PLC英文课件

ECET 4530
Industrial Motor Control
Lecture Slides
Functions of a Motor Controller
• Safe starting of a motor (or system)
- remote starting of the motor - following a required startup sequence - limiting the starting current - preventing startup under certain conditions - detecting a locked-rotor condition - allowing for no-load startup of the motor
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Types of Motor Controllers
• Manual • Semi-automatic • Automatic - Once operational, the controller responds to signals from pilot devices to initiate any required events.
Motor Controller
ON/OFF Switch
Questions to Ask
• Can the motor be safely started by applying full rated voltage? • Does the motor need to reverse direction? • Does the motor require braking? • Is speed control required? • Is motor protection required? • Do I need a “complex” controller or will a simple solution suffice??? Think K.I.S.S.
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Common Motor Control Devices
Contactor - The auxiliary contacts may be NO or NC - The electromagnetic may be supplied by a DC or an AC source, at the same level as the load or at a lower “control” level depending on the contactor’s design - Contactors are designed to break the load’s normal operational current but are NOT designed to disrupt “short-circuit” current like a circuit breaker
Questions to Ask
• Can the motor be safely started by applying full rated voltage?
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Questions to Ask
• Can the motor be safely started by applying full rated voltage? • Does the motor need to reverse direction? • Does the motor require braking? • Is speed control required?
• Manual • Semi-automatic - operator initiates an event (by pressing a button, etc.) but the motor controller then automatically handles the event, possibly requiring a series of small, sequential steps
(Pilot devices are devices that monitor speed, temperature, pressure, time, level, or other conditions and signal the controller when a trigger point is reached)
Contacts remain open-circuited unless button is pressed
Electric Contacts
Common Motor Control Devices
Push Buttons Normally Open (NO) Normally Closed (NC)
Common Motor Control Devices
Contactor - Main power contacts provide power to the motor or other high-current “load” - Auxiliary contacts may be used to provide logic to other parts of the motor controller - An electromagnet provides the necessary force to change the position of the contacts - The enclosure houses the contacts and the electromagnet
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Common Motor Control Devices
Contactor - Main power contacts provide power to the motor or other high-current “load” Note that although contactors are basically chosen by the current carrying capacity of these contacts, they are “rated” in terms of horsepower relating to the maximum size motor that they can control.
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Types of Motor Controllers
• Manual - controller is operated by hand - every change in operational state requires direct intervention by an operator
Types of Motor Controllers

Types of Motor Controllers
• Manual • Semi-automatic • Automatic - Once operational, the controller responds to signals from pilot devices to initiate any required events. - May use relay logic, digital logic or a programmable logic controller
Common Motor Control Devices
• Push Button • Contactor
Common Motor Control Devices
Contactor - Electrically controlled switch or relay used to provide power to high-current devices such as motors, furnaces, distributed lighting, etc.
Contacts remain short-circuited unless button is pressed
Common Motor Control Devices
Push Buttons Normally Open (NO) Normally Closed (NC) Combination
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Questions to Ask
• Can the motor be safely started by applying full rated voltage? • Does the motor need to reverse direction? • Does the motor require braking? • Is speed control required? • Is motor protection required?
• • • • Safe starting of a motor Safe stopping a motor Reverse the motor’s direction of rotation Control the speed of the motor
- operator adjustable speed control - automated/programmed operation
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Common Motor Control Devices
Push Buttons Normally Open (NO) Normally Closed (NC)
User presses in this direction Button (shown in normal or at-rest position)
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Functions of a Motor Controller
• • • • • • Safe starting of a motor Safe stopping a motor Reverse the motor’s direction of rotation Control the speed of the motor Provide braking to decrease motor’s speed Protect the motor from overloading, overheating, runaway, or other unsafe operating conditions