PFC for AC Induction Motors
Power factor (pf) is defined as
the ratio of the real power (P) to apparent power (S). Speaking simply, power factor can be explained as a
means to measure real work done (as measured by watts), as opposed to reactive power, which is lost energy
(technically power.) Adding real and reactive power gives us apparent power, which the electric company
provides. Almost everything that does work for us is a resistive load (e.g., light bulbs) or an inductive
load (e.g., AC Induction motors.) What is missing is a matching amount of capacitive load.
This causes a sort of imbalance that can waste energy and disrupt other devices on the line if it’s not
corrected. PFC that is implemented inside devices has become an important part of the
design of power systems for many products since the European Union has enacted standards in this area
that are needed for CE marking on certain products.
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Digital Isolation for AC Induction Motors
Isolation is
critical to protect both an electronics system and the user from potentially hazardous voltages, or where a
high level of electrical isolation between electronics systems is necessary. Digital isolators are known for
their speed of data transmission, high level of magnetic immunity, and long life expectancy. Used in
combination with isolated power supplies, these devices protect circuits from high voltages, prevent current
flow between remote system grounds, and avoid the creation of current loops. Digital
isolators can be used to implement isolation in designs without the cost, size, power,
performance, and reliability constraints found with optocouplers.
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USB Receptacle for AC Induction Motors
USB plugs and
receptacles are designed to reduce human error by their unique shape; they fit together in
only one way. USB plugs and receptacles are Type A
(connecting to hosts or hubs) or Type B (connecting to devices) and are available
3 sizes: standard, mini, and micro. Type A plugs always face upstream, Type B faces downstream. USB is used
in many applications covering all areas of electronics that require communication, but more commonly with
devices that need fast or easy connections for interaction with computers. Since USB
provides a small charging current as well, it is becoming a de facto standard for charging portable
devices.
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Switches for AC Induction Motors
Switches are devices that
provide manual input or control for equipment, a device, or a process. Switches serve many
purposes, provide immediate emergency control, local control, or indication; and are available in many
formats, shapes, sizes, and colors. Switches and buttons are important in everyday use from light switches
or buttons to automatic switches that shut off a motor when an attached gate has fully shut.
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RS-485 Products for AC Induction Motors
RS-485 is an electrical-only
standard, in contrast to complete interface standards which define physical, functional, and electrical
specifications. RS-485 signaling can be used with many protocols such as Profibus,
Interbus, Modbus, or BACnet, depending on the requirements of the end user. Sometimes controller area
network (CAN) or EtherNet are preferred for network requirements. RS-485 has a 10 Mbps maximum data rate (@
40 feet) and a 4000 foot maximum cable length (@100 kbps.) RS-485 is robust and well suited for long
distance networking in a noisy environment.
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CAN Products for AC Induction Motors
CAN is an acronym for
Controller Area Network and refers to a fault-tolerant communications protocol that is
flexible for system design, supports multiple network topologies, and has become a de facto standard for
high integrity serial communications in industrial and automotive embedded applications. In a CAN network,
several short pieces of data like a motor’s run status, temperature, or RPM is broadcast over the entire
network at up to 1 megabit per second (Mbps.) CAN is meant for applications that have to
report and consume numerous but small pieces of data consistently among nodes and has the ability to
self-diagnose and repair data errors. CAN is well-suited to environments with machinery, since CAN is
designed to be reliable in rugged environments that include interference or introduce noise. CAN is also
well-suited to the transportation industry.
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USB for AC Induction Motors
USB is a standard connection
interface between computers and digital devices. A USB transceiver is a physical layer
device that prepares data for transmission and then sends to, and receives data from, another transceiver.
The transceiver detects connection and provides the low level USB protocol and signaling.
The term "transceiver" indicates an implementation of both transmit and receive functions. It transmits and
receives, encodes and decodes data, provides error indication, implements buffers to stage data until it can
be managed, and adjusts for the clock rate from the serial stream on the USB SuperSpeed bus to match that of
the “link layer” higher up on the communication stack.
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ESD for AC Induction Motors
Electrostatic Discharge
(ESD) is a naturally occurring phenomenon. If you have ever been zapped by a socks-wearing
kid who has just discovered static charge build up, you have experienced ESD first hand.
ESD is like a miniature, localized lightning bolt caused by an electrical discharge. ESD can have seriously
damaging effects on an integrated chip or system and cause poor performance or failure later on by merely
weakening the circuits.
