# How do we measure water activity?

### What is water activity?

As described in a previous blog (Water Activity and Moisture Content: What is the Difference?) water activity is the the measurement of the free water in a substance. The free water is any water that is not chemically bound to anything and is free to move in and out of a sample. The ability of the water to move in such a way is what allows us to measure water activity.

### Partial pressure of water vapour.

Air is made up of a mixture of gasses. Each of the gasses is responsible for part of the overall air pressure. For example, at 23 °C / 35 %rh the water vapour in the air is responsible for just under 1% of the overall air pressure – around 9.8 hPa is exerted by water vapour out of 1013.2 hPa for the total mixture of gasses. The partial pressure of water vapour is in a constant state of flux and is influenced by water moving in and out of any materials exposed to the air. The air can only hold so much water. At 23 °C, the partial pressure of water vapour can only go as high as 28.1 hPa (approximately 2.8%) before the air is saturated.

### What is diffusion?

Diffusion is the movement of particles of liquid or gas from an area of high concentration to an area of lower concentration. The particles will continue to move until an equilibrium is reached and the concentration is consistent and stable across the whole available space. In terms of water vapour, think of drying wet clothes. When you hang wet cloths to dry them, the concentration of water in the clothes is much higher than the concentration in the air around them. Because the water in the clothes is not chemically bonded to the material, it is able to move out of the clothes into the air around them until the amount of water in the air is the same as the amount in the fabric, at which point an equilibrium has been reached. This will increase the overall partial pressure of water vapour in the air. When you hang your clothes outside on a dry day, there is plenty of space for the water to move into, but if you hang them in a small room you will notice the humidity in that room increases, possibly even to a point where the clothes will not dry properly. It is this property that allows us to measure water activity.

### What has drying clothes got to do with measuring water activity?

In the same way that water will move in and out of your clothes, it will also move in and out of everything else to a different degree. If you cut an apple in half and leave it to one side, you will notice that it will dry out. This is because all of the free water in the apple is escaping into the air around it. Again, this will continue to happen until moisture levels are the same in the air around the apple as in the apple. In a large room this will essentially mean that most of the water will eventually leave the apple. If however, you were to put the sliced apple into a small container you will notice that it does not dry out in the same way. This is because the air space is much smaller, so it takes much less water from the apple to fill the air until an equilibrium is reached. If you were to measure the relative humidity in the container, you would notice that it will quickly increase before levelling off. Divide this final relative humidity by 100, and you have a good idea of the water activity of the slice of apple.

### How does this apply to water activity measurements in industry?

Generally, a water activity measurement device will simply be made of some kind of relative humidity sensor and a small, sealed sample container. When you put a sample into the container, water will move in and out of the sample until an equilibrium is reached, and the sensor will read the relative humidity. Once the temperature and relative humidity are stable, the machine will give its final reading.

### What has temperature got to do with it?

Just as temperature is a key influencing factor on relative humidity, it can also effect water activity. The exact effect that a change in temperature has on the water activity of a specific sample is impossible to know without testing the sample at a number of different temperatures. As such, when measuring water activity it is vital to make sure that sample temperature is consistent and stable.

### The scale of water activity.

Water activity is measured on a scale of 0 to 1. A water activity of 1 would occur if you measured absolutely pure water, almost an impossibility – The air above completely pure water will have a relative humidity of 100%. To get a water activity of 0, you would need to measure something with no water at all. Given that there is always water in the air, the likelihood is that if something has been exposed to the air it will contain at least some water, so a water activity of 0 is again more or less impossible.

If you have any questions about anything in this blog, or would like to discuss water activity measurement in general and how it can be applied, please don’t hesitate to give us a call on 01293 571000 or email instruments@rotronic.co.uk.

Rotronic UK

# Rotronic Monitoring System integration. Pulling data into your systems

Data Integration is Key

Data integration is one of the primary requirements for many of our customers. I have previously discussed how RMS easily supports the integration of external data, but this posts takes a look at how RMS allows you the export data.

Of course RMS provides excellent graphing, statics and reporting as part of its core functionality, however here we are discussing the tools that will more likely be used for Machine to Machine (M2M) integration.

