Television shows, such as CSI and Bones, have popularised the importance of forensics with fantastic graphics that vividly illustrate the forces involved during the impact of a bullet on the human body. Although such graphics are used to add to the gritty reality of the story line they also illustrate the importance of accurately measuring the complex forces that rapidly occur and then dissipate in ballistic tests.
Similarly research into the testing and certification of car safety belts and child restraint systems involves capturing transient data as accurately as possible to ensure that they provide maximum safety despite the massive forces that can occur in a car crash.
Capturing such data requires high sampling rates of up to 100MS/s (100 million samples per second) that can only be met by high-end data acquisition systems. In many transient tests, such as ballistics, the measurement data must be reliably recorded as part of a one-time measurement. This requires reliable triggering during the data acquisition while the increasingly small explosive charges that are used in these tests generate correspondingly high signal frequencies that need to be captured.
High sampling rates
Earlier this year HBM launched its Genesis HighSpeed products to meet the need for high-speed data acquisition and transient recording. These shares exceptionally high sampling rates ranging from 100kS/s up to 100MS/s per channel. Based on modular platforms, a system can be configured to meet the exact needs of any specific application, regardless of the number of channels.
However, simply gathering data at high-speed is only part of the problem since evaluating the results is key to the success of any structural tests. To meet this need, HBM has developed a patented feature called StatStream, which removes the need for a paper chart recorder when evaluating test data, speeding up the analysis into the bargain.
In standard PC data acquisition systems the data throughput to the hard disk is exactly the same as the data output from the hard disk. This means that a ten-minute measurement made at full hard disk bandwidth requires 10 minutes to replay; its effectiveness is limited.
StatStream produces several parallel, reduced data streams in real-time that are saved with the raw data during measurement. When displaying, for example, a10Gbyte data set on the screen, the display is generated from a reduced data set. All statistical parameters, such as minimum and maximum values, are saved with the data to ensure that every interference spike, even if it is only one sample wide, is always displayed. By zooming in on the data, sub-data sets of increasing size are used until the raw data sets are finally displayed at the sample level.
Faster processing
During acquisition, the additional StatStream information is generated without performance degradation using special Digital Signal Processors. The additional information increases the size of the data set by only 3 to 4% but replay is up to 1,000 times faster than that available from conventional PC systems; for example, an 8Gbyte data set is displayed in only three seconds.
The integrated StatStream technology enables HBM’s Perception software to calculate and display maximum values for parameters such as pressure in ballistics tests in just a few seconds. The modular Perception software improves the functionality of the Genesis HighSpeed range by precisely matching the hardware and the application to form a true electronic chart recorder.
The latest version of Perception adds live fast Fourier transform (FFT) capabilities to the complete HBM Genesis HighSpeed product family, allowing users to visualise signals simultaneously in both time and frequency domains. FFT is particularly useful, especially for customers that are just starting out in frequency domain analysis, because of its ease of use and high flexibility. For example, FFT can be enabled for transferring signals currently shown in the time domain to the frequency domain with a single click.
The ability of the software to integrate with other tools is important. To meet these demands Perception utilises an integrated Customer Software Interface (CSI) enabling user-specific plug-ins to be created that are fully integrated with the Perception operator interface. This means that the user can specify and automate tasks for inclusion in the workflow. Equally, close integration with Microsoft Office allows the user to transfer tables, displays and results easily into Word or Excel.
This has proved beneficial to a German manufacturer of combustion engine pistons in analysing cylinder pressure measurements. A requirement of the tests was to determine which cycle of tests had the highest maximum pressure, which showed the lowest maximum and to determine the average pressure cycle. All of these results had to be shown as functions of the piston’s angle position with the results from the analysis – and not the raw data – saved.
By using the CSI it was possible to add specific dedicated analysis routines to the standard Perception program that met the client’s requirements. The routine automatically searches the pressure injection cycles test results for the specified results and produces three traces that are displayed along with the peak pressure value and cycle count.