Case Studies
Radioactive Nuclear-Decay Detection
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.
GAGE'S SOLUTION
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 m secs. 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 m secs per channel. After that, a nominal 30 m secs 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 + 4cards*30] = 165 m secs
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.
PRODUCT RECOMMENDED
8 x CS14100-1M
1 x Master Multi-Card Upgrade for CS14100
7 x Slave Multi-Card Upgrade for CS14100
Instrument Mainframe IM2020D (w/ 10xPCI-slots, 8xISA-slots)
CompuScope SDK for C/C++ for Windows
This application note is provided "as is" without any warranties of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability or fitness for a particular purpose. Gage Applied Technologies further does not warrant the accuracy and completeness of the material contained herein. Gage Applied Technologies may make changes to this material, or to the products described in it, at any time without notice.
print this
email this
