"The goal of Internet of things (IOT) and industrial IOT (iiot) is the same, both of which are to transform sensor data streams into useful information. However, for developers, the biggest difference lies in the basic requirements, including power supply, connectivity, and design reliability and robustness.
IOT requires small size, battery power and wireless connection, which means using low-power MCU with integrated RF subsystem for Bluetooth or Wi Fi communication. On the contrary, the combined effects of poor working conditions, a large number of local sensors and legacy systems promote the demand for robust interconnection and the use of edge devices that can unload traditional PLCs.
This article will address some of the unique requirements of iiot applications relative to consumer iots. This shows that despite the additional requirements, developers can still find a variety of solutions to meet the specific requirements for applications in any field.
Differences between consumer and industrial iots
The application goals of IOT and iiot are similar. Both strive to obtain useful information from the data stream collected by sensors. Both depend on the multi-layer method used by peripheral devices to communicate with advanced applications directly or through some intermediate resources. However, in addition to these similarities, the nature of their respective requirements leads to essential differences in the design and connectivity of peripheral equipment.
For example, IOT sensor designs for health and fitness are generally not similar to iiot peripheral sensors and actuators required to accurately monitor and reliably control industrial equipment in harsh environments. Similarly, the connectivity of IOT and iiot networks may bring completely different requirements.
Connectivity typically represents one of the characteristics between IOT and iiot system implementations. As described below, iiot traditionally relies on the hard connection between programmable logic controller (PLC) and other hosts, and the principle of this method is still very effective today. In sharp contrast, IOT applications for personal and home use usually revolve around applications running on users' smartphones or other mobile devices, and connect to IOT devices or wearable devices through Bluetooth or Wi Fi LAN.
IOT device designs for home or office applications often have significant limitations in power and size. For these applications, consumers expect the batteries of most IOT devices and all wearable devices to be powered for a long time after one charge. IOT design for wearable products or products placed in prominent positions at home or office usually has additional product engineering requirements in terms of ease of use, waterproof and dustproof, minimum design packaging and other characteristics related to other mainstream consumer products. At the same time, design cost and simplicity have become a great concern for organizations seeking to deliver competitive products faster.
The emergence of low-power wireless MCU provides a solution to these often conflicting requirements. Wireless MCU provides a simpler method by integrating RF subsystem with processor core, which not only reduces the number of parts, but also eliminates the design problems related to RF integration, so as to speed up the overall development.
Dialog semiconductor's da1458x series devices and other wireless MCU integrate a processor core, Bluetooth RF subsystem, solid single-chip memory and a large number of analog and digital peripherals. MCU revolves around low-power 32-bit arm ® Cortex ®- M0 processor core construction, designed to minimize the power consumption of battery powered products. The integrated low-power Bluetooth core and RF subsystem of MCU only use 3.4 Ma for transmitting (TX) and 3.7 Ma for receiving (Rx). The overall typical power consumption of MCU is 4.88 Ma and 5.28 Ma respectively.
Memory expansion
Dialog provides various versions of da1458x MCU optimized for specific work requirements. For example, da14581 is optimized for wireless charging applications, while da14585 and da14586 are suitable for wearable devices and smart home applications that require small size, low power consumption and large storage space.
Dialog semiconductor da14585 includes 96 kilobytes of SRAM working memory; 128 Kbytes ROM for boot code and Bluetooth stack; And 64 kilobytes of OTP memory for application code, Bluetooth profile and configuration data. Da14586 provides the same features as da14585, but adds 2 megabit on-chip flash memory blocks, which has little impact on the total power consumption during normal operation.
If the device requires larger program memory, developers can easily add an external flash memory device using the SPI or I2C interface of MCU, such as Winbond electronics w25x20 2 megabit flash memory or w25x40 4 megabit flash memory (Figure 1). The flash memory device is packaged in a 2 x 3 mm small pinless device (uson), which will only moderately increase the design package. On the other hand, using external flash memory will increase the power consumption compared with using OTP of MCU or built-in flash memory of da14586. The reasons for the increase of power consumption include: the longer SRAM loading time of external flash memory, the higher programming current level of external flash memory, the higher current level of external flash memory during standby and even power-off mode.
Sensor data
For sensor data acquisition, engineers can use analog-to-digital converters (ADCs) integrated in wireless MCU such as dialog Bluetooth MCU. In some cases, the Engineer may be able to feed the sensor output directly to the ADC port of the MCU, and may buffer it through a simple operational amplifier.
However, for most IOT applications, more analog signal chains are required for sensor load, linearity, temperature compensation, signal swing, noise and other considerations. Even if built using available analog front end (AFE) equipment, independent sensor design will increase complexity and often delay the completion of the project. However, by using more smart sensors, developers can quickly create IOT designs, which include only a few components in addition to a single wireless MCU and smart sensors.
Smart sensors combine appropriate sensors with a complete sensor signal chain. These signal chains are optimized for specific sensor types, and an analog front end composed of power amplifier, filter and multiplexer is combined to provide conditional signals to the integrated ADC. These intelligent sensors usually integrate digital signal processing engine, and can perform a large number of sensor signal processing operations independently of the host MCU. For example, the TDK invensense icm-20789 integrated measurement unit (IMU) integrates a digital motion processor, which is designed to execute motion processing algorithms independently of the main processor. The device can handle all aspects of data generation - obtaining data from sensors, processing data, and saving data in FIFO for later access by host MCU.
