Power Management for Industrial Field Devices

Abstract

A field device (14) for use in an industrial process includes a transducer (20) configured to connect to the industrial process and control or monitor a process variable of the industrial process. A main communication circuit (38) communicates information with a remote location related to the process variable. A wireless communication module (32) includes an energy storage device (152) and power monitoring electronics connected to the energy storage device, the power monitoring electronics having a power output and a power status output. The wireless communication circuit (150) of the wireless communication module (32) is configured to wirelessly communicate and execute multiple high priority tasks and multiple low priority tasks. The high priority tasks are executed asynchronously, and the multiple low priority tasks are executed only when the power status indicates there is sufficient power.

Description

[Technical Field]

[0001] The present invention relates to industrial process control or monitoring systems, and more particularly to field devices in such systems that include wireless communication capabilities. [Background technology]

[0002] In industrial environments, control systems are used to monitor and control the inventory, etc., of industrial and chemical processes. Typically, control systems perform these functions using field devices that are distributed at key locations in the industrial process and connected by process control loops to control circuits in the control room. The term "field device" refers to any device that performs the functions of a distributed control or process monitoring system, including all devices, now known or yet to be known, used to measure, control, and monitor industrial processes.

[0003] Some field devices include transducers. A transducer is understood to mean either a device that generates an output signal based on a physical input or a device that generates a physical output based on an input signal. Typically, a transducer converts an input into an output having a different form. Types of transducers include various analytical instruments, pressure sensors, thermistors, thermocouples, strain gauges, flow transmitters, positioners, actuators, solenoids, indicator lights, etc.

[0004] Typically, each field device also includes communication circuitry used to communicate with a process control room or other circuitry over a process control loop. In some installations, the process control loop is also used to deliver regulated current and / or voltage to the field device to power the field device. The process control loop also carries data in either analog or digital form.

[0005] Traditionally, analog field devices are connected to a control room by a two-wire process control current loop, with each device connected to the control room by a single two-wire control loop. Typically, a voltage difference is maintained between the two wires within a voltage range of 12 to 45 volts in analog mode and 9 to 50 volts in digital mode. Some analog field devices transmit signals to the control room by modulating the current through the current loop to a current proportional to the sensed process variable. Other analog field devices can perform actions under the control of the control room by controlling the magnitude of the current through the loop. Additionally, or instead, the process control loop can carry digital signals used to communicate with field devices. Digital communication is a much greater degree of communication than analog communication. Field devices that communicate digitally can respond to and selectively communicate with the control room and / or other field devices. Furthermore, such devices can provide additional signaling, such as diagnostics and / or alarms.

[0006] In some installations, wireless technology is used to communicate with field devices. Wireless operation simplifies the wiring and setup of field devices. Currently, fully wireless installations are used in which field devices are designed to obtain power using batteries, solar cells, or other technologies without using any wired connections. However, the majority of field devices are hard-wired to the process control room. Even in such hard-wired devices, it may be desirable to provide wireless communication. This can be used for diagnostics, obtaining readings by an operator in the field, or device configuration. However, wireless communication circuitry requires power to operate. This power requirement is in addition to the power used to operate other circuits in the device. If the wireless communication circuitry exceeds its power budget, the field device may fail to operate and the device may go offline. Summary of the Invention [Problem to be solved by the invention]

[0007] A field device for use in an industrial process includes a transducer configured to connect to the industrial process and control or monitor a process variable of the industrial process. A primary communication circuit communicates information with a remote location related to the process variable. A wireless communication module includes an energy storage device and power monitoring electronics connected to the energy storage device, the energy monitoring electronics having a power output and a power status output. The wireless communication circuit of the wireless communication module is configured to communicate wirelessly and to execute multiple high priority tasks and multiple low priority tasks. The high priority tasks are executed asynchronously, and the multiple low priority tasks are executed only if the power status output indicates there is sufficient power.

