Abstract: A self powered trip indicator remotely reads out parameters such as the type of trip detected in a contactor or motor starter circuit controllably coupling a power line to a load. The contactor circuit imposes signalling pulses on a trip status signal following a transition of the signal to a fault-indicating level, the pulses representing the parameters. The remote trip indicator derives operative power from the trip signal, and decodes the parameter from the pulses, using a decoder such as a counter to accumulate a binary multiple count of pulses, the result being indicated on LEDs coupled to outputs of the decoder. A switching circuit generates a short reset pulse to the counter at a leading transition following a pulse or level of a width exceeding a time limited by an RC combination coupled to the counter reset input.

Abstract: A transition sensor is responsive to transition of a positive temperature coefficient resistive element from a nominal low resistance state to a protective high resistance state. A positive temperature coefficient (PTC) element is placed in a power distribution circuit between a power source and a load. Excessive load current in the event of a high current fault heats the PTC element to a threshold temperature at which the PTC element transitions into a protective state of high resistance, limiting current flow to the load. The LED of an optoisolator is coupled in parallel with the PTC element, preferably with a resistor in series with the LED. Under nominal current conditions the voltage across the LED is less than its forward bias voltage. During a high current fault, the LED becomes forward biased and switches on the optoisolator phototransistor to operate an alerting device such as an audible alarm and/or a light.

Abstract: A controller such as a programmable logic controller (PLC) is coupled to a load such as a contactor or motor starter through an interface that operates over a range of DC or AC voltage and couples a Start output of the controller to the load through a low current switch such as an opto-relay. The interface has a charging circuit coupled to the controller output, with a switching transistor, a load resistor and a capacitor in series. The low current switch is operated from accumulated charge in the capacitor and couples power to the load device. Charging of the capacitor to a threshold switches off of the transistor for an interval timed by a one-shot, during which the low current switch remains activated due to current draining from the capacitor. In an AC embodiment with a triac controller output, the capacitor continues to power the low current switch for the remainder of the positive AC half cycle, regardless of the triac, which may cease conduction due to lack of sufficient loading.

Abstract: The coil holding current of a contactor is regulated to the lesser of two measurements of coil current during each cycle of the full-wave rectified control voltage to compensate for induced flux in the coil generated by load current through the main contacts of the contactor, thereby preventing uncontrolled drop out of the contactor.

Abstract: Microprocessor based apparatus for controlling an electrical load, such as a motor, includes an external capacitor for storing an analog equivalent of a digitally modeled heat state signal, such as the I.sup.2 t characteristic of the motor. The voltage on the capacitor decays to mimic motor cooling when the microprocessor is powered down with deenergization of the motor. The stored analog signal is updated by periodically converting the analog signal to a retrieved digital heat state signal which is compared to the latest calculated value of the heat state signal. If the retrieved value is below the present calculated value, an input/output port is set to a high output state to charge up the storage capacitor. If the retrieved value is above the calculated value, the port is configured as an output port with a low state to reduce the voltage on the capacitor.

Abstract: A method and apparatus for remotely displaying information about heat in a motor having an associated motor-starting contactor with an overload relay system is provided. The apparatus includes a suitably programmed microprocessor which obtains a signal representative of current in the motor, squares the current and multiplies by time. This actual I.sup.2 t value is then used to calculate a signal representative of a relationship between the actual I.sup.2 t value and a target value at which the contacts of the motor-starting contactor will open due to an overload current situation. This relationship is preferably a percentage which is then displayed on either an LED bar type display or a digital display. The display may also include a "trip" indicator and a "reset allowed" indicator.

Abstract: Control circuitry is disclosed for electrical starters, contactors and the like having a starting winding and a serially coupled holding winding wherein the holding winding is shorted until the separable main contacts have closed which includes circuitry which obviates the need for relatively precise sensing of the position of the separable main contacts to control the holding winding. In one embodiment of the invention, the unshorting of the holding winding is delayed a predetermined number of cycles after the separable main contacts have closed to avoid the necessity of relatively accurate mechanical sensing of the position of the separable main contacts. In this embodiment a relatively less expensive field effect transistor or the like is used to short out the holding winding until the separable main contacts have closed. This allows the use of a relatively less expensive limit switch with a substantially smaller DC capability.