Everything you need to know about lead-free O2 sensors
Why is everyone talking about lead-free O2 sensors?
The safety industry has historically relied upon lead-based sensors for monitoring O2 in fixed and portable gas detectors. These sensors, which work on a galvanic operating principle, are widely available, low-cost and typically reliable for their relatively short life. This long-standing preference was disrupted however, with the advent of RoHS, a piece of EU legislation which will soon ban the use of lead in instruments sold in the EU and harmonised regions.
In recent years, with RoHS implementation moving ever closer, instrument manufacturers have endeavoured to future-proof their instruments through the integration of lead-free O2 sensor technology, in both new and existing instrument ranges.
Whilst RoHS may have been seen as an inconvenience by some in the gas detection industry, it has driven the development of modern lead-free O2 sensors, in-turn enabling huge advances in instrument performance and significantly reducing maintenance needs.
As the number of OEMs and end-users who see the benefits of modern lead-free O2 sensors grows, we are seeing rapidly increased adoption and a collective raising of expectations with respect to instrument performance.
In the paragraphs that follow, we provide our view of where the industry is with RoHS and provide various resources we believe will benefit your business.
So firstly, what is RoHS?
RoHS is a piece of EU legislation which will ultimately outlaw the use of lead-based O2 sensors in the EU and harmonised regions.
After many years of exemptions and extensions specifically for the safety industry, the clock is now ticking on full enforcement, and instrument manufacturers should be prepared if they wish to continue selling into affected regions.
Beyond this basic principle, RoHS is a complex topic and one which generates a lot of questions from our customers... not only 'what is RoHS', but;
- Is it only the EU which is impacted by RoHS?
- Is the use of lead in O2 sensors banned in the EU already?
- So when does the ban come into force?
- If I don't sell in the EU, how does this affect me?
- Where can I get further guidance on RoHS and its impact on my business?
We do our best to answer these questions and more on our dedicated RoHS web page. We expand further on our answers in our recently updated RoHS white paper.
When does RoHS come into force?
There is some misinformation in the market around when OEMs will need to comply with RoHS. The reality is that no decision has yet been made by the EU whist it considers outstanding exemption requests.
The final implementation timescales are dependant upon a decision being made, with minimal timeframes summarised below for each potential outcome.
Whilst exemption requests are still under consideration, our understanding (at the time of writing) from industry and regulatory peers is that it is likely that the exemption requests will be accepted in line with the recommendation of consultants, and subject to minimum implementation period of 18 months. This is however not guaranteed and therefore worst case scenario should also be considered.
You can read about our information sources and how we have come to this conclusion in full through our RoHS white paper.
How can instrument manufacturers comply with RoHS?
RoHS has driven OEMs to consider the wider health and environmental impact of their instruments, both topics which are increasingly high on the agenda of end-users when appointing supply chain partners.
As RoHS implementation draws ever closer, the key considerations for instrument OEMs who are currently using galvanic lead-based O2 sensors are;
- If you wish to continue selling into world areas which are subject to RoHS, you need to make sure you have a viable lead-free sensor for your instrument, which will likely mean a redesign or update of the instrument.
- Lead-based O2 sensors can still be supplied as spares for instruments that were/are sold pre-implementation.
- You won't be able to circumnavigate RoHS by selling instruments with sensors supplied separately as 'a kit of parts' as some manufacturers have done in the past.
- If your instruments are certified, you will likely need to go through all/some of that process again, regardless of which lead-free sensor option you choose.
- Even if you are selling in world areas which are not directly impacted by RoHS, you should be aware of the impact lead-free sensors are having on instrument performance. End-user specs are evolving in-line with the newest available technology, and devices relying upon galvanic sensors are fast becoming non-compliant.
For more details on these topics, take a look at our RoHS white paper, which provides further details around each of the points above.
What does the lead in a lead-based O2 sensor do?
Lead-based O2 sensors work on what is called a galvanic operating principle. This type of sensor relies upon a lead anode within the sensor body to facilitate the electrochemical reaction that is used to measure oxygen.
