Getting the job done successfully
It doesn't always have to be large and expensive measurement and data acquisition systems that provide valuable assistance in technical driving tests on rail vehicles. Miniaturized data loggers in particular are proving to be useful tools for comfort and driving safety measurements.
More comfort, more safety, more economy: when it comes to rail vehicles, the manufacturer has to take into account the various requirements of operators, passengers and legislators. Stadler Rail AG, a manufacturer of rail vehicles with a focus on regional trains, streetcars and customized rail vehicles, is well aware of this. The company, based in Bussnang, Switzerland, employs over 6000 people worldwide and is regarded as the leading manufacturer of rack-and-pinion rail vehicles. Stadler's specialists for vehicle dynamics are responsible for technical measurements. According to the two experts, Dipl.-Ing. Karl Tillmetz (Bussnang plant) and Dipl.-Ing. Claudia Kossmann (Altenrhein plant), their technical driving tests include driving safety and driving comfort tests. "For these tasks," says engineer Tillmetz, "Stadler is supported by MSR165 mini data loggers with integrated 3-axis acceleration sensors."
Countering the subjective perception of ride comfort with facts
The mini data loggers are developed and manufactured in Seuzach, near Winterthur. They are miniaturized and can be used autonomously. Using highly sensitive sensors, the MSR loggers record almost any physical and electrical measurement data such as temperature, humidity, pressure, brightness, vibrations and other electrical voltage values. The MSR data loggers are used at Stadler for various applications, for example to clarify sudden oscillation or vibration phenomena during the operation of a rail vehicle. According to the engineers, the characteristic features of MSR data loggers - autonomous, very small size, very large memory - are ideal when it comes to carrying out measurements quickly and, if necessary, incognito. The small data recorders are quickly installed and enable a quick statement to be made about the vibration ride comfort of a train. "Passenger demands in terms of ride comfort and therefore vibration behavior have risen steadily in recent years," explains Tillmetz. "With test runs in which we use the data loggers to record the accelerations on the floor in the carriage in all three spatial axes above the bogies and in the middle of the carriage, we ensure objective measured values and thus clarity in terms of ride comfort." Vehicle vibrations are recorded by Stadler in a frequency range of 0-100 Hz. According to engineer Kossmann, the sampling rate of the MSR data loggers is set to 400 Hz during the test drives. Measurement rates of up to 1600 measurements per second would be possible with the MSR165 model used, but would not make sense in the present application. For data recording, the loggers are attached to the floor (carpet) on base plates with spikes. The test drives are carried out at speeds that are as constant as possible (up to 200 km/h so far). Depending on the requirements, short individual measurements are sufficient, but sometimes measurement series lasting several days are also useful.
To evaluate the data, the engineers export all logger data as a .csv file to their own measurement evaluation software, called FAMOS. A routine programmed into the software filters the signals according to the European ride comfort standard EN 12299 (or UIC 513) and evaluates them using frequency analysis, statistics and target value comparison. Of course, the Stadler team does not only carry out comfort measurements on rail vehicles that are already in operation. With their tests on prototypes and during the initial acceptance of series vehicles, the experts ensure that the comfort values specified by the customer in the specifications are met.
Evaluation of dynamic driving stability
Clear standards and guidelines (EN 14363 and UIC 518) must also be adhered to for driving safety measurements. These are not only applied for new approvals, but must also be taken into account for modifications. As Dipl. Ing. Tillmetz points out as an example, the latter is currently the case with a Swiss customer - the Matterhorn Gotthard Bahn (MGB) - whose vehicles of the type BDkt (box carriages, built in 1990) are being modernized. The so-called "refit" by Stadler includes folding steps, automatic couplings, modern driver's cab and control technology and an adaptation of the exterior design to the current design guidelines of the MGB fleet. In order to prove the driving stability of the rail vehicles, test runs are carried out and the acceleration in the transverse direction of the chassis frame is recorded. To do this, Dipl.-Ing. Karl Tillmetz attaches a mini data logger to the chassis frame. The MGB trains built for 80 km/h had previously only been in operation at 65 km/h.
For operation in a train set with the KOMET vehicle family, the driving stability must now also be proven for 80 km/h (+10 km/h reserve). Tillmetz and his colleagues also use the mini data loggers for these tests. The test for driving safety is carried out in accordance with EN 14363 - the standard is actually valid for standard gauge. For the test measurements, the engineer again sets the measuring frequency of the data loggers to 400 Hz and attaches four of them to the running gear frame of the train, in the intermediate level of the wheels/wagon body at the position of the wheelset. The 15 g sensors now measure the accelerations in the transverse direction on the bogie frame above all wheelsets during the approximately 10-minute journeys. The measurements are taken over a total of approx. six hours during all shuttle runs. The "measuring trains" are always lined up between the scheduled trains. The constant speed of the train during the test runs is 60, 70, 80 or 90 km/h. All signals recorded by the data loggers are then filtered and evaluated using the FAMOS evaluation software in accordance with EN 14363 (frequency analysis, statistics, limit value comparison), thus enabling a precise statement to be made about the driving stability of the tested train.
New type variants: Developing for the future
According to Tillmetz and Kossmann, the applications of the MSR data loggers at Stadler are also reaching their limits. The two engineers wanted an even more precise resolution for measurement tasks. The 15 g sensor, which is installed in the MSR165 data loggers, has an accuracy of ±0.15 g with a resolution of 0.005 g. Although this is sufficient for their applications in most cases, according to Kossmann, an accuracy of 0.003 g would be desirable. It would be possible to use another data logger of the type MSR160, which has four analog inputs and can be equipped with its own sensors that correspond exactly to the desired measuring range. However, as these would have to be attached externally, they are not well suited to the applications required by Stadler. The measuring range of 15 g previously used for the MSR165 data logger is based on the fact that this type of logger was originally designed for shock measurements. Due to the great demand for applications in the field of transportation monitoring, MSR has even extended the measuring range to 200 g this year, so that even more intensive shock events with considerably greater forces can be recorded.
Are logger variants with a smaller measuring range now also being developed? "Yes," says MSR Managing Director Wendelin Egli. "Vibration measurements in different variants are a topic that we will be expanding." Due to the establishment of the MSR165 data logger, he is receiving an increasing number of inquiries from various sectors and sees potential. "We operate in a niche market with our data loggers," says the Managing Director. "Our business success is therefore sometimes based on the fact that we are close to our customers and, as a specialist, can meet their needs better, more effectively and more directly than companies that focus on the market as a whole. So if our customers want sensors with a smaller measuring range, we will do our utmost to fulfill their wishes." - Stadler would definitely welcome the offer of an MSR165 with a sensor with a smaller measuring range. Until then, according to Kossmann and Tillmetz, the MSR165 data logger with a 15 g sensor is still justified, because "it enables us to make quick and precise statements as well as uncomplicated and time-efficient measurements, all at a manageable cost."