Cash flow monitoring system

In a communications system for interchanging data among members of a plurality of remote electrically operated devices, each of said devices receiving power from a common set of power distribution lines, an improved data link assembly comprising:

• locally controlled clock means for generating a first cyclical waveform at a carrier frequency;
• transmitter means for applying said first cyclical waveform to said power distribution lines;
• phase shifting means for stepping the phase of said first cyclical waveform by predetermined increments in response to signals at a control input;
• transmission control means for providing signals at said control input to cause phase shifts of predetermined intervals representative of binary data to be impressed on said first cyclical waveform;
• means for receiving a second cyclical waveform at a frequency approximately the same as said carrier frequency appearing on said power distribution lines;
• phase comparison means responsive to the phase relationship between said first and second cyclical waveforms;
• and
• synchronization control means for providing signals at said control input to step the phase of said first cyclical waveform by said predetermined increments in order to bring said first cyclical waveform generally into a predetermined phase relationship with said second cyclical waveform during an initial period of data reception, whereupon subsequent phase shifts of said predetermined intervals in said second cyclical waveform representative of binary data may be detected, said synchronization control means operating during data reception only until said first cyclical waveform has been brought into said predetermined phase relationship with said second cyclical waveform.

In a communication system for interchanging data among members of a plurality of remote electrically operated devices, each of said devices receiving power from a common set of power distribution lines, an improved data link assembly comprising:

• (a) a data link including:
• a clock for generating a first cyclical pulse train, said clock having a phase control input and means for varying the phase of said first cyclical pulse train in response to signals at said phase control input;
• transmitting means responsive to said first cyclical pulse train for applying a first carrier signal to said power distribution lines, said first carrier signal having a carrier frequency and being in a constant phase relationship with said first cyclical pulse train;
• receiving means responsive to a second carrier signal generally at said carrier frequency appearing on said power distribution lines, said receiving means having means for generating a second cyclical pulse train at the frequency of said second carrier signal and in a constant phase relationship with said second carrier signal;
• and
• phase comparison means responsive to said first cyclical pulse train from said clock and said second cyclical pulse train from said receiving means, said phase comparison means having means for producing a signal representative of the phase relationship between said first and second cyclical pulse trains;
• (b) signal receiving means and signal generating means together including:
• first means for applying signals to said phase control input on said clock to shift the phase of said first cyclical pulse train by 180.degree. to represent binary data bits to be transmitted;
• and
• second means for applying signals to said phase control input of said clock to step said phase by 90.degree. increments to bring said first cyclical pulse train into a predetermined phase relationship with said second cyclical pulse train during an initial period of data reception in order to permit said phase comparison means to be rendered sensitive to subsequent 180.degree. phase shifts in said second carrier signal, said second means for applying signals operating during data reception only until said first cyclical waveform has been brought into said predetermined phase relationship with said second cyclical waveform.

A system for communication between a central computer and at least one remote electrically operated device, said device receiving power from a set of power distribution lines, comprising:

• means associated with said central computer for sending a polling message on said power distribution line, said polling message having a time structure including a preamble at a carrier frequency followed by binary data represented by phase shifts relative to said preamble;
• a data link associated with said remote electrically operated device comprising:
• locally controlled clock means for generating a first cyclical waveform at a frequency close to said carrier frequency;
• transmitter means for applying said first cyclical waveform to said power distribution lines;
• phase shifting means for stepping the phase of said first cyclical waveform by predetermined increments in response to signals at a control input,
• transmission control means for providing signals at said control input to cause phase shifts of predetermined intervals representative of binary data to be impressed on said first cyclical waveform,
• means for receiving a second cyclical waveform at approximately said carrier frequency appearing on said power distribution lines,
• phase comparison means responsive to the phase relationship between said first and second cyclical waveforms, and
• synchronization control means for providing signals at said control input to step the phase of said first cyclical waveform in order to bring said first cyclical waveform generally into a predetermined phase relationship with said second cyclical waveform during an initial period of data reception, whereupon subsequent phase shifts of said predetermined intervals in said second cyclical waveform representative of binary data may be detected, said synchronization control means operating during data reception only until said first cyclical waveform has been brought into said predetermined phase relationship with said second cyclical waveform;
• said data link thus being operable initially to synchronize with said preamble, then to demodulate said data portion of said polling message, and finally to transmit a response on said power distribution lines.