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Theory of Operation
Electronics Overview
measurements without control from the PC and buffer the data until the PC
wants to take it.
SPM—Spectrophotometer Processor Main Board
The spectrophotometer processor main (SPM) board receives DC power
from the main power supply (MPS) and distributes it to a number of other
modules. These include the spectrophotometer lamp supply (SLS) board,
spectrophotometer data acquisition (SDA) board and from there the
spectrophotometer sipper interface (SSI) board and the spectrograph with
the diode array.
The SPM board interfaces to the controller, that is, the computer and other
devices, such as pumps, valves, the multicell transport, RS232 and other
peripheral devices. Shutter control allows for dark current or sample
measurements and utilizes the stray light filter. Stray-light correction is
calculated by combining information of two spectra, a spectrum measured
with the stray-light correction filter and a spectrum without the stray-light
correction filter in the light path. Memory for approximately 100 full spectra
is available and two SIMM sockets for extending the memory (to be able to
store several hundred spectra) are available.
SLS—Spectrophotometer Lamp Supply Board
The SLS board provides control and regulation for both, the tungsten and
deuterium lamps.
Spectrograph
The spectrograph contains the PDA (photodiode array) which gives an
analog signal proportional to the light level which falls on the individual
photodiode during a defined period of time. The photodiode array is
connected to the spectrophotometer data acqisition (SDA) board through the
spectrograph connector interface (SCI) board. A temperature sensor is
located on the diode-array for temperature compensation, that is, to reduce
drift. This is especially important for the SWNIR part of the spectrum where
drift with temperature is significant due to variation in the quantum
efficiency of the photodiodes.
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