I do use two 121GW for few months, but recently started doing some extra data logging intensively (which is the reason I got this meter really), and unfortunately it is broken in many ways. I tested both, 1.57, and 2.00 fw.
- SERIOUS: After some time of data logging to SD card, it stops updating values in the file. LCD is showing proper values, and says that new records are added to the file. However the file only starts having 3 values cycling forever (flat line forever). This can start after 1000 records, or after 10000, or somewhere in between, hard to say. If I do a data logging for a 3 days, it is 100% certain my data file will be ruined, and experiment waste of time, and possibly money. The worst part is you only learn about it later, when you read files back on a computer. Example at the bottom.
- SERIOUS: Data corruptions in files. Sometimes part of the file will be overwritten by further records, or by seemingly random bytes. This happened to me few times. More often than not actually. I am using a micro SD card that come with a meter, and was only used for data logging, firmware update, and putting pdf manual there, just to have it as a backup. I doubt it is a problem with micro SD card, but some coding bug, either in the firmware or sdfat library used.
- CONSIDERABLE: It looks like a there is a limit of 600000 records, after which the logging automatically stops. Please rise it at least 100 times, as I don't see much reason to have it, and it is somehow limiting.
- WISHLIST: When the data logging ends, please beep, every few minutes forever, until user press a button or change the range.
- SERIOUS: Each row has a "counter", which isn't very helpful. It should be a timestamp, either absolute clock value down to millisecond (or just to 1 second, if the logging interval is big). Or also good option is to have it relative to the start of data logging. I see both options having great applications, so I would suggest selecting abs/rel timestamp as a setup option.
- MEH: If the battery gets low during the data logging, data logging stops. But then meter is unusable. You need to restart the meter.
- SERIOUS WISHLIST: File format is a bit verbose and repetitive, not really helping with processing, and is wasteful. The type of measurement and units should only be said once, on the 0th row. After that they shouldn't be mentioned to save space, and there should be only 2 columns in simple measurement modes (timestamp and value), nothing more. And 4 columns in VA modes. 3 columns in VAC+Hz mode. etc. Not 15 columns!
- WOULD BE NICE: Not a fan of DOS/Windows line termination. If possible use Unix style line termination instead. It also does consume less space on SD card.
- SERIOUS: When having Interval of 0, the sampling rate is very non uniform, sometimes doing 1 per second, sometimes 10 per second, sometimes stopping for some time. And because records don't have timestamp, it makes data logging at interval 0, totally useless for anything, there is no way to reliably use them for anything. This comes back to the 4th point above.
- WISHLIST: Make BT protocol allow for transfering (copy/move) files out the meter via BT. Would allow me to log offline to SD card for days, or maybe an hour, then easily transfer files to phone or computer. It takes annoying time and effort to open the meter, and mess with the SD card, put everything together, etc. I am sure this can be done, and there is still space to do it easily in firmware.
- WISHLIST: I am not a fan of CSV format, and the fact that the one used now, also do have awkward header section at the top, and some summary and the bottom. I would prefer one line header, like # Time "VDC [mV]", followed simple space separated rows 12351.221 3.41. It is WAY easier to manipulate such format than using CSV. If you want, it can be a tab, instead of space.
- WISHLIST: Number formatting is somehow poor in the file. It often will show things like "00.053,DCA" or "0018.74,mVA", instead of simply showing more sane (and space saving) "0.053,DCA" or "18.74,mVA". I guess, somebody should learn how to use sprintf correctly and format values. When parsing such numbers like 0018.74 or 00.053, some programming languages libraries really don't like it, because it is often not a correct format of floating point literals.
- WISHLIST: As somebody mentioned. When SD data logging is on, the secondary display only shows the record number (counter), so you loose ability to see current and voltage in VA and mVA modes. I wish it would cycle between 3 values instead.