Machine to Machine (M2M) integration is absolutely key as data is increasingly being used for different purposes through businesses. So whilst RMS provides a highly secure and configurable platform for monitoring and alarming there are many weird and wonderful functions that it cannot provide. In this case we need to pull the data out and use it elsewhere.

Getting Data out of RMS

RMS is an SQL based system so we could of course query the SQL directly however there are many limitations with this approach especially security. Also via our RMS cloud platform absolutely no direct SQL access is available to end users.

Instead RMS supports a RESTful API, we’ll use a simple example to go through the basic steps.

RMS GET API

As before I’ll use some Python scripts in this example but if you prefer, POSTMAN is a great tool for testing these types of APIs.

Let’s breakdown the steps.

2. Use Token to request specific data
3. Use data as required

Step 1 – Request a Token.

For security reasons you cannot simply send a request and get whatever data you desire. First you must request a token from RMS. The token is linked to a user account and will only allow the data that is visible by that user to be accessed. When requesting a token you can also specify how long it is valid for. The maximum length is 30 days.

import json
import requests

url = ‘https://rms.rotronic.com/RMS/API/RequestToken.ashx&#8217;
headers = {‘Content-Type’ : ‘Application/json’, ‘Expect’ : ‘100-continue’, ‘Connnection’ : ‘Close’, ‘Host’ : ‘rms.rotronic.com’}

UsrID = “1”
User= “Jeremy”
PW = “########”
Exp = “30”

token = token.get(‘Token’)

The above request with suitable credentials will return something along these lines.

{‘UserId’: 1, ‘RequestType’: ‘DataHistory’, ‘Token’: ‘jUsTaNeXaMpLe_HRwOi8vd3d3LnczLm9yZy8yMDAxLzA0L3htbGRzaWctbW9yZSNobWFjLXNoYTI1NiIsInR5cCI6IkpXVCJ9.eyJVc2VySWQiOjM5MzEsIlJlcXVlc3RUeXBlIjoiRGF0YUhpc3RvcnkiLCJFeHBpcmF0aW9uIjoiMjAxOS0wNC0wM1QxNToyMzoyMC44MTgwODM4WiJ9.rtHHKvrE-7jnMNHUGazso_jUsTaNeXaMpLe’, ‘Status’: ‘OK’}

The API token being the jumble of text above. With the token in hand we can proceed with requesting our data.

Step 2 – Request Data

To request data we need the measuring point ID for the data we need which can be obtained from the RMS interface (every measured parameter has a unique ID within RMS that will not change and cannot be reused). We also define the From and To ranges as well as the number of values we wish to obtain (Count).

import json
import requests

url = ‘https://rms.rotronic.com/RMS/API/DataHistory.ashx&#8217;
headers = {‘Content-Type’ : ‘Application/json’, ‘Expect’ : ‘100-continue’, ‘Connnection’ : ‘Close’, ‘Host’ : ‘rms.rotronic.com’}

MPTID = “20”
From = “2019-03-04T08:00:00”
To = “2019-03-04T09:00:00”
Count = “10”
Token = “token from step 1”

post_payload = {‘ID’: MPTID,’From’: From,’To’:To,’Count’:Count,’Order’:’Asc’,’Token’: Token}
print (data)

The above request with suitable details will return something along these lines.

{‘Status’: ‘OK’, ‘ID’: 20, ‘Name’: ‘Humidity-18071604′, ‘Parameter’: ‘Humidity‘, ‘Unit’: ‘%rh‘, ‘Data’: [{‘Time’: ‘2019-03-04T08:00:14+01:00′, ‘Value’: ‘29.45%rh‘}, {‘Time’: ‘2019-03-04T08:05:14+01:00’, ‘Value’: ‘29.80%rh’}, {‘Time’: ‘2019-03-04T08:10:14+01:00’, ‘Value’: ‘29.61%rh’}, {‘Time’: ‘2019-03-04T08:15:14+01:00’, ‘Value’: ‘29.29%rh’}, {‘Time’: ‘2019-03-04T08:20:14+01:00’, ‘Value’: ‘29.80%rh’}]}

Step 3 – Use the data

So we have our data in JSON format from here it’s an easy step to chopping out the specific values and handing them over to some other code, machine or simply displaying them for yourself.