The electrochemical reaction within a galvanic O2 sensor consumes the active element of the lead anode, until such point it loses function and the sensor fails to operate. Depending upon sensor specification, the sacrificial nature of the lead anode will directly translate to a sensor operating life of approx. 1, 2 or 3 years.
In addition to having a limited lifetime, galvanic O2 sensors can be prone to other issues, both during and at the end of working life. Since the galvanic process can cause a build up of pressure within the sensor, a low-quality or badly designed lead-based O2 sensor may leak or split, in some cases causing irreversible damage to the host instrument.
A more detailed explanation of how galvanic O2 sensors work can be seen via the button below
So what options do OEMs have without lead?
Sensor manufacturers have been aware of the potential impact of RoHS for many years, and in that time, the industry has worked hard to deliver a viable lead-free alternative which does not rely on the galvanic principle. This work led to the development of the amperometric lead-free O2 sensor, a technology which is now utilised in many of the world's leading market-leading gas instruments.
Though adoption of amperometric O2 sensors was initially driven by RoHS, their presence in the market has exposed the shortcomings of galvanic sensors, and they are now overwhelmingly the preferred option for O2 monitoring, both in newly developed products and those undergoing a refresh.
First introduced almost 10 years ago, amperometric O2 sensors have driven improvements in instrument performance whilst significantly reducing the maintenance burden and its associated cost on instrument users.
What is an amperometric lead-free O2 sensor
Amperometric sensors differ significantly from their galvanic predecessors in that they require no anode to function and are therefore free of consumable content. This is the defining factor which allows amperometric O2 sensors to perform for 5+ years with minimal output drift.
With no need for an anode, amperometric sensors do not require lead in their construction. Not only does this make them inherently RoHS compliant, but it frees them from the build-up of internal pressure, which so often causes leakage and failures in galvanic sensors.
With a working principle which is not dissimilar to that of a simple CO sensor, amperometric O2 sensors are built on a stable platform which delivers both enhanced performance and stability over galvanic sensors.
When they first came to market almost a decade ago, amperometric lead-free O2 sensors were comparable to galvanic sensors in performance and higher in price - both of these factors have changed significantly in the time since.
Not only are modern lead-free amperometric O2 sensors similar in price to galvanic sensors, but their performance is now far superior. In fact, the latest amperometric lead-free O2 sensors outperform galvanic sensors in all key performance criteria, from response time to temperature range and most significantly, sensor life.
A more detailed explanation of how amperometric O2 sensors work can be seen via the button below
What are the benefits of amperometric O2 sensors?
The benefits of modern amperometric lead-free sensors over galvanic alternatives are numerous, including;
- Up to 7 times faster T90 response time - this, coupled with quicker recovery, makes for safer, more accurate instruments, particularly when used in low-O2 applications such as inerting
- Extended 5-year+ working life - directly translates to increased reliability / reduced downtime and negates the need for costly and logistics-heavy annual / periodic maintenance associated with lead-based sensors
- Inherent leak-free design - amperometric O2 sensors work on an entirely different principle to galvanic sensors, meaning they are not subject to the build-up of internal pressure, which can lead to leaks in galvanic sensors. Being inherently leak-free, amperometric sensors result in less instrument downtime and mitigate the need for costly repairs
- Broad temperature range - the working temperature range of amperometric O2 sensors is typically wider than that of galvanic sensors, meaning devices can reliably function over a wider range of environmental conditions
- Improved baseline offset - this results in a greater level of precision in oxygen readings, especially at low concentrations
- Higher resolution - means amperometric sensors typically respond faster and more accurately to small changes in O2 concentration
- Reduced output drift - with drift as low as 5% over the lifetime of the sensor, OEMs and end-users alike can have greater confidence in their instruments and increase calibration intervals
- One size fits all - with the ability to perform equally well in both pumped and diffusion instruments, modern amperometric sensors negate the need for different sensors for each instrument model
- Standardisation - in light of the performance enhancements that amperometric O2 sensors bring to instruments, many of the worlds' leading OEMs have chosen to standardise on this technology globally rather than to carry multiple SKUs
- Compliance with end-user requirements - as gas detection users become increasingly aware of environmental and health impacts, coupled with the need to reduce maintenance costs, many are now specifying long-life lead-free sensors as a critical requirement in their tender documentation. Manufacturers who do not have a long-life option within their range run the risk of being omitted from competitive bids
- Ease of integration - with a start-up time of less than two minutes from zero power, uniquely, our latest lead-free sensor release, the S+4OXLFF, does not need a continuous bias. This extends battery life in portable instruments and, in the case of fixed instruments, reduces downtime during commissioning, servicing and in the event of a power outage
What are the key considerations for an OEM when switching to lead-free O2 sensors?
