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U1252A AC Voltage residue

Question asked by limingz on Dec 14, 2014
Latest reply on May 6, 2015 by
I have a U1252A handheld DMM. 
When the meter is set to AC V or AC mV, and the input is shorted by a short wire, the residue reading is about 15 counts. In the AC mV range, the residue is 14uV. 
This meter has similar residue in DC mV range, but only 2 counts in the DC V range. 
Is there anyway to reduce this residue in AC mV range? I suspect that the error may be contributed by either the power supply noise, or the ADC reference voltage noise. All the onboard capacitors are 100uF in MAX, which could leads to a power supply noise in the 14uV range. 
I tried the 34401a and 34410a at the same setting. The 34401a has about 2-3 counts (2-3uV) of residue, and the 34410a has <10 counts (1uV) of residue. 
Is there a way to remove the AV mV residue on the U1252A?