The challenges of monitoring
It is a common misconception that the Victorians built their railways on engineering principles that were way in excess of what was actually needed. This may have been true for the grandest of bridges or tunnels, but it was certainly not always the case for cuttings and embankments. Many of these earthworks exhibit weaknesses, and instances of bank slips and landslides occur from time to time. The tragedy at Carmont last year only emphasised how fragile some of the UK’s rail infrastructure is. Climate change and weather extremes have not helped and millions of pounds are having to be spent on stabilising the worst locations.
Knowing that something is going to fail before it actually does is very much part of modern-day engineering. To achieve that, sensors are needed where vulnerabilities exist to detect movement or abnormal conditions. A range of equipment is available for different kinds of foreseen problems. But that is almost the easy bit; retrieving and acting upon the information provided on a near-continuous real-time basis is essential, otherwise the insight will be valueless. Real-time means switching from traditional data loggers – with the need to sift through gigabytes of historic data – to smart sensors communicating ‘live’ using hybridised edge computing to know what is right and wrong, and when to cry for help.
One company that believes it has a system that provides a consistent means of overcoming this challenge is Iridium, in conjunction with rail partner Radio Data Networks (RDN). Rail Engineer recently spoke with them to learn all about it.
Company backgrounds
Most people will remember Motorola – an American company that was at the forefront of mobile radio development. Iridium, the satellite communications company, was born of Motorola, but, due to a number of flawed assumptions and impatient Motorola investment, the company went under, only to be bought out of bankruptcy by a group of investors and has since risen from the ashes. Whilst still offering a satellite-based mobile radio product, it has ventured into the world of infrastructure monitoring. With an HQ near Washington DC, it now has operational centres around the world, with the UK base being close to Stansted Airport.
Infrastructure monitoring is big business and the company has connected up one million devices worldwide.
The directors of RDN have been behind several highly-acclaimed innovations in the rail industry, from the development of real-time rail temperature monitoring system back in 2000 through to hot box detection.
UK based, operating from their own innovation centre a few miles from Iridium’s European HQ, RDN’s past experience was instrumental in their successful rapid design and deployment of the apparatus used in 2018 for Iridium’s trials with Network Rail’s North West Region as part of an innovation project.
System architecture
The measurement and interconnection chain is relatively simple. Firstly, you need a sensor. This will vary according to what is to be monitored, ranging from earth movements, temperature, flooding, bridge scour and track position to even more routine things such as the detection of copper theft. Many of these sensors will be in remote locations where landline provision or even mobile radio coverage may be non-existent. With the latter being subject to a constant state of flux as cellular operators advance their system to a higher G number, it makes justifying long-term investment in cellular-based equipment questionable due to the ever-present problem of obsolescence.
From the sensor, a local radio link connects the data to a collection point, noting that there may be more than one sensor in the area. The ‘collection point’ is deliberately nothing more than an inconspicuous grey GRP box. Tucked within it is the Iridium modem – formerly known as the Iridium Remote Telemetry Unit (RTU) – a cigarette packet size unit which is the gateway element that connects to a satellite link. This unit has been engineered to be lightweight and easy to carry, with a universal bracket to enable pole, post, rockface or OLE stanchion mounting. Being an ultra-low power device, the RTU’s internal controller provides sensor communications control and a smart adaptive Artificial Intelligence, enabling the elimination of the need for mains power or a solar panel, but still giving months, years or even decades of service.
Data is transmitted and then downloaded from the satellite into Iridium’s control centre in Arizona, from where it is delivered typically over a virtual private network (VPN) link to the customer’s operational centre.
Component parts
There are many manufacturers of sensors, depending on the type of monitoring that is required. RDN have spent the last decade pioneering smart ultra-low power devices; many of them are highly applicable to the challenges faced by the rail industry and range from flooding to geostructural movement. Iridium is, however, agnostic to these and has a working relationship with many sensor companies in case something different is required.
In one of RDN’s applications, the link from the sensor to the ‘grey box’ is provided through RDN’s national private Ofcom-licensed data channels. This is already proven in the utility sector and used by the likes of the Environment Agency for flooding and other critical risks. RDN can create private networks ranging from a few metres to several kilometres and are legally protected. This then enables the Iridium uplink to be shared amongst a number of distributed sensors.
Having established the connectivity, the data flow needs to be considered. Most sensors are looking for change, rather than an absolute measurement. Thus, when considering earthworks, it may only be necessary to transmit a reading every 24 hours. Similarly, if measuring a river flow, the sensor would be set within a range of flow rates considered to be normal and only if the flow increases beyond these limits would more frequent readings be transmitted. A river in full flood might receive sensor signals every few minutes.
Understanding satellite communication
Most people have heard of satellites with geostationary orbits approximately 36,000km above the earth’s surface, in a fixed location above the equator from where communication takes place. It might be thought that this would be the ideal scenario for sensor monitoring, but there are disadvantages. If the user device does not have a direct line of sight to the satellite or the path is a low angle, changes in topography can cause the signal to be lost. Also, if the sensor is moved to another location even close by, the signal can be affected.
The Iridium solution is to have 66 satellites in a Low Earth Orbit (LEO) approximately 800km above ground level. These are meshed together with full resilience and redundancy, meaning that if one satellite fails, there will be others that can intercept the signal. These satellites are constantly moving so don’t suffer from low-angle measurements. Since, at some point, the angle will be low, it has been found that even a sensor in a tunnel will give a signal once there is a direct line of sight between the tunnel entrance and the satellite. Iridium’s L-band spectrum based devices are proven to be weather independent. Iridium is the only LEO network provider of this type and has a unique satellite network.
The cost question
Whilst all this sounds good, it comes down to cost if organisations are going to use the system. In broad terms, a typical price of £5K per site can be used for budgeting purposes. This includes the acquisition of the sensor(s), the facilitation with Radio Data Networks of the local VHF link (including the ‘grey box’), the provision of the satellite modem plus one year’s satellite air time and the setting up of the VPN link back to the customer’s control centre.
Around the world there are in excess of 1.5M subscribers. Several thousand are in use within the UK, mainly with the utility companies. There are several railways with devices, but mention is made of Canada where Iridium Certus communications terminals are being used to support connectivity for the PTC (Positive Train Control) project. Network Rail is also continuing to show interest.
Thanks to Alan Briggs in Scotland and Jordan Hassin in the USA for the interview and for providing the visuals accompanying this article.
