Kipp & Zonen BREWER MK IV User manual

INSTRUCTION MANUAL
OM
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BA
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C230/B
Mk IV

REVISION HISTORY
REV DESCRIPTION DCN # DATE APPD
B Update 99-16-12
C Update 07-16-10

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MANUFACTURER'S GUARANTEE / WARRANTY
If a warranty statement is not included in a purchasing contract, then the following warranty
statement shall apply.
NEW PRODUCT WARRANTY AND LIMITATION OF LIABILITY
KIPP & ZONEN B.V. hereby warrants to its products to be free from defects in material and
workmanship for a period of two years from date of purchase.
KIPP & ZONEN 's obligation under this warranty is strictly and exclusively limited to repairing or
replacing, at KIPP & ZONEN 's discretion, any such equipment and / or parts thereof which have
failed under normal use and service. Expressly this warranty does not apply to any equipment and /
or parts which have been improperly installed, been subject to abuse, neglect and / or accident.
The foregoing warranty is in lieu of any other warranties, expressed or implied, and includes,
without limitations, any implied warranty of merchantability or fitness for a particular purpose, and of
any other obligations of liabilities whatsoever in any event for payment of any incidental or
consequential damages, including, without limitation damages or injury to a person or property.
An authorization must be obtained from KIPP & ZONEN prior to the return of any equipment or
parts thereof. Returned material is to be turned to the factory, or other location as may be directed
by KIPP & ZONEN, freight prepaid and will be returned freight prepaid. KIPP & ZONEN is not
responsible for any transportation, insurance, demurrage, brokerage, duties, or councillor charges,
etc.
This warranty is given to the original purchaser and may not be transferred without direct written
consent of KIPP & ZONEN.
Should an extended warranty be purchased, then the aforementioned in its entirety is applicable for
the entire period of time covered by said extended warranty.

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Recommendations by Environment Canada
Mark III Brewer Ozone Spectrophotometers are recommended by Environment Canada (EC) as the
significantly superior model of Brewer instrument with which to measure ozone in the ultraviolet
(UV) region of the spectrum. EC strongly discourages the use of other models of the Brewer
instrument for the measurement of ultraviolet radiation or ozone in the UV because of the much
poorer stray light performance of the single monochromator versions of the instrument.

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1SYSTEM OVERVIEW...................................................................................................................... 7
2SYSTEM DESCRIPTION................................................................................................................. 9
2.1 SPECTROPHOTOMETER ....................................................................................................10
2.1.1 Mechanical Construction .............................................................................................11
2.2 SOLAR TRACKING ................................................................................................................ 20
2.2.1 Zenith Positioning System ...........................................................................................20
2.2.2 Azimuth Positioning System......................................................................................... 20
2.3 COMPUTER EQUIPMENT ..................................................................................................... 21
3BREWER SYSTEM SETUP .......................................................................................................... 23
3.1 SPECTROPHOTOMETER UNPACKING AND SETUP.......................................................... 25
3.2 TRIPOD UNPACKING AND SETUP ....................................................................................... 25
3.3 AZIMUTH TRACKER UNPACKING AND SETUP .................................................................. 25
3.4 MOUNTING THE BREWER ................................................................................................... 26
3.5 BREWER OPERATING SOFTWARE..................................................................................... 27
3.6 COMPUTER SETUP............................................................................................................... 27
3.7 BREWER / COMPUTER INTEGRATION ............................................................................... 28
3.8 MAIN MENU COMPUTER DISPLAY ...................................................................................... 30
3.9 INITIAL TESTS........................................................................................................................ 30
3.10 FINAL INSTALLATION.......................................................................................................31
4BREWER COMMANDS................................................................................................................. 33
4.1 RESERVED KEYS: Home, Del, Ctrl+Break...........................................................................33
4.2 BREWER COMMAND SUMMARY........................................................................................33
5ROUTINE OPERATIONS and MINOR MAINTENANCE ............................................................... 47
5.1 DAILY TASKS ........................................................................................................................47
5.2 WEEKLY TASKS ...................................................................................................................50
5.3 INFREQUENT TASKS ...........................................................................................................50
5.4 MINOR MAINTENANCE ........................................................................................................50
6UV STABILITY CHECK - QS ........................................................................................................ 55
7SOLAR AND LUNAR SITING - SI, SIM ......................................................................................... 59
8BREWER SCHEDULES - SE, SKC, SK........................................................................................ 61
APPENDIX A BREWER DATA FILES............................................................................................ 63
APPENDIX B CONFIGURATION FILES........................................................................................ 79
APPENDIX C UV PROCESSING................................................................................................... 85
LAMP DATA ANALYSIS ................................................................................................................. 85
LAMP DATA ANALYSIS ................................................................................................................. 85
Brewer Response Files .........................................................................................................85
Lamp Irradiance Files............................................................................................................86
UV DATA ANALYSIS PROGRAMS ................................................................................................ 87
Using AB_UVDAT.EXE.........................................................................................................87
Using RD_UX.EXE................................................................................................................87
APPENDIX D NOBREWER ........................................................................................................... 89
TABLE OF CONTENTS

