Author Topic: I do not know which measure frequency right Brymen BM867 or BM079 (Read 7816 times)

gameru · « **on:** October 09, 2015, 11:33:41 pm »

Greetings
Today i received the clamp meter Brymen BM079,and I wanted to compare it to BM867.
I have a UPS APC (BE700G-GR) with frequency waveform - stepped.Both BM867 and BM079 read voltage idem,but the frequency no.BM079 show 50Hz and BM867 98-100Hz. The standard in my country 230V-50Hz.
Then i measure voltage on Mustek ups (PowerMust 400) who has frequency waveform - stepped.Both read voltage an frequency idem
In the case of APC (BE700G-GR) who indicating frequency correct?

Nerull · « **Reply #1 on:** October 09, 2015, 11:44:38 pm »

The UPS is still going to output 50Hz since devices may depend on it, but the stepped waveform could be confusing the counter in one of the meters. The waveform is unlikely to be identical between both UPSes, which is why it may not happen on both.

Just how approximate the output wave is varies by model, sometimes its pretty damn far from a sine wave.

gameru · « **Reply #2 on:** October 10, 2015, 12:51:50 am »

I know is it far from a sine wave.I saw some video on Youtube,analyzes output with an oscilloscope.
I had great expectations from Brymen BM867,i thought I will not have problems like that

Lightages · « **Reply #3 on:** October 10, 2015, 01:11:56 am »

It seems to me that at that low frequency the BM869S is seeing double the frequency because it is AC coupled in frequency mode. It therefore sees each falling and rising edge and therefore sees double the frequency. I will go and investigate.

Lightages · « **Reply #4 on:** October 10, 2015, 02:59:31 am »

It was as I suspected. I set up my AWG to make a stepped square wave like many UPS and inverters output. I measured the frequency using the different modes possible on the BM869S. In everything other than the mV setting, I read 50Hz. In the mV switch setting I measured 100Hz. I measured double the frequency in mV swtich setting until I reached 2kHz. So either it is overloading in a strange way or it is AC coupled to a very high frequency.

gameru · « **Reply #5 on:** October 10, 2015, 10:57:36 am »

Thank you for answer.
I sent an email to Brymen to inform them about this problem
Honest,I do not know what to say because i had great confidence in Brymen DMM

Wytnucls · « **Reply #6 on:** October 10, 2015, 12:47:52 pm »

Seems to me like the meter may have an hysteresis problem, detecting a noisy step as an extra rising edge. Try to capture the waveform from your BE700, if you have access to an oscilloscope.

SteveLy · « **Reply #7 on:** October 10, 2015, 01:18:26 pm »

AC coupling on badly distorted sine wave sounds like the most likely explanation. In the graphic Nerull posted, the blue right hand side waveform AC-coupled (i.e., high-pass filtered) will give you two prominent zero-crossing rising edges per cycle. It's not likely to be a triggering on noise issue.

Marco · « **Reply #8 on:** October 10, 2015, 01:42:13 pm »

Quote from: gameru on October 10, 2015, 12:51:50 am

I know is it far from a sine wave.I saw some video on Youtube,analyzes output with an oscilloscope.
I had great expectations from Brymen BM867,i thought I will not have problems like that

I think it's a problem of expectation, it's not like they use auto-correlation. If you have say a 10% full scale bounce in the waveform at the zero crossing then you can't really blame the way it reads it on them, it's because of your signal.

PS. the mV range lack of hysteresis is on them, but that's not what is causing your issues.

gameru · « **Reply #9 on:** October 10, 2015, 05:46:51 pm »

Unfortunately i don't have oscilloscope,and i do not know anyone who have.
I make some research, and i discover if i putting out battery from unit with the condition it still be connected to unit, the DMM BM867 measuring correctly frequency.
I discover one more thing.When I try to measure frequency with both (BM867 and BM079),the BM867 not measuring correctly. I did a video
I thought if it is True RMS there will be no problems at a frequency of more than 45Hz.

I want to apologize for my english,i know i don't speak good.

