Introduction

This document explores the advanced features of GaGe CompuScope Digitizers in a variety of applications, featuring insights from Dr. Andrew Dawson. A seasoned physicist and leader, Dr. Dawson holds a Doctorate in experimental solid-state physics from McGill University and has extensive experience in ultrasonic material analysis. As an application engineer for GaGe, his experience has exposed him to a wide variety of digitizer applications, making this a valuable resource for understanding cutting edge advancements in the field.

Question 1: Can You Provide some Features of GaGe CompuScope Digitizers that are useful in Non-Destructive Testing (NDT) applications?

Ultrasonic NDT generally refers to ultrasonic inspection of materials, but this answer applies equally well to medical ultrasonics. The three most powerful CompuScope features for ultrasonics are:

1. High Vertical Resolution: High vertical CompuScope resolution provides the direct benefit of  lowering the minimum ultrasonic echo detectability threshold. Flaw echoes from materials can be  arbitrarily small and often follow large sample wall echoes that inhibit amplification. An 8-bit  oscilloscope, therefore, can only detect echoes that are larger than 1/256th of a large wall echo (since 28 = 256). By contrast, a 16-bit digitizer provides a minimum ultrasonic detectability threshold that is 256x smaller.

2. High Sampling Speed: Vitrek usually recommends a CompuScope sampling rate that is 10X the ultrasonic center frequency. Since CompuScope models sample at up to several GigaSamples per second (GS/s), Gage CompuScopes can accept signals from ultrasonic transducers with center frequencies of up to several hundred MHz, which covers most ultrasonic applications.

3. High Data Transfer Speed: Modern CompuScopes can transfer data to a host PC through the PCI Express bus at rates of over to 5 GB/s, which allows users to acquire ultrasonic triggers that repeat at rates more than 100 kHz. This fast transfer speed provides the direct benefit of reducing scan times in ultrasonic scanning applications or of providing better time resolution in applications where the ultrasonic signal evolves over time.

Secondary CompuScope features that are useful in ultrasonics include:

  • Multiple Record: CompuScopes can operate in Multiple Record mode, wherein the CompuScope re-arms itself within a microsecond for the next acquisition for the very fastest trigger rates.
  • Signal Averaging: Allows multiple acquisitions to be combined onboard a CompuScope to remove random noise so that the smallest echoes may be detected.
  • Trigger Out: Trigger your ultrasonic Pulser-received with a CompuScope’s Trigger Output to remove jitter associated with asynchronous sampling.

For more information on ultrasonics using Gage CompuScopes, please see:

Question 2: I understand GaGe CompuScopes can stream waveform data continuously to the PCI Express bus. However, I have a rapid and unending series of ultrasonic triggers. Can I still use streaming?

Yes. It seems that most streaming applications entail continuous and unbroken recording that is initiated by a single trigger and that may last for minutes or hours. The classic example application is communications, where users may continuously monitor a signal for minutes or hours.

Some users, however, have a rapidly repeating trigger after which they want to acquire relatively short waveforms of perhaps a few thousand points each. These users can stream in Multiple Record mode, where the CompuScope acquires a short waveform and then re-arms itself within 1 microsecond for the next waveform acquisition. Multiple Record Mode suppresses uninteresting data that occurs between triggers and so improves the overall transfer efficiency.

PCI Express (PCIe) Bidirectional Transfer Speeds in Gigabytes per Second (GB/s) for each Generation.

Building Blocks of Real-Time High-Speed Data Acquisition System with Integrated PCIe Instruments.

For more information on streaming acquisition using Gage CompuScopes, please see:

Question 3: The Gage Sabre CompuScope has 4 channels that can simultaneously sample at up to 250 MS/s. However, I have 12 channels that I want to sample simultaneously sample at 250 MS/s. Can I synchronize three 4-channel RazorMaxs?

Yes. First, any number of CompuScopes that may be physically installed within a PC may also be independently controlled through the CompuScope Software Drivers. Synchronizing the sampling clocks and triggers on all CompuScopes for simultaneous acquisition may be done easily with external cabling.

