The customer has a requirement for PC-based waveform digitizer cards to digitize shaped pulses derived from nuclear-decay detectors. These pulses vary in their rate (frequency of occurrence) and amplitude. Their shape is approximately Gaussian with a full-width at half the maximum amplitude (FWHM) of 3-5 microseconds. The characterization of each pulse is critical for the accurate and precise determination of the activity of radioactive materials. These materials have very low count-rates (0.02 pulses per minute) to relatively high count-rates (>1000 pulses per minute).
Important to the measurement process are the speed and reliability of the waveform digitizer cards in order to digitize pulses continuously with minimal probability of missing a decay event. The re-displaying of digitized pulses during the data acquisition is an important capability and needs to be done in near real-time.
They need 4 cards, each able to simultaneously digitize two input-voltage signals at a minimum of 50 Million samples per second, with a voltage-resolution of at least 1 part in 4096. This means that they need 12-bits of vertical resolution. The number of points per record is up to 4096 points, with each channel needing a minimum of 256 k words of acquisition memory.
We recommended the CompuScope 14100. With a CS14100 in Memory-Mode, at the externally-clocked sampling-rate of 50 MS/s in single-channel mode, a minimal-sized 256 point acquisition would take 5.12 msecs. To then transfer that 512 Bytes (2 Bytes per Sample) acquisition to PC-RAM using PCI bus-mastering (at over 100 MB/s) for displaying and saving, would take less than 5 msecs per channel. After that, a nominal 30 msecs per card is required to rearm for the next trigger.
Therefore, for an eight-card system, this gives a total cycle-time of about Pulse Repeat Interval:
(PRI) = [5 + 8 channels * 5 + 4 Cards * 30] = 165 msecs
Best-Case Scenario, the repetitive-trigger Pulse Repeat Frequency (PRF) is less than 6kHz. This is 6 times more than their upper requirement of >1000Hz (pulses-per-minute).
Theoretically, we cannot guarantee to display every pulse nor can we guarantee that there will be no missed triggers. Video refresh is a big bottleneck as it is for any GUI-based software application. In our own Windows-based GageScope PC Oscilloscope Software design, we generally target a 30 Hz refresh-rate or better to ensure that it is flicker-free. The customer's own customized software-development can also account for this. We have therefore suggested the C/C++ software development kit. As an added bonus, the SDK includes the Standard Edition of GageScope Software.
We encourage you to contact us and discuss your research & development application in more detail with our engineering team. GaGe can provide tailored custom data acquisition hardware and software solutions to meet specific application requirements.