Analog electronic thermal motor protection
And s in the last century, with the rise of a semiconductor simulator and popularization, emerge a batch of reliable performance, functional diversity of electronic motor thermal protector provides the reliable operation of the motor with a reliable guarantee, the recognized by the public, with its own brand characteristics represented by south Korean, In the domestic market has a certain influence, and their product variety, complete specifications, the main features include: lack of phase, overload, owe flow, phase unbalance, phase sequence, grounding, short circuit, under-voltage, current, according to the sound and light alarm and analog output, etc., but this kind of product there are still some insurmountable defects, including the following aspects:
1. The setting accuracy is not high, simulated electronic thermal protection is using potentiometer is rated current setting, however, to make the rotation of the potentiometer arm Angle and its resistance to the good linear relationship is difficult, especially in the mass production is hard to do, in addition, the operator of the setting error is also hard to avoid, This is especially true for products that do not display set values.
2. The sampling accuracy is not high, and the analog circuit is at a loss for the nonlinear problems of ct. Even if it can be corrected, the circuit will become very complicated, and even cannot be used in practice. And actually to be made of silicon steel sheet current transformer in the wide range of linear is very difficult, the industry knows that used in the motor thermal protector sampling current transformer should be considered one of the biggest scope to be protected at least seven times the motor rated current because the motor in locked-rotor cases at the rated current of 5 to 7 times; In addition, the sampling circuit itself also has nonlinear problems. Based on these technical problems, achieving high-precision sampling naturally becomes an empty talk.
3. Can not achieve a variety of protection functions in one of the full protection, with the development of society, people's requirements for motor protection are becoming higher and higher, hope that the thermal motor protection function diversification, reliable performance, simple wiring, intuitive interface, and small volume, these are pure analog lines can not be achieved.
In view of the above reasons, motor thermal protectors for purely analog circuits are gradually being replaced by other more advanced technology products.
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