Jim Yanik wrote:

chuck wrote in
:


Tim Shoppa wrote:

On Feb 28, 9:27 pm, "Too_Many_Tools"
wrote:

I have a well stocked test bench at home containing a range of
analog, digital and RF test equipment as I am sure most of you also
do.

Well the question I have is how do you handle the calibration of
your equipment? What do you use for calibration standards for
resistance, voltage, current and frequency?

It depends entirely on what you need the equipment for.

If for any legal reason you need NBS traceability, then the question
of how and how often is already answered by your regulatory agencies.

If you don't, then I cannot imagine that a couple off-the-shelf
precision resistors, voltage references, and frequency references
(total cost: $10) would not be good enough for sanity checking for
almost any pedestrian uses.

If you're the sort who keeps equipment on your bench just to
calibrate equipment on your bench just to calibrate equipment on your
bench, then any rational argument about traceability is pointless
because you've already set yourself up in an infinite circular loop.

Tim.


reminds me of the local TV station techs who insisted that the video gear
of theirs I serviced and calibrated was off,and it turned out their 75 Ohm
termination was 87ohms.Other techs double-terminated monitors and
complained of low brightness,tried to tweak it in,screwed it all up.
Or they would have a "reference" generator at the end of 100's of feet of
coax and complain it was a few percent off.


A lot of good points have been made already so I'll just add a small
one.

Don't mess with calibration of quality equipment unless you have
reason to believe the calibration is off AND THAT IS ADVERSELY
AFFECTING YOUR WORK PRODUCTS. An amazing amount of electronics work
has been done using equipment with non-current calibration stickers,
some of which was out of calibration.

If metrology is something that interests you as a hobby, then jump
into it and have fun. Tim's last paragraph ought to be printed and
framed.

Chuck


this is good advice,because without a service manual and cal procedure,you
have no way of knowing what adjustments INTERACT with others.
Adjust a power supply,and gain and timing goes out the window.
Freq.response tweaks can affect more than one area of the signal.


for example,
TEK 475s have multiple vertical gain adjustments,and different adjustments
for the 2/5-10mv ranges.And the gain affects F-response.

Some TV stations had so much RFI that even a VOM had trouble reading
properly on any scale!