NBSIR 74-580

Spectral Characteristics of

Additional Bar Code Readers. II

Julius Cohen

Electronic-Optical Development Section

Measurement Engineering Division

Institute for Applied Technology

September 1974

Supplemental Report

Prepared for Office of Postal Technology Research

U. S. Postal Service

Rockville, Maryland 20852

NBSIR 74-580

SPECTRAL CHARACTERISTICS OF

ADDITIONAL BAR CODE READERS. II

Julius Cohen

Electronic-Optical Development Section

Measurement Engineering Division

Institute for Applied Technology

September 1974

Supplemental Report

Prepared for Office of Postal Technology Research

U. S. Postal Service

Rockville, Maryland 20852

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

SPECTRAL CHARACTERISTICS OF ADDITIONAL BAR CODE READERS. II

1. Introduction

This report deals with the measured spectral characteristics of

two bar code readers submitted by the U.S. Postal Service Laboratory

under Task No. 1, Agreement No. 74-02934 (Mod. No. 1). The readers

shall be identified here as Reader No. 1 and Reader No. 2 as listed in

the Task Statement. Two auxiliary filters, a yellow and a dark red,

were supplied with Reader No. 2.

The present work is an extension of previous work at NBS, and

details of the experimental approach and procedure have been reported

in "Spectral Characteristics of Bar, Half-Bar Code Readers, Final

Report" [1]. This report is Intended to be supplementary to the

former.

2 . Obj ective

The objective is to measure the relative spectral output as a function of wavelength in the interval of approximately 450 to 1200 nm.

3. Experimental Procedure and Apparatus

Radiation emitted from an incandescent tungsten-ribbon filament

passes through (1) a limiting aperture; (2) a calibrated, continuously

variable filter, or wedge; (3) a discrete bandpass filter(s) (to

suppress undesired orders), and finally impinges upon the photodetectors

.

The photodetectors are then replaced by a thermopile and the measurements

repeated. The ratio of photodetector-to thermopile signal is the

relative response of the former. The product of the relative response

and the relative spectral radiance of the reader's lamp filaments is the

relative spectral output of the system.

The present experimental procedure is similar to that previously

described [1], but a few changes were made in the measurement apparatus

and precedure:

1. The limiting circular aperture was replaced by a narrow

slit of reduced width for high spectral purity;

2. An improved calibration of the optical wedge was obtained

with the aid of newly acquired filters used for blocking

unwanted orders. Table 2 of the Appendix lists the

supplemental blocking filter (s) selected for use at

various wavelength intervals;
2

3. A more efficient thermopile shroud, with integral filter

box for discrete filters, was used for exclusion of stray

thermal and optical radiations;

4. The operating temperature of the reader's lamp filament was measured in situ with an optical pyrometer, and the observed

temperature converted to so-called true temperature by making

a correction for spectral emissivity [2]. The relative

spectral radiance of the lamp was obtained from a knowledge

of lamp filament operating temperature [3].

Although Reader No. 2 was supplied with two auxiliary filters,

a

yellow and a dark red, the spectral output of this reader was determined

without the use of these auxiliary filters. However, the transmittance

of each filter was measured with a spectrophotometer over the region

of 450 to 1080 nm; cf Table 4, columns 8 and 9. The product of the

spectral output of the reader (unmodified) and the transmittance

yielded the spectral output of the reader with auxiliary filter.

3 . Results

Figures 1 and 2 are plots of normalized relative spectral outputs vs. wavelength, for Readers No. 1 and 2. Spectral outputs obtained with (1)

the wedge-blocking filter combination, and (2) the narrow-band interference

filters are shown, and their agreement is seen to be close. The spectral

outputs of the readers are seen to be similar. Figure 2 shows also the

spectral output which would be obtained if the auxiliary yellow or dark red

filter, provided by the U.S.P.S., were used.

The wavelength at which the spectral output peaks, and the wavelengths

at which the spectral output is 50% of the peak are tabulated below.

Table 1. Summary of relative spectral output

Reader No. Wavelength at Peak, 50% Wavelengths at response

nm nm

1 850 650; 1015

2 850 635; 1000

2 with yellow

filter 660 575; 745

2 with red

filter 860 720; 1000

The measured data, arranged sequentially for calculation of spectral

output, are given in Tables 3 and 4 of the Appendix.
3

Appendix

This Appendix consists of three Tables, as follows:

Table 2 lists the supplemental filters used to block the

undesired orders transmitted by the wedge.

Table 3 contains the measured data and intermediate calculations

used to determine the spectral output of Reader No. 1. Similar

information for Reader No. 2 is given in Table 4.
Table 2. Supplemental filters used with wedge

Wavelength

nm

interval

,

Filter No.

