SR830 data storage for rs232

Hi,

I found a LabVIEW code here which can storage data from input signal (e.g.A/I)in SR830 and transfer it by the GPIB.

I used function generator to generate a sine wave with frequency:30Hz& Vp-p:100mVolt , conencting to SR830.

Clearly ,I got a correct result when i used the code by GPIB communication interface(left graph).

Than,I tried to change the communication interface RS232 to accept the same signal,but it has mistakes(right graph).

 Here is original code "data storage for GPIB"

Here is rewrite code for RS232 by myself,but what's wrong i did?