Abstract:
A modular input/output (I/O) system for field wiring includes a plurality of base units into which electronics modules providing appropriate signal processing are plugged. A backplane in each base unit provides leads between the electronics module and associated terminals to which the field wiring is connected and also hosts a communications bus through which the electronics modules on serially connected base members communicate with a controller. Switching modules plugged into some of the base members selectively switch field signals applied to terminals for an associated electronics module to another electronics module for redundancy, or switch test signals into the associated electronics module in place of the field wiring signals. The test signals are generated by yet another of the electronics modules while still another electronics module generates control signals for the switching modules.

Description:
Commonly owned, concurrently filed U.S. patent application entitled: MODULAR INPUT/OUTPUT SYSTEM WITH FLEXIBLE INTERFACE WITH FIELD WIRING and identified by Ser. No. 08/846,943. 
     Commonly owned, concurrently filed U.S. patent application entitled: MODULAR I/O SYSTEM WITH TWO-WAY CONNECTORS BETWEEN UNITS AND A COMMON LOCK FOR MULTIPLE PLUG-IN MODULES and identified by Ser. No. 08/846,946. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to input/output apparatus for interfacing field wiring with an electronic control or monitoring system. More particularly, it relates to a modular system with redundancy and a built-in test capability. 
     2. Background Information 
     Electronic control systems and monitoring systems such as process controls systems require communication with the outside world. This includes receiving inputs such as commands and process conditions provided by various sensors. transducers and/or contacts, and generating output such as control signals, status and results. This interaction is provided by input/output (I/O) hardware or firmware. The signals pass through the I/O can be analog or digital. Typically, the I/O includes signal processing circuitry which, for example, can limit the range of analog signals, provide filtering, amplification or attenuation, surge protection, isolation, pulse shaping for digital signals, analog to digital or digital-to-analog conversion and other signal conditioning. 
     Process control and monitoring systems for high integrity applications often require capabilities such as redundancy and on-line testability to ensure high reliability and availability. I/O redundancy requires the capability to diagnose that a problem has occurred with an I/O signal and then to be able to switch the field connections to back-up I/O circuitry of the same type for signal processing. On-line testability functions require the capability to disconnect the field connections from an I/O circuit and substitute simulated test signals. Such redundancy and testing capabilities are commonly required in nuclear and chemical processing industries. These functions typically add significant cost to I/O sub-systems and require specialized hardware and software. 
     There is a need for improved I/O systems for field wiring, particularly more cost-effective arrangements for implementing redundancy and testability functions. 
     SUMMARY OF THE INVENTION 
     This need and others are satisfied by the invention which is directed to a modular input/output (I/O) system providing modular redundancy and test functions. More particularly the invention is directed to a modular I/O system which includes a plurality of electronics module mounted in bases, terminal means associated with each module, including terminals mounted on the bases to which the field wiring can be connected, and electrical conductors in the bases connecting the electronics module to the associated terminal means. The modular system further includes a plug-in personality or switching module associated with at least one of the electronics module. The switching module has switching means connecting with the electrical conductors in the base for effecting selectable connections between the at least one electronics module and the terminal means. One of the electronics module is a control module which generates a control signal controlling the switch means of the switching module for effecting the selectable connections for the at least one electronics module. 
     In accordance with one aspect of the invention, a second electronics module is provided which is redundant to the first electronics module. Transfer means connect the terminal means associated with the first electronics module with the terminal means of the second electronics module. The switching module associated with the first electronics module selectively switches the terminals associated with the first module to the first electronics module and alternatively to the second electronics module, so that the second electronics module can serve as a back-up for the first electronics module. The control electronics module provides the control signals for effecting switching of terminals associated with the first electronics module to those associated with the second electronics module. The second electronics module can provide redundancy for a number of first electronics modules, each of which has a switching module which selectively switches associated terminals to the second or back-up module so that the second module serves as a back-up for a number of electronics modules. Again, the control module provides the control signals effecting the switching which determines which one of the first modules will have its inputs switched to the back-up module. 
