Abstract:
A network diagnostic module coupleable to a distributed process control network that controls an industrial process via field devices coupled to the network includes a power block coupleable to the network and configured to power the network diagnostic module with energy received from the network, a communications block coupleable to the network and configured to bi-directionally communicate over the network, and a diagnostics block coupleable to the network and configured to make diagnostic measurements of network and protocol parameters of the network. The network diagnostic module is not itself a field device that detects or controls any process variable of the industrial process, enabling the network diagnostic module to be placed essentially anywhere along the network to permanently monitor the network.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a control system for real-time distributed control, and more specifically, to a diagnostic device or module for the control system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Automated industrial systems have field devices that monitor, control, and operate an industrial process. Each field device detects or control process variables of the industrial process. 
         [0003]    The field devices communicate with a control processor or head through a trunk that transmits power to the field devices and transmits data signals (which can include operating commands) between the control processor and the field devices. The field devices each attach to the trunk via a spur or branch connection. The field devices can be distributed throughout the industrial plant, and the data transmittal rates allow essentially real-time control of the process. 
         [0004]    Standardized network configurations such as Fieldbus or Profibus PA™ have been developed for distributed control systems that include standardized power and communication protocols. For example, the FOUNDATION™ Fieldbus H1 protocol is an all-digital, serial, two-way communication network that sends DC power and AC signals over a twisted two-wire trunk cable and enables the control processor to communicate with and control a number of field devices. 
         [0005]    Diagnostic devices have been developed to monitor and diagnose problems with the physical layer of the communication network. These devices are useful during startup to verify proper installation of a new network or the new installation of a field device on the network, and in the longer term, to provide early diagnosis of field device faults and monitor the health of the interconnecting network itself. 
         [0006]    Conventional diagnostic devices for a distributed control system such as a FOUNDATION™ Fieldbus H1 network or Profibus TA™ fall into two major categories: 
         [0007]    (a) handheld diagnostic tools intended for temporary attachment to the network, and 
         [0008]    (b) permanently mounted diagnostic tools mounted at the network power supply in the control cabinet. 
         [0009]    Handheld tools generally provide a display screen to display diagnostic data and may include a USB serial port that transmits the data to a personal computer. The diagnostic data is not transmitted back to the control processor over the communications network, and the handheld tool is not designed for permanent installation on the network. 
         [0010]    Permanently mounted diagnostic tools are usually located in the same cabinet as the network power supply and require their own power supply. Being adjacent the power supply places the tools far from the harsh operating environments where the field devices are located and where most faults and physical network problems occur, thereby limiting the effective sensitivity and effectiveness of these devices. Permanently mounted diagnostic tools may monitor a number of different networks and not monitor any one of the networks continuously, and may use a communications protocol different from the network protocol. 
         [0011]    Eryurek et al. U.S. Pat. No. 6,859,755 discloses incorporating a network diagnostic tool within a field device located on the network. The diagnostic tool includes a power module, a network communications interface, and diagnostic circuitry. The power module draws power from the network to power the diagnostic tool as well as the field device. The diagnostic circuitry measures a number of parameters related to the network, and the diagnostic data can be transmitted to the control processor over the network by the network communications interface. 
         [0012]    There are disadvantages in incorporating a network diagnostic tool in a field device. A field device having an incorporated network diagnostic tool is more expensive than a field device without such a tool. Furthermore, the network locations to which the network diagnostic tool can be attached are limited to only those network locations in which a field device can be attached, and so are limited to ends of spurs or branch connections. These locations may not be optimal for network diagnostics. 
         [0013]    Providing redundant diagnostic tools on the network can be expensive because more field devices with such tools must be provided, and the redundant diagnostic tools are separated along the network that may prevent locating the multiple diagnostic tools at optimum locations on the network. 
         [0014]    Thus there is a need for a diagnostic tool that can be installed permanently on the network away from the power supply and located independently of the field devices, with the ability to have multiple diagnostic tools to be coupled to the network at locations independent of one another and the field devices. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    The invention is a network diagnostic module coupleable to a distributed process control network that controls an industrial process via field devices coupled to the network. 
         [0016]    A network diagnostic module in accordance with the present invention includes a power block coupleable to the network and configured to power the network diagnostic module with energy received from the network, a communications block coupleable to the network and configured to bi-directionally communicate over the network, and a diagnostics block coupleable to the network and configured to measure and obtain electrical and protocol parameters of the network. 
