SITA Messtechnik GmbH – Operating Instructions SITA ConSpector
Fluorescence of contamination
In production aids, fluorescence is largely due to the aromatic ring systems contained in additives
but primarily also in the mineral oil itself, as well as the unsaturated structures of the oils and fats.
Carboxylic acids and their esters as well as aliphatic ketones fluoresce, too. The fluorescence
measurement detects slightest traces of fluorescent substances.
Exceptions are substances that do not fluoresce when excited with UV light. Those include some
silicon oils, saturated organic compounds as well as short unsaturated hydrocarbons, metals and
their oxides. Processing aids such as oils, greases, cooling lubricants and release agents are tech-
nical liquids that also contain numerous additives, which can likewise contribute to fluorescence.
By adding fluorescent pigments or dyes as fluorescent markers, a non-fluorescent substance can
also be detected.
Photobleaching
Photobleaching is a dynamic process in which the contamination is photochemically destroyed by
UV excitation, thereby diminishing its ability to fluoresce. The strength of the photo-bleaching effect
depends on the substance. The SITA ConSpector was designed in such a way that the sampling
time of a measuring point keeps the photo-bleaching effect as low as possible. When measuring
in a sample mixed with the magnetic stirrer, the medium is also permanently exchanged and a
photo-bleaching effect will generally not be visible.
Defining limits for bath contamination
The displayed measurement value in RFU increases with increasing bath contamination (see appli-
cation examples). Based on reference samples or empirically by the effect on the part quality, a
limit value (alarm) of the contamination level can be defined. If this limit value is exceeded, the
device issues a warning and the plant operator can immediately initiate the necessary measures.
2.2 Examples of Applications
The quick and simple monitoring of the contamination level of the process baths is used as the
basis for process optimisation and achieving high process reliability. The SITA ConSpector captures
process-related changes and allows them to be compensated for through process management
measures. An example of this is the appropriately metered addition of cleaning components and
the removal of the contamination introduced with the immersed parts through bath maintenance.
Overdosing practiced for safety reasons and the premature new bath formulation can be avoided
by monitoring the contamination level.
The following examples illustrate the connection between the fluorescence intensity in RFU output
by the SITA ConSpector and the concentration of the contamination in the bath.
To Next Page
Loading...