Like all smart sensors, icm-20789's high integration and standard I2C and SPI ports ensure fast design and implementation. Developers only need to add a few additional components, including Texas Instruments tlv702 Series Low Dropout (LDO) regulators (Figure 2). When the data acquisition is completed, the intelligent sensor can wake up the sleeping MCU to process the data.
The combination of efficient MCU low power consumption mode and independent intelligent sensor operation provides a powerful platform for developers to design energy-efficient IOT devices.
Harsh environment
Like IOT applications, iiot uses multiple data streams to provide useful information. However, using iiot, developers who built sensor networks found themselves able to cope with harsh operating conditions, sensor layout and maintenance constraints, and the combination of older sensor devices and host systems.
Unlike most IOT applications, battery powered devices are generally unavailable in industrial environments. Busy operators have no time to replace the battery. In the dusty and noisy environment, even manual processing of these micro devices can be a problem. As with any electronic device intended for use in this environment, developers need to create robust mechanical and electrical designs that can cope with dust, liquids, physical stresses, electrical interference, and so on.
To solve these problems, industrial automation designers have evolved solutions that can withstand harsh environments using sensor modules hardwired to PLC through robust interconnection and communication protocols. In the interconnection system, M12 has become the preferred interconnection solution for industrial Ethernet, analog interface and digital series interface.
M12 interconnection system has various components and pin configurations available, which provides a standard and stable solution for maintaining reliable connection of peripheral equipment at various voltage and current levels. For example, M12 cable assemblies such as Molex 1200700156 have IP67 protection grade and rated voltage and current of 250 V and 4 a per contact.
In the communication protocol, IO link also appears in industrial automation and iiot deployment. At the signal level, IO link provides a standard connection protocol that can support both legacy analog sensor systems and the latest digital sensors. With the introduction of dedicated IO link devices, developers only need to connect the peripheral device MCU to dedicated IO link transceivers such as Maxim integrated max14827a and add an IO link master device such as Maxim integrated max14819 on the local host system or PLC to perform IO link connection. The developer uses a standard four contact M12 interconnect assembly (such as Molex 1200700156 mentioned earlier) to complete the IO link connection between the peripheral sensor and the host / PLC.
Distributed gateway
The use of robust M12 interconnection and IO link communication can solve the basic requirements of data and signal connection in industrial environment. Iiot not only continues the requirements of traditional automation systems, but also greatly expands it with a usually larger number of sensor devices. In turn, the proliferation of peripheral sensors and IO channels has brought great challenges to the industrial environment, at least in terms of logistics. Not only does the existing PLC have the threat of IO overload, but also the sharp increase in the number of cables will greatly increase the laying of facility cables.
In order to solve the increasing sensor load related to iiot, organizations are looking for more flexible methods that can compensate traditional PLC. In the alternative, the compact I / O processing system provides an off the shelf solution to deal with the I / O expansion related to iiot. The simplest function of these compact systems is to act as micro PLCs, providing a rapid solution for dealing with sensor feed surges that exceed the capacity of the facility's existing PLCs. In an industrial environment, organizations can distribute these small systems throughout the facility and place them near the equipment to reduce cable laying or in series with older PLCs to expand I / O channel functions.
The simplest function of micro PLCs such as Maxim integrated pocket IO system is to be used as I / O channel expander to provide a large number of digital, analog and IO link interfaces. Pocket IO platform provides 30 I / O channels, including analog IO, digital I / O, RS485 channel, encoder motor control port and the combination of four IO link main channels. The control program of the platform runs on the Intel Edison board installed on the main board in the three board combination of the platform (Figure 3).
Using its rich IO and program features, pocket IO platform not only provides direct alternative solutions, but also provides reference design for customization requirements.
Pocket IO and other platforms not only reduce the IO burden increased by PLC, but also provide a simpler alternative to program development. The traditional PLC uses a special programming language, such as ladder logic, which will make the PLC program migration between different PLC platforms very complex.
Because pocket IO and other small systems are based on traditional processors, developers can use standard languages such as C / C + + and familiar development environment to program their micro PLC and other edge devices. For example, in pocket IO reference design, developers can use Arduino sketch and its integrated development environment (IDE) to quickly implement functions to process signals.
Edge device flexibility
The role played by micro PLCs and other iiot edge devices hardly exists in IOT applications. In IOT, Wi Fi routers (and proprietary centers) largely provide only local connections between peripheral devices and the Internet. In contrast, iiot edge devices also play a key role in providing local processing for peripheral devices.
With its local processing power, edge devices enable developers to loosen the tight coupling between factory floor sensors and higher-level application hosts or cloud based resources. By running applications on edge devices, developers can eliminate loop delays to and from the cloud. In this way, developers can realize faster control loops and reduce the reporting delay on the user interface next to key equipment and its operators.
The ability to disconnect peripherals from the cloud will provide more advantages if it maintains the availability of key businesses. Cloud service providers use functions such as shadow devices to maintain application availability. The shadow device is located in the cloud and is the model of the corresponding peripheral device. It is used to track its status during normal operation and provide device display when the cloud connection fails.
In contrast, services such as Amazon Web services (AWS) and greenrass allow edge devices to provide local versions of some cloud based services, including machine learning services. Therefore, more advanced services can continue to run locally, even though cloud response time and even availability change.
At a more basic level, edge devices can also improve availability by providing diversified options such as narrowband cellular services in remote locations with no or poor Internet connection. To provide effective wireless options for iiot connections, cellular service providers will quickly take action
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