Case Studies
Echo-Cardiography Experiment
THE PROBLEM
This Customer is involved in an Echocardiography experiment. The customer already has an ultrasound imager with a built-in A/D converter which can output 12 bit image data which must be analyzed with the customer's proprietary algorithms on a PC platform.
In order to accomplish this, it is required to bring 12 bit digital data at 35 MHz clock rate into an IBM PC. This data is arriving in a burst mode with a repeat frequency of 12.8 KHz with 1000 samples arriving in 28 uS followed by no data for the next 50 uS. There are 512 such data bursts per frame and 25 frames per second.
The customer would like to collect at least a few seconds of data. On top of that, they require 8 channels of analog A/D, each channel sampling at 40 KHz. These channels are for monitoring the electrocardiograph and other signals during the experiment.
GAGE'S SOLUTION
To determine which product will best meet the application requirements we will first work out what the data throughput rate is and what the total memory requirements for this application will be.
Data Throughput = Repeat Frequency per second * number of sample points per burst
= 12.8 KHz * 1000
= 12,800 * 1000
= 12.8 MSPS
Total Memory Requirement:
The customer needs to capture for at least a few seconds - let's assume that the capture time is 3 seconds.
Total Memory Requirement = Data Throughput * Time in seconds
= 12.8 MSPS * 3 seconds
= 38.4 MegaSamples
The total memory requirement is 38.4 MegaSamples. The CompuScope 8012 ISA cards have memory buffers up to 16 MegaSamples, therefore, it would not be possible to store 38.4 MegaSamples in the on-board memory of the ISA bus product line. This means that the ISA bus CompuScope 8012 cannot satisfy the requirement of this application.
The customer can, however, solve the problem by using a PCI bus CompuScope 8012/DIM and stream data to the PC's memory. The data throughput required for this application is 12.8 MSPS which is well within the 50 MSPS (100 MB/s) throughput specification of the CompuScope 8012/PCI in Real-Time mode.
The Digital Input Module (DIM) is an ISA bus PC board which attaches to the footprint of the A/D converters used on the CompuScope 8012/PCI, thereby providing the user a direct path to the on-board memory management circuitry.
Since the CompuScope 8012/DIM takes in 24 bits of data on every clock edge, the customer will be wasting half of the PC memory if they input only 12 bits. In other words, the Total Memory Requirement will be twice what was calculated earlier (76.8 MegaSamples or 153.6 MegaBytes instead of 38.4 MegaSamples or 76.8 MegaBytes).
Alternatively, the customer may demultiplex the 12 bit data into a 24 bit word before inputting it to the CompuScope 8012/PCI.
For the 8 analog inputs, the customer has two options:
Option #1:
The customer can purchase an off-the-shelf A/D card from National Instruments, Keithley or Computer Boards which can sample at an aggregate rate of (8 x 40 KHz) = 320 KHz.
The Problem with this approach is that the ISA bus on almost all computers is bridged through the PCI bus and any appreciable activity on the ISA bus causes severe degradation of the PCI bus bandwidth.
This application uses up a significant portion of the PCI bus bandwidth, so using an ISA A/D card at a relatively fast rate of 320 KHz may result in lost data from the CompuScope 8012/PCI DIM.
Option #2:
The customer can simply use a multi-card system from Gage comprised of 4 CompuScope 225 cards in a Master/ Slave configuration, each card having 512 K of memory. By using the on board memory, we eliminate the problem of slowing down data transfer on the bus for the PCI streaming. When the CompuScope 8012/PCI DIM is done its capturing, we can go back and read the 8 channel data from the CompuScope 225 cards.
The same trigger signal will be fed to both the CompuScope 8012/PCI DIM and the CompuScope 225 multi-card system to synchronize the start of capture.
The customer will also need a reliable PC to do all of this. The Gage PC 586 industrial PC with a passive ISA/PCI backplane can provide the ideal solution. Gage can supply all of this as a turn-key system.
PRODUCT RECOMMENDED
CompuScope 8012/PCI DIM with External Clock
4x CompuScope 225 in a master/slave configuration
GageScope Multi-Card software
Gage PC 586
Pre-Tested System Option
Software drivers of the customers choice.
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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