All posts by rotronicuk

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?

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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. 

Figure 1: Diffusion is the process by which particles move from an area of high concentration to an area of low concentration.

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.

Water activity
Figure 2: Water activity devices measure the relative humidity of the air around a sample after an equilibrium has been reached

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

Rotronic UK

Branching Out: Why do some trees lose their leaves during winter?

When we leave behind the warm, bright summer days and enter into the cold darkness of winter, deciduous trees all around the UK start to lose their leaves – Why? In this blog, we will have a brief look at why a tree may suddenly decide that is is no longer economical to sustain the leaves clinging to the ends of its branches.

To drop, or not to drop?

Leaves are very beneficial to trees. The chlorophyll contained within them allows the leaves to use the energy from the sun to convert carbon dioxide and water into glucose and oxygen. For optimal efficiency, most leaves have a large surface area, maximising the amount of sunlight they can absorb. In addition to this, the underside of the leaf is covered in tiny pores called stomata. These stomata are there to let carbon dioxide into the leaf, and oxygen out. However, with the movement of CO2 and O2, in and out of the cell, some of the plants valuable stock of water can also escape as a vapour.

The trade off: do the benefits of have having leaves outweigh the drawbacks.

During the long summer days, the leaves take in plenty of light to make enough glucose to offset the problem of a little water loss. However, as days get shorter, and light levels are reduced, the leaves make less glucose every day. At some point, the loss of water through the leaf, and the energy expended by the tree in maintaining the leaf, can no longer be justified by the amount of glucose being made, so the leaf is ejected.

Water Loss…

We had to get relative humidity in here some how, so here it is. The relative humidity of the air around a leaf can have a significant effect on the rate at which water is lost through the stomata. The action of diffusion, by which molecules of a gas move from an area of high concentration to an area of low concentration, means that when there is a large difference between the partial pressure of water inside the leaf compared to outside, water vapour will escape much more quickly compared to when the partial pressures inside and outside the leaf are relatively similar. To combat this, some leaves have tiny hairs on the underside which can help trap moisture close to the outside of the leaf surface, thus reducing the partial pressure difference and reducing unnecessary water loss.


The stomata can also be opened and closed by the guard cells to minimise water loss, but when they are closed, less CO2 can get in to the leaf, meaning photosynthesis is reduced.

Job security in the leaf world is poor. As soon as a leaf is deemed by the tree to be more of a hindrance than a help, hormones are released which trigger specialised cells near the stem of the leaf to cut it free.

Before the leaf is let go, the tree breaks down molecules in the leaf to take back as many nutrients as possible. The green chlorophyll is one of the first molecules to be broken down, resulting in the change of colour from green to brown.

Happy Christmas & Best wishes for the new year.

Rotronic UK

Extending GxP Monitoring Systems – Comfortably and easily


Rotronic offers you the opportunity to economically upgrade your current environmental monitoring system (EMS) with a state-of-the-art EMS designed in collaboration with the pharmaceutical industry.

Universal Device Integration

The Rotronic Monitoring System (RMS) can provide the perfect solution for all your monitoring needs. RMS is an advanced modular monitoring system with all data available securely via any device, anywhere. RMS provides users with exactly the data they need and in the format they require with extensive reporting and configurable alarms. More importantly, RMS can support existing hardware and interface with other software/hardware platforms. RMS can be provided as a hosted cloud service or with a traditional license whereby the client installs the system on their servers (local or cloud).

Many third-party devices can easily integrate with RMS. Analogue devices can be connected using the RMS analogue to digital converter, or the “RMS-converter” can be used to integrate other digital devices. To avoid the risk of data loss during an interruption in communication between a device and the RMS server, both the analogue and digital inputs are available with local, internal logging. Once the connection is re-established, data will be automatically downloaded from the device and online graphs will be back-filled.

Rotronic RMS Architecture

With the RMS continuous environmental monitoring system RMS, Rotronic meets the requirements of “IoT” and “M2M”.