Any change to sensor selection generates additional workload for instrument OEMs, be it the need to amend documentation, update certification or make updates to firmware or hardware.
With the opportunity to improve instrument performance significantly and with fewer barriers to entry than previous versions, the integration of amperometric O2 sensors is easier than ever.
Engineering resource - switching from a lead-based galvanic sensor to a lead-free amperometric sensor will require a change to circuitry, something which many of the world's leading OEMs have seen as a small price to pay in order for their instruments to exploit the many benefits of the latest technology. At DD-Scientific, we make our customers' lives as easy as possible by providing sample circuits as well as access to our in-house electronics specialists who have supported many other customers in transitioning to amperometric technology.
Price - when the first amperometric lead-free sensors came to market more than a decade ago, they were at a higher price point than traditional lead-based sensors. As adoption has increased and production methodology has improved, their price point has fallen. The cost of DDS lead-free O2 sensors is now comparable to that of traditional lead-based O2 sensors. This, coupled with an extended life, means the cost of ownership through the use of an amperometric O2 sensor is reduced by up to five times over the life of an instrument.
Battery life - previously, amperometric sensors required the instrument to provide a permanent bias in order to avoid a prolonged start-up time when the sensor is re-energised. This was typically achieved through the use of a coin-cell or a direct power supply to the sensor. In the case of battery instruments, this would drain the battery, even when the instrument was turned off. This meant reduced battery run-time and resulted in prolonged start-up times in the event that the battery was fully discharged. Uniquely, the S+4OXLFF lead-free amperometric O2 sensor does not need a permanent bias and is fully functional within two minutes from a state of zero-power. This feature removes this historic barrier to entry and is equally beneficial to fixed instruments, which can be zeroed within minutes of installation or a sensor change. Additionally, following a power outage, fixed instruments can quickly resume full functionality when utilising S+4OXLFF.
Return on investment - any change to sensor specification will consume an instrument OEM's resource, be it making engineering changes, amending certification or updating software/firmware.
Whilst the notion of a 'drop-in replacement' may initially be attractive, integration will still require engineering / certification resources and will likely result in an instrument with lesser performance when compared with your current devices and those of your competitors.
In choosing to move to an amperometric lead-free O2 sensor, manufacturers have the opportunity to deliver more on their investment, not only by bringing their instruments in line with RoHS, but also by enhancing device performance and elevating their position in the market.
Is there such a thing as a 'drop-in replacement' for lead-based galvanic O2 sensors?
The concept of a lead-free 'drop-in' replacement O2 sensor was long heralded as the answer to RoHS and a natural progression for the safety industry. A 'like-for-like' sensor would, in theory, minimise integration efforts for OEMs without negatively impacting the O2 sensor spares business upon which many businesses relied.
The challenge for manufacturers looking to develop a drop-in replacement was finding a suitable RoHS compliant anode material to use in place of lead. Roll forward 20 years and this challenge has ultimately proven insurmountable.
Though the concept of a 'drop-in replacement' might seem logical based upon the reduced need for engineering input, this technology should be approached with caution. Not only is the technology not yet field-proven, but the viability of these ‘drop-in’ replacements is questionable given their performance is inferior, not only when compared to modern amperometric O2 sensors but also to their galvanic predecessors.
Below is a comparison of key performance and commercial factors between our leading lead-based S+4OX, a third-party galvanic 'drop in replacement' and our latest amperometric lead-free sensor, the S+4OXLFF.
In the many years it has taken for galvanic lead-free sensors to come to market, amperometric sensors have fallen in price and improved in performance, leap-frogging galvanic technology and placing them firmly as the market-leading technology for O2 detection in safety applications.