The flexibility of RMS is an important requirement for our customers especially those with existing systems. Using RMS as the central platform ensures precision measurements, secure and reliable data collection and easy access to data. Using our  APIs then allows this data to be utilised in wider business operations.

Customer examples using the API include

• Live temperature data included in packaging labels
• Automated calibration certificate generation using reference values from RMS
• Visualisation of RMS data on 3rd party software for building efficiency displays

Conclusion

This article focuses on our RESTful API however we have many other options for integration of data including relay output modules, analogue output modules, direct SQL connection. In addition our RMS-Integrator hardware offers direct communication with devices via MODBUS, SNMP and MySQL.

Dr Jeremy Wingate
Rotronic UK

# What is the latest monitoring system from Rotronic? A practical answer and a technical answer.

The Rotronic Monitoring System (RMS) has now been officially launched globally for 12 months and in use at some key clients for over two years.

RMS is a modern continuous monitoring system that embraces open architecture and interoperability as well as providing a compliant system for validated applications.

But how is this achieved and what exactly is RMS. There are two ways I find myself answering this…

• The technical answer – for IT project managers, system integrators and cyber security managers.
• The practical answer – for end users, project managers and smaller organisations.

### What is RMS – The Practical Answer…

The practical answer is more visible via our online demonstration (request guest access here) and via the details on our RMS satellite website.

In short RMS provides a modern and complete monitoring system with a detailed web interface. The system provides users with ease of access to data, reliable and manageable alarms and extensive reporting. Importantly RMS can support existing hardware and interact with other software/hardware platforms.

RMS can be provided as a hosted cloud service or using a traditional licence whereby the client installs the system on their servers (local or cloud).

In summary RMS provides amongst other things…

• Live interactive charts
• Full reporting and automated/scheduled report generation
• Complete event logging in line with GxP requirements
• Full alarming with logic and time schedules
• Email, phone, sms, relay and custom protocol alarm outputs
• Auto back fill and retrospective alarms (ideal for transport logging)
• Interactive layouts
• Complete user rights management
• Compliant to GxP designed around ease of validation

This slideshow requires JavaScript.

Core RMS hardware includes Ethernet, WiFi, industrial wireless and RS485 devices as well as full support for existing Rotronic devices, 3rd party analogue devices and 3rd party digital devices using any of the above interfaces. The below graphic outlines the wide range of options available.

### What is RMS – The Technical Answer…

Let’s now go a bit deeper. For many organisations once end-users approve of a system the challenge is getting the system approved and installed in line with wider corporate policies and security. So far we have found that in discussions with IT project managers and cyber security managers, RMS has met their requirements – usually much to the surprise of the end users who perhaps initially expect a protracted battle! Typically for larger more secure organisations software is required to be installed within their network rather than using the Rotronic Cloud service. Below we discuss the main elements of this type of RMS installation.

RMS has two core elements.

1. Webservice; This is software aspect of RMS. The webservice provides the interactive webpage to present data for end users and allow system configuration. The webservice also works in the background to interact with hardware and the database. Typically the webpage will be part of the local intranet with an address like rms.yourorganisation.com, optionally the webpage can also be made accessible from the internet outside your organisation (like our cloud service which is available at http://rms.rotronic.com/rms – request guest access to the demo system here). For the clients (end users) no special software or plugins are required just a standard web-browser.

More technically the RMS webservice is built around ASP.Net framework and runs under Windows IIS (internet information services). The webservice therefore requires a Windows Server (2008, 2012 or 2016). The RMS software can be run on a standard PC with IIS enabled but this is not usually advised except for specific applications.

A note on RMS hardware; All Rotronic hardware initiates communication with the webservice via port 80. For cloud applications this means only port 80 must be opened outbound to allow the devices to initiate outbound communications to the server. All gateways have standard IP configurations (DHCP or fixed).

