Fluke 289 and uCurrent Gold real world improvement? - Page 1
Forum section: electronics / testgear

author: jonatanrullman
author_rank: Contributor
timestamp: June 25, 2014, 01:46:42 pm
content: Hi everyone,I just spoiled myself a little and got a Fluke 289 even though it's actually far, far, far out of my league from a knowledge point of view. But I have a few good uses for it and overall it seemed like the best choice so that I'm limited by incompetence rather than equipment.Also, there was a promo and I got it at a ridiculous price, I paid about US$850 with VAT and shipping and I got the TLK289 kit with leads and a bag. Considering the normal base cost of an 289 is about US$970 and the TLK289 kit is another US$200-250 here in Sweden I thought it was a steal.Anyway. Since what I mainly do is tinker with Arduino based projects and some of them will be low powered battery type of projects where measuring an expected battery life is somewhat critical, I think I have a use for accurate current measurements coupled with the 289's datalogging capabilites. Being as I'm a big fan of Dave and his videos (along with Martin Lortons) was invaluable for me when choosing the right multimeter I obviously stumbled across the uCurrent Gold, which seems really nice.I am however not sure what real world improvement there is in the uCurrent Gold over the 289 on it's own as it seems that the 289 has fairly good stats to begin with.Can anyone with better understanding of this subject give me some kind of reference for how much inaccuracy the 289 is going to induce over the uCurrent Gold? Is it worth the AU$79 plus whatever shipping is (can't seem to find out without actually paying for the product) and then most likely another 25% VAT and US$14 to the postal services?I can't seem to find the detailed specs for the 289, perhaps Fluke doesn't want them to be seen.What I can find is that it is rated at a burden voltage of 1.8mV/mA for mA and 0.1mV/uA and an accuracy of 0.05% (I would assume +2 at least) for the 500 uA-range, although that could be blatant marketing from Flukes side as they had bundled all the DC current together.Cheers

author: rob77
author_rank: Super Contributor
timestamp: June 25, 2014, 02:27:49 pm
content: 1.8mV per mA burden voltage is a lot ! and actually the lower burden volatge is the improvement uCurrent gives you

author: robrenz
author_rank: Super Contributor
timestamp: June 25, 2014, 02:46:00 pm
content: Like rob77 said, Burden voltage is one main difference as inhow much the measurement process itself loads the circuit. Obviously you want to measure without influencing the circuit and high burden voltage can seriously load a circuit.

author: jonatanrullman
author_rank: Contributor
timestamp: June 25, 2014, 03:01:36 pm
content: Yes, so far I've gathered as well. But I don't know what that better burden voltage, accuracy etc. translates to in real world improvement. Is it 10% better at measuring currents below 50uA or is it 10 000% better at measuring current below 50mA. I have no idea.Cheers

author: jpb
author_rank: Super Contributor
timestamp: June 25, 2014, 03:12:27 pm
content: Quote from: jonatanrullman on June 25, 2014, 03:01:36 pmWith burden voltage it will depend on the I(V) characteristics (impedance) of what you're measuring and also of the source.If you were say measuring a diode with an exponential I(V) characteristic powered from a fixed voltage source then the voltage dropped across the meter (and hence no longer dropped across the diode) might lead to a very large change in current. If you were measuring the current through the same diode biased from a fixed current source or from a fairly high voltage with a large series resistance then the burden voltage would effectively just be a small change to the large impedance and introduce very little error.Burden Vortage, in simple terms, is just adding a bit of series resistance with the ammeter. A perfect ammeter has no resistance so there is no voltage drop across it. Obviously it will be very circuit dependent the effect of adding a bit of resistance.

author: jonatanrullman
author_rank: Contributor
timestamp: June 25, 2014, 03:52:03 pm
content: Quote from: jpb on June 25, 2014, 03:12:27 pmI see, quite the advanced subject then. Sounds like it's not possible to give even a general answer without discussing details about an hypothetical circuit.Suffice it to conclude that 1.8mV/mA and 0.1mV/uA is far to high in many situations and the characteristics of the uCurrent Gold would be highly beneficial in those scenarios while introducing very little extra complexity and problems in circuits that would not benefit as much?Cheers

author: rob77
author_rank: Super Contributor
timestamp: June 25, 2014, 03:53:33 pm
content: real world example - you measure current 200mA with a burden voltage of that fluke 1.8mV/mA - you will have a voltage drop on the fluke of 200x1.8 = 360mV... now if your device is powered with 3.3V then you'll end up with less than 3V for your device - therefore you're not measuring the current draw at 3.3V anymore... so you super-duper expensive meter can have whatever accuracy.... but you'll simply not measure accurately because of that high burden voltage. you wanted to know what's the current draw at 3.3V , not the current draw at 2.94V

author: jonatanrullman
author_rank: Contributor
timestamp: June 25, 2014, 04:39:50 pm
content: Quote from: rob77 on June 25, 2014, 03:53:33 pmWell, congratulations, you've managed to explain burden voltage excellently in 50 words.Even if the source voltage would probably more often be 9V that's still quite a significant difference if I want to get numbers that are somewhat accurate. I'm not sure how far down I need to get (this is still a hypothetical situation) but I imagine that at 50uA we're still a problem with about 5mV burden, which shouldn't affect short term readings but could very well set the whole equation off if the device is in sleep mode 99% of the time at that draw and we are extrapolating the battery life over several months. The likeliness of that situation I won't speculate about but from a purely hypothetical standpoint it could arise. It will obviously be more likely that I measure in the mA range and then it will obviously be 1,8mV and a much bigger problem.Sounds like it might be a wise investment over all. And I can share it will all my other hobby electronics friends (like all three of them).Cheers

author: maelli
author_rank: Contributor
timestamp: June 25, 2014, 05:14:53 pm
content: have a fluke 289 too, found it in the garbage, with nothing else than the fuse holder and battery contacts broken ;-)on the current input it has this resistance (measured with another multimeter:uA range: 101OhmsmA range: 2.2Ohmsit is better than my amprobe 37xr-a, that one hasuA range: 1kOhms (!)mA range: 11.27 Ohms

author: Gallymimus
author_rank: Regular Contributor
timestamp: June 26, 2014, 05:05:20 am
content: Ugh,The 289 is such junk compared to the 189. They really went backwards. Slower startup time, slower autoranging, about 1/3rd the battery life. TAKES MORE BATTERIES, and it's bigger... BUT at least is has a fancy graphical display right?! I really hate my 289.

