Abstract:
A process sensor assembly comprises a hollow protective housing, a temperature sensor, a process transmitter, and a transient protector. The temperature sensor includes a probe extending out of the hollow protective housing to a sensing location, and a top plate movably secured to the hollow protective housing so as to allow travel within the hollow protective housing with vibrations of the probe. The process transmitter is configured to process and transmit sensor signals from the temperature sensor, and is retained on the top plate to move with the temperature sensor within the hollow protective housing. The transient protector is configured to condition power for to the process transmitter, and is anchored to the process transmitter so as to move with the process transmitter within the hollow protective housing.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to industrial process field devices, and more particularly to DIN-type temperature transmitters. 
         [0002]    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 include transmitters that 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. 
         [0003]    Process transmitters are used to monitor a variety of parameters of industrial processes, including pressure, temperature, viscosity, and flow rate. Each field device typically comprises a sealed enclosure containing a transmitter, one or more sensors, and connecting electronics. Process transmitters comprise wired or wireless transceivers, as well as electronics for processing sensor and control signals, diagnostic reports, and for receiving power. Large scale industrial manufacturing facilities typically employ many field devices distributed across a wide area. These field devices usually communicate with a common control or monitoring device, allowing industrial processes to be centrally monitored and controlled. 
         [0004]    Sensor assemblies for sensing process fluid temperatures and changes in temperature commonly include at least one temperature sensor such as a thermocouple, resistive temperature detector, or thermistor housed in a thermowell extending into the fluid flow. The thermowell protects the temperature sensor from physical damage caused by direct contact with the process fluid (e.g. impacts, corrosion, etc.), while efficiently conducting heat between the fluid and the temperature sensor. DIN-type temperature sensors, in particular, comprise long, slender probes that extend from a flat mounting plate to a sensor tip containing a sensor element. The elongated probe situates the sensor tip at the bottom of the thermowell, surrounded by the process flow. Impingement of the thermowell on process flow creates turbulence in the process fluid via vortex shedding. This turbulence, in turn, contributes to vibration of both the thermowell and the sensor probe inside it. To avoid sensor damage caused by this vibration, many sensor assemblies mount the sensor flexibly with respect to process piping (e.g. via a spring loaded assembly), allowing the probe to move together with the vibrating thermowell. Flying leads connect the sensor probe to signal processing electronics within the process transmitter. 
         [0005]    Field devices can be powered by direct electrical connection to power utilities such as 120V AC utilities, by control system DC power supplies, by energy storage devices such as long-life chemical batteries or supercapacitors, or by local power sources such as solar panels or vibrational energy harvesters. Field devices powered by local power sources or utility grids may experience transient power surges that can damage or degrade sensitive process transmitter electronics. 
       SUMMARY 
       [0006]    The present invention is directed toward a process sensor assembly comprising a hollow protective housing, a temperature sensor, a process transmitter, and a transient protector. The temperature sensor includes a probe extending out of the hollow protective housing to a sensing location, and a top plate movably secured to the hollow protective housing so as to allow travel within the hollow protective housing. The process transmitter is configured to process and transmit sensor signals from the temperature sensor, and is retained on the top plate to move with the temperature sensor within the hollow protective housing. The transient protector is configured to condition power to the process transmitter, and is anchored to the process transmitter so as to move with the process transmitter within the hollow protective housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an exploded view of a process sensor assembly including a process transmitter and a transient protector. 
           [0008]      FIGS. 2   a  and  2   b  are perspective views of the process transmitter and transient protector of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    The present invention is a transient protector configured to attach to and move together with a DIN (German Institute for Standardization)-type temperature transmitter secured to a DIN temperature sensor. 
         [0010]      FIG. 1  depicts process sensor assembly  10 , comprising process connection  12  on process piping  14 , sensor  16  (with top plate  18 , probe  20 , sensor tip  22 , and flying leads  24 ), process transmitter  26 , fasteners  28 , springs  30 , connection head  32 , extension  34 , thermowell  36 , threading  38 ,  40 , and  42 , transient protector  44  (with transient protector terminals  46 ), mating connection  48 , and connection head cover  50 . 