     In accordance with another aspect of the invention, one of the electronics modules is a test module which generates test signals. In this case, the terminal means associated with the first electronics module includes field terminals to which the field wiring is connected and test terminals to which the test signals are applied. The switching module associated with the first electronics module then selectively connects the first electronics module to the field terminals and alternatively to the test terminals. Again, another electronics module serves as a control module generating the control signal which controls the selective switching of the switching module. Also, the test module can generate test signals for a plurality of the electronics modules each of which has a switching module to alternatively connect the test terminals to the electronics module in place of the field terminals. Alternatively, the test signals can be supplied by separate test equipment. 
     In accordance with yet another aspect of the invention, the base members support communications buses which connect all of the electronics modules with a controller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
     FIG. 1 is exploded isometric view of a modular I/O unit in accordance with the invention. 
     FIG. 1a is a partially exploded isometric view showing the interconnection of modules with a backplane within the modular I/O unit. 
     FIG. 2 is a top view of the housing of the modular I/O unit of FIG. 1 with the electronics and personality modules removed. 
     FIG. 3 is a side view of the I/O modular unit of FIG. 1 shown assembled. 
     FIG. 4 is a sectional view through the terminals which form part of the modular I/O unit taken along the line 4--4 in FIG. 1. 
     FIG. 5 is a schematic circuit diagram illustrating redundancy provided as one aspect of the invention. 
     FIG. 6 is a schematic diagram illustrating implementation of a test function in accordance with another aspect of the invention. 
     FIG. 7 is a front elevation view of a process control system incorporating a controller and a number of modular I/O units incorporating the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1, 1a, 2 and 3, the modular input/output (I/O) system 1 of the invention includes as its basic components a base 3 in which a backplane 5 and a bank 7 of electrical terminals 9 are permanently mounted, and a pair of interchangeable electronics modules 11 and personality modules 13. Base 3 includes a bottom member 15 and top member 17 between which the backplane 5 is clamped. The backplane 5 has a pattern 19 of electrical conductors, to be described in more detail below, which selectively connect terminals 9 to the electronics modules 11 and personality module 13. In the system shown, the housing 3 supports dual arrangements of terminals 9, electronics modules 11 and personality modules 13. It will be understood that other arrangements could include a housing or base mounting a single set of a bank of terminals, an electronics module and a personality module, or three or more sets of these components. The base 3 is secured to a mounting rail 12 such as a standard DIN rail by a clamp 14, as seen in FIG. 3. This clamp is actuated by a screw 16 accessible through the top member 17 of the base, as shown in FIG. 2. 
     The terminals 9 of each bank of terminals 7, are conveniently arranged in three tiers which can be labeled A, B and C for a three-phase electrical system. As shown in the cross-section of FIG. 4, each of the terminals includes a contact 21 which extends downward and terminates in a pointed end which engages holes ss (see FIGS. 1 and 1a) in the backplane 5 where it is connected to the circuitry 19. Terminal screws 23 engaged in clamps 25 secure the contacts 21 to field wiring 27. 
     The electronics module 11 includes a housing 29 in which are mounted a pair of circuit cards 31 and 33. The circuit card 31 contains the I/O signal processing circuitry 35. Depending upon the particular application, signal processing circuitry 35 performs one or more functions which can include filtering, amplification or attenuation, surge protection, isolation, range limiting or scaling, and pulse shaping or other signal conditioning. The second card 33 in the electronics module housing 29 is the communications card through which signals are transmitted between the signal conditioning circuitry 35 and the processing system for which the I/O is provided. Mounted on the signal processing card 31 and the communications card 33 adjacent an opening 39 in the bottom in the housing 29 are electrical connectors 41 and 43, respectively. 
     The personality module 13 is a switching module. It includes a housing 45 containing a circuit card 47 having switching circuitry 49, which as will be seen. can have a plurality of configurations. An electrical connector 51 is provided on the bottom edge of the circuit card 47 adjacent an opening 53 in the housing 45. 
