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Flow Measurement with Orifice Plates

Dwyer Instruments offers many types of flow measuring products including orifice plates, which are used as a flow sensing element with a differential pressure monitor.

Orifice Plates

Orifice plates are a primary flow element, detecting the flow of a fluid passing through the plate by sensing the pressure drop across the plate. When a fluid flows through a restriction in a pipe, it creates a pressure difference between upstream and downstream of the restriction. This pressure difference is proportional to flow rate according to Bernoulli’s principal, similar to a Pitot tube.  Orifice plates are commonly used as they are simple to use, low cost, work with gases or liquids, and require low maintenance.  Adversely, they do have large pressure losses with about 50% of the pressure drop not recoverable.  Continue reading “Flow Measurement with Orifice Plates”

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How Electromagnetic Flowmeters Work

Electromagnetic flowmeters, also known as magnetic flowmeters or magmeters, use Faraday’s Law of Electromagnetic Induction to determine the flow of liquid in a pipe. In an electromagnetic flowmeter, a magnetic field is generated and channeled into the liquid flowing through the pipe. Following Faraday’s Law, flow of a conductive liquid through the magnetic field will cause a voltage signal to be sensed by electrodes located on the flow tube walls. When the fluid moves faster, more voltage is generated. Faraday’s Law states that the voltage generated is proportional to the movement of the flowing liquid. The electronic transmitter processes the voltage signal to determine liquid flow.

In contrast with many other flowmeter technologies, electromagnetic flowmeter technology produces signals that are linear with flow. As such, the turndown associated with magnetic flowmeters can approach 20:1 or better without sacrificing accuracy. Continue reading “How Electromagnetic Flowmeters Work”

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How Ultrasonic Flowmeters Work

animation of flow moving through ultrasonic flowmeter

animation of flow moving through ultrasonic flowmeterUltrasonic flowmeters use sound waves to determine the velocity of a fluid flowing in a pipe. At no flow conditions, the frequencies of an ultrasonic wave transmitted into a pipe and its reflections from the fluid are the same. Under flowing conditions, the frequency of the reflected wave is different due to the Doppler effect. When the fluid moves faster, the frequency shift increases linearly. The transmitter processes signals from the transmitted wave and its reflections to determine the flow rate. Continue reading “How Ultrasonic Flowmeters Work”

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How Paddlewheel Flowmeters Work

Paddlewheel flowmeters use the mechanical energy of the fluid to rotate a paddlewheel (just like a riverboat) in the flow stream. Paddles on the rotor are inserted into the flow to transform energy from the flow stream into rotational energy. The rotor shaft spins on bearings. When the fluid moves faster, the paddlewheel spins proportionally faster. Shaft rotation can be sensed mechanically or by detecting the movement of the paddles.

Paddle movement is often detected magnetically, with each paddle or embedded piece of metal generating a pulse. When the fluid moves faster, more pulses are generated. The transmitter processes the pulse signal to determine the flow of the fluid. Continue reading “How Paddlewheel Flowmeters Work”