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3M employee and church chorister Art Fry needed something to temporarily mark pages in his hymnal. He was in luck because his colleague, Spencer Silver, accidentally developed a glue that was too weak for other purposes. After initially discouraging consumer response, Post-it Notes became a hit in 1979.
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| Number | Title | Issue Date |
| 4896242 | Direct AC-DC converter fault protection system In a direct AC/AC converter, fault protection is performed with a minimal number of fault detecting devices and the rating of such fault detecting devices is reduced while still being able to respond quickly to a fault current. This is achieved by using a... | 01/23/1990 |
| 4893211 | Method and circuit for providing adjustable control of short circuit current through a semiconductor device A method for limiting short circuit current flow in a Field Effect Transistor (FET) to limit the power dissipated therein includes sensing a rise in the drain-to-source voltage of the transistor and clamping the gate-to-source voltage to a predetermined a... | 01/09/1990 |
| 4890183 | Device for detecting cutoff and short circuit defects in at least one electrical circuit portion The invention relates to a device for detecting cutoff and short circuit defects in at least one electrical circuit portion. The detecting device (10) is intended to verify a circuit portion (11) connected to the terminals of a source of direct current (T... | 12/26/1989 |
| 4890184 | Molded case circuit breaker actuator-accessory unit An integrated protection unit is a circuit breaker which includes basic overcurrent protection facility along with selective electrical accessories. A molded plastic accessory access cover secured to the integrated protection unit cover protects the acces... | 12/26/1989 |
| 4885657 | Thyristor with turn-off facility and overvoltage protection In a thyristor with turn-off facility (AT) and overvoltage protection, the voltage limitation is achieved by a parallel-connected controllable resistor, in particular in the form of a J-FET (JF) which is driven by an overvoltage sensor (OS). The separatio... | 12/05/1989 |
| 4878143 | Line current to time interpolator A line current to time interpolator circuit senses the magnitude of current in a power distribution line and develops and AC voltage indicative of the current magnitude. The AC voltage is phase shifted multiple times to produce a number of phase shifted r... | 10/31/1989 |
| 4876624 | Apparatus for detecting unsymmetrical bipolar waveforms A predetermined unsymmetry of a bipolar waveform is detected by apparatus which includes a circuit which generates a pulse for each zero crossing of the waveform. Each zero crossing pulse triggers a first retriggerable one-shot for a first interval T... | 10/24/1989 |
| 4873602 | Ripple attenuator for AC power transmission line protective relays A circuit for preventing the generation of an erroneous output signal from a protective relay for detecting faults in a three phase alternating current electrical power distribution system, which relay uses a full wave rectified signal as an operate quant... | 10/10/1989 |
| 4868412 | Distributed control system A control system is provided in which a plurality of independent control elements are each capable of generating a random value and determining a time delay as a function of that random value. Each of the control elements accesses the magnitude of a sense... | 09/19/1989 |
| 4862308 | Power bus fault detection and protection system A power bus fault detector for detecting faults in a predefined portion of an electrical power bus having at least one phase. Power feed lines are coupled to the predefined portion of the power bus by circuit breakers. Current transformers are used to det... | 08/29/1989 |
| 4851759 | Unity-gain current-limiting circuit A highly accurate current-limiting circuit prevents an output current (IOUT) flowing through an output line (LOUT) from exceeding a specified value (ILIM) of an input current (IIN) flowing through an input line ... | 07/25/1989 |
| 4847723 | Volt-per-hertz protection apparatus An inverse-time timer for a volt/Hertz ratio relay includes a ladder of level detectors associated with a like series of counters connected in cascade with a variable voltage-to-frequency connector responsive to the v/Hz ratio signal for controlling the c... | 07/11/1989 |
| 4839770 | Control circuit with validity-determining arrangement An arrangement is provided for checking the validity of a sensed-current signal from a current-sensing device. The sensed-current signal represents the current in a line. An associated control circuit utilizes the sensed-current signal to indicate or pred... | 06/13/1989 |
| 4837653 | Quasi-power measurement circuit A circuit for signaling when an electrical component is consuming excessive power and for protecting the electrical component from the excessive power. The electrical component is connected to a circuit which supplies and measures the current through and ... | 06/06/1989 |
| 4837672 | Switched mode power supply An electronically switched power supply that automatically adjusts its operation to produce a fixed output voltage as input voltages of different magnitudes are applied at different times and which has a circuit breaker and circuit breaker control circuit... | 06/06/1989 |
| 4835652 | Bi-directional DC power controller with fault protection A bi-directional DC power controller is provided with a bi-directional DC switch connected between a pair of terminals for connection to a pair of line power conductors. A first difference amplifier is connected to receive voltages at these terminals and ... | 05/30/1989 |
| 4833414 | Method and apparatus for the identification of a faulty conductor in a multiple supply line A method of and apparatus for determining which if any phase of duplex supply lines wherein each phase w is assigned two conductors w1 and w2. The method and apparatus use an asymmetry value, for example a function of the relationship (output of 9) of the... | 05/23/1989 |
| 4831484 | Electrical safety barrier for protection of electrical load elements placed in potentially hazardous locations The barrier input and output each have two terminals. In at least one connection between the barrier input and the barrier output, there is an electronic in-line control element having a control input as well as, in series with the in-line control element... | 05/16/1989 |
| 4831483 | Abnormality detection alarm circuit for output circuit To turn off an output transistor and generate an alarm whenever a load driven by the output transistor is shorted or opened, the abnormality detection alarm circuit comprises a short detection circuit; an open detection circuit; a delay circuit; an output... | 05/16/1989 |
