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.
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.
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 recommend the GaGePC 580, an Instrument Grade PC featuring front access for all CompuScope connectors. The high performance CPU card in the 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. 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.
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.