This patent relates generally to bus based process communication systems used to perform process control operations in a process plant or other process, and more particularly to an integrated bus controller and bus based power supply for use in a process control communication system.
Process control systems are widely used in factories and/or process plants in which products are manufactured or processes are controlled (e.g., chemical manufacturing, power plant control, oil refinery, etc.) to produce a product of some sort. Process control systems are also used in the harvesting of natural resources such as, for example, oil and gas drilling and handling processes, etc. Virtually any manufacturing process, resource harvesting process, etc. can be automated through the application of one or more process control systems.
The manner in which process control systems are implemented has evolved over the years. Older generations of process control systems were typically implemented using dedicated, centralized hardware. However, modern process control systems are typically implemented using a highly distributed network of workstations, intelligent controllers, smart field devices, and the like, some or all of which may perform a portion of an overall process control strategy or scheme. In particular, most modern process control systems include smart field devices and other process control components that are communicatively coupled to each other and/or to one or more process controllers via one or more digital or combined digital and analog data busses. Of course, many of these modern process control systems may also include non-smart field devices such as, for example, 4-20 milliamp (MA) devices, 0-10 volts direct current (VDC) devices, etc., which are typically directly coupled to controllers, as opposed to using a shared digital data bus or the like.
More particularly, modern process control systems, such as distributed or scalable process control systems, typically include one or more process controllers communicatively coupled to each other, to at least one host or operator workstation and to one or more field devices via analog, digital or combined analog/digital buses. The field devices, which may be, for example, valves, valve positioners, switches and transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process such as opening or closing valves and measuring process parameters. The process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, and uses this information to implement one or more control routines to generate control signals which are sent over the buses to the field devices to control the operation of the process. Information from the field devices and the controller is typically made available to one or more applications executed by the operator workstation to enable an operator to perform any desired function with respect to the process, such as viewing the current state of the process, modifying the operation of the process, etc.
Some process control systems, such as the DeltaV™ system sold by Emerson Process Management, use function blocks or groups of function blocks, referred to as modules, located in the process controller or in different field devices or input/output (I/O) controller devices to perform control operations. In these cases, the process controller or other device is capable of including and executing one or more function blocks or modules, each of which receives inputs from and/or provides outputs to other function blocks (either within the same device or within different devices), and performs some process control operation, such as measuring or detecting a process parameter, controlling a device, or performing a control operation, such as implementing a proportional-derivative-integral (PID) control routine. The different function blocks and modules within a process control system are generally configured to communicate with each other (e.g., over a bus) to form one or more process control loops.
In many cases, process controllers are programmed to execute a different algorithm, sub-routine or control loop (which are all control routines) for each of a number of different loops defined for, or contained within a process, such as flow control loops, temperature control loops, pressure control loops, etc. Generally speaking, each such control loop includes one or more input blocks, such as an analog input (AI) function block, a control block, such as a proportional-integral-derivative (PID) or a fuzzy logic control function block, and an output block, such as an analog output (AO) function block. Control routines, and the function blocks that implement such routines, have been configured in accordance with a number of control techniques including, for example, PID control, fuzzy logic control, and model-based control techniques such as a Smith predictor or model predictive control (MPC).
This increased amount of controller functionality results in increased levels of data transfer that must occur between different devices within a process control system to support the controller functionality. Thus, one particularly important aspect of modern process control system design involves the manner in which field devices are communicatively coupled to each other, to the process controllers and to other systems or devices within a process control system or a process plant. In general, the various communication channels, links and paths that enable the field devices to function within the process control system are commonly collectively referred to as an input/output (I/O) communication network.
The communication network topology and physical connections or paths used to implement an I/O communication network can have a substantial impact on the robustness or the integrity of field device communications, particularly when the I/O communication network is subjected to environmental factors or conditions associated with the process control system. For example, many industrial control applications often subject field devices and their associated I/O communication networks to harsh physical environments (e.g., high, low or highly variable ambient temperatures, vibrations, corrosive gases or liquids, etc.), difficult electrical environments (e.g., high noise environments, poor power quality, and transient voltages), etc. As a result, numerous different types of I/O communication networks and communication protocols have been developed to be used to provide communications on those networks.
