Fluke 233 cut off under 20mA - Page 1
Forum section: electronics / testgear

author: kdl1950
author_rank: Contributor
timestamp: April 22, 2023, 06:22:47 pm
content: Hi guys,I have a question about the Fluke 233.Data sheet says:AC Current Range 1mA to 10A Accuracy 1.5% + 3DC Current Range 1mA to 10A Accuracy 1.0% + 3Okay, so far so good.But my 233 cuts off everything under 20mA.See pictures.Can someone explain me why?If it has something to do with the accuracy, can someone calculate it for me?Would be really nice. Am currently stumped.Greets from Germany

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 22, 2023, 10:06:03 pm
content: What happens if you manually change ranges to the lowest AC current range?

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 23, 2023, 01:24:45 am
content: Quote from: Kim Christensen on April 22, 2023, 10:06:03 pmIt's at the lowest range which is the 6A range. The 233 doesn't have mA range. But according to the specs it should at least display 13mA.

author: kdl1950
author_rank: Contributor
timestamp: April 23, 2023, 05:09:17 am
content: BeBuLamar are right.6A is the lowest current range.I have set up a test circuit with a potentiometer.So I can regulate the current. 0mA and then comes 20mA. No value in between. The pictures were taken right on the limit.

author: J-R
author_rank: Super Contributor
timestamp: April 23, 2023, 07:51:35 am
content: According to page 41 of the manual (https://dam-assets.fluke.com/s3fs-public/233_____umeng0000.pdf), all AC current "ranges are specified from 5 % of range to 100 % of range."AC voltage is from 1% to 100%.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 23, 2023, 08:19:13 am
content: Quote from: J-R on April 23, 2023, 07:51:35 amSo readings under 300mA may or may not be accurate enough to be useful? That's quite poor, for a Fluke product.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 23, 2023, 11:47:15 am
content: The 233 selling point is the remot display. Not so much for other features.

author: Fungus
author_rank: Super Contributor
timestamp: April 23, 2023, 12:07:25 pm
content: Quote from: AVGresponding on April 23, 2023, 08:19:13 amThat's just the way TRMS chips work.PS: Fluke sells average responding meters, too. Choose your poison.

author: J-R
author_rank: Super Contributor
timestamp: April 23, 2023, 09:36:23 pm
content: Also, it's a 6,000 count DMM with no mA or uA jack, so it's going to be a common limitation for that design.I think the main point of confusion for the OP is that the datasheet states 0.1mA, which is obviously a marketing department snafu. I would e-mail Fluke support along with the 233 serial number and point out the mistake. Maybe they will appreciate the heads up?

author: Martin72
author_rank: Super Contributor
timestamp: April 23, 2023, 11:05:35 pm
content: Never saw such behaviour on any multimeter I had or we have at work.But I know this from one of our power analyzer, it have a (switchable) mode when a value is so low that the analyzer couldn´t measure it with the specified accuracy, it will show zero instead of "something".If this is the same on this fluke meter, they should mention it in the specs/manual.

author: J-R
author_rank: Super Contributor
timestamp: April 23, 2023, 11:29:17 pm
content: Not sure why this is news to some of the high-post-count members here.It's very common to have a DMM state AC functions and/or accuracy are only valid from a certain percentage of the range. For example, Brymen typically has undefined below 5% and extra error counts to be added up to 20%.

author: Martin72
author_rank: Super Contributor
timestamp: April 23, 2023, 11:43:00 pm
content: It is "new" that the meter shows nothing instead of "something"...

author: bdunham7
author_rank: Super Contributor
timestamp: April 23, 2023, 11:56:41 pm
content: Quote from: Martin72 on April 23, 2023, 11:05:35 pmIf it uses an analog TRMS converter like the AD737 (and the 233 likely uses exactly thatactually probably not since it only goes to 1kHz) you end up with a 'residual counts' error with zero input and a correspondingly lesser error as you increase the input to the specified threshold, often 5% of range. This may be a positive or negative residuum and in the negative case, the result is a zero reading before you get to zero. Due to the design and calibration of the AD737 or similar chip, the residual counts have little to do with accuracy above the threshold.My old F289 had ~200 residual counts, my replacement has zero. Both are perfectly accurate above the specified minimum. AsFunguscorrectly points out, you can buy an averaging meter. A quick test of two meters shows that my F289 has a substantial (>5%) error on the 5V range at 1% of scale (50mV) and reads zero at 10mV, but the F27 reads 10mV correctly (10 counts, to the count) and only errs by 1 count at 1mV, meaning it displays 2 when the actual value is 1 count. No analog TRMS setup can do that, AFAIK.Since the F233 only has a 6A range, that means that the 5% threshold is indeed 300mA and the residual counts error will start to matter below that. I imagine the magnitude of the actual residual error is probably 20-30 counts, meaning some meters might give you random numbers up to 30 or so counts with no inputs and others will go to zero at or below about 30mA input. The important point to remember is that the meter stopped being usably accurate well before you get to the point of zeroing out--if you wanted to measure 50mA with this meter, you'd only get a guess. At 100mA, maybe a good guess.I forgot to mention, some meters zero out the residual counts in software before you get to zero. This doesn't necessarily mean that they are accurate at every level where they give a reading. RTFM and don't bet too heavily on exceeding the specs by a lot.

