1141 offset compensation using NI-DAQmx in C or VB

[RDonaldson]

There is very little information available on how to compensate for offsets using the 1141 modules and DAQmx. One message that I can find says to use "DAQmxSetAIAutoZeroMode" to pass the argument "DAQmx_Val_Once" but this raises no error and appears to do nothing. The Message example that is referred to is in Labview but I am not using Labview. Is there an example in C or VB available or does someone have one they would share?

[ryan_d]

Hi RDonaldson,

To get the proper nulling of the input offset voltage enable the calibration ground and use this value to null the offset voltage of subsequent DC coupled measurements. If you're doing this and still experience the offset, please post back.

Have a great day!

[RDonaldson]

I have done this using the Traditional drivers but I can not seem to find the Method or Function that does the same thing with DAQmx and the 1141s. I have the auto zero working in DAQmx for the 6030E which is connected to the SCXI and 1141. I have looked for hours and I can not find the equivalent DAQmx Method or Function that shunts the 1141 inputs to find the offset 1141 offset. What is it?

[Brad_K]

Hello RDonaldson,

Calling DAQmxSetAIAutoZeroMode(taskHandle, "", DAQmx_Val_Once) should make DAQmx ground the SCXI-1141's inputs, read the offset, unground the inputs, and subtract the offset from your measurements automatically. It does the offset measurement when the task is reserved (which is usually when you call DAQmxStartTask() unless you're using DAQmxTaskControl() for finer-grained task state control).

You can also tell the SCXI-1141 to ground all its inputs by calling DAQmxSetAICoupling(taskHandle, "", DAQmx_Val_GND) before you start your task. Then you can read the offset yourself by reading data from the task. Setting the AI coupling to DAQmx_Val_DC will unground the inputs.

Brad


Message Edited by Brad K on 12-14-2007 01:39 PM