Abstract:
A wireless field device is disclosed. The wireless field device includes an enclosure having a processor disposed within the enclosure. A power module may also be located inside the enclosure and be coupled to the processor. A wireless communication module is operably coupled to the processor and is configured to communicate using radio-frequency signals. An antenna is coupled to the wireless communication module. A radome mounted to the electronics enclosure is formed of a polymeric material. The radome has a chamber inside that contains the antenna.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 60/847,901, filed Sep. 28, 2006, the content of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     In industrial settings, control systems are used to monitor and control inventories of industrial and chemical processes, and the like. Typically, the control system performs these functions using field devices distributed at key locations in the industrial process and coupled to the control circuitry in the control room by a process control loop. The term “field device” refers to any device that performs a function in a distributed control or process monitoring system, including all devices used in the measurement, control and monitoring of industrial processes. 
     Field devices are used by the process control and measurement industry for a variety of purposes. Usually, such devices have a field-hardened enclosure so that they can be installed outdoors in relatively rugged environments and are able to withstand climatological extremes of temperature, humidity, vibration, mechanical shock, et cetera. These devices also can typically operate on relatively low power. For example, field devices are currently available that receive all of their operating power from a known 4-20 mA loop. 
     Some field devices include a transducer. A transducer is understood to mean either a device that generates an electrical output based on a physical input or that generates a physical output based on an electrical input signal. Typically, a transducer transforms an input into an output having a different form. Types of transducers include various analytical equipment, pressure sensors, thermistors, thermocouples, strain gauges, flow transmitters, positioners, actuators, solenoids, indicator lights, and others. 
     Typically, each field device also includes communication circuitry that is used for communicating with a process control room, or other circuitry, over a process control loop. In some installations, the process control loop is also used to deliver a regulated current and/or voltage to the field device for powering the field device. 
     Traditionally, analog field devices have been connected to the control room by two-wire process control current loops, with each device being connected to the control room by a single two-wire control loop. Typically, a voltage differential is maintained between the two wires within a range of voltages from 12-45 volts for analog mode and 9-50 volts for digital mode. Some analog field devices transmit a signal to the control room by modulating the current running through the current loop to a current that is proportional to a sensed process variable. Other analog field devices can perform an action under the control of the control room by controlling the magnitude of the current through the loop. In addition to, or in the alternative, the process control loop can carry digital signals used for communication with field devices. Digital communication allows a much larger degree of communication than analog communication. Moreover, digital devices also do not require separate wiring for each field device. Field devices that communicate digitally can respond to and communicate selectively with the control room and/or other field devices. Further, such devices can provide additional signaling such as diagnostics and/or alarms. 
     In some installations, wireless technologies have begun to be used to communicate with field devices. Wireless operation simplifies field device wiring and setup. One particular form of wireless communication in industrial locations is known as wireless mesh networking. This is a relatively new communication technology that is proven useful for low cost, battery-powered, wireless communication in commercial measurement applications. Wireless mesh networking is generally a short-range wireless communication system that employs low-power radio-frequency communications and are generally not targeted for long distance, plant-to-plant, pad-to-pad or station-to-station communications. While embodiments of the present invention will generally be described with respect to wireless mesh networking communication, embodiments of the present invention are generally applicable to any field device that employs any form of radio-frequency communication. 
     In general, wireless radio-frequency communication requires the use of an antenna. In such harsh industrial settings, the antenna is a relatively fragile physical component. Moreover, should the antenna break off, communication to the field device itself may be compromised. If the antenna seal to the housing is damaged or degraded (for example by UV exposure or hydrolytic degradation) the environmental seal can fail and cause damage to the device. 
     Providing a rugged radio frequency antenna for use with field devices in industrial locations would provide more robust wireless field device communication and benefit the art of industrial process measurement and control. 
