

1) Housing

2) Pulsed uv lamp and ancillary equipment

3) Sample holders

Filter case

5) Photomult iplier tube, mount, and dark slide

6) Entrance port for Detector Calibrator

6
2.2a(l) Housing

The housing is the structure for holding the various components,

principally optical, in the proper relative positions in the

Measurement unit, as illustrated schematically in Figure 3

and photographically in Figure ^. Photographs of the partially

disassembled housing show the front view in Figure 5 and the

rear in Figure 6, The basic design consists of top and

bottom plates, held together by a front plate, with three

identical openings at the rear into which external appendages

can be mounted. These external units are the pulsed uv lamp,

filter carrier and PMT, etc. The sample holder is mounted

at the center of the front plate.

The internal structure of the housing consists of three

tunnel baffle assemblies having a common design, but which

allow attachment of specific aperture plates as needed.

These baffle assemblies are removable from the rear, as can

be seen in Figure 6.

At the opening in the front where the sample holder has been

removed, the front baffle assembly is visible in Figure 5.

This assembly has three detachable aperture plates for optical

access to the sample under test. Specifications for these

plates are given under the descriptions of the specific

components

.

The top has a removable cover for physical access to the

interior of the housing and to the mounting screws which

hold the housing to the base plate.

2.2a(2) Pulsed uv lamp

Unless noted, the components described below can be seen in

the photograph. Figure 7.

This is a commercial, pencil-type, low-pressure, mercuryvapor lamp similar to that used in phosphormeter and facer

canceler machines. Its principal emission is at 253.7 nanometres, with a secondarily strong emission at 5^6.1 nanometres

and weaker emission at all the other mercury line wavelengths.

Only the 25^ nm line is used from the pulsed uv lamp; it will

be noted later that the Detector Calibrator, employing the

same type of lamp, utilizes both 25^ and 5^6 nm wavelengths.

The pulsed uv lamp is excited periodically at a duty cycle

of 10 milliseconds on, 90 milliseconds off. During the time

of excitation, a pulse of 570 volts through ^0 000 ohms is

applied to the lamp, resulting in a peak current of approximately 10 milliamperes . The emitted radiation reaching the

standard under calibration is in the order of 20 microwatts

per square centimetre.

7
The pulsed uv lamp is mounted In a thermally-insulated block

of aluminum heated to approximately ^5°C, to help insure

precise repetition of pulsed radiation from the lamp. An

electronic temperature controller, passin^^ current through

a 10-ohm resistor embedded in the block, serves to maintain

the block temperature. Regulation is by means of a nullbalance circuit, using positive and negative voltage supplies

plus a thermistor whose resistance is 88 ohms at the design

temperature. The exact temperature at which the lamp is

controlled is not critical.

The exit port of the pulsed uv lamp house contains a removable

aperture plate with an opening 1/8 inch wide by one inch

(3.2 X 25.^ mm) high. Immediately in front of this, toward

the test standard, is a slide shutter. In the up position,

the shutter is closed and the uv radiation is blocked completely

There is also an auxilliary mercury lamp designated a "keepalive" lamp of the same type, mounted so as to radiate into

the cavity where the pulsed lamp is located, but not into

the exit aperture. It operates at a constant current of

approximately 0.l8 milliampere.

The uv-pass filter, whose function is to block all but the

25^ nm emission of the pulsed lamp, is located Just beyond

the shutter for the pulsed lamp seen in Figure 6.

The radiation from the pulsed uv lamp is masked before it

reaches the phosphor standard by the defining aperture plate

which can be seen in Figure 5. As designed, the irradiated

area on the phosphor standards is 0.5 inch (12.7 mm) wide,

slightly narrower than the phosphor wafer. In height the

irradiated zone extends from l/l6 inch (1.5 mm) above to

1/16 inch below the boundaries of the 1-1/2 inch (38.2 mm)

vertical dimension of the wafers in the fluorescent standards.

2.2a(3) Sample holder

Two sample holders are provided, one to handle mounted

phosphorescent and fluorescent standards, the other for

unmounted samples such as coated paper sheets. The two holders

are shown in Figure 8. The thickness of the front face on

the two styles is such as to position the luminescent surface

in the same plane of measurement, namely 0.25 inch (6,3 mm)

from the front plate of the housing.

8
There are also two sizes of masks, one or the other of

which must always be used. These are designed to match

the wafer size in the phosphor standards. The smaller

mask is for phosphorescence measurements; the larger , for

fluorescence. There are small notches at the top right

corner of the masks to facilitate their proper orientation

with respect to the locating pins protruding from the front

plate of the housing. For identification, the mask for

phosphorescent standards has one notch, while the mask for

fluorescent standards has two notches.

The sample holders can be interchanged readily, but each

type of holder must be held in place with its specific

mounting screws. There are four thumbscrews for the holder

for phosphormeter standards and four flat head screws for

the plate to be used with unmounted samples.

Before phosphormeter standards are inserted into the holder,

the handle actuating the pressure plate should be turned

down. Raising the handle then clamps the standard in the

proper position for measurement. If the standard is removed

with the handle upward, no harm will be done except for

possible abrasion of the exterior. It is recommended that

the handle be in the down position whenever a standard is

inserted or removed.

2.2a(4) Filter case

This is the rectangular box v;hich contains two movable carriages

for holding the filters through which light must pass in order

to reach the photomult iplier tube. The two carriages are

designated Front and Rear, with the former closer to the sample

holder. The overall filter case, its light-tight cover and

one removed carriage are shov/n in Figure 9. In the mounted

position, the handles of the two carriages protrude through

the cover at the top of the filter case. Each carriage can

hold two packages of 2 x 2 inch (50.8 mm) filters, one above

the other, having a maximum thickness of 3/8 inch (9.^^ nim)

total thickness. In operation, selection of the required filter

package is accomplished by raising or lowering the appropriate

carriage. The filter package in use when the handle is raised,

is the one farther from the handle. Tiiis can be seen in

Figure 9. Spring-loaded mechanical detents in the carriages

assure proper positioning of the filters in the optical path.

In normal operation of the system, the front filter carriage

is loaded with fixed specific sets of filters. However, the

filter in the rear carriage must be changed for each of the

following operations:

9
1) Phosphorescence, green or red standards

2) Fluorescence, red channel

3) Fluorescence, yellow channel

These filters are to be Inserted in the slot marked "VIS"

of the rear carriage, the location farther from the handle.

Filter positions

The appropriate filters in their respective positions are

listed below, together with their functions. All labeled

filters should be positioned so that the labels are at the

top and toward the sample holder.

Front carriage, UV position

This position carries an attenuator for reducing the effective

sensitivity of the PMT to ultraviolet radiation by a factor

of approximately 100. The exact attenuation is not critical,

since the same factor is involved in the calibration of

detector sensitivity. The initial attenuator is made of three

sheets of fine wire mesh and one sheet of perforated stainless

steel. This attenuator is not .removed from the carriage.

Front carriage, VIS position

This position carries a permanently-installed combination of

two filters, designed to block ultraviolet and infrared

radiation, and to pass only visible light from about ^50 to

650 nanometers. This filter insures that the detector receives

only the intended visible emission from phosphorescent and

fluorescent standards.

The filters in current use are a low-fluorescence, yellow

glass filter labeled AJW 730515, 353 ADM, 26-^11^1-5, followed

by a short-wave-pass interference filter which transmits

below 650 nm and blocks above this wavelength. The latter

is marked LEI SWP-65OO.

Rear carriage, UV position

Open, no filter

Rear carriage, VIS position

Single filters are to be placed in this position according

to the type of measurement being made. In particular, this

is to allow separate measurement of fluorescent standards

respectively. The specific filters are:

10
1) Phosphorescence, either preen or red - no filter

2) Fluorescence, red channel - marked Fl, 396^9-?

This is a band-pass Interference filter, with a width at half height of approximately 3^ nm

centered at 6l2 nanometres. Transmi tt ance data

for this filter are ^^iven in NBS Report 10 596

to the USPS entitled "Development of Phosphormeter

Standards, Measurement Techniques, and Specification

of Solar Cell Characteristics", 1971.

3) Fluorescence, yellow channel - marked Dl , 396^9-1

This is a band-pass Interference filter, with a

v/idth at half height of approximately 15 nm

centered at 576 nanometres.

2.2a(5) Photomult iplier tube, mount, and slide shutter

This assembly bolts to the exit side of the filter case; the

components are shown separately in the photograph. Figure 10.

The PMT has an eleven-stage, "Venetian blind" multiplier

structure. The window is of fused silica, since the tube

must detect radiation at 25^< nanometres. The cathode sensitivity extends to 850 nm (10^ of peak sensitivity) according

to the manufacturer's data and independent measurements. Data

on the spectral response of this tube are given in I^onthly

Report No. 3, Table 1 and Figure 2. It is designated as tyr)e

9558 QMA. While the PFIT rating lists a maximum average anode

current of 1000 microamperes, the actual current in the

instrument is limited to 10 microamperes peak to minimize

fatigue effects. The tube was supplied complete with magnetic

shield and internally-contained voltage divider. Additional

details on the PMT and its operation are included in Section

2.2d(6).

2.2a(6) Entrance port for Detector Calibrator

The entrance port can be seen in Figures 7 and 11. It is

designed with an exterior shoulder to fit into the exit port

of the Detector Calibrator unit. There is also a slide shutter

to block radiation from the calibrator unit until needed. As

with all other shutters, it is closed in the up position.

