Measurements Principles - Xylem SI Analytics AVS 370 Manual De Instrucciones

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Measurements principles

a) Optoelectronic sensing of the liquid meniscus
The near-infrared light which is generated in LEDs located in the upper section of the measurement
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stand AVS /S is conducted through a glass-fibre light-conductor cable onto the measurement planes.
The light shines through the viscometer before it arrives at another light-conductor cable located on
the opposite side; inside this second cable, the light is conducted to a receiver in the upper section of
the measurement stand. While the liquid meniscus passes through the measurement planes, the lens-
like effect of the meniscus causes a short-term darkening of the light beam, followed by a
magnification. This process generates a measurement signal which can be evaluated accurately.
Fig.1 Viscometer for optoelectronic measurements
b) Viscometer with thermistor sensors (TC viscometer)
In the case of TC viscometers, glass-coated thermistors serving as sensors are molten in on the level
of the measurement planes. While the meniscus passes through the measurement planes, the
differences in the thermal conductivity properties of air and liquid lead to a change in the heat balance.
The thermistors of the TC viscometers are molten hermetically tightly into the glass coating of the
viscometer, so that the viscometers located inside are chemically resistant to all kinds of substances
other than strong leaches, fluoric solutions, or concentrated hot phosphate solutions.
Fig. 2 Viscometer for optoelectronic measurements