SR830 data storage

[pankajain]

I am planning to develop the C-V measurement set-up of MOS capacitors using SR830 lock-in amplifier. I am using 2 instruments in my experiment. One is the source meter with the help of which I am providing a linear voltage ramp from -10 to +10 volts to the MOS capacitor.I want to store  the corresponding  values in the channel 2 of the lock-in. I have the labview drivers for the SR 830 lock-in. I am using the data storage vi for storing the data. I want to plot this data from the lock-in (y axis) vs the data from the source meter (x axis). The problem is that the variation in the channel 2 is very small in milli volts whereas the data storage vi captures the values only in volts. The values in the instrument can be changed from volts to millivolts but the data storage vi captures the values only in volts. As the values are very small, the data storage vi is showing constant values (for eg. 0.002 volts) whereas the values are actually varying from 2.1 mV to 2.9 mV. I hope you understand the problem. Please reply.

[GerdW]

Hi pankajain,

change the "data storage vi" to save more digits!

Well, you gave a lot of information, but not exactly the needed...
Either attach the "data storage vi" so we can have a look at it.
Or search for some format codes in the vi. Set them to "%.6g" (or similar...).

[pankajain]

Thanks for your reply. Actually I am new to labview. I am attaching the data storage.vi. Please have a look at it. Kindly suggest me a solution

[Mathan]

Dear pankajain,

You have missed the attachment.

Mathan

[pankajain]

Sorry I forgot to attach the vi.

[GerdW]

Hi pankajain,

in the "Data storage example.vi" there are some SR830 command which seem related to resolution of saved data. See comment in attached vi and look into the manual!

[pankajain]

wwll. the manual says that 1,0,%d stands for reading the data in floating point form, but nothing is said about the precision. I think 8.0 stands for precision but I am not sure in what manner. In your first reply, you said something about using %.6, can you elaborate on that

[GerdW]

Hi pankajain,

read the context help for "format into string"...

You will find (after clicking some links) a big table containing explanations for all those format codes.
"%x.y" is describing number of digits x with precision y. A format code of "%8.2f" will result in a floating point number with 8 digits and 2 digits of precision (after decimal separator) like "12345.67"- atleast in LabView. The SR830 seems to use a slightly different format string when you say %d will give floating point numbers...


Message Edited by GerdW on 05-06-2008 04:13 PM