     SUMMARY 
     A wireless field device is disclosed. The wireless field device includes an enclosure having a processor disposed within the enclosure. A power module may also be located inside the enclosure and be coupled to the processor. A wireless communication module is operably coupled to the processor and is configured to communicate using radio-frequency signals. An antenna is coupled to the wireless communication module. A radome is mounted to the enclosure and is formed of a polymeric material. The radome has a chamber inside that contains the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a wireless field device in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagrammatic view of a wireless field device in accordance with an embodiment of the present invention. 
         FIG. 3  is an exploded isometric view of an antenna and radome assembly in accordance with an embodiment of the present invention. 
         FIG. 4  is an exploded isometric view of an antenna and radome assembly in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram of a wireless field device in accordance with an embodiment of the present invention. Wireless field device  100  includes enclosure  102  illustrated diagrammatically as a rectangular box. However, the rectangular box is not intended to depict the actual shape of the enclosure  102 . Wireless communication module  104  is disposed within enclosure  102  and is electrically coupled to antenna  106  via connection  108 . Wireless communication module  104  is also coupled to controller  110  as well as power module  112 . Wireless communication module  104  includes any suitable circuitry useful for generating radio frequency signals. 
     Depending on the application, wireless communication module  104  may be adapted to communicate in accordance with any suitable wireless communication protocol including, but not limited to: wireless networking technologies (such as IEEE 802.11(b) wireless access points and wireless networking devices built by Linksys of Irvine, Calif.), cellular or digital networking technologies (such as Microburst® by Aeris Communications Inc. of San Jose, Calif.), ultra wide band, global system for mobile communications (GSM), general packet radio services (GPRS), code division multiple access (CDMA), spread spectrum technology, short messaging service/text messaging (SMS), or any other suitable radio frequency wireless technology. Further, known data collision technology can be employed such that multiple field devices employing modules similar to wireless communication module  104  can coexist and operate within wireless operating range of on another. Such collision prevention can include a number of different radio-frequency channels and/or spread spectrum techniques. Additionally, communication module  104  can be a commercially available Bluetooth communication module. In the embodiment illustrated in  FIG. 1 , wireless communication module  104  is a component within enclosure  102  that is coupled to antenna  106 . 
     Controller  110  is coupled to wireless communication module  104  and communicates bi-directionally with wireless communication module  104 . Controller  110  is any circuit or arrangement that is able to execute one or more instructions to obtain a desired result. Preferably, controller  110  includes a microprocessor, but can also include suitable support circuitry such as onboard memory, communication busses, et cetera. 
     Each of wireless communication module  104  and controller  110  is coupled to power module  112 . Power module  112  may preferably supply all requisite electrical energy for the operation of field device  102  to wireless communication module  104  and controller  110 . Power module  112  includes any device that is able to supply stored or generated electricity to wireless communication module  104  and controller  110 . Examples of devices that can comprise power module  112  include batteries (rechargeable nor not), capacitors, solar arrays, thermoelectric generators, vibration-based generators, wind-based generators, fuel cells, et cetera. Alternatively, the power module may be connected to a two-wire process control loop and obtain and store power for use by the wireless communication module. 
     Transducer  114  is coupled to controller  110  and interfaces field device  102  to a physical process. Examples of transducers include sensors, actuators, solenoids, indicator lights, et cetera. Essentially, transducer  114  is any device that is able to transform a signal from controller  110  into a physical manifestation, such as a valve movement, or any device that generates an electrical signal to controller  110  based upon a real world condition, such as a process fluid pressure. 
     In accordance with an embodiment of the present invention antenna  106  is encased within a robust polymeric radome  116  that physically couples to enclosure  102 . As used herein, a “radome” is intended to mean a housing for a radio antenna; transparent to radio waves. As such, for the purposes of this patent document, the radome need not be “dome-shaped.”  FIG. 2  is a diagrammatic view of field device  100  including enclosure  102  with radome  116  mounted thereon. While  FIG. 2  illustrates a type of field device known as a process fluid pressure transmitter, any field device can be used. Additionally, while  FIG. 2  illustrates radome  116  extending vertically above enclosure  102 , radome  116  can extend in any suitable direction. 