- WISHLIST: Ability to set an option to also log the ambient temperature on the same line as any other measurement. i.e. # Time "VDC [mV]" "T [degC]", with lines 12351.221 3.41 24.3. I do plenty of measurements spanning days, and devices I test are temperature sensitive (resistors, batteries, power devices requiring cooling, etc), and having both value and ambient temperature, would allow me to understand things better. Especially in the summer, when even inside my house I can see 20 deg C temperature swings during a day!
As of the auto ranging in the SD data logging mode: I don't really care much. If it can be implemented without performance impact, that would be nice. But then how you make sure it is clear from the data file which range was used when and what is accuracy in each row? I would be happy with fixed range, as I use it now. As long other serious issues are resolved.
There are few other things I would like to be fixed or mentioned.
- It is not clear from manual if NiMH AA cells are supported. Manual should fix it, say they can be used, or must not be used.
- As of hardware. Well, if there is ever a successor of the meter. I hope it has a bit better LCD, i.e. has a maybe a 14-segemnt characters in the top display, or a small dot matrix character (or graphicals) display there (8x5 for each character?). It would really help to have ability to display 10-12 characters there, and not make them weird. The added benefit is ability to show possibly both current and voltage at the secondary display non stop, and also get rid of the suffixes on the right side of the LCD (mV, mA, A, V, Hz), etc. As they become redundant. It would also make usage of setup menu way easier (with long strings displayed easily as rolling text).
- Another wishlist's would be to consider an ESP32 of course, which also has WiFi and BT, and way more ROM and RAM. A lot of interesting things could be done with it.
There are some other minor things that do bother me about the 121GW, but really, the data logging issues are the biggest problem right now, making it not usable at the moment.
START,2019/08/14,19:37:37,
ID,170800000,
INTERVAL,001,sec,
,MAIN,,,SUB-1,,,SUB-2,,,Remark,
No. ,Func. ,Value,Unit,Func. ,Value,Unit,Func. ,Value,Unit,
1,DCmVA,0018.74,mVA,DCV,01.3872,V,DCmA,013.512,mA,,
2,DCmVA,0018.74,mVA,DCV,01.3872,V,DCmA,013.512,mA,,
3,DCmVA,0018.74,mVA,DCV,01.3872,V,DCmA,013.511,mA,,
4,DCmVA,0018.74,mVA,DCV,01.3874,V,DCmA,013.511,mA,,
5,DCmVA,0018.74,mVA,DCV,01.3874,V,DCmA,013.511,mA,,
6,DCmVA,0018.74,mVA,DCV,01.3874,V,DCmA,013.510,mA,,
7,DCmVA,0018.74,mVA,DCV,01.3874,V,DCmA,013.510,mA,,
8,DCmVA,0018.74,mVA,DCV,01.3872,V,DCmA,013.510,mA,,
9,DCmVA,0018.74,mVA,DCV,01.3872,V,DCmA,013.510,mA,,
10,DCmVA,0018.74,mVA,DCV,01.3872,V,DCmA,013.510,mA,,
11,DCmVA,0018.73,mVA,DCV,01.3870,V,DCmA,013.510,mA,,
12,DCmVA,0018.73,mVA,DCV,01.3870,V,DCmA,013.510,mA,,
13,DCmVA,0018.73,mVA,DCV,01.3870,V,DCmA,013.509,mA,,
14,DCmVA,0018.73,mVA,DCV,01.3870,V,DCmA,013.509,mA,,
15,DCmVA,0018.73,mVA,DCV,01.3869,V,DCmA,013.509,mA,,
16,DCmVA,0018.73,mVA,DCV,01.3869,V,DCmA,013.509,mA,,
... // all good
14382,DCmVA,0017.26,mVA,DCV,01.3311,V,DCmA,012.967,mA,,
14383,DCmVA,0017.26,mVA,DCV,01.3311,V,DCmA,012.967,mA,,
14384,DCmVA,0017.26,mVA,DCV,01.3311,V,DCmA,012.967,mA,,
14385,DCmVA,0017.25,mVA,DCV,01.3311,V,DCmA,012.966,mA,,
14386,DCmVA,0017.25,mVA,DCV,01.3311,V,DCmA,012.966,mA,,
14387,DCmVA,0017.25,mVA,DCV,01.3311,V,DCmA,012.966,mA,,
14388,DCmVA,0017.25,mVA,DCV,01.3311,V,DCmA,012.966,mA,,
14389,DCmVA,0017.25,mVA,DCV,01.3311,V,DCmA,012.966,mA,,
... // still all good
21238,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.874,mA,,
21239,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.874,mA,,
21240,DCmVA,0017.02,mVA,DCV,01.3219,V,DCmA,012.876,mA,,
21241,DCmVA,0017.02,mVA,DCV,01.3219,V,DCmA,012.876,mA,,
21242,DCmVA,0017.02,mVA,DCV,01.3219,V,DCmA,012.876,mA,,
21243,DCmVA,0017.02,mVA,DCV,01.3219,V,DCmA,012.876,mA,,
21244,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.875,mA,,
21245,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21246,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21247,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.876,mA,,