The Internet of Things (IoT), and Machine to Machine (M2M) communication are key factors in industry 4.0 design principals – launched at the Hannover Fair in Germany in 2011. One of the most important characteristics being interoperability, devices, machines, and people must be easily able to connect and communicate.

An IOT ecosystem comprises sensors which transmit data to the Internet via a “gateway” where it is stored securely in a certified data centre. This data can then be accessed, analysed, and forwarded to remote devices via the Internet.

This leads to another key design principal: decentralised decision making. From remote devices, analysis can be carried out, decisions made, and commands sent, all via the Internet, to IoT devices.

Remote access to devices allows for a third design principal: technical assistance. Services and support can be offered and carried out as a direct result of the output from one of the many devices in the IoT ecosystem.

Rotronic Monitoring System RMS: On-Premise or SAAS Solutions (Public or Exclusive)


Contact us to discuss your monitoring requirements whether GxP, Industrial or Commercial.

T. 01293 571000   E.   W. 



In 2018 the UK automotive sector was valued at £82 billion and employed 823,000 people.

As the trends towards automated, low carbon and electrical vehicles increase the requirements of modern testing and certification are critical. In this customer application we explore how one of the UK’s largest automotive test companies is meeting these new challenges helped by the adoption of the cutting edge Rotronic Monitoring System (RMS).

Automotive Test and Validation

In 2017 the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) was introduced.  This lab test required the assessment of fuel consumption as well as CO2 and pollutant emissions from cars during
• Test cycles based on real-driving data
• Test cycles based on a variety of driving phases
• Test cycles using both heaviest and lightest power-train configurations

Facilities that provide these tests and have access to suitable test tracks are increasingly in high demand. Prior to testing cars must be preconditioned at specific environmental
conditions and during lab testing these conditions are replicated.


The Application

In order to meet ongoing quality demands and compliance to the latest Vehicle Emissions Regulations (WLTP), our client required a solution to improve and enhance their monitoring capability in several key test areas. Latest standards required more frequent ambient measurements as well as five-minute rolling averages. Engine testing is undertaken in multiple soaking areas operating at different temperatures, ranging from -20 °C to +50 °C, requiring numerous temperature and humidity sensors monitoring different parts and areas of the test vehicles.

The Challenge
It is no longer practical to use a range of different monitoring platforms for every specific application. For the automotive industry the growth of the latest 5G and electric car technology provides new validation and testing challenges, a monitoring platform must be able to adapt to meet these new requirements easily. For our client the system had to be centrally managed with all data accessible from anywhere on site. Reporting, alarming and a clear audit trail were vital. Already having experience with a range of hardware and software it was clear that the system had to utilise standard IT infrastructure and software platforms.

Rolling road for vehicle testing

Hardware Integration and Standardisation

Investing in a monitoring system traditionally locked customers in to one supplier. Where possible, RMS has been designed to support Industry 4.0 open integration and interoperability. As such, RMS software is built as a standard web service. All data sits on a standard SQL database. Industrial device interoperability is never easy, RMS provides
options via simple APIs for many applications and analogue input modules for existing analogue hardware. When a robust and secure integration solution for digital hardware is required it can be professionally integrated using our RMS-Convertor module.

The result is that end users can add supported 3rd party devices with a few clicks. These devices benefit from secure data backup and auto-recovery of data in the event of any system downtime, as well as all the normal charting, reporting and alarming features RMS offers.

Project Overview

Our client engineers favoured Red Lion E3 modules, a proven industrial I/O device from Red Lion Controls. The E3 range includes 16 channel thermocouple devices, ideal for automotive testing. Integration was achieved in partnership with Rotronic R&D. Using a trial Red Lion E3 device Rotronic was able to fully integrate the unit. Final testing was undertaken by the client to confirm that the devices performed as required.

A key feature was that the Red Lion E3 modules have the ability to daisy chain Ethernet devices. Therefore, using a single port the 16x channel Red Lion module was networked along with a high accuracy humidity and temperature RMS LAN logger to every engine test cell providing a robust, elegant solution for this industrial application.