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LCD Displays for AC Induction Motors
LCD means "liquid
crystal display." It is an electronically driven flat panel screen that orients liquid
crystals within the panel in a direction that blocks or transmits light coming from behind the
panel. LCDs are a low cost, energy efficient visual display that can be controlled in
segments or as individual pixels, in shades of black and gray or in full color. LCDs have most commonly
replaced bulky cathode ray tubes in televisions and computers and are available in all sizes. Liquid
crystals were first discovered in 1888, but were first put into common use in the early 1970s as electronic
digital-display watches.
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Processors for AC Induction Motors
The term "processor" refers
to an electronic device that performs computational functions and carries out the instructions of a stored
program. Other terms for processor are microprocessor, central processing
unit, and digital signal processor. Essentially, the processor refers to "the
brains of a computer."
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Drivers for AC Induction Motors
Designers of power electronic circuits must
often drive power switches that feed DC, AC, or power signals to a variety of workloads. Logic-level
electronic circuits provide the driving signals. In general, however, the power sources and their loads have
reference levels different from that of the control circuitry (ground). MOSFET selection begins by choosing
devices that can handle the required current, then giving careful consideration to thermal dissipation in
high current applications.
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ADCs for AC Induction Motors
An Analog-to-Digital Converter
(ADC or A/D converter) measures the magnitude of an input analog signal
and converts it to a digital number that is proportional to the magnitude of the voltage or current. An
ADC often converts signals collected from the real-world to digital signals for processing.
One of the more important specifications of an ADC is the resolution that it offers, which is the number of
discrete values (represented in bits) that the ADC produces in relation to the analog signal it is
converting. The more bits, the higher the resolution. A higher resolution yields a more accurate
approximation of the analog input.
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Power Stage for AC Induction Motors
Some applications must feed high levels of
current and voltage to power heavy electrical loads. The power stage is a circuit of
electronically-controlled transistors that act as high current switches. In applications powering heavy
loads, the power stage is the driving force. MOSFETs or IGBTs are commonly
used in a "bridge" configuration to drive motors. Selection for the power stage begins by
choosing devices that can handle the required current, and careful consideration must be given to thermal
dissipation. MOSFETs and IGBTs are transistors capable of withstanding the
duty of switching high power signals, and mean "metal–oxide–semiconductor field-effect transistor" and
"insulated gate bipolar transistor", respectively.
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Amplifiers for AC Induction Motors
A precision amplifier is
used for sensors to preserve accuracy. It increases the amplitude of weak signals it receives while
introducing as little noise as possible so that the signal transfers an accurate or precise measure of what
it is sensing. Amplifiers have enormous voltage gain, often use feedback of the output
signal back to the input of the amplifier to operate, and can be classified in different ways. An
amplifier can be identified by the device they are intended to drive (e.g., audio
amplifier), the input that they are to amplify (e.g. sensing amplifier), the frequency range of the signal
(e.g., RF, audio), and by the function that they perform (e.g. buffer amplifier,
current-sensing amplifier.)
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Temp Sensors for AC Induction Motors
A temperature sensor is a
device that measures cold or heat as a temperature or temperature gradient. Many
applications require some implementation of temperature sensing and measurement. For motors, the operating
temperature inside the case is monitored by the processor and set to alarm or shut down at temperatures
higher than the normal operating temperature of the motor. If a motor runs at too high of a
temperature for too long, it can reduce the life of the motor. Operating temperature is an
indication of the general operating health of the motor. Higher temperatures inside the
motor case can mean too high of a load is placed on the motor, since as load increases,
motor current consumption increases to meet the load requirements.
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Hall Effect Sensors for AC Induction Motors
Hall Effect sensors are
magnetically biased transducers that vary output voltage or current in response to changes in a magnetic
field. Hall Effect sensors can be designed to sense rotary movement of a motor shaft. The rotation of the
motor shaft changes the IC's position with respect to the magnets, and thus detects the
change in flux density. The output of the IC is converted to a linear output over 90 degrees of shaft
travel. The Hall Effect sensor gets its name from Edwin Hall, who, in 1879 discovered that
a voltage difference can be produced across an electrical conductor where the magnetic field is
perpendicular to the direction of current flow.
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Encoders for AC Induction Motors
An encoder, when used with
motors, is an electro-mechanical apparatus that translates the angular position of the shaft of the motor
into an electronic signal that a processor can understand. The information is then used to calculate and
report on speed of the motor, distance, revolutions per minute (RPM) or position, usually for the purpose of
automatic feedback control, some kind of intervention, or shutdown.
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