450 - 580 CS 4-96 and CS 1-69

600 - 720 CS 3-68 and CS 1--69

740 - 1100 CS 7-69
5

j Table 3. Computation of spectral characteristic of Reader No. 1

(1) (2) (3) (A) (5) (6) (7)

Wavelength, Detector Thermopile Ratio Source System System

nin reading T" p P d 1 n P (2) TP 1 a f 1 VP ciTipr* 1" TP 1 arbitrary arbitrary (3) radiance output output

units units (T=2620K) (relative) (normalized)

Wedge data

1 450 0.010 0.118 0.085 0.272 0.023 2.5

520 .064 .30 .21 0.682 .14 15.4

580 .028 .11 .25 1.177 .29 31.6

600 .21 .705 .30 1.361 .41 43.8

620 .24 .77 .31 1.552 .48 51.7

640 .26 .825 .32 1.747 .56 60.0

660 .27 .84 .32 1.942 .62 66.7

680 .27 .84 .32 2.136 .68 73.5

700 .25 .80 .31 2.328 .72 77.6

720 .22 .74 .30 2.514 .75 81.0

' 740 .39 1.28 .30 2,694 .81 86.8

760 .41 1.46 .28 2.866 .80 86.1

780 .41 1.48 .28 3.030 .85 91.1

810 .40 1.45 .27 3.256 .88 94.4

860 . 37 1.41 .26 3.581 .93 100.0

900 .31 1.35 .23 3.791 .87 93.7

940 .26 1.26 .20 3.956 .79 85.0

960 .21 1.18 .18 4.023 .72 77.8

1

. XX u . OU . Xj /i 19 7 J / . / 1020 .080 .70 .11 4.164 .46 49.2

. \j J-/ . U / X H • X7 J . -5U . u

j 1060 .015 .295 .051 4.213 .22 23.1

1080 .006 .186 .032 4.226 .14 14.5

1100 .003 .105 .029 4.231 .12 13.2

Filter data

450 0.020 0.17 0.12 0.272 0.033 3.5

520 .087 .48 . 18 0 . 682 1 2 580 .093 .338 .28 1.177 .33 35.5

700 .75 2.20 .34 2.328 .79 85.1

810 1.14 3.98 .29 3.256 .94 101.4

900 0.68 2.90 .23 3.791 .87 93.7

1000 .31 2.45 .13 4.127 .54 57.7
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References

Greenough, M. L., et al, "Spectral Characteristics of Bar,

Half-Bar Code Readers, Final Report, NBS Report 10 943,

October 1972).

"Handbook of Chemistry and Physics," 44th ed. , p. 3098

(The Chemical Rubber Publishing Co., Cleveland, Ohio, 1962-1963).

Pivovonsky, M. , and Nagel, M. R. , "Tables of Blackbody Radiation

Functions," pp. 69 and 90 (The Macmillan Co., New York, N. Y., 1961).
9

NBS-IMA (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUIU.K A I ION OR RKPORT NO.

NBSIR 74-580

2. Ciov't Accession

No.

3. Recipient's Accession No.

4. TITLR AND SUHTITIJSPECTRAL CHARACTERISTICS OF ADDITIONAL BAR CODE READERS. II

5. Public ation Oatc September 1974

6. Performing Organization Code

7. AUTHOR(S) ^ Julius Cohen

8. Performing Organ. Report No.

9. PERFORMING ORCANIZATION NAMF ANII AODRi-.S.S NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proje. t/Task/Work Unit No. 44604A7

11. Contract /Grant No.

12. Sponsoring Organization Name and f'omplcte Address (Street, City, Stale, ZIP)

Office of Postal Technology Research

U. S. Postal Service

Rockville, Maryland 20852

13. Type of Report & Period Covered

Supplemental

14. Sponsoring Agency Code

15. ^nr'Pl.l-.MFNTAKY NOU S This report is supplementary to " Spectral Characteristics of Bar, Half-Bar Code Readers

Final Report, "NBS Report 10 943 (October 1972).

16. AKSTRACyr (A 200-word or less (actual summary of most sig/iilicanl information. If document includes a significant

bibliography or literature survey, mention it here.)

The spectral characteristics of two bar code readers (submitted by the U.S.

Postal Service under Task No. 1, Agreement No. 74-02934 [Mod. No. 1]) have

been measured as a function of wavelength in the approximate interval of 450

to 1200 nm.

17. Kl'Y 'X'ORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Bar code reader; filters; optical wedge; photodetector ; relative spectral output;

wavelength

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[~ 1 Order 1 rom National Technical Information Service fN TI.S) Springfield, Virginia 221')l

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