Wytnucls · « **Reply #10 on:** October 10, 2015, 06:52:47 pm »

From the Fluke 87V manual:
If a reading seems to be a multiple of what you
expect, the input signal may be distorted. Distortion
can cause multiple triggerings of the frequency
counter. Selecting a higher voltage range might solve
this problem by decreasing the sensitivity of the
Meter. You can also try selecting a dc range, which
raises the trigger level. In general, the lowest
frequency displayed is the correct one.

Wytnucls · « **Reply #11 on:** October 11, 2015, 06:51:22 am »

Quote from: Lightages on October 10, 2015, 02:59:31 am

It was as I suspected. I set up my AWG to make a stepped square wave like many UPS and inverters output. I measured the frequency using the different modes possible on the BM869S. In everything other than the mV setting, I read 50Hz. In the mV switch setting I measured 100Hz. I measured double the frequency in mV swtich setting until I reached 2kHz. So either it is overloading in a strange way or it is AC coupled to a very high frequency.

The Fluke 185 is always AC coupled, unless the duty cycle mode is activated. It then becomes DC coupled on all relevant ranges.
It reads a 50Hz step sine waveforms properly (mV or V), displaying the correct frequency, while AC coupled.
Like the Fluke 87V, triggering can be changed from rising to falling edge, which may help with an unstable waveform.

gameru · « **Reply #12 on:** October 11, 2015, 10:20:33 am »

K,i understand because signal may be distorted much the BM867 can't read correct.And BM079 it is helped by VFD filter,this is why read fair frequency.
But,can someone explain me why when i putting out battery from unit with the condition it still be connected to unit, the DMM BM867 measuring correctly frequency.
I posted a picture and 1 video
I ask because i am a novice

Wytnucls · « **Reply #13 on:** October 11, 2015, 11:27:34 am »

The VFD filter of the clamp meter could possibly affect the waveform being measured by the Brymen BM867.

Wytnucls · « **Reply #14 on:** October 11, 2015, 11:37:54 am »

Quote from: SteveLy on October 10, 2015, 01:18:26 pm

AC coupling on badly distorted sine wave sounds like the most likely explanation. In the graphic Nerull posted, the blue right hand side waveform AC-coupled (i.e., high-pass filtered) will give you two prominent zero-crossing rising edges per cycle. It's not likely to be a triggering on noise issue.

None of my meters get fooled by such waveform:

gameru · « **Reply #15 on:** October 11, 2015, 11:41:30 am »

K,I understand how it works with BM867 and BM079.
And i want to thank you all, and especially to a person who has not posted here,is about

KIRIAKOS .I talked a lot with him via PM an emaill and made me understand things which i don't know.It's a very social person

Lightages · « **Reply #16 on:** October 12, 2015, 02:45:40 am »

Actually I just reviewed the waveform I made with Easywave in higher detail on my scope and it was pretty messy and could be seen as 100Hz easily. I made cleaner file and it reads as 50Hz. So it depends on how many zero crossing there are in the waveform being measured and I assume the waveform of the OP in question is not that clean and ambiguous for a meter to read,

Wytnucls · « **Reply #17 on:** October 12, 2015, 08:51:56 am »

Ran a test with a 3Vpp cardiac waveform at 50Hz with UT-71D and Fluke 185.
Both meters, AC coupled, detected it as 150Hz, until the volt range was changed to 40/50V manually. (trigger 10% of range?)
The 185 read the correct 50Hz frequency in DC coupling mode on the Hz range, with the duty cycle active.
The 71D appears to be always AC coupled, even on the Hz range.
In conclusion, multimeters are not very good at measuring the frequency of complicated waveforms. Rather rely on the oscilloscope display for less ambiguity.

gameru · « **Reply #18 on:** October 12, 2015, 01:08:51 pm »

Maybe in one year i buy a oscilloscope.
At the moment budget does not allow me.
Thank you for sacrifice your time for me

gameru · « **Reply #19 on:** November 07, 2015, 04:45:42 pm »

Greeting
If anyone is interested of Brymen BM079,now is a review from Kiriakos (http://www.ittsb.eu/BRYMEN%20BM079%20Review.html)
I think there are people interested of BM079this is the reason why I made this notice.


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Author Topic: I do not know which measure frequency right Brymen BM867 or BM079 (Read 7816 times)

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