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U1271A/U1272A/U1273A/U1273AX models/likes/dislikes/tips

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Zbig:

--- Quote from: electr_peter on April 21, 2015, 06:38:05 am ---Also, both off and LowZ positions have a low impedance of ~1.7kOhm, be aware of this.

--- End quote ---

And when we're at it, 230V across 1.7kOhm amounts to ~30W and 1000V - almost... 600W of dissipated power!? :scared: No way. What's really going on there? Is there a PTC in series with the shunt? If that's the case, shouldn't they be mentioning the widely varying input impedance in the datasheet? :-//

EDIT:
I'll answer this myself: yup, there is! That's probably what these several PTCs shown in Dave's teardown are doing. I've measured the Keysight's input resistance right after it was measuring mains voltage for a minute with another DMM. Sure enough, as the PTCs cooled down, the resistance dropped from several tens of kOhms to - wait for it - some 1.5kOhms, which is actually less than the initial 1.7kOhms! Go figure. I wonder if that recovery period doesn't affect other kinds of measurements.

Zbig:

--- Quote from: LaurentR on April 21, 2015, 06:45:50 pm ---If you have more likes and dislikes about those DMMs, keep posting!

--- End quote ---

There's one more thing I find mildly annoying. My cheap and portable UNI-T UT33A emits a warning beep some time before it goes to auto-sleep so you have a chance to prevent it by pressing a button. Keysight doesn't do that - it just beeps the exact moment it's switching off. Fortunately, you can either override the APO temporarily when turning the meter on or permanently - from the menu.

LaurentR:
Updated the original post with a bunch of new material including what has been said in this thread.

Some other comments:

- For safety reasons I am not fully understanding, the new recent firmware has a default LPF on DC measurements. I have found that this noticeably slows down the display rate and stabilization time of DC measurements. I turned it off in setup.

- I found that sometimes the mVDC range has a substantial offset (typically ~20uV, sometimes up to 50uV) that slowly drifts back to 0 in most cases. The spec clearly says the offset (20 counts == 20uV) is only with offset Nulled out, but I am surprised the offset sometimes stays for a while. I though it would be some thermal effect that goes away by itself, but no.


--- Quote from: electr_peter on April 21, 2015, 06:38:05 am ---U1272 beep cannot be fully turned off - beeper is not completely disconnected and you can hear faint clicks in silent room. You only have option of beeps or silence (meaning only one setting for turn on beep, button beeps, continuity beep). Separate settings would be nice.

--- End quote ---

I remember the U1272A doing the faint clicks in silent mode, but the U1273A doesn't do it. I wonder if it's linked to the U1272A's backlight continuity feature (even if it's turned off).

128er:

--- Quote from: LaurentR on April 24, 2015, 05:03:39 am ---Some other comments:

- For safety reasons I am not fully understanding, the new recent firmware has a default LPF on DC measurements. I have found that this noticeably slows down the display rate and stabilization time of DC measurements. I turned it off in setup.

--- End quote ---

http://cp.literature.agilent.com/litweb/pdf/U1273A-01-S.pdf

electr_peter:

--- Quote from: Zbig on April 22, 2015, 09:51:47 pm ---
--- Quote from: LaurentR on April 21, 2015, 06:45:50 pm ---If you have more likes and dislikes about those DMMs, keep posting!

--- End quote ---

There's one more thing I find mildly annoying. My cheap and portable UNI-T UT33A emits a warning beep some time before it goes to auto-sleep so you have a chance to prevent it by pressing a button. Keysight doesn't do that - it just beeps the exact moment it's switching off. Fortunately, you can either override the APO temporarily when turning the meter on or permanently - from the menu.

--- End quote ---
I actually prefer meter not giving pre-emptive warning with sound for APO. Case in point - Amprobe AM-240. It has APO turned on by default. After some time it emits super annoying beeping sound, then waits few minutes, beeps again and turns off. I hate this behaviour - just beep once before actual turn off. There is no need to inform annoy anyone that "Hey, I have reached half timer mark for APO".


--- Quote from: LaurentR on April 24, 2015, 05:03:39 am ---- I found that sometimes the mVDC range has a substantial offset (typically ~20uV, sometimes up to 50uV) that slowly drifts back to 0 in most cases. The spec clearly says the offset (20 counts == 20uV) is only with offset Nulled out, but I am surprised the offset sometimes stays for a while. I though it would be some thermal effect that goes away by itself, but no.

--- End quote ---
Is DMM connected to something during measurement? (open leads -> random readings) Is filters turned on? Low range is sensitive to all sorts of interference pick-up, especially with long leads.


--- Quote ---I remember the U1272A doing the faint clicks in silent mode, but the U1273A doesn't do it. I wonder if it's linked to the U1272A's backlight continuity feature (even if it's turned off).

--- End quote ---
In case of U1272A, buzzer circuit is not completely turned of in HW or SW. U1273A model probably has different buzzer circuitry because it can play melodies.

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