Precision Measurement Engineering, Inc.
The fluorometer channel consists of a fluorometer endcap, blue excitation L.E.D., optical filters, mirrors, lens, and associated circuitry. The circuits are located on the 5500 circuit board. The other components are located within the fluorometer endcap. The fluorometer's block diagram shows the electrical circuit.
The fluorometer operates by exciting the sample volume with a pulsing 455 NM blue light at 1000 Hz with a 50% on, 50% off duty cycle. Under this condition, chlorophyll emits a pulsing red 685 NM light that is received by a photo-diode. The photo-diode output is first amplified by a DC amplifier, then strongly amplified by an AC amplifier. These circuits together have the effect of rejecting constant ambient lighting and only passing the pulsing chlorophyll response. The output of the AC amplifier is rectified by a phase synchronous rectifier, filtered, and passed to the circuit output where it is connected to the SCAMP fluorometer channel.
The circuit has an adjustment that controls the
amount of amplification, thus allowing overall sensitivity control. The system has a
linear sensitivity to fluorescence, but has significant output with only distilled water
in the sample volume due to the slight fluorescence of various materials used to implement
the optical components. The photos below show the fluorometer addition.