Fuselage Shell Testing at IMA Dresden With HBK

Flexible Equipment for a Varied Range of Measurement Tasks

For the fuselage shell test, IMA Dresden is commissioning a test bench that has been developed from scratch. The design of the servo-hydraulic test bench is a proprietary development borne out of extensive in-house experience, as Gerd Striegler, Head of Measurement Technology at IMA Dresden, explains: “The modified design makes the test bench more flexible for different tests, component dimensions and test standards.” What’s more, several types of stress can be exerted simultaneously and tested in a realistic manner.

The new test bench uses about 30 hydraulic actuators with suitable HBK force transducers, so that it can simulate motion-related tensile, compressive and shear stresses. The reactions to these are measured by 500 strain gauges applied on the test specimen. To achieve this, IMA Dresden relies fully on the QuantumX data acquisition system from HBK for recording the strain gauge signals in various bridge configurations and digitally conditioning them for further processing.

QuantumX is a plug-and-measure solution with comprehensive support of TEDS (Transducer Electronic Data Sheet) technology, which enables fast and flexible adaptation of the test bench in whichever way is needed. The sensor characteristics of each individual sensor are automatically read out from the TEDS chip installed in the sensor or connector, and thus significantly reducing setup times when reconfiguring measurement tasks. Manual entries – frequently the cause of errors – are no longer needed.

Freely Scalable Measurement System

With test benches of this scale, the QuantumX MX1615B, which is far more than just a measurement module, really demonstrates its versatility. The compact design includes 16 measurement inputs with universal channels. The high channel density means the system is freely scalable but also has a smaller footprint. Therefore, each module is flexible and can be distributed as required close to the measurement spots of the test specimen, both as an individual device and interconnected in a large system. In practice, each module can be removed on a day-to-day basis – for small-scale tests, for example – or modules added if more channels are needed.

Christof Salcher, Director Product Management at HBK, names further advantages of this solution: “The individual modules can be used either single or highly distributed and interconnected with a single cable. Synchronous digitization close to the measurement point saves the need for extensive sense leads, enables faster setups and improves signal quality. Together with our catman software it is truly an easy-to-use overall solution solving many testing challenges.”

The modules transmit the data via Ethernet directly to the HBK catman software running on a PC for data visualization, online and post-process analysis, data storage and remote monitoring. For the large test benches commonly used at IMA Dresden, the software also supports visualization on several screens.

Real-Time Control With Maximum Precision

According to Striegler, the biggest advantage of digital data acquisition and processing for IMA Dresden comes in the second stage: “The latest generation test bench uses the measurement data in parallel in real time for test automation.” In structural tests of large components, for applying the load one controller simultaneously actuates several hydraulic actuators. Thanks to real-time control, the controller is able to observe the measurement data during this process, and automatically stop the test or adapt the test program if the data is above or below the set characteristic values.

By contrast, in conventional systems real-time control involves converting the digital measurement data back into analog signals with standardized voltage, and the signals are then fed back into an analog feedback system. A second digitization process is then needed in order for the control system to process the impulses. “In practice, this means that not only is extensive wiring and time needed, but also, above all, the precision suffers,” explains Christof Salcher. “The fully digital measurement and control chain receives the signal in its full quality and can be achieved by using simple Ethernet cables.” Last but not least, using fewer electronics and cables brings considerable cost advantages.

Transparent Configuration, Simple Maintenance

IMA Dresden also benefits from the controller’s direct access to individual sensors. This way, different monitoring parameters can be flexibly adjusted as desired. At the same time, the fully digitized system enables targeted troubleshooting, a faster response time and therefore higher availability of the overall system for demanding testing tasks. The reduced complexity is also evident from the improved maintenance options.

The test bench is managed by the controller system, which communicates synchronously with the QuantumX system via interfaces. The interface technology connects the entire measurement and control chain between the sensors, DAQ system, software and hydraulics control system, in which all components work smoothly together.

Precise Technology for Reliable Digitization

IMA Dresden is gradually digitizing all its test benches and converting them to the new data acquisition method using reliable systems from HBK, says Striegler: “With the new generation of test benches, we are getting an upgrade that scales in line with the more demanding requirements facing both test benches and the measurement tasks.” Another major advantage for IMA Dresden is found in test appliances for mobile and in-field use. The PTP (Precision Time Protocol, IEEE 1588:2008) allows time synchronous data acquisition via Ethernet and creates additional possibilities when working with distributed devices. Real-time Ethernet on the other hand allows low latency real-time communication with limited bandwidth. 

Another key benefit is the standards of the measurement chain elements from HBK, which IMA Dresden has been using for a long time: “In setups as complex as this, the components are generally of different brands,” explains Striegler. “The interfaces of the HBK products and their flexibility enable us to seamlessly connect all the components of a measurement system, and this is especially advantageous when existing test benches get their update for data acquisition one by one.”