At the same time, end-user expectations have progressed beyond the capabilities of galvanic sensors and whilst specifications may not explicitly state the need for amperometric sensors, their expectations with respect to T90 and sensor life often mean that a modern lead-free amperometric O2 sensor is not only preferred but, by default, it may be the only compliant option.
A word of caution
Gas sensors are a safety critical instrument component, and there are a number of important considerations when switching from one sensor type to another, be it a different part number, brand or technology. Too often, this fundamental principle is diluted through an extended supply chain and commercially driven messaging. At DD-Scientific, we endeavour to ensure that every sensor supplied is instrument-compatible and fit for purpose.
In the case of instrument manufacturers, key considerations with respect to suitability are typically captured within new product introduction (NPI) and new product variant (NPV) methodology, which ensures compatibility of alternative sensors prior to release.
In the case of end-users and service providers, who are perhaps more likely to consider substituting one sensor for another, they should be aware that;
- Installation of a non-approved sensor will almost certainly invalidate manufacturer warranty
- The use of a sensor which is non certified will likely invalidate safety critical certification such as IECEx and ATEX
- If the performance of a ‘drop-in’ replacement falls short of the sensor it is replacing, the performance of the device is downgraded, creating a potentially hazardous scenario for the user.
- An instrument is factory configured to operate with a specific sensor specification. When the sensor model is changed to one with different performance characteristics, for instance, temperature response, the accuracy of the device, and therefore its fundamental purpose as a life-saving piece of equipment, is compromised.
Our stance on sensor compatability is that only the OEM can fully verify suitability of an alternative sensor. On this basis, we advise that any non-OEM who is considering replacing a gas sensor with an alternative brand, part-number or technology should first seek guidance from the original equipment manufacture.
What is the most sustainable type of O2 sensor?
Galvanic sensors have an inherently short life of 1, 2, or sometimes 3 years depending upon specification. This sees them require multiple planned replacements over the life of an instrument - a costly exercise which presents a logistical challenge for anything but the smallest of fleets. When service intervals are missed, lead-based O2 sensors can leak, potentially causing catastrophic damage to instruments.
Aside from the direct overhead associated with replacement of O2 sensors, there are other consequential costs, be it the need to hire-instruments to cover downtime, or the frequent replacement of perfectly good CO & H2S sensors 'as a matter of course' alongside the O2 sensor.
'Sustainability' has been cited as a key reason to continue using galvanic sensors by one manufacturer, but let's be frank - there is nothing sustainable about changing your O2 sensor every 2 years!
In contrast to relatively short-lived galvanic sensors, amperometric lead-free O2 sensors are inherently maintenance-free and will frequently outlive the instrument in which they are installed. Given that 1 x amperometric O2 sensor will be required to support the five-year life of an instrument vs. 3 x lead-free galvanic sensors, it is clear which is the more sustainable option.
What is the best available O2 sensor for my instruments?
Whether you are looking to update an old instrument or to launch a new product, the benefits of amperometric O2 sensors far outweigh those of galvanic sensors.
Of the lead-free O2 sensors we offer, the S+4OXLFF presents the best available amperometric lead-free solution for O2 monitoring.
Not only does the LFF out-perform other O2 sensors in all key performance criteria, but it is easier to integrate, delivers a better experience for end-users and is at a price-point which provides return on investment like no other.
Make the switch to Lead-free O2 with DD-Scientific
Whether you are integrating lead-free O2 sensors into a new product or looking to upgrade a legacy device, DD-Scientific are here to help.
As with any the adoption of any new technology, switching to lead-free can be challenging for OEMs. We work hard to make it as easy as possible for our customers and have worked with many OEMs to successfully incorporate lead-free O2 sensors into both new and existing instrument designs.
Lead-free O2 sensors require a different approach to PCB design and instrument operation compared to traditional lead-based O2 sensors. Our experience has proven that the transition is often not as difficult as OEMs anticipate and provides numerous benefits both to manufacturer and end-user.
If you are looking to integrate lead-free sensors into your instrument we will be happy to share our experience and provide both technical and electronics design support.