Case Studies
Radar Application Requiring Large Record Lengths in a Rackmount Environment
THE PROBLEM
The customer needs to acquire data from his radar system at a sampling rate of 1.5 MSPS for two channels (I & Q). At the moment, this data must be acquired for at least 10 seconds, but the record length may increase by almost 100 times in the future.
This equipment needs to be installed in a rackmounted environment, so the host computer must have rackmount capability. An integrated monitor is also important as it eliminates the need to purchase a rack-mounted monitor. Keyboard and mouse must also be rackmountable.
The customer needs to make this purchase in fairly short order and requires quick delivery of the system.
GAGE'S SOLUTION
Let us analyze the data storage requirements for this application. At a sampling rate of 1.5 MSPS, 1.5 million samples is collected in one second. For ten seconds, the amount of data collected is 15 million samples per channel.
With two channels being acquired simultaneously, a total of 30 Msamples of data storage is required.
This amount of storage can be achieved using two ISA bus CompuScope 1012 cards with 16 Meg of on-board memory each, but this system will become expensive, with just the board prices exceeding $30,000.
The most cost-effective solution for this application is to use a CompuScope 1012/PCI, Gage's 12 bit 20 MSPS A/D card on the PCI bus, and to stream data to the PC memory.
The CompuScope 1012/PCI is capable of digitizing two input signals simultaneously (it has two A/D chips on-board) under the control of either an internal or external clock.
The CompuScope 1012/PCI is capable of acquiring data in either the Memory Mode or the Real Time Mode.
Memory Mode
In Memory Mode, data is captured and stored in SRAM memory on-board the CompuScope 1012/PCI. In other words, the PCI bus does not access to the data until the acquisition is stopped.This obviously means that the maximum record length you can capture without a break in the signal is limited by the on-board memory. The maximum on-board memory you can get with the CompuScope 1012/PCI is 4 Megasamples in single channel mode and, more specifically for this application, 2 Megasamples per channel.
Real Time Mode
In Real Time Mode, the digitized data is not stored in on-board memory. Instead, it is piped out over the PCI bus into PC's DRAM memory using a FIFO on the CompuScope 1012/PCI.In this mode, the maximum memory depth is limited by the amount of PC DRAM. For a PC populated with 64 Megabytes of DRAM, the maximum buffer memory available is given by:
Memory Available = Motherboard DRAM - Memory Required for O/S & Program = 64 Mbytes - 2 MB (for DOS, e.g.) = 62 Mbytes
Since it takes 2 bytes to store each of the 12 bit samples, the maximum record length you can get with 64 MB DRAM is 31 Msamples. If this memory is divided between two channels, each channel gets a record length of 15.5 Msamples.
In order to house the CompuScope 1012/PCI, we highly recommend the GagePC 580, the revolutionary Instrument Grade PC featuring a built-in color monitor (which answers to the customer's exact requirements) and front access for all CompuScope connectors. The high performance Pentium 200 MHz CPU card in GagePC 580 can house up to 128 MB of RAM.
Finally, if there is a need to store larger record lengths, Real Time Mode can be used to stream data to a SCSI device using an "Ultra Wide" adapter such as the Adaptec 2940/UW. Gage can supply this adapter with the system, so the customer can interface to an external, removable SCSI drive for storage of long record lengths. The SCSI connector will come out the front of the GagePC 580, making it easier to interface to the external device.
A rackmount keyboard and mouse, both housed in a NEMA sealed rackmount enclosure, can also be supplied with the system so the customer can mount everything in his rack.
PRODUCT RECOMMENDED
GagePC 580 with 64 Megabytes of DRAM
CompuScope 1012/PCI, Gage's 12 bit 20 MSPS A/D card on the PCI bus
Rackmount keyboard and mouse housed in a NEMA sealed rackmount enclosure
"Ultra Wide" SCSI adapter such as the Adaptec 2940/UW
High performance external hard drive connected via SCSI adapter for data streaming
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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