Patent Publication Number: US-8538732-B2

Title: Appendable system and devices for data acquisition, analysis and control

Description:
RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 12/264,834 filed Nov. 4, 2008, now U.S. Pat. No. 7,848,906 entitled “Appendable System and Devices for Data Acquisition, Analysis and Control,” which is a divisional of U.S. patent application Ser. No. 11/361,772 filed Feb. 24, 2006, now U.S. Pat. No. 7,447,612 entitled “Appendable System and Devices for Data Acquisition, Analysis and Control,” which is a continuation of U.S. patent application Ser. No. 10/091,805 filed Mar. 6, 2002, now U.S. Pat. No. 7,035,773 entitled “Appendable System and Devices for Data Acquisition, Analysis and Control,” the entire disclosures of which are hereby incorporated by reference herein. 
    
    
     FIELD OF TECHNOLOGY 
     The present invention relates generally to process control systems and, more specifically, to a system and devices that may be appended or attached to process control equipment and/or other entities to perform data acquisition activities, data analysis activities and/or process control activities. 
     DESCRIPTION OF THE RELATED ART 
     Modern process control systems are typically microprocessor-based distributed control systems (DCSs). A traditional DCS configuration includes one or more user interface devices, such as workstations, connected by a databus (e.g., Ethernet) to one or more controllers. The controllers are generally located physically close to a controlled process and are connected to numerous electronic monitoring devices and field devices such as electronic sensors, transmitters, current-to-pressure transducers, valve positioners, etc. that are located throughout the process. 
     In a traditional DCS, control tasks are distributed by providing a control algorithm within each of the controllers. The controllers independently execute the control algorithms to control the field devices coupled to the controllers. This decentralization of control tasks provides greater overall system flexibility. For example, if a user desires to add a new process or part of a process to the DCS, the user can add an additional controller (having an appropriate control algorithm) connected to appropriate sensors, actuators, etc. Alternatively, if the user desires to modify an existing process, new control parameters or control algorithms may, for example, be downloaded from a user interface to an appropriate controller via the databus. 
     To provide for improved modularity and inter-manufacturer compatibility, process controls manufacturers have more recently moved toward even further decentralization of control within a process. These more recent approaches are based on smart field devices that communicate using an open protocol such as the HART®, PROFIBUS®, WORLDFIP®, Device-Net®, CAN, and Fieldbus protocols. These smart field devices are essentially microprocessor-based devices such as sensors, actuators, etc. that, in some cases, such as with Fieldbus devices, also perform some control loop functions traditionally executed by a DCS controller. Because some smart field devices provide control capability and communicate using an open protocol, field devices from a variety of manufacturers can communicate with each other on a common digital databus and can interoperate to execute a control loop without the intervention of a traditional DCS controller. 
     As is well known, smart field devices such as, for example, Fieldbus devices, may include one or more logical function blocks that perform control functions or portions of a control function. These function blocks may, for example, perform analog input functions, analog output functions, proportional-integral-derivative (PID) control functions, or any other desired control functions. The function blocks within a smart field device may be communicatively linked with other function blocks within that smart field device or with function blocks within other smart field devices to carry out any desired control function. For example, an analog input block may be used to monitor a fluid flow via a flow sensor and a PID block may process a fluid flow value provided by the analog input block to provide responsive signals via an analog output block to an actuator that modulates the position of a valve plug. Thus, these function blocks may be communicatively linked to one another to form a PID-based control loop that controls the flow of a fluid through a valve. 
     As is also well known, smart field devices facilitate the design and configuration of relatively large process control systems by enabling system designers and operators to design and configure a large process control system in a hierarchical, modular or building block fashion. In other words, relatively small portions of the overall process control system can be designed and configured separately and linked together to form larger portions of the overall system. However, once implemented and operational, a process control system that uses smart field devices may be relatively difficult to reconfigure or modify because the smart field devices are typically physically integrated with the equipment, sensors, etc. used throughout the process control system or plant. For example, a smart water valve may have water pipes connected to its input and output ports via threaded engagements, solder, etc. and may have electrical conduits connected to it that encase wires, which may provide power and convey other signals associated with the monitoring and control of the valve. Similarly, a smart temperature sensor may have a temperature probe portion that is threaded into an immersion well within a water pipe, a tank, or any other piece of equipment within the process control system. The smart temperature sensor may also have an electrical conduit connected to it that encases power and/or other signal carrying wires extending from the temperature sensor to other devices such as, for example, a controller or any other device within the process control system or plant. 
     Although the high degree of physical integration typically found within process control systems that employ smart field devices provides a high degree of mechanical and electrical integrity, such systems are relatively expensive to install and commission because their installation typically requires significant amounts of trade labor (e.g., electricians, plumbers, etc.). Furthermore, the high degree of mechanical integration also typically requires the process control equipment used within the system or plant to provide mechanical interfaces that enable attachment of the smart field devices needed to monitor and/or control the equipment. In some cases, a mechanical interface provided by the equipment manufacturer may have to be modified in the field by an appropriate tradesperson to enable installation of the smart field device. In still other cases, the equipment manufacturer may not provide any mechanical interface and a tradesperson may have to fabricate an appropriate interface in the field. In either case, a significant amount of labor and cost is typically incurred as a result of having to mechanically integrate the smart field devices within the process control plant or system. 
     Another difficulty associated with adding smart field devices or, more generally, a monitoring and/or automation system, to a process or plant that does not currently have any such devices, is that these systems typically lack the necessary electrical (e.g., power) and communications infrastructure. As a result, adding smart devices to such a system typically requires a substantial amount of labor and cost. Insufficient infrastructure, or the complete lack thereof, is particularly problematic for monitoring and control applications that involve the sensing and/or control of a relatively few parameters in a remote geographic location. For such applications, it may be virtually impossible to install the electrical and communications infrastructure needed to support the use of smart field devices and, even if it were possible to do so, the costs associated with such an undertaking may be impossible to justify. 
     While the higher installation costs and the relative difficulty (and high costs) associated with reconfiguring (i.e., physically moving and/or adding smart field devices and/or equipment) a process control system that is implemented using known smart field devices, or adding smart field devices to a system or plant that does not currently have any such devices, can be justified for relatively large process control systems or plants, these high costs are typically difficult to justify or cannot be justified for smaller systems or plants. Additionally, retrofitting or adding smart field devices to relatively small process plants or systems may be particularly problematic because the physical integration of the smart field devices with the system or plant typically requires some or all of the plant or system to be shut down for a significant amount of time. For example, a small plant or factory that does not currently have a plant automation system may theoretically be able to increase production volume and quality by retrofitting an automation system based on smart field devices to its existing plant or system. However, the benefits of retrofitting such an automation system to the small plant or factory may not sufficiently offset the relatively high costs associated with installation of the smart field devices, the costs associated with having to slow or shut down production for a significant amount of time and the perceived business risks associated with lost production, the inability to supply customers with product, the possibility that the new automation system may result in unpredictable production volume and quality variations, etc. 
