Page 25 - Instrumentation and Measurement
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FIGURE 2.17 Total radiation pyrometer.
2.4 Level Measurement
Methods used to measure the level of liquid in a vessel include those based on:
1. Floats whose position is directly related to the liquid level.
2. Archimedes’ principle and a measurement of the upthrust acting on an object partially immersed
in the liquid; the term displacer is used.
3. A change in electrical conductivity when the liquid rises between two probes.
4. A change in capacitance as the liquid rises up between the plates of a capacitor.
5. Ultrasonic radiation method.
The following gives examples of the above methods used for liquid level measurements.
2.4.1 Floats
Figure 2.18 shows a simple float system. The float is at one end of a pivoted rod with the other end
connected to the slider of a potentiometer. Changes in level cause the float to move and hence move
the slider over the potentiometer resistance track and so give a potential difference output related to
the liquid level.
FIGURE 2.18 Potentiometer float gauge.
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