Electronics > Repair

3458A

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drhex:
@Frank: I did have a nice basement lab when I was still in Germany, incl a 3458A in really nice nick, but sold everything when moving to UK - here, I don't have meaningful temp control sadly. Will measure and document.

drhex:
First three days:
Day   Date                 Time                 TEMP?       CAL? 72                    PPM rel day 1    Av drift      Drift day by day
1   14/12/2024   9:00:00 PM   38.35   1.000859540            
2   15/12/2024   4:05:00 AM   38.1           1.000859590   1   0.049957060   0.02498   -0.049957060
3   16/12/2024   11:00:00 PM   37.6           1.000859560   1   0.019982824   0.00666   0.029974234

So much better than spec so far (.43 ppm/day) even in a non temperature controlled environment, 3458A has been running continously.
Voltage at rest fluctuates between -0.71 to -0.55 µV which seems fine. Open input still goes up to about 11V then changes range which drops it down to about 7V again. This is with a shorted shielded cable, nothing fancy.
Outside of the instrument looks s***, have ordered parts from Keysight. Also have caps etc here to get the power supplies sorted.
Seems to me I made a decent buy?

And no, it isn't warped, just a pic from the auction...

drhex:
So given my temperature is all over the place is it even worthwhile continuing to measure day by day change? I assume you can't cancel TEMP changes out somehow?
1   14/12/2024   9:00:00 PM   38.35   1.00085954            
2   15/12/2024   4:05:00 AM   38.10   1.00085959   1   0.049957060   0.02498   -0.049957060
3   16/12/2024   11:00:00 PM   37.60   1.00085956   1   0.019982824   0.00666   0.029974234
4   17/12/2024   9:50:00 PM   37.85   1.00085942   1   -0.119896944   0.02997   0.139879765
5   18/12/2024   7:54:00 PM   38.45   1.00085932   1   -0.219811064   0.04396   0.099914132
6   19/12/2024   12:00:00 AM   37.45   1.00085914   1   -0.399656479   0.06661   0.179845455

Dr. Frank:

--- Quote from: drhex on December 19, 2024, 06:58:55 pm ---So given my temperature is all over the place is it even worthwhile continuing to measure day by day change? I assume you can't cancel TEMP changes out somehow?
1   14/12/2024   9:00:00 PM   38.35   1.00085954            
2   15/12/2024   4:05:00 AM   38.10   1.00085959   1   0.049957060   0.02498   -0.049957060
3   16/12/2024   11:00:00 PM   37.60   1.00085956   1   0.019982824   0.00666   0.029974234
4   17/12/2024   9:50:00 PM   37.85   1.00085942   1   -0.119896944   0.02997   0.139879765
5   18/12/2024   7:54:00 PM   38.45   1.00085932   1   -0.219811064   0.04396   0.099914132
6   19/12/2024   12:00:00 AM   37.45   1.00085914   1   -0.399656479   0.06661   0.179845455

--- End quote ---

As said, you can cancel TEMP variations by using a stable environment, or you can determine the T.C. of U180 and subtract this effect from the CAL? 72 parameter, hopefully chosing the correct sign. I guess, latter is automatically done by Ians program. 

Frank

Kleinstein:

--- Quote from: drhex on December 19, 2024, 06:58:55 pm ---So given my temperature is all over the place is it even worthwhile continuing to measure day by day change? I assume you can't cancel TEMP changes out somehow?

--- End quote ---
To a certain degree one can correct the temperature effect. With data for a longer time window the individual measurements also get less critical.

After a long time not using the meter, there and be some additional drift anyway.
So far the drift data look good, though still a bit short to be really sure. The limit should be seen more as 3 ppm per week instead of 0.43 ppm per day.

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