More particularly, to support the execution of the control routines in a distributed process control system, a typical industrial or process plant has a centralized control room that is communicatively connected with one or more of the distributed process controllers and process I/O subsystems which, in turn, are connected to the one or more field devices that perform control activities within the plant, such as measuring process variables or performing physical actions in the plant (e.g., opening or closing a valve). Traditionally, analog field devices have been connected to the controller by two-wire or four-wire current loops for both signal transmission and the supply of power. An analog field device that transmits a signal to the control room (e.g., a sensor or a transmitter) modulates the current running through the current loop, such that the current is proportional to the sensed process variable. On the other hand, analog field devices that perform an action under control of the control room are controlled by the magnitude of the current through the loop.
More recently however, process control communication systems have been developed that superimpose digital data on the current loop used to transmit the analog signals. For example, the Highway Addressable Remote Transducer (HART®) protocol uses the loop current magnitude to send and receive analog signals, but also superimposes a digital carrier signal on the current loop signal to enable two-way field communication with smart field instruments. Still further, other protocols have been developed that provide all digital communications on a bus associated with an I/O communication network. For example, the FOUNDATION® Fieldbus protocol, which is generally referred to as the Fieldbus protocol, provides all digital communications on a bus associated with an all-digital I/O communication network. The Fieldbus protocol actually includes two sub-protocols, including the H1 protocol which supports data transfers at a rate up to 31.25 kilobits per second while powering field devices coupled to the network, and the H2 protocol which supports data transfers at a rate up to 2.5 megabits per second but without providing power to the field devices via the bus. With these types of communication protocols, smart field devices, which are typically all digital in nature, support a number of maintenance modes and enhanced functions not provided by older control systems. However, these digital based communication protocols also typically require a bus controller device, sometimes referred to as a link controller device, to assure proper communications on the bus, to interface to external devices, such as process controllers and user interface devices that are not attached to the I/O communication network, etc.
As noted above, some of the I/O communication networks and the protocols associated with these networks have been developed to provide power to the field devices connected to the network bus in addition to communicating digital and/or analog signals on the network bus. Providing power on the network bus (referred to herein as bus power) enables the I/O communication network itself to power the field devices and other devices connected to the I/O communication network, thereby eliminating the need to provide a separate power source for each field device, controller, etc. connected to the I/O communication network. This feature is very useful in process control systems that are implemented outdoors, in harsh environments, or in remote or not easily accessible locations. However, the bus power feature is also very useful in enclosed plants and other more traditional locations, as it reduces the cabling and wiring needed to provide separate power signals to each of the field devices within a process control system.
Typically, I/O communication networks that provide bus power include a separate power module or power supply device that is connected to the bus to place the appropriate power signal onto the bus to be used to power the other devices connected to the bus. In some cases, such as in the Fieldbus H1 protocol, the power supply may be redundant in nature and may be isolated from the bus by an impedance network that prevents the power supply from interfering with the flow of digital signals on the network bus. Thus, in many instances, the configuration of an I/O communication network that provides bus power requires that separate power supply devices be connected to the bus, in addition to the bus controller and the field devices connected to the bus, to be able to provide power on the bus. These systems may also require additional devices disposed between the power supply devices and the bus to isolate the power supplies from the digital communications on the network bus. These requirements lead to additional hardware and wiring being needed for the I/O communication network, require additional space in the cabinets which house the hardware for the I/O communication network, and require additional configuration and wiring activities when setting up and configuring the I/O communication network. Moreover, the additional set up and configuration procedures, which generally entail setting up and wiring hardware together to create the I/O communication network, lead to more errors and potential problems in the implementation and running of a particular I/O communication network.
An integrated bus controller and power supply device includes a typical or standard bus controller and a bus power supply disposed in a common housing, the size and external configuration of which may match a standard bus controller device associated with a typical I/O communication network. The bus controller of the integrated device may store and implement one or more protocol or communication control routines to enforce or ensure proper communications occur on the bus between the one or more devices, e.g., field devices, connected to the I/O communication network, while the bus power supply of the integrated device generates and provides the appropriate power signal for the bus of the I/O communication network, the power signal being used to power the devices connected to the I/O communication network. The integrated bus controller and power supply device can be easily connected to the bus of the I/O communication network to provide both bus controller functionality and bus power supply functionality for the I/O communication network, without the need of configuring and attaching separate, dedicated bus controller and power supply devices to the bus and having to wire those devices together using multiple terminal blocks.