         [0017]    An important feature of the network diagnostic module is that it is not a field device—the network diagnostic module is dedicated to diagnostics and is not configured to detect or control any process variable of the industrial process. 
         [0018]    Because the network diagnostic module is not a field device, the module can be installed on the network independently of the field devices. This enables the module to be coupled to the network almost anywhere along the network, including being spaced away from the field devices. Since the field devices are normally located at the end of spurs or branches of the network, this enables the network diagnostic module to be located at a point along the network better suited for obtaining network diagnostics or more convenient for user access. 
         [0019]    In a preferred embodiment, the network diagnostic module in accordance with the present invention is configured for use in a FOUNDATION™ Fieldbus H1 network, and is seen as another field device or node on the network by the control processor. The diagnostic module obtains its power from the communications network like a conventional networked-powered field device, communicates to the control processor over the network utilizing the Foundation Fieldbus H1 protocol, and can be polled by the control processor. 
         [0020]    The network diagnostic module of the present invention can be configured to communicate with the control processor only if a fault is detected on the network, or if a request for data is made of the network diagnostic module by the control processor. 
         [0021]    Multiple network diagnostic modules of the present invention can be installed as nodes on the network for backup purposes in the event an active network diagnostic module should fail or malfunction. 
         [0022]    In possible embodiments, the network diagnostic module of the present invention can be coupled to a device coupler that enables spurs or branching of the network. 
         [0023]    In further possible embodiments, the network diagnostic module of the present invention can be provided with two terminals for connection to the two twisted wires of the communication network. In alternative embodiments, the network diagnostic module of the present invention can be designed to interface with a communications bus, such as the PHOENIX CONTACT T-BUS™, that mediates communication with the Fieldbus network, and can be configured as “snap on” module for mounting on a DIN rail. 
         [0024]    Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing sheets illustrating one or more illustrative embodiments of the invention. 
     
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         [0025]      FIG. 1  is a block diagram of a network diagnostic module in accordance with the present invention; 
           [0026]      FIG. 2  illustrates a pair of the network diagnostic modules shown in  FIG. 1  forming part of a modular control system; and 
           [0027]      FIG. 3  illustrates a network diagnostic module in accordance with the present invention attached to a spur extending from a device coupler. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]      FIG. 1  illustrates a dedicated network diagnostic module in accordance with the present invention. The illustrated diagnostic module  10  is configured for use with a FOUNDATION™ Fieldbus H1 network and includes a trunk interface  12  for coupling the module  10  to the network. The illustrated trunk interface  12  includes two terminals  14   a,    14   b  for connection to the F+ and F− wires of the two-wire trunk cable of the fieldbus network and a third terminal  14   c  for attaching to a shield wire if present. The diagnostic module  10  is shown with the terminals  14   a,    14   b,    14   c  connected to the signal, ground, and shield wires of a network trunk  16 . 
         [0029]    The diagnostic tool  10  includes a power block  18 , a communications block  20 , a diagnostic block  22 , and a controller or processor  24 . 
         [0030]    The power block  18  draws electrical energy for the diagnostic module  10  from the network trunk  16  and provides power to the other blocks  20 ,  22 ,  24  and any additional internal components of the diagnostics module as indicated by electrical connections  26 ,  28 ,  30  interconnecting the power block  18  with the other blocks. The power block  18  does not provide power to any field device or other device on the network. 
         [0031]    The communications block  20  is configured to understand the FOUNDATION™ Fieldbus H1 network protocol and can read data transmitted along the network trunk  16  and can transmit data along the network trunk  16 . The communications block  20  is configured to enable the diagnostic module  10  to be seen as another field device or node on the network by the network&#39;s control processor. 
         [0032]    The diagnostics block  22  includes the necessary circuitry and analog-to-digital converters for measuring and digitizing a number of electrical and protocol parameters of the network trunk  16  when the diagnostics module  10  is connected to the trunk  16 . Examples of measurements include, but are not limited to: 
         [0033]    segment DC voltage; 
         [0034]    detection of shield shorted to F+ or F−; 
         [0035]    LAS address; 
         [0036]    number of active devices; 
         [0037]    lowest device signal amplitude, including value, address, and date/time; 
         [0038]    noise by frequency band, including average, peak, and date/time of peak in he LF, FF, and HF bands; 
         [0039]    device add/drop, including most recent add/drop address, device add/drop, and date/time of device add/drop; and 
         [0040]    individual device measurements (up to 24 devices for the illustrated embodiment) including device PD tag, device address, signal level, added/dropped, and retransmits. 