Product Focus – Rotronic Monitoring System (RMS)

High accuracy and high frequency multi parameter monitoring including temperature, humidity, pressure and dew point.
• On premise or cloud software solution
• Support for wired and wireless data loggers
• No local end user software required just a web-browser
• Full historic record and summary reporting
• High accuracy and high frequency ambient temperature and humidity monitoring
• Ability to calculate and record 5 minute rolling averages with alarms
• Extensive support for 3rd party devices and data streams

Read the case study from Red Lion on this project here; 

Contact us to discuss your monitoring requirements be they GxP, Industrial or Commercial.

Dr Jeremy Wingate

Invitation to the Sensor & Instrumentation Live Show – 25th-26th September 2019 – NEC Birmingham


The Sensor and Instrumentation Live event is celebrating its 10th year in 2019, Rotronic and Michell Instruments will be teaming up to exhibit at the event and can be found on stand 72 at the NEC, Birmingham. Come along to the stand to gain expert knowledge from not one, but two leading instrumentation companies’ part of the Process Sensing Technologies (PST) group. They will also be representing PST companies Ntron Gas Measurement, Dynament and Status Scientific.

The stand will cover a variety of applications:

  • Humidity and temperature calibration in laboratories.
  • Room Monitoring (RMS Rotronic monitoring system).
  • Humidity and temperature analysis in the pharmaceutical industry, production processes, storage, test facilities and many more applications.
  • Oxygen and humidity control, improving end product quality in additive manufacturing.

Michell Instruments and Rotronic will be exhibiting their extensive range of products,


with Rotronic presenting their full range of humidity temperature and dew point instrumentation which includes handhelds, data loggers and transmitters. A feature at the event includes their own Rotronic Monitoring System (RMS), a cloud-based platform that integrates both Rotronic and third-party equipment to provide users with real-time monitoring information for use in applications such as warehouses and pharmaceutical production.

SF82 – Dew Point Transmitter

Michell Instruments will showcase their latest dew-point transmitter the SF82, designed specifically for compressed air dryers it can cover a range of -60 to +60 °C dew point, demonstrating its suitability for dryer control. This new sensor is fast responding providing highly stable, long-term measurement reliability. Alongside this Michell Instruments will provide an insight on their range of world leading dew-point transmitters, chilled mirror instruments, oxygen analyzers and relative humidity products.

Information on products and services from sister companies Ntron Gas Measurement, Dynament and Status Scientific will be available at the event. You can discover more about the PST combined range of instruments and sensors for gas analysis and process control by attending the Sensors and Instrumentation live event.



Advanced Industrial Temperature and Humidity Probes


Well known as a leading manufacturer of precision temperature and humidity sensors with the widest measurement ranges -100…200 °C, 0…100 %rh, Rotronic has developed its industrial range of probes still further providing even higher performance. Included is an awaited industrial probe for the Rotronic continuous environmental monitoring integrated system (RMS) with all data available anywhere and on any device. Applications include manufacturing, pharmaceutical, food, process monitoring, cosmetic, paper, textile, brick & tile industry, dryers, climate test chambers.


The new probes are available in a choice of 100 mm length (2 m or 5 m factory fitted cable) and 250 mm length with fitted 2 m cable. The RMS fast response digital probe is available in 100 mm length with 2 m fitted cable. All probes are Ø15 mm and manufactured in industrial PPS material


  • The latest Rotronic HYGROMER® HT-1 state of the art sensor is fitted, it measures temperature and humidity and calculates dew point values.
  • Highest possible measurement accuracy ±0.8 %rh, ±0.1 °C (10…30 °C), fast and stable response, highest long-term stability and robust mechanical construction with PTFE surface protection.
  • Continuous measurement is now achievable at up to 190 °C constant environment level (200 °C peak load), 93 °Cdp.
  • Connector housing electronics are now potted; the sensor head is steam tight.
  • Filters have been specially designed to suit all applications, their purpose it to protect the sensors from mechanical damage. Polyethylene, wire mesh, sinter steel and Teflon types are available.

