Abstract: Timing the firing of thyristors in a motor controller is done by using a microprocessor for timing relative to the event of current reaching zero, and by using hardware that generates firing signals in response to the voltage crossing zero. A motor controller has: thyristors for connecting the motor to a source of AC electrical energy; motor voltage zero crossing circuitry and motor current zero crossing circuitry for measuring a LAG TIME indicative of the time interval between the event of voltage applied; to the motor crossing zero and current flow to the motor reaching zero; a microprocessor generating a desired OFF TIME indicative of a desired time interval between the event of current flow to the motor reaching zero and firing of the thyristors; phase angle controller circuitry for firing the thyristors at a firing time after the event that the voltage applied to the motor crosses zero, the firing time being computed by adding the LAG TIME and the OFF TIME.

Abstract: A reduced voltage starter for gradually starting a polyphase motor having an acceleration control circuit for gradually applying power to the motor and detector circuits for detecting various fault conditions for terminating power to the motor. A shorted solid state switch detector senses when one of the semiconductor switches applying power to the motor is shorted to terminate the application of power from the remaining phases. A phase angle control circuit insures a uniform application of power to the motor. A phase rotation detection circuit detects when the three phases are in other than their correct sequence and terminates power in the event of such detection. An underload detection circuit senses when the current drops beneath a preselected reference after the motor has reached its full speed and terminates power in response to such detection. A line-to-line-to-line-to-neutral convertor produces signals representative of the line-to-neutral voltages which are necessary for other circuit functions.

Abstract: A gate drive circuit for a thyristor has a power supply and an amplifier for supplying current to a gate electrode of the thyristor. A timing signal is generated to initiate conduction of the thyristor. A voltage level signal is generated in response to a voltage from cathode to anode of the thyristor to indicate a reduction in the cathode to anode voltage of the thyristor when the voltage is reduced by conduction of the thyristor. Current is supplied to the gate electrode of the thyristor in response to the timing signal, and current ceases to flow to the gate electrode of the thyristor at a predetermined time interval following generation of the voltage level signal indicative of a collapse in cathode to anode voltage of the thyristor caused by conduction of the thyristor, and the predetermined time interval is chosen to be of sufficient duration to permit conduction of the thyristor to reach a stable value before current flow to the gate electrode of the thyristor substantially ceases.

Abstract: A system for sensing the phase of a three-phase AC system and detecting phase reversal and undervoltage and phase unbalance and for providing a switching function when the system is not functioning properly.

Abstract: A thermal overload detector and interrupter has a current transformer for monitoring load current and providing a current value signal, a microprocessor for calculating values related to load current and the thermal characteristics of a load, and an interrupter for selectively conducting and interrupting load current. The microprocessor computes a square current value from the current value signal and multiplies the square current value by a predetermined constant to obtain a multiplied square current value. The predetermined constant is related to the heat transfer characteristics of the load. A present running sum is computed in the microprocessor by adding the multiplied square current value to a past test value. The microprocessor then computes a proportionate present running sum by multiplying the present running sum by the predetermined constant. A present test value is computed by subtracting the proportionate present running sum from the present running sum.

Abstract: A reduced voltage starter for gradually starting a polyphase motor having an acceleration control circuit for gradually applying power to the motor and detector circuits for detecting various fault conditions for terminating power to the motor. A shorted solid state switch detector senses when one of the semiconductor switches applying power to the motor is shorted to terminate the application of power from the remaining phases. A phase angle control circuit insures a uniform application of power to the motor. A phase rotation detection circuit detects when the three phases are in other than their correct sequence and terminates power in the event of such detection. An underload detection circuit senses when the current drops beneath a preselected reference after the motor has reached its full speed and terminates power in response to such detection. A line-to-line to line-to-neutral converter produces signals representative of the line-to-neutral voltages which are necessary for other circuit functions.

Abstract: A machine tool timing relay has immunity from electrical noise on a control signal, and has an oscillator capable of generating pulses having a predetermined frequency, a means for adjusting the predetermined frequency over a continuous range of frequencies, a counter capable of counting the pulses and capable of generating an output signal after a predetermined number of the pulses are counted, means responsive to a start signal for initiating the counter to count the pulses, an optical isolator circuit responsive to the control signal for generating a light, detecting the light, and generating the start signal in response to detecting the light in order to isolate the counter from electrical noise mixed with the control signal, an electrical contact, and an output circuit responsive to the output signal for operating the electrical contact when the counter generates the output signal so that the contact is operated after the counter counts a predetermined number of the pulses.

Abstract: A reference current lag for a motor controller is selected so that the reference current lag approximates the motor current lag when the motor is fully loaded. A motor controller has a plurality of thyristors for controlling electric current flow to the motor. A firing circuit fires the thyristors at a selected firing angle. A current lag, as a phase angle between a power line voltage applied to the motor and electric current flow to the motor, is measured. The selected firing angle is adjusted so that the measured current lag is substantially equal to a reference current lag. A temporary value of the reference current lag is selected. The motor current is monitored, and in the event that the motor current becomes between an upper predetermined motor current and a lower predetermined motor current, the reference current lag is given a final value.

Abstract: A motor controller with means responsive to a motor condition for preventing termination of power to the motor in response to fault conditions when these fault conditions occur during start-up of the motor.

Abstract: Gradual starting of an electric motor is provided by increasing the voltage applied to the motor. A reduced voltage starter controls the application of a voltage derived from a line voltage to a motor by using a voltage ramp acceleration control circuit comprising, means for generating a ramp voltage having a predetermined rate of rise, means for controlling the voltage applied to the motor in response to the ramp voltage, means for sensing that the motor is running at substantially full speed, and means responsive to the means for sensing that the motor is running at substantially full speed for increasing the predetermined rate of rise of the ramp voltage, whereby under conditions where the motor is running at substantially full speed before the voltage applied to the motor reaches the line voltage, then the voltage applied to the motor will rise at the increased predetermined rate of rise of the ramp voltage.

Abstract: This disclosure depicts a novel abort cycle timer circuit for use with an AC source of electrical power and for operating electrical controls for machinery. The circuit provides a substantially DC voltage and current, first and second relays with normally open and normally closed contacts and a timing abort circuit. Opening a first of two switches causes the second of the two relays to energize after a time delay. Opening both switches causes the second relay to deenergize after a predetermined time. The novel circuit has improved immunity to electrical and magnetic noise.

Abstract: An anti-telegraph circuit for locking out the circuit controlling the flow of direct current in a coil winding of an electromagnetically operated switching device, such as a contactor, from an alternating current source whenever improper control voltages are present which would cause repeated operations of the armature picking up and falling out of its sealed position.