SCXI-1121 voltage problem

[ilia.art]

I have SCXI-1121 conected with SCXI-1327 on chasis PXI-1052. the excitation voltage is vibrating within 1mv, which makes my measurements unusable and also, instead of 3.33v I get  3.35v in one channel, and 3.345 on second.  is it normal with this device? Or should I send it for repair? or, may be I should use some filter to stabilise excitation?  

[Sarah_Y]

Hi ilia.art,

Did you use a multimeter to measure the voltage on each channel?  Or a high impedance probe?  According to the data sheet, the excitation voltage should be 3.333 V plus or minus 0.04%, so it is possible that your board is out of spec, but it's important to make sure that the measurements were taken correctly before you waste your time and money to send it back.  What are you using this excitation voltage for and how important is this accuracy to your application?  The more information you provide about your application, the more we'll be able to help.

If you do decide that you are interested in sending your card back, you can call our customer service department at (800) 531-5066 and they will help you start the process to do an RMA (Return Merchandise Authorization).  Or if you have a support contract, you can create a service request and save some time on hold to get routed to an applications engineer who will begin the process for you.

[ilia.art]

Thanks for response.

to measure the excitation on channel 0, I'm using channel 1 input, and for channel 1 excitation - channel0 input. I thought that it would be the best measurement type in my case, as during work I will still use same method, measure excitation on the same channel. the acuracy is very important on my aplication, as I'm using string potentiometers (unimeasure PA series)  to measure speed and acceleration for dropping basket. the variation of voltage makes my measurements unuseful, because everything is measured in very short period of time. voltage i need to use is 3.333v and it needs to be very stable. 

I'll try to use other methods for measurements and diagnostics... will see

[Sarah_Y]

Hi ilia.art,

When was the last time you had your device calibrated?  The excitation voltage is speced to be 3.333 V +/- 0.04% which puts the voltage in the range of 3.332 to 3.334 V.  I'm not sure how bad of an oscillation you are seeing, but when I tried out the 1121 in my office, it was fairly stable.  Regardless of the oscillation, based on the voltages you were seeing, as long as you were using an appropriate multimeter or scope to measure these voltages, it sounds like your device has drifted out of spec.