     Some manufacturers have attempted to address the above-noted problems by providing sensing devices that can be more easily retrofitted to equipment. However, these devices are not typically capable of carrying out process control activities because they do not provide information (e.g., sensed parameters, process conditions, etc.) on a continuous, periodic or real-time basis. In other words, while these devices may be capable of sensing information in connection with a piece of equipment, a process parameter, etc., they are not typically capable of timely providing this information, when the information is first available, to an overall process control routine. Instead, most, if not all, of these devices collect large amounts of information and send consolidated summaries or reports to a workstation or the like long after most of the information has been acquired. For example, Control Systems International (CSI) manufactures a diagnostic system for use with rotating equipment (e.g., electric motors, turbines, etc.). The CSI system includes vibration monitors that can be attached directly to a motor, or any other structure. The CSI vibration monitors collect and store vibration information for relatively long periods of time and convey this vibration information or data to a workstation or another computer system that uses the long-term vibration information or data to diagnose the conditions of the various pieces of equipment being monitored. Unfortunately, the CSI system functions as an off-line diagnostic system and, thus, cannot be effectively used for process control activities, real-time or periodic monitoring activities, etc. 
     SUMMARY 
     The appendable system and devices described herein may be appended to process control equipment and/or other entities to perform data acquisition activities, data analysis activities and/or process control activities. Generally speaking, the appendable system and devices described herein may be used to provide a highly scalable monitoring and/or control system that can be easily added, appended or retrofitted to a new or established process system or plant in a cost effective manner. Additionally, the appendable system and devices described herein provide a relatively high degree of application flexibility by, for example, facilitating physical modification and/or reconfiguration of the control system such as adding and/or physically moving sensors, actuators, equipment, etc. associated with the process control system. 
     In one aspect, an appendable device may include a housing adapted to be mounted to a surface, a memory disposed within the housing and an input/output interface disposed within the housing. The input/output interface may be adapted to communicate with one of a sensor and a control output operatively coupled to the appendable device. The appendable device may also include a processor disposed within the housing and communicatively coupled to the memory. The processor may be programmed to communicate with the input/output interface and to communicate information related to the one of the sensor and the control output, as the information becomes available, to another device via a communication network. Because the appendable device described herein can communicate information to other devices, workstations, etc. when the information becomes available, the appendable device may be effectively used for process control activities, real-time data monitoring activities, etc. 
     In another aspect, an appendable device, may include an antenna, a transceiver communicatively coupled to the antenna and a processor communicatively coupled to the transceiver. The processor may be programmed to perform one of a periodic data monitoring activity and a process control activity. The appendable device may also include a memory communicatively coupled to the processor, an input/output interface adapted to operatively couple the processor to one of a sensor and a control output and a housing that holds the transceiver, the processor, the memory and the input/output interface. The housing may be adapted to be attached to a surface. 
     In yet another aspect, an appendable system for controlling a process may include a plurality of appendable devices. Each of the appendable devices may include an antenna, a transceiver, a processor, a memory, an input/output interface adapted to enable the processor to communicate with one of a sensor and a control output, and a housing adapted to facilitate surface mounting of the appendable device. The appendable system may also include a computer system adapted to communicate with one or more of the plurality of appendable devices so that a first one of the plurality of appendable devices senses a first parameter of the process and a second one of the plurality of appendable devices controls a second parameter of the process based on the first sensed parameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary block diagram of an appendable or attachable device that may be used to perform data acquisition activities, data analysis activities and/or process control activities; 
         FIG. 2  is an exemplary diagrammatic view that depicts one manner in which one or more appendable devices, similar or identical to that shown in  FIG. 1 , may be used to automate a process control system or plant; 
         FIG. 3  is an exemplary functional block diagram that depicts one possible logical configuration of the workstation shown in  FIG. 2 ; and 
         FIG. 4  is a block diagram that depicts an exemplary system topology that may be used to implement a process monitoring and/or control system using the appendable system and devices shown in  FIGS. 1-3 . 
     
    
    
     DETAILED DESCRIPTION 
     The appendable system and devices described herein may be appended to process control equipment and/or other entities to perform data acquisition activities, data analysis activities and/or process control activities. Generally speaking, the appendable system and devices described herein may be used to provide a highly scalable monitoring and/or control system that can be easily added, appended or retrofitted to a process system or plant in a cost effective manner. Additionally, the appendable system and devices provide a relatively high degree of application flexibility by, for example, facilitating physical modification and/or reconfiguration of the control system, which may involve adding and/or physically moving sensors, actuators, equipment, etc. associated with the process control system. 
     More particularly, the appendable system and devices may be physically mounted, attached or appended to one or more surfaces or pieces of equipment within a new or established process plant or system in a relatively non-invasive manner. Specifically, the appendable or attachable devices may be configured to facilitate simple field installation or retrofit of the devices to equipment without requiring a shutdown of the equipment and/or the process plant of which that equipment is a part. Such simplified and cost effective installation may be enabled by fastening mechanisms such as band clamps, Velcro™ magnets, self-tapping or self-threading screws, adhesives, etc. that do not typically require the services of a tradesperson such as, for example, an electrician, a plumber, a pipe fitter, etc. Additionally, the appendable devices may derive or generate their power using, for example, a super capacitor, an internal battery, vibrations induced by the equipment to which the devices are mounted, attached or appended, a photoelectric array, currents induced by a magnetic field, etc. and may communicate with each other and/or controllers, workstations, computer systems, etc. using any suitable wireless communication method, media and/or protocol, thereby minimizing or eliminating the need for preexisting electrical and communications infrastructure, the need for invasive electrical connections, the shutdown of equipment and/or the system or plant, and the costly services of an electrician or other tradesperson. 
     While the appendable system and devices described herein are described in connection with a process control application, the appendable system and devices may be used in less complex applications such as, for example, simple data acquisition and/or monitoring applications, simple single-loop stand alone control applications, simple alarming applications, etc. Additionally, the appendable system and devices described herein may be integrated within a more complex process control system, which may control one or more large process control plants dispersed over a wide geographic region. For example, the appendable system and devices may be integrated with a DeltaV™ process control system, if desired, or any other similar or different process control system. 
       FIG. 1  is an exemplary schematic block diagram of an appendable or attachable device  10  that may be used to perform data acquisition activities, data analysis activities and/or control activities such as, for example, monitoring or controlling a piece of equipment a process and/or a system. As shown in  FIG. 1 , the appendable device  10  includes a housing  12  in which a transceiver  14 , a processor  16 , a memory  18  and an input/output (I/O) interface  20  are disposed. The appendable device  10  may also include an internal power source  22 , an antenna  24 , one or more internal sensors  26  and  28  and one or more external sensors  30  and  32 . Additionally, one or more sensors  34  and  36  and/or other devices may be field wired or otherwise electrically coupled to the appendable device  10  via a connection or termination portion  38 . The connection or termination portion  38  enables a field technician or any other person to connect additional or different sensors or other devices to the appendable device  10 , to replace damaged or failing sensors and other devices, etc. Still further, one or more control outputs  40  and  42  such as, for example, relays, contactors, analog voltage or current outputs, frequency outputs, etc. may be connected either directly or via the termination portion  38  to the appendable device  10 . 
