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# LSBrms Unit Meaning for the System Noise Specification

Updated Sep 12, 2018

• NI-DAQmx

## Issue Details

The product data sheet for my DAQ device gives a specification for system noise in units of LSBrms. How do I interpret the LSBrms value?

## Solution

LSBrms stands for least significant bit root-mean-square and it measures the power of the system noise in terms of the smallest detectable change in voltage.

The "rms" of LSBrms refers to the amount of power in the system noise and the "LSB" in LSBrms refers to the smallest detectable change in voltage. Therefore, the LSBrms gives the power of the system noise in terms of the smallest detectable change in voltage. For example, if we have a 16-bit DAQ board and we are measuring from a range of -10 to 10 volts, then our smallest detectable change in voltage is equal to (range/resolution) = (20/(2^16)) = 0.305 mV. If our LSBrms value for system noise is 0.5, then our system noise is (0.5*0.305) = 0.153 mVrms.