There are two cabling methods that may be used to synchronize triggering on multiple CompuScopes. In the Fan-out Method, an External Trigger signal is split into multiple copies that are connected to each CompuScope. This method minimizes the relative delay in the triggering of each CompuScope. The Cascade method connects the External Trigger signal to the first CompuScope, which then triggers the second CompuScope, which then triggers the third CompuScope, and so on. This trigger cascade is implemented by connecting the Trigger Out output signal from one CompuScope to the Trigger In(External Trigger) input of the subsequent CompuScope. The Cascade method is good for applications involving very fast triggers.

There are also two methods of driving all CompuScopes with a common sampling clock. A clocking signal is copied as in the Fan-out method and connected to the Clock In input of all CompuScopes. The clocking signal may be an external clocking signal with a frequency of the desired sampling rate or a 10 MHz reference signal. The former choice provides the best short-term phase stability, while the a 10 MHz reference signal is often easier to obtain and manage and is sufficient in many applications.

For more information on synchronizing multiple Gage CompuScopes, please see:

Question 4: Can my CompuScope be used to replace a spectrum analyzer?

Yes. Broadly speaking, there are two types of spectrum analyzers: a swept-tuned spectrum analyzer and a Fourier Transform spectrum analyzer. The latter is nothing but a digitizer that performs Fourier transforms upon the acquired waveform data. Since GageScope – Gage’s flagship oscilloscope software – includes Fourier analysis (FFT) capability, it can be used to operate a CompuScope just like a spectrum analyzer. A CompuScope may also be configured to operate like a swept-tuned spectrum analyzer, but it requires a down-converter instrument to be placed in the signal path.

For more information on using a CompuScope under GageScope like a spectrum analyzer, please see:

Question 5: My signal shows jitter and I can’t get rid of it. The jitter seems to get worse at lower sampling rates.

The jitter that you observe is no failing of your CompuScope or your signal set up but is a fundamental consequence of a sampling clock and signal trigger that are asynchronous or unrelated. This is usually the case that leads to one—sample jitter on acquired signals. This principle is commensurate with your observation that the jitter decreases with sampling rate. As the sampling rate lowers, the sampling interval, which is equal to the extent of the jitter, increases. For example, at a 1000 MS/s sampling rate, we would expect jitter with an extent of 1 nanosecond, while at a 100 MS/s sampling rate, the jitter would increase to 10 nanoseconds For more information on onesample jitter, please see:

Question 6: I know that Gage provides complete Software Development Kits (SDKs) for C, LabVIEW and MATLAB that allow users to program their Gage CompuScope in these environments. Does Gage provide support for any other programming environments?

First, the Gage C/C# SDK provides support for both C and C++ and for C# within the .NET framework. This SDK provides several sample programs for each of theseenvironments in addition to their complete project files. C Support is available under the standard Windows and under the Linux operating system.

The C/C# SDK provides the most extensive list of sample programs and the best possible performance since the CompuScope drivers are written in C. While the C/C# SDK provides complete project files for MS Visual Studio under Windows, other compilers may easily be accommodated.

The C/C# SDK provides auxiliary support for the Python programming environment and it the best starting point for unsupported environments, such as Visual Basic. The user needs only to call the Gage driver DLL in the same manner and sequence as the C sample programs to implement support.

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Question 7: Can you provide an overview of why someone would use the CompuScope 10 MHz reference clocking feature.

One method of synchronizing an external signal to a CompuScope sampling rate is to provide a synchronous high-speed external clocking signal to the CompuScope’s ADC chips. Unfortunately, such a clocking signal is not always available. Many signal sources, however, are equipped with a synchronous 10 MHz reference signal output. This signal may be connected directly to a CompuScope to make its internal sampling rate synchronous with it. For example, a 500 MHz CompuScope sampling rate will be disciplined so that it is exactly 50X the 10 MHz reference input frequency. This way, the phase between the signal and the sampling clock will not drift but will remain locked over time.

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