[volt-nuts] Fluke 845AB Null Detector

[Alan Scrimgeour]

Oops! Forgot to check the manual.
Your memory is correct.
Mine meets the noise spec. but the zero control covers too large a range and 
consequently it's impossible to turn it in small enough increments to zero 
perfectly.
This is what the 845AB manual says about noise (and zero):
------------------------------------------------------
MAXIMUM NOISE (input shorted)
RANGE                    NOISE (peak-to-peak)
1 µV                          0.20 µV
3 µV                          0.25 µV
10 uV - 1000 V      0.30 µV

STABILITY OF ZERO
Better than 0.15 µV/hour
Better than 0.3 µV/day

TEMPERATURE COEFFICIENT OF ZERO
Less than 0.1 µV/°C from 15° C to 35°C
Less than 0.2 µV/°C from 0° C to 50°C

ZERO CONTROL RANGE
±5 µV minimum
------------------------------------------------------

Alan


----- Original Message ----- 
From: "Mark Sims" <holrum at hotmail.com>
To: <volt-nuts at febo.com>
Sent: Friday, March 19, 2010 6:35 PM
Subject: [volt-nuts] Fluke 883AB differential voltmeter


>
> The noise spec on the 845 is 0.2 uV (if I remember correctly).  Mine seems 
> to be mostly within 0.1 uV.
>
> As far as battery replacement,  I still used nicads (since I had them). 
> One advantage of nicads over nimh cells is they are more robust.  They 
> tolerate overcharge better and have much better "shelf life".
>
> On a lot of replacements I do use the low self discharge NiMH cells. 
> Their self discharge rate does seem to be greater than advertised...
>
> For circuits that trickle charge nicads (at say C/12),  replacement with 
> NiMH cells will give a C/36 charge rate (assuming three times the nicad 
> capacity).   This is OK,  particularly if you don't leave them on charge 
> permanently.
>
> Speaking of overcharging NiMH cells...  I put a dead 3200 maH 6 cell pack 
> on a constant 1.5 A charge and went to the local surplus store...  no 
> problem...  back in a couple of hours.   Got stuck in a nasty traffic jam, 
> got back in 3.5 hours.   The pack had exploded and let the magic smoke out 
> of one of the cells...  actually magic carbon dust.  Parts of the pack 
> were scattered over a 10 foot radius.  Nasty black powder everywhere... 
> parts of pack stuck to walls...  etc...
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