The integrated bus controller and power supply device can be configured in a number of different manners, each of which enables the device to be used in a simplex configuration, in which only one integrated bus controller and power supply device is connected to a particular I/O communication network, or in a redundant configuration, in which two integrated bus controller and power supply devices are connected to a particular I/O communication network to provide redundancy of both bus or protocol controller functionality and power supply functionality for the I/O communication network. Additionally, a simplified terminal block may be used to simultaneously connect one or multiple integrated bus controller and power supply devices to an I/O communication network in either a simplex or redundant configuration.
The use of the integrated bus controller and power supply device with its associated features reduces the hardware and wiring needed for an I/O communication network that includes bus power, reduces the configuration and set up activities needed to set up and configure a bus powered I/O communication network, and reduces the cabinetry space needed for or associated with a typical bus powered I/O communication network. Still further, the integrated bus controller and power supply device makes setting up redundant functionality in an I/O communication network much more easy, as it provides redundancy of both controller functionality and power supply functionality with two basic devices and a single terminal block, instead of needing at least four basic devices and multiple terminal blocks, as is typically needed in prior art systems.
Referring now to
The field devices 20-27 may be any types of devices, such as sensors, valves, transmitters, positioners, etc., while the I/O or bus controller devices 30 and 32 may be any types of I/O devices conforming to any desired communication or controller protocol. In the embodiment illustrated in
The controller 12 includes a processor 36 that implements or oversees one or more process control routines (stored in a memory 37), which may include control loops, stored therein or otherwise associated therewith and communicates with the devices 20-27, the host computers 16 and the data historian 14 to control a process in any desired manner. It should be noted that any control routines or modules described herein may have parts thereof implemented or executed by different controllers or other devices if so desired. Likewise, the control routines or modules described herein to be implemented within the process control system 10 may take any form, including software, firmware, hardware, etc. For the purpose of this disclosure, a process control module may be any part or portion of a process control system including, for example, a routine, a block or any element thereof, stored on any computer readable medium. Control routines, which may be modules or any part of a control procedure such as a subroutine, parts of a subroutine (such as lines of code), etc., may be implemented in any desired software format, such as using object oriented programming, using ladder logic, sequential function charts, function block diagrams, or using any other software programming language or design paradigm. Likewise, the control routines may be hard-coded into, for example, one or more EPROMs, EEPROMs, application specific integrated circuits (ASICs), or any other hardware or firmware elements. Still further, the control routines may be designed using any design tools, including graphical design tools or any other type of software/hardware/firmware programming or design tools. Thus, the process controller 12 may be configured to implement a control strategy or control routine in any desired manner.
In some embodiments, the process controller 12 implements a control strategy using what are commonly referred to as function blocks, wherein each function block is an object or other part (e.g., a subroutine) of an overall control routine and operates in conjunction with other function blocks (via communications called links) to implement process control loops within the process control system 10. Function blocks typically perform one of an input function, such as that associated with a transmitter, a sensor or other process parameter measurement device, a control function, such as that associated with a control routine that performs PID, fuzzy logic, etc. control, or an output function which controls the operation of some device, such as a valve, to perform some physical function within the process control system 10. Of course, hybrid and other types of function blocks exist. Function blocks may be stored in and executed by the controller 12, which is typically the case when these function blocks are used for, or are associated with standard 4-20 ma devices and some types of smart field devices such as HART and Fieldbus devices, or may be stored in and implemented by the field devices themselves, which can be the case with Fieldbus devices.
