Abstract: The multiplexer in a multichannel, secure digital communication system repetitively embeds a sequence of byte length uniquely coded synchronizing signals in each of n successive frames of one channel of a multichannel, time multiplexed digital bit stream. Redundant protective relay data and associated parity check data are embedded in four of the n frames in a second, preferably adjacent channel, with the remaining of the n frames in the second channel containing additional of the uniquely coded synchronizing signals. The time multiplexed serial bit stream is transmitted to a remote station, preferably by fiber optic communications media. The most recent bits of the received serial bit stream equal in number to the number of bits spanned by the two channels in n frames are retained in n-1 serially connected serial in, serial out shift registers. Sixteen bit portions, a frame apart, of the retained most recent bits of the serial bit stream are applied to n serial in, parallel out shift registers.

Abstract: A microprocessor controlled motor starter is utilized in which an operator can preprogram within limits the number of starts which a motor can be subjected to in a programmed period of time to thus prevent destruction of the motor by accumulated overheating. Significantly more heat is generated during a start of a motor than during the run mode. The foregoing is accomplished by utilizing memory locations in which accumulated times from a first start are sequentially stored in order. If the time found in the latest memory location is larger than the predetermined maximum allowable time then the start is allowed to take place. If it is less than that time then the start is prevented from taking place and a readout alerts the operator as to how much time must expire before the next allowable start may take place.

Abstract: A microprocessor controlled motor starter is utilized in which the short term temperature differential between the rotor bars and the rotor end bells is accounted for by the microprocessor-based system as a function of operator programmed stall time and locked rotor current for the particular rotor in question. The latter information is supplied to the operator by the manufacturer of the motor. The foregoing takes into account a slight deviation between the shutdown temperature, which should be predicted as a function of the manufacturer's data, and the actual shutdown temperature as expressed by an exponential. In the event that the short term temperature differential is exceeded, the microprocessor will enter a TRIP routine causing the motor controller to shut the motor down, thus preventing serious damage to the motor.

Abstract: A microprocessor controlled motor starter is utilized in which the sign values of two phases of voltage are sampled and stored prior to actual motor startup to determine if a phase reversal, a phase imbalance, or a phase loss exists. If any of the preceding conditions exist, the motor start operation is aborted. This generally requires sampling the signs of the appropriate voltages three times during each voltage cycle at approximately equal intervals of 120.degree., give or take 10.degree. or so, and then forming a matrix of voltage signs versus sampling intervals. By comparing diagonal measurements of the sign values in the matrix for three diagonals in a direction of advancing time, phase loss or imbalance can be determined. The determining factor is that each diagonal must contain two values which should be equal, that is, both should be digital ones or both should be digital zeros. If such is the case for the three diagonal measurements, then no phase imbalance or loss exists.

Abstract: A microprocessor control motor starter is utilized in which the microprocessor measures the status of AC input signals which are coupled thereto by way of an isolating electro-optical device. The electro-optical device provides a square wave output signal. Thirty-six samples are made to determine if the output signal is at a digital "1" level or a digital "0" level. If more than 18 digital "1's" are found, that is an indication that the device has failed and a trip operation is initiated by the microprocessor. If less than 18 but greater than some arbitrarily chosen small number such as 6 is found, that is an indication that the switch empowering the optoelectrical device is in a closed but valid disposition. If a number less than 6 is found, that is an indication that the switch is in the open disposition. If the device is failed, the microprocessor will trip the motor.

Abstract: A microprocessor control motor starter is utilized in which a capacitor-backed random access memory is utilized to store certain critical data about the status of a motor so that if the power supply voltage temporarily drops below a certain value the critical information will not be lost. The microprocessor which controls the motor attempts to reinitialize itself as in the case long term power outage. A subroutine is provided which determines whether the motor can immediately be placed in the state it was in before the power outage occurred, or whether an automatic restart may take place, or whether the motor must be operator restarted manually.