Abstract: A portable electric device in which a surveying arrangement is incorporated for permitting a reading of the corresponding operating condition. The surveying arrangement consists of a visual reading instrument which is arranged on the casing so as to be within the range of vision and which is indicating respective characteristic data of the corresponding operating condition.

Abstract: Speed regulation, either closed loop or open loop, in a hand-held electric tool such as a drill, a miller, a saw or, in particular, combination tools for home use, is carried out by use of a microcomputer. Then-present operating conditions such as the speed of the drill bit, the direction of rotation of the bit, the presently engaged gear, etc. are indicated by a display which has a plurality of fields which are selectively lit. Alternatively, the display can include a seven-segment indicator for displaying the speed. Overload indication is also furnished, as is an automatic shutoff when the motor current exceeds its nominal value. The display, overload indication and shutoff, etc. are all computer-controlled.

Abstract: A universal motor is energized by a speed setting circuit during one half wave and a speed control circuit during the next half wave of each cycle of an AC supply. The speed setting and speed control circuits each have a separate timing circuit including a capacitor. There is thus no residual charge on the capacitor of the speed setting circuit remaining from the operation of the speed control circuit during the preceding half wave. The residual charge prevented the setting of low motor speeds in the known systems. The speed control circuit includes a storage capacitor transformer coupled to the motor so that its initial charge corresponds to the current through the motor during the preceding half wave. The charge is transferred to a second capacitor. When the voltage across the second capacitor reaches a predetermined threshold valve, a switch in the speed control circuit becomes conductive and current flows through the motor.

Abstract: A first thyristor, under control of a speed setting provided in an RC circuit varies the phase duration of current supply to the motor during positive halfwaves of the a c supply, and a second thyristor controlled in accordance with the motor current provided through the first thyristor determines the phase angle during which current flows through the motor in the negative halfwave of the voltage supply, so as to maintain the speed at the set value under varying conditions of load. During positive halfwaves, a capacitor is charged to a voltage corresponding to the amount of current flow through the motor and during the following negative halfwave, the charge is increased at a rate set by an RC circuit, resulting in turning on the second thyristor early under heavy load conditions, and late under light load conditions, and indeed not at all under idling conditions.