       FIG. 3  is an exploded isometric view of an antenna assembly for use in industrial locations in accordance with an embodiment of the present invention. Antenna assembly  188  includes coaxial antenna  106  coupled to cable  120 , which cable  120  is coupleable to wireless communication module  104  on a circuit board (not shown in  FIG. 3 ) within housing  102 . Cabling  120  may be in the form of a coaxial cable, or any other suitable arrangement. Antenna  106  has an outer diameter  122  that is sized to fit slidably within chamber  124  of radome  116 . In order to fix the position of antenna  106  within radome  116  in a robust manner, a retainer  124  is preferably employed. Retainer  124  has an internal diameter  126  that is sized to slide over the outside diameter of cable  120  and press into region  128  within radome  116  in order to provide strain relief for cable  120  as well as the cable/solder joint. Additionally, adhesive can be used to provide further strain relief. O-ring  130  is also preferably used to help seal the radome-to-adapter connection from the environment. O-ring  130  is preferably an elastomeric radial O-ring, but can take any suitable form, and may be constructed from any other suitable material. 
     Radome  116  is formed of a relatively rigid polymer that is able to pass radio-frequency signals therethrough. Preferably, radome  116  is formed of a plastic that has a hardness of approximately 77 Shore D, has an insulation resistance that is at or less than 1 GOhm, and is capable of sustaining a 7 Joule impact after a 4 hour soak at −45 degrees Fahrenheit. One suitable example of a plastic that is well-suited for the construction of radome  116  is sold under the trade designation Valox 3706 PBT, available from SABIC Innovative Plastics of Pittsfield, Mass. However, other suitable thermoplastic resins may also be used. Thermoplastic is particularly advantageous because it is easily molded. Other suitable examples of materials that can be used to form radome  116  include Valox Resin V3900WX and Valox 357U, which are available from SABIC Innovative Plastics. 
     Radome  116  preferably includes an externally threaded region  132  that cooperates with an internally threaded region on housing  102  to provide a mechanical connection for antenna assembly  118 . Additionally, bottom surface  134  of radome  116  preferably includes a number of locking tabs  136  that cooperate with features on housing  102  in order to prevent inadvertent loosening of the radome-to-housing connection. While tabs  136  are shown in  FIG. 3 , other physical arrangements that can prevent the inadvertent rotation of radome  116  can also be employed. 
       FIG. 4  is a diagrammatic view of an industrial antenna assembly in accordance with another embodiment of the present invention. Assembly  200  includes many of the same components depicted in the embodiment described with respect to  FIG. 3 , and like components are numbered similarly. The primary difference between the embodiments illustrated in  FIGS. 3 and 4  is the form of the antenna itself. Specifically,  FIG. 3  represents a coaxial style antenna, while the embodiment illustrated in  FIG. 4  illustrates printed circuit board antenna  202 . In the embodiment illustrated in  FIG. 4 , radome  116  preferably includes a slot that is sized to accept printed circuit board  202 . Further, as illustrated in  FIG. 4 , the slot generally tapers such that the far end  204  of the slot has a width that is less than that near opening  206 . This tapered slot helps create an interference fit near the end  204  with end  208  of printed circuit board antenna  202 . This interference fit helps prevent relative motion of printed circuit board antenna  202  to radome  116  during vibration. 
     Embodiments of the present invention generally provide an antenna assembly that is suitable for the harsh environments in which field devices operate. The antenna radome is made from a polymer that is able to pass radio frequencies therethrough. Further, the radome forms part of the electronics enclosure and preferably complies with the various design criteria and specifications for field devices. Examples of desirable ratings with which the assembly may comply include, without limitation: an F1 rating by UL 746 C (weatherability); strict flammability requirements such as a V2 rating per UL 94 (UL 94, The Standard for Flammability of Plastic Materials for Parts in Devices and Appliances, which is now harmonized with IEC 60707, 60695-11-10 and 60695-11-20 and ISO 9772 and 9773); impact resistance; chemical resistance; thermal shock resistance; NEMA 4x; and IP 65. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.