As illustrated by the exploded block 40 of
The power supply module 56 also includes a set of four output terminals on a terminal block 63, and one of the sets of output terminals is used to connect the controller 52A to an I/O communication network bus 64 having a segment protector 66 and field devices 68 connected thereto. The terminal block 63 or the power supplies 60A-60D may include a bus isolation device which operates to isolate the direct current (DC) power supplied by the power supplies 60A-60D from the digital signals on the bus 64. Moreover, as illustrated in
As will be understood, the power supply module 56, and in particular, one of the redundant sets of power supplies 60A-60D, provides power on the Fieldbus segment 64 associated with the segment protector 66. Additionally the power supply module 56 connects the H1 bus controller 52A to the segment bus 64 to enable powering of and control of the field devices 68 on the segment 64. In this case, the field devices 68 are illustrated as FOUNDATION® Fieldbus compliant field devices, although the network 64 could be associated with and use other types of devices and communication protocols including, for example, Actuator Sensor Interface (ASI), DeviceNet, etc. In this prior art configuration, however, the bus powered Fieldbus communication network 64 uses a power supply module 56 that is separate from the segment protector 66, the field devices 68 and the H1 bus controller cards 52A and 52B. Moreover, this configuration requires that the bus controllers 52A and 52B be connected through a first output terminal block 54 associated with the controller cards 52A and 52B to the input terminal block of the power supply module 56, and that these bus controllers 52A and 52B then be connected to one or more of the Fieldbus segments, such as the segment 64, through the output terminal block 63 on the power supply module 56. As a result, this configuration requires separate installation spaces (e.g., cabinetry space) for each of the different bus controller cards 52A and 52B, the power supply module 56 and the terminal blocks 54 and 63. Moreover, this set up requires complicated configuration procedures and configuration activities when installing and configuring the bus based communication system associated with, for example, the Fieldbus segment 64. Additionally, to connect the bus controllers 52A and 52B and the power supplies 60A, 60B, 60C or 60D in a redundant configuration to provide redundancy on the segment 64, the bus controller cards 52A and 52B must be wired individually for redundancy, and two of the sets of power supplies 60A-60D and the diagnostics module 62 must also be set up and wired individually to provide redundancy on the segment 64.
As illustrated in
In any event, as illustrated in
Moreover, an impedance device 98 is disposed within the terminal block 74 and is connected between the diode 92 and the output 94 of the terminal block 74 to provide isolation between the power supply 82 and the segment or bus 64. Generally speaking, the impedance device 98 isolates the higher frequency signals on the network 64 from the power supply 82, to prevent the power supply 82, which may be a voltage controlled power supply, from absorbing or canceling the digital signals on the network 64. The impedance device 98 may be, for example, an active component such as an active gyrator network, or a may be a passive component such as an inductor or a set of inductors. In one embodiment, the impedance device 98 may be a passive 5 mH impedance inductor. Such impedance devices are generally used in, for example, terminal blocks of power supply modules for Fieldbus H1 networks, to effectively prevent the power supply, which is typically a voltage driven power supply, from trying to compensate for and eliminate the high frequency voltage signals on the Fieldbus segment. In operation, the impedance device 98 acts as a filter (with respect to the power supply 82) and prevents the digital signals on the segment 64, which are changing at a high rate of speed, from reaching the power supply 82 to thereby prevent the power supply 82 from trying to drive the segment 64 to a constant DC voltage at all frequencies.
Additionally, as illustrated in
Thus, as will be understood, the single integrated bus controller and power supply device 72 of
As illustrated in
Similar to the simplex terminal block 74 of
The power supply 82 receives an external 24 DC volt power signal and uses this signal to produce bus voltage to be provided to the bus 64, and additionally produces a 5 volt DC signal or other power signal to be used to power certain of the circuitry within the device 72. The bus voltage produced by the power supply 82 is provided through a current sense module 110 which operates to sense current flow out of the power supply 82. The current sense module 110 produces and provides a current measurement signal to a diagnostic supervisor microcontroller 112, which operates to provide supervisory diagnostic control of the power supply 82. In particular, the microcontroller 112 may perform diagnostics within the device 72 to assure proper current flow to the bus 64, i.e., current flow within established or rated ranges, based on the output of the current sense module 110. The bus power signal is also provided through the current sense module 110 to an output control switch 114, which may be any desired type of switching circuitry under the control of the diagnostic supervisor microcontroller 112. The output of the output control circuit 114 is provided back to the diagnostics and supervisory microcontroller 112 as an output voltage measurement or voltage sense.
The diagnostics and supervisory microcontroller 112, which is powered by the 5 volt DC signal produced by the power supply 82, uses the current measurement provided by the current sense module 110 and the voltage measurement provided at the output of the switch 114 to detect current and voltage problems, such as current overload, low or high voltage, fluctuating voltage, etc., any of which may be caused by failure of or problems within the power supply 82. Based on these measurements, the diagnostic supervisory microcontroller 112 may provide an output to the output control switch 114 to switch off or prevent flow of current and voltage from the power supply 82 to the power output 90 of the card 72. Thus, the diagnostic and supervisory microcontroller 112 may operate to prevent power from flowing through the diode 92 to the output 90 of the card 72 based on detected conditions within the device 72.