     In general, the processor  16  may execute one or more software routines  44  stored in the memory  18  to perform data acquisition or monitoring activities, data analysis activities and/or control activities. For example, one or more of the sensors  26 - 36  may convey electrical signals or information to the processor  16  via the I/O interface  16 . In turn, the processor  16  may process these electrical signals or information and, as described in greater detail in connection with  FIG. 2 , may send some or all of the processing results to a controller or workstation and/or to one or more other appendable devices via the transceiver  14  and the antenna  24 . Alternatively, or additionally, the processor  16  may send control signals or other signals to one or more of the control outputs  40  and  42  via the I/O interface  20  to carry out control activities such as, for example, turning a motor on or off, varying the speed of a motor, opening or closing a valve, a damper actuator or some other operator, etc. 
     The software routines  44  stored in the memory  18  may also enable the appendable device  10  to perform alarming functions (e.g., notifying an operator and/or another device within a control system that a control parameter is outside of a predetermined range, has exceeded a threshold, etc.) and self-diagnostic functions (e.g., detection of a failing or failed sensor, communications problems, etc.). In addition, if desired, the software routines  44  may also enable the appendable device  10  to perform security functions such as, for example, communications encryption, user authorizations (e.g., authenticate a user, approve a user for a requested level of access, etc.), etc. to prevent unauthorized persons from accessing information and/or affecting the operations of the appendable device  10 . 
     As shown in  FIG. 1 , the appendable device  10  may include one or more internal sensors, such as the sensors  26  and  28 , and/or may receive signals from one or more external sensors such as the sensors  30 - 36 . In any case, various types and/or combinations of sensors may be used as needed to suit particular applications. For example, a group or combination of sensors may sense one or more parameters such as vibration, acceleration, temperature, humidity, acidity, turbidity, the presence and/or concentration of one or more chemicals and gasses, flow, altitude, geographic location, direction or heading, thickness, corrosion rate, color, level, angular velocity, speed, pressure, pulse rate, or any other desired parameter. In some cases, a group of sensors that senses a particular combination of parameters may be especially advantageous. For example, a sensor that senses angular velocity, angular acceleration and vibration may be particularly useful for monitoring the output shaft or drive mechanism of a large motor or engine to determine whether bearing maintenance may be needed, whether a potentially dangerous condition exists, etc. Combining sensed parameters in this manner may minimize the effort required to attach or append the devices and/or sensors needed to carry out a given application and may most efficiently use the amount of space available near to or on the equipment being monitored and/or controlled. 
     Additionally, for some applications, sensors that sense particular parameters may be mounted internally (e.g. the sensors  26  and  28 ) and other sensors, which may sense other parameters, may be externally connected to the appendable device  10  either through the termination portion  38  or directly via wires, for example, as shown in the case of the external sensors  30  and  32 . For example, in some applications it may be advantageous to mount an acceleration or vibration sensor within the device  10  to eliminate the need to mount both the device  10  and a separate sensor to the piece of equipment. However, in some applications, space constraints may make it impossible to physically mount the device  10  directly to the part of the equipment that needs to be monitored. In such cases, the acceleration or vibration sensor may be external to the device  10  (e.g., one of the sensors  30 - 36 ) to enable independent mounting of the device  10  and the sensor. In the case of a motor, for example, the device  10  (i.e., its housing  12 ) may be attached to a wall, a sheet metal surface, etc. that is near to the motor while the external acceleration or vibration sensor may be mounted near to the shaft or a bearing of the motor. 
     Still further, the appendable device  10  may be connected to or may include i.e., may have mounted internally) one or more control outputs such as, for example, the control outputs  40  and  42 . These control outputs may include individual or combinations of outputs such as, for example, high and/or low voltage dry contact outputs, contactors, relays, analog outputs such as 4-20 milliamp (mA), 0-10 volts, etc., digital outputs, variable frequency and/or pulse width signals, digital words and/or more complex digital messages or information, etc. In any case, the external control outputs  40  and  42  may facilitate attachment of the control outputs  40  and  42  near a particular piece of equipment and/or a portion of that equipment. For example, in the case where the control output is a relay or a contactor, the control output may be mounted on or near a motor to facilitate the use of the relay or contactor as a mechanism for controlling the supply of power to the motor. Additionally or alternatively, one or more of the control outputs may be mounted internally within the appendable device  10  and the connection of external equipment and/or other devices to those control outputs may be implemented via the connection portion  38 , wires, etc. 
     The electrical connections between the external sensors  30 - 36  and control outputs  40  and  42  may be implemented using any desired technique. By way of example, the sensors  30  and  32  and the control output  40  may be electrically connected or coupled to the appendable device  10  via wires or cables  46 , each of which may include one or more individual wires or conductors as needed. Additionally, each of the wires or cables  46  may include electrical shielding to minimize or eliminate the effects of interference or noise on the performance of the sensors  30  and  32  and the control output  40 . The cables  46  may be made from any desired material or materials to suit the environmental characteristics (e.g., the temperature, humidity, etc.) associated with a particular application and/or to suit the characteristics of the signals carried by the cables  46  (e.g., high current, high voltage, low-level signals, high frequency signals, etc.). To maximize environmental ruggedness, the cables or wires  46  may be permanently fixed via soldering, welding, crimping, etc. to their respective sensors and control output and the appendable device  10 . For example, in a case where one or both of the sensors  30  and  32  are adapted to sense accelerations or vibrations, it may be desirable to permanently weld or solder the cables associated with those sensors to eliminate or minimize the possibility of a failure (e.g., a breaking or opening) of the electrical connections between the device  10  and the sensors  30  and  32 . In general, welded or soldered connections may be preferred for those applications in which adverse environmental characteristics such as high humidity levels, condensation, high vibration levels, excessive shocks or impacts, etc. could easily degrade or compromise other types of connections such as, plugable connectors, crimped connections, etc. 
     Alternatively or additionally, the cables or wires  46  may include plugable or modular connectors (not shown) that facilitate easy field attachment and or replacement of sensors, control outputs, etc. associated with the device  10 . Such plugable connectors may be positioned at either end of the cables or wires  46  or at some point between the ends of the cables or wires  46 . By way of example, the ends of the cables  46  farthest from the device  10  may have one-half of the plugable connector (i.e., either the male or the female portion) and the sensors and/or control outputs may have the other, complementary half of the connector. In this manner, sensors and control outputs may be attached to the cables or wires  46  as needed, sensors may be replaced, serviced or upgraded, etc. Of course, some or all of the male and female connector portions could be located between the sensors and control outputs and the device  10  so that the connection of the male and female connector portions occurs somewhere between the sensor or control output and the device  10 . Alternatively or additionally, some of all of the connector portions may be located at the device  10  (e.g., fixed to the housing  12 ) so that the connection occurs at or near the device  10 . 
