260 MULTIMETER CAL`

[Kyoungmin Kim]

HELLO!!!
I am Msgt. Kim from Korea.
I have a question about 260 calibration.
In TO33K1-4-716-1, page B-128, Step 4.7; There are "limits" coloum.
I wonder about that "limits" because there are written like this "10+/-2.5degree of arc length"
what does that mean?
PLZ let me know....

[USMCPMEL]

That procedure and step is for a Simpson 260 Series 6XLPM meter. What that is referring too since this is an analog meter is the arc length of the scale on the meter. It has been a long time since I have seen a Simpson 260 but I believe if memory serves that is basically the same as 2.5% of the total scale so if it is 0-100 ohms  then plus or minus 2.5 ohms.

[John Treekiller]

The degree of scale spec given in degrees because the ohm scale is logarithmic so a defined +/- ohms number cannot be determined.  All Simpson 260 ( ) meters are set up with an arc of 100º.  The black DC scale has 50 divisions.  When measuring degrees of arc use the black DC scale range as a reference.  ±2.5º of arc is equivalent to ±1.25 divisions on the DC scale; ±2º of arc is equivalent to ±1 divisions on the DC scale.  The optimum place to verify the Ohms scale would be at center scale.  Hope this helps.

[USMCPMEL]

I knew I was missing something there lol... Long time no analog...

[John Treekiller]

It's fresh in my mind because we just had an issue on the same problem here.
Semper Fi

[Lost in Place]

John....This hurts my head!!!  However, it is good that the Arc is proportional to the Divisions.

[John Treekiller]

Wish I could claim credit for the explanation, but it was partially plagerized from an e-mail from another writer and partially from a submitted AFTO 22.  When I was cal'ing 260s I usually just made an educated? guess.

[beadwork]

This is a log scale (not linear) so the tolerance results in a physical gap (0.035") that is applied to the plus side and minus side of the scale from the nominal value.  You'd need to use something that will accurately measure this gap so you can then better guestimate the tolerance limits which will be different on the plus side from the minus side.

[Hawaii596]

It's been a LOOOONNNGGG time since I've cal'd 260's.  I think our lab still gets a couple a year.  I used to do box loads of them in the early 1980s.  One small input I have is that the spec on a 260 is mostly needle slop (including hysteresis, parallax, etc.).  The needle is the big contributor.  So the reasoning behind the spec written that way is because the needle slop works out that way.

[jimmyc]

there are several other procedures (meggers mostly i believe) that use arc instead of a scale reading. 

[CalibratorJ]

.035 inches of arc sounds familiar. I hate meggers.