Chelsea Technologies Group
tracka
User Guide HB179 Issue 7.0
between battery operation and externally supplied power, preferentially protecting the battery
pack while external power is available.
4.1 CONTROL BOARD
The control board is designed around a Tattletale Model 7 datalogger from Onset Corporation
(Pocasset MA, USA) and a PCMCIA Flashdisk (M-Systems, Santa Ana CA, USA). The automatic
data protection, absence of moving parts and the low power consumption of a flashdisk makes
this solution applicable for mooring applications, where vibration and power saving concerns are
critical.
The main datalogger is controlled by a supervisory circuit to achieve maximum power
management. Toggling the magnet switch or pre-programmed operations will place the
instrument into wake-up state. Further communication from the Interface connector through a RS-
422 transceiver on the power board allows protocols stored in NVRAM to be modified or
deleted. The instrument operating program is burned into the datalogger flash ROM during FRRF
assembly at CI and is set to auto-launch whenever the power supervisor circuit dictates.
The datalogger has a variable speed digital clock, which is set according to the tasks executed
by the instrument. During periods of numerical computation, the clock speed is increased to 16
MHz to efficiently process and reduce the raw fluorescence data. At other times the
microcontroller clock is automatically reduced to 32 kHz to minimise power consumption. The
controller board has shutdown control over the remaining subsystems, maintaining the proper
duty cycle for further minimisation of power consumption.
4.2 INTERFACE BOARD
The interface board executes the FRRF protocols, provides interface to the auxiliary sensors
and handles A/D and D/A conversions. It is based around an Atmel 6005 field programmable
gate array (FPGA) which emulates the logic circuitry for generating FRRF flash protocols, and
twin 10 bit flash AD converters. The FPGA implements all the glue logic, generates timing for
FRR protocols, data acquisition and conversion, and interfaces between the controller board and
the external PAR sensor.
4.3 FLASHER BOARD
The flasher board is responsible for triggering the LED light sources at 200kHz repetition rates.
For each optical channel there are six chains of LEDs connected in parallel, with each chain of
14 LEDs connected in series. The entire flash board assembly is mounted in a shielded
enclosure to minimise electronic noise.
An optical rod position in the centre of each lamp assembly provides a reference signal
proportional to the flash intensity. This signal is measured on the Reference board
simultaneously to the fluorescence emission. This excitation light data is presented to the user
as REFERENCE data.
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