| 摘要 |
A motor overload coil control is disclosed for use in a motor starter/relay contactor. The control includes an 8-bit, 8-pin microcontroller that together with an I/O reduction circuit, is capable of functioning 13 I/O's with only 5 I/O pins on the microcontroller. Three remote signals are prioritized and reduced on one input line to the microcontroller. The control includes three-phase current measurement from three Hall effect current sensors positioned one on each leg. The system includes current integration to provide a single current input to the microcontroller. A full load amperage (FLA) adjustment allows use on a wide range of motors. The microcontroller uses the FLA adjustment and the current signal to find an appropriate I2t value for real-time monitoring of the operating temperature of the motor. A status indicator is provided having an LED output to show the status of the system and indicate the motor temperature, when appropriate. After the coil is initially pulled in, the microcontroller generates a PWM signal to keep the appropriate coil pulled in with reduced power. The system includes an internal 24VDC sensor to ensure proper DC voltage level, and to adjust the PWM for variances in voltage levels. Pushbutton test and reset switches are provided, as well as a solid state remote reset.
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