author: J-R
author_rank: Super Contributor
timestamp: April 24, 2023, 12:28:05 am
content: https://web.archive.org/web/20121104004609/http://www.gellerlabs.com/34401A%20AC%20zero.htm

author: bdunham7
author_rank: Super Contributor
timestamp: April 24, 2023, 12:32:20 am
content: Quote from: J-R on April 23, 2023, 09:36:23 pmI agree--the datasheet is both technically wrong and badly misleading in this regard.https://www.fluke-direct.com/pdfs/cache/www.fluke-direct.com/233-nist/datasheet/233-nist-datasheet.pdf

author: J-R
author_rank: Super Contributor
timestamp: April 24, 2023, 01:03:44 am
content: The DMM development process definitely leads to some odd results, such as the 233 missing the mA/uA function. Another one is why the yellow select button is on the body and not the detachable screen portion.I suspect things start with a marketing drone inventing a product design based on some competitor, imaginary use case or random customer requests. Then the engineers have to make it.Another major oddity is how few clamp meters have a mV range. None of Brymen's do, for example. The Uni-T UT210D has only DCmV. The UEi DL489 does have it for both AC and DC, and is the only clamp meter I have with such a feature. Someone probably thought having a major missing feature like that would require everyone to have both a clamp meter and a regular DMM, boosting sales.

author: bdunham7
author_rank: Super Contributor
timestamp: April 24, 2023, 02:59:12 am
content: Quote from: J-R on April 24, 2023, 12:28:05 amI'm not convinced that the 34401A is actually one of the meters that uses a simple "display zero if reading is below x.xxxmVAC" in software because it doesn't quite behave like that. Perhaps they selected all the AD637 chips for negative residuals or perhaps the circuit can be tweaked to acheive this reliably? Or there is something I don't see in the schematics that simply tapers off inputs below some threshold? It isn't a clean zero, there's always a few counts hanging about.Edit: I should mention that my 34401A sample size is one and my firmware version is 10-05-02.

author: alm
author_rank: Super Contributor
timestamp: April 25, 2023, 06:41:56 am
content: Quote from: bdunham7 on April 24, 2023, 12:32:20 amI agree it's misleading, but the form 0.1 mA - 6 A is commonly used to indicate 6 A with 0.1 mA resolution. It's not like the unit will read 0.1 mA DC with any kind of accuracy or stability. Although in the case where it won't even display 0.1 mA AC it is obviously misleading. Since the OP is in the EU, they could complain to the seller (not Fluke) that they received a non-conforming product that does not meet reasonable expectations based on the data sheet.Quote from: J-R on April 24, 2023, 01:03:44 amThat's just them targeting specific markets. Clamp meters are usually aimed at (industrial) electricians who don't have much use for mV. Having more functions would clog up the function dial and make it more expensive. Fluke used to have a 112 DMM aimed at HVAC technicians which had 6A/10A and an uA range. The uA range was aimed at measuring flame sensors. It had no mA ranges because this is not necessary for troubleshooting HVAC systems. If you need the missing functions/ranges, then don't buy that meter.

author: J-R
author_rank: Super Contributor
timestamp: April 25, 2023, 07:55:28 am
content: The F233 is only capable of 1mA resolution, so 0.1mA is completely wrong in all respects.I do not agree with the argument that clamp meters are missing mV because they are targeted for industrial electricians. It's very hard to find this feature missing on an industrial handheld DMM. Also, many DMMs combine the mV range into the V switch position. The 87V does this for mV AC, the UT210D does this for mV DC, the U1233A does this for both AC & DC.

author: Fungus
author_rank: Super Contributor
timestamp: April 25, 2023, 08:10:36 am
content: Quote from: J-R on April 25, 2023, 07:55:28 amThat's just Fluke protecting their 87V cash-cow. All their other meters are designed aroundnotbeing a substitute for the 87V, eg. missing mV, missing uA, or whatever.They're a business and out to make as much money as possible, let's not pretend they're anything else. They're certainly not competitive or innovative any more.