         [0041]    The processor  24  is coupled to both the communications block  20  and the diagnostics block  22  by respective connections  32 ,  34 . The processor  24  receives digitized data from the diagnostics block  22 , can send or receive data from the network  14  through the communications block  20 , and can respond to polling requests transmitted through the network  16  and directed to the diagnostics module  10 . The processor  24  can optionally be configured to communicate with the network control processor only if a fault is detected, or if a request for data is received from the control processor. 
         [0042]    The processor  24  may be configured to carry out some initial analysis of the diagnostic data received from the diagnostic block  22  and forward the results of such analysis to the control processor  44 . The processor  24  may also be configured to generate and transmit an alarm to the control processor of the trunk network  16  if the diagnostic block  22  detects a protocol parameter exceeding a predetermined limit or being outside of a predetermined range. 
         [0043]    The processor  24  preferably includes a microprocessor and related memory and operating software (not shown) to perform the functions of the processor  24  and to store operating parameters related to operation of the diagnostics module  10  itself. 
         [0044]    Software and firmware updates for the diagnostic module  10  can be supplied through the network  16 . If desired, the processor  24  can be connected to a USB port (not shown) or other I/O port built into the module  10  for updating software and firmware as needed. 
         [0045]    Because the diagnostic module  10  is not a field device (although the diagnostic module  10  does “cloak” itself to be seen by the control processor as a field device), that is, the diagnostic module  10  does not itself detect or control process variables, there is a great deal of versatility available in locating a diagnostic module  10  on the network. For example,  FIG. 2  illustrates two like diagnostic modules  10   a,    10   b  forming part of a FOUNDATION™ Fieldbus H1 network. 
         [0046]    The network includes a modular control system  42  for transmitting power and data between a control processor  44  that receives and transmits signals along a trunk  46  and field devices  48   a,    48   b,    48   c,  and  48   d.  Each field device  48   a - c  is located in a hazardous area  50 . Field device  48   d  is located in a safe area  52 . 
         [0047]    Although the trunk  46  is shown extending directly from the control processor  44  to the control system  42 , there may be other device couplers (not shown) or other control systems similar to the control system  42  located downstream from the control system  42  or located along the trunk  46  between the control processor  44  and the control system  42 . 
         [0048]    The control system  42  is connected between the trunk  46  and the field devices  48  and transmits power from the trunk  42  to the field devices  48  and transmits data signals between the trunk  46  and the field devices  48 . The field devices  48  may be process controllers, measurement devices, and the like as is well known in the art. 
         [0049]    The control system  42  includes a trunk module  54  that connects the system  42  to the trunk  46 . The trunk module  54  is connected to a local bus or backplane  55  having two lines, F+ and F− lines  56 ,  58  respectively, that conduct both DC power from the trunk module  46  and AC data signals to and from the trunk module  46  along the backplane  55 , and a shield line  60 . A commercially available segmented backplane that can be adapted for use as the backplane  55  is the T-BUS (trademark) modular rail bus manufactured by the applicant. 
         [0050]    Attached to the backplane  55  are a number of field modules  62   a,    62   b,  and  62   c.  The field modules  62  are removably mounted on an elongate support or rail  64  extending along the backplane that is preferably located in a control cabinet or other enclosure (not shown). Each field module  62  forms an intrinsically safe connection to a respective field device  48  located in the hazardous area  50 . Also attached to the backplane and removably mounted on the rail  66  is an additional field module  66  that forms a non-intrinsically safe connection to the field device  48   d  located in the safe zone  52 . The field modules  64  and other details of the control system  42  are disclosed in more detail in Helfrick, et al. U.S. Pat. No. 7,940,508 (the &#39;508 patent is assigned to and presently owned by the applicant and is incorporated by reference as if fully set forth herein). 
         [0051]    The diagnostic module  10   a  is mounted on the rail  66  adjacent the field module  64 . The terminals  14   a,    14   b,    14   c  of the diagnostic module  10   a  are configured to be connected to the backplane lines  56 ,  58 ,  60  respectively when the diagnostic module  10   a  is mounted on rail  66 . 
