Sensors And Connectivity In Smart Industry

By Vishal Goyal, Senior Manager – Technical Marketing, Analog and MEMS group, RF, Sensors and Analog custom products, India, ASEAN and ANZ, STMicroelectronics

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ST has introduced a humidity sensor HTS221 which includes a sensing element and an analog front end to provide the measurement information by digital serial interface. The sensing element consists of a polymer dielectric planar capacitor structure able to detect relative humidity variations.

MEMS Microphone

MEMS Microphone is audio sensor that converts sound signals into electrical signals. MEMS Microphones are increasingly preferred over conventional microphones as they offer higher SNR, small form factor, digital interface, better RF immunity and high robustness against vibration. The sensors are in in machines for applications such as videography, surveillance, spying etc.

Important characteristics for sensors in Smart Industry

Machines are subjective to extreme conditions including vibration, noise and environment. A sensor used in an industrial machine should have high shock survival capability, should capture less noise and fast enough to capture all vibration. Its performance should not vary with change in environment parameters such as temperature and humidity. And finally it should have high reliability and performance.

Role of Algorithms

Software libraries play an important role to convert raw sensor data into meaningful use case. The algorithm augment the function of sensor beyond their stated features. The algorithm also combine the input from various sensors and create a context aware output.
The three motion sensors – accelerometer, gyroscope and magnetic compass – have their own advantages and disadvantages. Sensor limitations include imperfect calibration, drift over time or temperature and random noise. Magnetometer and Accelerometer are subject to distortions and gyroscope has inherent drift. Sensor fusion library is used to calibrate there sensors with each other to create a condition which gives accurate result in all scenarios. It not only give calibrated sensor outputs but also angles, heading angle information and quaternions.

Connectivity technologies for Smart Machines

There are various connectivity options considered for machines. BLE and Wi-Fi are used for smart phone connectivity. I would rephrase

Sub-1GHz technology is used to connect sensors network with proprietary protocol combining a real low-power consumption with long distance coverage. Cellular and Sigfox are used to collect information from machine directly to telecom infrastructures.

The map of various technologies on scale of distance and power consumption is listed below. We will discuss lower power technologies such as BLE, RF sub-1GHz and Sigfox in a greater detail.

Bluetooth low Energy – Bluetooth Smart [BLE]

Bluetooth Smart or Bluetooth Low Energy [BLE] enables low power connectivity to machines. It is suitable for low range machines particularly the toy machines. It enable two way communications between machines and control devices such as smartphone, tablet, laptop and dedicated remote controller. BLE allows machines to have incredible battery life which is not possible using traditional wireless technologies such as Wi-Fi and Classical Bluetooth.

Bluetooth Low Energy works in license free 2.4GHz ISM band. The standard is governed by Bluetooth Special Interest Group (SIG) and is support all the major smartphone brands.
There are two major partitioning available in BLE devices.

a. Network processor

A network processor is a BLE device which is running BLE protocol including controller, Host and stack. But it need a separate microcontroller for its functioning with main microcontroller running BLE profiles and application. This platform is also platform independent so offers wide flexibility to user to select best fit microcontroller or operating system. BlueNRG-MS is a network processor offered by ST and compatible with BLE 4.1. This IC can act as Master and Slave at the same time. So it is possible to have a remote controller acting as slave to Smartphone but master of machine.

b. System on Chip

System on Chip (SOC) is a devices which is an independent chipset and includes controller, Host, stack profiles and application. BlueNRG-1 from ST is BLE 4.2 certified SOC and includes 15 GPIOs, I2C, SPI, UART, PWM, PDM and 160kB of RAM. This IC also offers advance security and privacy features offered by BLE 4.2.

RF sub-1GHz

RF sub-1GHz as the name suggests carries signal over sub-1GHz frequencies. Different countries have defined different frequencies which can be freely used for Industrial and scientific usage.

Below are some of free bands available in various countries
• North America : 315, 433, 915Mhz
• Europe : 433, 868Mhz
• India : 433, 865-867Mhz

The advantage of sub-1GHz frequencies is that they are relatively quieter bands, have a longer range and consume low current. Down side is that they do not offer direct smartphone connectivity and not universally present.

Sigfox is subscription based LPWAN service based on sub-1GHz frequencies. Sigfox allows connectivity directly to telecom infrastructure and in-turn to cloud. It can give connectivity over several Km. In machines Sigfox can be used for tracking and to send sensor data to the cloud. It is low data rate technology directly to telecom infrastructure so not expected to replace direct control connectivity options such as BLE and RF sub-1GHz direct peer to peer connection.

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