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5 Performance Measurement
5.2.3 The Digital Thermometer
The measuring principle is the same as with the transducer, but the device features a
digital display. The display may be a separate handheld device or may be mounted
directly to the probe.
5.3 Flow Rate Measurement
5.3.1 Reservoir
A direct method for measuring volume flow rate is the filling of a reservoir calibrated in volume units or placed onto a balance.
5.3.2 Flow Over a Weir
When a liquid flows over a weir, flow rate is determined by the height of the liquid
surface compared to the deepest point of the weir, as is sketched in Fig. 5.3. Rectangular and triangular weirs are applied. Formulae for volume flow rate are
where w is the width of the rectangular weir, α half the angle of opening of the
triangular weir and H the height of the liquid level. Coefficients
, and
R
T
C C
∆ are
determined according to standards.
( )
( )
(
) and
(
),
3
5
3
T
8 15
R
2
Q
C w 2g H
Q
C tg 2g H
D
a
D
=
+
=
+
Fig. 5.3 Flow over a weir