Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2000-01-18
2001-11-20
Trieu, Van T (Department: 2632)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S315000
Reexamination Certificate
active
06320494
ABSTRACT:
BACKGROUND OF THE INVENTION
Certain communication systems have a local station and a remote station drawing its operating power from the local station. That is, the remote station has no power source other than the local station. It is often convenient if only a single pair of conductors connects the stations. For example, there may already be existing only a single pair of conductors, and adding another pair will be costly. Thus, for a system comprising a local station providing power to and communicating with a remote station with only a single pair of conductors connecting them, both data and power must be carried on that same pair of conductors.
Carrying both power and data on the same pair of conductors creates a more complex problem, but one which has previously been solved in a number of different ways. In these earlier systems, the communication is uniplex, i.e., is in only one direction, from the local to the remote station, or vice versa. For example, U.S. Pat. Nos. 3,659,277 (Brown) and U.S. Pat. No. 5,635,896 (Tinsley et al) both disclose a local receiver which provides power to and receives data from a remote transmitter.
In certain of these situations where a local station provides power for both itself and a remote station, it would be more useful if duplex (two way) communication between the stations was available. Best of all would be a system with full duplex operation, where simultaneous communication in both directions is possible, rather than half duplex, where communication in only one direction at any given instant is possible.
One situation in particular where a single pair of conductors carrying both power and full duplex communication has utility is in detecting flame within boilers and other combustion devices. The most common technologies now in use include a discharge tube to detect UV radiation emanating from the flame. Such discharge tubes are located in close proximity to and in line of sight of the combustion chamber and require a pair of conductors for connection to the flame signal processor. There are alternative solid state UV detectors which often require a local preamplifier to process the small signals generated by variations in the UV radiation emitted by the flame. Since two wires are already available, it is much easier in the retrofit situation to use only the existing wiring. Further, if new wiring is installed to increase the number of wires between the flame signal processor and the flame detector, there is additional cost and increased possibility of miswiring. Communication between the flame detector and the processor allows testing of the detector. Power must be supplied to the detector to operate the sensor in some cases, and to operate a preamplifier.
BRIEF DESCRIPTION OF THE INVENTION
We have discovered a system which has a local station providing power to both itself and to a remote station on a single pair of conductors, and which also allows full duplex communication between the stations at all times on the single pair of conductors. In this system, we rely on variations in current for communicating in one direction, and variations in voltage for communicating in the other direction.
Such a system comprises in the local station, a variable voltage power supply having first and second supply terminals and a supply control terminal. This power supply provides a first preselected power voltage between the first and second supply terminals responsive to a first value of a supply control signal at the control terminal, and a second preselected power voltage lower than the first power voltage between the first and second supply terminals responsive to a second value of the supply control signal.
The local station also includes a current sensor having a first sensor terminal connected to the first supply terminal, a second sensor terminal in electrical connection to the first sensor terminal and supplying current received at the first sensor terminal. The current sensor also includes a current signal terminal providing a current sensor signal having a first value responsive to current greater than a preselected value flowing from the first to the second sensor terminal, and a second value otherwise.
The remote station includes a voltage sensor having first and second voltage sensor terminals for connection through the pair of conductors respectively to the second sensor terminal and to the second power terminal. The voltage sensor provides a voltage sensor signal at a voltage signal terminal. The voltage sensor signal has a first value when the voltage between the first and second voltage sensor terminals is greater than a preselected value, and a second value otherwise.
The remote station also includes a current shunt connected between the third and fourth sensor terminals. The shunt has a current control terminal for receiving a remote data signal. The current shunt presents a non-zero first impedance responsive to a first value of the remote data signal, and a second impedance greater than the first impedance responsive to a second value of the remote data signal.
This structure allows the current sensor to provide a current sensor signal which reproduces the data content of the remote data signal and the voltage sensor to provide a voltage sensor signal which reproduces the data content of the local data signal.
In one version of this system the remote station includes a voltage regulator receiving unregulated power from the local station through the pair of conductors, and providing regulated voltage. The remote station can also include a load receiving the regulated voltage. The load, voltage regulator, and shunt then collectively form between the first and second conductors a composite impedance having high and low impedance values as the switch is respectively open and closed. We prefer that the high and low impedance values of the composite impedance cause current flow through the conductors, respectively above and below a datum current value regardless of which of the first and second preselected power voltages is provided by the power supply. This specific structure allows this system to simultaneously transmit data both ways between the local and remote stations.
One useful application for this system is in powering and communicating with a remote sensor such as a flame detector in a furnace or boiler, and periodically testing that it is operating properly. A sensor controller in the remote station can disable its operation in some way, which for a flame detector will cause the flame detector output to change from indicating flame present to for a brief period of time, indicating flame failure. If this change in the flame detector output does not occur, then the system can be safely shut down before an undetected flame failure occurs.
REFERENCES:
patent: 3659277 (1972-04-01), Brown
patent: 3938129 (1976-02-01), Smither
patent: 4234926 (1980-11-01), Wallace et al.
patent: 5365223 (1994-11-01), Sigafus
patent: 5635896 (1997-06-01), Tinsley et al.
patent: 6281784 (2001-08-01), Redgate et al.
patent: 94309734.5 (1995-06-01), None
patent: PCT/NO96/00076 (1996-10-01), None
patent: PCT/AU99/00151 (1999-09-01), None
Bartels James I.
Juntunen Robert D.
Planer Norman G.
Honeywell International , Inc.
Trieu Van T
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