Case Studies
Digitizing Ultrasonic Signals at 16 MSPS for 10 Seconds
THE PROBLEM
The customer has an ultrasonic signal that he wants to digitize with either 8 or 12 bit resolution. The sampling rate required for this application is a minimum of 16 MSPS (20 MSPS is acceptable). Finally, the data must be acquired for a full 10 seconds.
The data is not coming in continuously: it is arriving in bursts one millisecond apart (PRF = 1 KHz). For each trigger the customer wants to capture approximately 200 us of data.
Once this data is acquired, the customer wants it saved to the hard drive as a standard MSDOS file, so his analysis programs (written in LabVIEW) can read the data.
GAGE'S SOLUTION
Let us first calculate the amount of data needed to capture for each trigger.
This is given by the simple equation:
# of points = Capture Time (in seconds) x Sample Rate (in Hertz) = 200us x 20 MSPS = 200 e-6 x 20 e+6 = 4000 points
We also know that the Pulse Repeat Frequency (PRF) is 1 KHz. Therefore the number of triggers received per second is 1000.
As such, the total number of triggers received in 10 seconds will be 10,000.
Now we can calculate the total amount of data collected in 10 seconds:
Total Amount of Data = Number of Triggers x Number of Points per Trigger = 10,000 x 4,000 = 40,000,000 sample points
The only way this many points can be collected is if we use a PCI bus CompuScope card, which can stream data to the PC memory in between triggers at rates high enough to guarantee no missing triggers.
The ideal product for this application is the CompuScope 1012/PCI. This card can digitize the analog input signal at rates up to 20 MSPS and then transfer the data to PC's memory (DRAM) at rates up to 100 MB/s.
Since the CompuScope 1012/PCI is a 12-bit digitizer and each 12-bit sample occupies 2 bytes, the maximum PCI bus transfer rate to PC DRAM is 50 MS/s.
At the full 50MS/s transfer speed, the amount of time it will take to transfer 4000 points collected for each trigger is given by :
Transfer Time = # of Points / Transfer Rate = 4000 / 50,000,000 = 80 us
This calculation proves that there is more than enough time to acquire the 4000 points of data, transfer them into PC DRAM and re-arm the card well before the next trigger comes in.
Gage can supply the source code of a program that does almost exactly what is presented here.
Gage can also supply a complete "Turn-Key" system: A/D Card, PC and software, should this be desired. The GagePC line of high quality, rugged and reliable Instrument Grade PCs is ideal for applications such as this one, which makes no compromises on acquisition speed, data integrity and digitization quality.
PRODUCT RECOMMENDED
CompuScope 1012/PCI
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.
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