HANSATECH FMS1, Manual

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11 Section 1: Measurement Principles and Hardware
© 2017 Hansatech Instruments Ltd
Fig. 1-2 . Fluorescence signal detected by the FMS under modulating beam only conditions (A),
under actinic light plus modulating beam before (B) and after (C) the rapid pulse peak tracking
electronics.
The pulsed fluorescence that is induced by the modulation beam is effectively used to probe the
efficiency of light-use for photosystem II photochemistry. Clearly it is important that the
measuring technique itself does not induce changes in the
physiology of the sample under investigation.
Exposure of a sample to a powerful pulsed light source may be expected to introduce a significant
artifact into the measurement. However, FMS has been specifically designed to avoid such
problems by using a modulating beam of very short duration pulses (1.8 µsec) with long off period
between pulses. The net result is that the integrated amount of radiation incident upon the
sample from the modulating beam is very small (<0.05 µmolm-2s-1), too small to induce
significant physiological change in the sample (Schreiber et al. 1986), yet powerful enough to
provide a reliable signal for fluorescence analysis.
The interpretation of fluorescence signals has developed considerably since the early experiments
of Kautsky and Hirsch (1931) with several techniques employed to
determine information about the photosynthetic performance of PSII (Baker 1991).
The FMS hardware and software has been designed to incorporate these techniques
into simple routines which store appropriate fluorescence measurements and
automatically calculate key parameters. The principles and procedures behind these
are discussed in relation to instrument control with the FMS Windows software and
scripting language ( Section 2 ).
Several “non-specific” parameter functions have also been included. The aim of these
is to give sufficient flexibility to experiment and develop novel protocols. These are