A relative humidity sensor for any application?

As we continue to measure relative humidity in more and more environments with ever increasing accuracy demands, we are pushing the humble capacitive humidity sensor into new realms.

Accuracy, drift, operating range and chemical resistance are key challenges for the relative humidity sensor industry. Our sensor experts work hard to develop new polymers and construction methods to ensure the best performance. At the same time advanced electronics and probe housings enable digital calibration and complex temperature corrections to further increase accuracy and performance. A final and often neglected part of ensuring a relative humidity probes performance is its filter. The correct filter ensures fast response and environmental protection. Filters also offer mechanical protection and eliminate damage caused by extreme airflow.

However understanding why sensors fail is often difficult to predict or understand. In many cases the chemicals and contaminants that sensors are exposed to are unknown. In these situations often selecting the best sensor can only be achieved through mutual relationships built around quality support and service.

In the UK we have worked closely with many customers and in combination with our Swiss technical divisions to select and develop solutions for some highly aggressive and challenging environments. Some of these projects are examined below in more detail.

Hydrogen peroxide vapour sterilisation.

– Hydrogen peroxide vapour is used to chemically sterilise environments and products by generating a vapour of toxic Hydrogen Peroxide. When the humidity reaches the dew point of the surfaces condensation forms sterilising all surfaces. However the chemicals are also highly aggressive to humidity sensors and constant cycles of saturation worsen the effects.

– Making use of Rotronic’s specifically designed H2O2 resistant sensor as well as additional conformal coating to protect exposed connections in further combination with improved customer understanding around handling and storage, has resulted in a solution that has exceeded customer expectations. Importantly, whilst this was not achieved first time around, through a partnership driven towards the end goal we achieved success.

Chemical damage Chemical degradation on the sensor surface
Commercial composting.

– Accelerated commercial composting is an impressive sight to see. The chemical and biological processes occurring are complex and surprisingly aggressive. The wrong materials can literally become part of the final compost if you are not careful. Chemically resistant sensors help to provide some longevity to instruments but one of the key areas requiring extra attention is around cable and filter design. Modifying a standard industrial grade sensor with bio-resilient cables ensures the probes are not eaten alive!

Highly accelerated life testing.

– As a supplier to many chamber manufacturers and companies providing testing services this is a common application. Chambers are cycled between high and low temperatures and humidities to simulate many years aging over a short period of time. The same effects are happening to the humidity sensor – critical for the control or validation of the chamber conditions. Using industrial sensors with electronics isolated away from chamber space reduces the effects of the sudden changes. But also care taken placing the sensor away from humidity outlets and well into the chamber to avoid stem conduction all help to avoid the sensor becoming saturated as temperature cycle – which is one of the main causes for corrosion and drift. Finally, careful filter maintenance is always important.

Swimming pool monitoring and control.

– Our featured image shows chemical formation on a non-Rotronic sensors connections. Rotronic uses inert metals in the sensor design to reduce the re-activity of the sensor to chemicals in the environments. Swimming pools have a mix of high humidity, chemicals and high temperatures which work together to corrode unprotected electronics. Sensor location is key to avoid direct exposure to spray and neat chemicals. Suitable filters and if required chemical resistant sensors have proven highly successful where other instruments have failed.

So you can see not all applications are easy and we have not even begun to explore the basic issues of accurate measurement and control present with every humidity sensor installation. However our belief and aim is that through communication and partnerships we can provide the right product to ensure the desired mix of performance, resilience and price for our customers – it’s not easy but it makes life interesting!

Dr. Jeremy Wingate

Rotronic UK

Reducing UKAS calibration uncertainties

At Rotronic UK our UKAS laboratory have worked hard to make a name for itself in high quality calibrations and service. Thanks to constant improvements in measurement procedures the laboratory is growing into one of the most advanced commercial facilities in this specialised field. The ISO 17025 accredited calibration of humidity and temperature sensors and dew point instruments confirms performance and is increasingly a requirement of industry regulations and company quality management systems. The UKAS laboratory at Rotronic UK has spent the last two years increasing confidence in the calibrations performed and as a consequence lowering the Calibration and Measurement Capability (CMC) of the laboratory. Significant improvements have been made in the measurement procedures for dew point and temperature in air, enabling the following UKAS Accredited CMCs:

Dew/Frost point measurement (°Cdp/fp) • -60 to -40 °Cfp; uncertainty ±0.14 °Cfp • -40 °Cfp to +60 °Cdp; uncertainty ±0.11 °Cdp • +60 °Cdp to 70 °Cdp; uncertainty ±0.12 °Cdp

Temperature in air/ °C • -60 °C to 0 °C; uncertainty ±0.08 °C to 0.06 °C • 0 °C to +70 °C; uncertainty ±0.05 °C • +70 °C to +150 °C; uncertainty ±0.07 °C to 0.16 °C

Relative Humidity (RH)/%rh In the laboratory RH is derived from vapour pressure formulations. Improvements in dew point and temperature in air CMCs therefore affect the RH CMCs profoundly. The improvement lies in the range 0 to 70 °C; in the worst case RH CMC is ±1.0 %rh. In all parts of the HC2-S specified range covered by the accreditation the CMC is better than the specification of the probe. This is the first time this has been achieved. With the new temperature in air calibration range (-60 °C to +150 °C) and new dew/frost point calibration range (-60 °Cdp and up to +70 °Cdp) the laboratory’s RH calibration range has been extended up to 70 °C and 98 %rh. For example, at the new upper limit of 70 °C/98 %rh the CMC is ±0.6%rh and with these levels of calibration measurement uncertainty and range of accredited calibration services the purpose-built laboratory is one of the most advanced commercial facilities in the world.