         [0052]    Thee diagnostic module  10   a  communicates with the control processor  44  through the backplane  55  and the trunk  46 , and monitors the electrical and protocol parameters related to the spur lines or field segments extending from the field modules  62 ,  66  and the field devices attached thereto. 
         [0053]    The diagnostic information about the network obtained from the diagnostics block of the diagnostic module  10   a  is transmitted to the control processor  44 , and the diagnostic module  10   a  can handle requests for information from the control processor  44 . The diagnostic information received from the diagnostic module  10   a  can be used by the control processor  44  itself, or may be transferred by the control processor  44  to a separate maintenance module (not shown) off the network for more sophisticated numerical analysis of the performance, current operating state, and predicted future operating states of the network and the various field devices. 
         [0054]    The diagnostic module  10   b  is mounted on the rail  66  adjacent the diagnostic module  10   a  and connected to the backplane lines  56 ,  58 ,  60  as described with respect to the diagnostic module  10   a.  The diagnostic module  10   b  is intended to be a redundant diagnostic module that can take over the duties of the diagnostic module  10   a  should the diagnostic module  10   a  itself fail or otherwise malfunction. 
         [0055]    Other network diagnostic modules in accordance with the present invention can be connected to other segments of the network shown in  FIG. 2 . For example, a network diagnostic module could be placed in the segment joining the field module  62   b  and the field device  48   b.  If the network diagnostic module is designed to operate with voltages and currents that render the network diagnostic module intrinsically safe, the module could be placed within the hazardous area  50 . 
         [0056]    For clarity the trunk module  54 , the field modules  62 ,  66 , and the diagnostic modules  10  are drawn spaced apart in  FIG. 2 , but it should be understood that the modules are preferably arranged immediately side-by-side of one another to conserve space within the cabinet. 
         [0057]    The illustrated field modules  62 ,  64  are “single spur” modules, that is, a field module  62 ,  64  connects to only a single field device. Alternatively, one or more of the field modules  62 ,  64  can each be a “multiple spur” device that can connect with two, three, four, or perhaps more field devices. It should be understood that the number of intrinsically safe field modules  62 , non-intrinsically safe field modules  64 , and diagnostic modules  38 ,  40  forming the control system  42  can differ from that shown in  FIG. 2 . 
         [0058]    The terminals  14  of the illustrated network diagnostic module  10  are configured to attach to a T-BUS (trademark) modular rail bus. In other possible embodiments, the terminals of a network diagnostic module of the present invention can be configured for connection to wires, twisted wires, or other types of network communication buses. 
         [0059]    The illustrated embodiment of the network diagnostic module is configured to operate with the FOUNDATION™ Fieldbus H1 protocol. Other process network protocols and network configurations are known, including without limitation other fieldbus or fieldbus-like protocols, PROFIBUS PA (trademark) protocol, ControlNet protocol, P-Net protocol, SwiftNet protocol, WorldFIP protocol, Interbus-S protocol, and FOUNDATION™ Fieldbus H2 protocol, and so other embodiments of the network diagnostic module can be configured for such other protocols or configurations. 
         [0060]    Network diagnostic modules in accordance with the present invention may also be configured to attach to or be part of a device coupler that enables spurs or branching of the network.  FIG. 3  illustrates a network diagnostic module  110  in accordance with the present invention operatively connected to a spur line  112  branching from a conventional device coupler  114 . 
         [0061]    The illustrated device coupler  114  is connected in series with a trunk  116  like the trunk  46  extending from a control processor  118 . One or more sets of field devices  120  are connected to respective spur lines  112   b,    112   c,    112   d,  each spur line  112  having two wires for transmitting power and data and a shield wire. The network diagnostic module  110  operates in the same manner as the network diagnostic module  10  but its terminals are configured the same as conventional field devices. 
         [0062]    The network field device  110  is configured to be at the end of a spur, that is, to be at the downstream end of a spur. In other embodiments the field device  110  can be configured to “pass through” power and data to upstream and downstream devices. In such embodiments the network field device could be located essentially anywhere in the network—including at the power supply end of the trunk or on any spur in parallel with any field device. 
         [0063]    While one or more embodiments of the invention have been described in detail, it is understood that this is capable of modification and that the invention is not limited to the precise details set forth but includes such changes and alterations as fall within the purview of the following claims.