Pulse or digital communications – Cable systems and components
Patent
1997-10-03
2000-08-29
Pham, Chi H.
Pulse or digital communications
Cable systems and components
375259, 327 50, 327108, 326 30, 333 24R, 379402, H04B 300, H04L 2500
Patent
active
061119180
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and a means for two-way data communication between a central unit and a number of stations, and the communication takes place via a single two-wire line, with the central unit and the stations places successively along the line.
On example of a more specified system, is a system for collecting measurement values from a number of stations having sensors or measuring probes which monitor electrical/physical parameters. However, a station lay also be a control unit which in addition to the monitoring function, also controls parameters of a system attached to the station. In addition to the transmission of information from one single station to the central unit, it is also possible to put the system in a mode where information from one station can be transmitted to another station.
A more specific example of utilization of the invention, is monitoring of voltage and temperature in lead accumulators in a submarine or electrical emergency batteries in power plants, telecom or similar installations. It is a common feature in such uses that the accumulator cells are placed together as a battery of cells in a room which is classified as explosive.
However, as a principle, the present invention represents a quite general system for, using many stations attached to the same two-wire line, both transmitting and receiving signals between a common central unit, hereafter also referred to as "group interface", and single stations connected to the two-wire line, possibly also signals between the stations. In important embodiments care has been taken to provide galvanic separation, i.e. no direct DC connection, between the various units and between the units and the line. In further important embodiments, supply voltage and timing signals are also provided to the single stations via the two-wire line.
In accordance with the invention a method is provided for two-way data communication such as stated in the appended patent claim 1. Favourable embodiments of the method in accordance with the invention are defined precisely in the appended method claims 2-13. The invention also comprises a system for two-way data communication, and the system is defined precisely in the appended patent claim 14. Further favourable embodiments of the system are indicated in the appended patent claims 15-20. The invention shall now be illuminated further with reference to embodiment examples, and while referring to the appended drawings, where
FIG. 1 shows a system in accordance with the invention in an embodiment with galvanic separation between the elements, and where addressing of the single stations takes place by signalling from the central unit,
FIG. 2 shows a system where a central unit and stations are connected to a high-voltage power line and uses this line as a signal transmission medium,
FIG. 3 shows a system which is rather similar to the system appearing in FIG. 1, however with a third, special line which is used in connection with addressing of the stations, and
FIG. 4 shows a system where addressing is made by means of a device for applying a variable DC voltage to the two-wire line.
It is first referred to FIG. 1. The system central unit CU, also referred to as the common group interface, comprises an oscillator O, a voltage divider network R1, R2, and an attached PET switch F1. The switch F1 is controlled from the processor .mu.P. The oscillator O is also connected to the processor .mu.P which uses the signal from the oscillator in connection with timing/synchronizing.
D1 and D2 are diodes facing in opposite directions and connected in parallel, the diode D2 being series connected with a resistor RA. A1 is an amplifier (comparator) for measuring current through RA. In the embodiment appearing in the figure, galvanic separation between the central unit CU and the two-wire line SL is provided by means of a transformer TO. Instead of a transformer one may possibly use two capacitors as a galvanic separation means.
One of the stations connected to the two-wire SL appears in the right hand
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Engellenner Thomas J.
Pham Chi H.
Webster Bryan
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