[volt-nuts] Two 4338B high resistance meters fail on the same range - Keysight can't adjust EEPROM of either.

[geoelectronics at rallstech.net]

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, <geoelectronics at rallstech.net> 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
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