What Is the Maximum Rate of High Speed Capture for NI 7344 and 7350?Hardware: Motion Control>>Controllers>>PCI-7344
Problem: The 7344 user manual lists the following specifications for high speed capture: Capture latency................................<100 ns Capture accuracy .............................1 count Max repetitive capture rate..............1 kHz The 7350 series user manual lists these specifications: Max capture latency ........................100 ns Capture accuracy .............................1 count Max capture rate (non-buffered) .....150 Hz Max buffered capture rate ..............2 kHz per axis Can you explain these specifications, specifically what the capture rate means? Solution: Capture latency is the amount of time that may pass between the time a trigger-line goes high (external or RTSI), and the time when the position of the axis is captured and placed in a storage location. For both the 7344 and 7350 series board, this is less than 100 ns, which is fast enough to be accurate to one encoder count. The maximum capture rate is a little trickier. The 7344 can only capture one position per axis, since it does not buffer previous captures. The hardware is capable of being rearmed 1000 times a second, so the maximum repetitive capture rate is 1KHz. In practical use, however, you would want to read each value from the card and then rearm the capture trigger. This takes more time, and the bottleneck becomes the rate at which your computer can send commands and receive data. This can be affected by your CPU speed, how many other devices your computer is controlling, and how many other processes your computer is handling. As a general rule of thumb it is possible to read between 100 and 150 captures a second (100 - 150 Hz). The 7350 series implements a buffer to allow multiple captures. This means that you can make multiple high speed captures, and then read them out in larger groups. This allows for more efficient use of the bus as well as assuring no data is lost. This is why the specification for the 7350 series boards has 2 parts: one for non-buffered (which is essentially the same way of capturing positions as the 7344) and one for buffered. Related Links: 7350 Hardware User Manual 7344/7334 Hardware User Manual Attachments:
Report Date: 10/21/2003 Last Updated: 10/21/2003 Document ID: 32K7DM85 |
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