Sensors & transducers
speeds can generate high acceleration vibration at high frequencies (20g at 1kHz for example). These represent a very small vibration displacement (few um) but have a large impact on the transducer as the high charge output from the piezo-ceramic material causes saturation in the integration circuitry and subsequently an erroneous reading. The sensors primary purpose is to
measure vibration at the machine running speed, typically in the range of 10Hz to 50Hz and to avoid spurious readings its important there are no low frequency structural movements (<3Hz) present on the machine. Since the sensor has limited filtering capabilities, a low frequency event can have a significantly large impact on the measured reading due to the inherent integration in the device (higher gain at lower frequencies). This type of issue is rare, but is a reminder
to ensure the transducer is well mounted and best practice applied to the routing of the connecting cable. Sensonics has recognised the need for a
sensor which can meet the demands of protecting smaller machinery such as fans and pumps which can be utilised on a wide range of plant with reduced sensitivity to auxiliary systems. The VEL/GDC is an electro dynamic sensor providing a 4-20mA current sink output proportional to velocity vibration and offers the advantage of offering double isolation in conjunction with a low impedance circuit making it suitable for high noise environments. Due to the electro dynamic nature of the sensor assembly both high and low frequency events are filtered mechanically and since no integration is required the arrangement is immune to the saturation seen in piezoelectric devices.
Sensonics
www.sensonics.co.uk Indoor AIr QuAlIty And CoronAvIrus
intense discussion. Since airborne transmission of COVID-19 became a known infection route, experts worldwide have been working on approaches to minimise the risk of indoor viral spread that can potentially be exacerbated by heating ventilation and air conditioning (HVAC) systems. This is because the virus can persist on respiratory droplets or aerosols that can either be transported to different areas by air currents and survive in environments with insufficient air refresh rates. Many large buildings, from offices to schools
W
and hospitals, make use of centralised HVAC systems. This means that the majority of the key infrastructure can be housed in a single, localised area, making for easier maintenance and monitoring. At present, most large HVAC systems have some type of monitoring system, both as a way of checking environmental conditions like temperature but also for monitoring air quality. Maintaining good air quality is important
for building and environmental health. As well as being implicated in reducing employee productivity, poor indoor air quality can often be used as an indicator for a working environment with a high risk of airborne COVID-19 spread. For indoor environments, the World Health Organization (WHO) recommends regular exchanges of up to six times an hour, depending on room size and occupancy, as a way of reducing indoor COVID-19 transmission risks. For sealed buildings, air exchange can only
be performed by the HVAC system. If no air exchange occurs in a room, carbon dioxide levels will rise at a rate dependent on the occupancy of the room. Therefore, carbon dioxide levels are often used as a proxy of ‘building health’, with excess carbon dioxide levels being considered one of the signs of poor air quality. A very recent study, still awaiting peer review, has shown that carbon dioxide levels are also a good proxy for COVID-19 infection risk in an area.
Gas MonitorinG for BuildinG HealtH
Gas monitoring devices are an essential part of creating responsive, active HVAC systems that can offer up to 19 per cent cost efficiency savings due to their enhanced energy efficiency. They can be used to check for leaks of gases such as carbon monoxide for safety purposes and to assess carbon dioxide levels as a means of monitoring air quality. This is important for not just minimising COVID-19 transmission, but also as a means of avoiding ‘Sick Building Syndrome,’ which is thought to be related to high carbon dioxide concentrations.
Instrumentation Monthly February 2021
ith the global COVID-19 pandemic continuing, indoor air quality remains a topic of
Current best practice for minimising indoor
COVID-19 transmission requires a multi- pronged strategy of reducing building occupancy, encouraging social distancing, and increased ventilation. Inclusion of filters in HVAC systems can help, such as MERV 13, as can air cleaners like HEPA, GUV, etc., and ventilation rates should meet those outlined in the ASHRAE 62.1 standards, with air flushes between occupancies. Edinburgh Sensors offers a range of
nondispersive infrared (NDIR) based gas sensors for carbon dioxide monitoring. Molecules such as carbon dioxide absorb infrared light very strongly, and so NDIR sensors can detect even very small concentrations of such gases. This is why two of Edinburgh Sensors’ most popular OEM sensors for carbon dioxide detection, the Gascard NG, and Guardian NG, can detect concentrations in the range of 0 – 100 per cent. Real-time data collection and monitoring is
key for ensuring good air quality and reducing COVID-19 transmission risk and so all of Edinburgh Sensors’ monitors offer several options for integration into HVAC control networks. The Gascard NG has an onboard R232 connection as well as options for TCIP/IP communications protocol. The sensor comes with free data logging software that simply requires an additional cable to connect the sensor to the computer. The Guardian NG offers measurement
accuracy of ± two per cent and zero stability, which is ± two per cent of the range (over 12 months). It has a detection range of 30 m and is an easy-to-install wall-mounted device. The IP54-rated enclosure protects the sensor from dust and water ingress. While it is possible to interface the Guardian NG with external logging systems, the device comes with an interface that can be used to directly view historical readings as well as a built-in alarm system that can be programmed to alert building occupants when carbon dioxide levels exceed a given value. Edinburgh Sensors can provide technical
advice and support on the best gas monitoring solution for your existing HVAC systems and how to best integrate them for optimal measurements of indoor air quality.
Edinburgh Sensors
edinburghsensors.com
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