4192a dc bias sweep display c rounding to integer

[JoelWS]

Hi, I'm trying to use the 4192a to do auto sweep of dc bias while recording CP and DF. The program is working fine except that the output string from the GPIB read function always rounds down the Display C (dc bias).

For example I sweep -2 to +2 V at 0.5 V increments and I read out:

V-000002, V-000001, V-000001, V+000000, V+000000, V+000000, V+000001, V+000001, V+000002

In the 4192a programming specs there doesn't seem to be a code that let's me select the output accuracy. The panel readout Display C on the hardware is reading out the correct values (eg in 0.5 V increments) and the data looks fine.

I realize that I can just create the x axis array from my input parameters but it's just irksome that it's not working like (I think) it should.

Suggestions?

[margasan]

Hello Joel,

I will double the check the device`s manual,to verify if there is a command to adjust the display resolution. I guess you are using the driver from ni.com/idnet, is not uncommon to find some unexpected behavior as this driver is not certified or supported by National Instruments. you can always try to modify the driver`s code.

Regards

Mart G

[JoelWS]

I think I'm looking at the driver. I'm new to Labview but the driver seems to be the "collection of sub-vi's" that I'm plugging in to that directly communicate with the instrument via the GPIB read/write functions; ie they formulate command strings and read the device output.

If that's the case and these are as low level as I can get then I think maybe there is nothing I can do. There are no programming commands documented in the 4192a manual that allow you to select the output format, I think. There are pins inside the instrument that do but I think they are set to display max precision. At least that's what I see on the front panel.

Thanks for your comment Matt

[Dennis_Knutson]

Are you actually seeing just integer values in the raw string that is returned or is it simply on your front panel indicator? You would actually need to open the subVI that is doing the read and probe the output of the VISA/GPIB Read to see the raw data.

[JoelWS]

Thanks, Dennis. Yeah, that's exactly what I did and while the front panel on the physical machine read out decimal the GPIB string reads rounded down integers when I put a probe on it. The front panel indicator in my vi also reads out the rounded values, of course.

The other two displays give decimal values in the GPIB returned string as well as on the machine. I don't know why the x-axis is different.

But, I solved this to my minimal satisfaction my creating the forward and backward sweep 1D arrays for the x-axis based on the sweep parameters. It works, just a little more effort.