U1252A交流电压残留物

我有一台U1252A手持式数字万用表。
当仪表设置为AC V或AC mV，并且通过短线短路输入时，残留读数约为15计数。
在AC mV范围内，残留物为14uV。
该仪表在DC mV范围内具有类似的残留，但在DC V范围内仅有2个计数。
无论如何减少交流mV范围内的残留物？
我怀疑该错误可能是由电源噪声或ADC参考电压噪声引起的。
MAX中所有板载电容均为100uF，这可能导致14uV范围内的电源噪声。
我在相同的设置下尝试了34401a和34410a。
34401a有大约2-3个计数（2-3uV）的残留物，34410a有没有办法去除U1252A上的AV mV残留物？



     以下为原文

  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?