Agilent U1242B  - Page 1
Forum section: electronics / general

author: PetrosA
author_rank: Frequent Contributor
timestamp: November 13, 2011, 01:23:25 am
content: I just got a 1242B and one of the first things I noticed was how long it sometimes takes to reach a stable reading in ACV mode - up to 20 seconds! That's with the leads plugged in to mains when turning on and meter set to ACV default, so no switching from DC to AC first. Can anyone else confirm the 20 seconds settle time?Also, one thing that's puzzling me that I can't find in the manual is this: In Harmonic Ratio mode, plugged into 120V 60 Hz mains, if I set it to MAX/MIN/AVG mode, the max and min readings seem normal (2.0; 0.0) but the avg reading is whacky - 398.8 or something around there. What the heck is going on with the avg reading?

author: JSnyder
author_rank: Contributor
timestamp: November 13, 2011, 02:02:43 am
content: Just a point of comparison, I just tested mine as it stays out on the bench all of the time. It took about ~5 sec to settle at 118.7vac maybe even less, I tested multiple times. the harmonic ratio worked as expected when hooked up in the(min max avg) mode(0.0,0.0,0.0) I just tested this again and found the same thing as you, the avg reading seemed over the place, it also slowly counted down from the high value as i was looking at it (actual average 0.1) (meter reading 78.88 and slowly dropping). It appears to only happen with small min/max readings, it worked perfectly when the min was 1.0 and the max was 29.5. That being said, I don't use this function at all really, more of a novelty for me. (useful in an industrial setting)

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 13, 2011, 02:21:31 am
content: How the U1272A behaves at the same conditions ?

author: PetrosA
author_rank: Frequent Contributor
timestamp: November 13, 2011, 04:05:35 am
content: I got it specifically for the harmonic ratio function, since the U1272A doesn't have that (kinda strange...) and I'll need that at work in the next few days. I'm also seeing the 5 second settle time from time to time. It seems like it'll settle faster once it's been in V mode for a while, but it can still overshoot and take a second or two just from removing the leads in Auto mode. I'll have to set up a transformer and test going between 120V and 12V to see what happens. The U1272A settles much faster on a voltage reading.

author: BravoV
author_rank: Super Contributor
timestamp: November 13, 2011, 05:41:35 am
content: 20 seconds is very long time and I've watched yours, agree its slow.Here, short video testing of my U1242B, measuring mains at 220 volt, not lightning fast, but I wouldn't call that slow either.

author: Unknown
author_rank: Unknown
timestamp: November 13, 2011, 02:42:37 pm
content: The harmonic ration average looks like a firmware bug to me, maybe they screwed up a conversion to percents somewhere? Is the long ACV settling time only after you switch from harmonic ratio? If not, then it looks like a hardware issue to me. Does it also affect other functions like DCV or resistance? I would talk to your distributor or Agilent to see if they can explain the behavior or consider it DOA.

author: FenderBender
author_rank: Super Contributor
timestamp: November 13, 2011, 02:47:22 pm
content: A lil off topic but does anyone have a teardown?

author: kek
author_rank: Regular Contributor
timestamp: November 13, 2011, 10:43:58 pm
content: My u1242b has a real problem while trying to auto range on ACV too. When measuring the 120V mains, it will sometimes start showing over 1000V and take way too long to settle on the expected reading. It also has a problems trying to autorange when measuring the AC ripple on a DC signal. When I select the range manually, it is very fast however.It is also unable to read any ACV under 10 mV (under 12.6 mV to be exact).Even my chinese Fluke 17B can do better than that. Even after I adjusted it on my kitchen table with scissorsKen

author: Unknown
author_rank: Unknown
timestamp: November 14, 2011, 12:16:34 am
content: Quote from: kek on November 13, 2011, 10:43:58 pmThis seems like a bad design (or QC?) issue. I guess showing too high a value is less of a safety hazard than showing too low a value. I believe Fluke issued a recall for some of the 170 series meters because they would take too long to show a that you were measuring a dangerous voltage. Does increasing the minimum frequency in the settings help in any way?Quote from: kek on November 13, 2011, 10:43:58 pmI'm quite sure that the Fluke 17B is not true RMS. True RMS converters have a non-linearity near zero, which is why true RMS DMMs are usually not specified below 5% of the range or so (check the detailed specs). Seethis document from Keithleyor the voltage measurement section of the manual for any recent Fluke DMM with true RMS ability (eg. page 15 of theFluke 87V manual).

author: kek
author_rank: Regular Contributor
timestamp: November 14, 2011, 01:00:44 am
content: Quote from: alm on November 14, 2011, 12:16:34 amI tried the low mVAC measurements on a few different meters: Fluke 289, Fluke 8050a, Agilent u1242b, Fluke 17b, Fluke 79II, Fluke 8050a. The only meter that returned a result of zero was the Agilent u1242b. I ass/U/me 'd a true RMS would be better than an average responding meter in all situations. Learn something new every day, thanks!Ken