Author Topic: EEVblog 121GW Multimeter Issues  (Read 94889 times)

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Offline Seppy

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Re: EEVblog 121GW Multimeter Issues
« Reply #750 on: September 05, 2018, 11:38:26 am »
Thanks JS but I'll wait and see what Dave comes back with as I registered the issue on the web site's "Report an Issue".

Geoff

OK...so my bad!! This is the text from the web site;

Note: When upgrading a multimeter the “.bin” file must be renamed “EEVBlog.bin”:

So being a literal being, that's exactly what I did already knowing it was a bin file, I assumed the program looked at the "name" wanting to see a .bin. So I had in effect EEVBlog.bin.bin. The penny dropped when I saw Dave's email from EEVBlog with a included file to try. Now I have v1.26.

Sorry all for the distraction. I'll now email Dave and apologies  :palm:

Geoff

*David's email (me)
 

Offline JS

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Re: EEVblog 121GW Multimeter Issues
« Reply #751 on: September 09, 2018, 07:07:56 am »
Hi, new one, I've seen some comments on this but now I'm aeeing it on my meter. On the low ohms range sometimes it just measures zero when you short the leads, or a low resistance path, sometimes as expected I need to zero out the leads and it's left with a few counts and sometimes it is left with a few tens of counts left.

Turning it off and on again changes this, in which of the states it is at.

Have you seen this? Do you know something about that?

JS

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Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #752 on: September 10, 2018, 07:14:57 am »
On this 600V meter, the latest version of the manual August 30, 2018, still confusingly specifies AC and DC VA as 500VA without mentioning its limited to 50V for whatever reason :(
 

Offline JS

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Re: EEVblog 121GW Multimeter Issues
« Reply #753 on: September 10, 2018, 06:42:25 pm »
On this 600V meter, the latest version of the manual August 30, 2018, still confusingly specifies AC and DC VA as 500VA without mentioning its limited to 50V for whatever reason :(
I don't understand that limitation, everything is in the meter to measure higher voltages and that's all that should be required. I guess I'm missing something but measuring VA directly on mains would be nice.

JS
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Offline CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #754 on: September 11, 2018, 07:41:11 am »
Agree with that , this could be usefull sometime for DC ( ex. power supply ) and AC ( mains , power amplifiers ) . 10A x 500V .  For minuscule VA ranges i can't think of any practical usage ... I remember reading somewhere that David said that is not enough "room " in the micro for all ranges and in this case some lower ranges must disappear .
« Last Edit: September 11, 2018, 07:43:35 am by CDaniel »
 
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Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #755 on: September 11, 2018, 03:40:08 pm »
I thought Dave did a poll on the VA mode and there was little interest in going higher.
How electrically robust is your meter?? http://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Online Brumby

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Re: EEVblog 121GW Multimeter Issues
« Reply #756 on: September 11, 2018, 05:10:01 pm »
I would have thought higher VA on mains would be better served with one of those mains power monitor products like the "Kill-a-Watt".
 

Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #757 on: September 12, 2018, 02:44:19 am »
I've seen a few people change out the shunt in the Kill-a-Watt to use it for lower current devices.  I assumed a meter like the 121GW would fit nicely as they have the scaling built-in already.  I never understood the reason why they limited it to 50V.  The prototype was limited as well. 
How electrically robust is your meter?? http://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Online HKJ

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Re: EEVblog 121GW Multimeter Issues
« Reply #758 on: September 12, 2018, 02:53:45 am »
I've seen a few people change out the shunt in the Kill-a-Watt to use it for lower current devices.  I assumed a meter like the 121GW would fit nicely as they have the scaling built-in already.  I never understood the reason why they limited it to 50V.  The prototype was limited as well.

A VA meter is not very useful on mains, usual you want W.
 

Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #759 on: September 12, 2018, 02:59:22 am »
Maybe that's why they limit it.  Personally, I have no need for it but was surprised to see it limited.
How electrically robust is your meter?? http://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #760 on: September 12, 2018, 09:36:56 am »
We have a beefy micro in the 121GW, maybe some fancy smoothing such as Savitzky–Golay filtering?

