PXI 6733 smallest voltage for external reference?

[Mystogan]

Hi, I need to know, what is the smallest voltage possible for external reference?

I couldnt find this information anywhere, I just found, the internal reference is 20Vpp and the device is 16 bit, so the LSB is 312uV.

If I connect the EXT_REF with smaller voltage, let say 5V, the reference becomes 10Vpp and the LSB becomes 156uV.

What is the smallest voltage that I can use, in other words, what is the smallest LSB I can get with this device?

regards,

yan.

[JohannesM]

In prinziple you can decrease the external reference as you wish. But be aware of the error margin you create.

You can see in the following graph that the measurement error consists of three parts, which have different reaction to the range:

It all ends up to the following equation:

You can see that the gain error (the first part) is only half the equation to finding the actual accuracy of the generation. So, assuming that we have zero temperature drift, if we can greatly reduce our gain error by providing a highly accurate reference signal, then we are still left with the offset error that is independent of the reference signal.

You will also add additional error margin by using the external source, which ofcause has to be calibrated separetly, and adds an additional voltage drift. I therefor would recommend not to use reference voltages below 0.5V.

[Mystogan]

hi Jo,

thanks for your information. Can you tell me where do you get the information from?

And I still have one thing to ask. Can I generate the 0,5 V DC as reference from the device self (without using other device), for example from AO0 then connecting AO0 to EXT_REF with cable? 

Because I think, once the device generates a DC voltage in 1 channel, the voltage stays in the channel. That means, I should be able to generate the DC and feed the EXT_REF with it, then use the other channel for other signals generation.

Thanks,

Yan.