[sdiy] Trying to establish confidence in my test equipment

[Bob Weigel]

Well...ideally you can get a precision voltage reference set up  that is 
guaranteed within the spec you need.  I have an HP with 6 digits of 
precision which is nice for this kind of thing. Every now and then you 
can get one on ebay pretty cheap! 

But anyway..obviously the first guess would be the first two are way 
more accurate.  I've known flukes to be badly out of calibration (as in 
the demented story of my interaction with a certain head of service on 
an amplifier problem where I was being given bad information based out 
their out of calibration fluke meter that they never bothered to check 
zero on !! :-)  )

Anyway the other three strongly bear witness that the fluke has a slight 
linearity problem.  I'm guessing the keithly is set about .3% too wide 
or so also from the data of the other two.  Beckman stuff I've used but 
never had to check the precision to that degree on.  Never seen a radio 
spares... but those two look in fairly strong correlation and if it's 
also a pro quality unit then odds are the voltages are right within a 
couple mV of those readings' span. -Bob

Chris Manders wrote:

>Hi Folks
>
>Thanks to all of your input on my last question of
>'VCO standards - CV to give what frequency' I have
>decided on a range.
>
>I built Ray Wilsons excellent Keyboard circuit
>detailed here: (It works well).
>http://www.musicfromouterspace.com/analogsynth/keybrdcontroller.html
>
>Here's a poser for all of you.
>
>I now come to calibrate this circuit.
>I have FOUR meters. Two I obtained recently, and do
>not know the calibration history.
>I was trying to calibrate the output of this circuit
>(connected to a three Octave keyboard) for an output
>of 0.640 Volts Bottom C to 3.640 Volts top C. Here is
>what I got:
>
>Meter                  Low Reading    High Reading
>
>Radio Spares M810      0.640          3.622
>Beckman Ind. DM78      0.643          3.64
>Fluke 8010A            0.64           3.59
>Keighley 178           0.650          3.672
>
>The last two Multimeters are of unknown calibration,
>but are the highest quality meters I have (I think).
>The top two meters are sealed units - Calibration
>impossible.
>
>My question now is . . . er . . . what is best?
>I don't even know what the Keighley 178 meter is
>worth, although it has a good 4 digit accuracy as
>shown.
>
>Clearly here one meter (the Fluke) says I could be
>50mV under, and one meter (Keighley) says I am 22mV
>over.
>
>What would peoples opinions be of my results?
>Do you think I have a 'bee in my bonnet', and these
>results are actually within acceptable limits for this
>circuit?
>What would be the best thing to do? (I think it would
>be too costly and difficult to get the bottom two
>meters calibrated).
>
>I am familiar with the quality of FLUKE meters, but
>'Keighley'? Are they good quality? Worth the same as
>Fluke?
>
>Thanks for any advice
>Chris
>
>
>__________________________________________________
>Do You Yahoo!?
>Tired of spam?  Yahoo! Mail has the best spam protection around 
>http://mail.yahoo.com 
>
>
>  
>