     The wires or cables  46  may be, or may include, a pigtail arrangement whereby a pigtail (i.e. one or more wires) extending from each sensor or control output may be connected to a corresponding pigtail extending from the device  10  via twist-on wire connectors, crimp connectors, solder and shrink tubing, etc. Alternatively or additionally, the sensors and control outputs may include screw terminals, solder pads, jacks (e.g., RCA-type, banana, etc.) or any other suitable connector designed to receive a wire or cable. 
     In general, the wires or cables  46  may be provided in fixed lengths (a plurality of different lengths may be available to suit particular applications) at the time the device  10  is manufactured, thereby minimizing or eliminating the labor and costs associated with having to connect sensors, control outputs, etc. to the device  10  in the field near the equipment or system being monitored and/or controlled. While such fixed length cables or wires  46  can minimize or eliminate labor, particularly expensive trade labor such as, for example, electrician labor, such fixed lengths may make it more difficult or, in some cases, impossible to mount the appendable device  10  and one or more of the sensors and control outputs in their respective ideal or best locations. For example, the longest available cables  46  may be too short to enable a desired or required mounting distance between a sensor or control output and the device  10 . On the other hand, the shortest available cable may provide an excessive amount of extra cable or wire that consumes an undesirable amount of space or an amount of space that is not available surrounding apiece of equipment. 
     The connection or termination portion  38  may include a plurality of screw terminals, some or all of which are removable or plugable. Such screw terminals may be configured to accept spade-type connectors, wire ends, etc. Alternatively, or additionally, the termination portion  38  may include one or more jacks such as, for example, RCA-type jacks, banana plug jacks, etc. Preferably, but not necessarily, the termination portion  38  is integrally attached or formed with the housing  12  of the device  10  to provide strain relief, to protect the electrical terminations therein from the effects of the environment surrounding the device  10 , etc. 
     Internal sensors (e.g., the sensors  26  and  28 ) and internal control outputs (not shown) may be mounted to a printed circuit board and/or may be fixed to the housing  12 . For example, the housing  12  may include bosses, standoffs, plastic snaps, etc. to which a sensor may be directly mounted or attached and/or to which a printed circuit board (having sensors and/or control outputs mounted thereto) is attached. Alternatively or additionally, the internal sensors and control outputs may be potted, glued or otherwise fixed within the housing  12 . 
     As shown in  FIG. 1 , the power source  22  may be disposed within the housing  12  of the appendable device  10 . The power source  22  may be implemented using any suitable technology and/or technique. For example, the power source  22  may be a battery, either rechargeable or disposable, may be based on a super capacitor, may be a photoelectric cell or array of cells, may be a vibration driven generator, may be an induction-type power source, etc. In the case of a vibration-based power source, the power source  22  may be charged and/or may provide electrical output as long as the device  10  is vibrated at an amplitude greater than a predetermined level and at a frequency greater than a predetermined frequency. Such a vibration-based power source enables the device  10  to be mounted to a piece of rotating equipment, for example, and to derive its power from the vibrations generated by the rotating equipment. As a result, such a vibration-based power source eliminates the need to install external power supply wires or cables, which may be particularly advantageous in situations where the equipment being monitored and/or controlled is physically remote and/or difficult to access with respect to suitable sources of power for the device  10 . 
     In the case where the power source  22  uses induction to produce energy for use by the device  10 , a coil, loops of wire, etc. may be used to generate currents in response to varying magnetic fields that impinge on the device  10 . The coil, loops of wire, etc. may be formed integrally with a printed circuit board using conductive traces, which may be formed using conductive ink, etched copper, etc., and/or may be discrete wire loops or coils that are attached to a printed circuit board, attached to the housing  12 , etc. Of course, the antenna  24  may be used to serve both a communications function (i.e., receiving and sending communication signals) and a power generation function in which magnetic fields impinging on the antenna  24 , which may or may not also be carrying any communication information, induce currents in the antenna  24  that are processed by the power source  22  to provide suitable voltages and currents to the circuitry within the device  10 . Of course, the power source  22  may include multiple types or combinations of power generation technologies and techniques. For example, a photoelectric cell or array, a vibration powered generator or an induction device may store energy in a super capacitor or a rechargeable battery for use by the device  10 . 
     While the power source  22  is depicted in  FIG. 1  as being mounted within the appendable device  10 , the power source  22  could alternatively be mounted external to the housing  12  to facilitate replacement of the power source  22 , if needed. Still further, the appendable device  10  may be adapted to receive power from an external source such as, for example, an external transformer or power supply supplying alternating current (AC) or direct current (DC) power, readily available line voltage (e.g., 120 volts AC), etc. in which case field wiring of the external power source to the device  10  would be required. 
     The processor  16  may be a special purpose processing unit such as, for example, an application specific integrated circuit (ASIC), may be a microcontroller or may be a general purpose microprocessor unit. The memory  18  may be a separate unit or device as shown in  FIG. 1  or may be integral with the microcontroller, ASIC, etc. that performs the functions of the processor  16 . Alternatively, the memory  18  may be distributed within one or more of the other blocks shown in  FIG. 1 . Any suitable type of memory technology or combination of memory technologies may be used including random access memory (RAM), read-only memory (ROM), electrically erasable programmable read only memory (EEPROM), flash memory, erasable programmable read only memory (EPROM), magnetic memory media, optical memory media, etc. 
     In general, the I/O interface  20  enables the processor  16  to communicate with the sensors  26 ,  28  and  30 - 36  and the control outputs  40  and  42 . More specifically, the I/O interface  20  may include an analog-to-digital (A/D) convertor, one or more amplifiers, filters (e.g., anti-aliasing, noise reduction, etc.), electrical isolation devices such as, for example, optical isolators, transformers, etc., passive and/or active protection circuitry such as, for example, transient suppression and electrostatic discharge protection devices, etc. Although the I/O interface  20  is shown as a separate functional block in  FIG. 1 , some or all of the functions performed by the I/O interface  20  may be integrated within the processor  16 . For example, in the case where the functions performed by the processor  16  are implemented using a microcontroller, the microcontroller may also include an on-board A/D convertor. 
     The transceiver  14  may use any desired wireless communication technology and protocol. For example, the transceiver  14  may be adapted to use a spread spectrum communication technique, which is a well-known communication technique and, thus, is not described in greater detail herein. In addition, the transceiver  14  may perform one or more techniques that improve the integrity and/or quality of the information being transmitted and/or received by the device  10 . For example, error detection and correction techniques such as Bose-Chadhuri-Hocquenghem (BCH) or fire coding may be used to improve the quality of the information being processed by the processor  16  and/or the information being sent by the processor  16  to other systems and devices. Further, the transceiver  16  may use redundant transmission techniques (e.g., duplicate message transmission) and/or n-level parity techniques to improve the quality or integrity of communications. As with the I/O interface  20  described above, one or more of the functions performed by the transceiver  14  may be performed by the device that performs the functions of the processor  16 . For example, the routines  44  may include software that, when executed by the processor  16 , perform one or more error detection techniques. 
