Product development is never-ending

The history of Lufft road sensor development, blogged from our CEO Klaus Hirzel! In our IRS product line, every product benefit from the experience of previous developments. After 20 years of developing passive road sensors, we are convinced that the IRS31pro is the best passive sensor that Lufft has ever developed.


Quality is never so good that we can not improve it still further.

When, in the mid 90s of the last century, Lufft decided to develop weather stations for traffic applications, we were not the first. There were already a few suppliers on the market. Meteorological systems for traffic applications are nothing more than high-precision weather stations that are also installed in this form by meteorologists worldwide and used to predict the weather (forecasting, nowcasting). Meteorological experts often support the siting of these “ice warning systems”, typically along highways.

The main difference from a meteorological system is that the conditions are measured on roadways and airport runways. Another important distinction is that, to measure precipitation, traffic weather systems require different sensor technology than that used in classic meteorology. This will not be discussed further in this post.

Consequently, special sensors that are not used in conventional weather logging are the “ticket” into traffic meteorology. Today, experts distinguish between “invasive” sensors (which are built into the roadway) and “non-invasive” sensors, which provide non-contact measurement.

Lufft already had 6 years experience in the worldwide installation of agro-meteorological weather stations when we started to develop road weather systems. When the manufacturers of road sensors refused to supply their products to us (only invasive sensors existed at that time), the development of our own sensors began – and was destined to reach a scale undreamt of at that time.

We were used to starting a development, planning on the basis of more or less reliable development times, and completing the development.  After a certain maturity period, smaller residual faults were eliminated and the mature product was sold for a few years until the product life cycle came to an end and a follow-on product was developed.

The first passive road sensor made by Lufft was the IRS20. Followed by the IRS21. Then came the IRS31. And this fall we introduce the IRS31Pro to the world markets.

The names indicate that the products benefit from the experience of previous developments. In addition to the different generations of these passive sensors, Lufft now has active road sensors, temperature sensors for roadways and non-contact sensors – mobile and stationary. Product families of this type come into being through our customers who approach us with ever-expanding needs. There is no better basis for product development than listening to customers and implementing their needs in innovative products.

The first IRS20 road sensor already had to meet many requirements: measure surface and below-ground temperatures, detect road conditions and salinity, and display water film height. Salinity can be determined by measuring conductivity. However, using this method to also measure water film height is a problem, because the salt seriously distorts the measured value. In the IRS20 (an intelligent sensor with built-in microprocessor), therefore, a road condition model was derived from the “raw values” (temperature, salinity and wetness) and used to calculate the conditions, such as dry, moist, wet, critical, etc.

An important innovative aspect of our development was to build this IRS20 sensor technology in 2 parts. This allowed the electronics to be removed from the housing (e.g. for laboratory testing after several years of use), without having to uninstall the housing from the road. Lufft was the only manufacturer to take this approach, which our competitors now also employ today.

The IRS21 development eliminated the disadvantage of conductivity measurement for the water film, where for the first time ever a patented radar method for “film height measurement” was used in the road. Until then it had not been possible to use such technology commercially (only militarily). As a result, for the first time, water film height was no longer calculated or estimated but measured with high precision. IRS21 measurement certificates issued by the Lufft laboratory show the characteristics and performance of the sensor over the entire measuring range for each delivered sensor, typically 0-4000 microns, corresponding to 0 to 4 mm. Moisture occurs from 10-30 microns, wetness from 100-200 microns (caused by rainfall) and aquaplaning is observed from 0.7 mm = 700 microns.

This radar method for water film measurement is a major reason why, in the last 10 years, almost all road traffic management systems in Germany were equipped with Lufft weather sensors.

In the IRS21 design, there was a small dish in which a defined amount of water could collect. Once the basin was completely filled, the percentage of “salt in the water” could be precisely determined and, from this, the freezing temperature calculated. In the case of passive sensors this value is calculated; for active sensors, however, this is determined through measurement by heating and cooling.

On highways, these sensors are installed in the “center” of the fast lane. Often though, the water film is minimized due to heavy traffic, which meant that it was not always possible for the dish to completely fill with water. When this occurred, no reading could be transmitted.

The IRS31 development avoided this disadvantage, whereby the water quantity is measured exclusively by the installed radar sensor. Water on the highways is highly dynamic – even the ancient Greeks knew that “tanta re” (everything flows). As a result of the existing transverse gradient on roads of approximately 2°, there is never a stable water film on the sensor. Strongly fluctuating water films and high frequency measurements (measurement every 10 seconds, output interval 1 minute) give rise to unstable freezing temperature values, complicating decision-making for winter maintenance services in practice.


 Lufft launches the IRS31Pro this fall:

Again there is an (extremely small, minimized) dish that can be filled much more frequently than in the IRS21 design and provides stable freezing temperature measurements. The radar method for the water film produces precise measurements in the micron range, as evidenced by laboratory certificates. Temperature accuracy of 0.2°C is extremely important for gritting operations in Central Europe (temperatures often around zero).


IRS31Pro-UMB with two sensors for subsurface temperature

The two-piece housing design allows long-term use and also means that the sensors can be laboratory-checked after a few years in circulation. And for airport applications, the IRS31 “talks” to the ARS31 and through the active measurement method thereby receives the results for the freezing temperature, independent of mixture.

The survivability of the design has been proven at airports. Some of the sensors were installed in the touch-down zone of the heaviest aircraft in the world.

After 20 years of developing passive road sensors, we are convinced that the IRS31Pro is the best passive sensor that Lufft has ever developed. But we also know that, in a few years, the IRS41 will emerge.

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