| 4825327 | Negative and zero sequence directional overcurrent unit for AC power transmission line protection A protective relay for detecting faults within a predetermined protected zone of a three phase alternating current electrical power distribution system, of the type which utilizes at least one restraint signal in conjunction with at least one operate sign... | 04/25/1989 |
| 4819122 | Over-current timer modulator A modulator circuit for providing a modulating signal to the timing circuit in a constant off time current mode controller so as to extend the off time in response to an overload condition. A switch connects the output voltage from a current sense amplifi... | 04/04/1989 |
| 4819121 | Security apparatus for power converter A security apparatus adapted to a power converter, including a power converting circuit connected between a DC power source and an AC system; a phase detector circuit for detecting the voltage phase of the AC system to provide a phase detection signal; a ... | 04/04/1989 |
| 4819124 | Overcurrent detector and circuit breaker A solid state overcurrent detector is provided with a current sensor means (200) having an OR circuit (130) connected by its input terminals to output terminals of burden circuits (41,42,43). A phase selecting circuit (400) for selecting the largest phase... | 04/04/1989 |
| 4814935 | Circuit breaker reactive to three time-overcurrent characteristics A circuit breaker having three level discriminating circuits and time-current operating circuits, respectively corresponding to an instantaneous releasing, a short time characteristic releasing and a long time characteristic releasing of disconnectable co... | 03/21/1989 |
| 4803592 | Power control and fault isolation indicator A power supply system, which supplies a number of different A.C. and D.C. voltage levels to a plurality of loads, is monitored at a number of points for undervoltage, overvoltage and/or overcurrent fault conditions. A diagnostics logic circuit, which is f... | 02/07/1989 |
| 4797775 | Symmetrical fault current detector Excess currents due to faults in an electrical power system are generally larger than excess currents due to the magnetization of distribution transformers. Discrimination has hitherto relied on a threshold detector. Magnetizing currents are, however, asy... | 01/10/1989 |
| 4797774 | Signal conditioning circuit A signal conditioning circuit including power terminals adapted to be connected to a direct current power source, sensor terminals adapted to receive a direct current signal from at least one electrical sensing device and output terminals adapted to be co... | 01/10/1989 |
| 4796148 | Current-sensing arrangement utilizing two current-sensing signals An improved current-sensing arrangement and method are provided for supplying a signal that suitably represents line current over a wide current range. The current-sensing arrangement utilizes the signals from an iron core transformer and an air core tran... | 01/03/1989 |
| 4796145 | Semiconductor module A semiconductor module includes two switching devices operated by the PWM control signal, current detectors for detecting currents through the respective switching devices, and bypass units operated by the corresponding opposite current detector for shunt... | 01/03/1989 |
| 4788620 | Static trip circuit breaker with automatic circuit trimming Electronic trip units employed within static trip circuit breakers are individually calibrated and automatically adjusted to ensure that the trip transfer characteristics are within specification requirements. A trimming network within the trip unit circu... | 11/29/1988 |
| 4783690 | Power semiconductor device with main current section and emulation current section A power semiconductor device incorporates in its active, or current-carrying, region a main current section and an emulation current section. The active region is surrounded by a common device termination region. This is accomplished through provision of ... | 11/08/1988 |
| 4782422 | I2 t monitoring circuit An I2 t monitoring circuit utilizes a multiplier to provide a signal that is representative of the squared value of a monitored current. The squared signal minus a DC level is provided as an input to a voltage-to-frequency converter and the out... | 11/01/1988 |
| 4780789 | Method for generating circuit-breaking signals A method for generating a circuit-breaking signal in dependence upon the magnitude and duration of an excess current, where a measured quantity, derived from the excess current, is sampled, is converted into digital values, and these values are weighted i... | 10/25/1988 |
| 4780786 | Solid-state trip unit of an electrical circuit breaker with contact wear indicator A digital solid-state trip unit of an electrical circuit breaker is equipped with an electrical contact wear indicator enabling the degree of wear of these contacts to be known. Each time the circuit breaker performs a break, the microprocessor determines... | 10/25/1988 |
| 4777554 | Method and apparatus for detecting charger abnormality A charger abnormality detecting device and method uses a current detector for detecting a current flowing between a photoconductive drum and a charger arranged near the drum, a current detector for detecting a current flowing through the charger, and a vo... | 10/11/1988 |
| 4774621 | Protective control method and apparatus In an apparatus for producing data concerning a fault in an AC electric power system, an AC electric quantity is sampled at a frequency which is a multiple of the rated frequency of the AC electric quantity, and is stored, for later use as predicted value... | 09/27/1988 |
| 4771357 | Power driver having short circuit protection A power driver including a switch (17) that connects between a power input terminal (12) and a power output terminal (13). A current sense unit (22) provides an over current sense signal if an over current condition should exist with respect to the switch... | 09/13/1988 |
| 4769735 | Inverse-time relay An inverse-time relay is disclosed which comprises a voltage dividing circuit for dividing a d.c. voltage proportional to a current value in a line to be protected by a plurality of ratios different from one another thereby to provide a plurality of volta... | 09/06/1988 |
| 4764838 | Regulated alternator with positive fault related shut down apparatus A permanent magnet generator and rectifier is connected to the exciter of an alternator and a separate rectifier provides a D.C. voltage supply to a voltage regulator. A thyristor is connected in series with a second fuse across the exciter rectifier to s... | 08/16/1988 |
| 4761706 | Method for generating a tripping signal as a function of the magnitude and the duration of an overcurrent A method for generating a tripping signal as a function of an overcurrent. Sampled measurement values are converted into digital values which are weighted and added up according to a predetermined function. If the sum value is above a predetermined refere... | 08/02/1988 |
