Digital Signal Processing

Crystal Instruments developed sophisticated software tools for digital signal processing. A variety of powerful algorithms for digital signal processing purposes are executed in two operation modes: (1) The algorithms are implemented in the hardware during real-time digital signal processing using a unique technology, Configurable Signal Analysis or, (2) The algorithms are executed in EDM-PA (Post Analyzer Software) for post-analysis processing.

The Post Analyzer application is used for the post-processing of previously recorded time-stream data. The post processing can include data conditioning, Fourier transform operations, and additional specialized analyses such as order tracking and octave analysis.

Both real-time digital signal processing and post processing use the Configurable Signal Analysis technology. The typical algorithms include:

• Data Conditioning Only: Apply math operations (+-*/), scaling, or real-time digital filters to the time streams. All time streams can be displayed or recorded. Transient capture and spectral analysis are not available in this template.

• Transient Capture: Apply data conditioning to native time streams, and then transform the time streams into block signals using various Acquisition Modes.

• Linear Spectrum: Apply data conditioning to native time streams, transform the time streams into block signals, and then apply data window and FFT.

• Auto-Power Spectrum: Apply data conditioning to native time streams, transform the time streams into block signals, and then apply data window and FFT to calculate auto spectra. FRF/Coh will not be calculated.

• Frequency Response: Apply data conditioning to native time streams, transform the time streams into block signals, and then apply data window and FFT to calculate auto spectra, cross spectra, frequency response and coherence functions.

• Octave Analysis: Apply 1/1, 1/3, 1/6 or 1/12 octave filters to time streams and generate octave spectra and filter r.m.s. time traces. It conforms to ANSI std. S1.11:2004 and IEC 61260-1995.

• Sound Level Meter: Sound Level Meter (SLM) template provides various overall sound level readings, time and frequency weighting according to IEC 61672-2002.

• Order Tracking Analysis: Use digital re-sampling and FFT or DFT to calculate the normalized order spectra and order tracks. Order tracks have no phase information. This is mainly used in engineering run-up and run-down tests.

• Swept Sine Measurement: Swept sine is controlled by input or output profiles with auto-gain capability. Tracking filters are applied to measure the spectra, FRF, or transmissibility signals.

• Shock Response Spectrum: Signals from original channels can be applied with data conditioning. SRS will be applied in order to measure the desired spectrum. Time stream can be displayed and recorded. Frequency signals can be displayed or saved.

Configurable Signal Analysis for Real-Time Digital Signal Processing

When the Configurable Signal Analysis for Real Time Digital Signal Processing software is installed on the Crystal Instruments CoCo, the math processing functions will be included based on purchased software options. The function set and the data processing logic for any given test for real time digital signal processing is different and is defined by a project, the Configurable Signal Analysis project. For each test, the project has different sets of definitions. The user has the choice to enable or disable certain sets of parameters, functions, display signals, recording signals or the signals to be saved when this project is edited.

The CSA software for real time digital signal processing allows the CoCo-80X to fit into different applications while it maintains its maximum simplicity of use for these specific applications.

For example, assume a user wants to conduct the auto-power spectral analysis and prefers to use free-run to acquire the data; whereas another user wants to conduct the auto-power spectral analysis and always uses manual arm trigger for acquiring data. In a conventional programming approach, both free-run and manual arm trigger are programmed and fixed in the software user interface. However, with the implementation of the CSA, the former user can enable the Free-Run option for the Acquisition Mode in the CSA editing phase while the latter user can enable the Manual Arm option. This two step setup process is shown below:

After editing their CSA projects and downloading the projects the CoCo unit, the former user will see only the Free Run under the Acquisition Mode selection while the latter sees only the Manual Arm Trigger. In many cases, the application engineers of CoCo-80X sales channels or skilled CoCo users will program the CSA project. The less experienced technician or users who conduct repetitive tests do not need to edit the projects. These less experienced users simply make accurate selections on the CoCo-80X and execute the CSA operation.

Advantage of Configurable Signal Analysis

Configurable Signal Analysis (CSA) is a new concept introduced and adopted by Crystal Instruments’ latest generation of dynamic signal analyzer systems, including the CoCo-80X. Configurable Signal Analysis allows the user to dynamically configure the digital signal processing (DSP) functions so the data processing flow can be customized from application to application. The result is a portable, handheld signal analyzer customized to include specialized, powerful functions while maintaining a very clean and simple user interface for day to day operations. Configurable Signal Analysis (CSA) is a unique feature that is currently available only in Crystal Instruments products.

Traditionally, dynamic measurement instruments could only realize fixed data analysis functions. These functions were configured by the manufacturer before the products were shipped to the user. While the user could change some of the parameters in the preset algorithms, they usually had little control over the data processing flow and the sequence of the applied math functions. With this type of design philosophy, the user interface of dynamic measurement systems tended to grow more complicated as more functions were added to meet all the different users specialized needs. Important customers had to wait for the next version for their special request to be adopted by the vendor and small customers had little chance of getting their unique needs met if the function was not widely used.

The new CSA concept completely changes this paradigm. It is designed to keep the user interface very simple while letting each user customize the analysis functions either on their own or with the assistance of Crystal Instruments support.

Contrary to the traditional approach, CSA is user customizable. With CSA, the user can flexibly apply various math operations to live data streams without changing the installed program. The processing algorithm is a combination of user customizable math functions. Most of these algorithms are fairly simple, such as add, subtract, multiply and divide operations. Some others are very sophisticated, such as calculating Frequency Response Functions (FRFs) between all the channels. The user can choose and apply the analysis functions as needed, or combine them to meet their particular needs. The user can also cascade these algorithms in sequence combining several functions to generate a very advanced new function. With this approach, the CoCo Digital Signal Processing (DSP) systems are enabled with “unlimited” application functionality.

Recommended for Digital Signal Processing

The CoCo-80X (and CoCo-90X) dynamic signal analyzer and vibration data collector are recommended by Crystal Instruments for frequency response function (FRF) measurement.