     The antenna  24  enables the device  10  to perform wireless communication activities with other appendable devices similar or identical to the device  10 , other controllers, workstations, etc., or any other wireless communication devices such as cellular phones, pagers, hand-held computers e.g., personal data assistants), lap-top computers, etc. More specifically, the antenna  24  may be optimized for a particular frequency or range of frequencies, for particular interference response characteristics or, more generally, to suit any particular application or applications. The antenna  24  may be implemented using a wire whip that is attached to the housing  12  and/or a circuit board within the housing  12 . Alternatively, the antenna  24  may be implemented using one or more loops of wire or conductive traces that may be integral with the housing  12  or a printed circuit board within the housing  12 . 
     The various functional blocks and devices shown within the housing  12  of the device  10  may be implemented using any suitable technology or combination of technologies. For example, the circuitry needed to perform the functional blocks shown within the device  10  may be implemented using discrete components, one or more ASICs, integrated circuits, etc. that may be mounted to a printed circuit board having one or more layers, a ceramic substrate such as that used in fabricating hybrid circuitry, etc. in the case that the circuitry is implemented using integrated circuits, one or more of the integrated circuits may be mounted to a circuit substrate using a die-down configuration in which silicon die are mounted and wire-bonded directly to a circuit substrate and then encapsulated in silicone gel, epoxy or the like to protect the circuitry and environmentally sensitive wire bond connections. Still further, the circuitry within the device  10  may be implemented using multiple circuit substrates that are interconnected via wires, plugable connectors, soldered headers, etc. To protect the circuitry within the device  10  from environmental stresses such as vibration, shock, moisture, etc., the circuitry may be encapsulated or potted in epoxy, silicone gel, a urethane dip or spray, etc. 
     The housing  12  may be of any suitable shape or geometry that facilitates mounting or attachment of the device  10  to a variety of types of equipment, surfaces, etc. For example, the housing  12  may have a cylindrical or puck-like geometry, may have a cube or box-like geometry or may have any other desired geometry. The housing  12  may consist of multiple parts or components that are fastened together using glue, ultrasonic welds, threaded fasteners, rivets, etc., or may be a substantially unitary structure. Any suitable material or combination of materials may be used to fabricate the housing  12 . For example, the housing may be made of plastic, which may be injection molded, or may be made of metal, which may be molded, stamped and/or welded. Of course, the housing  12  may be made of multiple types of materials so that particular portions of the housing  12  are made of materials best suited to perform the functions performed by those portions of the housing  12 . For example, the housing  12  may include a base plate or mounting plate portion (not shown) that is made from heavy gauge stamped steel to provide a highly rugged portion that can be screwed, bolted, riveted, etc. to a piece of equipment, a sheet metal surface, etc. without damaging the device  10  or the mounting plate. In addition to a rugged mounting plate, the housing  12  may also include a plastic cover or cap (not shown), which may be less rugged than the mounting plate, that covers the circuitry, the antenna  24  or any other internal portions of the device  10  to prevent dust, fingers, screwdrivers, metal filings, etc. from damaging or impairing the operation of the circuitry within device  10 . More generally, the materials and geometry of the housing  12  may be selected to suit any particular application. For example, applications involving hazardous environments (e.g., explosive conditions, caustic gasses, etc. or rugged environments (e.g., high shock, impact, acceleration, vibration, liquid water, etc.) may require a housing that completely encapsulates the circuitry of the device  10 . On the other hand, applications involving environmental conditions that are relatively benign in nature (e.g., measuring a temperature in an office space), may only require that the housing  12  functions to prevent debris or dust, fingers and/or other objects from contacting sensitive circuitry directly. 
     The housing  12  may be configured to facilitate mounting of the device  10  to apiece of equipment. For example, the housing  12  may have through-holes, mounting feet or tabs with through-holes, slots, etc. that enable a field technician to fasten the device  10  to a sheet metal surface or another suitable surface using self-tapping screws, self-threading screws, rivets, etc. Alternatively or additionally, the housing  12  may include features that enable a band clamp, tie-wrap or the like to be used to fasten the device  10  to a piece of equipment or to an object proximate to that piece of equipment. Further, the housing  12  may include a surface, surfaces or some other feature that enables an adhesive, double-sided tape, Velcro™, magnets, pop rivets, etc. to be used to fasten or attach the device  10  to a piece of equipment or a surface. Still further, the housing  12  and the device  10  may be configured to enable the device  10  to be mounted by simply placing or resting the device  10  on a piece of equipment, thereby eliminating the need for additional fasteners and/or attachment mechanisms. 
       FIG. 2  is an exemplary diagrammatic view that depicts one manner in which one or more appendable devices, such as the device  10  shown in  FIG. 1 , may be used to automate a process control system or plant  100 . By way of example, the plant  100  shown in  FIG. 1  is a portion of a bakery that produces cookies. Of course, the appendable devices described herein, such as the exemplary device  10  shown in  FIG. 1 , may be used in any other type of system or plant having a higher or a lower degree of complexity than the system  100  shown in  FIG. 2 . 
     More specifically, the plant  100  shown in  FIG. 1  includes a cookie making process or portion  102  that includes a dough mixing process or portion  104 , a baking process or portion  106  and a packaging process or portion  108 . The cookie making process  102  may also include other processes, portions or subsystems such as, for example, a cookie cutting or shaping process, a quality control process, a decorative topping process, etc., none of which are shown in  FIG. 2  for purposes of clarity. 
     In general, the operation of the cookie making process or portion  102  may be controlled via a workstation  110  or any other suitable type of computer system. As shown in  FIG. 2 , the workstation  110  includes a transceiver  112  that enables the workstation  110  to communicate with one or more appendable devices, such as the device  10 , using any desirable wireless communication technology and protocol. The workstation  110  may also include one or more software routines  114  that, when executed by a processor (not shown) within the workstation  110 , enable the workstation  110  to monitor, analyze and/or control the cookie making process  102 , as well as other processes (e.g., the dough mixing process  104 , the packaging process  108 , etc.) within the plant  100  or at other plants (not shown) in a desired manner. 
     As can be seen in  FIG. 2 , the dough mixing process  104  provides raw cookies  116  to the baking process  106  and, in turn, the baking process  106  provides baked cookies  118  to the packaging process  108  which, in general, sorts cookies and places predetermined amounts of the sorted cookies in one or more styles and sizes of packages that enable convenient shipping and sale of the cookies  118 . As can also be seen from  FIG. 2 , the baking process or portion  106  includes a conveyor  120 , which is driven by a motor  122 , and an oven  124  having heating elements  126  and  128 . Additionally, the baking process or portion  106  includes a plurality of appendable devices  130 - 142 , all of which are associated with the oven  124 , the motor  122 , etc. and/or other portions of the baking process  106  as described in greater detail below. 
