Fluke 87v - Ohm Range over 660 ohms - Page 1
Forum section: electronics / repair

author: GNRFreak69
author_rank: Newbie
timestamp: January 13, 2024, 07:37:13 pm
content: I have a Fluke 87v acting a bit odd. Not sure if this is normal.1K ohm pot turned all the way down shows 1-2 ohms, As I turn the pot, it goes smoothly up to 660 ohms.Once I advance the pot past 660 ohms, it switches to Kohms, and shows .660k ohm correctly on that scale, but why can it not show me 680 ohms or 700ohms.Do I have something set wrong?It's just annoying.ThanksJeff

author: bdunham7
author_rank: Super Contributor
timestamp: January 13, 2024, 07:42:53 pm
content: No, it is just ranging up to the 6K scale. 660 ohms and 0.660k are the same thing, of course, and that's just how they're showing the values. You might try putting the meter in Hi-Res mode and see if you like the results better.

author: MarkF
author_rank: Super Contributor
timestamp: January 13, 2024, 09:13:53 pm
content: No. It's a 6000 count multimeter.That means it can't show values over 6000 in any range scale.(i.e. 6.000, 60.00, 600.0, 6000)

author: GNRFreak69
author_rank: Newbie
timestamp: January 13, 2024, 10:21:12 pm
content: Thanks Guys. I sorta figured that was what was going on, but thanks for confirming.

author: J-R
author_rank: Super Contributor
timestamp: January 14, 2024, 02:26:06 am
content: To clarify/correct a few things, the 87V is precisely 6,600 counts in normal mode and 19,999 counts in Hi Res mode.Hi Res mode actually will not help in this specific situation because switching to Hi Res mode actually reduces the upper limit of each range.So for example in normal mode in the 6V range you could display 6.600V, but in Hi Res you can only display 1.9999V. In the next range up, you could display 6.600V in Hi-Res mode but that offers no benefit in for this specific value (6.600V).Similarly, for resistance you can display 660.0 Ohms but switching to Hi Res will require going up a range so there is still no benefit.Hi Res mode still seems valuable due to two main reasons:- Adding the leading 1 doesn't require much extra space on the screen so the overall dimensions don't have to increase.- The calibration set points for the 87V are at half scale, so 3.300V for the 6V range. Hi Res mode can take advantage of the increased accuracy from 0 to 1.9999V.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 14, 2024, 02:30:37 am
content: yeah, i personally hate all dmm with pseudo high resolution modes, since you explain it so wellin some cases, the real ranges are calibrated and the high resolution is calculatedeven say the ones with the famous real 50,000 count and the pseudo 500k count pfffthey have calibrated the 50k counts not the other 500k ...this is precision over resolution ... never ending debate on other threads loll

author: J-R
author_rank: Super Contributor
timestamp: January 14, 2024, 05:48:36 am
content: The high res modes of the 87V and the BM869s are definitely usable (but it depends, more on that later). Perhaps most of the negativity revolves around the marketing decisions, especially for the Brymen. When I received mine I know I was put off by the limitations, but they could have just been more clear and I wouldn't have been so annoyed. For the Fluke I think they should have flipped it around and made it a 20k count DMM all the time but made the 6k count mode be a "fast" mode.I'd say all DMMs are going to do a fair amount of calculations/statistical analysis from the ADC output, but it's hard to fake too much and get away with it. If you only have a 14-bit ADC, then when you store the calibration point I don't see a way to get usable 20-bit values later, no matter how you massage the data. They have one single ADC making x-bit numbers, and that is what is used to store the calibration data. (Interestingly, the Fluke 8558A/8588A does have dual ADCs, one 28-bit for high accuracy/resolution at 8.5 digits and one 18-bit for speed at 6.5 digits.) So if 50% of your values are 1.0000V and 50% are 1.0001V, then it's reasonable to consider the actual value to be 1.00005V. But this requires the samples themselves to be quite good.Based on my experiences with the 87V and BM869s, both can easily do the job so I don't think they are relying too much on math to save them, although it's obvious there is some amount of filtering/oversampling.For the BM869s I've found the accuracy greatly suffers if you're very far off from the calibration temperature. I last calibrated mine at 73F and at 63F it's about 80 counts low in 500k count mode.