         [0011]    Sensor assembly  10  is a system for monitoring temperature or change in temperature of a process fluid near process connection  12  of process piping  14 . Process piping  14  is a duct or tube carrying fluid flow for an industrial process. Process piping  14  may, for instance, be configured to carry a viscous fluid such as an oil slurry or a viscous manufacturing material. Process connection  12  is an attachment point that facilitates the connection of a flange mounted instrument to measure at least one characteristic of process flow F; in this case, temperature. Process connection  12  is depicted as a threaded nipple connection, but may in other embodiments be a flange connection, or any other appropriate sealing connection type. Process piping may additionally feature a plurality of flange connections for mounting other transducers, such as flow rate, pressure or pH sensors. In the illustrated embodiment, process connection  12  provides an attachment point for thermowell  36  and probe  20 , and an aperture in process piping  14  through which thermowell  36  and probe  20  can extend to situate sensor tip  22  inside process fluid flow. Process fluids may, for instance, include chemicals or particulates that can be damaging or otherwise detrimental to the operation of sensor  16 . For applications where direct exposure to process fluid flow is unlikely to erode sensor  16 , thermowell  36  may in some instances be replaced by other fluid seals sufficient to protect electronics of process transmitter  26  and sensor  16  from harm. 
         [0012]    Sensor  16  is a DIN-type temperature sensor with top plate  18 , probe  20 , sensor tip  22 , and flying leads  24 . Top plate  18  is an anchor plate with attachment holes for movably securing sensor  16  to connection head  32 . When process sensor assembly  10  is fully assembled, top plate  18  abuts the bottom of process transmitter  26 . Probe  20  is a narrow, elongated tube extending from top plate  18  to sensor tip  22 . Probe  20  passes through extension  34  and into thermowell  36  to situate sensor tip  22  at the bottom of thermowell  36 . Sensor tip  22  is a temperature sensitive transducer portion of sensor  16  containing a sensor such as a resistive temperature detector (RTD) or thermocouple used to sense process fluid temperature or change in temperature. When process sensor assembly  10  is fully assembled, sensor tip  22  is situated at the bottom extent of thermowell  36 , within process piping  14  and adjacent process fluid flow through thermowell  36 . Flying leads  24  are wired connections extending from probe  20  at top plate  18 . Flying leads  24  connect sensor  16  to process transmitter  26 , as described in further detail below with respect to  FIGS. 2   a  and  2   b.    
         [0013]    Process transmitter  26  is a signal processing and/or transmission device that receives and processes signals from sensor  16  to produce at least one measurement of temperature or change in temperature in the process flow. Process transmitter  26  may, for instance, be a logic-capable device configured to extract a digital process measurement from voltage or current signals received from sensor  16 . Process transmitter  26  may further include diagnostic or failure reporting components, and may include persistent memory to store measurement, control, and diagnostic data relating to sensor performance and/or process parameters. Process transmitter  26  need not be a temperature-specific component, but may instead be capable of interfacing with a variety of different sensor types. In the illustrated embodiment, process transmitter  26  transmits temperature measurements to a remote device such as a control or monitoring system or a measurement data backup server. Process transmitter  26  may be a wireless or wired transmitter. In some embodiments, process transmitter  26  may include or be attached to a local operator interface including, for example, a screen and/or keypad. 
         [0014]    Fasteners  28  and springs  30  flexibly secure sensor  16  and process transmitter  26  to connection head  32 . Fasteners  28  can, for example, be screws, bolts, or pins that pass vertically (according to the orientation of  FIGS. 1 ,  2   a , and  2   b ) through apertures in process transmitter  26  and sensor  16 , and anchor in connection head  32 . Fasteners  28  may, in some embodiments, screw into threading within connection head  32 . Springs  30  are disposed between heads of fasteners  28  and process transmitter  26 . Springs  30  flexibly retain process transmitter  26  and sensor  16  such that sensor tip  22  is situated at the bottom extent of thermowell  36 , while taking in tolerances to allow sensor  16  and process transmitter  26  to maintain direct contact with thermowell  26 . This freedom of movement prevents impact damage to sensor  22  during environmental disturbances such as vibration. Process transmitter  26  and sensor  16  move together, so that flying leads  24  are not disconnected or disrupted by movement of sensor  16 . 