author: EEVblog
author_rank: Unknown
timestamp: June 26, 2014, 05:34:27 am
content: It's all explained in my uCurrent article:http://alternatezone.com/electronics/ucurrent/uCurrentArticle.pdf

author: EEVblog
author_rank: Unknown
timestamp: June 26, 2014, 05:40:36 am
content: The traditional way to overcome burden voltage is to increase your power supply whilst measuring the circuit voltage after your ammeter with a 2nd meter. That way your circuit gets the correct voltage and there is no potential (no pun intended) error.But it's not always convenient to do this, and doesn't take into account current spikes.The uCurrent is not perfect though, as it only has 3 ranges, so depending up on the value you want to measure, you might have to compromise between burden voltage and resolution. Still better than practically any multimeter though.

author: jimjam
author_rank: Regular Contributor
timestamp: June 26, 2014, 08:38:43 am
content: Quote from: Gallymimus on June 26, 2014, 05:05:20 amWould you like to sell it for cheap?Just teasing youQuote from: maelli on June 25, 2014, 05:14:53 pmDoes anyone know these measurements for Brymen BM869 ?

author: jimjam
author_rank: Regular Contributor
timestamp: June 26, 2014, 08:40:34 am
content: I'm curious... do bench multimeters have a similar issue with burden voltage in their uA?

author: EEVblog
author_rank: Unknown
timestamp: June 26, 2014, 09:19:08 am
content: Quote from: jimjam on June 26, 2014, 08:40:34 amYep, practically all of them.

author: jpb
author_rank: Super Contributor
timestamp: June 26, 2014, 09:49:58 am
content: Quote from: jimjam on June 26, 2014, 08:40:34 amThe figures for the Keithley 2000 for example are10 mA range 0.15V100 mA range 0.03V1A range 0.3V3A range 1VBasically these come from the fact that it uses a 0.1 ohm shunt resistor for measurements on all ranges except the 10 mA one and I guess the internal connections and perhaps protection circuitry add another 0.2 ohms.Ironically for low currents in the 10 mA range it needs to use a higher value shunt resistor to get the resolution so it uses 10 ohms and there seems to be another 5 ohms floating around as well.Burden voltage is intrinsic to the way in which DMMs measure current - if you use a shunt resistor then there has to be burden voltage. It is probably more fundamental than that - you can't measure current without absorbing some of its energy - there has to be some voltage to drive the current through your measurement apparatus - in the case of the microcurrent this is very small.

author: robrenz
author_rank: Super Contributor
timestamp: June 26, 2014, 12:28:00 pm
content: AFIK the Fluke 8808A is the only bench multimeter that has a feedback ammeter (no shunt) on the two lowest ranges with less than 1mV total burden voltage. Many source measure units use feedback ammeters yielding burden voltages less than 100µV.

author: jonatanrullman
author_rank: Contributor
timestamp: June 27, 2014, 01:04:05 pm
content: Quote from: Gallymimus on June 26, 2014, 05:05:20 amI can see what you are getting at there. The 289 for me is a compromise of features over function, so to speak.I actually started out looking at fairly low end multimeters like the UT-71E but reviews really were not in favour. So I upped the ante a little, all the while looking longingly at the 87V, to the likes of Brymen 869 and the Agilent U1242 but found them either lacking or generelly unknown with few reviews.I then looking for a short while at the Extech range but eliminated them because they just seemed either lacking in features or outdated.I finally decided that to get what I wanted, which had all the time increased as I learned of more neat features (like Fluke's auto hold) from watching videos and reading, I would pretty much have to go up to the real McCoy and buy premium stuff. So I compared 87V and 289 to Agilent U1252, U1272 as well as, briefly, a few similar Gossen and then eliminated both the U1252 and the 87V for simply not giving me just what I wanted (data logging was a big thing here and U1252 was more expensive than U1272 I think) and finally I settled on the 289 because of the promo. Along the way I think I watched both Dave's and Martin Lorton's videos of 189/287/289 and U1271 like four times each without being able to decide which to get, the Fluke was obviously much better in almost every way but the U1272A was about US£300 cheaper.In the end I'm getting Fluke quality with high end accuracy and a lot of minor features that I believe can come in handy compared to the 87V for example. But I'm giving up battery life and getting a screen that is worse for daily use as well as the horrible boot time, but I'm gaining a lot else. In the end the price wasn't all that much of a difference for the Flukes, the 87V without anything costs about US$685 and, as previously mentioned, my 289 with the TLK289 kit cost about US$850. Also they included TL175 leads in the base kit for the 289, I thought it was going to be TL71.Cheers

author: Gallymimus
author_rank: Regular Contributor
timestamp: June 28, 2014, 01:35:34 am
content: Quote from: jimjam on June 26, 2014, 08:38:43 amhehe, I'd actually ALMOST consider trading it for a 189