Dr. Jeremy Wingate
Rotronic UK

New states of matter… making a mess of my slide pack

How many states of matter are there?… Hold that answer, first I’ll explain why…

We regularly provide formal and informal training, in fact it is something we  feel differentiates us, helps us learn and is a great  way to keep in contact with the industry. With a team including ex-NPL staff, Oxford graduates, PhDs, one of the best UKAS laboratories in Europe and years of combined experience in the fields of humidity, dew point and temperature  we feel we are well placed to offer these expertise.

One of the first things we discuss when learning about the principles of humidity, are the states of matter. It s vital to understand solids, liquids and gases before we can go on to vapour pressure, dew point, frost point and triple points etc.

I have yet to find someone who doesn’t know the three states but this light introduction acts as a good starting point to the deeper subject.

However, I am regularly corrected that plasma is the forth state of matter (not relevant for our discussions as such but still valid all the same). So I have corrected my slides accordingly.

What happened next, I struggled to believe at first when I was told… Apparently within chickens we can find another state of matter!! Seriously… chickens. To be exact the chickens eyeball. It is called ‘disordered hyperuniformity’ and in simple terms it is a state that has some crystal like properties and some liquid like properties.

A state of chicken
A state of chicken; Courtesy of Joseph Corbo and Timothy Lau, Washington University in St. Louis

The  arrangement of cells was discovered by researchers at  Princeton University and Washington University in St. Louis. Full details can be found here on the Princeton site. http://www.princeton.edu/main/news/archive/S39/32/02E70/

What next I thought, and where best to look but wikipedia… A quick search highlights that the four fundamental states of matter are just the tip of the iceberg.

There are; Non-classical states, Low-temperature states, High-energy states, Very high energy states … the list goes on and this is just a glance at wikipedia!

The latest (unless another has just been discovered) is the quantum droplet and apart from being the most recently discovered comes with a great picture.

Quantum Droplet
Quantum Droplet; Credit: Baxley/JILA

Part particle, part liquid, it is termed a “quasiparticle”. I wont attempt to explain it here but if you are interested is it nicely explained on the Scientific American website, which includes a link to the original Nature paper. http://www.scientificamerican.com/article/dropleton-quantum-droplet-quasiparticle/

So back to the question; how many states of matter are there? I will stick to answering that with” there are four fundamental states of matter…” I think the rest we’ll leave out of our training courses for now!

Dr. Jeremy Wingate
Rotronic UK

Looking internally for the ways forward

We tend to spend most of our time looking out to the industry and marketplace for the future trends and next opportunities. However, last week the staff at Rotronic UK spent some useful time reflecting on our recent history, current methods of working and how to develop ourselves for the future – whatever it maybe.

In the sessions, led by our in house project and change manager we were encouraged to explore our ideal future both personally and for the UK arm of Rotronic. Sessions were run for our service and calibration teams and separately for sales and admin teams.  The sessions provided a useful opportunity to learn from each other and better understand the internal processes we all take for granted. As well as providing time to explore what the key issues are ad what we would like to see in the future.

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Some clear areas were identified for the future but not so broad that we will be unable to tackle them and report back on progress in the coming weeks and months. Our change guru is now digesting the sessions and we will begin a 3 – 6 month period of putting into practice and reflecting on the new goals and actions we have collectively embraced.

As a small team in the UK working in within a complex field and highly diverse marketplaces it is important to maximise the internal knowledge and skills we have. In addition, we are all focused towards precision measurement and quality service; things that cannot be achieved without a consistent effort and shared values.

There is always room for improvement but hopefully we are remaining open-minded and have a positive drive for the future.

Some of the new ventures and changes will be important for our customers and partners… we will keep you posted!!

Dr. Jeremy Wingate
Rotronic UK

CO2 sensors for Schools – Rotronic Success Story

Rotronic CO2 sensors installed in Högalidskolan school in Stockholm in August 2012

Högalidsskolan school, opened in 1921, is located on the beautiful hills of Southern Stockholm and is home to one of the so-called ”palace” schools. The building consists of the three blocks, A, B and
C. Whereas some years ago the school had to cater for the needs of 1100 (later 900) pupils between 6 and 16, this primary school now  hosts 660 pupils, since their numbers were reduced due to a planned
renovation costing 167 MSEK.

In a meeting with headmaster Mattias Boström we discussed the importance of the indoor climate in the school. Old buildings generally have a natural draft as ventilation, but energy savings and the call for a more comfortable indoor temperature during wintertime resulted in less natural draft and, as a consequence, higher CO2 emissions.

