[ARC5] Meter Calibration

[brianclarke01 at optusnet.com.au]

	Hello Wayne, 

	It depends on what kind of 'calibration' you want. Do you want your
meters to read correctly, or do you want to know how far out they are.
And to what tolerance? 1%, 0,1%, 0.01% of NIST at FSD? 

	1. The most complex level is where you get your instrument to read
within a nat's whisker of National Standards on every range. That
usually requires that all range resistors be changed in some way. This
usually means a trip to the cal lab with your bank manager, and needs
repeating every so often. You only need this level if the customer
demands traceability to NIST. 

	2. The next most complex is to produce a table for each meter that
tells you what a 'true' reading would be when your meter reads X. With
this one, you could visit an electronics lab at a local university and
ask for access to a Weston cell or their latest equivalent. You would
be expected to use a potentiometer across a battery, and compare your
meter with a Weston standard cell, or their local equivalent, in a
bridge arrangement using a very sensitive galvanometer. This
potentiometer is the real deal - it comprises a uniform
cross-sectioned wire about a metre long stretched over a metre rule,
with a moveable contact - not your volume control type of pot. There
are small, portable calibrators that have a Weston cell and galvo
built in - often used by railway engineers and similar - that come up
for auction from time to time. How do I know? I have one. 

	3. Lacking access to a Weston standard cell, you could try using your
car battery. After the car has been standing a day or so, at 20 C, the
battery should be about 12.2 V with no load. Then either measure the
voltage with all your meters and draw up correlation tables, or make
your own potentiomater, possibly using piano wire. 

	4. An intermediate level between the first two is to take your
favorite meter to the cal lab to have the full cal done on it - or go
to the local university and get a lab techo to do a quick and dirty
against their kit. Bring it home and produce the correlational tables
for all your other meters yourself, making up your own potentiometer -
as per my third para. 

	5. The simplest method is to use democracy - accept the reading that
most of your meters produce when they agree sufficiently closely for
what you want. Unfortunately, democracy sounds fine in government 200
years ago, but doesn't work in modern practice. Scientists and
electronics engineers do not use democracy - it is a snare and a
delusion - if you have kept all your meters in the same environment
for a long time, they may all have drifted in the same direction. Or
not. 

	Hope that helps. 

	73 de Brian, VK2GCE. 

	  

	  

	----- Original Message -----

	  From:"Robert Eleazer"  

To:
Cc:
Sent:Thu, 1 Aug 2013 21:25:45 -0400
Subject:[ARC5] Meter Calibration

I have quite a collection of multimeters and voltmeters. Some PSM-6's.
Some PSM-45's. A couple of Me-297's. A USM-33. A USM-34. A Simpson 260
in a super-nice rolltop carry case. An NLI TouchTest 20 with real red
glowing LEDs. A brand spanking new HP Model 410B. 

And I don't trust any of them, at least not very much. I quit using
those super cheap chicom digital meters because each one gave me a
different reading. But collectively all of the others have the same
problem.

Anyone know how you can go about calibrating at least the voltage
readings on these fine equipments? That is, using stone knives and
bearskins, not a million dollar test set.

Thanks,

Wayne 
______________________________________________________________
ARC5 mailing list
Home: http://mailman.qth.net/mailman/listinfo/arc5
Help: http://mailman.qthnet/mmfaq.htm
Post: mailto:ARC5 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

-------------------------
Email sent using Optus Webmail