Author Topic: Brymen Crest and Min/Max Function VDC Capability  (Read 3554 times)

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Offline splat2030

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Brymen Crest and Min/Max Function VDC Capability
« on: September 17, 2022, 12:59:02 pm »
Hello All,

I have been looking to purchase a multimeter for automotive/general usage, but I would like something with a very good min/max function that is capable of measuring the instantaneous max. voltage drop at my 12VDC car battery when under the load of cranking the starter. The overall application of the meter is personal use, so unfortunately the higher end meters like the Fluke in the video below are out of the budget. The Brymen BM-829s has caught my interest because the manual states that their crest function is capable of a 1ms (1000X/s) sampling rate, and the normal min/max function is capable of a 50ms (20X/s) sampling rate. This meter has signifiantly better specs than other similar meters I have looked at such as the UNI-T UT161D, which has a min/max function with a sampling rate of only 333-500ms (2-3X/s). Does the Brymen 1ms crest function work with DC voltage, and would it be fast enough to capture the max. voltage drop in this application? Does anyone have any real world experience using either the Bryman crest or min/max in this application that can provide any further input as to its suitability?


Below is a link to a video showing this starting system/battery test:
« Last Edit: September 17, 2022, 01:08:01 pm by splat2030 »
 
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Offline unknownparticle

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #1 on: September 17, 2022, 01:56:41 pm »
How about Dave's 121GW, that has bluetooth data logging, so you can be remote from the meter and view on your phone.
DC coupling is the devils work!!
 

Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #2 on: September 17, 2022, 02:27:18 pm »
I did peruse the manual for the 121GW, but I'm not sure it would be suitable for my application because it states that the 1ms peak button is only for AC voltage. It also does not list a specific sampling rate for the min/max function, so I assume that it defaults to the 5X/s update rate listed in the general specifications. The Brymen BM-829s manual does not state whether the 1ms crest function works for DC voltage, but even if it doesn't it would appear that the min/max function is on the order of 4X as fast than the 121GW if it functions per spec. under real world conditions.
« Last Edit: September 17, 2022, 03:00:06 pm by splat2030 »
 

Offline joeqsmith

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #3 on: September 17, 2022, 02:46:03 pm »
Depending what you are trying to measure, maybe you could just make a simple peak detector probe.   
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Offline unknownparticle

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #4 on: September 17, 2022, 03:34:51 pm »
I admit to only skimming the text in your post, so excuse me for that.
So, there maybe a better solution than a DMM. I have a battery analyser which can test the battery and charging system of a vehicle and record data in real time and hold it for examination.  Mine is a Konnwei KW600, which I think has been superseded by the KW650.  Check it out on Amazon, and the manual is available as PDF from the manufacturer.  I haven't gone through it in detail but it may suit your purposes, at a low price. Mine has worked very well and has predicted a failing battery a couple of times. First time I sort of took the result of the test with a pinch of salt, that battery then failed suddenly 2 months later!  Second time, on another vehicle, I changed it before that happened!
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Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #5 on: September 17, 2022, 04:19:03 pm »
I know there are other faster/better methods of checking the charging system such as with a dedicated tester or an oscilloscope, but I'm just trying to keep it simple and relatively cost effective at this stage with one piece of equipment since I need to buy a decent multimeter for doing other things as well.
« Last Edit: September 17, 2022, 04:24:38 pm by splat2030 »
 

Offline joeqsmith

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #6 on: September 17, 2022, 04:41:28 pm »
Looking at the following:
https://www.richtek.com/Design%20Support/Technical%20Document/AN066?sc_lang=en

You want to detect a dip with a minimum time of 13.5ms (t6).    It would be easy enough to create a simple test pulse to demo it but I don't have the meter you are asking about.   
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Offline mqsaharan

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #7 on: September 18, 2022, 04:41:25 am »
Check out the reviews on https://lygte-info.dk/info/DMMReviews.html by HKJ. He has reviewed many cheap as well as expensive meters. He is also a member here.
Under the section "Measurements" you'll find the details about min/max/peak functions.
 

Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #8 on: September 18, 2022, 09:46:01 am »
Looking at the following:
https://www.richtek.com/Design%20Support/Technical%20Document/AN066?sc_lang=en

You want to detect a dip with a minimum time of 13.5ms (t6).    It would be easy enough to create a simple test pulse to demo it but I don't have the meter you are asking about.

Thanks for the reference to the 13.5 ms, so now I know what level of accuracy I need. I am pretty new to the world of electronics, so it's probably outside of my current ability to make something to test this.
 

Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #9 on: September 18, 2022, 09:48:10 am »
Check out the reviews on https://lygte-info.dk/info/DMMReviews.html by HKJ. He has reviewed many cheap as well as expensive meters. He is also a member here.
Under the section "Measurements" you'll find the details about min/max/peak functions.

Thanks for the link, lots of good data there. I see he has tested the Brymen BM-829s min/max function, and states it needs 570ms to capture a voltage. The Brymen manual states that the min/max function takes a reading every 50ms, so any ideas why there would be such a large discrepancy?
« Last Edit: September 18, 2022, 10:16:13 am by splat2030 »
 

Online Fungus

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #10 on: September 18, 2022, 03:21:41 pm »
Thanks for the link, lots of good data there. I see he has tested the Brymen BM-829s min/max function, and states it needs 570ms to capture a voltage. The Brymen manual states that the min/max function takes a reading every 50ms, so any ideas why there would be such a large discrepancy?

That page also says: "Peak (Creast) needs about 0.7ms to capture a DC voltage, it may use multiple captures to get the final value. "  :)


Reason: "Min-Max" is not the same as "Crest" on a Brymen.

"Min-Max" works with the values displayed on screen, Crest uses raw/unprocessed ADC readings and is much faster.

You can see the difference if you use it on AC voltage. Min-Max gives TRMS values, crest doesn't.

https://www.eevblog.com/forum/testgear/brymen-bm257s-minmax-vs-5ms-crest-capture-mode/
« Last Edit: September 18, 2022, 03:25:20 pm by Fungus »
 

Offline joeqsmith

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #11 on: September 18, 2022, 03:22:24 pm »
If you check the manual for the meter used in the video you linked, it should be fast enough to capture that 13.5ms dip.   

https://assets.fluke.com/manuals/87______umeng0800.pdf

The Brymen BM789 and BM869s can both easily measure it (yes in DC crest mode).   Guessing they offer other meters that could measure it as well.   I looked at their automotive meter.  The one thing I did not like about it was it would not save every parameter and required more fiddling than I would have liked.   

**
Should add, when I wrote both meters can easily measure this,  I set up a one-shot pulse (single pulse) that idles at 11V, then jumps to 16V for 5ms, then down to 6V for 5ms, then returns to 11V.   
« Last Edit: September 18, 2022, 03:31:51 pm by joeqsmith »
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Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #12 on: September 18, 2022, 03:59:52 pm »
Thanks for the link, lots of good data there. I see he has tested the Brymen BM-829s min/max function, and states it needs 570ms to capture a voltage. The Brymen manual states that the min/max function takes a reading every 50ms, so any ideas why there would be such a large discrepancy?

That page also says: "Peak (Creast) needs about 0.7ms to capture a DC voltage, it may use multiple captures to get the final value. "  :)


Reason: "Min-Max" is not the same as "Crest" on a Brymen.

"Min-Max" works with the values displayed on screen, Crest uses raw/unprocessed ADC readings and is much faster.

You can see the difference if you use it on AC voltage. Min-Max gives TRMS values, crest doesn't.

https://www.eevblog.com/forum/testgear/brymen-bm257s-minmax-vs-5ms-crest-capture-mode/

The problem is that the tested signal duration required to record the correct voltage value was longer than the manual specified screen refresh rate of 5X/sec or 200ms. If the min/max simply recorded the minimum value displayed to the screen, then I would think it should be able to record the correct voltage value in 200ms, and not require the 570ms that was measured. If it does truly work the way you described, then the screen refresh rate is actually 1.7X/second, and not the 5X/second specified in the manual.