[0008] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended for use as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all of the disadvantages noted in the Background. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an example industrial process control field device including a wireless communication module. [Figure 2] FIG. 2 is a block diagram of the field device shown in FIG. [Figure 3] 1 is a voltage versus time graph showing voltage levels. [Figure 4] 1 is a diagram illustrating the operation of an energy management system of a wireless communication module. [Figure 5] 1 is a graph of energy levels versus time while a wireless communication module is performing a computational task. [Figure 6] 6 is a flowchart illustrating the execution of computational tasks according to the graph of FIG. 5. [Figure 7] 10 is a graph of the stored energy level of the system versus time while RF communications are disabled. [Figure 8] 1 is a graph of accumulated energy levels versus time while an advertising wireless communication event is being performed. [Figure 9] 1 is a graph of stored energy level versus time while a connection wireless communication event is being performed. [Figure 10] 2 is a simplified block diagram of the field device of FIG. 1 showing the wireless communication module in greater detail. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Elements identified by the same or similar reference numerals represent the same or similar elements. In addition, for ease of understanding, some of the components shown in each drawing may be omitted.

[0011] Various embodiments of the present disclosure may be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0012] The present invention includes an industrial process control field device having a transducer configured to control or monitor a process variable of an industrial process. The device includes a main communication circuit for communicating information regarding the process variable. A wireless communication module is configured for wireless communication using the wireless communication circuit and is powered by power stored in an energy storage device. Power monitoring electronics monitor available power and / or power usage. Power can be determined by measuring the voltage of the energy storage device or through some other means. Tasks performed by the wireless communication module are controlled based on an output from the power monitoring electronics.

[0013] 1 and 2 are schematic and block diagrams of an exemplary field device 14 including a wireless communication module 32 according to the present invention. A process control or monitoring system 10 includes a control room or control system 12 connected to one or more field devices 14 via a two-wire process control loop 16. Examples of process control loops 16 include analog 4-20 mA communication, hybrid protocols (including both analog and digital communication standards), and all-digital protocols (such as the FOUNDATION® Fieldbus standard and Ethernet APL (Advanced Physical Layer)). Generally, the process control loop protocol can provide power to the field device and enable communication between the field device and other devices. Additionally, the process control loop 16 can include a wireless process control loop, such as one compliant with WirelessHART® (IEC 62591) or ISA100.11a (IEC 62734), or another wireless communication protocol, such as WiFi, LoRa, Sigfox, BLE, or any other suitable protocol, including a custom communication protocol. As used herein, this is referred to as the main communication circuit 38.

[0014] Field device 14 includes circuitry 18 connected to actuator / transducer 20 and connected to process control loop 16 via terminal block 21 within housing 23. Field device 14 is depicted as a process variable (PV) sensor in that it connects to the process and senses and provides an indication of a condition of the process, such as temperature, pressure, level, pH, flow rate, etc. Other examples of field devices include valves, actuators, controllers, and displays.

[0015] Generally, field devices are characterized by their ability to operate in the "field," where they are exposed to environmental stresses such as temperature, humidity, and pressure. In addition to environmental stresses, field devices often must withstand exposure to corrosive, hazardous, and / or explosive atmospheres. Furthermore, such devices must also operate in the presence of vibration and / or electromagnetic interference.

[0016] The field device 14 includes an internal main communication / power module 38, a controller 35, a wireless communication module 32, and an actuator / transducer 20. The communication / power module 38 may connect to an auxiliary power source or may include a battery to power the field device 14. Some field instruments also use built-in solar cells. Power may also be provided from the wired process control loop 16 or from another external source, including a solar panel. Power from the power source 38 operates the controller 35 to interact with the actuator / transducer 20 and the wireless communication module 32. The wireless communication module 32, in turn, interacts with other devices via an antenna 26, as indicated by reference numeral 24. Depending on the application, the wireless communication module 32 may be adapted to communicate according to any suitable wireless communication protocol, including, but not limited to, wireless networking technologies (such as IEEE 802.11b wireless access points and wireless network devices manufactured by Linksys, Inc., Irvine, California), Bluetooth® (BLE), cellular or digital networking technologies (such as Microburst® manufactured by Aeris Communications Inc., San Jose, California), ultra-wideband, free-space optics, Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), Code Division Multiple Access (CDMA), spread spectrum technology, infrared communication technology, SMS (Short Message Service / Text Message), or other suitable wireless technologies. Also, known data collision prevention techniques may be employed to allow multiple units to coexist within a wireless operating range. Such collision prevention may include using several different radio frequency channels and / or spread spectrum techniques.

