Electronics > Metrology

Keysight 34465A intermittent wrong readout ?

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I don' think this is a broken meter. It is more like a user error in doing a long time measurement with Auto zero turned off.

Than there seem to be a more minor software/ firmware bug, that may cause a unintended AZ cycle one in a while - still not clear which keys were pressed and if this may be OK. Anyway the non AZ mode is usually not really useful for with manual reading - though there is the rare case of choosing the non AZ mode to get less disturbance from current spikes at the input with a very sensitive signal source.  With a shorter run time, they may still be some jump in the curve, just not as visible.

Dr. Frank:

--- Quote from: oz2cpu on January 15, 2022, 12:58:48 am ---you mean Auto zero ? see attached
i turned that off as you see, that is why i love to take pictures of the screens, this way i can remember better what is going on.
next time i see the problem, i better try record a video, and then press a button.
this is a sw bug, that no normal mortal will discover,
it takes days to show up, and goes away when i touch a button, very wierd
display update / refresh / saver ?
the unit looks like it is alive

--- End quote ---

using AZ OFF during long term measurements is definitely a false usage of the instrument. I wonder, why you don't observe a continuous drift of the reading of your source.
Anyhow, are you sure to use a very stable source, so you would have any chance of detecting such effects? You might use the data logging feature of the 34465A to monitor the drift behavior.

The sudden return to the "correct" value at key press might be due to the description in the manual:
AZ OFF: the instrument uses the last measured zero measurement and subtracts it from each measurement.
It takes a new zero measurement each time you change the function, range or integration

You also use 10MOhm input impedance, instead of AUTO, which would be High Z. (Why?)
There once existed a 3ppm difference between both modes and which was corrected with FW 2.11.
Another deeply hidden >10ppm error was corrected with 2.14, that was connected to the HV compensation of the 100:1 divider.
I did not find any further such errors later on, especially I did not see such a dip during my usual stability measurements on 34465A and 470A, so I doubt that your finding is another one.

Which FW version do you use?
Hopefully 3.0 at least, where all these former errors were corrected, and the DIGI option is available for free.

I also do not understand, why your unit should be locked for FW updates, another user error, evidently.
There's a specific procedure to unlock the instrument with a standard pass code (see manual), and then you are surely able to do FW updates yourself, either over USB connection, or via memory stick.
The update utility is required.
A good description video from Keysight is available online, performed by Jim Durr. Search for: 34460A, 34461A, 34465A, 34470A TrueVolt Updating Firmware from USB, IOS, or Linux
Jim supported me many years ago to notify Keysight about the two above mentioned faults, and get FW updates, I think he's retired as of today, what a pity.

Last, you can better make screen shots of your settings and put it here as a bmp or png  file. Search manual for 'screen shot'.
You can also use the WEB interface to steer and virtually display your 34465A instrument, and make a screenshot there.

Anyhow, I would be interested in your findings, provided you're using correct settings of your instrument.

PS: There once was another Keysight video: Updating Firmware From the Front Panel of Truevolt Series DMM
It's currently not available, due to maintenance operation on the Keysight knowledge database.

     I thought that was a temporary error, a spike.  If that's the case, I wouldn't think lack of AZ is the issue (that I'd expect to cause a drift rather than a spike).  I would rather guess EMI and the other meter was just too slow to pick it up.

finally i got this behavior on a video
hope this explain in more detail what is going on (sometimes the error value, is a bit worse, but you get the point)



--- Quote from: oz2cpu on January 23, 2022, 01:45:40 pm ---NEWS !!
finally i got this behavior on a video
hope this explain in more detail what is going on (sometimes the error value, is a bit worse, but you get the point)

--- End quote ---

Yes, it makes it crystal clear that this is happening because you inappropriately have Auto Zero turned off, just as everyone here has speculated.  See the second paragraph of Dr. Frank's reply for the most detailed, exact description of what is going on.


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