Abstract: A distributed data acquisition system comprising multiple, physically unconnected, data acquisition units that can be in wireless communication with a remote host, timestamps measurement data with sub-microsecond time base accuracy of sampling clock relative to an absolute timeframe. Each unit has a GPS receiver for deriving an absolute time. An analog-to-digital converter samples measurement data using a sampling clock. A hardware logic circuit, such as a field programmable gate array, associates batches of the measurement data with corresponding timestamps representing the current absolute time. A time offset bias may be compensated by a comparison of timestamps with nominal time based on start time and nominal sampling rate. Additionally, the sampling clock may be synchronized using time pulses from the GPS receiver. An initial start of ADC sampling by all data acquisition units may be also synchronized.

Abstract: A measurement system has a data acquisition architecture in one or more channels with storage in multiple sensor ranges. At least one sensor channel provides an analog measurement input signal, which is split into first and second amplifier-ADC paths, where a first path has relatively higher gain and smaller range than a second path. The digitized data is subject to cross-channel calibration that can serve as a trigger for the transfer of the two data streams into nonvolatile memory. The incoming data are temporarily stored for a specified period in a circular buffer, so that the trigger can also facilitate transfer of pre-trigger data from the buffer into the memory. A processor determines the presence or absence of any clipping of the higher-gain/smaller-range data and selects analysis of that smaller range data if no clipping is detected, but of the larger range data if clipping is detected.

Abstract: For cross-channel spectral analysis of measurement data from multiple recording units with independent sampling clocks, a processing method corrects phase mismatch between the data received over the different channels. Blocks of sampled measurement data are buffered in a hardware logic circuit and timestamps are associated with successive blocks through a hardware interrupt to a GPS receiver of each recording unit. For each first channel data block, the block's starting point, a closest point in time in a data block of the second channel, and the starting point of that second channel data block are determined, using GPS timestamps associated with those data blocks, nominal sampling rate and block size. Phase correction based on the time offset between starting points of the pairs of data blocks and the interval between starting points of successive blocks is applied in the frequency domain after a time-to-frequency domain transformation. Multiple frames of phase-corrected spectra may then be averaged.

Abstract: For cross-channel spectral analysis of measurement data from multiple recording units with independent sampling clocks, a processing method corrects phase mismatch between the data received over the different channels. Blocks of sampled measurement data are buffered in a hardware logic circuit and timestamps are associated with successive blocks through a hardware interrupt to a GPS receiver of each recording unit. For each first channel data block, the block's starting point, a closest point in time in a data block of the second channel, and the starting point of that second channel data block are determined, using GPS timestamps associated with those data blocks, nominal sampling rate and block size. Phase correction based on the time offset between starting points of the pairs of data blocks and the interval between starting points of successive blocks is applied in the frequency domain after a time-to-frequency domain transformation. Multiple frames of phase-corrected spectra may then be averaged.

Abstract: A method uses a distributed data acquisition system with multiple, physically unconnected, data acquisition units, that can be in wireless communication with a remote host, to timestamp measurement data with sub-microsecond time base accuracy of sampling clock relative to an absolute timeframe. A current absolute time is derived from messages received from a satellite radio beacon positioning system (GPS). Measurement data is sampled by each unit at a specified sampling rate. Using hardware logic, batches of sampled data are associated with corresponding timestamps representing the absolute time at which the data was sampled. Data and timestamps may be transmitted to the host. A time offset bias is compensated by comparing timestamps against a nominal time based on start time and nominal sampling rate. The sampling clock rate may be disciplined using time pulses from the GPS receiver. An initial start of data sampling by all units can also be synchronized.

Abstract: A distributed data acquisition system comprising multiple, physically unconnected, data acquisition units that can be in wireless communication with a remote host, timestamps measurement data with sub-microsecond time base accuracy of sampling clock relative to an absolute timeframe. Each unit has a GPS receiver for deriving an absolute time. An analog-to-digital converter samples measurement data using a sampling clock. A hardware logic circuit, such as a field programmable gate array, associates batches of the measurement data with corresponding timestamps representing the current absolute time. A time offset bias may be compensated by a comparison of timestamps with nominal time based on start time and nominal sampling rate. Additionally, the sampling clock may be synchronized using time pulses from the GPS receiver. An initial start of ADC sampling by all data acquisition units may be also synchronized.

Abstract: A method uses a distributed data acquisition system with multiple, physically unconnected, data acquisition units, that can be in wireless communication with a remote host, to timestamp measurement data with sub-microsecond time base accuracy of sampling clock relative to an absolute timeframe. A current absolute time is derived from messages received from a satellite radio beacon positioning system (GPS). Measurement data is sampled by each unit at a specified sampling rate. Using hardware logic, batches of sampled data are associated with corresponding timestamps representing the absolute time at which the data was sampled. Data and timestamps may be transmitted to the host. A time offset bias is compensated by comparing timestamps against a nominal time based on start time and nominal sampling rate. The sampling clock rate may be disciplined using time pulses from the GPS receiver. An initial start of data sampling by all units can also be synchronized.

