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Humidity and temperature measurement
Temperature and humidity represent two of the most commonly measured parameters whether for industrial processes, building management and performance or critical parameter monitoring inhealthcare and pharmaceuticals. The emergence of wireless sensor networks is opening up a whole new area of opportunity for such measurements by allowing cost effective real time continuous monitoring, access to measurements unreachableusing wired or manual methods and flexibility in reconfiguring an installation to allow optimum sensor point location.
What is a wireless sensor network ?
A wireless sensor network (WSN) is a wireless network consisting of distributed autonomous devices using sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants, at different locations. In addition to one or more sensors, each node in a sensor network is typically equipped with a radio transceiver or other wireless communications device, a small microcontroller, and an energy source, usually a battery.
A sensor network normally constitutes a wireless ad-hoc (mesh) network, meaning that each sensor supports a multi-hop routing algorithm (data may travel along various paths through the network to its desired destination).The applications for WSNs are many and varied. They are used in commercial and industrial applications to monitor data that would be difficult or expensive to monitor using wired sensors. They could be deployed in wilderness areas, where they would remain for many years (monitoring some environmental variables) without the need to recharge/replace their power supplies. They could form a perimeter about a property and monitor the progression of intruders (passing information from one node to the next).
Limitations of wired and existing wireless solutions
Studies show that up to 90% of actionable process and environmental data remains uncollected. Wired monitoring systems are expensive and unrealistic in challenging physical environments, and manual monitoring has proven simply to be cost-prohibitive.
There are a number of traditional wireless solutions which fall into the category of point-to-point or point-to-multipoint. The reliability of these networks is set by the quality of the radio link between the central access point and each endpoint. In industrial settings it can be hard to find a location for an access point that provides dependable communications with each endpoint. Moving an access point to improve communications with one endpoint will often degrade communications with other endpoints.
Temperature measurement
Real-time temperature monitoring of work-in-process (WIP) inventory or of stages in a manufacturing process provides continual insight and information about operations that otherwise could not have been obtained. Maintaining tight temperature controls and streamlining compliance reporting is vital to optimising the output of processes and minimising costs. Wireless temperature monitoring solutions can reliably and simply help meet all monitoring and record-keeping objectives. With capability from -100°C to +540°C with wireless Pt100 sensing nodes to over 1000°C with wireless thermocouple transmitters, few temperature monitoring requirements cannot be met.
Monitor inventory in storage and work-in-process
Manual ‘spot checking’ of product temperatures is costly, insufficient and prone to inaccuracies – a wireless temperature monitoring solution can provide the precise temperature of work-in-process and inventory at all times, allowing action to be taken immediately when required and increasing overall throughput and yield.
Improve process efficiencies – Monitor process parameters
Whether monitoring refrigerators and incubators in pharmaceutical manufacturing or the coolant temperature in an arc-furnace, having a real-time view into processes will only lead to enhanced optimisation, fewer lost or destroyed batches and greater overall manufacturing efficiencies.
Reduce compliance costs and risks -s Produce accurate reports
Outright failure to comply with internally or externally mandated regulations is not an option and mistakes in compliance record keeping can bring about costly fines and penalties. A solution that offers real-time temperature monitoring can not only eliminate error-prone manual data-entry and record-keeping, but also can generate alerts via email or pager as process temperatures exceed pre-defined specifications.
Sensors
A wide range of wireless temperature sensors can be used to meet specific needs – from spring-loaded RTDs for metal coil temperature monitoring to solution-immersed RTDs for pharmaceutical monitoring – due to the flexibility of the wireless sensing nodes a wide range of Pt100 and thermocouple sensors offered by established suppliers manufacturers can be employed.
Whilst the focus here is on use of existing sensor with wireless nodes the freedom that wireless provides in terms of access to previously inaccessible sensing points has given rise to the demand for sensors which can withstand the environment that is to be monitored whether it is the high temperature inside a jet engine compressor or the environmental conditions in a farmers field.
Humidity Monitoring
Humidity monitoring is an essential requirement in many industries ranging from food quality monitoring to environmental conditions in computer data centres. Although these are widely differing applications the basic need to have continuous, flexible monitoring applies.
