Idiomas disponibles
Idiomas disponibles
1.2
Capillary viscometry
Capillary viscometry is the most accurate method for the determination of the viscosity of liquids with a
Newtonian flowing behaviour. The measurement as such consists in a time measurement. The time measured
is that which a specific quantity of liquid requires to pass through a capillary having a defined width and length.
Conventionally, this process is watched with the human eye, and the flow time is measured manually using a
stop watch.
In the case of the AVS
is captured on the measurement planes, either in an optoelectronic manner by means of light barriers, or else
on a thermo-resistivity basis by thermistors.
1.3
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
®
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 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. 2 Viscometer for optoelectronic measurements
®
470, as with all viscometry measuring devices from SI Analytics
39
®
,
the liquid meniscus
