Like sonar, ultrasonic transducers can detect detailed qualities of surfaces by bouncing sound waves off them. Today’s sensors are cheap, compact and have a vast range of applications.
The simplest ultrasound detectors in use are passive microphones but the majority of applications use a transducer - a device that combines a sound emitter and echo receiver. They are tuned to frequencies above 18 kHz, therefore inaudible to the human ear. Sound can be generated in a variety of ways but the most common methods are piezoelectric and capacitive (creating an electrostatic field between a back-plate and a diaphragm).
The vast majority operate in a straightforward way: they measure the time lapse between the signal generation and the arrival of its reflection. This simple principle can be tuned and adapted to achieve an impressive variety of functions. Sensors can detect and record speed, weather, size, material levels, numbers of items, condensation, contours and profiles, distance or proximity. Their targets can be large or tiny, near or distant, stationary or moving. When fitted in mobile vehicles and containers, geolocation reporting is often incorporated onto the same devices.
Some of the uses of proximity sensors are familiar - such as reversing vehicles and intruder alarms - but they have far more potential. Detectors can calculate accurate distances to the intercepted surface. The basic formula is simple: L = 1/2 × T × C - (L being the distance, T the time between transmission and reception, and C the speed of sound). Variations in the speed of sound can be allowed for as required and many sensors can work underwater or within other fluids where sound propagates differently. Detected surfaces can be irregular or diffuse, such as wire mesh, yet the sensors are resistant to interference from mist or dust.
This principle allows sensors to monitor the level of material in tanks and silos, highly valuable for any business reliant on continuous feedlines or just-in-time reordering. Ultrasound sensors can be set to detect a concise point or to average a broad irregular field of objects such as those in municipal recycling bins. Despite irregular contents, ultrasound sensors can issue automated alerts to the collection or refilling company, ensuring perfect logistical efficiency.
Sensors are also being deployed to monitor water levels in rivers and reservoirs, facilitating river management, water supplies, flood control and protecting natural habitats. Similarly, they can monitor levels when filling boxes and bottles or the cups in a drink dispenser.
Speed cameras use infra-red but discrete ultrasonic transducers can apply the same principle to estimate the speed and direction of moving objects. There are a variety of ways to implement this; sensors can emit a series of pulses, calculating the change in distance over a given time, multiple sensors can triangulate in several dimensions, and (in principle) a Doppler effect could be calculated from pitch modulations.
Engine and motor speeds can also be safely monitored using discrete acoustic sensors.
A basic requirement on many production lines, acoustic sensors have no difficulty calculating the exact number of items that pass through an acoustic signal. Sensors can also sort boxes of different sizes, providing independent counts; useful for economic packing into delivery vehicles.
Some of the applications are surprising, for example linking a sensor to a rotating anemometer and/or weather vane can transmit constant information about wind speed and direction for meteorological purposes. Locating them at entry and exit points can ensure car park or building occupancy is not exceeded or that all personnel have been evacuated.
Medical ultrasound scanners are familiar, but profile sensing is now highly versatile and affordable. It can be implemented into semi-automated or robotic assembly lines, or to support shaping and finishing processes. A simple, but vital, application is to monitor stacking. They can also accurately monitor roll diameters and coil winding and unwinding operations.
The possibilities for acoustic sensing are vastly extended by transmitting the output from smart sensors across the “internet of things”. Multiple outputs can then be combined in a single sophisticated web-based interface and monitored in real time from any convenient location. Smart sensors can then be easily interfaced with microcontrollers and actuators to provide sophisticated remote control and record details into enterprise management software.
Many businesses have yet to realise the wealth of opportunities that come from linking smart sensors to the IoT. Off-the-shelf devices are cheap and unobtrusive. For more demanding applications, bespoke algorithms can be implemented in the device firmware or in software at the collection point.
Many businesses, not just factories, can benefit from sensors. They can monitor doors, count products, maintain temperatures, control production lines, automate stock records and optimise a host of other functions from the most simple to the most complex. They are cheaper and more capable than ever before: if you aren’t using them already you should be exploring the possibilities, but how you connect them is a key consideration.
Arguably, a door-bell is a simple wired sensor but a door bell can also be wireless. Even in the case of door bells, the best solution may be deployment-specific. Here are some of the key advantages and disadvantages to consider when deciding how to connect your sensors.
Quick, and therefore cheap, installation is often a decisive advantage in favour of wireless sensor systems. Wireless is frequently the only sensible solution in listed buildings or on sites already crowded with infrastructure. It is usually more viable when the site is split between several locations. Wireless connection easily causes less disruption to ongoing operations and less damage to plaster and floorboards.
In contrast, once you have paid for the equipment and installation, running costs should favour wired networks that do not need to lease bandwidth. Nevertheless, wireless IoT solutions are usually cheaper overall - as are future modifications, equipment relocations and network extensions.
A downside to connectivity is always the potential for intrusion or data corruption. IoT and Cloud solutions offer a range of protections and many come free - relieving you of a significant IT burden. Wired networks keep more points of vulnerability in-house, but are only more secure if you have personnel who know how to protect them. New security enhancements - such as SDN - can provide signal encryption and dynamic routing with minimal IT overheads.
Wired Ethernet networks are often a sound decision when all of your infrastructure is reachable. Wireless solutions have an obvious advantage if you need to connect remote equipment. If you are a utility operator, a farmer with multiple scattered assets, or a transportation company whose assets are moving, other options make little sense.
When your assets are in exposed locations, even inside a factory, remember that not all wired switches, routers and hubs are robust when subjected to extreme temperatures, moisture, grit, or power spikes. Wifi is therefore more reliable in harsh environments.
Wireless sensors are easy to replace or relocate without rewiring anything. You can also easily extend the network to incorporate additional operations, even when they are in a different building. Wired networks often require IT engineers to keep them running properly.
In contrast, wireless networks rarely require attention - they communicate over the Internet, which is maintained for you. Wireless technology makes it easier to benefit from upgrades and patches, or new Cloud software as it comes along.
By linking your devices using the IoT, your wireless network and Cloud resources can become scalable to fluctuating demands. If your production scales down, so does your consumption of bandwidth. If it scales up, extra capacity should be available on demand. With the right contracts in place, your sensor-control infrastructure can become a fixed and predictable percentage of your operating overheads. By comparison, a physical network always costs money to expand and returns nothing when it contracts.
Some wireless sensors rely on batteries. The advantage of batteries is that your wireless devices stay on and connected even in a power failure. The downside of batteries is that changing them usually takes a sensor offline (although this can be avoided using capacitive power storage). Conversely, wired sensors will always fail if their whole network fails or has to be powered down for maintenance.
Even in a total blackout, battery-powered wireless sensors continue sending your data to the Cloud via the IoT and you can continue monitoring them with your smartphone.
Any network issue could interrupt wireless services, so if 100% continuity is vital to your operations, a fall-back plan is important. However, wired networks are also susceptible to power failures and other interruptions, so backup plans could be needed anyway.
Electromagnetic interference from power lines is unlikely to affect physically wired equipment but sometimes causes a problem for wireless sensors. There are usually workarounds or shielding solutions for these local problems.
The choice between wired and wireless need not be either/or. A good IoT development team will help you to integrate wireless sensors with wired ones according to the issues in different locations - and enjoy the benefits of both.
