Intelligent sensors for smart cities
Fitting the bill: remote sensing products are helping to gather the vast amount of data needed for smart infrastructure systems.
Smart cities’ is a term that is bandied around a great deal these days. Urban planners and infrastructure engineers believe that inserting intelligence into utilities distribution — electricity, gas and water — and into the crucial elements of city structures, such as bridges and buildings, will help to optimise the flow of resources, minimise energy use, provide accurate billing for domestic and business consumers and schedule structural maintenance.
However, for all the possible advantages, there are technical challenges. One of the most obvious is in how to gather all the information needed to operate such a widespread system. It’s a problem of sensors — they must be robust, cheap, easy to maintain and reliable, as their readings will be used to determine billing.
‘Traditionally, gas, electricity and water meters have been mechanical,’ said Nick Collier, head of science and technology at UK development consultancy Sagentia. ‘They’re low cost, they meet the accuracy requirements and they’re really well trusted. But with the advent of smart metering, you need to have remote sensing of meters, which means that you have to think about electronics and power.’
Sagentia works in sensor systems for both medical and domestic/industrial applications and has a specialism in finding low-cost ways to find sensing solutions for its clients. ‘My group has PhD-qualified physicists, mathematicians, chemists and materials scientists who have a very broad understanding of the types of things that can be measured; we apply that to a lot of customer problems,’ Collier said.
‘We’re particularly strong in non-contact position sensors, which work by electrical induction; we also have optical sensors that detect fluorescence and colour, image sensors that use low-cost cameras and acoustic sensors for ultrasonic flow metering.’
Position sensors are useful for rendering mechanical meters machine readable. One example was a project with Mastermeter, which makes water meters that work on the odometer principle, with a brass body containing a turbine wheel that spins in the water flow, operating a mechanical odometer with a series of numbered wheels labelled from 0 to 9, exactly as you’d see in an older car. ‘The industry still likes those, because they’re easy to read and they work even if the electricity goes down, but they needed to be computer readable,’ Collier said.
The solution used non-contact position sensors, he added. ‘We mounted a very small, round printed circuit board [PCB] into the side of each wheel, which is metallised. Next to that, we mounted another round PCB with a series of tracks on it, which act as antennas. We pulse those at several megahertz and look for a reflection from the metal on the wheel-mounted PCB. That tells us what position the wheel is in, and looking at the signal from all of the wheels gives us the reading.’
The industry still likes mechanical odometers because they’re easy to read and they work even if the electricity goes down
Nick Collier, Sagentia
One advantage of this technology is that the sensor itself requires no battery. ‘It’s powered by the act of reading it: the reader carries a powered wand that sends the pulse signals into the static PCB,’ Collier said. ‘The meter could be down a pit in quite a nasty environment, but the pit lid would have a contact pad on it that the reader could touch, and that would power up the sensor to give a reading. That’s good for the smart metering world.’
Sensors that require no battery need much less maintenance, he said, and can be deployed in large networks. ‘You have to think about how to power the output and how it’s going to communicate with the outside world,’ added Collier. ‘And the challenge is actually more on the radio-frequency [RF] side — if you look at the power distribution between meter reading and communication, it’s the communication that takes more of the power.’
Sensors that require no battery need much less maintenance and can be used in large networks
One way around this is to power the system using energy harvested from the environment. Sagentia designed a system for district heating systems that use steam pipes. ‘We’ve developed a system that uses the differential between the high-temperature steam and the lower ambient temperature to generate enough electricity to run the sensor and to transmit its reading,’ said Collier. The system uses arrays of thermocouples in parallel to generate a current flow.
Other solutions have been developed by companies such as EnOcean, a spin-off from Siemens. These use a piezo-electric material that contracts on heating, generating a voltage that sends a spark across a gap. This generates a radio signal that can be picked up by a reciever base station. ‘What’s clever is that the act of sensing a change of temperature generates its own signal — you only communicate when the temperature changes,’ Collier added.
Other approaches use a small transformer to step up the few millivolts generated from photovoltaics or vibration-powered energy-harvesting systems to about 3V and using that to constantly trickle-charge a small battery.
‘We’re now seeing all the elements coming together for commercially viable systems of independently powered RF sensors that don’t need to be hardwired into a network, and the challenge for companies like ourselves is to act as system integrators to find the right market for them,’ Collier said. ‘They aren’t lower cost than a battery — the advantage is in the increased functionality and reduced installation costs. Factory automation is probably going to be the biggest initial market for these systems, with smart cities following on later, but I’d hope to see such systems in the domestic or office environment within a few years.’
Michell Instruments says its MDM300 IS portable dew-point hygrometer is particularly suitable for ensuring the safety of compressed natural gas (CNG) filling stations. CNG has to have a very low water dewpoint at pressure, the company added, because if the gas is saturated with water it can damage engines. The sensor system can be used to check dewpoint after the gas is dried to ensure that it is delivered at the right water content.
Talk the torque
Kistler Instruments’ new KiTorq torque measuring flange is suitable for electric motors and internal combustion engines. Consisting of a moving measuring unit and a static evaluation unit, the sensor can provide frequency, as well as analogue and digital signals, with an accuracy of 0.05 per cent; a speed sensor with 60 pulses per revolution is incorporated into the standard model.
Chesterfield-based Strain Solutions is using Micro-Epsilon’s thermoIMAGER TIM160 radiometric thermal-imaging camera to conduct the thermal non-destructive evaluation of materials, where it is used to detect the minute changes in temperature when parts are bent, fabricated or work hardened. The critical factors for selecting the TIM160 were its fast response rate and high thermal resolution per pixel, said Strain Solutions’ managing director Richard Greene. ‘We like the software’s ability to stream every frame to memory, which allows the full, uncompressed, raw data to be captured for post-processing at a later stage,’ he added.
Gill Sensors’ new ultrasonic fuel flowmeter has won the Autosport Engineering Best Technical Innovation and Graham Jones Innovation of the Year awards. Using ultrasonics to detect bidirectional flow rate to 0.3 per cent accuracy in real time, the meter uses no moving parts, unlike the conventional impeller flowmeter; this decreases pressure drop across the sensor, eliminating mechanical damping and allowing the measurement of high-frequency pulsating flows. Gill developed the sensor specifically for motorsport, making it resistant to aggressive ethanol blends.