Still further, the diagnostics and supervisor microcontroller 112 may provide an output to drive a light emitting diode (LED) 118, which may be visible through the housing 86 of the card 72, to indicate the operational status of the power supply system within the device 72. Thus, in one example, the diagnostics and supervisory microcontroller 112 may cause the LED 118 to be lit whenever the power supply 82 is operating properly to supply power to the output 90 of the card 72, and may turn the LED 118 off when a problem has occurred or when the power supply 82 is not working properly.
Still further, the diagnostic and supervisory microcontroller 112 may provide one or more signals indicating a failure of the power supply 82 or other diagnostic information to the controller 80 through an isolation circuit 120. The isolation circuit 120 may be, for example, an optical isolation circuit or any other desired type of isolation circuit. The main purpose of this isolation circuit 120 is to prevent cross-talk between the two different channels implemented by the device 72 so as to prevent power signals or digital signals from one channel from bleeding over into the other channel as noise. In any event, the microcontroller 112 may perform monitoring to diagnose the functionality of the power supply by monitoring output voltage, output current, hardware condition (e.g., reference voltage) and this diagnostic information may be communicated by means of a discrete optically isolated output to a discrete input of the controller 80 within the housing 86. The conditions that may trigger an output to the controller 80 may include the detection of under voltage, over voltage, over current, a hardware malfunction, etc. The fault status may also be indicated using the red LED 118 (one of which is provided per power supply channel) according to Namur NE44. The design of the power supply system also allows providing a discrete output using a serial interface on the device 72 (not shown). This feature can be implemented on the device 72 to allow a supervisory system to access the detailed diagnostic information (e.g. total output current) from the device 72 at any desired time.
The communication between the microcontroller 112 and the process controller 80, which occurs within the same device housing 86, allows the bus controller 80 to operate better based on the diagnostic information provided by the microcontroller 112. In particular, the bus controller 80 can receive diagnostic information directly from the power supply circuitry in the same housing of the card 72, thereby receiving this information more quickly and being able to operate on this information immediately in order to, for example, switch over to a backup bus controller or take any other action on the bus 64 as necessary based on the diagnostic information from the microcontroller 112. Furthermore, the controller 80 may inform a user of problems via, for example, the backplane bus or other network to which a user is connected to the controller 80. Still further, because the bus controller 80 is powered from an external source, instead of from the power supply 82 within the housing 86, the bus controller 80 can continue to operate even when the associated power supply 82 fails.
As illustrated in
Importantly, the use of a voltage mode MAU 124, as opposed to a current-mode MAU, which is currently used in many H1 controller cards, reduces the power absorbed within the device 72, enabling the device 72 to dissipate enough heat to be able to have all of the components illustrated in
As noted above, all of the circuitry associated with both the bus controller 80 and the power supply 82, including the diagnostic and supervisory microcontroller 112, the current sense 110, the output control switch 114, the redundancy coupling circuit 92 and the LED 118 may be disposed on or may be connected to one circuit board within the housing 86, while the controller 80 and, if desired, the voltage mode Fieldbus MAU 124 may be disposed on a second circuit board within the housing 86 of the device 72. Here, the proximity of the different devices connected together in the same housing, without the need for external device to device connections as needed in the system of
As will be understood, the bus controller 80 operates as in interface device between a first network bus in the form of the Fieldbus segment bus 64 and a second network bus in the form of the backplane bus that establishes a network connection to the process controller 12 (
While the integrated bus controller and power supply device 172 and the terminal block 174 of
It is considered advantageous to use a passive inductor, for example, a 5 mH inductor, to implement the bus impedance device 198 (of
In any event, as long as the integrated bus controller and power supply device 172 is running in a simplex configuration (as shown in
To correct for or to compensate for this impedance difference, the impedance of the devices 198A may be changeable or alterable (e.g., by a switch) to make impedance seen by the network 64 the same in the redundant configuration of
In a redundant configuration illustrated in
It has been found that the designs of the integrated bus controller and power supplies disclosed herein can be implemented to meet the typical design requirements for bus powered networks, such as Fieldbus H1 networks, while achieving a heat dissipation load within the tolerance of a typical controller only device, (e.g., a typical H1 bus controller only card). Moreover, these designs, for both simplex and redundant configurations, can be made without impacting signal quality, robustness and heat loading over known devices for these networks. In fact, the lower power dissipation of these devices enables increased packing density inside control room cabinets, and the compact design thus saves control room cabinet space. Still further, the use of passive power conditioning units (e.g., passive inductor networks for the devices 98, 198 and 298), ensures long service life and ensures the best Fieldbus signal for reliable data transmission. Still further, these designs can be implemented in a Fieldbus design based on and using existing H1 bus controller only card electrical designs, requiring no changes or modifications to the firmware of these devices.