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APPENDIX E UMKEHR PROCESSING ........................................................................................ 91
APPENDIX F FACTORY TESTS ................................................................................................... 93
Setup and Calibration Tests..........................................................................................................93
AZ: Zero the Azimuth Tracker ..............................................................................................94
DT: Photomultiplier Deadtime Test .......................................................................................94
HG: Mercury-Line Wavelength Calibration...........................................................................96
Humidity Sensor Test............................................................................................................97
Inter-Comparison Calibration ..............................................................................................100
RS: Slitmask Motor Run/Stop Test ....................................................................................100
SC: Scan Test on Direct Sun .............................................................................................101
SH Shutter-Motor (Slitmask Motor) Timing Test .................................................................102
SL: Standard Lamp Test .....................................................................................................103
SR: Azimuth Tracker Steps-per-Revolution Calibration.....................................................104
Stray Light Measurement ....................................................................................................104
Thermal Tests .....................................................................................................................105
APPENDIX G PRELIMINARY DATA REDUCTION ....................................................................... 107
Converting Raw Counts to Light Intensity...................................................................................107
Converting Raw Data to Count Rates.........................................................................................107
Compensating for Deadtime .......................................................................................................108
Compensating for Temperature..................................................................................................108
Compensating for Rayleigh Scattering (DS only)........................................................................108
Computing Single and Double Ratios .........................................................................................109
Determining O3and SO2from Direct-Sun Data..........................................................................109
Determining O3and SO2from Zenith-Sky Data........................................................................... 110
APPENDIX H COMPUTER / BREWER INTERFACE (TELETYPE) .............................................111
APPENDIX I FIRMWARE LOG ...................................................................................................... 125
Format:........................................................................................................................................125
Log Items ....................................................................................................................................125
APPENDIX J BREWCMD.EXE .................................................................................................... 131