2.2b Detector Calibrator unit

This unit is a structure designed to hold the stabilized lowpressure mercury vapor lamp at a specified distance from the

barium sulfate reflectance sample. At this distance (currently

90 centimetres) the Irradiance has been measured in the Optical

Radiation Section of UBS, for the 25^ and 5^6 nm lines emitted

by the lamp. In the formula for efficacy, derived later, it

11
will be seen that it is the relative vislble/uv liTadiance

ratio which is desired. While the distance is thus not

critical, it is good practice to operate at the calibrated

position. To facilitate positioning of the calibration

lamp at any desired distance from the sample position, a metric scale is mounted on the side of the calibrator.

"^he photograph, Figure 11, shov/s an exterior view of the

Detector Calibrator unit. Essentially it is a one-metre

tunnel which contains a track-mounted mercury vapor lamp.

It is fully baffled Inside with removable aperture plates,

to minimize internal reflections. There is also a holder

for filters mounted in front of the lamp house. "^he bottom

of the tunnel is arranged with a light-trap to admit air for

the cooling fan associated with the lamp. Sliding cover

sections plus a light-shielding cover over the ventilated

lamp house serve to keep the ambient room light from affecting

the calibrations.

Calibration performed on the lamp in free space with specific

filters shows

:

25^ nm line - 0.5^2 microv/att per square centimetre

with band pass interference filter marked

"411. OVV

5 '1 6 nm line - 0. 07 88 microwatt per square centlm.etre

with band pass interference filter marked

"221.12"

The irradlance ratio, visible/uv, is O.0788 divided by 0.502,

or 0.1570.

2.2c Conversion to PMII values

The several steps v/h-ich must be performed in order to evaluate

phosphor standards in the HBT. calibrator are listed below and

described in sections 2.2g(1) through g which follow.

1) Determination of Phosphor ratio

This is the ratio of PTfT output under tv/o conditions

of measurement with pulsed uv lamp. It is proportional to the luminescent activity of the phosphor

standard. This ratio is determined for every

standard being evaluated, either phosphorescent or

fluorescent

.

2) Determination of Detector ratio

'T'his is the ratio of PMT outputs under the two

conditions of measurement with the continuousoutput lamp of the detector calibrator. It is

proportional to the relative uv/visible sensitivity

12
of the PMT. This ratio should be determined in

every measurement session for phosphor standards,

or at least once per week. The procedure is

independent of whether phosphorescent or fluorescent

standards are beinp; measured.

In addition to Steps (1) and (2) above, pre-determination of

certain other factors is required, resulting in a multiplying

constant which must be recalculated from tim.e to time on a

long-term basis. - These additional factors are:

3) Determination of Irradiance ratio

This ratio is indicative of the relative visible/uv

irradiance provided by the detector calibrator unit.

It should be measured every 100 hours of use of the

lamp in the Detector Calibrator unit.

4) Determination of visible reflectance of barium

sulfate standard.

This standard consists of barium sulfate powder

under the quartz windov; of a phosphor wafer holder.

Relatively infrequent measurement is required.

5) Determination of spectral response of the PMT and

associated filters.

The relative spectral sensitivity of the PMT is

expected to change slowly vrith time, requiring only

infrequent checking or correction. Measurement

of spectral sensitivity is difficult to carry out

with high accuracy and so small changes will not be

detectable with certainty.

From steps (4) and (5) a correction factor must be computed,

equal to the ratio (4)/(5). In the event that the barium

sulfate standard or the photomultiplier tube is replaced,

introduction of the recomputed correction factor into the

formula for efficacy which follows will compensate for any

effects upon measured values. The next step is:

6) Computation of efficacy

Efficacy = (Phos. ratio)x(Det. rat io) x( Irrad. ratio) x ( Corr. factor).

13
where :

Phos. ratio Ratio of PMT outputs = with pulsed uv lamp

PMT output, visible

PMT output, uv

Det. ratio = Ratio of PMT outputs

with Detector Calibrator

PMT output, 2^4 nm

PMT output, 5^6 nm

Irrad. ratio Ratio of measured

irradiances from

Detector Calibrator

Irradiance, ^46 nm

Irradiance , 2 5 ^ nm

Corr. factor Corr. for visible reflectance of barium sulfate std.

Correction for spectral response of PMT and filters

or

:

Efficacy = (1) X (2) X (3) X (4)

15)

usinp; results from the numbered steps above.

The result is a dimensionless factor expressing the

emitted phosphorescent energy compared to that which

.

, a perfectly diffusing surface would reflect under the

same conditions of uv illumination.

7) Conversion of efficacy to HBS-PMU values

This is the PMU evaluation of phosphor standard for

the visual phosphorescent or fluorescent contribution

only. NBS-PMU values are computed by multiplying

the measured efficacy by a known conversion factor

which has previously been determined from phosphor

standards of assigned values.

The final step is:

8) Computation of tentative working values of PMU for

phosphor standards.

To the NBS-PMU value derived in step (7) there must

be added a correction constant C to take into account

extraneous sources of response in the phosphormeters

.

For green phosphorescent standards, C = 1.0; for red,

C = 8.0; for red fluorescent, C = zero. Since the

correction constant C is difficult to evaluate, bestvaluation estimates are in current use and the resultant working values are denoted NBS-PMU (T).
Because certain of the above eight items require more detailed

comment than is provided in the step-by-step procedures listed

in Sections 3 and ^, additional notes on these items are

supplied immediately below.

2.2c(l) Phosphor ratio

This is the ratio of signal output when measuring the visible

light emission of a phosphor standard, to the output when

measuring the reflected ultraviolet from a barium sulfate

reflectance sample. In order to minimize drift effects in

the intensity of the pulsed uv lamp, it is necessary to

measure the reflected uv both before and after any readings

on phosphor standards. Furthermore, since the uv lamp does

not always display a flat-topped pulse of uv output, it is

also necessary to develop a weighted average intensity for

the pulse. The v/eighting is designed to emphasize the

amplitude toward the end of the pulse to simulate the storage

action of phosphorescence. This is accomplished by sampling

the instantaneous uv pulse signal at 10 time intervals during

the pulse. Each sam.ple is multiplied by a weirhting factor

which is largest for the sample at the end of the uv pulse.

The sum of the weighted samples is then divided by the sum. of

the weighting factors to yield the uv pulse amplitude which

is actually effective in the excitation of phosphorescent

activity. If the uv pulse had a flat top, the weighted value

would be equal to the instantaneous samples. Hov;ever, when

the pulse exhibits som.e decay, as is the normal case, the

compensation for decay is introduced by using the weighting

process

.

Because the green and red phosphors have greatly different

decay rates (3.6 vs. 22 milliseconds, for example, to decay

to 1/e or 37p).it is necessary to compute separate effective

uv pulse amplitudes for red and green phosphors, using two

sets of v;eighting coefficients.

To reduce the labor of the v/eighting computations while meeting

the requirement of before-and-aft er observation of uv pulse

amplitude, it is recommended that m,easurement sessions follow

this general pattern:

1) iv^easurement of the 10 samples of uv pulse amplitude

2) " green phssphorescent standards to be

evaluated

3) " 10 samples of uv pulse amplitude

4) " red phosphorescent standards to be

evaluated

) " 10 samples of uv pulse amplitude

15
Computation, however, in items (1) and (5) can be reduced to

that for green only and red only, respectively, if the above

sequence is followed.

If there is a significant drift between the be fore-and-after

pulse amplitudes it will be necessary to interpolate values

according to the times of phosphorescence measurement compared

to those of the uv pulse amplitude.

Because the luminescent emission of the phosphor standards is

very small compared to the reflected uv from the barium

sulfate reflectance standard, it is necessary to attenuate the

latter by about 100 times to bring the PMT output within the

range of the meter circuits. This is accomplished by placing

a multi-layer mesh screen in front of the PMT whenever uv

measurements are being made. Since this attenuator is also

in the path during the uv phase of detector calibration, the

attenuator transmit tance cancels out in the product of Phosphor

and Detector ratios, and so does not require separate determination .

2. 2c (2) Detector ratio

This is the ratio of observed PMT output when the detector

calibrator is operated separately with its pass-selection

filters for the mercury 25^ and 5^6 nanometre lines respectively.

The ratio is obtained by noting the PMT output voltage when

set up for uv emission from the detector calibrator, dividing

this by the PMT output with the calibrator set for visible

(5^<C nm) emission. Although the uv 25'^ nm uv line is strong

in the mercury vapor lamp, the presence of the attenuator

reduces the PMT output to less than 10 percent of the output

from the ^^6 nanometre line. Typically the Detector ratio is

in the order of 0.06 to 0.07.

Details of the procedural steps involved in determining the

Detector ratio are given in Section ^. The determination of

Detector ratio is not required when the system is used in the

Comparator mode, since this mode employs only relative output

indications

.

2 . 2 c ( 3 ) Irradiance ratio

The current value of this ratio of visible/uv irradiance,

based upon the calibration performed in 1972, is 0.1570, as

was derived in Section 2.2b - Detector calibrator. This value

will be used until a recalibrat ion gives a different value.

16
2.2c(^) Reflectance of barium sulfate standard

Two standards are necessary, one having a window area equal

to that of the phosphorescent standards, the other equal to

that of the fluorescent standards. The reflectances of these

have been measured as 0.976 and 0.9^8 on an Automatic Color

Brightness Tester. These measured reflectances take Into

account the losses due to the quartz window covering the

barium sulfate surfaces.

Until the determination and final introduction of all filter

characteristics, a temporary reflectance value of 1.00 has

been assigned to the barium sulfate standards.

