After Acquiring Data When i saw the number of samples , Some are lost ,Why?

[Agnivesh_Kumar]

I am acquiring data from DAQ card , and sample my signal with the rate of 50KHz . So when i collect the samples and check the number of samples some are lost .

When i run my VI for 2 second it will collect 80000 samples inspite of 100000.

[smercurio_fc]

Are you doing software timing or hardware timing? Please provide the way you are configuring the DAQ task, and what VIs you are using to actually read the data. How many samples did you tell DAQmx Read to read?

[johnsold]

How large are the buffers?  Can they hold 100000 samples?  Are you getting any errors?

Lynn

[Agnivesh_Kumar]

Sir, I am using Measurement Computing PCI DAS 1200 DAQ card .

It has 16 Single ended and 8 differntial Channels. Sampling Rate is 330KHz.

and i make the Vi for acquiring the data with 50 KHz Samplig rate. Actuly i am new to labview so i am not understanding what is buffer size of this , how to check this . but i make the Vi using while loop.

[johnsold]

I do not know anything about the Measurement Computing device or their drivers.

Buffers can exist in both hardware and software.  A hardware buffer is memory on the DAQ card which stores readings until the software driver can retrieve them.  Software buffers temporarily store readins in the computer memory space allocated to the driver routines until the data can be passed to the application.  Some boards have no buffers at all while others may have storage for hundreds, thousands, or even millions of samples.  Hundreds or a few thousands seem to be common on many devices.  Except for image capture boards hardware buffers larger than tens of thousands of samples are not very common.

How many samples do you read on each iteration of your loop? How many channels are you measuring? How fast does your loop run? Do you get any errors? These things all interact to determine whether you can get the data at the rate you want.

Lynn

[Agnivesh_Kumar]

Sir,

when i run my Vi for 1sec with the rate of 50 KHz then i got only 30000 samples , and for 2 second i got 80000 samples.

And i am using only single chanel.

And number of samples are 5000 with the rate of 50KHz. I am sending you my Vi that i am using and the output also.

[altenbach]

Please show us all the control values you are currently using. Why is the error out not wired? What value do you get on the "rate" output?

I don't understand why you use a while loop and a time target, since the number of samples is fully determined by the rate and count settings.

[Agnivesh_Kumar]

Control Values are: Board No :0

                             Count : 5000

                             Sampling Rate : 50000

                             Range : 0 to 5 Volt

Indicator value:       Rate is same exact as input rate 50000

Sir i am using while loop because i have to collect the data continiouslyfrom the tape. and time target is because of to run my program for specific time like for 2 Seconds or for any time .

Sir is any other method to do this?  please tell me

and sir what is the difference beetween foreground and background operation, because i have already inbuilt Vis which i already sent to you. But there is same Vi with Background operation. Is this cause the lost of samples?

[Dennis_Knutson]

I'm not convinced yet that you are actually losing samples. Set the VI to your normal inputs and run it. When it stops, go to the edit menu and select Make Current Values Default. Save it. Attach the saved VI as well as the file you write to.

p.s. Do you not want to save the result of each acquisition?

[Agnivesh_Kumar]

Yes sir i wannt to save the data of each execution for specific time . Sir i am sending you my final Vi which i am using today. but it is also not working my DAQ card is 12 bit .