Xylem SI Analytics AVS 370 Manual De Instrucciones página 32

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1.7
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
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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.2 Viscometer for optoelectronic measurements
b) Viscometer with thermistor sensors (TC viscometer)
In the case of TC viscometers, glass-coated thermistors serving as sensors are inserted 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 inserted hermetically tightly into the glass coating of the viscometer.
Fig. 3 Viscometer for optoelectronic measurements