     The appendable devices  130  and  132  are configured to sense temperature using respective temperature sensing elements  144  and  146  which, as shown in  FIG. 2 , are external to and remotely situated from the devices  130  and  132 . Preferably, but not necessarily, the temperature sensing elements  144  and  146  are situated within the oven  124  to best sense the ambient temperature surrounding the cookies passing through the oven  124 . Further, because two independent heating elements (i.e., the heating elements  126  and  128 ) are used in the oven  124 , two ambient temperature zones may be established and each of the sensing elements  144  and  146  may only measure the temperature in their respective zones. 
     The devices  130  and  132  may be appended or attached to the oven  124  in any desired manner. For example, in the case where the surfaces to which the devices  130  and  132  are to be attached are sheet metal, self-tapping or self-threading screws may be used to attach the devices  130  and  132  to the oven  124 . Alternatively, the devices  130  and  132  may be attached to the oven  124  using double-sided tape or any other suitable adhesive, Velcro™, etc. The temperature sensing elements  144  and  146  may be supplied as part of the oven  124 , in which case the devices  130  and  132  may include appropriate input connections via pigtails (i.e., wires) and/or a termination portion having screw terminals that facilitate the electrical connection of the temperature sensing elements  144  and  146  to their respective devices  130  and  132 . If one or both of the temperature sensing elements  144  and  146  are not supplied with the oven  124 , one or both of the temperature sensing elements  144  and  146  may be provided with the devices  130  and  132  (i.e., permanently attached via wires, attached via a modular connector, termination portion, etc.). 
     The appendable devices  134  and  136  include control outputs that are configured to control the amount of power flowing through the respective heating elements  126  and  128 , thereby controlling the heat generated by the elements  126  and  128  and the ambient temperature within the oven  124 . For example, if the heating elements  126  and  128  are electric heating elements, the devices  134  and  136  may provide dry contact outputs that may be operated by the devices  134  and  136  to control the flow of electrical current to the heating elements  126  and  128 . As with the devices  130  and  132 , the devices  134  and  136  may be attached or appended to the oven  124  in any desired manner. However, because the devices  134  and  136  are located on a horizontally oriented surface of the oven  124 , the devices  134  and  136  may be mounted to the oven  124  by simply resting the devices  134  and  136  on top of the oven  124  without using any additional fasteners, glue, etc. Additionally, the electrical connections between the heating elements  126  and  128 , their respective devices  134  and  136  and a source of electrical power may be implemented using any desired technique including pigtails and twist-on wire connectors, screw terminals, modular connectors, etc. 
     The appendable device  138  is configured to sense the color (i.e., the doneness) of the baked cookies  118 . The device  138  may, for example, include an internally mounted charge coupled device (CCD) that captures digital images of the baked cookies  118  via an aperture or opening in the housing of the device  138 . As described in greater detail below, information relating to the doneness of the baked cookies  118  may be used to better control the baking process  106  to more efficiently produce higher quality cookies. 
     The appendable device  140  is configured to provide a control output that varies the speed of the motor  122  and the appendable device  142  is configured to sense the rotational speed of the conveyor  120 . As with the other appendable devices  130 - 138 , the devices  140  and  142  may be physically attached and electrically interconnected to their respective portions of the baking process  106  using any of the techniques described herein. 
     Each of the appendable devices  130 - 142  has an antenna that enables the device to communicate with other ones of the devices  130 - 142  and/or with the workstation  110  using any desired wireless communication technique. Additionally, although not shown in  FIG. 2 , the appendable devices  130 - 142  and/or the workstation  110  may be configured to communicate with cellular phones, pagers, laptop computers, hand-held computers, or any other device capable of wireless communication Likewise, the appendable devices  130 - 142  may be configured to engage in wireless communications with other workstations or appendable devices that are located in other portions of the cookie making process  102 , other portions of the plant or bakery  100 , other plants, etc. 
     In operation, the appendable devices  130 - 142  may cooperate with the workstation  110  and each other to control the cookie making process  102  and, in particular, the baking process or portion  106 . More specifically, the appendable device  138 , which measures or senses the color of the baked cookies  118 , may provide color information to the workstation  110  via a wireless communication link. In turn, the workstation  110  may analyze the received color information and may control the baking process  106  by sending commands and/or other information to the appendable devices  134 ,  136  and  140 , which are configured as control output devices and which may vary the ambient temperature within the oven  124  and/or the speed of the conveyor  120  to control the extent to which cookies are baked by the oven  124  (i.e., the doneness of the cookies). 
     For example, the workstation  110  may receive color information from the device  138  indicating that the baked cookies  118  are dark brown in color. In this case, the workstation  110 , after analyzing the color information, may send control information, messages or commands to the device  140  and/or the device  142  to cause the speed of the conveyor  120  to increase, thereby exposing the cookies for less time to the ambient temperature within the oven  124  and reducing the baking time. On the other hand, if the workstation  110  receives color information from the device  138  indicating that the baked cookies  118  are a pale tan color, the workstation  110  may send control information, messages or commands that cause the speed of the conveyor  120  to decrease, thereby increasing the baking time of the cookies. Of course, the workstation  110  may employ any desired control loop techniques to control the baking time (i.e., the conveyor speed) in an appropriate manner. For example, control loops having proportional, integral and/or derivative (PID) control parameters may be used, if desired. Such PID-based control loops or techniques are well known and, thus, are not described in greater detail herein. 
     There are many ways in which the workstation  110  and the devices  140  and  142  may interoperate to control the speed of the conveyor  120 . For example, the workstation  110  may send command information, control information, etc. to the appendable device  142  instructing the device  142  to control the speed of the conveyor  120  to a particular speed. The device  142  may then measure the speed of the conveyor  120  and send commands, messages, control information, etc. to the device  140  which, in turn, causes the speed of the motor  122  to be increased or decreased as needed to maintain the conveyor speed targeted by the device  142 . By way of example only, the device  140  may include a 4-20 mA control output device and the device  142  may send control information, commands, etc. to the device  140  that cause the device  140  to provide a particular current corresponding to the rotational speed targeted by the device  142  to the motor  122 . Thus, as can be seen from the above example, the workstation  110  does not necessarily have to be directly involved in communicating with the device  140  and the device  142  to control the speed of the motor  122 . Rather, the workstation  110  may communicate directly with the device  142  and the device  142  may be configured to communicate directly with the device  140  to carry out a closed-loop speed control of the motor  122  and the conveyor  120 . 