2 . 2 c ( 5 ) opectral response of PMT and filters

The purpose of PMT and filter factor is primarily to allow

replacement of these elements without affecting the overall

system's evaluation of phosphor standards. While not required

for operation in the Comparator mode, the spectral response

factor must be obtained in the Calibrator mode, where the

evaluations of phosphor standards are referenced to the measured

irradiance from the detector calibrator.

Quantitatively the spectral response factor is a numeric

constant expressing the effect upon PMT output of distributing

a given amount of radiant power over a spectral region matching

that of the phosphorescent emission vs. concentrating the same

power at the single wavelength of 5^6 nanometres. The relative

PMT output for these two conditions is the spectral response

factor.

The process of determining the spectral response factor is

one of numeric integration, involving the spectral characteristics of the phot omultiplier tube, the luminescent materials

and any filters. Certain conditions are imposed upon these

characteristics for use in computation; these are:

1) The relative spectral response function of the

PMT is to be normalized to unity at 5^*6 nanometres.

2) The relative spectral emittance function for a phosphor is to be adjusted so that the total area

(sum of the ordinates throughout the region in

which the phosphor emits) will be unity.

An individual function is associated with each

phosphor type.

3) Filter response characteristics are to be given

in terms of spectral t ransmittance , always less

than unity.

17
The above characteristics should be reported for wavelength

intervals of 5 nanometres throughout the region covered by

the useful phosphor output, or 4^0 to 870 nanometres.

The combined product (1) x (2) x (3) is to be computed for

each wavelength, using in (2) and (3) the characteristics

for each phosphor and filter as appropriate. The precise

value at S46.1 nm should also be computed for (1) x (3) in

order to establish the response at the wavelength of the

detector calibrator source. The spectral response factor

is obtained by summing of the products (1) x (2) x (3), and

dividing the sum by (1) x (3) at 5^1(^.1 nanometres.

This computation of the sum of the products (1) x (2) x (3) at

each wavelength is to be performed for the following specific

combinations

:

a) f-reen phosphorescent standards

In item (2) the emittance function for green phosphorescent standards is to be used. For item (3)

it is the composite transm.it tance function for the

uv-blocking and the infrared-blocking filters, since

these two are always used together.

b) Red phosphorescent standards

Gam^e as above except that (2) requires the red

phosphorescent emittance function.

c) Red fluorescent standards, r^^d channel

Item (2) requires the red fluorescent em.ittance function.

Item (3) requires, in addition to the composite above,

inclusion of the t ransmit tance function for the red bandpass filter v/hich is currently identified as Fl.

d) Red fluorescent standards, yellow channel

Item (2) requires the yellow fluorescent emittance function

Item (3) requires in addition to the composite above,

inclusion of the transmit tance function for the yellow

bandpass filter identified as Rl.

e) Background fluorescent standards, red channel

Same as (c) above

f) Background fluorescent standards, yellov; channel

Same as (d) above

18
The product (1) x (3) which is the response at 5^*^>.l nm

is required only once since the detector is always calibrated

usinp the ultraviolet and infrared blockinp filters, without

the supplementary filters used in evaluations of fluorescent

standards

,

Typical spectral response factors are:

Standards Typical values

Green phos. l.no^t

Red phos. 0.6^1

Red fluor. , red channel

Red fluor., yellow channel 0.0157

Bkgnd fluor., red channel 0.0129

Bkp:nd fluor., yellow channel 0.310

2.2c(6) Computation of efficacy

Efficacy is to be computed for each phosphor standard being

evaluated. While single values are found for the phosphorescent

standards, dual values (red and yellow channels) are needed for

fluorescent standards.

The formula for efficacy is:

Phosphor Detector Irradiance Reflectance of

Efficacy = ratio ratio ratio barium sulfate std.

Spectral response factor

In each computation it is important to apply the correct

spectral response factor appropriate to the measurement step

being conducted. When the indicated computation has been

carried out, each phosphorescent standard will have one

efficacy value. Fluorescent standards on the other hand will

have both red and yellow channel values of efficacy. Some

typical values for standards are:

19
Standard

Green phos.

Red phos.

Red fluor, - red

" - yellow

Bkgnd fluor. - red

(2 PMIJ)

" , - yellov;

Momlnal

PMU value

22

22

22

22

2

Typical value

of efficacy

0.0020

0.0023

0. 0030

0. 0039

0. 0007

0.0037

(Temporary values

with spectral

response factor

assumed eoual

1.000)

2.2c(7) Conversion of efficacy to NBS-Pf-lU values

The riBS-PMU value for phosphor standards is computed by

multiplying the efficacy by a pre-determined constant. This

constant has been established as the optimum conversion factor

using a designated reference set of phosphor standards. From

an intercomparison of the readings on the MBS instrument and

on phosphormeters , the following conversion factors have been

adopted

:

Standard

Factor for Converting

Efficacy to NB3-PMU

Green phos. 10 583

Red phos. 0 771

Red fluor. - red channel 8 06^ . (Temporary

values with

Tt - yellov/ channel 882 spectral

response

Background fluor. - red channel 8 nfi^ factor

assum^ed equal

1! " - yellow channel 882 ^ 1. 000)

I7hen the conversions to IJBS-Pr/'U have been completed, all

phosphorescent standards will have single values and fluorescent standards will have dual values, one for the red and one

for the yellow channel. These values represent phosphor

activity in the visible portion of the spectrum. however,

because of phosphormeter design there are responses to other

elements in the phosphor standards. These elements are not

subject to precise calibration at present, but investigation

has resulted in estimated corrections. The final step in the

computation of working PMU values is applying these corrections

20
2.2c(8) Computation of working PPIU values

The v/orking values for phosphor standards differ from the

IJBS-PMU values computed above by the correction indicated

belov/. The resultant values are marked as NBS-PMU(T) on

the standards.

Green phos. stds

nBS-PriU(T) = ?IBS-PMU +1.0

Red phos. stds

NBS-Pr"U(T) = !IBS-PMU +8.0

Fluorescent stds (Red and Background)

nBS-PMU(T) = .MBS-PriJ (red channel) - NBS-Pr^U (yellov;

channel)

Each phosphor standard has been labeled v;ith the nBo-PWU(T)

value as the only item visible to the operator. lloviever

the components entering into this final step of conversion

are given on the underlying label. If desired, they may be

seen by removing the screws holding the metal name plate of

the standard.

2. 2d Electronics unit

The block diagram of the Electronics Unit is shown in Figure

13. The basic sections are:

1) Oscillator

2) Binary counter

3) Lamp drive

4) Sample delay

5) Sample period

6) Photomult ipller tube, PMT (located in Measurement unit)

7) PMT amplifier A-^ 8) Integrator

9) Meter amplifier

10) Digital voltmeter

11) Pov;er supplies

Each of the above is described belov; in correspondingly

numbered sections. Signal test points are listed in Figure

20. Locations of components are shown in Figures 21 and 22.

2.2d(l) Oscillator

The function of this circuit is to provide overall timing

signals controlling the repetition rate and duty cycles of

the measurement process. The circuit output is a pulse of

3.5 m.icroseconds duration repeated 2000 times per second.

21
A circuit diapram is given in Figure 14. It Is a relaxation

oscillator whose period is controlled by the time constant

(RC product) of CI and Rl +R2. Adjustment of the exact frequency is accomplished through varying PI, as described in

Section 2.2e. In the circuit of Figure l4, transistors Ql

and Q2 form the oscillator, with the output being amplified

by Q3 to -5 volts. The output waveform is available on a

test terminal at the rear of the chassis (TPl).

2.2d(2) Binary counter

The function of the binary counter is to provide the following

outputs from the single input of pulses at 2000 hertz.

a) Lamp drive input, a 10-millisecond pulse at 0 volt

repeated 10 times per second. Between pulses the

output is +5 volts.

b) Sample delay pulses, switch selectable at 0, Q, 10

and 96 milliseconds delay from the leading edge of

the lamp drive pulse above. The waveforms for 9,

10 and 96-ms delay go positive to +5 volts at the

leading edge of the lamp drive pulse, and return

to 0 volt at the designated delay time. For the

0-ms delay, a wave form which returns to 0 volt

coincidentally with the leading edge of the lamp

drive pulse is provided with its positive-going

excursion at 3^ milliseconds before then.

The binary counter is arranged for two counting ratios, 200X

in the CHECK condition and 201X in the RUN. By synchronizing

the oscillator frequency with the 60 hertz line power in

CHECK and then operating off-synchronization, the effects of

any spurious pickup of 60-hertz related signals can be

averaged. For example, in the RUN condition the period is

actually 100.5 milliseconds, hence each time of sampling

luminescent signals occurs 0.5 millisecond later with respect

to 60-hertz interference. This corresponds to a progressive

phase delay of 0.5 7 I/60 second x 36O degrees, or about 11°

later after eac?i passage of 6 complete cycles (60 cycles per

second x 0.1 second). In approximately 3 seconds all possible

phaslngs have been covered in one full cycle of 3C0 degrees.

Thus if the signal averaging time is made long enough, the

cancellation of hum pickup is relatively complete.

V/hlle the exact operating period of signal sampling is thus

0.1005 second Instead of 0.1000 second, for all practical

purposes the difference results in negligible effect upon the

measured luminescent activity of phosphor standards. For

simplicity of discussion, however , all timings are described

in terms of the CHECK condition, where the period is set to

precisely 0.1000 second.

