User guide

Chelsea Technologies Group
FAST
tracka
User Guide HB179 Issue 7.0
Page
17
of
47
3.12.2 External PAR Sensor
The FAST
tracka
is supplied with a CI PAR sensor. For details on use and calibration data refer to
the PAR sensor User Guide provided with the PAR sensor.
3.12.3 Photomultiplier Tube (PMT)
To allow fine scale measurement of the variable fluorescence at low chlorophyll concentrations
(down to 0.1 µg/l) a PMT is used as a fluorescence detector. Care should be exercised to
ensure that the PMT is not exposed to excessive light levels (e.g. direct sunlight shining into the
emission windows). Exposing the PMT optics to direct sunlight will damage the photocathode at
the very least temporarily, and perhaps irreparably given enough exposure. The FAST
tracka
incorporates an automatic shut down circuit to the PMT high voltage supply. When exposed to
high ambient light, the sensor is switched off to prevent damage to the photocathode. A three
second delay time is implemented before the PMT detector subsystem is repowered and
checked.
Shining of bright lights into the emission windows to test instrument activity is strongly
discouraged. Similarly, leaving the instrument on deck during a sunny day with the emission
windows facing direct sunlight is also strongly discouraged. The sun block and the dark
chamber are provided with the instrument. Attempting to operate the instrument without the sun
block in place will at the least seriously compromise data integrity, and in the worst case allow
damage to occur to the detector circuitry.
The FAST
tracka
will automatically check the PMT operation on power up with a self initiated
internal calibration routine. The calibration check will indicate whether or not the PMT has suffered
any permanent damage either due to damaging light or improper setting of the PMT gain in
software. Should the check fail, the instrument will return a warning to the user indicating an
uncalibrated PMT system. The self calibration should be performed with the optical head
hooded from ambient light.
3.13 INSTRUMENT DATA OUTPUT
The FAST
tracka
FRR data may be output in two different but not exclusive manners. Two
parameters (i.e. F
m
and F
0
) are calculated in real time using internal approximations. Using
software settings, all data may be passed to the internal flashdisk for storage and later retrieval.
In addition, the approximated F
m
and F
0
values can be scaled to a 0 to 5V output and
presented on separate analogue channels via the Analogue Output connector. See the
Analogue Output section for further details.
The FAST
tracka
differs significantly from other active fluorimeters in the type of information which is
gathered, processed, and presented to the user. The FAST
tracka
incorporates an integral 20 MB
flashdisk (a solid state hard drive) to store data until a later offload, thus removing the need for
customising or otherwise adapting non-compatible CTD systems. The inclusion of an intelligent
data logger into the instrument design allows the instrument to be used much more flexibly than
simply as a sensor.