Hi,
First I want to make this clear, I can still recommend Traceless the 34465a from Keysight it is not a bad DMM!
The things I show below like this concern small deviations at the PPM level when using the Autrtocal function.
My assumption when I bought the 34465a was that if my lab temperature was stable at 26C and I used the Autocal function then the few PPM that the Autocal function corrects,
would remain stable if the temperature in the measurement environment did not change.
The corrected value of the autocal function drifts downward at two instruments I tested.
And a 34465a reference meter at Keysight's factory to which my meter was compared had the same drift after using the Autocal function.
And again, this does not make the 34465a a bad DMM, just that the Markereers at Keysight wanted an extra feature on their 34465a version to be able to sell the 34465a for a higher price.
So I paid the higher price, but the functiue doesn't work well, and I find that a bit sad.
I can still take accurate measurements as needed as I also have an Agilent 3458a standing by. but for good stability this DMM will need to be on for at least 12 hours,
I choose to keep 24 hours on and that also means the sound of an F16 next to you from the fan.
OK some pictures,
Here you can see the drift on my 34465a after using the autocal function.
This meter was paralleled to two 34461a and my 3458a DMM for verification so that I had some assurance that there were no measurement errors involved.
.
This is one of the measurements the Keysight factory made of my Unit and their reference 34465a DMM.
My 34465a is the orange line and the blue line is the reference DMM.
In the green frame that I placed in the picture is a special test from Keysight, as far as I understand it, there the Autocal function that is always present in this DMM series is disabled.
I was told that this function is not available to the users, as it is only for the fabrication or calibration process.
But the drift in both instruments is readily noticeable.
And again, the orange line is again my DMM.
.
I have no idea what the behavior of the Autocal function is at larger temperature deviations, say e.g. as a 34465a in a 19-Inch rack mounted with equipment and whether the Autocal will also drift more percentage-wise.
It may well be that the few PPM I have experienced is the "base" drift and if the ambient temperature is e.g. 25 degrees higher in a 19-Inch rack that this base drift I am measuring will cancel out against e.g. 15PPM drift that the Autocal function corrects.
I have no way to check this, I do not own a climate box to do good measurements in this regard.
Some tipsIf you are going to make precision measurements keep in mind these things, among others:
Provide a measurement room with a stable temperature.
No varying Sun, no drafts.
Do not place your DMM in a place where it is heated by other measuring instruments.
Clean the inputs of your DMM regularly with alcohol and Q-Tips.
Preferably do not use banana connectors, they are slow to warm up and if you do want to use them, make sure they are gold plated and also cleaned with alcohol.
For most precision measurements use a pair from a CAT5e cable that is full copper and a pair of Q-Tips to secure this pair in the inputs of the DMM and clean them with alcohol.
Keep the wiring as short as possible, wiring always twisted!
Keep telephones and other transmitting equipment away from your test rig, and yes, also the phone in your pocket or that of your colleagues.
Also think about SMPS power supplies, these are often lighthouses as far as EMC is concerned, always think about that when you have strange outliers in your measurements, it's really not always the 1/F noise of your voltage reference or your D.U.T.
I'm sure a good number of people here on the forum can add to this list with tips.
My TEK DMM4050 meters and also my Keithley 6500 do not have an autocal function for the user, so I cannot compare my 34465a with that,
And again the 34465a is NOT a bad DMM!
I hoop this helps and if there are question, i like to hear them.
Kind regards,
Bram