NI-PCI 6221 'sampling rate'

[tan0207]

Our system has NI-pci 6221 card, SCXI-1000 chassis, 2 x  SCXI-1102, 1 SCXI-1100, 2 x TC-2095, 1 BNC-2095 and sensors. Software WinXP, VI Logger Lite 2.01.
 
The problems is I can not set the scan rate slower than 214.748s (rate 4mHz or lower), could you tell me what is the cause of this problem.
 
Regards,
 
Mr Tan Nguyen

[tan0207]

Hi Matthew,
 
The problem is the number 214.748s relate to the Rate(Hz): 4mHz or any number lower.
If I set Rate(Hz): 5mHz I got sampling rate 200s, but if smaller Rate(Hz) was set, it always show sampling rate 214.748s, where is that number come from?
 
Regards,
 
Mr Tan Nguyen