Measurements Principles - Xylem SI Analytics ViscoPump II Mode D'emploi

ViscoPump II

1.6 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
stand 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.
Measurement planes
start of the measurement
Thermistor
Measurement planes
stop of the measurement
Fig. 2 Viscometer for optoelectronic measurements
Basics
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