         [0015]    Connection head  32  is a protective casing or housing disposed about process transmitter  26  and transient protector  44  to protect sensitive electronics therein. In the depicted embodiment, connection head  32  is mounted on extension  34  via threading  38 . As depicted, extension  34  is a rigid coupling that supports connection head  32  at a distance from process piping  14 , and carries sensor probe  20 . Extension  34  may, for instance, distance process transmitter  26  from high-temperature processes within process piping  14 , thereby protecting sensitive electronics from exposure to excessive temperatures. Although connection head  32  is shown mounted to extension  34 , some embodiments of process system  10  may instead mount connection head  32  directly to thermowell  36 , eschewing extension  34 . Thermowell  36  is a protective body that surrounds probe  20  and sensor tip  22  within process piping  14 . Thermowell  36  may, for instance, be a hollow tapered sheath affixed to and disposed through process connection  12  via threading  42 . In alternative embodiments, thermowell  36  may interface with process connection  12  via a flat face seal, or other fluid seal. Thermowell  36  may, in various embodiments, be formed of brass, steel, copper, or any other material with high thermal conductance, so as to efficiently conduct heat from process fluid to sensor tip  22 . 
         [0016]    As described in further detail below with respect to  FIGS. 2   a  and  2   b , process transmitter  26  receives power serially through transient protector  44  from a power source. Transient protector  44  receives power from transient protector power terminals  46 , and conditions this power for use by process transmitter  26 . Transient protector power terminals  46  may, for instance, receive power via leads connecting to an energy harvesting device, control system power supply, or utility grid (not shown). Transient protector  44  attaches to process transmitter  26  via mating connection  48 , such that transient protector  44  travels together with process transmitter  26  and sensor  16  with vibration of thermowell  36 . Mating connection  48  may, for instance, be a dovetail slot and tab connection. Once transient protector  44  and process transmitter  26  are both installed within connection head  32 , connection head cover  50  attaches to connection head  32  to seal process transmitter  26 , transient protector  44 , and sensor  16  from the environment. 
         [0017]      FIGS. 2   a  and  2   b  are two perspective views of a single embodiment of process transmitter  26  and transient protector  44 .  FIG. 2   a  shows transient protector  44  detached from process transmitter  26 , while  FIG. 2   b  shows transient protector  44  fastened to process transmitter  26 .  FIGS. 2   a  and  2   b  depict process transmitter  26 , fasteners  28 , springs  30 , transient protector  44 , transient protector power terminals  46 , power connection tabs  52 , process transmitter power terminals  54 , power terminal screws  56 , mating connection  58  on flat surface  60 , flying lead hole  62 , sensor terminals  64 , flexible ground  66 , and mating connection  68 . 
         [0018]    As described above with respect to  FIG. 1 , process transmitter  26  is a signal processing and/or transmission device that receives and processes temperature signals from sensor  16 . Process transmitter  26  is flexibly retained to connection head  32  by springs  30  and fasteners  28 , such that process transmitter  26  abuts top plate  18 , and rides up and down fasteners  28  together with sensor  16 . The flexible coupling provided by fasteners  28  and springs  30  between process transmitter  26  and connection head  32  takes in tolerances to ensure that sensor tip  22  remains in contact with the bottom of thermowell  36 , even during vibrations or shocks to thermowell  36 . Process transmitter  26  receives sensor inputs from sensor  16  via flying leads  24 , which pass up through flying lead hole  62 , and attach to sensor terminals  64 . Sensor terminals  64  are depicted as screw terminals, but may more generally be any type of sensor signal connection. Sensor terminals  64  may, in some embodiments, provide a connection interface for multiple sensors  16 , and/or for output lines transmitting sensor readouts to an external device such as a control or monitoring system. Alternatively or additionally, process transmitter  26  may be a wireless device capable of communicating with a control or monitoring system, and/or with other process transmitters, via wireless communication. 