[0017] The wireless communication module 32 may also include transducers for multiple wireless communication methods. For example, wireless communication may be performed using a relatively long-range communication method such as GSM or GPRS, while a secondary or additional communication method may be provided to a technician or operator near the device using, for example, IEEE 802.11b or Bluetooth.

[0018] One technique for managing the power requirements of a wireless communication module is disclosed in U.S. Patent Application Publication No. 2019 / 0246353, entitled "Method and Apparatus for Controlling Communication Data Rates of a Low Energy Device," assigned to Fisher Controls International LLC, and incorporated herein by reference in its entirety. FIG. 3 shows a graph of voltage versus time for such a configuration. As shown in FIG. 3, the energy storage device recharges based on the input current supplied to the wireless communication module and discharges based on the particular task or process the module performs. The voltage drop shown in FIG. 3 is based on a Bluetooth® event.

[0019] In Figure 3, UTP is the upper trip point where the energy storage device is substantially fully charged. When this state occurs, a high voltage level is indicated using a GPIO (General Purpose I / O) line to the controller. Otherwise, if the voltage level falls below UTP, the GPIO line goes low. LTP is the lower trip point where the energy storage device is almost fully depleted, and another GPIO line goes from high to low in this case.

[0020] One technique that can be used to manage the communications module's power uses a Kalman filter (a linear quadratic estimator) to estimate the energy stored in the energy storage device and responsively control power usage by the communications module 32. The Kalman filter is used to estimate discharge and recharge rates during operation. The communications module performs multiple computational tasks depending on the available energy approximation determined by the Kalman filter. A single computational task can also be performed multiple times based on the estimated stored energy. If the estimated stored power is sufficient, the communications module can enable its radio and connect to a remote device.

[0021] This configuration allows for the estimation of discharge and recharge rates based on past rates. However, the input current supplied to the communication module may fluctuate, potentially resulting in inaccurate estimates of stored energy. As an example, if a field device 14 is connected to a HART® loop current 16 operating at 20 mA, the energy storage device recharges faster, allowing the DC power supply on the field device's main board to supply a higher current to the communication module 32. However, based on such an approximation, if the loop current later changes to its minimum value, i.e., 3.5 mA, the recharge rate of the energy storage device drops significantly. This can cause the energy storage unit voltage to reach a low voltage point (LTP) and ultimately reach the minimum MCU voltage, resulting in a brownout condition and resetting the communication module. Furthermore, when using such estimates to schedule the execution of computational tasks, throughput may be inconsistent if the energy supplied to the communication module is dynamically changing.

[0022] The present invention provides a power management system for the communication module 32 in a field device 14 that remains independent of the device's operating mode, whether it is a loop-powered, power-constrained, or auxiliary-powered device. The system manages power usage for various tasks performed by the communication module, including radio operation (transmit and / or receive), inter-processor communication (IPC), and computational tasks. When the process control loop is operating at a low current level, the loop-powered device can only provide a small amount of power to the communication module. For example, a small input current of approximately 300 μA to a communication module operating at 4.3 V, or 1.29 mW of power, can be provided. When the loop is operating at a higher current level, the input current can be higher, resulting in the communication module 32 receiving more current, e.g., 4 mA. The communication module 32 includes an energy storage device, such as a storage capacitor, that is recharged based on the input current to the module and discharged based on the quiescent current used by the module 32. For example, if the module's microcontroller is active, the module may draw as much as 10mA of current when the radio is actively transmitting at 5dBm transmit power, and the microcontroller can draw higher current depending on the number of peripherals active as well as the radio itself.

