PATENT
Universal Digital Input Module in a Process Automation Controller
United States Patent Application 20120044015
Inventors:
Magu, Ashish (Arundel, GB)
Application Number:
12/858186
Publication Date:
02/23/2012
Assignee:
Invensys Systems Inc. (Foxboro, MA, US)
Abstract:
In a process automation controller, a universal digital input module is provided. The universal digital input module comprises a plurality of digital input channels, each channel to sink a first current at a first voltage level associated with an input having a digital high value and to sink a second current at a second voltage level associated with the input having a digital high value, wherein the first current is greater than the second current and wherein the first voltage is less than the second voltage.
BACKGROUND
Process automation and automated control have experienced great growth over the last sixty-five years and have contributed to strong productivity growth in industry, as manual operations performed by human beings have been replaced by automatically controlled operations. One may categorize automated control into discrete automation, batch control, and process control.
Discrete automation may be exemplified by an automated canning or bottling line: content is deposited in the container, the container is sealed, and the container is packaged for shipment, while the materials are moved along one or more conveyors possibly handled by a number of automated stations performing an operation. Discrete automation may also be exemplified by an automobile assembly line. Discrete automation controllers may monitor events such as the passage of a container past an electric eye, the opening and/or closing of a gate, and other events. Discrete automation controllers may turn conveyors on and off, may open and/or close gates, may open and close valves in response to control strategies or control logic and in response to the monitored events.
Batch control may be exemplified by chemical processing where several materials are flowing together and are heated to a desired temperature and pressure and perhaps agitated or processed in a centrifuge. Batch control may be involved in brewing beer and fabricating pharmaceuticals. Batch control controllers may monitor temperatures, pressures, fluid flow velocities, weights, and other parameters. Batch control may send control commands to modulate valves and motors to achieve desired control parameters. When the batch of material has been processed, the batch is completed. Alternatively, at the completion of batch processing, water, barley malt, hops, and syrup have been fermented and transformed into beer ready for bottling.
Process control may also be referred to as continuous process control. Process control may be exemplified by a glass fabrication plant or by a crude oil fractionating plant (also referred to in some contexts as an oil refinery). It is the nature of these processes that they are most economically operated when they run continuously. For example, shutting down a glass manufacturing plant to make a repair or to replace equipment may entail substantial start-up costs involved in bringing one or more ovens back up to operating temperatures. Likewise, unexpected interruption of a continuous process, for example caused by a component failure, may cause losses related to damaged product. A process controller may monitor temperatures, pressures, fluid flow, weights, valve positions, motor speeds, electrical currents, and other parameters.
The process controller may monitor a discrete input from an electrical contactor mechanically coupled to a monitored device—for example a limit switch coupled to an open position of a valve or a closed position of a valve. In some embodiments, the process controller may source a voltage to a first contact point of the contactor. When the contactor is open, there is no path for electrical flow through the contactor, and a monitoring line from the process controller that is coupled to a second contact point of the contactor senses no voltage and/or current flow through the contractor. When the contactor is closed, a conduction path between the first and second contact points is established, and the monitoring line from the process controller senses voltage and current conduction. A process controller may supply about 18 volts electrical power to a contactor. After accounting for voltage drops in the electronic circuitry, the voltage sensed by the process controller when a contactor is closed may be about 12 volts. This diminished voltage sensed by the process controller may be referred to in some contexts as a wetting voltage. The process controller may modulate these physical parameters using analog outputs as well as discrete outputs. The analog output may comprise a voltage that varies substantially continuously from about a zero volts voltage level to about a ten volts voltage level with currents in the range from 0 milliamps to about 20 milliamps. The voltage and current levels indicated above may be different in some cases and with different equipment.
SUMMARY
In an embodiment, a universal digital input module for use in a process automation controller is disclosed. The universal digital input module comprises a plurality of digital input channels, each channel to sink a first current at a first voltage level associated with an input having a digital high value and to sink a second current at a second voltage level associated with the input having a digital high value, wherein the first current is greater than the second current and wherein the first voltage is less than the second voltage.
In an embodiment, a method of receiving a discrete input in a process automation controller is disclosed. The method comprises in response to a discrete input at a first voltage, sinking a first current, wherein the input corresponds to a digital input high value and in response to the discrete input at a second voltage, sinking a second current, wherein the input corresponds to a digital high value. The first voltage is less than the second voltage and the first current is greater than the second current.
In an embodiment, a digital input module for use in a process automation controller is disclosed. The digital input module comprises a plurality of digital input channels, each channel to sink a first current when a digital high value is received from a contactor input device and to sink a second current when the digital high value is received from a digital logic device. The first current is greater than the second current.
These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.
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