Smooth Mode on Keysight U1272A & U1282A DMM: How does it work? - Page 1
Forum section: electronics / testgear

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: February 11, 2017, 08:07:05 pm
content: Hello,I can’t figure out how the smooth feature on Keysight DMMs works. I already contacted Agilent s ome years ago and asked them to explain it to me for the U1272A. Luckily an Agilent engineer called me back and we talked together for quite a long time and he tried me to explain how that feature works. But I didn’t get it until nowIt’s the only feature I don’t understand.Now I got the new U1282A and it performs exactly the same!That how I understand the feature when I read themanual of the new U1282A (p119 & p120):The smooth feature is made for noise; it filter only small variations in the signal strength. If the signal strength changes significantly (1V --> 2V), the smooth feature restarts and the new signal strength will be displayed instantly.The smooth feature is realized by SW and performs like a sliding average (electrically equivalent to RC low pass): it shows the arithmetic mean of the last samples. The older U1272A makes 7 samples/s; the new U1282A makes 5 samples/s.With the setting „tiME“ the user can adjust the number of samples that goes into the calculation:The number indicates the amount of last samples that goes into the calculation of the mean. The last letter indicates whether the smooth function is disabled „d“ or enabled „E“.With the setting „AhoLd“ the user can adjust the threshold that restarts the smooth feature when a significant change of the signal strength occurs.The number indicates the amount of counts (multiplied with 10 in high res mode) that has to be overcome by a change of the signal to restart the smooth feature. E.g. when the DMM measures 1.0000V, then one must change the signal to 1.0500V to restart the smooth feature if the number is set to 0050.E.The last letter indicates whether the threshold is disabled „d“ or enabled „E“.Please tell me what I understand wrong.I can’t see how the smooth feature influences the reading of the DMM.Example:I adjust tiME to 9999.E and AhoLD to 9999.E. It’s the highest amount smooth with the highest threshold (I have also tried other settings). I connest the DMM to the PSU that outputs 1V. The DMM shows 1.0000V. Now I increade the voltage by 10mV; the reading of the DMM changes instantly to 1.0100V!!! No difference compared to the deactivated smooth mode.

author: Muttley Snickers
author_rank: Unknown
timestamp: February 11, 2017, 09:47:36 pm
content: I'm not currently in front of a computer nor the manuals but from memory the auto hold threshold and smooth mode value are somewhat independent of each other, the range selection for smooth mode is 0001 to 0009 with the later being the maximum filtering applied, the auto hold threshold is only valid and applicable when the auto hold mode is enabled and activated.

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: February 12, 2017, 12:23:42 pm
content: Quote from: Muttley Snickers on February 11, 2017, 09:47:36 pmOn p120 the manual says:

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: February 15, 2017, 11:05:36 am
content: I start to believe, that the most people don't know how the smooth function works.Martin Lorton had also problems with it:

author: Muttley Snickers
author_rank: Unknown
timestamp: February 15, 2017, 11:22:57 am
content: Greetings medvedev,The problem I have found with the smooth mode on both series of these meters is that more often than not is has very little if any effect on applied voltages, the only practical advice I can offer in relation to the smooth mode settings on these meters is to not take the user manuals as gospel and conduct your own evaluation and assessment with a meter on the bench exactly as I have already done although I’m still to a certain extent none the wiser.It is well known that the smooth mode range setting for the U1272A is in fact 0001 to 0009 as I previously pointed out but if you were to take the user manual as a guide it states that the range is between 0001 to 9999 as displayed in the first image below and this has been confirmed both by Keysight themselves and others that this information is incorrect. Based on this documentation error for the U1272A if applied to the U1282A using a range of between 0001 to 0009 the smooth mode feature does work in some instances but I’ve also found it rather difficult to determine to what extent it has any effect.

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: February 15, 2017, 03:02:23 pm
content: Quote from: Muttley Snickers on February 15, 2017, 11:22:57 amThanks for the info Muttley Snickers!I think Keysight should update the firmware or the manuals and explain what exactly the smooth mode is filtering and how it works.

author: Keysight DanielBogdanoff
author_rank: Unknown
timestamp: February 15, 2017, 11:49:08 pm
content: I'll pass this feedback to the DMM team, thanks!Quote from: medvedev on February 15, 2017, 03:02:23 pm

author: electr_peter
author_rank: Unknown
timestamp: April 08, 2017, 08:28:41 pm
content: Quote from: Keysight_DanielBogdanoff on February 15, 2017, 11:49:08 pmIs there any update on DMM smoothing feature?