LabVIEW
why the no of samples acquired from the cDAQ channels is very less
Hello Kodeeswaran,
I'm not sure I understand the behavior you are describing, but the sampling behaviors for the CompactDAQ (cDAQ) modules are described in the NI cDAQ-9172 User Guide and Specifications here. Specifically, I would recommend that you examine the section called "Analog Input" starting on page 12. There is a section called "Slow Sampling Rate Modules" starting on page 18 that I think may be especially pertinent. I have copied that section below for your reference.
"Slow Sample Rate Modules
Some C Series analog input modules are specifically designed for
measuring signals that vary slowly, such as temperature. Because of their
slow rate, it is not appropriate for these modules to constrain the AI Sample
Clock to operate at or slower than their maximum rate. When using such a
module in the cDAQ chassis, the maximum Sample Clock rate can run
faster than the maximum rate for the module. When operating at a rate
faster than these slow rate modules can support, the slow rate module
returns the same point repeatedly, until a new conversion completes. The
first point is acquired when the task is committed. The second point is
acquired after the start trigger.
For example, if running an AI task at 1 kHz using a module with a
maximum rate of 10 Hz, the slow module returns 100 samples of the first
point, followed by 100 samples of the second point, etc. Other modules in
the task will return 1,000 new data points per second, which is normal.
When performing a single-point acquisition, no points are repeated.
Refer to the KnowledgeBase document, C Series Modules Supported in the
NI cDAQ-9172, for more information. To access this KnowledgeBase,
go to ni.com/info and enter the info code rdcdaq."
Does this help explain the behavior you are seeing?
I'm not sure I understand the behavior you are describing, but the sampling behaviors for the CompactDAQ (cDAQ) modules are described in the NI cDAQ-9172 User Guide and Specifications here. Specifically, I would recommend that you examine the section called "Analog Input" starting on page 12. There is a section called "Slow Sampling Rate Modules" starting on page 18 that I think may be especially pertinent. I have copied that section below for your reference.
"Slow Sample Rate Modules
Some C Series analog input modules are specifically designed for
measuring signals that vary slowly, such as temperature. Because of their
slow rate, it is not appropriate for these modules to constrain the AI Sample
Clock to operate at or slower than their maximum rate. When using such a
module in the cDAQ chassis, the maximum Sample Clock rate can run
faster than the maximum rate for the module. When operating at a rate
faster than these slow rate modules can support, the slow rate module
returns the same point repeatedly, until a new conversion completes. The
first point is acquired when the task is committed. The second point is
acquired after the start trigger.
For example, if running an AI task at 1 kHz using a module with a
maximum rate of 10 Hz, the slow module returns 100 samples of the first
point, followed by 100 samples of the second point, etc. Other modules in
the task will return 1,000 new data points per second, which is normal.
When performing a single-point acquisition, no points are repeated.
Refer to the KnowledgeBase document, C Series Modules Supported in the
NI cDAQ-9172, for more information. To access this KnowledgeBase,
go to ni.com/info and enter the info code rdcdaq."
Does this help explain the behavior you are seeing?
Message Edited by Matt A on 09-18-2007 12:22 PM
