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water level ditector

# water level ditector - A Circuit for Water Level Detection...

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A Circuit for Water Level Detection and Control Author: Shao-Quan Lu Graduate Student, Institute of Electrical Engineering, National Yunlin University of Science and Technology, Touliu, Yunlin 640, Tai- wan Introduction For the residents who live in high buildings, low water pressure is a very common problem, espe- cially when many people use the water at the same time. Therefore, many people install a water tower on the roof of the building. The water is stored at a water tank at the basement first. Then it is pumped into the water tower on the roof using a pumping motor. In this manner, the low wa- ter-pressure problem can be improved and the water can be used in a more efficient way. Traditional water level controller can control the water between two levels. However, since the con- troller is usually placed at the top of the water tower, corrosion and mal-function may occur due to the effect of humidity to the controller. Meanwhile, if the water level of the basement tank is too low, the pumping motor may be burned because there is no water to pump. Traditional Water Level Controller Traditional water level controller uses floating balls as the sensors for level detection, which is de- picted in Figure 1. As shown in the figure, the controller has two floating balls (will be called ball A and ball B hereafter) placed at two levels (will be called level H and level L hereafter). According to the positions of the two balls, the switch of the pumping motor is set to be on or off. The operation theory is as shown in the following table: A Circuit for Water Level Detection and Control 1

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Step Description 1 When the water level of the water tank is lower than level L, due to the effect of gravity, the weights of ball A and ball B will be heavy enough to make the switch be closed. This will turn on the pumping water to pump water into the water tower. 2 When the water level reaches level L, due to the effect of floating force, ball B will float on the water. However, the weight of ball A is still enough to make the switch be on. There- fore, the pumping motor keeps on pumping water. 3 When the water reaches level H, due to effect of floating force, ball A and ball B have no weight on the switch. Therefore, the motor stops pumping water. 4 When the residents use the water, the water will be lower than level H first. In this case, though the weight of ball A is on the switch, it is not heavy enough to turn on the motor. If the water is lower then level L, the weights of ball A and ball B will make the switch be closed and turn on the pumping motor. 5 Repeating the above procedure, the water in the water tower can be controlled between level H and level L. Using floating balls as the sensors for water level control has the advantages of simple structure and low cost. However, as mentioned above, since the contact switch of the pumping motor is usu- ally placed at the top of water tower, the humidity may corrode the contact point of the switch. This will cause the switch to mal-function. Meanwhile, since there are no means to detect the water
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