Induction Motor Braking Methods There are several different methods useful for causing an AC induction motor to brake, or slow down: DC injection uses the technique of energizing the stator windings with low-current DC instead of high-current AC as is the case when the motor runs. Dynamic braking works the motor as a generator, dissipating […]
DC Motor Speed Control Using PWM DC motors exhibit the following relationships between mechanical and electrical quantities: Torque: Speed: A very simple method for controlling the speed and torque characteristics of a wound-field (nonpermanent magnet) DC motor is to control the amount of current through the field winding: Decreasing the field control resistor’s resistance allows
How does an Electrical Conductivity Probe Work ? The electrical conductivity of liquids is an important analytical measurement in many industrial processes. This measurement is one of the more non-specific types of analytical technologies, because it does not discriminate between different conductive substances dissolved in the solution. For this reason, conductivity measurement is found in
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Insertion Flowmeters This article does not describe a particular type of flowmeter, but rather a design that may be implemented for several different kinds of flow measurement technologies. When the pipe carrying process fluid is large in size, it may be impractical or cost-prohibitive to install a full-diameter flowmeter to measure fluid flow rate. A
Change of Quantity Flow Measurement Flow, by definition, is the passage of material from one location to another over time. So far my articles have explored technologies for measuring flow rate en route from source to destination. However, a completely different method exists for measuring flow rates: measuring how much material has either departed or
Weighfeeders A special type flowmeter suited for powdered or granular solids is the weighfeeder. One of the most common weighfeeder designs consists of a conveyor belt with a section supported by rollers coupled to one or more load cells, such that a fixed length of the belt is continuously weighed: The load cell measures the
Thermal Flowmeters Wind chill is a phenomenon common to anyone who has ever lived in a cold environment. When the ambient air temperature is substantially colder than the temperature of your body, heat will transfer from your body to the surrounding air. If there is no breeze to move air past your body, the air
Coriolis Flowmeters Coriolis flowmeters are incredibly versatile and accurate, but their internal operation can be difficult to understand. Put into very simple terms, a Coriolis flowmeter works by shaking one or more tubes carrying the flowing fluid, then precisely measuring the frequency and phase of that shaking. The back-and-forth shaking is driven by an electromagnetic
Magnetic Flowmeters When an electrical conductor moves perpendicular to a magnetic field, a voltage is induced in that conductor perpendicular to both the magnetic flux lines and the direction of motion. This phenomenon is known as electromagnetic induction, and it is the basic principle upon which all electro-mechanical generators operate. In a generator mechanism, the
Turbine Flowmeters Turbine flowmeters use a free-spinning turbine wheel to measure fluid velocity, much like a miniature windmill installed in the flow stream. The fundamental design goal of a turbine flowmeter is to make the turbine element as free-spinning as possible, so no torque will be required to sustain the turbine’s rotation. If this goal