It seems that min/max on any of these meters is going to be much too slow, however, I am concerned about the accuracy when using the crest function. BM829s Manual states +250 digits for signals greater than 1ms in crest, and I would be in the 60.00V range to measure 12.6 volts. This would result in a tolerance of approx +/- 2.5 volts (.01*250), which pretty much would make it useless for this reading with that poor of accuracy.
« Last Edit: September 18, 2022, 04:36:31 pm by splat2030 »
 

Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #13 on: September 18, 2022, 04:22:55 pm »
If you check the manual for the meter used in the video you linked, it should be fast enough to capture that 13.5ms dip.   

https://assets.fluke.com/manuals/87______umeng0800.pdf

The Brymen BM789 and BM869s can both easily measure it (yes in DC crest mode).   Guessing they offer other meters that could measure it as well.   I looked at their automotive meter.  The one thing I did not like about it was it would not save every parameter and required more fiddling than I would have liked.   

**
Should add, when I wrote both meters can easily measure this,  I set up a one-shot pulse (single pulse) that idles at 11V, then jumps to 16V for 5ms, then down to 6V for 5ms, then returns to 11V.

The interesting thing I noticed after watching that video again closer is that he just pressed the min/max button one time, which would have put the Fluke 87 in the 100ms nominal response setting, and not the peak 1ms setting. This setting requires a minimum signal duration of 200ms per the Fluke manual from your link, so I don't think his reading of 9.96 volts is actually the true minimum voltage if the signal is only 13.5ms.

I have also been looking at the BM789, and the crest function appears to have the best specs. of all the Brymen meters I have looked at. Manual states it can record with an accuracy of +100 digits at a duration of .35ms, however, the tolerance would still be quite large at +/- 1.0 volts when measuring 12.6 volts in 6000 count mode. What kind of accuracy did you see when you took those measurements?

Would it be possible for you to test the minimum signal duration in VDC for the regular min/max mode as well? Manual states that min/max records 10X/second or 100ms, but also states that the min signal duration is 300ms, which seems pretty slow compared to their spec for the BM839 at 200ms. Very interested to know how close this would come to the spec.
« Last Edit: September 18, 2022, 05:06:49 pm by splat2030 »
 

Online Fungus

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #14 on: September 18, 2022, 04:54:31 pm »
It seems that min/max on any of these meters is going to be much too slow, however, I am concerned about the accuracy when using the crest function. BM829s Manual states +250 digits for signals greater than 1ms in crest, and I would be in the 60.00V range to measure 12.6 volts. This would result in a tolerance of approx +/- 2.5 volts (.01*250), which pretty much would make it useless for this reading with that poor of accuracy.

My Brymen BM857s is +100 digits on 50,000 counts. That's 0.1V accuracy on the 50V range.

It's one of Brymen's "professional" meters (ie. designed to be thrown in toolboxes) and it only costs 10 Euros more than the BM829s.

https://brymen.eu/shop/bm857s/

I'm sure there's other Brymens with similar specs.
« Last Edit: September 18, 2022, 06:24:20 pm by Fungus »
 

Offline joeqsmith

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #15 on: September 18, 2022, 05:30:31 pm »
If you check the manual for the meter used in the video you linked, it should be fast enough to capture that 13.5ms dip.   

https://assets.fluke.com/manuals/87______umeng0800.pdf

The Brymen BM789 and BM869s can both easily measure it (yes in DC crest mode).   Guessing they offer other meters that could measure it as well.   I looked at their automotive meter.  The one thing I did not like about it was it would not save every parameter and required more fiddling than I would have liked.   

**
Should add, when I wrote both meters can easily measure this,  I set up a one-shot pulse (single pulse) that idles at 11V, then jumps to 16V for 5ms, then down to 6V for 5ms, then returns to 11V.

I have also been looking at the BM789, and the crest function appears to have the best specs. of all the Brymen meters. Manual states it can record with an accuracy of +100 digits at a duration of .35ms, however, the tolerance would still be quite large at +/- 1.0 volts when measuring 12.6 volts in 6000 count mode. What kind of accuracy did you see when you took those measurements?

Would it be possible for you to test the minimum signal duration in VDC for the regular min/max mode as well? Manual states that min/max records 10X/second or 100ms, but also states that the min signal duration is 300ms which seems pretty slow compared to their spec for the BM839 at 200ms. Very interested to know how close this would come to the spec.