Abstract: A vibration testing system for structures visually displays vibration analysis information in the form of a graphic animation using a 3D model of the object. While only a subset of the surface points of the object model correspond to sensors on the structure, an interpolation feature of the system allows deformation information for all points of the model to be estimated. Interpolation weights can be calculated in advance to allow for real-time display of a test. Color can be used to enhance visualization of vibration amplitudes. The visualization can be performed offline after a vibration test has been completed to show modal analysis results or can be done in real-time using either blocks or RMS data obtained while the vibration testing is still on-going. This is especially useful for adjusting test parameters, such as the excitation location, amplitude or both, for more effective testing.

Abstract: A vibration testing system for structures visually displays vibration analysis information in the form of a graphic animation using a 3D model of the object. While only a subset of the surface points of the object model correspond to sensors on the structure, an interpolation feature of the system allows deformation information for all points of the model to be estimated. Interpolation weights can be calculated in advance to allow for real-time display of a test. Color can be used to enhance visualization of vibration amplitudes. The visualization can be performed offline after a vibration test has been completed to show modal analysis results or can be done in real-time using either blocks or RMS data obtained while the vibration testing is still on-going. This is especially useful for adjusting test parameters, such as the excitation location, amplitude or both, for more effective testing.

Abstract: A modal vibration analysis system and corresponding method is provided. Exciters are coupled to a structure under test for generating vibrations in the structure. Sensors are coupled to the structure at multiple locations for sensing vibrations generated in response to the excitations. A controller provides drive signals to the exciters such that the sensor signals have a target output spectrum with specified characteristics in multiple designated frequency domains of the spectrum, characterized by a random phase for each frequency. Modal analysis processes digitized sensor signals with a Fast Fourier Transform conducted at two or more specified data sampling rates to synthesize a spectrum containing data points with finer frequency resolution for lower frequency range, and regular frequency resolution for higher frequency range. From the multi-resolution spectra, natural frequencies and damping coefficients are determined at each mode, and a mode shape at each natural frequency is computed.

Abstract: An integrated controller for an environmental testing system simultaneously controls and synchronizes vibration, temperature, and humidity in an environment test chamber over a specified reliability test duration, and performs condition-based measurement and processing of vibration data obtained from the environment test chamber for one or more specified trigger conditions. The controller executes a combined run schedule using a single internal clock and a hardware processor, to generate parameter control commands for the environment test chamber that remain synchronized to the single internal clock over the duration of a test, even one that lasts for weeks or months. This permits multi-variate processing of measured instantaneous values of temperature, humidity, and vibration to obtain, e.g., condition-dependent vibration power spectra and averages for available conditions of temperature, humidity, or both.

Abstract: A modal vibration analysis system and corresponding method is provided. A set of one or more exciters is coupled to a structure under test for generating vibrations in the structure. A set of sensors are coupled to the structure at multiple locations for sensing vibrations generated in the structure in response to the excitations. A controller receives sensor signals corresponding to the sensed vibrations from the set of sensors and provides drive signals to the set of exciters such that the sensor signals have a target output spectrum with specified characteristics in multiple designated frequency domains of the spectrum, characterized by a random phase for each frequency. Modal analysis processes digitized sensor signals with a Fast Fourier Transform conducted at two or more specified data sample rates to synthesize a spectrum containing data points with higher resolution for lower frequency range, and regular resolution for higher frequency range.

Abstract: A plurality of measurement devices have analog sensors that measure the dynamic signals of physical events, sample the data into digital format with time synchronized clocks and generate time stamped Ethernet messages that are sent to a remote host. The remote host has a master clock that evaluates decoded time stamped messages from the measurement devices and sends back a message with a time correction error signal relative to the master clock. This feedback signal is used by the measurement devices to correct a local clock for data sampling and new message generation. Eight wire cable and associated connectors are used to handle three channels of traffic, with four wires dedicated to Ethernet messages as one channel, another two wires dedicated to reset and other commands as a second channel and another two wires to transmit power from the host to the measurement devices as a third channel.

Abstract: A plurality of measurement devices have analog sensors that measure the dynamic signals of physical events, sample the data into digital format with time synchronized clocks and generate time stamped Ethernet messages that are sent to a remote host. The remote host has a master clock that evaluates decoded time stamped messages from the measurement devices and sends back a message with a time correction error signal relative to the master clock. This feedback signal is used by the measurement devices to correct a local clock for data sampling and new message generation. Eight wire cable and associated connectors are used to handle three channels of traffic, with four wires dedicated to Ethernet messages as one channel, another two wires dedicated to reset and other commands as a second channel and another two wires to transmit power from the host to the measurement devices as a third channel.

Abstract: In a data acquisition instrument with dual A/D converters in each measurement channel, phase corrections between the paths are computed using a locally generated calibration signal. The calibration signal goes through dual paths simultaneously and is stitched into a single signal for analysis by a processor running a Fourier transform where phase differences are easily identified and used to establish a phase correction signal applied to a single master clock supplying clock signals to both paths. A switch allows the calibration signal to be applied to each channel or to no channels when actual data is being collected.

Abstract: In a data acquisition instrument with dual A/D converters in each measurement channel, phase corrections between the paths are computed using a locally generated calibration signal. The calibration signal goes through dual paths simultaneously and is stitched into a single signal for analysis by a processor running a Fourier transform where phase differences are easily identified and used to establish a phase correction signal applied to a single master clock supplying clock signals to both paths. A switch allows the calibration signal to be applied to each channel or to no channels when actual data is being collected.