Communications: electrical – Systems – Network signaling
Reexamination Certificate
1999-09-29
2001-03-20
Lefkowitz, Edward (Department: 2736)
Communications: electrical
Systems
Network signaling
C340S664000, C361S086000, C361S087000
Reexamination Certificate
active
06204751
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a circuit and method of controlling transient currents resulting from connecting a load to power conductors. More particularly, the present invention relates to a networked system in which the power conductors provide electrical power to a plurality of nodes. The inventive circuit and method control the turn-on and reset of a voltage-controlled switch which connects a load at one of the nodes to the power conductors, thereby limiting transient currents on the power conductors.
2. Description of the Related Art
Networked control systems typically include a number of device nodes coupled to a set of common conductors for transmitting power and data. The node devices often include both sensors and actuators of various types, as well as microprocessor-based controllers or other command circuitry. Moreover, some sensor and actuator nodes may also include signal processing capabilities, memory devices, and so forth. Power supplies coupled to the network furnish electrical energy via the network media to operate the sensors, actuators and other devices requiring an external power source. In operation, networked sensors provide information via the physical communications media relating to the states of various operating parameters. Other devices on the network process the transmitted parameter data and command operation of networked actuators, such as relays, valves, electric motors, and so forth. One device network of this type is commercially available from the Allen-Bradley Company of Milwaukee, Wis. under the commercial designation, DeviceNet.
Unlike unpowered data networks, powered industrial control networks pose unique problems for the transmission of both electrical power and data to and from networked devices. For example, the provision of power conductors and data conductors in a single cable can result in unwanted noise and other interference between the conductors, ultimately leading to bit errors in the transmission of the digitized data. A source of such interference or noise is transient current on the power conductors that is generated, for example, by connecting or disconnecting networked devices, energizing or deenergizing networked actuators, etc. Such noise sources must be controlled to reduce the likelihood that the generated noise may corrupt data transmitted to networked devices and, ultimately, the overall reliability of the network.
In addition to data corruption, noise sources may produce other undesirable effects. For example, due to the inherent impedance and reactance of the power conductors, power conductor current transients can result in power conductor voltage transients, which, in turn, can interrupt operation of networked devices or even potentially damage networked devices. Accordingly, control of such current transients is further desirable to ensure continued and reliable operation of networked devices.
There is a need, therefore, for a device and method to control current transients that may result in detrimental voltage transients on the power conductors. Such a device and method would be particularly desirable to prevent interruptions in the operation and damage to networked devices which all receive power via the power conductors. Further, in networked systems in which the power conductors and data conductors are provided in a single network media cable, it would be desirable to control such current transients to reduce the risk of bit errors that may be introduced on the data conductors as a result of transients on the power conductors.
SUMMARY OF THE INVENTION
The invention provides a current transient control circuit and a method for controlling current transients designed to respond to the aforementioned needs. The current transient control circuit and method may be used in a network including a plurality of nodes connected to a media cable. The media cable includes first and second power conductors for providing electrical power to each of the nodes, and first and second data conductors for transmitting data between the nodes. The media cable further includes an insulative cover which extends over both the power conductors and the data conductors. Although in a preferred application of the invention the transient control circuit is disposed at one of the network nodes, it should be understood that the transient control circuit may also be used in non-networked applications.
In accordance with one aspect of the invention, the current transient control circuit includes an input, an output, a voltage-controlled current source electrically connected between the input and the output, and a turn-on circuit and a reset circuit which both are electrically connected to the current source. The current source has a first state in which a current flow is substantially prevented and a second state in which a current flow is generated. The turn-on circuit is configured to apply a turn-on voltage to the current source to place the current source in the second state. The turn-on circuit is furthered configured to limit the rate of rise of the turn-on voltage and the peak amplitude of the current flow generated while the current source is in the second state. The reset circuit is configured to reset the current source to the first state, in which current flow is substantially prevented, at a reset rate that is faster than the rate of rise of the turn-on voltage.
In accordance with another aspect of the invention, a transient control circuit includes a solid-state switch coupled between a power conductor and a load, a turn-on circuit coupled to the switch to control current flow through the switch, and a reset circuit coupled to the switch to reset the switch to a non-conductive state in which current flow through the switch is substantially prevented. The switch also has a conductive state in which the current flow through the switch can be maintained at a static level. The turn-on circuit controls the current flow through the switch during a transition period during which the switch transitions from the non-conductive state to the conductive state. During the transition period, the turn-on circuit limits the rate of increase and the peak amplitude of the current flow through the switch.
In yet another aspect of the invention, a transient control circuit includes a voltage-controlled switch electrically connected between a power connector and a load, and a turn-on circuit coupled to the switch to control a transition mode of operation during which the switch transitions from a non-conductive state to a static mode of operation. During the transition mode of operation, the turn-on circuit limits the rate of increase and the peak amplitude of current flow through the voltage-controlled switch.
In accordance with yet another aspect of the invention, a method of controlling transients on the power conductors of a network media cable is provided. The method includes electrically coupling a voltage-controlled switch between a first power conductor and the load, applying a voltage to the voltage-controlled switch to cause the switch to transition from a non-conductive state to a static mode of operation during a transition period, and controlling the applied voltage to limit the rise time of current flow during the switch during at least a portion of the transition period. The method also includes limiting the peak amplitude of the current flow during the transition period and resetting the switch from the static mode of operation to the non-conductive state when the magnitude of the voltage between the power conductors falls below a threshold value.
REFERENCES:
patent: 4156172 (1979-05-01), Hucker et al.
patent: 5153457 (1992-10-01), Martin et al.
patent: 5212619 (1993-05-01), Baudelot et al.
patent: 5726592 (1998-03-01), Schulte et al.
patent: 6095867 (2000-08-01), Brandt et al.
Bolda Daniel J.
Haensgen Steven T.
Horn John J.
Lefkowitz Edward
Rockwell Technologies LLC
Sangalli Diana M.
Walbrun William R.
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