PLC should pay attention to what problem - when motor fault detection - programmable logic

PLC is a micro controller, from this perspective, it emphasis lies in dealing with simple data and status, the difficulties and motor fault is measured, because need different sensors to determine whether a motor is relatively reasonable, the space is very small, but the motor is not suitable for a huge number of sensors installed, so through the PLC to determine whether a motor has a problem, often are simple types, such as overheating and flow, but the motor is normal needs a lot of dimension variable to describe.

simple power supply power frequency control of motor, such as not according to the speed control system of three-phase asynchronous motor, the working time, generally just according to the installed in the main circuit and overheating protection device, implementation of the so-called overload protection. Nature is also use some of the things of bimetallic strip, series to the main loop of the motor, when the motor current suddenly become larger, such as how many seconds more than rated current, bimetallic strip deformation because of the large current fever, push rod device, such as make contact state changes, the contact can be used to relay or PLC controller to cut off the main circuit, so as to protect the motor overload state for a long time, to avoid burning motor.

the above contact, can be normally open, also can be normally closed, generally with FR said, if there are multiple sets of such motor, at the same time in accordance with the overheating protection, respectively will output FR1, FR2, FR3, such contact signal, can be directly connected to the input terminal of PLC, can also through the intermediate relay isolation after input, such as the image below. And the primary loop interlock, is such a figure, just drew FR1 this loop, other is exactly the same, you can reference.

, in fact, this process, only have the effect of a similar isolation and data collection, completely can be done through traditional relay. There are, of course, the so-called integrated motor protector, the structure and overheating protection is similar, but added a lot of features, for example can be implemented through the years, locked-rotor, overvoltage, undervoltage, electric leakage, three-phase imbalance, lack of phase, bearing wear, even the stator in eccentric type, such as fault detection, its contact signal similar access to PLC, can realize the PLC control and management of fault.

motor protector role is to give comprehensive protection, in the motor overload, over current, lack of phase, locked-rotor, short circuit, overvoltage, undervoltage, electric leakage, three-phase imbalance, overheating, bearing wear, set the rotor eccentricity, shall report to the police or protection device. In fact, now many of the motor with a driving gear, such as asynchronous three-phase inverter is widely used in motor speed regulation, and the drive itself has brought all kinds of motor state detection, timely diagnose and deal with the fault, PLC controller only need to read the failure condition of frequency converter, you can indirectly control the motor fault.

because of PLC controller scan cycle, using PLC to detect and control the motor fault, need to notice this lag issues, especially the alarm overload, often need to respond in a short period of time, cut off the power supply in time, if because of the delayed scan cycle, motor burn asked risk occurs, some may even endanger the equipment and the personal, so using PLC to control the testing machine state is allowed, as a kind of quadratic nature of the monitoring should be handled, could not be used for real-time fault control.

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