[0023] The power management system of the present invention controls the operation of various tasks performed by the communications module 32. There are various operations performed by the microcontroller and radio circuitry that can consume energy. These are referred to herein as energy-consuming activities and include: Radio operation: The radio circuitry must transmit and / or receive when the communication module's radio is advertising its availability or communicating with another device. IPC (Inter-Processor Communication) Message Exchange: The microcontroller in the wireless communication module communicates with the microcontroller in the field device by exchanging data using, for example, SPI, UART, or I2C communication. Computational tasks: These are tasks performed by the microcontroller of the wireless communication module when performing certain procedures. These procedures may relate to: ·· Performing cryptographic algorithms for security operations, e.g., random number generation, or other tasks related to encryption and decryption. ··Storing data in an external non-volatile memory device. ··Firmware updates.

[0024] The power management system preferably operates with both loop and external (auxiliary) power supplies. Regardless of the device's power mode (loop or auxiliary), the power management system makes the following assumptions: The minimum input current supplied to the communication module 32 is at least above a minimum threshold. Also, a higher loop current or auxiliary power source can increase the recharge rate of the energy storage device. However, the power management system assumes that recharging will occur at a lower rate. The computational tasks performed by the communication module's microcontroller are executed one at a time in a round-robin fashion, each task running until all tasks are completed. Such computational tasks have a predefined worst-case energy consumption value. For example, asymmetric encryption using any single iteration as the computational task consumes less than 140uJ of energy. The energy management system does not depend on the discharge rate while executing any of the energy-consuming tasks. Instead, the system assumes that the energy consumed by these energy-consuming tasks is at most 140uJ for each task in one iteration. This technique does not require firmware runtime discharge rate calculations. ··In this configuration, the security and firmware update computation tasks are divided into multiple iterative functions with a single iteration energy consumption of less than 140uJ.

[0025] FIG. 4 illustrates the operation of the energy management system of the present invention. FIG. 4 illustrates the operation of various tasks related to the available energy stored in the energy storage device. An upper trip point (UTP) and a lower trip point (LTP) are shown. The illustrated tasks include radio events, computational tasks, and IPC events. A software buffer is also shown to provide an energy reserve before the LTP is reached and the system enters shutdown mode. When fully charged, the energy storage device stores the minimum amount of energy desired in certain embodiments, e.g., 500 uJ in one particular configuration. When the field device 14 is powered by an external auxiliary power source, the energy management system operates in a high-power mode.

[0026] Here, the energy management system does not use an estimate of the current charging rate based on an approximation model (e.g., a Kalman filter) based on past sampling, but instead operates on a time basis, waiting for the stored energy to reach an upper trip point after performing an energy consuming task.

[0027] Figure 5 is a graph of stored energy versus time, showing the energy discharge and recharge resulting from performing various tasks. As shown in Figure 5, the device does not calculate the discharge rate during operation. Instead, the worst-case energy consumption is subtracted as a static parameter. It is also assumed that no recharge occurs during task execution.

[0028] Once task execution is complete, the energy management system waits for the energy storage unit to recharge to the UTP level. Furthermore, during this recharge time, the microcontroller can be placed into deep sleep mode. Therefore, depending on the runtime recharge rate, the stored energy can reach the UTP in a shorter time at a higher recharge rate, or it can take a longer time at a lower recharge rate (e.g., a predetermined minimum recharge rate). The system waits for the stored charge to reach the UTP level, at which point it can wake up the controller by using the UTP line as a GPIO line and begin the next task.

[0029] The energy management system preferably does not allow the energy level to reach the LTP level. If the LTP energy level is reached, the system considers this a fault condition and immediately puts the microcontroller into deep sleep mode. This allows the system to recover from the lowest energy level without causing a microcontroller brownout.

[0030] In one configuration example, the energy between the UTP level and the LTP level is 450 uJ. This energy budget allows both synchronous energy-consuming tasks (low priority tasks) and asynchronous energy-consuming tasks (high priority tasks) to be performed as follows: Synchronous energy consumption tasks (scheduled events): Advertisement and connection wireless communication events. Advertisements occur periodically at any desired frequency. Connection events can also be periodic and use a negotiated time between the host and client device. ··Tasks are calculated using a round-robin schedule. For each synchronous event, the power management system waits for the UTP level to be reached, at which point the next synchronous event is executed. Asynchronous energy consumption tasks (unscheduled events) can occur at any time and are executed as follows: IPC (Inter-Processor Communication) The asynchronous event is executed using a pre-allocated amount of energy from the available energy stored in the energy storage device, for example, 160 uJ of energy as shown in Figure 4. After the IPC event, the energy storage unit is allowed to recover this allocated amount of energy before a subsequent IPC event is allowed to occur.