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MKIV OPERATOR’S MANUAL 7
1 SYSTEM OVERVIEW
The Brewer Spectrophotometer is a scientific instrument which measures Ultra Violet, or Visible,
radiation in the solar spectrum. By examining the differential absorption of select wavelengths in the
UVB portion of the spectrum, determinations of Total Column Ozone and Total Column Sulpher
Dioxide are inferred. In addition, especially with the MKIII double monochromator instrument,
accurate spectral intensity profiles of UV radiation in the 286.5 nm to 363 nm range are measured.
The the MKIV instrument measures intensity of radiation in the visible part of the spectrum (430-
450nm) and uses differential absorption in this region to infer Total Column Nitrogen Dioxide.
It is well recognized by the scientific community that marked fluctuations in atmospheric Ozone and
Sulphur Dioxide, and Nitrogen Dioxide concentrations are linked to a variety of adverse
environmental conditions. The ozone layer, which shields the Earth from the harmful effects of
solar ultraviolet radiation, is believed to be vulnerable to attack by fluorocarbons and other effluents.
Many scientists fear its depletion may irreversibly alter world climatic patterns.
Atmospheric sulphur dioxide and nitrogen dioxide are closely associated with the 'acid rain'
phenomenon which, like ozone depletion, has implications for the global environment.
Today's concern over the vulnerability of the ozone layer to destruction by atmospheric pollutants
has increased the demand for high-quality, globally-distributed, total Ozone and UV Spectral
measurements from a ground-based network of instrumentation. Since the early 1980’s, the
Atmospheric Environment Service of Environment Canada (AES) has conducted the development
of the Brewer Spectrophotometer for the purpose of supplementing instrumentation in the World
Ozone Network. Though the Dobson instrument has served its purpose well since the 1930’s, the
Brewer Spectrophotometer is today becoming the instrument of choice for researchers studying
Ozone, Sulphur Dioxide, Nitrogen Dioxide, and UV radiation.
At the request of the World Meteorological Organization, AES has endeavored to make the Brewer
Spectrophotometer commercially available to the international scientific community. The instrument
and its accompanying accessories are manufactured and marketed under license by KIPP &
ZONEN B.V., Delft, The Netherlands. As of 1998, more than 80 Brewer instruments have been
incorporated into the World Ozone Network and measurements are currently being taken at
research establishments in more than thirty different countries.
1. SYSTEM OVERVIEW

MKIV OPERATOR'S MANUAL
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The Brewer Spectrophotometer is the core component of a complete Brewer System which is
comprised of the following:
Brewer Spectrophotometer
Solar Tracking System
IBM PC or compatible Computer operating Brewer Software
Printer
All of the above equipment is available from KIPP & ZONEN B.V.. The Brewer Spectrophotometer
is supplied with a complete set of programs which control all aspects of data collection and some
analysis. The Computer is programmed to interact with an operator to control the Brewer in either a
manual or fully-automated mode of operation.
In both the manual and semi-automated modes, the operator initiates a specific observation or
instrument test by typing a simple 'command' on the Computer keyboard. Raw data is automatically
recorded on the Computer data drive, and real-time Ozone, UV, SO2, and NO2 results can be
printed.
In the fully-automated mode, a ‘Schedule’ in the Computer controls all operations. The Brewer is
automatically set to the proper observation configuration, then follows a user-defined observation
schedule.
Data is stored and analyzed in the same manner as in the manual or semi-automated mode.
The Brewer is designed to recover from a power failure, and will resume scheduled operation
subject to the computer system recovery, if the Brewer batch file has an automatic launch.
Figure 1.1: A Brewer System

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MKIV OPERATOR’S MANUAL 9
2 SYSTEM DESCRIPTION
The Brewer MKIV Spectrophotometer is an optical instrument designed to measure ground-level
intensities of attenuated solar radiation in either the UV or the Blue spectral region. The Brewer
contains a modified Ebert f/6 spectrometer, utilizing a 1200 line / mm holographic diffraction
grating, operated in the second order for UV and third order for the visible measurements.
The Brewer is designed for continuous outdoor operation and is therefore housed in a durable
weatherproof shell which protects the finely-tuned internal components. The instrument operates
reliably and accurately over a wide range of ambient temperature and humidity conditions.
Following is a brief description of the the major mechanical, optical, and electronic assemblies
which make up the basic instrument. A more complete description of the electronic assemblies is
provided in the Brewer Service Manual.
The Brewer system is comprised of a Spectrophotometer, a Solar Tracker, and Computer
equipment running control and data logging software.
Figure 2.1: Top View of Brewer Cover
2. SYSTEM DESCRIPTION

