Record all the data acquired by DAQ

Question

Hi all,
I have a problem when I tried to record all the data acquired by the DAQ card. My DAQ is NI 6259, and the Labview version is 2009.
Basically, what I need do is using multiple channels to get the voltages of different point, then I subtract values of two channel (V+ and V-) to get voltage value between two points. In my vi, the sampling mode is continuous and the rate is 100 KHz, DAQmx reading is inside a while loop, and the numbers of samples per channel is set to be 100. After each loop execution I would get 100 data.  I just used the format into file to write the data into a .txt file. It seems after 1 loop only the last one data is recorded instead of 100.  Previously I averaged the 100 data inside the acquisition loop to get one data, so the writing function is OK but it really slows down the program. So I want to write all the raw data to txt file so later I can process them in Matlab.  Is there any way to achieve this? Thank you very much.
The attached is the my vi for 2 channels voltage measurement and the current source control sub vi. I am new to Labview so the question really bothers me even after I read some similar topics in the forum.
Regards,
Hongxiang
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Attachments:
Dual Channel Voltage Measurement.vi ‏33 KB
Current Source 1.vi ‏49 KB

Answer 1

Thank you for you reply. I tried that, it actually record more data per pulse than before, but less pulses were  recorded (there should be 8 pulses in 20 seconds time but only 2 were recorded), I think it was because the for loop inside slows down the program execution, and sometimes the error 200279 occurred.  I think it would be better to separate the reading and recording process. Someone suggests me rather than writing to the file inside the loop, accumulate the data from all of the loop iterations to generate one large array containing all of the samples then pass that to Format Into File outside the loop. Do you know how to achieve that? I tried the as below, it seems totally wrong , only two data was written. 
(The subvi nameed 1 (see attachment) converts the 2D array to 1D ) Thanks.
Attachments:
2D_Data_Reader.vi ‏9 KB