Rotronic Probe Features

There is a digital interface with all current Rotronic devices enabling rapid probe exchange when calibration or service work are due thereby reducing process downtime to seconds (no calibration adjustment required).

Probes have an analogue 0…1 V output for interface with data acquisition systems and OEM applications.

Rotronic sensors can be calibrated and adjusted (if outside customer required tolerances) giving them a long service life.

The latest advanced industrial probes from Rotronic are a significant development.

Contact Rotronic to discuss your application or project.

T. 01293 571000   E.   W. 

Regulatory Storage of Medical Drugs

casestudyMedicines are sensitive products. Having them stored at temperatures too low or too high can affect their overall quality, potentially making them less effective and even causing adverse effects during use. This means that correct storage conditions are not only essential to ensure medicine quality, they are also required by law.

Why monitor environmental conditions?

Medicine control and EU GDP Guidelines suggest that suitable equipment and procedures should be in place to monitor the environment where medicinal products are stored. Environmental factors to be considered include temperature, light, humidity, and cleanliness. For example, many medicines should be stored between +15°C and +25°C to ensure their quality is maintained. Other temperature-sensitive drugs, such as insulin or some antibiotic liquids must be kept in refrigerators between +2°C and +8°C. If medicines are not stored at correct temperatures they muse be destroyed, resulting in large, unnecessary, financial losses.

How Rotronic can help?

Rotronic has over 50 years’ experience in environmental monitoring to GxP guidelines. With “RMS” Rotronic can provide a monitoring system that was developed based on GAMP5 recommendations, in collaboration with multiple experienced pharmaceutical users to comply with several industry regulations, including FDA CFR 21 Part 11 and EU Annex 11.

RMS is an advanced, modular monitoring system with all data available securely via any device, anywhere. It can provide users with exactly the data they need, in the format they require, with extensive reporting and configurable alarms.

One of the key features of RMS is that not only can it be used with Rotronic hardware, but it can also be used with existing hardware from other manufacturers, as well as interact with other software / hardware platforms. RMS can be provided as a hosted cloud service or using a traditional license whereby the client installs the system on their own servers (local or cloud).

In summary RMS provides….

  • Live and interactive charts for all monitored parameters
  • Full alarm and alerts, easily configured
  • All data available with automated scheduled report generation
  • Complete event logging and compliance with GxP requirements
  • Email, phone, SMS, relay and custom protocol alarm notifications
  • Automatic data back filling and retrospective alarms (ideal for transportation logging)
  • Interactive, user configurable on-screen layouts

Alarming / Reporting

The alarm function in RMS ensures users are alerted whenever conditions stray outside their set limits. For example, if a refrigerator is broken, causing its internal temperature to rise above limits, an alert is triggered, notifying users, via email, SMS, or phone call, to act before medicines are damaged. The warning function can also be used to warn users whenever environmental conditions get close their critical limits, giving time to react before the critical limit is reached. Depending on individual requirements, a detailed alarm report can be automatically generated and sent to selected users via email.

                                                            Rotronic products
RMS KITAutomated solution

The RMS Starter Kit for monitoring storage of medicines includes three wireless temperature loggers, a gateway (wireless receiver) and the corresponding software license. We have also included a service level agreement to help ensure a quick response to any questions that may arise.

Standalone solution

Data logger TL-1D or HL-1D Collage HL-1D.jpg
For a standalone solution, you can use our TL-1D temperature loggers or HL-1D humidity and temperature logger. These battery powered devices record environmental data which can be accessed by connecting the logger, via its USB port, to a PC running the free HW4-LITE software. These devices are not compatible with the RMS meaning data must be accessed manually. Once data has been downloaded, HW4 can be used to generate a detailed PDF report, which includes a graphical representation of the data, along with various statistics, and details of any period during which conditions where outside their alarm limits.

To find out more about our range of monitoring solutions, please contact us on 01293 571000 email: or visit