21248,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.876,mA,,
21249,DCmVA,0017.02,mVA,DCV,01.3219,V,DCmA,012.876,mA,,
21250,DCmVA,0017.02,mVA,DCV,01.3219,V,DCmA,012.876,mA,,
21251,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.874,mA,,
21252,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.874,mA,,
21253,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.874,mA,,
21254,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.874,mA,,
21255,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.875,mA,,
21256,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.875,mA,,
21257,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.875,mA,,
21258,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.874,mA,,
21259,DCmVA,0017.01,mVA,DCV,01.3219,V,DCmA,012.874,mA,,
21260,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.874,mA,,
21261,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.874,mA,,
21262,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21263,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21264,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21265,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21266,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21267,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21268,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21269,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.876,mA,,
21270,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.876,mA,,
21271,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.876,mA,,
21272,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.876,mA,,
21273,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21274,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21275,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21276,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
21277,DCmVA,0017.01,mVA,DCV,01.3218,V,DCmA,012.875,mA,,
... // stuck forever
113359,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.873,mA,,
113360,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113361,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113362,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113363,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113364,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113365,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113366,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113367,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113368,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113369,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113370,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113371,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113372,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113373,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113374,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113375,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.871,mA,,
113376,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.871,mA,,
113377,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.871,mA,,
113378,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113379,DCmVA,0017.01,mVA,DCV,01.3216,V,DCmA,012.872,mA,,
113380,DCmVA,0017.01,mVA,DCV,01.3215,V,DCmA,012.872,mA,,
113381,DCmVA,0017.01,mVA,DCV,01.3215,V,DCmA,012.872,mA,,
113382,DCmVA,0017.00,mVA,DCV,01.3215,V,DCmA,012.870,mA,,
113383,DCmVA,0017.00,mVA,DCV,01.3215,V,DCmA,012.870,mA,,
113384,DCmVA,0017.00,mVA,DCV,01.3215,V,DCmA,012.870,mA,,
113385,DCmVA,0017.00,mVA,DCV,01.3215,V,DCmA,012.871,mA,,
113386,DCmVA,0017.00,mVA,DCV,01.3215,V,DCmA,012.871,mA,,
113387,DCmVA,0017.00,mVA,DCV,01.3215,V,DCmA,012.871,mA,,
113388,DCmVA,0017.00,mVA,DCV,01.3215,V,DCmA,012.871,mA,,
113389,DCmVA,0017.01,mVA,DCV,01.3215,V,DCmA,012.873,mA,,
MAX,1,DCmVA,0018.74,mVA,
MIN,21477,DCmVA,0017.00,mVA,
After ~21250, it only logs ~17.01 mVA, even if display was showing to me ~14mVA. Voltage and current values in the output file fluctuate a little (3mV, and ~3mA), but that is all. The same happens on DC V range, when logging just voltage too, not just VA.
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