The min/max function on both meters (BM869s/789) would be far too slow to measure your 13.5ms.  For accuracy, I would defer to the manual.     

I have a Fluke 189 which has something called a Fast Min/Max mode.  This is a 5000 count mode with +/-100 count accuracy.    I don't own the 87 referenced in your video.  Looking at the manual they show a +/-40 count but then have a typical of +/-100 count for some modes. 

https://dam-assets.fluke.com/s3fs-public/87______umeng0800.pdf

How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
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Offline joeqsmith

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #16 on: September 18, 2022, 07:07:09 pm »
The interesting thing I noticed after watching that video again closer is that he just pressed the min/max button one time, which would have put the Fluke 87 in the 100ms nominal response setting, and not the peak 1ms setting. This setting requires a minimum signal duration of 200ms per the Fluke manual from your link, so I don't think his reading of 9.96 volts is actually the true minimum voltage if the signal is only 13.5ms.

Guessing that is true but he may know that and the number he tossed out for a minimum was based on that.  Hard to say.   You could write them and ask.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
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Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #17 on: September 19, 2022, 12:54:26 am »
It seems that min/max on any of these meters is going to be much too slow, however, I am concerned about the accuracy when using the crest function. BM829s Manual states +250 digits for signals greater than 1ms in crest, and I would be in the 60.00V range to measure 12.6 volts. This would result in a tolerance of approx +/- 2.5 volts (.01*250), which pretty much would make it useless for this reading with that poor of accuracy.

My Brymen BM857s is +100 digits on 50,000 counts. That's 0.1V accuracy on the 50V range.

It's one of Brymen's "professional" meters (ie. designed to be thrown in toolboxes) and it only costs 10 Euros more than the BM829s.

https://brymen.eu/shop/bm857s/

I'm sure there's other Brymens with similar specs.

It seemed like all of the meters I have looked at so far state that they revert to 4 digit display when in the crest/peak mode. I took a look at the manual for the BM857s, and oddly it doesn't list any specs for the meter at all. I had to pull the catalog brochure which states +100ms for changes greater than .8ms, but does not specify which scale the meter uses. Can you confirm with your meter that when you put it in crest mode you have a 5 digit display rather than 4 digit?

Neither the manual nor catalog brochure give any specs on the performance of the regular min/max function, did yours come with any other documentation that lists this?
 

Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #18 on: September 19, 2022, 01:19:23 am »
If you check the manual for the meter used in the video you linked, it should be fast enough to capture that 13.5ms dip.   

https://assets.fluke.com/manuals/87______umeng0800.pdf

The Brymen BM789 and BM869s can both easily measure it (yes in DC crest mode).   Guessing they offer other meters that could measure it as well.   I looked at their automotive meter.  The one thing I did not like about it was it would not save every parameter and required more fiddling than I would have liked.   

**
Should add, when I wrote both meters can easily measure this,  I set up a one-shot pulse (single pulse) that idles at 11V, then jumps to 16V for 5ms, then down to 6V for 5ms, then returns to 11V.

I have also been looking at the BM789, and the crest function appears to have the best specs. of all the Brymen meters. Manual states it can record with an accuracy of +100 digits at a duration of .35ms, however, the tolerance would still be quite large at +/- 1.0 volts when measuring 12.6 volts in 6000 count mode. What kind of accuracy did you see when you took those measurements?

Would it be possible for you to test the minimum signal duration in VDC for the regular min/max mode as well? Manual states that min/max records 10X/second or 100ms, but also states that the min signal duration is 300ms which seems pretty slow compared to their spec for the BM839 at 200ms. Very interested to know how close this would come to the spec.

The min/max function on both meters (BM869s/789) would be far too slow to measure your 13.5ms.  For accuracy, I would defer to the manual.     

I have a Fluke 189 which has something called a Fast Min/Max mode.  This is a 5000 count mode with +/-100 count accuracy.    I don't own the 87 referenced in your video.  Looking at the manual they show a +/-40 count but then have a typical of +/-100 count for some modes. 

https://dam-assets.fluke.com/s3fs-public/87______umeng0800.pdf

I was wondering how close you got to the true voltage value with the BM-789 in crest mode when you were measuring the 11V-16V pulse? Considering my calculation shows a tolerance of +/-1 volt when in the 60.00volt scale, was the meter actually capable of returning a value closer to actual than the stated tolerance?