         [0019]    Process transmitter  26  can be powered via transient protector  44  through power conduction tabs  52 , which interface with process transmitter power terminals  54  in the illustrated embodiment. As shown, process transmitter power terminals  54  are conductive screw terminals with power terminal screws  56  configured to accept power leads. In alternative embodiments, process transmitter power terminals  54  may instead be plug terminals or other non-screw terminals. Power conduction tabs  52  are conductive interfaces that meet process transmitter power terminal  54  and power terminal screws  56  to provide an electrical path from transient protector  44  to process transmitter  26 . Transient protector  44  is a power conditioning module that acts as a surge protector, shielding process transmitter  26  from potentially harmful voltage spikes. Transient protector  44  may, for instance, include a plurality of diodes, high voltage fuses, and/or metal oxide varistors (MOVs), and is configured with a let-through voltage suitable for use by process transmitter  26 . In the depicted embodiment, transient protector  44  receives power from an external source via transient protector power terminals  46  (e.g. through cables or wiring running through conduit passages in connection head  32  or connection head cover  50 ). Although transient protector power terminals  46  are depicted as conductive screw terminals, alternative embodiments of transient protector  44  may for instance use plug or clip terminals. Transient protector  44  is rated to a voltage level sufficient to handle expected surge values, which may vary depending on the power source. A utility grid power source, for instance, may necessitate a higher-rated transient protector  44  than a low power energy harvester, or a local generator. In some embodiments, transient protector  44  may contain further power conditioning electronics such as a voltage rectifier or inverter. 
         [0020]    Transient protector  44  attaches to mating connection  58  of process transmitter  26 . In the depicted embodiment, mating connection  58  is a dovetail slot disposed across half or less of flat surface  60 , which is a flat face of process transmitter  26  disposed to receive transient protector  44 . Mating connection  58  interfaces with mating connection  68 , depicted as a complementary dovetail tab. As depicted, connection  58  extends across less than half of flat surface  60  so as to prevent transient protector  44  from binding to process transmitter  26  and preventing transient protector  44  from being removed from process transmitter  26 . In alternative embodiments of process transmitter  26  and transient protector  44 , mating connections  58  and  68  may comprise one or more other configurations of slots, tabs, or catches suited to align power conduction tabs  52  with process transmitter power terminals  54 , and secure transient protector  44  to process transmitter  26 . In the depicted embodiment, flat surface  60  truncates the otherwise cylindrical shape of process transmitter, allowing both transient protector  44  and process transmitter  26  to fit within the limited confines of connection head  32  without striking or rubbing against connection head  32  when transient protector  44  and process transmitter  26  move relative to connection head  32  with sensor  16 . More generally, transient protector  44  and process transmitter  26  are contoured to fit within connection head  32  when process sensor assembly  10  is fully assembled. 
         [0021]    In the depicted embodiment, transient protector  44  slideably interfaces with process transmitter  26 . Transient protector  44  is installed by sliding transient protector from the position shown in  FIG. 2   a  to the position shown in  FIG. 2   b . Mating connections  58  and  68  serve both to align and to secure transient protector  44  relative to process transmitter  26 , such that power conduction tabs  52  slide into contact with process transmitter power terminals  54 . Power terminal screws  56  both electrically connect power conduction tabs  52  to process transmitter power terminal  54 , and lock transient protector  44  into its installation position relative to process transmitter  26 . 
         [0022]    In the depicted embodiment, transient protector  44  includes flexible ground  66 , a wired ground connection that terminates at connection head  32 . In such embodiments, connection head  32  is a conductive body that grounds transient protector  44  to process piping  14 . In alternative embodiments, flexible ground  66  may take other forms suited to ground transient protector  44  to connection head  32  without restricting the movement of transient protector  44 , process transmitter  26 , and sensor  16  relative to connection head  32 . In one such alternative flexible ground configuration, transient protector  44  may include a wired connection or a conductive tab or spring connection that contacts connection head  32  via fasteners  28 . According to this embodiment, fasteners  28  are formed of a conductive material that provides a ground path between transient protector  44  and connection head  32 . 
         [0023]    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.