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 Section 3. LEVEL MEASURING DEVICES
1. INTRODUCTION. To maintain accuracy obtained by a primary device, a
flowmeter must measure fluid level at the measuring point and precisely
convert it to flow rate. This entails choosing a level measuring device
appropriate for site conditions.
1.1 Operating Principles. Level measuring devices operate using either the
time for sonic echo response from surface to bottom of liquid flow or
differences in atmospheric pressure between surface and bottom of liquid
flow. The application of these principles is described in various meter
designs.
2. METER DESIGNS. Each of the meter types discussed are available with the
capability to integrate flow level data with preprogrammed data specific to
the site and provide an accurate flow rate.
2.1 Ultrasonic Level Meters. This type of level meter incorporates timing of
ultrasonic pulses and echoes to determine liquid level. A sensor/transducer
is fixed above the surface and is unaffected by the type of liquid (Figure
7-6) . The transducer emits a signal directed at the surface of the liquid and
measures the time interval of echo response.
2.2 Bubble Type Meter. The sensing probe for this type of meter is mounted
below the surface of the liquid (usually at the bottom) (Figure 7-7). The
FIGURE 7-6.
Ultrasonic Level Meter
7-8
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