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Differential Measurement Application Note

Submersible Pressure Transmitters used to Measure Differential Level
Application: Differential Measurement - Traveling Screen

Problem: Facilities such as power plants and waste treatment plants bring in large volumes of water through channels, either for use or treatment. Large bars or screens, called traveling screens, are placed in the channels to collect debris from the water. This prevents the debris from being drawn into the process where it could damage pumps and other equipment. Eventually, however, the screen becomes clogged and reduces flow.

Solution: AMETEK model 575F Intrinsically Safe Submersible Pressure Transmitter with LevelMate III

The LevelMate III Level System or a customer-supplied controller can be used to activate alarms or automatic cleaning equipment when the screen becomes clogged. Two Model 575/675 Submersible Transmitters (4-wire millivolt only) are connected to a meter/controller to provide differential measurement. One transmitter is placed upstream of the screen and one downstream–each transmitter the same distance from the floor of the channel. The meter/controller is programmed to see and display only the difference between the two transmitters. As the screen becomes clogged, the water level downstream of the screen becomes lower, resulting in a lower pressure measurement signal from the downstream transmitter. When the difference between the two transmitters reaches the programmed set points, the meter relays activate an alarm or an automatic cleaning system to remove the debris and restore flow. This method can be used for other differential pressure measurement applications within certain accuracy limits. For turbulent applications, the Model 675 Level Transmitter will stay in place due to the heavy base of the Shark Cage, weighing over seven pounds.

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