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Brymen BM789

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NoMoreMagicSmoke:

--- Quote from: joeqsmith on August 19, 2022, 02:29:34 pm ---
--- 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 ---

--- End quote ---

That makes sense. It also likely means that the root cause is an unexpected condition as a result of a manufacturing tolerance stackup.

I am really suspicious if it isn't a direct result of:

--- Quote from: EEVblog on August 02, 2022, 04:37:00 am ---FYI

--- Quote ---78608 version is only to enlarge allowance range for OHM hardware offset to reduce production failure rate. It does not affect meter performance.
--- End quote ---

--- End quote ---

Which would mean that the statement of "does not affect meter performance" isn't exactly true.   |O

The following is pure speculation, but I can certainly see how this can happen. R&D designed the meter and developed their tests around the design. The engineers may have even developed the original specifications to ensure that this scenario could not happen. After they start production the are seeing a higher than expected reject rate, and the process engineers determine that they can increase the tolerance to resolve the issue. The tests may have passed due to the test developers designing the bounds conditions around the original design, which might now no longer be the correct bounds conditions.

Regardless of how they got here. Based on Brymen's response to your previous inquiries, I would not be surprised if Brymen is currently in the process of developing new production change procedures to be absolutely certain this can't happen again.

NoMoreMagicSmoke:

--- Quote from: joeqsmith on August 19, 2022, 02:29:34 pm ---
--- 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 ---

--- End quote ---

Since I have a meter that does not exhibit this behavior, are you willing to compare your meter with the issue to mine?

- 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

I am curious how close your transition threshold is to the offending reading.

joeqsmith:
At 649.53 ohms it is stable.  Add one more ohm and it will hunt until 0.6759 where it is once again stable.   I'm sure it would change depending on the direction and range.   

NoMoreMagicSmoke:

--- Quote from: joeqsmith on August 20, 2022, 06:37:55 pm ---At 649.53 ohms it is stable.  Add one more ohm and it will hunt until 0.6759 where it is once again stable.   I'm sure it would change depending on the direction and range.   

--- End quote ---

Interesting. Does it only oscillate when going up? Or does it happen when going down as well?

joeqsmith:
I think it cleaned switched (no oscillation) going back down and the threshold was a different value all together. 

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