272 1100 Series FD Reference Manual
8 Theory of Operation
Reference System
A reference photodiode is located behind the cell and monitors the incoming
radiation through a diffusor window. The data are used to compensate the
fluorescence data for drift effects. The reference path provides multiple gain
stages which are set automatically according to the actual intensity.
Cell Detection
The system detects if a cell is inserted and switches off lamp operation, PMT
high voltage and monochromator rotation if no cell is present to prevent
injury (by UV radiation, high voltage or rotating parts) to the user.
Emission Monochromator Motor Control
A chopped motor driver IC provides the signal to run the excitation
monochromator motor in positioning or rotation mode.
Leak Sensor
A leak sensor is mounted in the instrument’s front chassis to detect leakage of
the cell assy. In case of a leakage, the complete Agilent 1100 System is shut
down to prevent system damage.
This block consists of a PTC for the leak detection and a NTC for the ambient
temperature compensation. A leak would cool down the PTC and this change
in resistance would generate a leak signal.
Digital Interface
The control and data lines from and to the Fluorescence Detector Main Board
(FLM) are buffered by Read- and Write ports. The signals from the main board
allow setting of the signal multiplexers, reference gain stages, lamp current
and to start the initial self-calibration of the A/D-converter. The port to the
main board drives the A/D-converter data and several control lines like cell
detection, overcurrent detection and lamp cover safety switch position.
The signals driving the lamp are derived from the FPGA on the Main Board
and have separate connections. This allows the lamp timing control without
processor interaction and guarantees a realtime control of the lamp operation.
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