22
The counter itself employs two type 7^93 integrated

circuits, each capable of countings to 16, or 256 for the

pair in cascade. The circuit dlap-ram is given in Figure 15.

By suitable selection of the binary outputs to produce ANDgated reset signals, the total count is shortened to 200X or

201X for the CHECK and RUN conditions. Other AND gates

generate the delayed timing signals at 0, 9> 10 and 96 milliseconds.

Charts of specific waveforms and other data too detailed for

inclusion in this report are kept on file in the development

laboratory. This Information is available upon request at

any time. Typical signals from the binary counter are noted

in Figure 20 - Test point list.

2.2d(3) Lamp drive

This circuit provides the necessary on-off switching of

current to the pulsed uv lamp. For the 10-millisecond , lampon interval during v/hich the voltage of the input terminal is

zero, a high voltage switching tube is turned on, drawing a current of approximately 10 milllamperes through the lamp.

The equivalent circuit at this time is 58O volts in series

with a resistance of 40,000 ohms. For the remaining 90 milliseconds of the cycle, the tube is turned off, so that the

current through the lamp is then essentially zero.

The circuit diagram is shown in Figure I6, where the input

transistor Q6 and the switch tube VI can be seen. During the

lamp-off time, the lamp drive input from the binary counter

is +5 volts, causing Q6 to be fully conducting. This holds

the control grid of VI at zero volt. Since the cathode of

VI is at +20 volts, with the screen grid at +50 volts, VI is

cut off, so that no current flows through the lamp.

When the input transistor Q6 is cut off by lowering the lamp

drive signal to zero input voltage, the control grid of VI

rises until the grid attempts to become positive with respect

to the cathode, by virtue of the current of approximately 0.15

milliampere flowing through R19. Most of the 3 milllamperes

through R23 and R24 flows in the screen grid circuit, causing

the screen voltage to drop to about 7 volts above the cathode.

During this conducting period the plate voltage is very close

to that of the cathode, bringing the switched side of the

lamp to approximately +25 volts. At the high side of the lamp

there is a combination of zener diodes, amounting to 400 volts

drop, in series with 40 000-ohm resistance. The parameters

in the circuit are chosen to provide reliable lamp starting,

through application of a pulse of sufficiently high voltage

with a resistive ballast capable of damping any tendencies

toward oscillation in the lamp.

23
Associated with the uv pulsed lamp is a keep-alive lamp whose

purpose is to assist further in reliable firing of the main

lamp. current through this keep-alive lamp is approximately

O.lO milliampere, as determined by a resistance of 4.7 megohm

in series with the 1000-volt power supply.

2.2d(4) Sample delay

This circuit provides additional time delay which is added

to the digitally-derived delay period (0,9,10 or 96 milliseconds) from the binary counter. Two ranges are provided,

allowing the addition of up to 11.0 ms in steps of 0.1 millisecond. The output signal is a voltage which goes to +5

volts when the input trigger, as selected by the right hand

dial of the SAMPLE DELAY switch, drops from +5 to 0 volts.

At the end of the additional delay period, the output of the

sample delay circuit drops from +5 to 0, triggering the onset

of the Sample Period circuit which follows. The total combination of delay periods allows v/ide freedom in selecting

the time of signal measurement, all measured from the time

the pulsed uv lamp is turned on.

A diagram is given in Figure 17. The duration of the sample

delay period is controlled by the RC product of Rll and C6

through CI3. These circuit elements are external to the time

delay generator type 74X21 integrated circuit module. Additional

capacitance may be added at this point, increasing the sample

delay by approximately 10 milliseconds per microfarad.

Waveforms for checking input and output are available at TP3

and TP4 respectively.

2.2d(5) Sample period

This circuit sets the time duration of the gating period

during which the PMT output sipjial is accepted for metering.

It is normally set for 50 microseconds. The output is at

approximately -13 volts when not sampling, rising to +15

volts for 50 microseconds during the sample period.

The diagram is included in Figure 17. The circuit uses the

type 74121 delay generator with external resistance and

capacitance RI6 and Cl4, set for 50 microseconds. An inverting

amplifier stage Q4 is employed at the output to supply the

relatively high level required by the following FET switch.

Waveforms for input and output are available at TP4 and TP5

respectively.

24
2.2d(6) Photomultipller tube (PMT)

The function of the PMT is to convert incident uv and visible

energy reflected or emitted from the standards to electrical

current at the tube's anode terminal, Normal maximum output

current is 10 microamperes.

The circuit diagram is given in Figure 18. The photomultipller

tube has a 2-inch (50.8 mm) diameter, flat-faced, end window

with a 4^ millimeter cathode and 11 dynodes of the Venetian

blind type having cesium antimony secondary emitting surfaces.

The cathode is of the S-20 or tri-alkali type, with a spectrosil (fused silica) window. The PMT type designation is

9558QMA.

The housing and shield protecting the PMT also contains the

socket-mounted voltage divider. The dynode voltage increments

in this divider are uniform, including the anode to the last

dynode. Cathode to first dynode voltage, however, is fixed by

a zener diode at 150 volts so that the variation in sensitivity

across the cathode is not changed when the overall PMT gain

is increased or decreased.

2.2d(7) PMT amplifier Al

The function of the PMT amplifier is to provide a high-level,

low-impedance, signal voltage which is proportional to the

PMT current. The output voltage range is from zero to +10

volts, corresponding to a maximum PMT current of 10 microamperes.

The circuit diagram is included in Figure l8, where the basic

element, an operational amplifier is shown. Feedback is

through a one-megohm resistor (R12), in parallel with a capacitance of 22 picofarad (C^). Together these set the high

frequency cutoff to 7 000 hertz in order to minimize noise

response for pulse amplitude measurements. When the Detector

Calibrator is used, it is necessary to average or smooth out

the 120-hertz ripple from the stabilized lamp. Therefore in

the COIITiriUOUS position of the METER sw, a large capacitor

(0.22 microfarad) is added in shunt with the feedback resistor.

This lowers the amplifier bandwidth to 0.7 hertz.

2.2d(8) Integrator

The function of the integrator is to accept the luminescent

signal from the PMT amplifier during the sample period and

to store or smooth out the signal to provide a stable

indication of PMT output. It can also be regarded as a

combination of pulse-stretching and low-pass filtering circuits.

25
The diagram of Figure 18 shows the circuit, with its two

major elements, the FET switch and the integrating capacitor.

During the 50-microsecond sample period the FET switch Q5

becomes a low impedance between its source and drain terminals.

In effect connecting the output of the PMT amplifier to the

0.5 microfarad storage capacitor C5. A resistance of I6OO ohms

(RI5) is inserted in series with the FET switch to limit the

peak current and to assure that the charging and discharging

rates are nearly similar. Between the sampling periods, the

gate of the FET switch is held negative at approximately -13

volts resulting in cutting off the FET switch, so that the

capacitor is then disconnected from the input. Thus the

storage capacitor is connected to the PMT signal for a 50-

microsecond sample period at a repetition rate of 10 times per

second. During the sample period the capacitor charges or

discharges toward the signal amplitude. This charge or discharge is only partial, since the time constant of R15 and

C5 is long, approximately 900 microseconds. When a step

function of input PMT signal is applied, as by opening or

closing the shutter slides, the capacitor voltage rises or

falls with a time constant of approximately 1.8 seconds. The

lengthening of the effective time constant by a factor of

2000 (1.8 f 900 X 10""^) is due to the duty cycle of the sample

period (50** 100 000 microseconds or 1/2000).

No test point is provided for the direct output of the storage

capacitor, since any resistive loading would cause a change

in stored PMT signals. Full scale signal at the capacitor is

+10 volts.

2.2d(9) Meter amplifier A2

This circuit provides isolation of the PMT signal voltage as

stored on the capacitor C5.

The diagram of Figure 18 shows the circuit configuration,

which is an operational amplifier connected as a voltage

follower having high-impedance input. At its output (TP8)

the integrated and stored PMT signals from C5 may be observed.

Full scale is +10 volts. This point is also the source of

signals displayed on the panel Oscilloscope.

2.2d(10) Digital voltmeter

This is 3-1/2 digit voltmeter having one millivolt resolution

up to 2.000 volts maximum. In order to accommodate the 10

volt signal range at the output of amplifier Ap, a 5:1 divider

(Rl^ and RI6) is employed at the input of the digital voltmeter. If for some reason increased sensitivity of the voltmeter by a factor of 5 is desired, the input resistor Rl4 may

be short-circuited. 1,

26
2.2d(ll) Power supplies

The group of power supplies in the Electronics unit deliver

regulated power for the purposes indicated below.

Voltage Current Use

+15 VDC 50 mA Amplifiers A1,A2

+5 VDC - Binary counter

-15 VDC ' 50 mA Amplifiers A1,A2

0 to 2000 VDC 10 mA PMT

0 to 1000 VDC 20 mA Pulsed uv lamp

Supplies delivering unregulated outputs are:

Voltage Current Use

+8 VDC 500 mA Heater for pulsed

uv lamp

-6 VDC 100 mA Heater for pulsed

uv lamp

The wiring diagram for these supplies and their control'

sv/itches is given in Figure 19.

2 . 2e Adjustment of controls in Electronic unit

There are four screw driver-operated controls which must be

adjusted according to specifications for proper operation of

the equipment. The adjustment procedures are covered individually in the appropriate paragraphs below.

2,2e(l) Frequency trim

V/ith the equipment turned on normally and warmed up for at

least 30 minutes:

1) Close the PULSED LAMP shutter by raising the slide

2) Set METER SW to PULSED

3) Remove any standard from sample holder, turn on

room lights.

