Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2000-01-25
2002-10-01
La, Anh V (Department: 2632)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S315000
Reexamination Certificate
active
06459363
ABSTRACT:
BACKGROUND
The present invention relates to the field of data communication systems and to distributed two wire communication systems. More particularly the invention relates to a two wire communication system utilising a communication protocol in which an electrical bi-polar waveform is used for data transmission and power transfer over a two wire conductor system. The protocol is a physical layer protocol which defines the electrical waveform applied to a two wire conductor system acting as the transmission means. The two wire conductor system is used to interconnect a Controller and at least one module but preferably a multiplicity of modules. Throughout the specification the term Controller will be used to describe a device which controls the two wire conductor and the term Module will be used to describe a device which connects to the two wire conductor. In operation the communication protocol allows data communication between the Controller and the Modules across the two wire conductor by a digital communication methodology which is provided by the bi-polar waveform structure as defined in the protocol. Power transfer via the two wire conductor from the controller to the modules is also achieved by the bi-polar waveform structure as defined by the protocol.
PRIOR ART
Two wire conductor systems are known in the electrical engineering and electronics fields as a means of data and power transmission. Systems of this type generally known as Down Line Powered two wire conductor communication system (DLPCS) typically employ a controller which drives power into the two wire conductor systems, controls the timing of data transfer and transmits and receives data.
They also employ modules which draw power from the two wire conductor and transmit and receive data DLPCS's can be classified into uni-polar DLPCS's and bi-polar DLPCS's. Most data and power transmission systems use different conductors for the transmission of data and the transmission of power. However, in low power applications where the length of the conductors between the Modules and the Controller is large, the transfer of power and data over the same two conductors can give large cost savings compared with multiple conductor systems. A unipolar DLPCS is a system where the Controller drives power down the two wire conductor using one voltage polarity. Data is transferred between the Controller and Modules by modulating the voltage (between voltages of the same polarity) and current (positive or negative). Power can be transferred from the Controller to the Modules while ever the line voltage are higher than the internal voltage of the Modules
A telephone system is an example of a uni polar DLPCS wherein power is drawn continuously from the line by the telephone which transmitts the voice signal by modulating the telephone's impedance. The change of impedance modulates the voltage and current on the two wire communication line. Digital data transfer via the telephone DLPCS usually requires special modulation techniques using modems.
Another uni-polar DLPCS provides for a controller and multiple modules connected to a two-wire line and supports digital data only. The modules draw power whenever the voltage is high. Digital data is transmitted and received by the modules during periods when the voltage on the two -wire line is ‘low’. The controller lengthens the ‘low’ voltage period if a low impedance is detected across the two-wire line. Modules transmit data by modulating their impedance in the ‘low’ voltage periods. An advantage of this signaling technique is that all modules connected to the two wire line receive all data transmitted over the two wire line. Module to module communication is also possible. The ‘low’ voltage disables power transmission so the controller can easily detect the data signal. A disadvantage of this approach is that the ‘low’ voltage has a low noise margin (the amount of noise voltage that is needed to corrupt the data). Another disadvantage is that it is difficult to adjust the speed of operation to accommodate different operational environments.
Another two wire utility data communication system for communicating utility meter readings over two wires is disclosed in Australian patent application 64664/94. The specification teaches communication systems used to transmit consumption data from a meter such as an electric, gas or water meter to remote meter reading units. The system described is very similar to a well known field known as M-BUS and provides for a controller and multiple modules connected to a two-wire line. The invention described comprises a reader/programmer for communicating with a utility meter or the like over at least two-wire lines. The system described includes means for generating an interrogate signal, means for demodulating a data signal received from the utility meter over the two-wire lines wherein the data signal consists of a current in the two-wire lines which varies in accordance with data being transmitted from the utility meter when the reader/programmer is connected via two wire lines and means for demodulating the data signal received from the utility meter over the wire lines wherein the data signal has characteristics which vary in accordance with the data being transmitted from the utility meter.
Each meter includes an encoder which converts consumption information displayed by a mechanical or electronic register associated with the meter to a form which can be transmitted over wires or the like to a remotely located meter reading unit. The specification also teaches the use of three wire communications for the system. When operating in the two wire mode the reader/programmer and encoder are inductively coupled.
The encoder includes circuitry for varying an impedance in accordance with data representing the quantity being measured by the meter to cause the current flowing between the encoder and the remote reader/programmer to be modulated in accordance with the data.
The system is relatively complicated in the coding and decoding of the signals in comparison to pulse duration signals and furthermore it does not permit use of 100% of data transmission time when transmitting power due to the nature of the uni-polar signaling used to transmit both power and data. The modules draw power while ever the voltage is ‘high’. The controller transmitts binary data to the modules by modulating the voltage between ‘high’ and zero voltage. The modules transmit data to the controller by modulating the line current on the two-wire line by varying the modules's impedance. This system works well when the module's data current is much larger than the power consumption current. It is therefore a disadvantage that power consumption is limited. Another disadvantage of this system is that modules can only receive data from the controller. Also the communication speed can be adjusted to meet unusual operating conditions but the speed is generally limited to fixed baud rates and it is difficult to change baud rates during operation.
Another known digital uni-polar DLPCS employs said two-wire protocol wherein the modules draw power when the voltage is high. In that system the controller transmits data to the modules by modulating the voltage between ‘high’ and zero voltage. The modules transmit data to the controller by modulating their impedance which modulates the line voltage and current. In this case all modules connected to the line can receive all data transmitted on the two-wire line as the modules modulate the voltage between ‘high’ and near zero voltage. The key disadvantage of this system is that very little power can be transmitted and communication speed has to be fixed.
Bi-polar DLPCS's are systems where the controller drives power down the two wire conductor using an alternating voltage polarity.
Data is transmitted between the controller and modules by modulating the voltage and /or current. The module's circuitry, which draws power from the line and enables data transfer by modulation of the voltage or the current, is m
Ramplin Mike
Walker Kevin
Ampcontrol Pty Ltd.
Foley & Hoag LLP
La Anh V
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