Still further, in a Fieldbus implementation, the designs can be made without causing a significant change in the size of the device housing over that of a typical H1 bus controller only card, because the addition of the power supply can be made without increasing the power consumption in the combined device in a manner that requires a change in the size of the housing. Thus, for example, the integrated bus controller and power supply devices 72, 172 and 272 described herein may be implemented in a Fieldbus network in a housing of the size of approximately 4 inches, by 6 inches by 1.5 inches.
The power dissipation caused by a typical existing Fieldbus H1 bus controller only card is 3 watts. This power is fully dissipated inside the housing of the current or typical Fieldbus H1 bus controller only card. Moreover, the existing MAU is powered from the H1 bus and the average current in the MAU is 12 mA. This power is also fully dissipated inside the H1 bus controller only card housing and the total power dissipation caused by the MAUs is calculated as VFB*2*12 mA (e.g., 672 mW at 28 V). Here, the maximum allowed total power dissipation in the Fieldbus H1 bus controller card housing is 7.5 W at 70° C. ambient temperature. These heat dissipation design criteria can be meet with the new integrated bus controller and power supply devices described herein. Moreover, the existing implementation of the Fieldbus H1 bus controller only card provides one discrete input per segment, and these inputs can be used by the new integrated designs described herein to signal fault conditions from the power supply.
In addition to power dissipation and signal quality, circuit space is an important issue in designing the integrated bus controller and power supply devices described herein. It is assumed that a maximum power dissipation of 7.5 W in a typical Fieldbus H1 bus controller card housing leads to a temperature rise from 70° C. to 85° C. inside the card housing. Furthermore, it is assumed that the bus controller circuit has a mean power dissipation of about 3 W (12 V*250 mA). Each of the two integrated Fieldbus MAUs of the bus controller card draws a current of 12 mA from the Fieldbus network, resulting in additional power dissipation inside the card housing of 0.672 W at 28 V or 0.72 W at 30 V Fieldbus voltage for both Fieldbus MAUs. Therefore, the maximum power dissipation for each of the two integrated Fieldbus power supplies may be as high as 1.914 W, providing an output voltage of 28 V or 1.89 W providing an output voltage of 30 V. Thus, the common power conditioning impedance design suggested herein produces an output voltage of 28-30 V at a maximum output current of 450 mA, resulting in a minimum power of 12.6 W that is supplied to the Fieldbus segment. The maximum resulting power dissipation inside the integrated bus controller and power supply card housing will be about 7.18 W, in which 2*1.93 W is used for the Fieldbus power supplies including diagnostics, 2*0.16 W is used for the voltage mode MAUs, and 3 W is used for the bus controller circuit. This leaves headroom of about 320 mW to the maximum allowed power dissipation of 7.5 W inside the card housing. The maximum power dissipation inside the terminal block will be about 0.53 W (2*1.3 ohms*450 mA2). The output voltage of the power supply is safely limited to 32 V according to IEC60079-15 and IEC60079-11 standards. This limit may be achieved by applying safety factors on the voltage limiting components and by applying the applicable distances in the layout. This configuration also allows using the integrated controller and power supply card in combination with approved segment protectors for Ex ic or Ex nL rated applications.
The power supply efficiency of a standard power supply for a Fieldbus network is typically 90% at room temperature and 24 V input voltage. The worst-case efficiency is about 87.5% over the specified input voltage range between 19.2 and 35 volts and temperature range between −40° C. and 70° C. If the power conditioning inductors are built into integrated bus controller and power supply card housing, the power dissipation of the power conditioning inductors needs to be taken into account when calculating the card power dissipation. This is not the case if the power conditioning inductors are built into the terminal block.
For the case in which the power conditioning inductors are located in the housing, the series resistance of the power conditioning inductor is typically 1 Ohm (±30% over temperature), depending on the size of the conditioner coil. Table 1 below provides some examples for output voltage/current pairs, which are reasonable for the integrated bus controller and power supply. The stated losses are losses inside the integrated bus controller and power supply housing.