4) Set SYNC switch to CHECK

5) Increase the sensitivity on the OSCILLOSCOPE until

a pattern with 120-hertz rip{')le can be seen.

27
6) Adjust the FREQ TRIM control with a screwdriver

until the pattern Is stable with respect to the

brip;ht trace dot. Stable is defined as not more

than 2 milliseconds drift in 5 seconds time. If

necessary adjust the intensity of the oscilloscope

beam to make the dot readily visible.

2.2e(2) Delay trim

With the equipment turned on and warmed up for 30 minutes:

1) Close the PMU shutter by raising the slide.

2) Set the left and center SAMPLE DELAY to zero, and

the right hand dial to 10 ms delay. Set the

oscilloscope sweep rate to one millisecond per

centimeter. Note the horizontal position of the

bright dot on the trace.

3) Set the left dial to 10 ms , and the center and

right dials to zero. The horizontal position

of the bright dot should be set with the DELAY

TRIM adjustment so that it coincides within 100

microseconds of the position found in (2) above,

2.2e(3) Zero adjust

With the equipment turned on and warmed up for at least

20 minutes:

1) Close the PMT shutter by raising the slide.

2) Turn the Zero Adjust control for an indication

on the Panel Meter which causes the polarity

display to swing between negative and positive.

The digits will be 000 in this condition.

As a check during operation, the indication should alv;ays

return to either +000 or -000 whenever the PMT shutter is

closed. It is not necessary to readjust the control unless

the indication is more than 001 (negative or positive).

2.2e(4) Sample period

With the equipment turned on and warmed up for 30 minutes:

1) Close the PMT shutter by raising the slide

2) Set all three SAMPLE DELAY dials to zero

28
Adjust the SAMPLE PERIOD control so that the

bright portion of the trace has a duration of

50+2 microseconds as indicated on the

oscilloscope. It may be necessary to reduce

the intensity setting of the beam in order

to observe the bright portion clearly.

29
-Comparator mode-phosphorescent standards3 . 0 Operating procedure. Comparator mode

Operation In the Comparator mode produces indications of relative

phosphorescent or fluorescent activity, permlttinp the comparative

evaluation of phosphor standards of similar type. Quantitative

evaluations of unknown phosphor standards can be performed to the

extent that applicable reference standards of known values are

available. .

In the operating: procedures which are listed below, a uniform

settlinp: time of 30 seconds should be allowed before readings

for standards are taken.

3.1 Comparator mode, phosphorescent standards

1) The first step in the operating procedure is to turn

on the instrument and wait for warm-up. The relevant

controls can be seen in Figure 12, and should be

turned on in the following order:

. OSCILLOSCOPE

, HEATER power

CIRCUIT power

PULSED LAMP power supply

PMT power supply

2) Allow 1[3 to 30 minutes for warm-up. During this

time the following control settings should be made

or checked.

Control Setting

METER SW set to PULSED

SYNC IT tl RUU

SAMPLE DELAY tl " 0 on left dial

" 0. "3 on center dial

" 10 on right dial

It

tl

PULSED LAMP supply tl It 1000 volts

DET, CAL power supply OFF

3) In the Measurement Unit, shov/n In Figure 4, the

following control positions should be or set or

verified

30
-Comparator mode-phosphorescent standardsControl et t Inp;

PULSED LAMP shutter slide down position (open)

PMT II up (closed)

DET CAL II ij up (closed)

FRONT FILTER handle down (uv-pass, attenuator)

REAR FILTER handle down (open)

MASK Phosphorescent mask in place

(one notch at upper ripht)

operating procedure requires the follov/inp: steps:

4) Remove top cover of filter case and REAR FILTER

carriage; then remove any filters and reinsert

the carriage.

5) Lift both FILTER handles by releasinp- the mechanical

stop at the left side. Set to the up position, for

the visible-pass condition.

6) Insert reference standard into sample holder and

turn handle up. This handle must always be down

when a standard is being inserted, and up for

measurement

.

7) Open PMT shutter completely by movinp slide down

to where the handle touches the base.

At this point there should be a rise-and-decay pulse

visible on the OSICLLOSCOPE , as well as a reading

on the DIGITAL METER. Verify that the right hand

switch on the SAMPLE DELAY is in position 10 by noting

that the bright dot in the trace comes near the

start of the phosphor decay.

8) Adjust the PMT voltage control by turning the thumbwheel sv/itches so that the PMT output is less than

10 volts, and that the digital panel meter (DPM) is

less than 2.000 volts. It is desirable to use the

highest PMT voltage that v/ill not produce overload

on the DPM for the highest-valued phosphor standard

in the group to be compared.

31
-Comparator mode-phorescent standards9) With the reference phosphorescent standard in

place, record the indicated output voltagie, allowinp;

approximately 30 seconds for settlinp time.

10) Replace the reference standard with others to be

measured, noting the outp<ut on each standard.

11) Reinsert the reference standard and remeasure for

indication of any drift which might result from

warm-up of the pulsed lamp or PMT.

12) Measure the apparent phosphorescent activity of

Standard IJ2 , which will be very low, since

instrument response to the zero phosphor standards

is very small.

13) Subtract the output of N2 from all other readings

to correct for the small response to the ceramic

wafer base.

1^) Compute the relative phosphorescent activity of

each tested standard v^ith respect to the reference,

then compute new IIBS-Pnu values by multiplying the

relative activity by the known value of the reference.

It is the visible phospliorescent activity (NBS-PMU)

of the reference standard which must be used in the

computat ion .

If drift is evident from a difference in the observed

beginning and ending values on the reference standard,

Interpolate on the basis of the time of measurement

to find the best value of the reference which is

applicable to each measurement on test standards.

15) Compute the nev/ v;orking value by adding the correction

for phosphormeter response to the ceramic wafer base.

Add 1.0 PMU to green phosphor standards and 8.0 to

red. Remove the old label and replace with a new one

with the new I]BS-Pr4TI(T) values. Log and plot the new

data on the appropriate forms.

16) Turn off the equipment when work is completed, using

the reverse of the order indicated in step (1).

32
3 . 2 Comparator mode, fluorescent standards

Fluorescent standards can be evaluated in the Comparator

mode, provided reference standards are available whose

separate red and yellow channel activities have been previously

evaluated. It is recommended that Red Fluorescent and Rackground or Balance Adjust standards respectively be employed

for this purpose. The normal stamped or calibrated rating of

these standards is based upon subtracting a fraction of the

yellow fluorescence from the red. The actual red channel

activity is typically 10 to 20 percent higher than the calibrated

rating of red fluorescent standards. Yellow channel activity

differs even more from the stamped ratings on background or

balance adjust standards. The actual yellow channel activity

may be as high as 10 to 20 PMU on standards whose stamped

ratings are 1 to 2 PMU.

For convenience the entire operating procedure is listed below,

however certain descriptions have been condensed on the

assumption of familiarity with the steps in 3.1 above.

1) Turn on the instrument switches in the follov/ing order,

the same order as indicated previously.

OSCILLOSCOPE

HEATER power

CIRCUIT power

PULSED LAr4P power supply

Prw power supply

2) Allow 15 to 30 minutes for warmup, making or checking the

following control settings:

Control Setting

r^TER SW. set to PULSED

SYMC set to RUIJ

SAMPLE DELAY set to 0 on left dial

"0.5 on center dial

" 9 on right dial II

PULSED LAMP

power supply

set to 1000 volts

33
-Comparator mode-fluorescent standards3) In the Measurement unit, set or verify the following

positions:

Control .Setting

PULSKD LAMP shutter slide down position (open)

Pr4T shutter slide up (closed)

DET. CAL. shutter slide u[) (closed)

FROIJT FILTER handle down (uv-pass, attenuated)

REAR FILTER handle down (open)

MASK Fluorescent mask (two notches)

at upper rlpht

The operating procedure requires the following steps:

4) Remove REAR FILTER carriage, insert the red channel

Fl filter Into the VIS. position, with the

engraved lettering at top, facing the sample holder.

Reinsert carriage into filter 'case and replace cover.

5) Lift both FILTER handles to the up position, for the

visible-pass condition.

6) Insert reference standard into sample holder and turn

handle up.

7) Open PMT shutter by moving slide down.

Signal and readings should be visible on f)anel. Verify

that SAMPLE DELAY Is at 9.3 milliseconds total, with the

trace dot coming during the uv pulse, near the end.

8) Adjust PMT voltage for high-level signal without overload

on highest standard to be tested.

9) With the reference fluorescent standard in place record

the indicated output voltage.

10) Replace the reference standard v/ith others to be measured,

noting the output from each.

11) Reinsert the reference standard and remeasure for drift

indication

.

1?) Measure the zero phosphor standard !J2.

34
-Comparator mode-fluorescent standards13) Multiply the output from N2 by 1.5 and subtract it

from all other output readings. Note that this

multlplyinp^ factor Is required only for fluorescent

standards v/here the wafer size is 50 per cent larger.

14) Compute the relative fluorescent activity of each

tested standard with respect to the reference, then

scale appropriately to find NBS-PMU values. Observe

caution that appropriate red and yellow channel

reference evaluations are used in the computations.

Take observed drift, if present, into account by

interpolation.

15) For fluorescent standards it is necessary to measure

and compute the IJBS-PMU value for both red and yellow

channels. It is therefore necessary to perform the

above procedure with the red PI filter and then repeat it with the yellow Bl filter. Therefore it is

necessary to go back to step (4) closing the PMT

shutter before replacing the filter.

