Fluke 87V HiRes Mode - Page 1
Forum section: electronics / testgear

author: do2
author_rank: Newbie
timestamp: December 10, 2018, 09:35:16 pm
content: I've got myself a Fluke 87V and I am a happy camperBut there is one thing that's puzzling me: According to the specs, a switch into HiRes-mode also reduces accuracy, namely the number of least significant digits increases by 10; see e.g.https://www.alliedelec.com/m/d/8cf21be95af06ae474858dd790972ba3.pdfSo, for instance if I measure DC Volts, instead of 1 least significant digit in standard mode I will have 10 in HiRes-mode.Where is the benefit, if the decimal point is shifted one count to the left side when you loose one digit of accuracy on the right at the same time?Do I oversee something here?

author: newbrain
author_rank: Super Contributor
timestamp: December 10, 2018, 10:11:47 pm
content: That's a nice DMM that will give you many years of flawless service!In HiRes mode theaccuracyof the instrument remain the same, so your measurements will have more or less the same error with respect to the true value.What one gains is increasedprecision, in the sense that having one more digit will make it easier to see trends and small variations, as the instrument has a finer resolution, and being a quality one, gives very repeatable measurements.E.g., my power supply, when set to 1.5V nominal, measures 1.499V in normal mode and 1.4991 in HiRes mode.If I slightly heat the DAC I can see a positive temperature coefficient in HiRes, reading 1.4992, 1.4993 etc., that I would otherwise miss.BTW, these values exactly match the ones on my 50000 counts 121GW DMM (same 0.05% accuracy, + 5 counts).

author: rsjsouza
author_rank: Super Contributor
timestamp: December 10, 2018, 11:14:43 pm
content: It looks like a similar scenario as Brymen's BM857 and its high res mode. Check the related discussion at:https://www.eevblog.com/forum/blog/eevblog-432-brymen-multimeters/msg197499/#msg197499

author: 0culus
author_rank: Super Contributor
timestamp: December 11, 2018, 12:40:43 am
content: FWIW, here's mine compared with my HP 3455A.

author: retiredcaps
author_rank: Super Contributor
timestamp: December 11, 2018, 04:07:12 am
content: Quote from: do2 on December 10, 2018, 09:35:16 pmWhen I was troubleshooting my car battery, it was helpful to put the 87 into 20,000 count mode so I could see if my battery was slowly losing or gaining charge.I wasn't worried about accuracy, just which way it was going without having to stand in -30C weather for several minutes in low resolution mode.

author: Fungus
author_rank: Super Contributor
timestamp: December 11, 2018, 07:36:56 am
content: The accuracy you're reading is the accuracyguaranteedby Fluke. If the meter's outside that range you need to get it fixed.Those meters usually will do better than that though, the extra digit isn't wasted when you switch to hi-res.Plus you can watch slow changes.

author: do2
author_rank: Newbie
timestamp: December 11, 2018, 09:58:59 am
content: Thank you to newbrain and the others for your informative replies!When cold starting the Fluke, I can see the last digit sometimes changing slightly. But this is just during the first few minutes. After that, each measurement shows the same value; that is, if the source is constant, of course