My confidence in the accuracies of regular min/max reported in the manual without 3rd party verification isn't great at this point considering that the two Bryman meters tested at the website referenced by mqsaharan (BM-829s, and BM-869s) both were way off compared to spec. The BM-829s took 570ms vs 50ms stated in the spec, and the BM869s took 350ms vs 50ms stated on the website. The BM789 seems to be their newest meter and has a much more detailed spec. for the min/max function in the manual, so I am curious whether this meter will actually perform closer to the spec. than the others. I will be using the regular min/max for other applications, so I would like to ensure whatever meter I get performs well in this function in addition to the crest/peak function.

https://lygte-info.dk/review/DMMBrymen%20BM829s%20UK.html

https://lygte-info.dk/review/DMMBrymen%20BM869s%20UK.html
« Last Edit: September 19, 2022, 02:28:58 am by splat2030 »
 

Online Fungus

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #19 on: September 19, 2022, 01:22:11 am »
I had to pull the catalog brochure which states +100ms for changes greater than .8ms

It's the "datasheet", not the "brochure", and it's +/-100 digits.  :)

but does not specify which scale the meter uses. Can you confirm with your meter that when you put it in crest mode you have a 5 digit display rather than 4 digit?

If I manual range to the 50V mode then press "crest" I get two digits before and two digits after the decimal point.

I find it very hard to believe the accuracy is 1V though, that would be completely useless.

I think we're not fully understanding the phrase "+100 digits for changes greater than .8ms".

I can understand that a change less than .8ms could be missed but what's meant by that wording?  :-//

I could do some measurement experiments but they won't prove much until that's cleared up.
« Last Edit: September 19, 2022, 01:48:49 am by Fungus »
 

Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #20 on: September 19, 2022, 02:04:17 am »
I had to pull the catalog brochure which states +100ms for changes greater than .8ms

It's the "datasheet", not the "brochure", and it's +/-100 digits.  :)

but does not specify which scale the meter uses. Can you confirm with your meter that when you put it in crest mode you have a 5 digit display rather than 4 digit?

If I manual range to the 50V mode then press "crest" I get two digits before and two digits after the decimal point.

I find it very hard to believe the accuracy is 1V though, that would be completely useless.

I think we're not fully understanding the phrase "+100 digits for changes greater than .8ms".

What's a "change"?

My understanding of the accuracy statement is that the crest function is capable of measuring changes in a measurement parameter that last for longer than .8ms, which is why they only assign a tolerance to values greater than this threshold. Any change in the parameter less than .8 ms does not get an assigned tolerance because the meter is not capable of registering it. I could be wrong, but this is how I interpreted it.

I looked at the specs for all of the 5+ digit display meters that Brymen lists on their website (860 series, 830 series, 780 series, and 850 series), and all but the 850 series explicitly state in the spec that they use a 4 digit resolution in crest mode, which would give a tolerance of +/- 1 for the best performing meters with +/- 100 digit accuracy in the 50.00 range (see attachments). A meter with a 4 digit display such as the BM829 has a statement similar to the 850 series catalog where it just lists the accuracy, I assume because the meter is only capable of displaying 4 digits. It would seem to me that perhaps this was a mistake with the 850 series documentation, and it should perform like the BM869 and BM789 in crest mode considering yours switches to 4 digit display just like the others. I have a hard time believing that Brymen's newest, most advanced, and more expensive meters like the BM789 and BM869 would be so much less capable than one of their oldest meters.

This video shows that the BM869s switches to 4 digit display in crest mode, but the measurement he takes is low enough to be within the 5.000V range. Low voltages like this should result in +/- .1 (.001*100) tolerance since there would be 3 decimal places of resolution.




« Last Edit: September 19, 2022, 07:31:38 am by splat2030 »
 

Offline radiolistener

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #21 on: September 19, 2022, 03:10:21 am »
Does the Brymen 1ms crest function work with DC voltage, and would it be fast enough to capture the max. voltage drop in this application?