MKIV OPERATOR'S MANUAL
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Figure 2.2: View of Brewer with Covers Removed
2.1 SPECTROPHOTOMETER
Table 2.1: Spectrophotometer Specifications
Slit wavelengths: ‘ozone’ (nm): 303.2 (Hg slit) , 306.3, 310.1, 313.5, 316.8,
320.1 NO2(nm): 426.4, 431.4, 437.3, 442.8, 448.1, 453.2
Mercury-calibration (O3mode) 302.15 nm
Resolution 0.6 nm in UV; approx 1nm in visible
Stability ±0.01 nm (over full temperature range)
Precision 0.006 ±0.002 nm
Measurement range 286.5 nm to 363.0 nm (in UV);
420 nm to 510 nm (in visible)
Exit-slit mask cycling 0.12 sec/slit, 1.6 sec for full cycle
O3Measurement accuracy ±1% (for direct-sun total ozone)
Ambient Operating temperature
range (still air)
0°C to +40°C (no heater)
-20C to +40°C (with heater option)
-50°C to +40°C (with complete cold weather kit)
Physical dimensions (external
weatherproof container)
Size: 71 by 50 by 28 cm
Weight: 34 kg
Power requirements
Brewer and Tracker
3 A @ 80 to 140 VAC ( with heater option)
1.5A @ 160 to 264 VAC
47 to 440 Hz

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MKIV OPERATOR’S MANUAL 11
2.1.1 Mechanical Construction
Refer to Figure 2.1 and Figure 2.2.
The Brewer Spectrophotometer is housed in a weatherproof enclosure constructed from two pieces
- a base, to which all optical and electronic assemblies are installed, and a removable cover. When
the cover is fastened in place, a weatherproof seal is formed between the top edge of the base and
the bottom of the cover. The dimensions of the assembled enclosure are 71 x 50 x 28 cm.
The Brewer instrument control panel can be viewed through a plexiglass window in the top of the
cover. Viewing ports for both the iris and the spectrometer entrance slit are visible through this
window.
In one corner of the cover is an inclined surface. A hole has been cut from this surface to provide
an opening which is properly positioned to pass direct sunlight or zenith skylight to the
spectrophotometer. This opening is covered by a quartz window [QW 1], which is secured by a
weatherproof seal. ( Items enclosed by square brackets, [ ], are references to the Selected Parts
List, Table 2-2, and Figure 2-4).
Three circular weatherproof connectors are mounted on the side of the Brewer base below the
weatherproof seal. A six-pin male connector marked AC POWER connects to the 120V (or 240 V)
AC power supply. A ten-pin female connector marked COMPUTER carries the RS-422 data
communication signals. A ten pin male connector marked AZIMUTH carries motor control and
monitor signals for the azimuth tracker.
All exposed surfaces of the spectrophotometer enclosure and mechanical linkages are painted with
an enamel for durability and to minimize radiative heating. All machined aluminum parts in the
spectrophotometer system are black-anodized to minimize scattered light and provide a protective
finish.
Mounted inside the Spectrophotometer is a cannister of desiccant which is designed to remove
moisture from the air as the Brewer ‘breathes’ with changes in temperature from night to day. The
desiccant is a ‘self indicating’ type, and can be conveniently removed, without tools, through the
base of the instrument.
This cannister will NOT remove moisture from within the spectrophotometer, and bags or trays of
loose desiccant are usually used for this purpose.
Moisture Sensor Option
As an optional feature, the spectrometer may be fitted with a Moisture Sensor. This option outputs
the moisture content of the spectrophotometer housing in gm/m3 and RH%, and can be used as an
indication of moisture leakage problems, or when internal desiccant requires changing. Two
humidity indicators are available on the Computer Monitor: the absolute humidity in grams/m3and a
temperature weighted moisture index. The moisture index is a relative number that indicates
whether the desicant requires changing. Consistent moisture index values of greater then 10
means that the desicant should be changed.
Heater / Fan Option
A heater / circulating fan assembly may also be included as an option for cold or humid climates, or
in cases where it is desired to maintain constant temperature or good air mixing within the
instrument. The air mixing feature is especially useful in moist climates, and it enables the internal
desiccant to be exposed to the total air volume. In addition, the mixed air will give a more
representitive value of moisture content if the Brewer is fitted with the moisture sensor option.
The heater will attempt to hold the Brewer’s internal temperature at or above a set minimum
temperature. The minimun temperature can be set at 10°C or 20°C. The minimum temperature is
selected by moving the jumper (J1) on the porportional heater controller (bolted to the Brewer
foreoptics supports near the zenith prism):
2. SYSTEM DESCRIPTION

