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Keysight DMM - Yay or nay?

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nctnico:
If you want to do really precise measurements then you'll need a room with climate conditioning (temperature + humidity) but by that time you enter calibration lab territoy. I'm not saying a 6.5 digit DMM is useless, but you'll have limitations in normal room / office conditions.

Traceless:
@nctnico: Well I could get an 3458A IIRC those have an oven to compensate for room temperature ;) - no just kidding. The 34465A is probably already overkill for most/all of my applications. I'm just a hobbyist and don't do high precision circuit design or anything like that.

Kleinstein:
The autocal function is not so much about a changing temperature, but more about using the meter for many years without calibration. The ACAL function does internal tests to remeasure resistor ratios and this way can reduce the drift. This can also help against temperature dirft, but the main point is the long term drift. It is rare that one needs a really accurate reading with a temperature way off.

AFAIK one does not have to use ACAL on the 34465 and the 34461 does no offer this option / point.
It is just inconvenient that the function does not seem to work all the way as intended. Chances are this is a SW problem, maybe related to some HW oddity. For the 34470 the ACAL seem to be even more problematic and for some reason KS seem to still have not really fixed it. They seem to have a problem if ACAL actually makes a difference to the normal cal factors. The problem with the 34465 may well be related though there are differences.
I still have some hope that they finally will fix it - though one never knows.  Some SW problems persist until the product is obsolete (e.g. extra LF noise in many Keithley meters, that is likely due to a SW quirk).

The ADC in the 3446x series is not the absolute best INL and linearity is an important factor in how good ACAL works.
The 34465 still has more current ranges, higher speed and tighter specs, though much of the internals seem to be very similar.

Traceless:

--- Quote from: Kleinstein on March 03, 2022, 11:12:25 pm ---The autocal function is not so much about a changing temperature, but more about using the meter for many years without calibration. The ACAL function does internal tests to remeasure resistor ratios and this way can reduce the drift. This can also help against temperature dirft, but the main point is the long term drift. It is rare that one needs a really accurate reading with a temperature way off.

--- End quote ---

So autocal is probably worthwhile despite the drift then, since I plan to use the device for a long time and probably will never send it off to a lab for calibration.


--- Quote from: Kleinstein on March 03, 2022, 11:12:25 pm ---AFAIK one does not have to use ACAL on the 34465 and the 34461 does no offer this option / point.

--- End quote ---

According to Bram you can't turn off autocal on the 34465A, so if I really didn't want autocal I'd have to go for the 34461A.


--- Quote from: Kleinstein on March 03, 2022, 11:12:25 pm ---It is just inconvenient that the function does not seem to work all the way as intended. Chances are this is a SW problem, maybe related to some HW oddity. For the 34470 the ACAL seem to be even more problematic and for some reason KS seem to still have not really fixed it. They seem to have a problem if ACAL actually makes a difference to the normal cal factors. The problem with the 34465 may well be related though there are differences. I still have some hope that they finally will fix it - though one never knows.  Some SW problems persist until the product is obsolete (e.g. extra LF noise in many Keithley meters, that is likely due to a SW quirk).

--- End quote ---

Who knows maybe if Bram starts a thread about his discovery in the metrology section and enough people start investigations, it might get Dave's attention. If he makes a video about that there is a good chance that Keysight will address the problem, unless it really is a HW issue that is not fixable via firmware.


--- Quote from: Kleinstein on March 03, 2022, 11:12:25 pm ---The ADC in the 3446x series is not the absolute best INL and linearity is an important factor in how good ACAL works.
The 34465 still has more current ranges, higher speed and tighter specs, though much of the internals seem to be very similar.

--- End quote ---

The high speed is exactly what im interested in. Also the additional ranges are nice.

nctnico:
As an owner of the 34461A I do have to say that the resistive range is lacking at the lower end of the range. Despite that the 34461A has 4 wire measurement, it is not  suitable to measure milli-Ohm resistors. It would need an extra (lower) range for that. The DMM6500 lowest resistance range is 1 Ohm where the lowest range on the 34461A / 34465A is 100 Ohms.

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