[0031] Field devices equipped with secondary power sources will not discharge below the UTP power level. For such devices, a UTP event is triggered immediately. After both the loop-powered and auxiliary-powered devices have performed their energy consumption tasks, the algorithm is as follows: - Determine the energy storage status. If not high, wait for UTP level to be reached. Otherwise For field devices with auxiliary power, set the UTP high event.

[0032] FIG. 6 is a simplified flowchart 100 of steps used by a power management system according to one example implementation. The process begins at block 102. At block 104, the UTP status is checked. If UTP is not high, the system waits for UTP high at block 106. At block 108, the available energy is set to the UTP level, and control is passed to block 110, where the next scheduled wireless communication event or computational task is executed. At block 114, the UTP level is checked. If UTP is high, control is passed to block 108. If UTP is not high, control is passed to block 116, where the worst-case (maximum) energy consumption of the wireless communication event or computational task is subtracted from the available energy, and control is passed back to block 106 to repeat the process. This allows the power management system to be used with both loop-powered and auxiliary-powered field devices.

[0033] Figure 7 shows a graph of the system's stored energy level versus time while wireless communications are disabled. Each computing task is executed in a round-robin fashion and runs to completion. The system waits for stored power to recover to UTP levels between each computing task.

[0034] 8 is a graph of accumulated energy levels versus time while an advertised wireless communication event is being performed. The advertised wireless communication event is being performed when the communication module is transmitting a signal indicating that it is ready to communicate. The operations during the advertised wireless communication event are as follows: Advertisement: A computational task is executed only if: ··There is enough energy to perform the selected computational task, and If the time required for the selected computing task to be completed and for the storage device to recover the expended energy is less than the time until the next advertising event begins, or ··There is enough energy to perform the selected computational task and the next advertising event, and ··The computational task is completed before the next advertising event.

[0035] 9 is a graph of accumulated energy levels versus time while a connection radio event is being performed. After each connection radio event is completed, the system disables further operation of the radio to reduce energy consumption so that subsequent computational tasks can be performed. The firmware performs individual computational tasks and continues if: ··When there is enough energy to perform the selected computational task. ··or ··If there are any computing tasks remaining to be executed in the list of computing tasks to be executed (round robin method). After one of the above checks fails, the system will suspend further computational task execution until a UTP high level is detected. Once the energy storage device reaches the UTP level, the system checks to determine if there are any remaining computational tasks to be performed from the list of computational tasks. If there are more computational tasks, the system executes the next selected computational task. When all the computational tasks in the list have been executed, the system waits for UTP high to be detected, then the system allows the wireless communication to generate the next wireless communication connection event, and then the system returns to the first bullet (·) above.

[0036] FIG. 10 is a simplified block diagram of the field device 14, showing the communications module 32 in more detail. The module 32 includes a Bluetooth® microcontroller (radio) 150 that communicates with the field device electronics microcontroller 35 via an IPC communication link. The microcontroller 150 includes radio circuitry connected to the antenna 26 for communication with a local portable terminal device, such as a mobile device 158. The microcontroller 150 operates according to instructions stored in its internal memory to provide the power management system described above. The microcontroller 150 receives power from the DC power source 38 and stores it in an energy storage device 152. The energy storage device 152 may include any suitable storage device, such as a capacitor or a battery. The power monitoring electronics 154 monitors the power stored in the energy storage device 152 and provides power to the microcontroller 150 along with UTP and LTP signals. The UTP and LTP signals may be determined based on, for example, voltage thresholds. The field device 14 may be powered by power received from the process control loop 16 or from an optional auxiliary power source 160.

