Fluke 233 fail - Page 1
Forum section: electronics / general

author: Bloch
author_rank: Unknown
timestamp: February 02, 2012, 12:13:34 pm
content: Power supply is set to 200mAThe Fluke 233Mode selected DC 0.201 AOKMode selected AC 0.202 AFAILMode selected AC 0.198 AFAILThe Fluke 177Mode selected DC 0.201 AOKMode selected AC 0.000 AOKI have 2 Fluke 177 and 2 Fluke 233 and they show more or less the same.That do you say ? Are this an know error on The Fluke 233 ?

author: samgab
author_rank: Frequent Contributor
timestamp: February 02, 2012, 01:25:34 pm
content: In the last picture you have the 177 set to frequency (Hz) mode.Perhaps the fail is with the user?

author: Bloch
author_rank: Unknown
timestamp: February 02, 2012, 02:25:41 pm
content: Quote from: samgab on February 02, 2012, 01:25:34 pmYou are rigth. New picture. Same problem

author: jahonen
author_rank: Super Contributor
timestamp: February 02, 2012, 03:00:19 pm
content: That result would make sense if the measurement would be AC+DC true RMS and not just AC RMS.Regards,Janne

author: Rufus
author_rank: Super Contributor
timestamp: February 02, 2012, 03:14:06 pm
content: Quote from: Bloch on February 02, 2012, 12:13:34 pmThe 233 user manual supplement states "AC Amps is DC coupled."

author: IanB
author_rank: Super Contributor
timestamp: February 02, 2012, 03:16:49 pm
content: Quote from: Bloch on February 02, 2012, 12:13:34 pmI'm confused. You pass 0.2 A through the meter and it reads 0.2 A, and you think something is wrong? Why?(You understand, of course, that 200 mA DCis also200 mA AC. It just happens to be AC with a frequency of 0 Hz.)

author: Bloch
author_rank: Unknown
timestamp: February 02, 2012, 03:22:52 pm
content: Well then must the 2 * Fluke 177 be wrong/broken then :-)And for the record in my book 0HZ is DC

author: IanB
author_rank: Super Contributor
timestamp: February 02, 2012, 03:30:59 pm
content: Yes, the 177 is either defective or user error. As mentioned above some meters can show DC+AC as two separate numbers, and the meter might be showing 0.00 as the AC component of a DC signal. You should check the manual and see what to expect.As for the 233 and the general case, the AC range on a meter shows all currents or voltages, whether AC or DC or a combination. If you pass 200 mA DC through a resistive circuit like a lamp it will be energized just as much as with 200 mA AC. This is especially true if you are considering RMS currents or voltages. 200 mA DC is 200 mA RMS by definition.

author: Bloch
author_rank: Unknown
timestamp: February 02, 2012, 04:01:13 pm
content: Ok i did find 2 more multimeters.Fluke 87YF-3700Same result.

author: DonRon
author_rank: Regular Contributor
timestamp: February 02, 2012, 04:52:08 pm
content: Hihad a look at the manuals for the Fluke 233 and 177.Fluke 233AC current is dc-coupledFluke 177AC current is ac-coupledSo I think everything is okay.(Fluke 87 manual also says Current Function: AC conversions are ac-coupled)Greet'sRon

author: Richard W.
author_rank: Regular Contributor
timestamp: February 02, 2012, 04:58:41 pm
content: Hello,don't worry, everything is gonna be alright :-)The AC-amps range of the Fluke 233 is DC coupled, so a DC current is also displayed in AC range(http://assets.fluke.com/manuals/233_____umeng0004.pdf)The Fluke 177 AC-amps range is not DC coupled, so a DC current is not displayed.If you try this with a dual display mode (Fluke 280 series for example) you could see the DC and the AC current separatly.regards

author: IanB
author_rank: Super Contributor
timestamp: February 02, 2012, 05:03:17 pm
content: Basically you have to read the manual and know what to expect from the meter. An instrument doesn't tell you reality, it gives you a filtered view of reality--and as the operator of the instrument you have to know what the instrument is doing to your signal between the measurement point and the display.

author: Bloch
author_rank: Unknown
timestamp: February 02, 2012, 05:30:47 pm
content: Thanks .....Well it is the first time I have used a DC coupled mulitimeter then.I may again be wrongA DC coupled mulitimeter is not so use full as the "old" type multimeter.1 example I want to measure ripple on a Power supply. Can do that with the DC coupled mulitimeter.Ps I can see "DC coupled" was added later so I am sure it is not mention in my manual

author: Unknown
author_rank: Unknown
timestamp: February 02, 2012, 09:22:48 pm
content: Just put a cap in series with the meter. That's all AC coupling usually is. Mind the voltage rating and the knee frequency for the low-pass filter you're forming. Not sure why the 233 is DC coupled, most meters are AC coupled, and some advanced meters have an AC+DC mode. It's definitely not the first Fluke DMM with a DC-coupled AC range, people have been bitten by this before on other meters. Maybe it has to do with the intended audience, which I guess is electricians?

author: IanB
author_rank: Super Contributor
timestamp: February 02, 2012, 09:37:21 pm
content: What's the use of "AC coupling" in a meter? At what minimum frequency do you expect the high pass filter to occur, and how steep is the roll off? I don't want a meter that works that way, and I am surprised to learn that such a meter even exists.Furthermore, if you want to measure true RMS you must consider all frequency components down to DC or you are getting a false reading. If the meter can display AC+DC separately that's good, but if the meter can only show one value, I want to knowallthe current flowing in my wire, or at least have a warning that there is a DC component the meter is hiding from me.

author: Unknown
author_rank: Unknown
timestamp: February 03, 2012, 01:32:01 am
content: Quote from: IanB on February 02, 2012, 09:37:21 pmFor measuring ripple for example, like Bloch stated. Note that the R in this RC filter is usually 1 Mohm, so even with 100 nF of capacitance the -3 dB point is already at ~1 Hz. Note that DC mode is acting as a low pass filter, too. NMRR rolls of at low frequencies. At 1 Hz signal will probably be recorded as a fluctuating DC signal. Most of the meters out there seem to be AC coupled and some of the fancy ones have AC + DC as an option. This is probably the only option for average-responding meters, since a DC voltage is not going to go well through that precision rectifier (unless they make it a bridge rectifier). AC + DC is usually only available on true RMS meters.Quote from: IanB on February 02, 2012, 09:37:21 pmAgreed that in some cases (like an unknown mix of AC and DC), AC+DC is preferable, which is why some meters offer that function. In many cases, you will have well defined AC and DC components, however. For example, you might have a +3.3 VDC supply rail with 100 mV of 60 Hz ripple, plus some high frequency hash that's probably beyond the meter's bandwidth.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 03, 2012, 02:09:40 am
content: Well,almost anyone doing faultfinding with analog circuits would find an AC range (at least for volts) which didn't also read the DC component extremely useful.The old Fluke 77 does have a real AC voltage range,but suffers from the opposite problem,in that if confronted with a signal consisting of pulses with return to zero between pulses,reads it as DC on the DC range.In a way,it is correct,but in the real world it can lead you astray.Of course,both of the above are good arguments for having an Oscilloscope.VK6ZGO