[ARC5] Meter Calibration

[Bruce Long]

Two comments


  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. 

I suggest the use of a lead acid battery as a calibration standard is a rather extreme meaure.  I suggest purchasing a new voltage reference ic, connecting it to a power supply as explained in the data sheet and using that as a voltage reference, .1% accuracy is easily and cheaply available




    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.

Having spent many years in university education and research labsI have a dim opinion of this suggestion.  Somewhere on campus there might be a modern piece of test equipment with current or recent cal but unless you work in that environment you are not likely to find it.  College equipment budgets are very limited and have been for many years.  Student lab equipment is generally not high performance and there is a high likelihood of it having been abused.  There is no provision for calibration in most cases. High tech research labs might be well equipped but in many cases the equipment is highly specialized.  Simple basic high accuracy test equipment may not be part of the lab inventory.

In the university research lab where i spent most of my years designing custom research grade measurment equipment,  if we needed a precise volt-amp- or resistance measurment I brought my 30 year old HP EBAY DVM from home to do the job.   I have several HP3478's and 3468s and i am amazed how well they agree with each other.  My 40 year old- or older HP thumb wheel dc power supplies are generally right on as well.

I do the following:
I have one HP3478 that i try to set aside from regular use, using it only for occasional high accuracy measurments.  Yes the calibratipon memory batteries have been replaced.  I have a small bin of high precision wirewound resistors usable for resistance standards purchased for pennies on the dollar at hamfests.

I use my network analyzer calibrated with open -short- 50Ohm standards for measurement of ac impedances

I throw out or give away measurement instruments that can't be trusted.

I use cheap Chinese meters for general troubleshooting so if I make a mistake it is a 15 dollar mistake instead of a $150 - or more- mistake.

Best wishes bruce