FISCHER FISCHERSCOPE X-RAY 4000 Series, Operator'S Manual

Page: 53 / 170

Monitoring the measurement devices Product Administration
FISCHERSCOPE
®
X-RAY 53
excitation. Any combination of substrates not allowed in this context
will be rejected. In any cases where a component of a layer is
secondarily excited by a component of the base material
fluorescence the definition "composition unknown" must not be
used but the substrate has to be defined explicitly. Equally this is
recommended if same element is content both of one ore more
layers and of the substrate.
Another specialty is the ratio method. This evaluation method
utilizes relative count rates or the method of "internal normalization"
(count rates of one or more layers relative to the count rate of the
substrate).
An example of this method comprises the measurement of samples
with an area which is smaller than the measuring spot size (wires,
lead frames, etc.). This method uses the fluorescence radiation of
the substrate, so it has to be known exactly, i.e. which elements the
substrate contains quantitatively. From this we conclude:
Base material "composition unknown" must not be used with

secondary excitation,

strong peak overlap,

multiple content of same element,

ratio method.
On the other hand, "composition unknown" is prerequisite if the
substrate is a source of substantial scattering, like with plastics,
fluids, light metals etc. Scattered radiation is not handled by the
fundamental parameter method and cannot be evaluated
theoretically by WinFTM. Therefore it has to be evaluated
empirically. The user must define base material as "unknown" in
applications where scattering is important and has to measure the
real substrate during normalization and calibration.
7.15 Monitoring the measurement devices
Why is it necessary to check the instrument?
Short answer: To ensure at all times that an instrument without or
at most with very small measurement deviations is available.
Technical background:
With the X-ray fluorescence method, as with any non-destructive
measurement method, the measurement data are calculated
indirectly.