Example temperature and humidity monitoring applications include :
- Monitoring aluminium coil cooling
- Monitoring steel melting arc-furnace cooling jackets
- Refrigerator and incubator monitoring for FDA compliance in manufacturing and test labs
- Monitoring cooling processes for baked goods
- Temperature control for meat-packing plant
- Electricity sub-station monitoring
Application examples
Heavy industry
An aluminium company has been a state-of-the-art manufacturer of aluminium sheet products in what is a commodity business since 1983. Their products include the fabrication of rigid container sheet, building products, automotive sheet, distributor sheet, and food can stock.
The customer’s manufacturing process takes raw aluminium billets and uses a cold rolling process to produce rolled aluminium goods. Rolling process technology is straightforward and provides little opportunity for improvement or optimisation.
Cooling stations are required to let the metal cool to 100 degrees after being heated to 225 degrees as a result of the rolling process. A cooling area is set up in the plant with an area about the size of a football field. An overhead crane operator manually monitors the temperature of about 100 rolls to determine when they are cool enough to move.
A meaningful throughput bottleneck was identified at the cooling station as the existing temperature measurement process required the crane operator to climb down from the crane regularly and perform direct measurements on the rolls.
A wireless temperature monitoring system was deployed in the plant, which automatically monitors the temperature of rolls in the cooling rack every minute. The data is wirelessly transmitted to a computer in the cab of the overhead crane. The operator can access the temperature information, and move the materials when the correct temperature is reached, thus eliminating the need to make manual measurements.
The customer has increased its plant throughput by 6 million pounds of rolled aluminium per year and its payback on the system was 3 months.
Computer data centre
With the increasing rack density of computing power and the introduction of technologies such as Power-over-Ethernet the environmental management challenges for data centre operations are getting increasingly difficult. Flexible and reliable environmental monitoring and control are crucial to give data centre managers the data they need to ensure smooth running. To ensure smooth running requires close control of temperature, humidity, wetness and airflow.
The power demands of newer high density computing equipment and the need to keep them cool are growing exponentially. This is causing major problems in terms of power supply capacity and environmental concerns. There is growing awareness of the need to improve monitoring in data centres to help identify hot spots where cooling is most critical. By directing air flow more effectively better use can be made of the existing cooling capacity. One key difficulty has been the lack of enough flexible temperature monitoring points in the facility to check performance in detail and raise alerts when hot spots arise. Traditional wired approaches can be too expensive and inflexible.
To solve this problem a wireless sensor mesh network can be used which is easy and quick to install with minimal disruption and allows monitoring points to be moved around and added without having to re-commission the whole network. Data collected by the sensors is fed back to a data analysis application which can be configured to raise alarms when limits are exceeded as well as logging the temperature and humidity data for further analysis. Alternatively, data from the wireless system can easily be interfaced with existing infrastructure monitoring systems if required.
Hospital pharmacy monitoring
The wireless system monitors ambient temperature and refrigerator temperatures in production, packing and storage areas. The wireless system is deployed in two physically dispersed areas. The pharmacy had a problem in that an important storage building was in a remote location over 350m away on the other side of the hospital site. In addition the main hospital buildings rise up on a hill in between the two locations making any ‘line of sight’ wireless solution impossible to implement. Due to cost and ongoing hospital improvement works a wired system was not an option. In this application a multi-hop wireless solution was the only viable solution.
By mounting mesh repeater nodes in weatherproof housings on the apex of two intervening buildings the remote store temperature data is relayed back to the main pharmacy system. The software provides fully compliant and easy-to-manage system and alarm status information. The application specifically takes advantage of some of the key benefits of wireless mesh networks – speed of installation, flexibility in use to accommodate difficult local conditions, lower installed cost and easy expansion to accommodate future needs. In this case it was the only practical way to get the job done.
Composting plant
With recycling and efficient management of compostable waste high on the agenda the technology being used to meet these challenges is evolving quickly.
One innovative company in the UK is processing the waste through large rotating drums to achieve the desired results. To ensure proper sterilisation of the finished compost the temperature and humidity of the drum contents in the final stage must be monitored continuously and an auditable data set maintained. Many methods had been tried but were unreliable and performed poorly. Following a very successful site trial using industrial mesh networking devices the company ordered a multi-point system to cover both the rotating sterilising drums and the plant ambient conditions.
With faultless data capture performance and reliability, IP66 housings and easy integration into the plant monitoring system, the system exactly meets this company’s challenging requirements.
Conclusion
The emergence of wireless sensor networks provides a wealth of opportunities to monitor temperature and humidity in previously inaccessible locations or to automate manual processes without the high cost of installing wiring which traditional solutions require.
Published: 10th Dec 2008 in AWE International
