Input noise interpretation

[CasparB]

The manual of the the NI 9237 (http://www.ni.com/pdf/manuals/374186e.pdf) page 28 gives me information about the input noise of this data acquisition device. The input noise is given as microvolt/volt. To which voltage is this input noise refered? Is this the excitation voltage or the noise on the excitation voltage?

In the first case the input noise for a half bridge measurement at a frequency of 25 kHZ and an excitation voltage of 2.5 Vwould be 2.5 * 1.6 = 4 microvolt

In the second case the input noise for a half bridge measurement at a frequency of 25 kHZ and an excitation voltage of 2.5 Vwould be 100e-6 * 1.6 = 1.6e-4 microvolt (assuming that the noise on the excitation voltage is 100 microvolt, like it is done in the specifications)

Thank you...

[enderWiggin10]

Hi CasparB,

This is in reference to the Excitation voltage applied, and is reported as such due to the ratiometric nature of the device.  You also can incorporate noise on the excitation votlage in the calculation by finding the maximum voltage fo the excitaiton.  In this case, with would be 100uV on the 2.5V excitation.

Best,

[CasparB]

Thanks you for the Information. This gives me some more questions:

1.   What is the source of this noise? Is it a thermal noise, does it come from the electricity supplied to the NI 9237?

2.   Is there a way to reduce the noise externally? If so, how can the noise be reduced?