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AMAZON multi-meters discounts AMAZON oscilloscope discounts The sounding tape and reel-type level sensor is sometimes called a fishing-reel level sensor. The name of this sensor comes from the fishing term sounding. In modern level sensors a weight is attached to a line and the line is lowered from the top of a tank. The weight will cause the line to have tension as long as it's suspended in air. When the weight comes into contact with the level of the material it's measuring, the amount of tension will be reduced and a sensor can detect this change. When the tension changes, a mechanism stops the line from lowering and begins to retrieve the line. A spool is used to reel the line in and the number of rotations the spool uses to reel the line completely to the top is measured and converted to a level measurement. Some of these sensors use a magnet in the spool and the number of times the magnet passes a detector is counted. In other applications a rotary potentiometer is connected to the spool and the number of rotations is converted directly into a change of resistance. In both types of sensors, the transducer signal is converted to a usable 4-20 mA output signal. If the spool uses a magnet and counter, the counter is reset when the tension changes and indicates the weight at its lowest point. When the reel begins to pull the line in, the counter will be ready to determine the amount of line that was lowered. Figs. 1, 2, and 3 show example applications using the sounding-type level sensor.
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