2. SQL Database; The second part of the RMS is its database. All device, configuration, user and measured data is stored within a standard MS-SQL database. The database is accessed by the webservice to store and read data as required. An existing SQL server can be used if available otherwise SQL-Express is free to install.

More technically the RMS database requires Microsoft-SQL Express or higher, the database can be on the same server as the webservice or a separate machine.

As RMS is built around standard server based systems, there is full support for load balancing and failover, as such should a webserver or sql server fail a redundant/spare can take over. This is standard procedure for larger IT systems.

Some other technical points about RMS.

• No personal data stored outside SQL database (hardware only stores unique serial code, date, time and measured values – as such no private data passes between hardware and software).
• Webpage data is binary coded and authentication uses AES128 encryption.
• Key exchange uses diffie-hellman key alogrithm.
• 3rd party data / device support is possible via RESTful API or direct interaction with SQL database.

An overview of the RMS communication can be seen here.

For many projects clearly we go much deeper but hopefully this provides an overview. Our experience to date has shown that RMS is closely inline with what our clients expect in terms of operations and security. Further developments are always underway, lead by our customers and their requirements.

Dr Jeremy Wingate
Rotronic UK

# Rotronic training course schedule 2016

We are pleased to announce our latest training course schedule for 2016. Courses include in partnership with Dave Ayres from Benrhos Ltd our practical 3 day temperature, humidity and dew point calibration and measurement uncertainty courses. In addition, for those seeking greater depth we are running dedicated courses on measurement uncertainty and ISO 17025 run by Lawrie Cronin and Dave Ayres

### Temperature Humidity and Dew Point – Measurement, Calibration and Uncertainty

8th – 10th March :: 12th – 14th July :: 15th – 17th November
– Three day course at Rotronic UK offices and UKAS laboratory
– Practical applied knowledge and best practice
– Max 8 attendees to ensuring tailored content

### Measurement Uncertainty for Laboratories and Plant

6th – 7th September
– Two day course at Rotronic UK offices
– Detailed knowledge for laboratory owners or process managers

### Setting up and working with ISO17025

8th September
– One day course at Rotronic UK offices
– Ideal for ISO17025 lab managers or those looking to apply

# Friday Video! How to Monitor, Alarm & Report you conditions with Rotronic

Relax for five minutes with your morning coffee or tea  and let Dirk explain about our HW4 software!

# Highlights from the Rotronic ISM 2014

A fantastic view of the Swiss mountains complimented an exciting glimpse of the future at the Rotronic International Sales Meeting 2014 in the Swiss mountain village of Grindelwald.

The biennial Rotronic ISM brings together distributors and subsidiaries from the global Rotronic network (or family as it feels when we are all together!).

The week long meeting provides an invaluable opportunity to share experiences, projects, new ideas and product updates along with the showing off latest developments and future trends for the company. Aside from the formal workshops, training courses and meetings is the opportunity to informally explore new ventures and insights from around the world – as well as sharing a beer or two of course.

The growing range of new product launches from the Swiss HQ, combined with further developments from the UK’s R&D group based around the HygroGen technology highlights that the outlook for the next two years will be very interesting! (check out our new Hygrogen and AwTherm specific satellite sites www.hygrogen.com)

The last day of the meeting ensured everyone forgot about instruments for a while as we made our way out into the mountains. Mixed groups were pitched against each other in a fairly weird and wonderful mix of traditional team alpine games including Alphorn blowing and milk chair shuffling (best not to ask)!! Competition was tight but fun had by all.

It was all wrapped up with a fantastic outdoor bbq and the Rotronic awards – the UK team getting an award for the best CO2 product sales performance over the past two years!

The ISM are important to maintain open communication and share knowledge. Combined with a delicate mix of hard work, fun and fantastic enthusiasm from all the those attending ensures that once again the ISM was a great success!

Several important announcements were made about new products and future developments including…

• New ATEX Range (launches very soon!)
• Heated HygroMet Probe (now available!)
• Two new videos coming soon (CO2 measurement and humidity overview)!