Does anyone have any real world experience using either the Bryman crest or min/max in this application that can provide any further input as to its suitability?
 

yes, CREST works with DC and works with AC. In both cases it has the same meaning - it captures min and max amplitude Voltage. For example if I measure mains in AC mode with CREST I see:
max=328.2 V
min=-328.3 V
AC = 240.3 Vrms

But you're needs to note that precision is significantly worse in CREST mode. Also this mode has some noise, so you will not be able to capture exact value, just min/max values of ADC noise around signal.

Also note that there is bandwidth limitation, so the error will be higher for shorter pulse.

Here is a short test, how CREST function of Brymen BM867S measures pulse with different length.
Actual max Voltage is 1.0142 V.
Actual min Voltage is -0.0130 V.

pulse duration = max Voltage / min Voltage
1000 ms = 1.031 / -0.029
100 ms = 1.026 / -0.029
10 ms = 1.028 / -0.027
5 ms = 1.021 / -0.029
4 ms = 1.016 / -0.029
3 ms = 1.006 / -0.029
2 ms = 0.899 / -0.029
1 ms = 0.566 / -0.029

Noise during measurement was about ±0.025 V, it means that it can show 0.566 V and after a second seconds can jump to 0.591 V.

As you can see measurement error starts to grow very significantly at about 2-3 ms pulse. And at 1 ms pulse measurement error is up to 50%
« Last Edit: September 19, 2022, 03:13:07 am by radiolistener »
 

Offline radiolistener

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #22 on: September 19, 2022, 03:17:28 am »
It would seem to me that perhaps this was a mistake with the 850 series documentation, and it should perform like the BM869 and BM789 in crest mode considering yours switches to 4 digit display just like the others. I have a hard time believing that Brymen's newest, most advanced, and more expensive meters like the BM789 and BM869 would be so much less capable than one of their oldest meters.

You're needs to understand that CREST mode shows raw ADC value at about 1000 times per second rate. There is no way to keep 5-6 digits precision at so fast measurement. This mode is not intended for precise measurement, it is intended to catch short Voltage pulses or to estimate amplitude Voltage of AC waveform. Other DMM cannot do that at all.
« Last Edit: September 19, 2022, 03:21:34 am by radiolistener »
 

Online Fungus

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #23 on: September 19, 2022, 10:20:43 am »
There is no way to keep 5-6 digits precision at so fast measurement.

Obviously, but people are suggesting it drops down to less then 2 digits.

My understanding of the accuracy statement is that the crest function is capable of measuring changes in a measurement parameter that last for longer than .8ms, which is why they only assign a tolerance to values greater than this threshold. Any change in the parameter less than .8 ms does not get an assigned tolerance because the meter is not capable of registering it. I could be wrong, but this is how I interpreted it.

OK, so a change that lasts for at least .8ms.

That makes sense.

+/- 100 digit accuracy

But this makes no sense. My Brymen drops down to 4 digits in crest mode so if I put it in the 50V range and tap a 9V battery with the probes, you're suggesting it can read anywhere between 8 and 11 volts?

It's an easy test to do...

I've got a 9V battery here and if I set it to the 50V range and measure the voltage I get "09.465V".

I pressed the crest button and tapped the battery terminal with the probe and I got "09.59V" on screen.
I did it again and got "09.62V".
Third time gave "09.60V".
Fourth time:  "09.60V"..
Fifth time:  "09.62V".

OK, it's a tiny bit high (1.4%) but the error is consistent with "10 displayed digits", ie. 0.1V.



The exact phrase use in the datasheet is: "Specified accuracy +/1 100 digits for changes > 0.8ms in duration"


I think that "specified accuracy" refers to the meter's accuracy in 50,000 count mode, not the "visible accuracy" of the number of digits displayed in crest mode.

It's consistent with my quick test and much more believable than the meter only having +/-1V accuracy (which would be completely useless!)
« Last Edit: September 19, 2022, 11:02:45 am by Fungus »
 

Offline splat2030

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Re: Brymen Crest and Min/Max Function VDC Capability
« Reply #24 on: September 19, 2022, 12:04:11 pm »
There is no way to keep 5-6 digits precision at so fast measurement.

Obviously, but people are suggesting it drops down to less then 2 digits.