Schools have long ago introduced ventilation routines, but these are difficult to stick to especially during the winter season because ventilation means cooling. In order to quickly reach acceptable CO2 levels, the consultant fi rm MAKAB recommended the installation of CO2 sensors to measure proper CO2 values in all areas where pupils are working.

After the installation of stand-alone CO2 sensors (no regulation system needed) in all 36 classrooms, it can be seen that in some rooms the CO2 level quickly crosses the threshold of 1000 ppm. Now, teachers and pupils are regularly checking whether the red LEDs on the sensors are lit to indicate that the 1000 ppm limit is exceeded.

Sometimes it is impossible to vacate the room immediately for CO2 remediation, but the sensor also displays the actual CO2 value and rate of change and thus is very valuable. The response from teachers and pupils so far has been very positive and shows that the CO2 sensor is a practical tool for keeping the indoor climate at
an acceptable quality.

After the renovation, the building will be equipped entirely with a new ventilation system with an advanced filtering to reduce particles in the air. But there will still remain a need to regularly check on the CO2, temperature and humidity levels.

Dr. Jeremy Wingate
Rotronic UK

Water Activity and Moisture Content… What is the difference?

Water Activity and Moisture Content are two very different parameters which are often confused and misused.

In a meeting today with a manufacturer of coffee capsules and pods, these differences were critical.

– Their  whole bean supplier provided each batch with  moisture content readings.

– However customers buying the coffee capsules and pods were asking for detailed water activity measurements for each batch. In addition for BRC Food Safety and shelf life validation of the final product, water activity was required.

Why are there these differences and can one measurement be used to determine both values?

Moisture content is probably the simplest value to understand.  It is simply the quantity of water contained in a material. Traditionally measured through loss of weight on drying. This method raises some issues, depending on the drying temperature you may not remove all water or may also remove other non water compounds.

More modern methods resolve these issues and use infra red absorption. This way the water content is directly measured, the method is non-destructive and far quicker. 

Moisture content is typically given as a percentage in terms of weight.

Infrared Moisture Measurement
Infrared Moisture Measurement – A measure of moisture content through IR adsorption

 

Water Activity (aW) is a measure of the free water in a sample, and ranges between 0…1.  Pure water would have an aW of 1.0. As water activity measures the ‘free’ or ‘active’ water in a sample it is more relevant to growth of organisms, chemical processes, enzyme activity and physical parameters like size and clumping as these are only effected by the water that can be chemically interacted with. Interestingly Water Activity is related to Moisture Content but it is product and temperature specific.

aW… is more relevant to growth of organisms, chemical processes, enzyme activity and physical parameters

Rotronic HygroLab
Rotronic HygroLab Water Activity Measurement – A measure of the ‘free’ water

What is free water? Water can be bound in materials in two broad ways.

1. Chemically Bound Water. Is bound so tightly that it cannot be utilised by bacteria, enzymes etc. It can be removed  through high temperature heating.

2. Free Water. Is bound through weak bonds, structural diffusion, capillary condensation and surface binding. It can be utilised by bacteria and can exchange with the environment, it is also removed through heating.

For instance a whole grape would have the same moisture content as two halves of the same grape. However the aW would be far lower in a whole grape as much of the water is bound inside the grape skin and only made free when the grape is cut in half!

Take a look at our Water Activity white paper or our Knowledge base for more information.

Introduction to Water Activity

Water Activity White Paper and Product Overview

Application note F004 – Water activity in the food industry

 

CO2… what’s it all about

In 2011 Rotronic expanded its range of measurement parameters to include Carbon Dioxide gas measurements and now provides a range of transmitters, loggers, large panel displays and handhelds.

CO2 is becoming an increasing important gas to monitor and control for several reasons. This post will explore some of the science, applications and future trends for this ubiquitous gas…

CO2 and Human Health

CO2 can seriously effect human health. Figure 1 shows this relationship and the possible implications.

Effects of CO2Figure 1 – CO2 levels 

Fresh air typically has around 350-450 ppm CO2 however in exhaled air levels increase to around 38,000 – 50,000ppm! Metabolism and exercise can increase the rate of CO2 production.

In the UK we typically have poorly ventilated buildings in addition with increasing drives for energy efficiency, buildings are becoming more air tight and if not managed carefully air change rates can be further reduced.  To demonstrate how quickly CO2 can rise through poor ventilation Figure 2 shows a log of CO2, Temperature and Humidity overnight in my bedroom! You can see levels quickly increase to >2400ppm. The rapid drop is due to an opened window

CO2 record
Figure 2 – CO2 levels overnight (CO2 in ppm)

 

This direct relationship between CO2 and human occupation is a useful tool. It allows building management systems to control ventilation rates precisely to the levels required based on occupation rates. This can significantly reduce energy usage especially with the incorporation of variable speed fans.

Recent projects at Google’s Irish Headquarters and the Apple offices in Cork have used these principles to save energy and improve working conditions for their staff and achieve additional LEED points.

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Regulations are increasing for CO2 monitoring. Areas of interest especially we are seeing include Schools, Catering Areas and Car Parks.

If you have any queries relating to CO2 let us know!

Dr. Jeremy Wingate
Rotronic UK