Hi guys. There are a few things with my new Fluke 289 gets under my skin . Please help me take a look and see if these are normal, thanks.1.
DC Volt and DC mVolt cannot be shorted to Zero: I know it is normal with AC volts that when you shorted the probe you still wouldn't get zero. But For DC voltage switches, what i know is you always gets zero when you short your probes, as long as the multimeter is functioning correctly.
But for either "VDC" and "mVDC" switches on my Fluke 289, I can't short the probes to read a zero. I have even tested with different probes:
VDC switch -- the best it can do is 0.0001 volt (@5V range). Very occasionally it gives a whole ZERO reading (0.0000 volts) but this happens like 1 in 500 or even 1 in 1000 times shorting the probes. The
VDC switch is the meter's primary DC voltage i guess it's only normal to read zero when shorted, doesn't matter how many zeroes heading the least significant digit. (I don't know this - nobody has told me so but I just "feel" "zeroing" is the only normal behavior - so i'm asking you guys if my concept is wrong)
"mVDC" switches -- it's worse with the milli volt DC switch. Aside from it never reads zero when shorting the probes, the "shorted reading" is unstable from +/- 0.003 mV ~ +/- 0.03x mV, and most of the time this reading is greater than 0.012 mV (i.e., 2 digits). I'm clueless why shorting the same probes the same way this reading may change (put the meter on the desk then get a reading, then leave where it is couple minutes and get another reading -- this usually is a different value). 2 things i don't understand about the mVDC switch:1. why it can't be zeroed (same question as i have with the VDC)
2. For mV DC switch, it shouldn't pick up EMF interference in the air like the AC volt switch does, so why does the "probe shorting voltage" vary from time to time?
2.
Fluctuating DC mVolt readings when probes open: The same behavior like you see with an AC voltage switch - floating reading only not that rapidly and radically. But it looks like that although it is a DC measurement, it's affected by electromagnetic fields/energies in the air. How come??
3.
The batteries inside multimeter? : This is something i've been think.. Does the voltage of AA batteries the multimeter uses affect the "shorted" reading? I assume more or less there is an effect but does it manifest on the readings??
So guys please help me on this: Is it normal these DC voltage switch cannot be ZEROed when shorting the probes, and why does the mVDC have a floating reading under open circuit?
Thanks.
(PS. I know Fluke 289 is a 50,000 count meter and it's supposed to be very sensitive. But my questions here today is all about DC ranges which is not affected by EMF in the air so there shouldn't be anything it's sensitive about?