Laser Scanning Microscope Interface
Customer Case
This customer needs to interface a scanning laser microscope to their PC so that image data can be acquired and stored. Data is received from the laser microscope via an optical sensor at 1300 line scans per image. Each scan has an 8 ms duration, but 2/3 of that time is scan time and 1/3 is flyback time (dead time). The customer has determined that a 1 us sample width (or faster) would be adequate. There is also a price vs. performance issue – the customer has a tight budget and wants the lowest-cost product that will do the job.
GaGe Case Solution
There are two possible solutions to this customer’s problem:
Option #1: Store a Single Frame in the CompuScope Card’s Onboard Memory
The customer could use GaGe’s on-board memory stacking feature, Multiple Record, to capture each scan line as it comes in. Since the line scan is 8 ms wide but only the first two-thirds of the line is scan data, the time for each line would be:
8 ms * 2/3 = 5.33 ms Total number of samples per line = total time / sample interval = 5.33 ms / 1 us = 5330 samples Total on-board memory required = total number of samples per line * number of lines = 5330 samples * 1300 = 6.93 Megasamples
In this case, the customer would need a 12-bit card which can store at least 8M of data in the single-channel mode using Multiple Record. CompuScope 512 is GaGe’s lowest-cost 12-bit card, but since it operates in dual-channel mode only (meaning that the 8M of on-board memory is shared between two channels), we would either have to choose the 16M version or halve our sample rate to keep costs down. In either case, the cost will be more than this customer’s alloted budget.
Option #2: Capture and Transfer Line-by-Line to PC Memory
This solution requires a line-by-line transfer to PC host memory. The critical factor here is to make sure the customer can transfer the required amount of data in the allotted time. If they cannot, they may miss a scan line-meaning that the resultant image would be missing lines-and this is unacceptable.
For this solution, we will need to take advantage of the faster transfer rates possible on the PCI Bus. The total time to capture was already calculated above. The time to capture each line would be:
8 ms * 2/3 = 5.33 ms
The transfer rate to PC Host memory is 50 MSPS (MegaSamples Per Second) for the CompuScope 512/PCI. Therefore, the time to transfer a single point would be:
1 / 50MSPS = 20 ns per point The time to transfer the line to PC memory = transfer time for one point * number of points = 20 ns * 5330 samples = 106.6 us
Rearm time for the card depends upon the customer’s program code, compiler, operating system and instruction time, but we can safely assume 5 us -10 us at worst case.
As seen in the chart below, we can safely capture, transfer and rearm with plenty of time to spare:
Option #2 would be the more cost-effective solution for this application, given that much less on-board memory is required.
GaGe would therefore recommend the CompuScope 512/PCI with 512K of on-board memory, using a line-by-line capture to PC memory using our Memory Mode transfer. Memory Mode transfer simply means that data is stored in on-board memory of the CompuScope card and can be read from on-board memory to PC host memory for display and/or analysis between acquisitions. This mode has the advantage of allowing very fast sample rates, as we have seen in this application.
GaGe Case Recommended Products
- CompuScope 512/PCI – 512K 12-bit, 5 MSPS A/D Card for PCI Bus with 512K Onboard Memory
Medical Application Request
We encourage you to contact us and discuss your medical application in more detail with our engineering team. GaGe can provide tailored custom data acquisition hardware and software solutions to meet specific application requirements.