Teledyne 6650 - Fluorescence Probe - Oil in Water analysis system - Manual (Page 20)

Setup & Operation Model 6650
12 Teledyne Analytical Instruments
Setup & Operation
The Fluorescence transmitter is designed to monitor the
fluorescence signal from a laboratory or process stream. Under certain
conditions the fluorescence range of the sample is well defined and can
be verified with standard reference materials such as zero and span
solutions of know concentrations. However, this is not always the case
when measuring fluorescence and is addressed in the design of the
product via the mode selection.
There are two modes which can be employed for calibration/set up
of the transmitter, namely mode 1, or mode 2. Typically when the user
does not know what the expected range or the fluorescent value of the
samples use mode 2 initialization. Mode 2 initialization requires the
initialization preset switch (refer to Figure 3-1 ) be held for >8 seconds.
In the mode 2 initialization the ratio of the fluorescent value to the
excitation value needs to be spanned properly in the display, since this
value is unknown the transmitter arbitrarily set to 20 times the original
ratio. This is done with or without the probe in a sample. Once a real
sample is available, the transmitter range may be determined. Once the
transmitter range is known, a calibrated range, using mode 1 operation,
may be set.
Mode 1 is used to set the full scale range of the unit but it does so
by splitting the range at the midpoint of the full scale. That is to say that
if you had a sample of concentration of X the full scale would be 2X.
The calibration sample would read 1000 counts and have a 12mA
output. If on the other hand you wanted a full scale range of X you
would have to dilute your sample to X/2 to get a full scale of X.
The display output is in arbitrary count units. To convert the
arbitrary unit to relevant engineering units the 4-20mA output must be
manipulated using an external device. The transmitter display cannot be
set to relevant engineering units. Additionally, the user can adjust the
output display over the full scale range once it has been established.
Note: The above readings are all based on defined excitation and
emission wavelengths for the given sample or intended
application.