16) Compute working values by subtracting the results of

the yellow channel readings in PMU from those of red

channel measurements. Label the phosphor standards

with the new NBS-PMU (T) values, removing old labels

as needed. Log and plot the new data on the appropriate forms.

17) Turn off the equipment v/hen work is completed, using

the reverse of the turn-on procedure.

35
-Calibrator mode-phosphorescent standards-

^ . 0 Operating procedure. Calibrator mode

This mode of operation results In evaluations of phosphor standards

without direct comparison with known reference standards. It can

be used to monitor the behavior of standards, includinp reference

standards, over an extended period of time. In the Calibrator mode,

evaluation of phosphor standards is referred to measurements of the

relative spectral irradiance from a standard tungsten-halogen lamp

in the ultraviolet and visible spectral regions. The procedure is

identical for green and red phosphorescent standards except that the

computations require different values of parameters.

When operating in the Calibrator mode, there is considerable detail

work which must be performed regardless of the number of standards

to be measured. Hence it will be found desirable to measure phosphor standards in batches. It is also recommended that reference

standards be included in the measured group whenever possible, to

provide data on standards and system performance.

^ . 1 Calibrator mode, phosphorescent standards

;. The detailed procedure is described below. While familiarity

with the operation as outlined previously is assumed, all of

the necessary steps are listed. Sample data sheets are shown in

Figure 23.

The operating procedure begins with turning on the equipment

in the order given and waiting for warm-up.

1) Turn on OSCILLOSCOPE

" " HEATER power

" " CIRCUIT power

" " PULSED LAMP power supply

" " PMT power supply

- 2) Allow 15 to 30 minutes for warm-up. Make or check

the following control settings:

Control

METER SW

SYNC

SAMPLE DELAY

PULSED LAMP supply

DET. CAL. power supply

Setting

set to PULSED

" " RUN

" " 0 on left dial

" " 0.5 on center dial

" " 0 on right dial

" " 1000 volts

" " ON

36
Calibrator mode-phosphorescent standardsIn the Measurement Unit, set or check the following

control positions:

Control Sett inp

PULSED LAMP shutter slide down position (open)

PMT " " up (closed)

DET. CAL.- " " up (closed)

FRONT FILTER handle down (uv-pass, attenuator)

MASK Phosphorescent mask in place

(one notch at upper right)

Take off cover of filter case, remove REAR FILTER

carriage, remove any filter(s), reinsert carriage

and replace cover. Put both FILTER handles in down

position.

Open PMT shutter by moving handle down

Insert barium sulfate reflectance standard in sample

holder

At this point a pulse signal should be visible on the

OSCILLOSCOPE as well as a reading on the DIGITAL METER.

The bright dot in the trace should be at the top and

near the start of the visible pulse.

Adjust the PMT supply voltage to produce an indication

of approximately 1.700 on the panel meter.

Record the indicated PMT output for this time sample

(0.5 millisecond). Note also the time of day at which

the observation was made.

Advance the sample delay to 1.5 milliseconds by

turning the left hand control to 1 millisecond. Record

the output for this sample delay.

Advance the left hand control in sample delay to the

next position (2 milliseconds), recording the observed

indication. Repeat this procedure until the last

sample at 9.5 milliseconds has been recorded. Then

note the time of the observation. This completes the

measurements necessary to determine the effective uv

pulse as reflected from the barium sulfate standard.

Remove the reflectance standard and insert the phosphorescent standard to be tested.

37
-Calibrator mode-phosphorescent standardsIB) Lift both FRONT and REAR FILn:R handles to the up,

or visible-pass, condition.

IH) Set the center and right controls in SAfiPLE DELAY

to a total of 10.5 milliseconds. Set the left

control to zero.

15) Record the indicated output for the tested standard,

noting also the time of day for the first standard.

16) Repeat for other standards in the test group. Usually

it will only be necessary to note the time for the

first and last standards in a group. It is recommended

that several reference standards also be included

in the test group.

17) Measure also the Zero Phosphor standard 112 or its

designated equivalent.

18) Go back to step (4) and repeat throguh step (11) in

order to measure the uv pulse amplitude. When a

large number of standards is to be calibrated (five

or more) this measurement of the uv pulse should be

performed every 15 or 20 minutes, unless experience

shows negligible drift. Do not change PMT supply

; voltage during these measurements involving the phosphor ratios

.

At this point the data have been taken from which the Phosphor

ratios can be determined. The next phase is to measure the

Detector ratio.

19) In the Measurement unit, set or check the controls

as follows:

Control Setting

PULSED LAMP shutter slide set to up (closed)

PMT " " " " up (closed)

DET. CAL. " " " " up (closed)

FRONT FILTER handle " " up (visible-pass)

REAR FILTER handle " " up

20) In the Electronics unit:

METER SW set to CONTINUOUS

21) In the Detecotr Calibrator Unit, set or check:

LAMP POSITION : pointer at 90 cm on scale

38
-Calibrator mode-phosphorescent standards22) Insert DET. CAL. FILTER narked 5^6 nm (221.12)

into holder in Detector Calibrator, to pass only

5^6 nm line from the internal calibrated lamp, Make

sure that filter is located in rear of holder, as

far toward the lamp as it will p-o,

23) Insert barium, sulfate reflectance standard No. 27

into sample holder.

2^) Open DET* CAL. and PMT shutters by movinr slides

down to base.

25) Observe indications on DIGITAL F^TEP. Increase PM^

voltage if necessary to brinp: readinfr to approximate

1.800 + 0.100 volts.

26) Record PP-T output for 5 nm radiance from the

Detector Calibrator.

27) Close DET. CAL. shutter by raisinp- slide, chanpe

DET. CAL. FILTER to uv-pass element desirnated

25^ nm (411.0^4), open DET. CAL. shutter.

28) Lower both PROIIT and RI^AR Filter handles, for uvpass conditions.

29) Record PI^ output for 25^ nm radiance from

Detector Calibrator.

This completes the measurement phases involved in the calibra

tion of phosphor standards. Turn off the DET. CAL. power

supply to conserve lamp life.

The next phase is the computation of efficacy, the visible

phosphorescent activity of the tested standards.

30) Subtract the measured value for the ZERO phosphor

standard IJ2 from all readinf^s of phosphorescent

activity derived in steps (15) and (l6).

31) Compute the effective uv pulse amplitude by multiplying the measured values fromi steps (9) through

(11) by the follov/ing constants.

39
-Calibrator mode-phosphorescent standardsDelay time Multiplier for Multiplier for

milliseconds green stds. red stds.

0.5 0.11 0.5^1

1.5 .13 .56

2.5 .15 .58

3.5 .18 .61

^ ^.5 .22 .65

5.5 .26 .68

6.5 .33 .72

7.5 .^2 .76

8.5 .56 .82 9.5 .81 .90

Divide the sum of

weighted products by 3.17 6,82

Perform this computation for the effective uv pulse

amplitude as applicable to ^reen and red. If an

observable drift is evident (more than 0.5 percent)

Interpolate to determine appropriate values to be

assigned to the measurements of phosphorescent

activity in steps (15) and (16).

32) Compute Phosphor ratios for all tested standards,

dividing the results of step (30), phosphorescent

emission, by those from (31)> weighted uv excitation.

33) Compute the Detector ratio by dividing the results

of step (29), response to uv from Detector Calibrator,

by (26) response to visible light from Det. Cal.

34) Compute Efficacy as the product of:

Efficacy = (Phos. ratio) ( Pet . ratio) ( 0 . ] 570) (0.976)

for green phosphorescent standards, and

Efficacy = ( Phos . rat io )( Det . rat io )( 0 . 1570 )( 0 . 976

)

(0.6iJl)

^ for red phosphorescent standards

35) Compute MBS-PMU v;ith the following conversion

constants

:

MBS-PMU = Efficacy x 10 583 for green phos. stds.

" = " 9 771 " red "

"

Ho
-Calibrator mode-phosphorescent standards36) Compute working USPS PMU values by adding 1.0

to the above for green standards, and 8.0 for

red. Label the phosphor standards with the

NBS-PMLJ(T) values and the date in month and

year, removing old labels as needed. Log and

plot the new data on the appropriate forms.

37) Turn off the equipment in the reverse of the

order indicated in step (1).

41
i\ . 2 Calibrator mode, fluorescent standards

The operating procedure begins with turning on the equipment

in the order given and waiting for warm-up.

1) Turn on OSCILLOSCOPE

" HEATER power

" CIRCUIT power

- ; • " PULSED LAMP power supply

" PMT power supply

2) Allow 15 to 30 minutes for warm-up. f'ake or check

the following control settings:

Control Setting

METER SW set to PULSED

' ' SYNC " RUN

SAMPLE DELAY " 0 on left dial

" 0,5 on center daal

" 9 on right dial

PULSED LAMP supply " 1000 volts

DET CAL power supply " ON

3) In the Measurement unit, set or check the following

control positions:

PULSED LAMP shutter slide down position (open)

PMT " " up (closed)

DET CAL " " up (closed)

FRONT FILTER handle down (uv-pass, attenuator)

(two notches at upper right)

4) Remove REAR FILTER carriage, insert the red channel

Fl filter into the VIS position, with engraved

lettering at top, facing the sample holder. Reinsert

carriage and replace cover. Lower both FILTER

handles

.

5) Open PMT shutter by moving handle down.

6) Insert barium sulfate reflectance standard in sample

holder.