MKIV OPERATOR'S MANUAL
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Jumper setting Minimum temperature
1-2 20°C
2-3 10°C
The default setting is a minimum temperature of 20°C.
Zenith Pointing System
Refer to Figure 2.3 and Table 2.3
A right-angle zenith prism [ZP 1] directs incoming light from the sun, the sky, or the test lamps onto
the optical axis of the instrument. For zenith angles in the range 0 °
to 90°the sun, or sky, is viewed through an inclined quartz window. At zenith angle 180°the
spectrometer views the calibration lamps, and at - 90°a teflon global UV diffuser occupies the field-
of-view.
Figure 2.3: Zenith Prism Targets
Table 2.3: Spectrometer Targets for Various Zenith Angles
Zenith angle (°) Object viewed by Spectrometer
0 to 90°Sky or sun
180°Calibration lamps
-90°UV diffuser
The prism is mounted in a retainer which rotates in a dual-bearing system which has negligible
lateral play. . The prism is rotated by a microprocessor controlled zenith stepper motor thru a 270-
degree rotation range limited by end stops. This system provides the necessary hardware and
electronics to enable the Spectrophotometer to track the sun or moon automatically in the Zenith
angle. Automated Zenith positioning is performed by driving the Zenith Prism with a stepper motor
mounted on the front end of the foreoptics frame. The zenith-stepper motor is controlled by the
Main Electronics board.

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MKIV OPERATOR’S MANUAL 13
Specifications of the Zenith Motor:
Resolution: ±0.13°
Accuracy (24 hours): ± 0.25°
Angular range: 270°
Table 2.2 Optical Components of Brewer Spectrophotometer
Identification Description
AP 1 Fixed aperture, 11.18 mm
ES 1 Entrance slit plate, dia: 26.37 mm, thk: 0.10 mm
Slit, length: 3.30 mm, width: 0.34 mm.
EX 1 Exit slit plate, length: 28.95 mm, width: 19.05 mm, thk: 0.10 mm
Slits, length: 5.08 mm, width(3): 0.589 mm, width(3): 0.632 mm.
FW 1 Filterwheel #1 made from aluminum gear material, with two
Ground G1-quartz disks, dia: 25.4 mm, width: 1.59 mm, and 2 film
Polarizers, dia: 25.4 mm, width: 1.59 mm.
FW 2 Filterwheel #2, made from aluminum gear material with 5
Neutral-density filters; each with dia: 25.4 mm,
Width: 1.59 mm; attenuations: 0.5, 1.0, 2.0, 2.5 decades
(prepared from G1 quartz blanks )
FW 3 Filter Wheel #3, made from aluminum gear material with with 4, 25mm
filter positions. Contains a UG-11 filter, a BG-12 filter and a UG-11/NiSO4
filter combination
GR 1 Grating, 1200 line/mm holographic plane reflectance,
dia: 50 mm, thickness: 10 mm (Jobin-Yvon)
HL 1 Tungsten-halogen lamp, 12 V, 20 W, Osram 64425, mounting:
Amel Socket for #28-8341 light source
IR 1 Iris diaphragm, aperture range: 2 to 12 mm (Edmund Scientific
catalogue #40997)
LE 1 Lens, double-convex, G1-quartz, focal length: 25.4 mm, dia: 25.4 mm
LE 2 Lens, plano-convex, G1-quartz, focal length: 76.2 mm, dia: 25.4 mm
LE 3 Lens, plano-convex, G1-quartz focal length: 50.8 mm, dia: 25.4 mm
LE 4 Lens, plano-convex, G1-quartz, focal length: 76.2 mm, dia: 25.4 mm
LE 5,6 Correction lens G1 quartz, dia: 25.4 mm, radius 1: 170.0 mm,
convex cylindrical, radius 2: 230.0 mm, concave spherical,
coating: magnesium fluoride
LE 7 Fabry lens, double-convex, G1 quartz, dia: 38.1 mm focal length: 38.1 mm
MI 1 Micrometer, metric, Starrett #463 MP,13-mm head, EDP #52444
ML 1
Mercury lamp, ozone-producing, General Electric G4S11;
mounting: 14-71 intermediate screwsocket
PM 1 Photomultiplier, EMI #9789QB05
QW 1 Quartz window, G1 quality 7.62 by 15.24 by 0.48 cm
SL 1 Slit mask, cylindrical sector, dia: 25.4 mm, thickness: 0.038mm
SM Spherical mirror, radius: 324 mm, ground from pyrex blank of
dimensions 25.4 by 165.1 by 50.8 mm, aluminized reflecting
surface, coated with magnesium fluoride
VL 1 Viewing lens, plano-convex, glass. Dia: 15 mm, focal length: 112 mm
VP 1,2 Viewing prism, right-angle, glass 7 by 8 by 7 mm
ZP 1 Zenith prism, right-angle, G1-quartz, 31.75- by 31.75-mm square face
2. SYSTEM DESCRIPTION

