| 摘要 |
A thermistor having a positive temperature coefficient is connected in series with a manually operated variable resistor in the turn-on control gate circuit of a thyristor (SCR1, TR1) which regulates the speed of a portable electrical tool, to be precise, this thermistor being thermally connected to the thyristor (SCR1, TR1) in order to provide overload protection for the tool motor and the thyristor (SCR1, TR1), which protection gradually reduces or increases the motor speed, to be precise in the case of overload currents, in order to keep the power supplied to the motor insufficient to drive the motor but adequate to allow the stopped motor to produce an audible humming tone and a vibration which can be felt in order in this way to indicate the presence of power on the tool motor.
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