Hi Hahnab,
You are seeing these longer time intervals because of the slower speed of the USB interface when compared with PCI. Although the data that is output is a very small amount of data that is sent over the USB interface, many other commands are sent to the device during each single point IO operation that take time. This overhead makes each single point operation take a longer time on USB than PCI.
Check out the following KB:
Title:
How Fast Is a DAQPad for Single Point I/O Operations?
Problem:
I am using a DAQPad for data acquisition (DAQ), and I have noticed that when I do a single-point DAQ operation, the measurement is slower than doing a comparable operation with a PCI board. In particular, I am running software-timed,
non-buffered analog input. Is this the expected behavior?
Solution :
DAQPads are offered for the Universal Serial Bus (USB) and the IEEE 1394 (also known as FireWire). Both of these standards use a high-speed serial communication protocol between the computer and the device with a bandwidth up to 12 MB/s for USB and 400 MB/s for FireWire.
During a single point operation, the DAQ device requires a complete set of configuration commands. This is done through serial communication (USB or FireWire), making the process slower than in a PCI-based board. The speed obtained for single point operation in a DAQPad is system dependent; this means that your computer processor, memory, bus speed, and other factors alter the speed at which you can do single-point operations with a DAQPad.
For example, on the DAQPad-6020E, timed non-buffered analog input operations are limited to about 50 Hz. At higher rates, the software may become unresponsive. On a FireWire device, you can expect st
able operation around 3,000 Hz. But again, these figures are system dependent. For more information please refer to the links below.
