| Vol.1 No.2 Subject: Flow Measurement News Date: 11-9-98 From: McCrometer, "The Flow Measurement Specialists" ........ http://www.mccrometer.com ........ ******************************************* This issue features a glossary of flow measurement terms. For more information in our complete line of flowmeters go to: http://www.mccrometer.com Commonly Used Terms in Flow Measurement Ever wondered what a Reynolds number or velocity profile really means? Here are some helpful definitions to the most common terms used in flow measurement. Density: Used to describe the mass per unit volume of a fluid. Water has more mass per cubic foot than air, so it's density is higher. Viscosity: Refers to how much a fluid resists flowing. For example, try stirring a vat of honey. The viscosity of the honey is high, so therefore stirring it will be difficult. Reynolds Number: A combination of all the factors that influence the flow in a pipe, including pipe diameter, density, velocity and viscosity. With this combination, we can describe flow in a pipe with a single number. For instance, if a flow has a Reynolds number of 100,000, it will act the same as flow in another pipe with a Reynolds number of 100,000. Velocity Profile: When a fluid moves through a pipe, friction tends to slow down the fluid near the walls. That means the flow near the wall is moving slower than the flow nearer the center of the pipe. The term "flow profile" is used to describe how the flow velocity varies in different parts of the pipe. Beta Ratio: Applies to differential pressure producers, like the V-Cone Flowmeter. A beta ratio describes how much open area is left in the pipe after the V-Cone is installed. A small beta such as 0.45 means just a little of the pipe is still open. Digital Signal: A digital signal is a series of electronic pulses being sent out through the wires attached to the meter. These pulses correlate to the amount of flow going through the meter. For example, a meter may send one electronic pulse for every 100 gallons of water passing through it. Analog Signal: This is another type of signal from meter electronics. A common analog signal is in the form 4 to 20 milliamps. The meter sends a continuous signal of current, where 4 mA typically means zero flow and 20 mA means maximum flow. The main difference between digital and analog signals is the analog is a continuous range, where as a digital signal is broken into pulses. Communication Signal: The last type of signal is referred to as a communication protocol. This implies that the meter is communicating with the control or data acquisition system. The protocol simply defines how the two instruments will "talk". This type of signal takes advantage of the smart capabilities of today's instrumentation. ******************************************* ©1998 by McCrometer, Inc./Printed in USA |