     The top member 17 of the base 3 has an opening 55 which forms side-by-side sockets 57 and 59 for plug in of the electronics module 11 and personality or switching module 13, respectively. Mounted on the backplane 5 in alignment with the socket 57 are electrical connectors 61 and 63 which mate with the connectors 41 and 43 in the electronics module. The connector 61 electrically connects the signal processing card 31 with the I/O circuits 19 on the backplane while the connector 63 connects the communications circuitry on the communications card 33 with communication busses indicated at 65 on the backplane. Connectors 67 on each end of the backplane connect the communication busses 65 with adjacent I/O units 1 or a controller in a manner to be discussed. The connectors 67 and communications bus 65 provide power to the electronics module 11 in addition to routing signals to and from the modules. 
     In a similar manner, the connector 51 on the circuit card 47 of the personality or switching module 13 mates with a connector 69 on the backplane 5 to connect to the switching circuitry 49 with the circuits 19 as the personality module 13 is plugged into the socket 59. Preferably, octagonal keys on the backplane 5 assure that only an electronics module of a given type having a matching key (not shown) can be plugged into the socket 57. 
     FIG. 5 is a schematic diagram illustrating application of the invention to provide redundancy for the electronics modules 11. As shown in the example, the circuitry 35 1  of electronics module 11 1  has two channels A and B, each with an analog to digital (A/D) converter 71 1a  and 71 1b  connected through back plane circuitry 19 1  and switching module 13 1  to associated terminals 9 1a  and 9 1b  connected to the field wiring 27. The A/D converters 71 convert the analog field signals on the field wiring 27 into digital signals for input to signal conditioning circuits 73 1  in the module 11 1 . The conditioned digital signals are transmitted to a controller 75 over communications bus 65. 
     The personality module 13 1  includes switch 79 1 . The switch 79 1  may be a relay as shown or solid state switching. The relay 79 has contacts 81 1a  and 81 1b  which in an unactuated position (not as shown in FIG. 5) connect the terminals 9 1a  and 9 1b  and the field wiring 27 to the associated electronics module 11 1 . When the relay 79 1  is actuated, as shown FIG. 5, the contacts 81 1a  and 81 1b  connect the field wiring to leads 83 1a  and 83 1b  in the module 13 1 . The leads 83 1a  and 83 2b  are connected through terminals 85 to transfer leads 87, which are connected through similar terminals 85 to leads 83 2a  and 83 2b  in an adjacent personality module 13 2 . These leads 83 2a  and 83 2b  extend through the module 13 2  and are connected through terminals 85 and additional transfer leads 87 to a third personality module 13 3 . The personality module 13 2 , also includes a switch 79 2  which may be a solid state switch or, as shown, a relay. Contacts 81 2a  and 81 2b  of the relay 79 2  are shown in their unactuated position in which they connect field wiring 27 through the associated terminals 9 2a  and 92 2b  to A/D converters 71 2a  and 71 2b  in the electronics module 11 2 . The third personality module 13 3  which is connected to the third electronics module 11 3  does not contain any switching but connects the transfer leads 87 through leads 83 3a  and 83 3b  to the backplane wiring 19 connected to the A/D converters 71 3a  and 71 3b  of the electronics module 11 3 . 
