Fluke 233 cut off under 20mA

[kdl1950]

Hi guys,
I have a question about the Fluke 233.

Data sheet says:
AC Current Range 1mA to 10A Accuracy 1.5% + 3
DC Current Range 1mA to 10A Accuracy 1.0% + 3

Okay, 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

[Kim Christensen]

What happens if you manually change ranges to the lowest AC current range?

[BeBuLamar]

What happens if you manually change ranges to the lowest AC current range?

It'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.

[kdl1950]

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.

[J-R]

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%.

[AVGresponding]

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%.

So readings under 300mA may or may not be accurate enough to be useful? That's quite poor, for a Fluke product.

[BeBuLamar]

The 233 selling point is the remot display. Not so much for other features.

[Fungus]

So readings under 300mA may or may not be accurate enough to be useful? That's quite poor, for a Fluke product.

That's just the way TRMS chips work.

PS: Fluke sells average responding meters, too. Choose your poison.

[J-R]

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?

[Martin72]

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.

[J-R]

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%.

[Martin72]

It is "new" that the meter shows nothing instead of "something"...

[bdunham7]

If this is the same on this fluke meter, they should mention it in the specs/manual.

If it uses an analog TRMS converter like the AD737 (and the 233 likely uses exactly that actually 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.  As Fungus correctly 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.

[J-R]

https://web.archive.org/web/20121104004609/http://www.gellerlabs.com/34401A%20AC%20zero.htm

[bdunham7]

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?

I 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

[J-R]

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.

[bdunham7]

https://web.archive.org/web/20121104004609/http://www.gellerlabs.com/34401A%20AC%20zero.htm

I'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.

[alm]

I agree--the datasheet is both technically wrong and badly misleading in this regard.

I 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.

The DMM development process definitely leads to some odd results, such as the 233 missing the mA/uA function. 
[...]
Another major oddity is how few clamp meters have a mV range.  None of Brymen's do, for example.

That'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.

[J-R]

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.

[Fungus]

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.

That's just Fluke protecting their 87V cash-cow. All their other meters are designed around not being 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.

[J-R]

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.

That's just Fluke protecting their 87V cash-cow. All their other meters are designed around not being 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.

As 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...

[bdunham7]

That's just Fluke protecting their 87V cash-cow. All their other meters are designed around not being 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.

That 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?" 

[kdl1950]

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.

[bdunham7]

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.

It 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.

[AVGresponding]

So readings under 300mA may or may not be accurate enough to be useful? That's quite poor, for a Fluke product.

That's just the way TRMS chips work.

PS: Fluke sells average responding meters, too. Choose your poison.

You'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.