In addition we were given a glimpse of the future… Rotronic UK unveiled the latest HygroGen2 features and the HG2’s bigger brother, the HygroGen2-XL.

Rotronic AG introduced a new ASIC for the Hygroclip probe range improving reliability and quality without affecting compatibility.

Beyond this there were several very exciting new product ranges on the horizon but these are still under wraps for now… watch this space 🙂

# Rotronic International Sales Meeting 2014 Grindelwald Photo Gallery

Great to see everyone at the 2014 ISM in Grindelwald!

# New training course dates! – Temperature and Humidity Measurement and Calibration Training.

Following the continued success of our training courses we have several new dates for October this year!

These courses are aimed at providing excellent theoretical and practical knowledge useful both for those new to the field or those looking to expand their knowledge.

##### Details and booking information can be found via the below links.

7th – 8th October 2014 :: Two Day Temperature Measurement and Calibration

9th October 2014 :: One Day Humidity Measurement and Calibration

Courses will be hosted by our partner Benrhos Limited in Wales and delivered by Dave Ayres (Benrhos) and Jeremy Wingate (Rotronic).

These excellent value courses are open to a maximum of 8 delegates ensuring course content can be targeted specifically to your needs.

##### Details and booking information can be found via the below links.

7th – 8th October 2014 :: Two Day Temperature Measurement and Calibration

9th October 2014 :: One Day Humidity Measurement and Calibration

##### Key areas covered include;
• Knowledge that is not available from other sources.
• Terminology and units.
• Fundamentals of each parameter.
• Best practice measurement.
• Calibration methodologies.
• How to interpret results and spot common errors.
• Measurement uncertainty.
• How to use uncertainty budgets and benefit from them.

Dr Jeremy Wingate
Rotronic UK

# White Paper – Save time and money with modern monitoring and calibration

The text below is taken from a Rotronic White Paper available here in full.

Companies across many industries needing to perform regular monitoring and calibration have never faced a more challenging environment. Stricter compliance requirements mean companies are under greater pressure to deliver accurate and reliable data, whilst internal budget restrictions demand the most cost effective and efficient solutions.

It is well known that accurate measurements reduce energy use and improve product consistency. Instrument users, calibration laboratories and manufacturers are constantly looking for smarter ways of operating and are responding with innovations that are transforming the measurement and calibration industry.

## New ways of working

Industrial environments are now more automated and interconnected than ever before and companies need to ensure that their infrastructure and processes have the ability to respond and adapt to industry changes. With the introduction of newer, more complex instrumentation, organisations can often be slow to recognise the additional business benefits that can be achieved by replacing a traditional method that (offers a short term result) with a more modern method (that delivers a longer term sustainable solution). Implementing a new approach can also help re-position the calibration process from being viewed simply as a cost to business to one that helps deliver improved process and energy efficiencies with a return on investment.

Historically, in-situ calibration has been the standard approach; however, advances in technology means that there is now a viable alternative whilst still maintaining the growing demand for on-site services. With the market moving away from analogue to digital signal processing, interchangeable digital sensors are proving to be a more practical solution for both large and small organisations alike. As businesses look for greater automation and productivity, modern interchangeable digital sensors are allowing calibration to be achieved much more quickly without the costly implications of operational downtime and on-site maintenance.

###### Why calibrate? – The only way to confirm performance In unsettled economic times it can be tempting to simply extend the intervals between calibration cycles or to forgo calibration altogether. However, neglecting system maintenance and calibration will result in reduced performance and a loss of measurement confidence, ultimately leading to a failure to meet compliance standards. Measurement drift over time negatively impacts on processes and quality. Regular, accredited calibration demonstrates compliance, but equally importantly, sends a message to customers that quality is taken seriously and that they can be confident in both the process and the final product.

Until recently most humidity calibrations were performed on-site in-situ. Larger organisations with multiple instruments generally found it more convenient to have their own in-house calibration instruments with dedicated technicians working on-site. Smaller organisations unwilling or unable to invest in on-site calibration equipment had the option to engage the services of a commercial calibration provider.