MKIV OPERATOR'S MANUAL
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Figure 2.4: Optical Elements of Brewer Spectrophotometer
Lamp Assembly
A quartz-halogen lamp [HL 1] provides a well-regulated light source which is used as a reference for
sensitivity measurements. The lamp is powered by a constant current source of nominal value 1.5
A, held to within 0.5% over a temperature range of –20°to +40°C. The intensity of the radiation
from the lamp under these conditions is stable to within 5%. The filament of the lamp is placed at
the focal point of a double-convex lens [LE 1] so that the light from the lamp is directed along the
optical axis by the zenith prism.
Beneath the halogen lamp is a mercury discharge lamp [ML 1], which provides a line source for
wavelength calibration. Ultraviolet radiation from the mercury lamp passes through the halogen
lamp to the zenith prism. While the actual light intensity of the lamp is not critical (a variation of
50% over the operational temperature range is normal), it must remain stable to within 5% for short
time periods (10 minutes).

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MKIV OPERATOR’S MANUAL 15
Figure 2.5: Top View of Spectrophotometer
FOREOPTICS
Refer to Figure 2.4 and Figure 2.5
The automated system drives stepper motors which control three elements in the foreoptics
assembly - the Iris Diaphragm, Filterwheel #1, and Filterwheel #2. The associated driving and
sensing electronics are integrated into the Main Electronics board. The Brewer software
automatically controls motors once the Configuration File has been appropriately configured.
Incoming light is directed through the foreoptics by the director prism [ZP 1], which may be rotated
to select light from either the zenith sky, the direct sun, or one of the two calibration lamps. A
mercury lamp provides a line source for wavelength calibration of the spectrometer, while a quartz-
halogen lamp provides a well regulated light source so that the relative spectral response of the
spectrometer may be monitored. Elements in the foreoptics provide adjustment for field-of-view,
neutral-density attenuation, ground-quartz diffusion, and selection of film polarizers.
Iris Diaphragm Assembly
An iris diaphragm [IR 1] is mounted in the foreoptics at the ultraviolet focus of a plano-convex lens
[LE 2]. This lens focuses ultraviolet objects at infinite distance onto the plane of the iris. A lever
arm which protrudes through the wall of the foreoptic tube controls the iris. At one limit of the lever
arm the iris aperture is 5mm ( iris closed), while at the other limit the aperture is approximately
15mm (iris open). The lever is actuated by the iris stepper motor.
2. SYSTEM DESCRIPTION

