John Ackermann N8UR wrote:
I'm interested in learning some basics about precision voltage
calibration (as can be realized by the hobbyist, not Josephson
Junction systems!). A Google search hasn't turned up anything like a tutorial.
Anyone know of any good app notes or other references on things like
standard cells, zener references, precision potentiometers, etc? –
and how to use them?
Thanks,
John
Search LTZ1000, LM399, and LH0070 at www.linear.com , also get app notes AN42, AN82, and AN86 - and by the way, most big parts houses have quit carrying these references - but they can be ordered direct from Linear Technology.
The LTZ1000 is used in HP3458A multimeters and a lot of voltage calibrators from Datron, Fluke, etc. The LM299 and LM399 were used in HP 3457A and HP3456A, and others.
more info on LM199/LM399 at national semiconductor, and a few app notes, AN 161 , AN184,
finding a good standard cell, is hard to do nowadays. I bought 6 units on ebay, 2 were from folks that had them and they were able to test and furnish data, and the other four were old and the voltage was too low to be stable. Basically if the voltage is not 1.0183 volts and above they are no good. They are finicky and I would read up on them before I would purchase one. NIST had a paper on them that explained the history of them, their construction, and how to handle them and the temperature conversion formulas for the saturated cells. Check out NIST 250-28 Solid State DC Voltage Calibrations, A Sub-PPM Automated 1-10 Volt DC Measuring System by Bruce E. Field, NBS Measurement Services: Standard Cell Calibrations, also by Bruce E. Field, Standard Cells - Their Construction, Maintenance and Characteristics by Walter J. Hamer all at NIST.
Look up Kelvin Varley dividers - I don't know if these folks are still in business Julie Labs and ESI. Leeds and Northrup made a few also.
HP had some app notes on measurements, look up the 3456A, 3457A, 3458A and it should show some app notes for them.
Zicor had AN177, I believe Intersil bought them
And Keithley had a free book called Low Level Measurements Handbook - Precision DC Current, Voltage, and Resistance Measurements thats worth a read.
If you can find a copy of Current Sources and Voltage References: A Design Reference for Electronics Engineers, by Linden Harrison, its a good read on a lot of semiconductor references in the last 15 years or so - I would see if you can find it in a library somewhere, if you purchase it its about $50-75 on the used market.
Brian - KD4FM
One of the best ways to ensure you get a good Weston standard cell is to make your own. However obtaining the Mercury and the Cadmium sulphate may be difficult. The mercury salts are easily produce by electrolysis in a dark enclosure (they are photosensitive).
Julie research labs are long gone, however http://www.ohm-labs.com/ make some of the instruments and standards they used to sell. They also claim to have taken over from Leeds and Northrup.
Also see: http://www.ietlabs.com/
Fluke still make the 720A KVD.
Bruce