author: J-R
author_rank: Super Contributor
timestamp: April 25, 2023, 09:08:25 am
content: Quote from: Fungus on April 25, 2023, 08:10:36 amAs I pointed out, Brymen does not make a clamp meter with mV either. So Brymen is "out to make as much money as possible, let's not pretend they're anything else. They're certainly not competitive or innovative any more." There, I fixed it for you...

author: bdunham7
author_rank: Super Contributor
timestamp: April 25, 2023, 01:51:34 pm
content: Quote from: Fungus on April 25, 2023, 08:10:36 amThat line is getting tiresome. You can go to the Fluke website and read about the huge variety of innovative products that they have come out with. The fact that they continue to sell a well-regarded popular legacy product for years on end despite it not having good 'bang for buck' compared to this months Aneng special is really not that relevant to the companies overall operations. I'm sure some new person at Fluke may say "The 87V is kind of old-tech and gee, parts are getting harder to source so why don't we refresh the model?"

author: kdl1950
author_rank: Contributor
timestamp: April 25, 2023, 04:51:59 pm
content: Many thanks for the replies and explanations.I agree with "bduham7“The datasheet is both technically wrong and badly misleading in this regard.It may well be true that this measuring device is not permitted in this area.Only it would have to be clearly marked in the description! The 20mA cut off is not described in the operating instructions and the service manual.If the meter only works up to 5% (300mA) AC/current, it should be „exactly“ described in the manual. And if I want to do it completely correct, the device shows "OL" below 300mA.For me the topic is closed.

author: bdunham7
author_rank: Super Contributor
timestamp: April 25, 2023, 06:01:25 pm
content: Quote from: kdl1950 on April 25, 2023, 04:51:59 pmIt is described appropriately in the fine print of the manual. And perhaps "UL" would be a better indication.I think the 'cutoff' may be a software iimplentation in this case. I tested my F116 on its 6V range and it seems that 20mV reads 21 or 22 counts but 19mV and below reads a solid 0.000. Testing on the Lo-Z 600V range, it reads down to the very low single counts, all the way to 000.1V for 100mV, however the indicator goes to 'DC' rather than 'AC' below 300mV or 3 counts. Still, it seems to have a TRMS residuum of less than 20 counts--which perhaps is just mine or perhaps they're all much lower than 20--and it still goes to zero on the 6V range.In the case of the F233, the 6A range presumably uses the 0.01R shunt, meaning full scale is 60mV, requiring a 10X gain amplifier. This may cause some noise that would be interpreted as instability or inaccuracy so they would have an additional reason to suppress it at zero.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 25, 2023, 06:37:33 pm
content: Quote from: Fungus on April 23, 2023, 12:07:25 pmYou're over-simplifying (what a surprise). The ACV ranges are TRMS, use the same TRMS IC, and are better specced, and also give additional uncertainty values when outside the nominal accuracy range.

author: Fungus
author_rank: Super Contributor
timestamp: April 26, 2023, 06:52:46 am
content: Quote from: J-R on April 25, 2023, 09:08:25 amCute, except:a) Brymen sells their meters at less than half the price of equivalent Flukes and they have more features and higher CAT ratings. Fluke doesn't even make a CAT IV 1000V meter, Brymen does.b) Brymen'scheapestnon-pocket meterdoesn't appear to be deliberately crippled in any way. What basic function is missing? It's not TRMS but for less than 60 Euros you get all basic measurement featuresplus600V CAT III protection and beep-jack alert. You want TRMS? You can have it for not much more.c) Brymen doesn't put crappy leads in the box with their flagship meter just to insult you a bit more.

author: Martin72
author_rank: Super Contributor
timestamp: April 26, 2023, 11:17:55 pm
content: Quote from: Fungus on April 25, 2023, 08:10:36 amHm?It´s their top-model, only the 287/289 are "above".So it´s normal when models beyond do not have all the features like the top model.QuoteHm again...

author: Black Phoenix
author_rank: Super Contributor
timestamp: April 27, 2023, 06:56:29 am
content: Quote from: Martin72 on April 26, 2023, 11:17:55 pmForget it, Fungus have a bone to pick with Fluke of some sort or their users, going by some of his comments in other threads.Cult followers of the Yellow Bumper meter that can do no wrong.Myself I use what it suits the job I have in fronr of me, being a UniT, a Brymen or a Zotek.That's the same as saying that Wiha is best and any Felo, Wera or Klein Tools user is dumb. Similar to the Makita VS Dewalt VS Milwaukee debacle of the power tools.