Kipp&Zonen Brewer MkIII - Manual (Page 23)

MKIII OPERATOR'S MANUAL 20
• 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 PTFE 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
mounted on a Tripod assembly and is levelled by means of adjustments on each tripod leg.
Between the Spectrophotometer and the Tracker is a control cable which carries positioning
commands from the Brewer electronics. The positioning commands are input to a motor driver,
which provides drive for a stepper motor. As the motor rotates, it turns a stainless steel vertical
shaft which, in a friction contact, rotates an aluminum plate fixed to the rotational body of the
tracker. The Tracker is fitted with an optical sensor which is used as a reference point, and a
‘Safety Switch’ which removes power to the motor in the event that a failure occurs in the reference
sensing system. The Tracker is fitted with its own power supply and power switch.