Overview
The technology described in this article was successfully used in the Ground Recorder System to achieve a very high measurement of dynamic range for a recent NASA project. This technology is now integrated into the CoCo-80X portable hardware platform by Crystal Instruments.
In 2007, Crystal Instruments (CI) was awarded US patent #7,302,354 B2 for a cross-calibration method featuring a unique dual ADC (Analog-to-Digital Converter) design for data acquisition applications. This highly successful patented technology is sold annually in thousands of units incorporating this innovative design. The dual ADC structure and its cross-calibration technique significantly simplifies the data collection process for users, particularly when measuring physical phenomena like shock, vibration, strain, or acoustic signals. This system eliminates the need for manual input range adjustments on CI hardware.
The dual ADC architecture, especially when applied to stable or gradually varying signals, has proven to be particularly effective over the past 15 years. For instance, in machine condition monitoring, it enables the gradual observation of vibration levels - a key indicator of machinery health. Similarly, in environmental vibration testing, the technology adeptly handles variable signal types, maintaining high reliability and user convenience.
Despite its widespread success, areas for improvement have been identified, particularly regarding transient signal processing where rapid changes occur.
Upgraded Technology
Technological advancements in electronic hardware, including more affordable data storage and faster processors, have led to significant improvements. The new approach involves storing data streams separately from the dual ADCs, either in volatile or non-volatile memory, rather than stitching them together when this working mode is selected. This method allows for comprehensive data capture during transient events without compromising signal integrity.
Data recording durations are based on application needs from milliseconds to days to ensure coverage of the entire transient process. During post-recording, the software will determine the most accurate data stream to use based on the occurrence of clipping in the smaller ADC range.
The following plot shows that when the amplitude of sine wave excitation is increased to above 500 mV, clipping of the green line appears. The plot illustrates when recorded signals from both ADC ranges are recorded and analyzed. In this case, the application software should switch to use the signal from a large ADC range while both are available.
This updated method doubles the amount of data typically recorded in a four-channel DAQ system. Advancements in hardware technology enable this significant increase in data volume. Clipping detection is simplified to ensure the most accurate and noise-free signals are used for analysis.
Unique Approach
Crystal Instruments’ approach differs significantly from conventional multi-channel recorders. Notably, our unique cross-channel calibration ensures unmatched precision between ADC channels. Users can choose between Auto and Dual modes according to their needs, a flexibility not provided by other systems. Our method also requires fewer sensors, reducing overall system complexity and cost.
Functionality and Advantages
The proposed method retains all the advantages of the dual ADC architecture while enhancing functionality and user convenience. It offers high dynamic range results, avoids artifacts from data stitching, and provides efficient transient signal handling while maintaining the system's integrity.
Users might wonder how Crystal Instruments’ implementation stands out and differs from a traditional data acquisition system that features multiple input channels, each with its own range settings.
Crystal Instruments’ method distinguishes itself with several powerful functionalities:
Cross-channel calibration: Unlike typical systems where each channel is independently calibrated against a standard source, Crystal Instruments’ dual-channel calibration aligns two ADC channels to achieve utmost precision. This ensures that the calibrated channels are perfectly synchronized, enhancing the overall accuracy of data acquisition.
Mode flexibility: CI systems allow users to switch between the traditional Auto mode and the newly introduced Dual mode, as outlined in this document. This option empowers users to select the optimal mode based on the specifics of their application and the nature of the signals being recorded. This is a feature not available in standard DAQ systems.
Sensor efficiency: Traditional systems may require twice the number of sensors due to their separate input channels. Crystal Instruments’ innovative approach halves this requirement by effectively utilizing the dual ADC architecture, thereby reducing the complexity and cost associated with sensor deployment.
Enhancements to Crystal Instruments’ dual ADC method provides several key advantages:
User convenience: the new approach eliminates the need for manual input range adjustments by retaining the dual ADC structure's core benefit, maintaining operational ease and efficiency.
High dynamic range results: the system analyzes the clipping status post-acquisition to ensure the selection of a data stream with an optimal signal-to-noise ratio. This automated process provides high-quality results without manual intervention.
Artifact elimination: unlike the original stitching method, the improved approach does not merge data streams, thereby preventing the introduction of artificial discrepancies between signals.
Enhanced transient handling: the updated system adeptly manages transient signals and accurately captures dynamic changes without losing fidelity.
In essence, this refined method builds upon the foundational advantages of the dual ADC structure while addressing its limitations, particularly in transient signal processing. This evolution marks a significant step forward in data acquisition technology, ensuring Crystal Instruments remains at the forefront of the industry.