42
-Calibrator mode-fluorescent standards7) A pulse signal should be visible on the OSCILLOSCOPE

as well as a reading on the DIGITAL METER. Verify

that the bright dot in the trace is at the top of the

pulse, near its end.

8) Adjust PMT supply voltage control to produce an

indication of approximately 1.700 on the panel meter.

9) Record the Pi^T output. Note also the time of the

observation.

10) Raise both FILTER handles to the visible-pass

condition.

11) Remove barium sulfate standard, replacing with those

to be measured, noting the output from each in the

appropriate log form. It is desirable to include one

of the reference red fluorescent standards with the

group to be measured.

12) Measure also the Zero Phosi^hor standard N2 or its

designated equivalent.

13) Remeasure the uv pulse amplitude by going back to

steps (6) (7) and (9). It will first be necessary

to lower the FILTER handles to the uv-pass,

attenuator, condition.

At this time the data have been taken from which Phosphor

ratios for the red channel can be determined. The next phase

is to measure Phosphor ratios for the yellow channel on the

same standards.

1^) Go back to step (4) and replace with the yellow

channel filter Bl, first closing the PMT shutter

slide. If more than 15 minutes have elapsed since

the last reading of uv pulse in step (13), repeat

the uv pulse measurement indicated in steps (6)

(7) and (9) before beginning the series of tested

standards. Do not change PMT supply storage.

I'j) Repeat the measurement steps (10) through (12)

with the yellow channel filter in the PMT filter case.

16) Repeat step (13) to produce the final uv pulse

amplitude, then continue below.

43
-Calibrator mode-fluorescent standardsAll data have now been taken for the Phosphor ratios in both

the red and the yellow channels. The next phase is to measure

the Detector ratio.

17) Close the PNT shutter slide by moving it up.

18) Remove the REAR FILTER carriage and extract the

filter. Reinsert carriage and replace cover.

' 19) In the Measurement unit, set or check the controls

as follows:

PULSED LAMP shutter slide set to up (closed)

PMT " " " up (closed)

DET CAL " " " up (closed)

FRONT FILTER handle " up (visible pass)

REAR FILTER " " up

20) In the Electronics unit:

METER SW set to CONTINUOUS

21) In the Detector Calibrator unit, set or check

LAMP POSITION pointer at 90 cm on

scale

22) Insert DET CAL FILTER marked 5^6 nm (221.12) into

holder in Detector Calibrator, to pass only 5^6 nm

line from the internal calibrated lamp. Make sure

that the filter is in the rear end of the holder,

as far toward the lamp as possible.

23) Insert barium sulfate reflectance standard F? into

sample holder.

2^]) Open DET CAL and PMT shutters by moving the slides

down to the base,

25) Observe indications on DIGITAL METER. Increase PMT

voltage as required to bring reading to approximately

1.800 ±0.100 volts.
-Calibrator mode-fluorescent standards26) Record PMT output for 5^6 nrn radiance from the

Detector Calibrator.

27) Close DET CAL shutter by raising slide, change DET

CAL FILTER to uv-pass element designated 25^ nm

(^11.0^), then open DET CAL shutter.

28) Lower both FRONT and REAR FILTER handles, for uvpass condition,

29) Record PMT output for 254 nm radiance from

Detector Calibrator.

This completes the measurement phases required in the calibration of fluorescent phosphor standards. Turn off the DET

CAL poiver supply to conserve lamp life. The next phase is the

computation of efficacy in the red and yellow channels.

30) T'lultiply the measured value for the 7ero phosphor

standard n2 by 1,5 and subtract from readings of

red-channel activity for all tested standards. Do

the same for the yellow channel outputs, using the

measured value of the yellow-channel for the N2

standard.

31) Determ.ine the effective uv pulse amplitude applicable

to each tested standard, interpolating according to

time of measurement if observed drift is more than

0.5 percent between initial and final values.

33) Compute Phosphor ratios for all tested standards,

dividing the results of step (30) fluorescent

emission, by those from (31)> uv excitation.

33) Compute the Detector ratio by dividing the results

of step (29), response to uv from Detector Calibrator,

by step (26), response to visible light from Det. Cal.

34 ) Compute efficacy separately for each tested standard

in the red and yellow channels as the product of:

Efficacy = (Phos. ratio)(Det. ratio) (0. IS70) (0.9^8)

(1.000)

35) Compute NBS-PMU separately for red and yellow channels

as

NBS-PMU = Efficacy x 8506 for red channel

" " X 930 " yellow "

45
-Calibrator mode- fluorescent standarcis36) Compute working PMU values by subtracting^ the

yellow from the red chiannel values of MBS-PMU:

HBS-PMU(T) = NBS-PMU (red channel) - lIBS-Pr4U (yellow

channel)

Remove old labels.

Label fluorescent standards with tlie nBS-PMU(T) values

and the date in month and year. Lop and plot the new

data on the appropriate forms.

37) Turn off the equipment in the reverse of the order

indicated in step (1).

i|6
5 . 0 Components

5 . 1 Five-year spare parts list

Certain of the components given the complete list in Section

5.2 are considered necessary for a five year maintenance

program. These are identified in the list of five-year spare

parts below, and have been set aside for contingency.

Item Quantity used

Quantity retained

as spares

Transistors

2N2219

2N3638

2IJ364 3

2N^^222

Integrated circuits

7400 2

7421 1

74121 2

7493 2

Operational amplifiers

40J.

Voltage regulator

MA7805

Vacuum tube

^CDf)

Diodes

1N4005

1N4747

1N4751

1IJ4764

Pulsed uv lamp 3

The remaining components are in common use and aside from the

complete units, are available from the NBS or other electronic

storerooms

.

47
5 . 2 Complete parts list

The following: is a list of the parts in the P^lectronic unit.

In keepinf^ with the policy prohibiting: the use of proprietary

names in agency reports, insofar as possible the components

are described in terms of technical characteristics. For the

few cases in which this is not feasible the descriptions are

supplemented by a separate list of manufacturers.

Resistors

Rl 10 000 ohms, 5/^ tol., 1/^1 watt

R2 8 100 " " " R3 2 200 " " " r4 2 200 " " " R5 22 000 " " " R6 2 200 " " " R7 100 000 " " "

. R8 ' 220 000 " " " R9 10 000 " " " RIO 470 " " " Rll 2 ^00 ohms, potentiometer, linear taper

R12 1.0 megohm 5^ tol., 1/4 watt

R13 100 000 ohms Sf' tol., 1/4 watt

R14 30 000 " "

" R15 1 600 " " " Rl6 25 000 " potentiometer, linear taper

R17 500 " 5/^ tol., 1/4 watt

Rl8 13 000 " "

" R19 51 000 " 10% Tol., 5 watts

R20 40 000 " "

" R21 1.0 megohm, 10% tol., 1/2 watt

• 1^22 1.0 " "

" R23 150 000 ohms " 2 watt

R24 150 000 " " " R25 4.7 megohms "

" R26 200 000 ohms 'j% tol., 1/4 watt

R27 200 000 " "

" R28 20 000 " 1% tol., 1 watt (wire wound)

R29 5 000 " " " "

Capacitors

01 0.0068 microfarad

C2 0.002 " C3 0.002 " C4 22 picofarad

C5 0.5 microfarad (polystyrene)

48
Capacitors

C6 0.1 microfarad, 5^ tol.. 200V

C7 0 .

2

II II It C8 0 .

3

II II II

C9 11 11 It

CIO u . U J.

»f 11 II C 11 U . U

n II II Clt: U . (J J

n It It C13 0.0^ It It 11 C14 0.0069 ti 10^ It C15 0.1 tt 20^ 50V

Cl6 50 II 15V

017 50 11 15V

Cl8 2000 11 15V

(0.1

(0.2

0.2 in

shunt

)

0.2 in

shunt

Transistors

Ql

02

Q3

Q5

Q6

2N 3638

2N 36i^3

2N 3643

2N 36^13

QN 4222 (FET)

QH 2219

Integrated circuits

Ul

U2

U3

U4

U5

U6

U7

7493

7493

7400

7400

7421

74121

74121

4-bit Binary counter

It It n Quad 2-Input Gate

II 11 It Dual 4-Input Gate

Monostable multivibrator

II II

Operational amplifiers

A1,A2 Type 40J, FET input, lOV at 5 mA output

4 r4Hz bandwidth, high input impedance

Voltage regulator

VRl

Tube

VI

MA7805, 5V, 500 mA

6CD6 Beam power amplifier

49
Diodes

Dl

D2

D3

D5

D6

D7

d8

D9

DBl

Lamps

Nl

U2

1N^005

lOOV, 10^ tol. 1 watt, Zener

11147^7

1N4 751

1M4005

IIn

II 20V

30V

MDA 920A-7 diode bridge, lA

NE 51 neon lamp

II II II

Transformers

Tl

Complete units

RT-202 18 VAC, center-tapped, l.OA or greater

T-21 6.3 VAC, center-tapped, l.OA or greater

Digital Voltmeter 0 to 1.999 VDC in steps of one

millivolt, input impedance greater

than 1 G

Power Supplies + 15

VDC

2000 VDC

1000 VDC

Oscilloscope

Stabilized uv lamp

Pulsed uv lamp

+ 15 VDC at 50 mA , 0.1^ regulation

0 to 200 VDC at 10 mA, 0.05^

regulation

0 to 1000 VDC at 20 mA, 0.1^

regulation

5 inch dia. CRT, freq. response

0 to 500 kHz, z-axis modulation,

panel mounted

Stabilized low pressure mercury

vapor source 25^ nm primary

emission, with regulated power

supply and temperature-controlled

lamp chamber

Type SPR-3 3, low pressure mercury

vapor source in quartz envelope,

diameter approximately 0.25 inch,

length 2 inches (6.3 x 51 mm)

50
Photomultlplier tube Type 9558 QMA, with 2-lnch (51 mm)

diameter, flat faced, end

window of fused silica.