MKIV OPERATOR'S MANUAL
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When the instrument is aligned to view sunlight, an image of the sun is focused at the centre of the
iris. With the iris closed, about three solar diameters of skylight around the sun pass through the
iris aperture into the spectrometer. With the iris open, about 10°of skylight enters the
spectrometer.
On the spectrometer side of the iris there is another plano-convex lens [LE 3]. This lens is
positioned such that its focal point is in the plane of the iris. Light passing through the iris aperture
is therefore collimated along the optical axis.
Lenses [LE 2, LE 3] in the iris-diaphragm assembly are mounted with their plane side facing the iris.
Filterwheels
Filterwheels [FW 1, FW 2] are mounted on bronze bearings in a filter-wheel housing. Each wheel
has six 25.4mm diameter holes spaced at 60 degree intervals. Each hole can be selected to
intersect the optical axis by rotating its filterwheel. The filterwheels are rotated by two
microprocessor controlled motors.
FW #1 contains one open hole ( #3 ), two film polarizers ( #0 and #5 ), a ground-quartz disk ( #1 ),
an opaque blank ( #2 ) and a second ground quartz disk + a neutral density filter ( #4 ). The ground-
quartz disk is used as a diffuser for direct-sun and lamp measurements. The opaque disk is used
for dark count tests. The film polarizer ( #0 ) is used for all zenith sky and Umkehr measurements.
This film polarizer is mounted such that its axis is perpedicular to the entrance slit. The second film
polarizer ( #5 ) is mounted such that its axis is parallel to the entrance slit. It is presently used only
for specialized research purposes. The open position (#3) is used for moon and UV observations.
The second ground quartz / N.D. filter is used in the NO2 mode of operation..
FW #2 contains an open hole ( #0 ) and five neutral-density filters providing ND=0.0, 0.5, 1.0, 1.5,
2.0 and 2.5 attenuation ( #0 through # 5 ). This filterwheel is used to automatically adjust the light
level entering the spectrometer.
[AP 1], an 11.18mm fixed aperture located on the spectrometer side of the filterwheel housing limits
the field-of-view of the spectrometer to f/6.
Both Filterwheels have black markings that are visible through the viewing window. The
number of markings indicate the position of the filter wheel (positions 0 through 5).
Foreoptic Viewing Ports
There are two viewing ports along the foreoptic assembly, through which may be viewed the iris
diaphragm and any images which are focused onto it, and the entrance slit.
At the bottom of each viewing port is a glass right-angle prism [VP 1, VP 2] mounted inside the
foreoptic tubing. The prisms are aligned so that the object to be viewed (iris or entrance slit)
appears centred in the viewing port. A plano-convex glass lens [VL 1, VL 2] is placed in each
viewing tube to magnify the image.
Rear Fore-Optics.
A plano convex lens [LE-4], whose plane suface faces the entrance slit of the spectrometers
focuses the collimated ultraviolet radiation onto the entrance slit of the spectrometer.
SPECTROMETER
The purpose of the spectrometer optical subassembly is to accept light through the entrance slit
and disperse it into a high-quality spectrum along the exit-slit focal plane. The spectrometer is a
modified Ebert type with focal length 16 cm, and aperture ratio f/6.
Six exit slits are positioned along the exit focal plane at the Ozone (or NO2) operating wavelengths -
303.2 nm (302.1 for mercury-wavelength calibration), 306.3/431.4 nm, 310.1/437.3 nm, 313.5/442.8
nm, 316.8/448.1 nm and 320.1/453.2 nm with 0.6/0.9 nm resolution. Wavelength is adjusted by
rotating the grating with a stepper motor which drives a micrometer acting on a lever arm. The
wavelength-calibration procedure is capable of measuring the wavelength setting with a precision of
0.0001 nm, and of controlling the wavelength setting to 0.006 nm.(in the UV region.

