Patent Application
20140274181
The present invention relates generally to industrial process field devices, and more particularly to an activity scheduling system for an industrial field device.
The term “field device” covers a broad range of process management devices that measure and control parameters such as pressure, temperature, and flow rate. Many field devices are transmitters which act as communication relays between a transducer for sensing or actuating an industrial process variable, and a remote control or monitoring device such as a computer in a control room. The output signal of a sensor, for example, is generally insufficient to communicate effectively with a remote control or monitoring device. A transmitter bridges this gap by receiving communication from the sensor, converting this signal to a form more effective for longer distance communication (for example, a modulated 4-20 mA current loop signal, or a wireless protocol signal), and transmitting the converted signal to the remote control or monitoring device.
Wireless field device networks are used to control and monitor disparate processes and environments. A single field device network may include field devices disposed to sense or actuate process parameters across a wide area, e.g. an oil field or manufacturing plant. In wireless network systems designed for sensor/actuator-based applications, many field devices in the network must be locally-powered because power utilities, such as 120V AC utilities or powered data buses, are not located nearby or are not allowed into hazardous locations where instrumentation, sensors, and actuators and safety monitors or human interface devices must be located without incurring great installation expense. “Locally-powered” means powered by a local power source, such as a self-contained electrochemical source (e.g., long-life batteries or fuel cells) or by a low-power energy-scavenging power source (e.g., vibration, solar, or thermoelectric). A common characteristic of local power sources is their limited energy capacity or limited power capacity, either stored, as in the case of a long-life battery, or produced, as in the case of a solar panel. Often, the economic need for low installation cost drives the need for battery-powered devices communicating as part of a wireless field device network. Effective utilization of a limited power source, such as a primary cell battery which cannot be recharged, is vital for a well-functioning wireless field device. Batteries are expected to last more than five years, and preferably last for a substantial portion of the life of the product.
In order to conserve power and network bandwidth, some wireless network protocols limit the amount of traffic any node or device can handle during any period of time by only turning device transceivers ON for limited amounts of time to listen for messages. Thus, to reduce average power, the protocol may allow duty-cycling of the transceivers between ON and OFF states. Some wireless network protocols may use a global duty cycle to save power such that the entire network is ON and OFF at the same time. Other protocols (e.g., TDMA-based protocols) may use a local duty cycle where only the communicating pair of nodes that are linked together are scheduled to turn ON and OFF in a synchronized fashion at predetermined times. Typically, the link is pre-determined by assigning each pair of communicating network nodes a specific periodic time slot for communication over a specified RF frequency channel. Each field device is assigned a time slot during commissioning, and activates periodically at a commissioned rate. Process sensing field devices commonly take sensor measurements only shortly before turning device transceivers ON. Both powering transceivers and taking sensor measurements consume considerable power, and device-to-device communication ties up network bandwidth. Generally, each field device performs at least one resource-intensive function (e.g. periodic wireless communication, periodic process sensing or actuation) repetitiously at a commissioned rate.
Specific field device applications may require that resource-intensive functions be performed at high rates during some periods, while needing only lower rates or no activity during other periods. Conventional field device networks either operate such field devices continually at the higher function rates necessitated during high demand periods, or recommission field devices for high and low demand periods from a central control or monitoring server. In the former case, continual operation at high function rates consumes power and bandwidth unnecessarily during low demand periods. In the latter case, recommissioning consumes power and bandwidth, and can result in packet loss during the recommissioning process.
The present invention is directed toward a field device assembly comprising a first process sensor, a wireless transceiver, and a processor. The first process sensor is disposed to sense a first process parameter. The wireless transceiver is configured to communicate wirelessly with a network manager. The processor is configured to process the sensed first process parameter, and to command the wireless transceiver and first process sensor to perform a first resource-intensive activity according to a first commissioned adaptive schedule whereby rates of the resource-intensive activity vary over time and/or based on sensed events.
In another embodiment, the present invention is directed towards a method of operating an industrial field device. The method comprises commissioning the field device with an adaptive schedule, performing a resource-intensive activity at a scheduled rate that varies over time based on the commissioned internal schedule, and varying the scheduled rate in response to sensed events specified by the preset internal schedule.
The present invention is a scheduling system for resource optimization in industrial process field devices. Field devices are commissioned with dynamic schedules that specify varying rates to engage in resource-intensive activities such as wireless signal transmission and reception, process parameter sensing, sensor calibration, and process parameter actuation. Each field device varies the rates of these resource-intensive activities according to its respective dynamic schedule, without need for recommissioning.
Host computer 16 is depicted as connected to gateway 12 via facility network 18, which may for instance be a secondary wired or wireless network distinct from the hub-and-spoke or mesh network of field devices 14. In alternative embodiments, host computer 16 may communicate wirelessly directly with gateway 12. In some embodiments, host computer and gateway 12 may be incorporated into a single device, with no intervening facility network 18.
