sensors supplement


of potential problems, you have to test every product. Similarly, root cause analysis is applied to production and delivery activities to ensure that on-time delivery benefits from close scrutiny and continuous improvement. In addition to the quality control activities


outlined previously, Alphasense also conducts what is internally known as ‘killer testing’ on samples from a batch of sensors. This involves testing sensors under extreme conditions of heat and humidity – to the point of destruction. Again, this informs the continuous improvement process, but competitors’ sensors are also included; more often failing sooner or in higher volumes than Alphasense sensors.


Technical SupporT


It is common for a number of technical questions to arise during the integration of an Alphasense sensor into an instrument. Around 95 per cent of queries are responded to by the Alphasense sales and technical team within a working day, with the remainder being handled by the company’s senior scientists and academic par tners. This highlights the advantages of locating the head office and the factory in the same place. The most common queries relate to the


interfacing of sensors with different devices, but they can also address issues such as cross- sensitivities and environmental effects. Other issues may result from customers’ own testing. For example, they may be using an inappropriate sample line or an inadequate flow rate to test the sensor. Occasionally, misunderstanding may result


from an expectation that a low-cost electrochemical sensor should perform in the same way as a calibrated reference gas analyser. It is impor tant, therefore, to appreciate that whilst reference gas analysers can be expected to provide defensible monitoring data, they are substantially more expensive, both in terms of capital cost and service/calibration.


parTnerShipS inTo The FuTure


The health and safety market is relatively mature, but new applications are being developed by Alphasense and its par tners. For example, personal monitors are becoming wearable monitors as the sensors become smaller, lighter and less power hungry. As a result, personal monitoring is becoming less obtrusive; providing accurate measurements for example, of the air being breathed. In the environmental market, low-cost


sensors are dramatically increasing the number of monitoring points. They are not replacing reference gas analysers, but are providing supplementary data of tremendous value. For example, scientists from Cambridge University used Alphasense sensors to monitor air quality all over the city of Cambridge. They found that while the local reference station was recording


36


acceptable air quality values, many of the low-cost monitors showed readings for gases such as nitrogen dioxide several times higher than the European limit. This helps to identify air quality hot spots and measure the effects of remediation. Similar advantages in air quality monitoring were achieved by the Breathe London project which utilised Alphasense sensors, located strategically on lamp posts, buildings and street infrastructure in central London. Looking forward, Alphasense’s par tners are


increasingly exploiting the benefits of advances in communications and of real-time monitoring networks. As outlined earlier, small, low-power, low-cost sensors enable users to monitor air quality where it matters, rather than where planning permission can be obtained to install a reference monitoring station. However, the value of a network is greater than the sum of the individual monitors because networks enable the tracking and visualisation of pollution as it moves through an area. Coupled with wind monitoring data, this also helps to identify the sources of pollution. Such networks are not necessarily designed to measure absolute, legally-defensible values. More impor tantly, they are looking to detect change. That might be change in air quality outside a school during drop-off, or change in air quality when a mitigation measure is implemented, or it might be a longer-term change; monitoring the


effects of pedestrianisation for example. Networks are also able to lower monitoring


uncer tainty because when one node repor ts significantly different data from the others, it may be due to a local source of pollution or an error, which can be checked. The quality of data from networks can be assured by co- locating a node with a reference station or, if that is not possible, some users locate one of the nodes close to a large expanse of water to help establish a value that is close to zero in the early hours of a Sunday as an example. Developments in low-cost sensors are also


enabling citizen science; smaller cheaper sensors make it easier for citizens to conduct their own monitoring, using the IoT to contribute to a central data management facility. Looking forward, the current trend in


developments will continue with sensors that are smaller, more sensitive, use less power, have less interference, measure wider ranges etc. However, the most remarkable developments will be in sensor and network intelligence. Automated monitoring systems will track the health status of sensors and networks will be able to calibrate themselves. In summary, there are many factors that


should be taken into consideration when choosing a sensor manufacturer to par tner with, but whilst cost is impor tant; sensor quality, reliability and suppor t are more so.


Alphasense www.alphasense.com August 2021 Instrumentation Monthly


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