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Role of sensors in industrial Internet revolution

Posted: 10 Jun 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Internet of Things? Industrial Internet? sensor networks? machine-to-machine? M2M?

Whether or not the Internet of Things will live up to its own hype, the concept has certainly got people thinking. Proposals range from the "Internet of Everything" to some more focused concepts such as the Industrial Internet; a term first introduced by electrical giant GE, and now understood to mean the automation of industrial environments using sensor networks and machine-to-machine (M2M) communications.

The report "Markets for Sensors in the Industrial Internet" published by market analyst Nano Markets in November 2014 included factory automation, building automation, the smart grid and public transport as Industrial Internet applications, and predicted the sector would consume more than $20 billion of sensors per year by 2019.

Tomorrow's technicians and maintenance staff will rely increasingly on rugged tablets to collect and process information from sensors integrated in industrial machinery, according to the VDC Research 2014 Strategic Insights for Industrial Automation and Sensors. VDC reckons the global market for position sensors alone will exceed $8 billion by 2018.

Industrial sensing applications
Position sensing is possible using technologies such as potentiometric, optical, magnetic, Hall-effect, magneto-resistive and inductive. Various types of inductive sensors are available, including linear and rotary variable differential transformers (LVDT/RVDT) capable of measuring displacement and position.

Inductive sensors can be very small and require no electronic circuitry, making them suitable for applications such as turbine valves, military and aerospace equipment, and industrial process controllers deployed in harsh environments.

Alternatively, LVDTs and RVDTs with built-in pre-calibrated signal conditioning help simplify external circuitry and system integration. Compatible control and instrumentation modules can further simplify design and accelerate time to market.

Photo-microsensors, on the other hand, are ideal for non-contact optical proximity or position detection. Various configurations are available, with or without an actuator, or with moulded mounting points for a custom actuator.

Various other options are available to satisfy differing requirements, such as sensors with raw phototransistor output or built-in amplifier, screw or push-fit mounting, electrical connection via PCB pins or miniature cable connector, and light-ON or dark-ON switching polarity. In addition, equipment designers must also choose the aperture size and sensing distance to meet the needs of the target application.

Turbidity measurement is another interesting application of optical sensing technology, for quantifying small particles of solid matter suspended in liquids. Applications include controlling industrial processes such as brewing, water bottling, pharmaceutical production, purification, or in aquaculture for monitoring marine water quality or studying the habitats of aquatic animals.

Turbidity can be quantified by measuring the depth of liquid needed to obscure a light source viewed through the liquid. In this case, turbidity is expressed in Jackson Turbidity Units (JTUs). The Nephelometric Turbidity Unit (NTU) is a more modern measure based on assessing the scattering of light by small particles in the liquid, using a detector placed alongside the light source.

A turbidity meter combines one or more sensors with data-acquisition and user-interface sub-systems, and various types are available such as handheld or bench-top meters for laboratory use, or inline meters for plant and process applications.

The combined optical turbidity sensor and temperature sensing module shown in the figure uses a phototransistor and diode to measure the transmission of light through a sample of liquid. This basic sensor is ideal for use in domestic appliances, and can help to reduce energy consumption by detecting when clothes are clean allowing the wash cycle to be shortened.

Figure: The combined optical turbidity sensor and temperature sensing module uses a phototransistor and diode to measure the transmission of light through a sample of liquid..

For temperature sensing, thermistors are known to be robust and reliable, and are available with various temperature ranges suitable for industrial, HVAC, medical, military/aerospace and other applications. The type of housing and attachment are important criteria that can help to simplify equipment design. Pipe-clamp probes for example, can be fitted directly to the outside of a hot water pipe and enable equipment designers to eliminate costly processes such as boring and sealing needed when installing an intrusive probe. These probes are convenient to use, with no need to buy or design a separate fitting.Designers can also choose from screw-on probes or moulded probes for various applications, as well as screw-in probes for immersion monitoring in equipment such as boilers. Alternatively, board-mount temperature sensors in chip packages, or ceramic or glass-encapsulated styles, allow local temperature sensing to be implemented neatly inside the housing of a control module, and can help save connections to external sensors.

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