     A fourth electronics module 11 4  serves as a control module which generates control signals for actuating the switches 79 1  and 79 2  in the switching or personality modules 13 1  and 13 2 , respectively. The electronics module 11 4  has digital output circuits DO 89 1  and 89 2  generating contact output signals which are passed by the circuity 19 4  on the backplane to the associated terminals 9 4 . Control leads 91 1  and 91 2  are connected between these terminals 9 4  and the switches 79 1  and 79 2 . The personality module 13 4  does not provide any switching. With neither of the switches 79 1  or 79 2  actuated, the electronics modules 11 1  and 11 2  are connected through the associated field terminals 9 1  and 9 2  to their assigned field wiring 27. Under these conditions, the redundant electronics module 11 3  is in a stand-by status. If the controller 75 detects a malfunction in one of the electronics modules 11 1  or 11 2  or if it is desired to take one of these electronics modules out of service such as for maintenance or testing, a signal is transmitted over the communications bus 65 to the control electronics module 11 4  to activate the appropriate digital output 89 1  or 89 2 . For example, if the electronics module 11 1  has failed in either channel, the DO 89 1  is actuated to generate a control signal which energizes the switch 79 1 . This actuates the contacts 81 1a  81 1b  to connect the terminals 9 1a  and 91 1b  and therefore the connected field wiring 27, to the leads 83 1a  and 831 b , which are passed through the terminals 85 and transfer leads 87 and by leads 82 2a  and 83 2b  through the switching module 13 2  to the switching module 13 3  where the signals are then connected to the redundant electronics module 11 3  by the leads 83 3a  and 83 3b . Alternatively, if controller 75 detects that the electronics module 11 2  has failed, the DO 892 b  in the control module 11 4  is actuated to generate a control signal which actuates the switch 79 2  to connect the terminals 9 2a  and 9 2b  to the spare electronics module 11 3  instead of the electronics module 11 2 . Only one of the switches 79 1  and 79 2  is energized at any one time. 
     If spare terminals 9 are available, the transfer leads 87 can be connected to the leads 83 through them, and the additional terminals 85 are not required. Furthermore, the redundant electronics modules such as the module 11 3  can serve as a back-up for just one module 11 1  for two electronics modules 11 1  and 11 2  as shown, or for any number of electronics modules 11. 
     FIG. 6 is a circuit diagram illustrating an application of the invention for implementing the test function. The electronics module 11 5  serves as a test module which generates test signals under control from the controller 75 through communications bus 65. The digital test signals are received by receiving circuit 92 and are converted to analog signals in the digital to analog (D/A) converters 93 1  and 93 2  for the two channels of the module 11 5 . The personality module 13 5  performs no switching functions so that the backplane circuits 19 5  deliver the test signals to the terminals 9 5 . Transfer leads 87 provide the test signals to terminals 85 on the personality modules 13 6  and 13 7 . The terminals 85 are connected to leads 83 6  and 83 7  in the switching modules 13 6  and 13 7 , respectively. Switches 79 6  and 79 7 , which again may be solid state switches or relays as shown, switch either the test signals on the leads 83 6  and 86 7  or field signals from the field wiring 27 provided through the terminals 9 6  and 9 7  and the backplane circuits 19 6  and 19 7 . Thus, the contacts 81 6a  and 81 6b  apply the test signals to the A/D converters 71 6a  and 71 6b  of the electronics module 11 6  when the switch 79 6  is actuated. The test signals are processed by the signal processing circuits 73 6  and returned to the controller 75 for analysis over the communications bus 65. Similarly, the contacts 81 7a  and 81 7b  apply the test signals to the appropriate channels of the electronics module 11 7  when the corresponding switch 79 7  is actuated. 
     The electronics module 11 4  again serves as a control module which generates control signals through the DOs 89 1  and 89 2  when commanded by the controller 75. As in the case of the redundancy function, if sufficient terminals 9 6  and 9 7  are available, the transfer leads 87 can be connected to the switching modules 13 6  and 13 7  through these terminals and leads in the backplane 19 6  and 19 7 , instead of through the separate connectors 85. Similarly, in the case of the redundancy function and the testing function, if sufficient terminals 9 are available, the control signals for the switches 79 can also be applied through these additional terminals and backplane wiring 19. In such a case, the switching module makes all the necessary connections through insertion in the socket in the base member. 
     Alternatively, separate test equipment can be used to supply the test signals which are selectively switched by the switches 79, or the switches 79 can be used to disconnect the field signals while test signals are injected through test points (not shown). 
     As shown in FIG. 7, the modular I/O units 1 may be arranged in branches 95 1  and 95 2  which are connected to the controller such as the single/redundant controller 75&#39;. The communications buses 65 and adjacent modular I/O units 1 are interconnected by the connectors 67 to connect each of modules to the controller 75&#39;. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended claims and any and all equivalents thereof.