Flow Measurement
Orifice plates, beta ratio, square root extraction, Coriolis, magnetic, vortex, ultrasonic, and rotameter principles.
- Explain DP flow measurement using orifice plates and the square root relationship
- Define beta ratio and its significance in orifice plate sizing
- Describe Coriolis and magnetic flowmeter operating principles
- Compare vortex, ultrasonic, and rotameter flow measurement technologies
Leçon 1
DP Flow Measurement & Orifice Plates
Orifice Plate Principle
The orifice plate is the most widely used flow measurement device in the process industry. It is a thin plate with a precisely machined hole (bore) inserted into the pipe. As fluid flows through the restriction, velocity increases and pressure decreases according to Bernoulli's principle. The pressure difference (DP) across the plate is proportional to the square of the flow rate.
This square relationship is critical: Flow is proportional to the square root of differential pressure. A DP transmitter measuring the pressure drop across the orifice produces a signal that varies with the square of flow, not linearly with flow.
Square Root Relationship
The purpose of a square root extractor with DP flowmeters is to linearize the flow signal. Without it, the DP signal is proportional to flow squared, making readings non-linear and difficult to interpret.
Square Root Extraction
A square root extractor is applied to the DP signal to convert it to a linear representation of flow. Most modern smart transmitters can perform this extraction internally. Without square root extraction, a 50% flow rate would produce only a 25% DP signal.
An orifice plate creates a DP proportional to the square of flow rate. A square root extractor linearizes the flow signal. This is one of the most tested flow measurement concepts.