As can be seen from Table 1, it is possible to provide for sufficient heat dissipation in the housing when the power conditioning inductor (i.e., the impedance device 98) is provided in the housing of the card 72.
As noted above, there are two general concepts for generating appropriate Fieldbus impedance in a power supply to decouple the DC voltage from the AC bus signal including the use of an active gyrator circuit and the use of a passive 5 mH impedance inductor. The active gyrator circuit needs a typical voltage drop of about 2.5 volts to provide acceptable bus impedance, even if only one terminator 100 is active on the bus. Most likely, standard circuits need an even higher voltage drop especially at higher current demands. This fact results in a typical power loss of 1 W (2.5 V*400 mA) for the active gyrator circuit compared to a much smaller power dissipation in the passive 5 mH inductor of typically 0.16 W (1 ohm*400 mA2).
Moreover, a common bus impedance configuration saves one inductor (and inductors are a significant contribution to cost). The signal quality of both the common and parallel bus impedance is good, so that the availability of the power is high in both passive configurations. Using a common bus impedance inductor with redundant solder connections provides the same availability as using redundant inductors related to high impedance failures of the power conditioner. However, an inter-winding short circuit in one inductor will always cause an interruption of bus communication because the resulting impedance is zero if one inductor fails short circuit in a parallel bus impedance configuration. The probability of an inter-winding short circuit or the mechanical cracking of an inductor core is only half when using a common bus impedance configuration as opposed to using a parallel bus impedance configuration.
Installing the power conditioner inductor inside the terminal block additionally reduces the dissipated power inside the integrated bus controller and power supply card allowing higher output power or reduced temperature rise inside the housing, and providing a higher availability. As a result, it may be best to use a common inductor installed in the terminal block if space inside the terminal block is available to do so. If it is impossible for any reason to place an inductor inside a terminal block, it may be necessary to control the impedance in a way that leaves the Fieldbus impedance unaffected by the redundancy configuration. This configuration can be achieved by actively switching between the inductors in the redundant power supplies or by using the or-ing elements in the power supplies to control the impedance.
As noted above, the proposed design of the integrated bus controller and power supply card uses galvanically isolated power supplies which generate regulated output voltages of typically 30 V to power the Fieldbus segments and 5 V to power the internal circuitry and the voltage mode Fieldbus MAU. As also noted above, the monitoring of the Fieldbus power is performed by a secondary side microcontroller in the housing. The output voltage, output current and hardware status is continuously monitored and any error condition is signaled to the bus controller via a galvanically isolated discrete output (or an optional serial link to transfer more detailed diagnostic information). A red LED for each segment additionally indicates the status of each Fieldbus power supply to the user. Moreover, the Fieldbus signal is processed using a voltage mode MAU which, as noted above, reduces power dissipation inside the integrated bus controller and power supply card housing in comparison to a traditional current mode MAU. The voltage mode MAU also improves jitter tolerance. This configuration thus enables increasing the output power of the Fieldbus power supplies.
Moreover, if desired, an advanced diagnostics functions device, such as a Pepperl+Fuchs Advanced Diagnostic Module (ADM) for FOUNDATION® Fieldbus may be used as a stand-alone module that can be wired to a powered Fieldbus network. In this case, a set of terminals may be provided on the integrated bus controller and power supply device to enable connection of the ADM directly into the integrated card. This connection could be provided either as a discrete input that communicates the alarm status of the ADM or as a connection to the serial communication port of the integrated card.
Although the forgoing text sets forth a detailed description of numerous different embodiments of the invention, it should be understood that the scope of the invention is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment of the invention because describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the invention. Thus, for example, while the integrated bus controller and power supply device described herein have been described for particular use with a Fieldbus H1 network, they could be used with other bus based I/O communication networks that include or provide bus power including, for example, ASI and DeviceNet networks.
Thus, many modifications and variations may be made in the techniques and structures described and illustrated herein without departing from the spirit and scope of the present invention. Accordingly, it should be understood that the methods and apparatus described herein are illustrative only and are not limiting upon the scope of the invention.
This application is a regularly filed application from, and claims priority to and the benefit of the filing date of U.S. Provisional Patent Application No. 61/238,967, entitled “Integrated Bus Controller and Power Supply Device for Use in a Process Control System,” which was filed on Sep. 1, 2009, the entire disclosure of which is hereby expressly incorporated by reference herein.
Number | Name | Date | Kind |
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