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EEVBlog 121GW Multimeter Firmware Details
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Terry01:

--- Quote from: Brumby on December 05, 2018, 12:38:46 am ---
--- Quote from: CDaniel on December 04, 2018, 04:53:04 pm ---With a power supply adjust the voltage up and down to see when is switching ranges .

--- End quote ---

To be clear here: 
Step 1: Use an adjustable power supply that can at least go from 3V to 7V.  Start at 3V or so and increase the voltage until you see the range change on the meter (watch the units and decimal point).  Make a note of the voltage when this happens.
Step 2: Continuing on from Step 1 - From the 7V level, decrease the voltage until you see the range change.  Make a note of this voltage.

The difference between these two voltages is the "hysteresis".  This is a designed behaviour meant to stop the frequent range changes you would get from a meter without this feature when a measured voltage fluctuates either side of the range switching point.

The issue is the magnitude of this hysteresis.  If it's too big then you could have a transient (for example) trigger a switch to a higher range and when the voltage settles it is under that "range up" switching point, but not below the "range down" switching point.  As well as being visually distracting, it also means you lose a whole digit of resolution.

This behaviour and the issues associated with it apply to all measurements and ranges - whether voltage, current, resistance or whatever.  I just used an easily achievable example for voltage.

--- End quote ---

Thanks for the explanation. I understand now what hysteresis is and can do this later this morning and will post the results.

Is anyone else having the problem I had yesterday with their meter not measuring in mA range? My 121GW was measuring 87mA in the A range but when I changed range to mA it would not measure. It kept showing OFL.  :-\

I have v1.54 firmware installed as it came from Welectron around a week ago.
ChrisG:

--- Quote from: joeqsmith on December 05, 2018, 02:26:28 am ---
--- Quote from: GeoffreyF on December 04, 2018, 02:52:57 am ---If the cover is not in place then the batteries are not securely in place. If the battery is interrupted for even a moment while loading, that would explain your issue.   Remove the cover and check how well the batteries stay in. You will see what I mean.

I had a close call on that myself once.  Keep the cover on when installing new firmware.

--- End quote ---

Good idea.  I ran the meter a fair amount with the back cover removed in order to have access to the SD card and have not had a problem with them falling out but I normally have the meter face up and flat down on the table.    If the battery is pulled, I would expect the meter to have no problems.  I assume the boot loader runs a CRC on the application area before trying to run it.  If it fails, it should just wait for the new image to be loaded.   It sounds like there is a fear that the meter actually has been bricked doing this.   So, do we know if this is actually a problem or not?

I do not know this no. What I could do is start to retest and check and fiddle around with other FW updates with the risk that I eventually brick it. So mwahhhh not sure. Also my selector knob is still quite crusty in terms of rotation and not up to standard for a 239.00 € item IMHO. In other words the shim solution did fix one thing and made something else worse. I do like the meters form factor, options, features though and I believe we should continue to develop on this going to version 2.0 in 2019 or so.

--- End quote ---
exe:

--- Quote from: Terry01 on December 05, 2018, 08:29:54 am ---Is anyone else having the problem I had yesterday with their meter not measuring in mA range? My 121GW was measuring 87mA in the A range but when I changed range to mA it would not measure. It kept showing OFL.  :-\

--- End quote ---

Did you change the current socket on the meter?
exe:

--- Quote from: joeqsmith on December 05, 2018, 12:46:26 pm ---If anyone has bricked one from upgrading the firmware, chime in.

--- End quote ---

Uhm, it's a standard stm32 mcu, can be reprogrammed via the swd intarface using a $5 programmer (but header is not soldered). I did brick it many times and was able to restore the original firmware and bootloader. Just be sure to dump the calibration table, I lost mine during experiments.
Terry01:

--- Quote from: exe on December 05, 2018, 11:32:45 am ---
--- Quote from: Terry01 on December 05, 2018, 08:29:54 am ---Is anyone else having the problem I had yesterday with their meter not measuring in mA range? My 121GW was measuring 87mA in the A range but when I changed range to mA it would not measure. It kept showing OFL.  :-\

--- End quote ---

Did you change the current socket on the meter?

--- End quote ---

Yes, just did it again and also with my 87v too. The Fluke did it no probs and the 121GW showed OFL. I used a half-"ish" used 9v battery and a 4 ohm power resister as a load.
I have another much more depleted 9v battery that is down to 200-300 uA using the same set up. Both meters measured this no problem.
I have just read that you are not supposed to use fresh lithium in the 121GW which i have so it may be my fault. I'll change them out later for normal batteries and see if it fixes it.
I'll let you know how I go with that.
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