On Thu, 15 Oct 2015, whit3rd wrote:

On Thursday, October 15, 2015 at 2:34:51 AM UTC-7, wrote:

I have an old Data Precision (USA) 1350 "3 1/2" Digit LED type Multimeter...
after performing a calibration the low K ohm scales are displaying readings are generally out by more then 5 percent.

So, the first step of calibration is adjusting the time bas
The next step is the Gain calibration by inputing a DC reference voltage...
The last step is balance, where a lead wire is tied back from the red banana jack to pin 36 (Hi Ref) AD7107, and is adjusted to 50 millivolts (+/- 50mv)

The multimeter readings are very good, except for the Low resistance scales.

Three possibilities: (1) weak battery - on low resistance, it might take
extra current to develop a measurable voltage across the terminals, and
battery voltage droops enough to decalibrate

(2) series resistance in selector switch contacts (assuming there's a
low-ohms switch
contact that selects a resistor to ratio against, and the switch
resistance is not insignificant)

On one my meters, an odd problem which I can't remember details did arise.
It was just reading wrong, otherwise it was fine. I actually opened it
up, expecting something wrong with the range/function switch, but nothing.
I have no idea how I got that far, or why I backed up and changed the
battery, but it was a weak battery. That had never happened with a DMM
with me before or after. Maybe I'm just lucky, I forget to turn off the
meter, so the battery dies completely, rather than landing in some spot
where it functions but not well.

No, maybe that wasn't the battery. It was the fuse. It was the original,
but for some reason had gone up in value, but still a finite value. So it
didn't make a noticeable difference with volts (I know I wasn't measuring
anything for preciseness at the time), but did affect the ohms range at
lower values, since it was something like 1K or thereabouts.

That was the odd thing, I hadn't expected the fuse to introduce a level of
resistance.

Michael

(3) recheck the 'balance' calibration, maladjusted offset to an op amp would make low-volts inputs
measure incorrectly, and that step probably involved twisting a knob; sometimes
they spring back after an adjustment.