     As with the control of conveyor speed or baking time described above, the oven temperature or baking temperature of the baking process  106  can be controlled via the interoperation of the appendable devices  130 - 138  and the workstation  110 . For example, the device  138  may send color information to the workstation  110  indicating that the baked cookies  118  are relatively dark in color (i.e., overdone) or relatively light in color (i.e., underdone). The workstation  110  may then communicate with the devices  130  and  132  to measure the ambient temperatures within the oven  124  and may send appropriate control messages, commands, etc. to the devices  134  and  136  to decrease or increase the amount of power that is provided to the heating elements  126  and  128  to decrease or increase the ambient temperature within the oven  124 . The workstation  110  may continue to receive oven temperature information from the devices  130  and  132  and may continue to send commands, messages or any other information to the devices  134  and  136  to vary the amount of power supplied to the heating elements  126  and  128  until the temperature measured by the temperature sensing elements  144  and  146  reaches the desired baking temperature. Of course, the workstation  110  may use any desired control loop techniques, including PID-based control, to control the baking temperature within the oven  124  in an appropriate manner. 
     As with the control of the conveyor speed, the workstation  110  does not necessarily have to communicate directly with all of the devices  130 - 136  to control the ambient temperature within the oven  124 . Instead, the workstation  110  may receive color (i.e., doneness) information from the device  138  and, in response may send commands, messages and/or other information associated with a particular desired baking temperature to the devices  130  and  132 . The devices  130  and  132  may then send commands, messages, etc. to their respective control output devices  134  and  136  to cause more or less power to be supplied to the heating elements  126  and  128 . 
     Of course, because the heating elements  126  and  128  can be controlled independently, the temperatures zones within the oven  124  that correspond to the temperature sensing elements  144  and  146  may be controlled to the same or different temperatures to suit a particular cookie baking application. Furthermore, it should be recognized that for some applications it may be desirable to maintain a constant temperature within all areas of the oven  124  and to vary only conveyor speed to control the extent to which cookies are baked. In still other applications, for example, it may be desirable to vary only the baking temperature while maintaining a constant conveyor speed, particularly in cases where upstream and downstream production processes (e.g., dough mixing, packaging, etc.) require a particular rate or line speed for efficient operation of the overall cookie making process  102 . Other applications may vary both oven temperature and conveyor speed to best optimize cookie quality, production efficiency or any other desired parameter. 
     While in operation, the appendable devices  130 - 142  can send alarm messages or notifications to the workstation  110  and/or directly to each other. For example, one or both of the devices  130  and  132 , which sense temperatures within the oven  124 , may detect an out-of-range temperature condition (e.g., that a temperature has exceeded or has fallen below a predetermined limit) and may send an appropriate alarm to the workstation  110 . The workstation  110  may then display the out-of-range temperature condition to a system user or operator via an alarm panel or banner or using any other desired display technique. Alternatively or additionally, the alarm information may be communicated directly to one or both of the devices  134  and  136  which, in turn, may respond to the alarm information by, for example, halting the flow of power to the heating elements  126  and  128 . 
     While the appendable devices  130 - 142  shown in  FIG. 2  are described as providing a single control output or a single sensory input, some or all of the devices  130 - 142  could have multiple sensory inputs and control outputs or combinations thereof. For example, a single appendable device having a temperature sensor input and a dry contact output may be substituted for the devices  130  and  134  as well as the devices  132  and  136 , thereby reducing the number of appendable devices that have to be mounted to or attached to the oven  124 , which may significantly reduce installation labor and costs and more efficiently utilize available mounting area on the oven  124 . Similarly, a single appendable device having a speed sensing input and a 4-20 mA control output could be substituted for the devices  140  and  142 . More generally, a single multi-purpose or generic appendable device having, for example, a temperature input, a dry contact control output, a 4-20 mA control output, a color sensing input and a speed sensing input may be used to implement the system shown in  FIG. 2 . Such a general purpose or generic appendable device would enable control of the baking process  106  by three or four such generic appendable devices rather than the seven devices shown in  FIG. 2 . Of course, the appendable devices described herein can be made to include any desired number and combination of sensing inputs and control outputs. 
     It is important to recognize that while the baking process  106  described in connection with  FIG. 2  is configured to enable wireless communications between the appendable devices  130 - 142  and the workstation  110 , between the appendable devices  130 - 142  via the workstation  110  (i.e., with the workstation  110  acting as a communication hub), directly between devices (i.e., without using the workstation  110  as a communication hub), other types of communication schemes using hardwired networks and techniques could be used instead of or in addition to the all-wireless system shown in  FIG. 2 . For example, some or all of the devices  130 - 142  shown in  FIG. 2  may be interconnected to each other and the workstation  110  via an ethernet network and may communicate with each other using any desired communication protocol, including, for example, the PROFIBUS protocol, the Foundation Fieldbus protocol, etc. 
     Still further, while  FIG. 2  depicts the cookie making process  102  as being controlled using a single workstation (i.e., the workstation  110 ), additional workstations may be employed. In that case, the functions performed by the software routines  114  may be distributed among the multiple workstations and may be performed within those workstations. Alternatively, a controller such as, for example, a DeltaV™-type controller may be used in addition to or instead of the workstation  110 . Still further, workstations and/or controllers could be eliminated completely and the devices  130 - 142  may be configured to communicate with each other using, for example, a peer-to-peer communication scheme. In that case, the functions performed by the software routines  114  could be distributed among the devices  130 - 142  that carry out, or that would be best suited to carry out, those functions. 
     Although the system or plant  100  shown in  FIG. 2  is depicted as having a workstation  110  and appendable devices  130 - 142  that control only a portion of the cookie making process  102  (i.e., the baking process  106 ), other processes such as the dough mixing process  104  and the packaging process  108  within the cookie making process  102 , or any other process or device within the plant  100 , may be controlled in a similar manner. 
     The appendable devices described herein may be used within a wide variety of applications in addition to the exemplary application shown in  FIG. 2 . Generally speaking, the appendable devices and system described herein may be used to carry out any type of process control activities, data management services, predictive control monitoring, etc. More specifically, the appendable devices and system described herein may be particularly well suited for use in monitoring and/or controlling the operations of a vineyard. For example, a plurality of appendable devices may be distributed among the vines to measure the moisture content and acidity of the vineyard soil and may instruct vineyard operators to (or may automatically) apply an appropriate type and amount of fertilizer to the vines, water the vines, etc. In another exemplary application, a plurality of appendable devices having internal location detectors (e.g., global positioning units) may be attached to cows or horses within a herd or multiple herds and may monitor or track the movements of the herd for a rancher. The rancher may use such herd location information to develop a maintenance plan for grazing areas, determine the fastest route to the herd, etc. In still another exemplary application, appendable devices may be attached to one or more patients or animals within a hospital or other facility to enable remote monitoring of patient physiological conditions, patient location, patient status (e.g., sleeping, moving, awake, etc.), etc. In yet another exemplary application, a plurality of appendable devices may be used to monitor and/or automatically control the level of water in a flood drainage system. In that application, each of the appendable devices may control the operation of a particular flood gate and/or or warning signal (e.g., a flashing light, siren, etc.) and may communicate the status of its water level, gate position, warning condition, etc. to the other appendable devices and/or to a central facility (e.g., a municipal facility). In this manner, municipalities may be better able to better avert potentially dangerous flood conditions or, in the event that a flood cannot be prevented, may be able to more quickly dispatch rescue personnel to flooded areas to minimize or prevent the loss of lives. 
