Products > Test Equipment
Brymen BM789
NoMoreMagicSmoke:
--- Quote from: floobydust on August 15, 2022, 06:55:54 pm ---
It's not really the bug that is a concern, it's the software testing coming across as weak. Autoranging is not rocket science. You flowchart and test at the boundary conditions such as a range change, and a range change gone wrong. And this issue is only a problem for people working in the 600 ohm world it seems.
--- End quote ---
I think you are underestimating the complexity of that simple statement. I tested my meter, and I found the following:
- My meter ranges up when the 66000 count threshold is reached
- My meter ranged down when the 61000 count threshold is reached
- My meter shows 6xxxx when the resistor is applied above the 63100 count reading
- My meter shows 06xxx when a resistor is applied below the 63100 count reading
None of these values correlate with the other users "magic values" that cause this issue which range from 65000-67000 counts. Now which "boundary condition" should they be testing to?
I expect that this bug is probably related to some perfect combination of hardware tolerance and firmware logic. It is highly probable that they did test the expected boundaries but the hardware in the test meters did not hit the magic values to cause this issue. Additionally, it is possible that they did test what they expected to be the boundaries, but the boundary might be slightly different than expected due to some tolerance related variance.
Yes, a company should test the boundaries. The problem is it is very likely that the test engineers performed extensive testing, but they missed that one magic permutation that caused some unfortunate bug to exist.
There is no complex product in existence that is without bugs. The important part is does the device have a bug that significantly affects it fit for use and end user satisfaction. Equally important (as I have said before) is how the company responds and what they do when a bug is discovered.
floobydust:
You decide to autorange up or down, on Ohms function. This is the boundary to test, in both directions that I'm talking about.
It involves changing the current-source (likely a resistor switched) and possibly the PGA and to a different (range) calibration factor, all at the same time (I don't have the Brymen chip datasheets to peruse but this is typical).
SURPRISE! This leaves you needing to range change in the opposite direction - which leads you to changing range again etc. and you see it's oscillating back and forth. As I've mentioned if you measure Ohms test current (using another DMM) while playing around with the potentiometer you should be able to see the changing/hunting. It could show up in other places at those boundaries as well.
No programmer expects to get stuck in a loop lol, that's why they have piles of hysteresis i.e. 66,000 vs 61,000 counts you mention.
Firmware algorithms around this can simply count the number of consecutive range changes done to see the hunting, the code itself can see what users are seeing and make an adjustment. It might be related to that range's calibration factor- unique to each multimeter. It can be a time delay needed to be added for settling time. Many hardware issues can cause it- but the point is it's too bad the bug is not easily fixed and slipped through testing.
joeqsmith:
--- Quote from: NoMoreMagicSmoke on August 19, 2022, 02:47:18 am ---There is no complex product in existence that is without bugs. The important part is does the device have a bug that significantly affects it fit for use and end user satisfaction. Equally important (as I have said before) is how the company responds and what they do when a bug is discovered.
--- End quote ---
I have heard back from Brymen and they explained in detail the problem as well as their corrective action. Indeed, some meters will not exhibit the inability to converge.
NoMoreMagicSmoke:
--- Quote from: joeqsmith on August 19, 2022, 12:49:48 pm ---
--- Quote from: NoMoreMagicSmoke on August 19, 2022, 02:47:18 am ---There is no complex product in existence that is without bugs. The important part is does the device have a bug that significantly affects it fit for use and end user satisfaction. Equally important (as I have said before) is how the company responds and what they do when a bug is discovered.
--- End quote ---
I have heard back from Brymen and they explained in detail the problem as well as their corrective action. Indeed, some meters will not exhibit the inability to converge.
--- End quote ---
Good to hear. Are you able to share their response?
joeqsmith:
--- Quote from: NoMoreMagicSmoke on August 19, 2022, 01:35:11 pm ---Are you able to share their response?
--- End quote ---
This will require a change to the firmware. In the future I hope to do a short clip showing the 789 before and after this update.
--- Quote ---After switching from 600Ω Range to 6kΩ Range, firmware used the first hi-speed AD conversion data to deduct "600Ω Range Offset" to check if further Range-Switching was in need. In case "600Ω Range" and "6kΩ Range" have significant offset difference, the unit may not be able to converge the measurements at around 640Ω ~ 660Ω region in auto-ranging operation mode. Thus not every unit will have this bug. Only the unit with extreme offset difference case has this bug.
--- End quote ---
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