Products > Test Equipment
Brymen Crest and Min/Max Function VDC Capability
Fungus:
--- Quote from: splat2030 on September 18, 2022, 09:48:10 am ---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?
--- End quote ---
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/
joeqsmith:
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.
splat2030:
--- Quote from: Fungus on September 18, 2022, 03:21:41 pm ---
--- Quote from: splat2030 on September 18, 2022, 09:48:10 am ---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?
--- End quote ---
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/
--- End quote ---
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.
splat2030:
--- Quote from: joeqsmith 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.
--- End quote ---
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.
Fungus:
--- Quote from: splat2030 on September 18, 2022, 03:59:52 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.
--- End quote ---
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.
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