Thank you I will open it. I was not trying to give advice, rules-of-thumb are simply shop guidelines we use to deal with our inadequate equipment (which are may when it comes to high precision).
George Dowell On 2018/05/02 09:36 AM, Dr. David Kirkby wrote: > On 2 May 2018 at 14:25, <[email protected]> wrote: > >> "This reflects my experience when using >> it to measure close tolerance resistors - measuring them at low voltages >> gives poor results, but at higher voltage, the resistances are measured >> more accurately." >> >> I noticed similar results in general, over years ad several instruments. >> Always wondered why, but we have a rule-of-thumb: if the part is to be >> used at X KiloVolts, test it at X Kilovlolt. > > I am sure your advice is good, but I based measurements on the best > resistors I could find at sensible prices from Farnell. > > The issue on the 4339B is the accuracy of the internal 0-1 kV voltage > source, if set to low voltages. I don't have the time at the moment to hunt > for the exact specifications, but the calibration certificate give the > output voltages the meter is set to, and the voltage limits. I calculated > them as a percentage. > > 0 V -> +/- 0.1 V (infinite percentage) > 10 V -> +/- 0.12 V (+/- 1.2%) > 25 V -> +/- 0.14 V (+/- 0.56%) > 50 V -> +/- 0.18 V (0.36%) > 100 V -> +/- 0.26 V (+/- 0.26%) > ...(I will miss out 200 V, 201 V, 250 V for safe of brevity) > 500 V -> +/- 1.3 V (+/- 0.26%) > 1000 V -> +/- 2.1 V ( +/- 0.21%) > > The basic uncertainty of the instrument is 0.6%, but clearly if the output > voltage is set to a low value, the percentage error in the voltage is high, > so the percentage error in the resistance will be high. The above would > suggest using a voltage under 50 V is going to compromise accuracy and > using 100 V or more is better. > > The uncertainty of the ammeter also depends on the range it is on, and not > surprisingly that has a higher percentage error on its lowest range (100 > pA) than on its highest range (100 uA). > > The Agilent 4339B is said to work from 1e3 to 1.6e16 ohm. Clearly to > measure 1000 ohm, any voltage above 0.1 V would exceed the full scale of > the ammeter on its least sensitive range (100 uA). Setting the source > voltage at 0.1 V is likely to result in significant errors reading a 1000 > ohm resistor. But clearly a "high resistance meter" is not designed to > measure 1000 ohm resistors. I expect a £5 handheld multimeter from China > would do a better job at measuring 1000 ohm than what this instrument > does. > > Sorry, I don't know about the HP 4328A. Personally I would have no concerns > about breaking the seals on an instrument of that age. I would consider it > prudent to check for any leaking electrolytic capacitors or other nastiness > that may reside inside an old instrument. > > Dave > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