Cathode diameter ^.4 mm, S20

or tri-alkali type. Elevenstage, Venetian-blind electron

multiplier of cesium antimony

surfaces. Mounted in magnetic

shield including socket and

voltage divider.

Manufacturers' data sheets and instruction manuals as

applicable have been assembled in a file for retention along

with the five-year spare parts.

51
5.3 List of Mechanical Drawings (In separate package)

Phosphor Standard Calibrator

No. Drawing

1 Overall Layout (not a working drawing)

2 Base and Top

3 Cover, Sides, Front

4 Baffles, Universal, & Parts

5 Front Baffle

6 PC Baffle

7 Sides of Filter Holder

8 Filter Carrier, Parts

9. Latch for Filter Handle

10 Front, Back for Filter Holder

11 Body for Dark Slide

12 Dark Slide

13 Mount for UV Lamp

14 Dark Slide for Lamp

Housing for UV Lamp, Parts

IS . Back Plate, Lever for Sample Holder

17 Front Plate, Mask for Sample Holder

18 Base Plate, Spacers

19 Dark Slide for Calibrator

20 Filter Shield (not used)

21 Parts for PMT Mount

22 Baffle Plates

23 UV Filter Holder

24 Parts for Light Shielding

25 Light Shield for Sample Holder

26 Flat Sample Holder

27 Sketches, Detector Calibrator

28 Bottom, Upper Plate, Det. Cal.

29 Sides and Ends, Det. Calibrator

30 Brace

31 Assembly of Tunnel Section, Det. Cal.

32 Overall Base

33 Small Tunnel for Detector Calibrator

34 Cover Plates for Det, Cal,

35 Baffle Plates for Det. Cal.

36 Parts for Lamp Cradle

37. Cover Plate, Etc. for Det. Cal.

38 Label Parts for Phosphor Standards

39 Cover, Parts, for UV Lamp

40 Filter Holder, Handle

41 Scale for Detector Calibrator

42 Baffles for Small Tunnel

52



REAR PMT FILTER HANDLE

(shown raised)

FRONT PMT FILTER HANDLE

(shown lowered)

FIGURE 4 MEASUREMENT UNIT
w

pqM

COMQMH

Pi<:

2:ww

113 <:wo

13O

Piw

Pi

1=) OM

P4

WH

<;

hj

(X, Ho

Pi

CM

wH-< > J

P^W

w

PiH

Pi P^ <
i-J M

Q
H<



I
INTENSITY

CONTROL

OSCILLOSCOPE

VERTICAL

GAIN

HORIZONTAL

SWEEP

RATE

CALIBRATION

CONTROLS

SYNC

SWITCH

s-'H<>y!-^>iOK STAfiOAsy j:,^i.i«J>A(i>fj

CIRCUIT

SWITCH

LAMP

HEATER

SWITCH

DIGITAL

PANEL

METER

METER

CIRCUIT

SWITCH

SAMPLE

DELAY

SWITCHES

PMT

POWER

SUPPLY

PMT

VOLTAGE

ADJUST

PULSED

LAMP

SUPPLY

LAMP

VOLTAGE

ADJUST

FIGURE 12 CONTROL PANEL OF ELECTRONICS UNIT

OSCILLATOR

FIGURE 14 DIAGRAM OF OSCILLATOR
CJ5
FIGURE 16 DIAGRAM OF LAMP DRIVE
LO

to

C5

CO

CO

ct: CI5

1 CO

NOTE - OTHER POUER SUPPLIES COHHECTEO DIRECTLY TO LINE OUTLETS

FIGURE 19 DIAGRAM OF POWER WIRING
Test Point List

Displayed Signal

Oscillator output

Pulsed lamp drive

Sample delay (digital)

Sample delay (analog)

Sample period

Sample period (gate)

PMT output

Integrator output

Source of V/aveform

Description

Sect

2. 2d(l), Fig. I'n

Sect2. 2d(2), Fig. 15

Sect2. 2d(2), Pig. 15

Sect

2. 2d(i|), Pig. 17

Sect. 2. 2d(5) , Pig. 17

Sect. 2. 2d(5), Pig. 17

Sect2. 2d(7), Pig. 18

Sect

2. 2d(8), (9), Fig.

FIGURE 20 TEST POINT LIST
O -J H Q

td Ed ^ CO

pq

J < P O p., Q

OS > o 3 HU Q w w 2 OS O 3 O PL,

PQHuHM

ISW3

w E-H ; i H M i I ©

C oM

H

2:

M o D

Pi

u

H OS

C_3

M

hJ

WQM>MQWHO>

h4

M PL, Q

if1 i I i

C/2

C/2 uMZo

PiHuw

hJ \

CJQ> W

h-l hJ

PL, o

PL, 2OMH<oH

EdOSou

Lab. No Sheet No. Dote _lh±ll

Ti"w\e

1

R fP. (^) (10) X

0.157

0) (7;

10 \o 0. ^ in . K

I. 6"

1. 6g3 .21 ^^g'

2 . 5"

.

3. b'

• 21

1. foil lb .H317

33

I.CH7 .

. ?' 1.334 r

3.11

'

.202 .00Zi2.

.0134 ,00 1.14

21 .33S' . 204 .6 i36 .001(4

23 ,32^ .0 i3l .00\07

.34M .340 .10 .0(37 .OOlli'

33!'' .107 .0133' .ooi\l

iG -34^ ,0140 .60210

n .M^ .207 00 2.17

.3H3 .101 ,0011''

\0 \^ .3H3 ,3i^ .013^ .oouH

NBS Form 254 _ Log Sheet. U S C OMM-N B S- D C FIG. 23 SAMPLE DATA SHEET (Sheet 1 of 3)
Lab. No Sheet No ^ Dote ^'A/^^

^l^^Ae 1 nstr

coe-f-f- z er;

R R. (3) ^

D, R- (lO) /

O.li'l

(0 C\0

/, 6 if? .20 5'' .0137 .00

G HI .135- .13/

10 3Z N2

10 F21

1. ^

.^"^

(. s ?

Lb'

i.K/

10 3b

1

= L^i ;

IO?>i 10.5 UITI i(,h . \00 .ooiof

R 20 cm (>oi

ci"or Ci)/\JT

• 113 0. - p.

NBS Form 254 - Log Sheet. U S C 0 M M- N B S- D C FIG. 23 SAMPLE DATA SHEET (Sheet 2 of 3)
Lab. No Sheet No. ^ Dote ^j^'h"^

{Lj* \Dlsa

Greedy C3j + I.O

(0 a) (4,-'

G If? .00

• OOli'^ 21.0

Vl -0 23.0

Z3 .60101 l>-3 21.3

Zf 001i{ 22.

1

ir OOl^l 11 ,?

Z<b OOIZO 12. 4» 13.

i

n ooin 12.3

,001/7 12,3 2S,3

002.17

13,'

RMS'? 23.

t

iH.o 12 ,0

NBS Form 254 _ Log Sheet. U S C 0 MM-N B S- D C FIG. 23 SAMPLE DATA SHEET (Sheet 3 of 3)

N8S-n4A (REV. 7-73) U.i DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR TJ+-552

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE .\ND SUBTITLE

Technical Manual for Phosphor Standards Calibrator

5. Publication Date October 197^

6. Performing Organization Code

7. AUT^Rtg) Greenough, H. K. Hammond, III 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U.S. Postal Service

Planning and New Development Dept.

11711 Parklawn Drive

Rockville, Md. 20852

13. Type of Report & Period Covered

Final Report 7/72-9/74 j 14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary o( most sigpilicant information. If document includes a significant

bibliography or literature survey, mention it here.) • This project involved two activities, 1) the fabrication and calibration of phosphor

standards for use in the Postal Service Model 4A8 Phosphormeter and 2) the construction

of an instrument to perform the calibration function. Both of these relate to standarization of the phosphorescent and fluorescent activity of the luminescent coating

applied to postage stamps by the Bureau of Engraving and Printing. The purpose of the

luminescent coatings is to facilitate detecting the orientation of envelopes in facercanceler machines during mail processing.

Work on the project entailed the fabrication of approximately 60 phosphor standards,

which are hand-sized aluminum blocks into which stamp-sized wafers of luminescent

materials are mounted. Fabrication was carried out following the specific procedures

supplied by the Postal Service, with however, authority to verify or alter the process

as necessary. On the other major project effort, an instrument was designed and constructed following in general the basic design of an earlier breadboard device developec

under a prior project. In the system, quantitative evaluations are ultimately referred

to calibrations at MBS of the relative irradiance of a lamp in the ultraviolet and

visible regions of the spectrum.

This report, one of two covering the project, is in the form of a technical manual for

the calibration instrument, and includes theory of operation, mechanical construction

and detailed operating procedures.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Fluorescence measurement; Instrvimentation, Itiminescence measuring;

Luminescence measurement; Phosphorescence measurement

13. AVAILABILITY Unlimited

i For Official Distribution. Do Not Release to NTIS

1 "Order From Sup. of Doc, U.S. Government Printing Office Washington. D.C. 20402. SD Cat. No. CH

! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

8k

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

USCOMM-OC 29042-P74

i

I

1