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MKIV OPERATOR’S MANUAL 17
At the exit of the spectrometer is a cylindrical mask which exposes only one wavelength slit at a
time. The mask is positioned by a stepper motor which cycles through all five operating
wavelengths, approximately once per second.
Spectrometer Detailed Description
Light enters the entrance slit and passes through a tilted lens [LE 5] which corrects for the coma
and astigmatic aberrations inherent in an Ebert system. The light is collimated by a spherical
mirror onto a diffraction grating where it is dispersed. A second mirror reflection focuses the
spectrum onto the focal plane of a slotted cylindrical slit mask positioned at the exit of the
spectrometer. After wavelength selection by the slit mask, the light passes through the exit slit
plate. Six exit slits are located along the focal plane at the appropriate wavelength positions.
Entrance and Exit Slit Plates
The entrance slit and six exit slits [ES 1, EX 1] are etched into 0.1-mm-thick disks of hard shim
steel. One of the six exit slits (slit #0) is used for wavelength calibration against the 302-nm group
of mercury lines; the other five are for intensity measurements and are nominally set at 306.3/431.4,
310.1/437.3, 313.5/442.6, 316.8/448.1, and 320.1/453.2 nm. The dimensions for the entrance and
exit slits are listed in the Selected Parts List.
Both slit plates are positioned on their respective housings by locating pins which orient the slit axis
to within 0. 1°. Both plates are blackened to minimize light reflections.
Correction Lens
The correction lens [LE 5] has a convex-cylindrical surface (radius 170.0 mm) and a concave-
spherical surface (radius 230.0 mm).
Both surfaces are coated with a layer of magnesium fluoride to minimize reflectance at 315.0 nm
for an incidence angle of 29°. The lens is mounted in the entrance-slit housing at an angle of 29°
to
the optical axis with the concave-spherical surface facing the entrance slit. The axis of the
cylindrical surface is positioned in the horizontal plane to within 1°.
Spherical Mirror
The spherical mirror [SM 1 ] has a 324 mm radius-of-curvature. The spherical surface is ground
from a rectangular pyrex blank. The surface is polished, coated with aluminum, and then coated
with magnesium fluoride to maximize reflection at 315.0 nm.
Spring-loaded mounts secure the spherical surfaces of the mirrors against three adjustment screws
which are normal to the spherical surfaces in the horizontal plane of the spectrometers. The mirrors
are allowed to move on a spherical surface defined by the three adjustment screws, up to a limit of
0.25 mm in the horizontal and vertical. Nylon screws prevent the mirrors from moving beyond this
limit.
Diffraction Grating
The diffraction grating [GR 1 ] is a 1200 line / mm holographic plane-reflectance type, operated in
the third order in the UV for ozone measurements, and in the second order in the Blue region. The
grating has optimum efficiency over the range 225 to 450 nm in the first order.
The grating is secured with high-quality adhesive to three small blocks which provide kinematic
mounts, as well as fine adjustment for rotation of the grating about the two axes perpendicular to
the grating grooves. The three blocks are thus part of the grating and are the basis of point, slot,
and plane mounts which allows adjustment by three screws fixed in the grating-mount plates. These
plates are suspended on a set of cross-springs which constrain the gratings to rotate in the vertical
axis (the axis parallel to the grating grooves). The cross-spring suspension acts as a frictionless
bearing. Rotation of the grating is controlled by two micrometers acting at the end of lever arms
such that a 0.03 mm adjustment of the micrometers represents approximately a 0.1 nm wavelength
change at the exit-slit plane.
2. SYSTEM DESCRIPTION