scan rate exceed the limit?

[fenny]

the program runs good when we use 600000hz as scan rate,but it gives error when we use 700000 hz as scan rate, saying that the scan rate exceed the hardware limit. but the manual of the hardware(DAQ board), gives 1250000 hz as the upper limit of scan rate.what is the possible true reason for this error?

[fenny]

for got to mention: this program is for 3 channel testing. but we have changed to use only one channel when we use 700000hz scan rate.

[RIO-Todd]

When entering the scan rate, you have to take into account how many channels you are scanning to determine the sampling rate. For instance, when scanning 3 channels at 700000 Hz, you are scanning through all 3 channels at 700000 Hz and so you're trying to make the board sample at 700000*3 Hz (2100000 Hz). This exceeds the limit of the hardware.

Even at 600000 Hz (sample rate of 600000*3 = 1800000 Hz) you are above the maximum sampling rate. 1250000 is specified maximum sampling rate but sometimes you can acquire above the maximum rate. I hope this helps.

Regards,

Todd D.
Applications Engineer
National Instruments