In most cases, trained instrument technicians are required for in-situ calibration work; the equipment is brought to the probes and generally only one probe can be calibrated at a time. One of the main disadvantages of this process is the impact that it has on production downtime, as typically a salt or chamber based calibration can take more than three hours. Moreover, as the processes or control systems are interrupted during calibration, the actual conditions can be unknown.

## Modern Ex-Situ Sensor Calibration

Companies keen to avoid the impacts of in-situ calibration and/or operational downtime caused by the replacement of failed hard wired instruments are opting instead for the flexibility and convenience of interchangeable sensors and modern portable calibration generators. Instead of bringing in equipment to calibrate in-situ, the technician brings pre-calibrated probes directly from the laboratory (on-site or external). Using interchangeable digital sensors, the pre-calibrated probes can be exchanged with the in-situ probes in seconds (known as hot swaps), saving time and avoiding operational disruption. If a wider system loop calibration is required, digital simulators are applied and provide any fixed values exactly and instantly. The old probes are then taken back to a calibration laboratory and calibrated accordingly. This adds the benefit that an external accredited laboratory can be used without issue.

## Improved accuracy and traceability?

By ensuring that all calibrations are performed within dedicated laboratories as opposed to ad-hoc locations, better procedures and instrumentation can be utilised. In addition, time pressures are usually reduced as processes and monitoring systems are unaffected during calibration. As such calibrations are typically performed to a higher standard leading to lower associated measurement uncertainty (every calibration will have an uncertainty associated with it – whether it is defined or not). Overall in most circumstances these methods deliver greater reliability, improved traceability and importantly, reduces on-site workload and limits operational downtime.

## CASE STUDY – Meeting the demands at the National Physical Laboratory, London.

When the National Physical Laboratory (NPL) in London needed to replace their entire building management system (BMS), they turned to Rotronic Instruments (UK) for an integrated solution to the sensors and calibration. The NPL was looking for both a complete range of temperature and humidity sensors and instrumentation, and the fulfilment of the calibration and commissioning needs of these instruments. Working closely with the project stakeholders, the Rotronic Instruments (UK) team developed a tailored solution, matching the instruments and service to the project requirements.

The decision by the NPL to replace the BMS was brought about by the need for tighter control, greater reliability and easier calibration. One of the key elements in achieving these objectives was the use of interchangeable probes. This immediately limited time-consuming and disruptive on-site sensor calibration to a minimum. Every probe’s digital output was calibrated in Rotronic Instruments’ (UK) UKAS accredited laboratory, and each transmitter’s analogue output was calibrated using a simulated digital input. To resolve any measurement errors in-situ between the calibrated sensors and uncalibrated BMS, each installed high accuracy instrument was loop calibrated and adjusted. Typical installations errors corrected for to date on the brand new BMS are ±0.5 %rh and ±0.25°C; a significant result for labs requiring tolerances of better than 1 %rh and 0.1°C.

Whilst the use of high performance instruments was essential, not every sensor location or application could justify this approach. However, mindful of the NPL’s long term objectives, even the lowest specification thermistor products were customised to provide long-term performance and low drift. Additionally, a robust commissioning procedure and training for key personnel was developed to enable ongoing commitment to delivering quality measurements. Finally, it was effective communication and regular on-site interaction with all the stakeholders that helped deliver a successful outcome to this substantial project.

## Summary

All companies that need to perform regular monitoring and instrument calibration should be constantly reviewing their processes and questioning whether their operations and procedures are delivering the maximum return for their business. As increased regulatory compliance and demands for improved energy efficiencies continue to grow, traditional processes may no longer offer the optimum solution. An organisational mindset change may be needed to move calibration from being seen as a fixed cost to a process that can help deliver business objectives through ongoing cost and energy efficiencies.

With the advent of calibration methods that can significantly reduce in-situ disruption, downtime is minimised, labour costs are reduced and productivity improved. Using interchangeable digital systems increases the accuracy and traceability of calibrations, resulting in higher quality product.

Choosing the right calibration methodology may require new thinking and a different approach, but those companies that get it right will end up with a modern, flexible system that both achieves compliance and delivers long term cost and energy efficiencies to their business.

# 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 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