       FIG. 3  is an exemplary functional block diagram that depicts one possible logical configuration  200  of the workstation  110  shown in  FIG. 2 . In this example, the workstation  110  is configured as a web server having a configuration service  202 , a real time data service  204 , a communications block  206 , a control block  208 , a database  210  and an events service  212 . Additionally, the server  110  may receive device profiles and/or configuration information  214  from one or more appendable devices. 
     The configuration service  202  may include functions that enable the workstation  110  to automatically detect the presence of appendable devices and automatically upload the profiles  214  associated with these detected devices and store this configuration and/or device profile information in the database  210 . The appendable devices described herein may be self-revealing during the configuration process and, thus, may be adapted to provide information such as, for example, the version of the device, a unique tag or identifier associated with the device, a manufacturer name associated with the device, the location of the device, etc. to the configuration service  202 . The configuration service  202  may also provide a graphical user interface or portal that enables a system user or operator to view the logical interrelationships between the appendable devices, other types of devices, workstations, controllers, etc. used within a system or plant. 
     The real-time data service  204  may enable the server  110  to continuously monitor parameters sensed by one or more appendable devices, the status of any device used within a process or plant, etc. The real-time data service  204  may also provide graphical views that enable a system user or operator to view real-time data in a graphical format, thereby enabling the user or system operator to recognize trends, erratic control performance, impending dangerous conditions, etc. 
     The communications block  206  may use any desired communication technique to enable the server  110  to communicate with appendable devices, or any other devices, systems, etc. that may be distributed within a plant, between plants, etc. For example, the communications block  206  may communicate in conformance with the well known TCP/IP communication protocol and may be adapted to send and receive information using messages that have been formatted according to an extensible markup language (e.g., XML). Of course, any other suitable communication protocol and message format can be used instead. In addition, the communications block  206  may perform security functions such as, for example, communications encryption, authenticated logins, etc. 
     The communications block  206  may also store communication path or route information that enables the appendable devices to communicate with each other and/or a central workstation or computer via a series of communication links provided by the appendable devices themselves. For example, a particular appendable device may communicate with another appendable device through a series of communications links involving one or more intervening appendable devices. As described in greater detail below, by enabling the appendable devices described herein to function as repeaters, relay stations, etc. appendable devices that are physically very remote from one another can communicate indirectly with each other through other appendable devices, which reduces the amount of power required by each of the appendable devices for transmitting information. Additionally, the communications block  206  may be adapted to determine the best communication path (i.e., series of communication links) to enable communication between any two nodes or devices within a system having a plurality of appendable devices. In the event that the communications block  206  determines that an initially selected communication path has become compromised (i.e., one or more nodes or appendable devices are unable to function as relays or repeaters), the communications block  206  may self-heal communications by determining a new best communication path using only those nodes or devices that are able to function as repeaters or relays. 
     The control block  208  provides the functionality of a controller and, thus, may be described generally as a virtual controller. Thus, the control block  208  may execute one or more process control loops, may perform various types of data analysis, etc. The events service  212  may process alarm or alert information and generate responsive notifications. The notifications may be conveyed to appropriate entities using email, printed reports, or using any other media or technique. For example, notifications may be sent via wireless media to pagers, cellular phones, hand-held computers, laptops, other workstations or computers, etc. 
       FIG. 4  is a block diagram that depicts an exemplary system topology  300  that may be used in implementing a process monitoring and/or control system using the appendable system and devices described herein. As shown in  FIG. 4 , the topology  300  includes a plurality of local stations  302 ,  304  and  306  that are communicatively coupled to a central monitoring, reporting and control station  308  and one or more users  310  via respective wireless communication links  312 - 320  and a wireless communication network  322 . 
     The local station  302  includes a plurality of nodes or clusters of nodes  324 ,  326  and  328 , each of which is communicatively coupled via respective wireless communication links  330 ,  332  and  334  to a local area network  336 . One or more workstations or other computer systems  338  and  340  may be communicatively coupled to the local area network  336 . Each of the nodes  324 - 328  may include one or more of the appendable devices described herein as well as plant or process equipment, or any other entities, being monitored and/or controlled. Thus, each of the nodes  324 - 328  may, for example, represent a portion of an overall process control system or plant, a particular geographic region in which monitoring and/or control activities are taking place, etc. The workstations  338  and  340  may be programmed to perform local configuration activities, diagnostic activities, monitoring activities, control activities, etc. Additionally, one or more of the workstations  338  and  340  may be configured to communicate via the wireless communication link  312  to enable the local station  302  to communicate with the other local stations  304  and  306 , the central station  308  and/or one or more of the users  310 . Although not shown in detail in  FIG. 4 , the local stations  304  and  306  may be similarly or identically configured to the local station  302 . 
     The wireless communication network  322  may be implemented using any desired technology or combination of technologies. For example, the communication network  322  may use a cellular communications technology that is based on circuit-switched communications and/or packet-switched communications. Alternatively or additionally, the communication network  322  may use the Internet for some or all communications. 
     The central station  308  may include one or more workstations or other computer systems (not shown) that perform communications routing activities, process monitoring activities, process control activities, reporting activities, etc. In general, the central station  308  may be configured or programmed to coordinate the interactions between the local stations  302 - 306  and the interactions between the users  310  and the local stations  302 - 306 . Of course, the central station  308  may also coordinate the activities within one or more of the local stations  302 - 306 . 
     The users  310  may include service technicians, engineers, plant managers, etc. that typically need access to information related to the operations within the local stations  302 - 306 . Additionally, the users  310  may desire to affect the operations (e.g., change a control strategy, parameter, etc.) from a remote location and, thus, the users  310  may communicate with one or more of the local stations  302 - 306  (either directly through the network  322  and the links  312 - 316  and  320  or indirectly through the network  322 , the central station  308  and the links  312 - 318  and  320 ) to effect a change in their operation. The hardware platforms employed by the each of the users  310  may be of any desired type. For example, cellular phones, laptop computers, hand-held computers, pagers, etc. may be used to suit the needs of a particular type of user, the geographic location of the user, etc. 
     If implemented in software, the functional blocks and software routines discussed herein may be stored in any computer readable memory such as on a magnetic disk, a laser disk, or other storage medium, in a RAM or ROM of a computer, controller, field device, etc. Likewise, this software may be delivered to a user or a device via any known or desired delivery method including, for example, over a communication channel such as a telephone line, the Internet, etc. 
     While the invention has been described with reference to specific examples, which are intended to be illustrative only and not to be limiting of the invention, it will be apparent to those of ordinary skill in the art that changes, additions or deletions may be made to the disclosed embodiments without departing from the spirit and scope of the invention.