My understanding of the accuracy statement is that the crest function is capable of measuring changes in a measurement parameter that last for longer than .8ms, which is why they only assign a tolerance to values greater than this threshold. Any change in the parameter less than .8 ms does not get an assigned tolerance because the meter is not capable of registering it. I could be wrong, but this is how I interpreted it.

OK, so a change that lasts for at least .8ms.

That makes sense.

+/- 100 digit accuracy

But this makes no sense. My Brymen drops down to 4 digits in crest mode so if I put it in the 50V range and tap a 9V battery with the probes, you're suggesting it can read anywhere between 8 and 11 volts?

It's an easy test to do...

I've got a 9V battery here and if I set it to the 50V range and measure the voltage I get "09.465V".

I pressed the crest button and tapped the battery terminal with the probe and I got "09.59V" on screen.
I did it again and got "09.62V".
Third time gave "09.60V".
Fourth time:  "09.60V"..
Fifth time:  "09.62V".

OK, it's a tiny bit high (1.4%) but the error is consistent with "10 displayed digits", ie. 0.1V.



The exact phrase use in the datasheet is: "Specified accuracy +/1 100 digits for changes > 0.8ms in duration"


I think that "specified accuracy" refers to the meter's accuracy in 50,000 count mode, not the "visible accuracy" of the number of digits displayed in crest mode.

It's consistent with my quick test and much more believable than the meter only having +/-1V accuracy (which would be completely useless!)

I agree with you that this accuracy level would be practically useless for my measurement, so I hope someone can point out where I have gone wrong in my understanding.

I am not suggesting that every meter will necessarily read to the limits of the tolerance range when taking a measurement, but any random meter could read at the max. or min. published tolerance and still be considered to be within spec. I assume that if these meters are tested for quality at some point during the manufacturing process, then one that reads say 10 volts in crest mode would pass and be sold to a customer assuming my interpretation of this accuracy statement is correct. Every meter is going to read a little differently due to manufacturing variances.

I'm not sure using a 9 volt battery like you are describing would adequately test the function of crest mode, because you are simply taking multiple measurements of a constant 9 volt source that doesn't see any rapid changes once you have the meter connected to the battery. I think a more accurate test would be to simulate a short duration voltage spike on a constant voltage source at varying time intervals.

The exact statement for the BM857s is "Specified accuracy +/- 100 digits for changes > 0.8ms in duration", but this is the only meter with a greater than 4 digit display in Brymen's lineup that doesn't also include an additional caveat statement "6000 count mode only", or "Resolution 5000 counts" when describing crest mode. I would be surprised if this meter is capable of .001 resolution in crest mode when the flagship BM869s is not.

My understanding is that the number of additional counts has a different effect on accuracy based on the resolution of the range you are measuring in. The resolution is .001 in 6.000V range, and the resolution is .01 in 60.00V range, so the effect on accuracy of +/- 100 counts is the difference between .1 and 1 in those two ranges. Since your BM857 meter switches to a resolution of .01 when you enter crest mode measuring 9V (09.00V), then +/- 100 digits should result in +/- 1V of tolerance, regardless of the normal screen resolution.

As an example calculation, if we assume that we are limited to the 6000 count mode for the crest function as is stated in the BM-839 manual, then the only ranges available in DCV are 6.000, 60.00, 600.0, 1000. To measure 9 V, the meter would have to be in the 60.00 V range, otherwise it should show an overload in 6.000 V range. The "specified accuracy" in the 60.00 V range for the BM-839 is +/-(.045% + 1D), so a reading of 9 V would give +/- .014 V (.00045*9 + .01*1), then because we are also in crest mode we need to add the additional +/-100 digits to this (.01*100) = 1 V. The total tolerance per spec for reading for 9 volts in crest mode using the 6000 count range would be +/- 1.014 V.

If we were reading say 5 V in the same 6000 count crest mode, then we would have a resolution of .001 (5.000V) because we are in the 6.000 V range, and the +/- 100 counts would only amount to +/-.1 V (100*.001). The specified accuracy would also be less at +/-.005V (.00045*9 + .001*1), resulting in a total tolerance of +/- .105 V.
« Last Edit: September 19, 2022, 12:51:26 pm by splat2030 »
 


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