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The major electronic subsystems of the instrument are:
•
Main power supply.
•
Main Electronics board - carries control program Flash EPROMs, and a serial
communications interface which runs at 1200 baud (bits per second) and provides the
following functions:
•
Input/Output Interface - on/off control of the calibration lamps, drives the wavelengh-
micrometer stepper motor and slit mask stepper motor.
•
Photon Counter - accumulates the amplified and scaled photon counts from the Pulse
Amplifier, and transfers these counts to the microprocessor.
Clock-Calendar - a real-time clock / calendar which, with the RAM, has battery
•
protection.
•
Analog-to-Digital (A/D) conversion - 24 single-ended, 10-bit A/D channels for
monitoring instrument voltages, currents, temperatures, and moisture, if that option is
included.
Pulse Amplifier - mounted in close proximity to the photomultiplier, amplifies and
•
scales the photon-pulse signal from the photomultiplier, and transmits the conditioned
photon signal to the Photon Counter
•
Lamp Control board - provides constant current control of the two test lamps in the
instrument. It also provides monitor information such as lamp voltage and current
which is sent to the A/D converter of the Main Electronics Board.
• High Voltage Control module - contains the high voltage supply and control circuitry as
one complete module. It also provides a monitor signal to indicate the level of the high
voltage and has an electrically adjustable potentiometer to allow for automated high
voltage testing.
ULTRA VIOLET DOME ASSEMBLY
Refer to Figure 2.3
The UV Dome Assembly is an optical assembly which enables the Brewer to measure global UV-B,
and portions of UV-A and UV-C, using a thin disc of teflon as a cosine collector. The disc is
mounted on top of the instrument under a 5-cm diameter quartz dome, and is thus exposed to the
global UV irradiance. Beneath the disc is a fixed reflecting prism which is located such that the disc
is in the spectrometer field-of-view when the zenith prism is set for a zenith angle of –90° .
Figure 2-3 shows an end view of the foreoptics with the UV subassembly in place.
2.2
SOLAR TRACKING
Within the Brewer software is an Ephemeris algorithm which calculates the azimuth and zenith
angles of both the Sun and the Moon as seen from the current location. Data required for this
calculation includes the geographic co-ordinates of the site, the GMT time, and GMT date. These
angles are further processed by the software, and positioning commands are sent to the Zenith
Drive system, and to the Azumith Tracker.
2.2.1
Zenith Positioning System
The Zenith positioning system is attached to the front end of the Foreoptics, and was described in
detail in Section 2.1.1.
2.2.2
Azimuth Positioning System
Refer to Figure 3.3 and Figure 5.2
The Azimuth Tracker is an all-weather positioning pedestal comprised of a weatherproof chassis
which houses a stepper motor, drive electronics, and a gearing mechanism. The tracker chassis is
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MKIV OPERATOR'S MANUAL
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