[0037] The power management system described herein offers many advantages. The system does not rely on approximations of stored power based on historical discharge and recharge rate data, which can have substantial variations from the actual rates. Furthermore, the same power management system can be used for both auxiliary-powered and loop-powered field devices. The system accounts for run-time variations in discharge and recharge rates by assuming the following: · In case of discharge, the worst case (maximum) discharge energy of any energy consuming task. When recharging, the system waits for the stored energy to reach the UTP level, so a higher recharge rate will result in the stored energy reaching UTP sooner. The system provides a power profile that can react quickly to changing energy conditions, enabling more robust wireless communications.

[0038] Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention.

Claims

1. 1. A field device for use in an industrial process, comprising: a transducer coupled to the industrial process and configured to control or monitor a process variable of the industrial process; a main communication circuit configured to communicate information with a remote location related to the process variable; A wireless communication module, energy storage device, power monitoring electronics connected to the energy storage device and having a power output and a power status output; and a wireless communication circuit configured to communicate wirelessly and to execute a plurality of high priority tasks and a plurality of low priority tasks, wherein the high priority tasks are executed asynchronously and the plurality of low priority tasks are executed only if a power status output indicates there is sufficient power; a wireless communication module including: a field device including:

2. The field device of claim 1 , wherein the low priority tasks are executed synchronously on a round robin schedule.

3. The field device of claim 2 , wherein the wireless communication circuitry includes a microcontroller, and the low priority task includes a computational task performed by the microcontroller.

4. The field device of claim 3 , wherein the computational tasks are performed synchronously based on an amount of energy stored in the energy storage device.

5. The field device of claim 2 , wherein the wireless communication circuitry includes a wireless communication, and the low priority task includes a wireless communication event performed by the wireless communication.

6. The field device of claim 5 , wherein the wireless communication event comprises an advertising event.

7. 7. The field device of claim 6, wherein the wireless communication circuitry includes a microcontroller, the low priority task includes a computational task executed by the microcontroller, the computational task is executed when sufficient energy is stored in the energy storage device to complete the computational task, and the sum of the time required to complete the computational task and the time for the energy storage device to recover the energy used by the computational task is less than the time until the next advertising event.

8. 7. The field device of claim 6, wherein the wireless communication circuitry includes a microcontroller, the low priority task includes a computational task executed by the microcontroller, and the computational task is executed if sufficient energy is stored in the energy storage device to complete both the computational task and a next advertising event, and the computational task is completed before the next advertising event.

9. The field device of claim 5 , wherein the wireless communication event comprises a connection wireless communication event.

10. 10. The field device of claim 9, wherein the wireless communication circuitry includes a microcontroller, the low priority task includes a computational task performed by the microcontroller, and the connected wireless communication event is not executed until all of the computational tasks are completed and sufficient energy stored in the energy storage device exceeds an upper trip point level.

11. 6. The field device of claim 5, wherein the wireless communication circuitry includes a microcontroller, the low priority task includes a computational task performed by the microcontroller, and the wireless communication is disabled while the computational task is being performed.

12. 10. The field device of claim 1, further comprising a field device microcontroller, the wireless communication circuitry comprising a microcontroller, and the high priority task comprising inter-processor communication between the microcontroller and the field device microcontroller.

13. The field device of claim 12 , wherein the inter-processor communication occurs when the energy stored in the energy storage device is above an upper trip point level.

14. 14. The field device of claim 13, wherein the subsequent inter-processor communication is performed if energy from a previous inter-processor communication is restored.

15. 10. The field device of claim 1, wherein the main communication circuitry connects to a two-wire process control loop, and the field device is powered by power received from the two-wire process control loop.

16. 10. The field device of claim 1, including a connection to an auxiliary power source, the field device being powered with power from the auxiliary power source.

17. 17. The field device of claim 16, wherein the upper trip point level is set to a high state.

18. The field device of claim 1 , wherein the energy storage device comprises a capacitor.

19. 10. The field device of claim 1, wherein the power status outputs of the power monitoring electronics include an upper trip point output and a lower trip point output.

20. The field device of claim 1 , wherein the power status output of the power monitoring electronics is determined based on a voltage of the energy storage device.

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