Network manager 20 is a software program that processes information from field devices 14, generating wireless links, control messages, communications schedules and data queries to suit the situation and application. Although network manager 20 is shown located on gateway 12, network manager 20 may alternatively be located on a computer remotely connected to gateway 12, for example host computer 16 or another computer connected to facility network 18.
Network manager 20 provides commissioning information for each field device 14 according to parameters set by host computer 16 or locally applied to field device 14, as described below with respect to
In this embodiment, housing 100 is a rigid, durable body which may be sealed to protect transceiver 104, processor 106, signal conditioner 108, memory 112, and power supply 114 against extreme temperatures and hazardous environments. Although transducer 110 is shown situated outside of housing 100, housing 100 may enclose transducer 110 in some embodiments of field device 14.
According to one embodiment, transceiver 104 is a signal transmitter/receiver which transmits and receives wireless signals via antenna 102. Processor 106 is a logic-capable data processor such as a microprocessor. Signal conditioner 108 comprises a digital and/or analog filter that operates on transducer signals to and/or from transducer 110. In some embodiments signal conditioner 108 may further comprise an analog/digital converter disposed to digitize sensor signals from transducer 110, or convert digital instructions into analog commands for transducer 110.
Transducer 110 can be a sensor that provides sensor readings to field device 14 for processing and transmission to control or monitoring system host computer 16, or an actuator that actuates a change in industrial process in response to signals received from computer 16 or network manager 20. Although the following description will focus on the embodiment where transducer 16 comprises a sensor, a person skilled in the art will understand that the invention could equally be applied to actuator systems. Although only one transducer 110 is depicted in
Memory 112 is a machine read-writable memory bank. Power supply 114 is an energy source powering transceiver 104, processor 106, signal conditioner 108, and memory 112. In some embodiments, power supply 114 may also drive transducer 110. In some embodiments, power supply 114 may be a limited capacity energy source such as a local energy harvester (e.g. a solar panel or a vibrational energy scavenger with limited output) or a storage device (e.g. a chemical battery or supercapacitor with limited charge).
To minimize energy drain on power supply 114 and usage of bandwidth in wireless process network 10, processor 106 activates transceiver 104 and/or transducer 110 according to the adaptive schedule (explained above) stored in memory 112. This adaptive schedule is received from host computer 16 via network manager 20 or a local configuration device during commissioning, and specifies different activation or activity rates for different time periods (e.g. times of day, days of the week, specific holidays), and/or in response to identified conditions (e.g. sensed values of transducer 110 falling within or outside of a particular range, either instantaneously or for a sustained period). More generally, processor 106 can activate or deactivate any resource-intensive function of field device 14 according to the adaptive schedule, as described below with respect to
Time keeper 116 is, in one embodiment, a real-time clock configured to provide processor 106 with a current time and date. This time and date is checked against the adaptive schedule stored in memory 112 to determine when rates of resource-intensive activities should be updated (see
After commissioning, processor 106 instructs transceiver 102 and transducer 110 to activate at the currently scheduled rate and times. (Step S2). This process continues until interrupted by a scheduled mode switch (Step S4), an event driven mode switch (Step S5), or a user override input (Step S6). Processor 104 periodically compares the current time and date as specified by time keeper 116 with the adaptive schedule stored in memory 112, and switches to a new mode with higher or rates of activity if indicated by the adaptive schedule. (Step S4). The period of this comparison is selected to be no greater than the minimum rate specified by the adaptive schedule for any activity. Similarly, processor 104 compares incoming data from transducer 110 and transceiver 104 with event flags specified by the adaptive schedule, and switches to an event driven mode where indicated by the adaptive schedule. (Step S5). Event-driven modes can override time-based modes specified in step S4, and can themselves have a duration or expiration time specified by the adaptive schedule and ascertained by comparison with time keeper 116. Absent a user override, field device 14 operates entirely based on the initially commissioned adaptive schedule stored in memory 112, without a need for recommissioning by gateway 12. (Step S6). Any override signal received via gateway 12 from a human or machine operator (e.g. from network manager 20 or a human operator at host computer 16) allows a new or altered adaptive schedule to be loaded onto memory 112. (Step S1).
Scheduled operation method 200 allows field device 14 to handle sustained operation at a variety of scheduled and/or event-driven activity rates without recommissioning. Method 200 thereby allows field device 14 to perform bandwidth- or power-intensive tasks only as often as needed for a current application or situation, reducing power draw on power supply 114 and congestion of wireless process network 10. Because a field device utilizing an adaptive schedule as described in scheduled operation method 200 does not require recommissioning to switch from one mode to another, dropped packets and network downtime due to recommissioning delays are minimized. Event-driven switches specified by the adaptive schedule allow field device 14 and wireless process network 10 to rapidly respond to arising process conditions, device faults, and sensor discrepancies.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