I noticed that the update rate for the mV range is the same as temperature/thermocouple. Is there is a specific limitation that necessitates the lower update rate?

My UT171C is faster than the 121GW with the same stability. I know Uni-T catches flack for not being fully up to snuff on some of the lower end models and I'd like to compare functionality between the two meters, but I feel the bias against Uni-T will make these comparisons useless by virtue of opinion only.

Call it an obsessive compulsive tendency, but the meter would show a lot more "polish" if the boot up/power-on sequence *didn't* flash the LCD backlight.
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #761 on: September 12, 2018, 10:08:53 am »
Both date and time is on the first row in the file, then it says what interval is used. So it is not impossible, just somehwat cumbersome. Add another column, copy the time from the top row, then next row is the one above+(interval in seconds)*(1/86400). If using excel or the like. Otherwise I suppose a script could be used...
But it would be very easy codewise to implement the timestamp into the log file, so we don't have to mess around like that.

The default setting is to sample and save points as fast as the ADC allows, hence the interval is not fixed but depends on the mode, range, etc. It is therefore impossible to calculate the time for each point using the default setting.

However it is true that if you change the settings and limit yourself to a slower sampling speed, i.e. not using the full potential of the meter, it does seem like the timing is consistent so that can assume a fixed number of seconds between each point. I tried it over 4 minutes using a stopwatch and I could not detect any drift or dropped points by eye at least. Hence I guess this is the recommended method for now.

In order to allow for faster sampling I guess you need the actual time in a column (seconds since start is probably easiest), as it would make analysis much easier without having to process the time manually every time. Also as a separate improvement I would remove the "mode" from being printed on every row, either print it once in the header or only print it when it changes (if you intend to include mode switching during logging in the future). This would save approx 10-30 % in space depending on the mode used.

I also noticed that the meter does not autorange during logging (it goes into manual ranging when starting the logging process). This is definitely a feature that I would like to see in future updates.

Edit:
More issues I noticed today:
  • The claimed "update rate" is 5 samples/s nominal, however my display only updates 1-2 times/s, hence the meter feels slow and unresponsive, is this an error in the manual or is the meter supposed to be faster?
  • When manually selecting the 10 A current range, the display tells you that you are in the 1000 A range. Perhaps there is no 10 indicator in the LCD and this is intended, if that is the case please update the manual.
  • There is a 1000 V range, however the manual specifies maximum 600 V for the input protection. Perhaps this is the same issue as above? Please update the manual.
  • There are no range indicators in the display for Frequency, Period, Capacitance. Perhaps indicators is lacking in the LCD? In that case I suggest to always show leading zeros in these modes when in a manual range. For example the 100 nF range, write 07.6 nF, instead of just 7.6 nF in order to indicate the amount of headroom available.
Additionally, all log files are dated 2006.09.02 (yyyy.mm.dd format used) @ 21:30:00. Yes, a timestamp is in the actual file, but that doesn't help things if you go searching through the files for one at a specific time. Timestamps for the actual sample should be trivial to do since there is a hardware RTC in the DMM. A solution some other logging packages takes is to either log the absolute time or even using a relative time in thousandths of a second. I've well enough versed in Excel to add fractional second timestamps if I have at least 1 second resolution added in, but when you are using the fastest ADC output, and given that there is no "end" timestamp in the log file, it is not possible to determine the duration of a logged session.
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #762 on: September 12, 2018, 11:29:30 am »
New bug, also logging related. Anyone with a freezer could verify this for me. Regardless of sample rate, negative Celsius temperature values are logged as 7.1-7.6 °C regardless of their value. Lost a couple days worth of logging as a result. This is on firmware 1.26
 

Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #763 on: September 12, 2018, 02:12:49 pm »
New bug, also logging related. Anyone with a freezer could verify this for me. Regardless of sample rate, negative Celsius temperature values are logged as 7.1-7.6 °C regardless of their value. Lost a couple days worth of logging as a result. This is on firmware 1.26
Just tried and no problem with 1.26
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #764 on: September 12, 2018, 06:30:25 pm »
Thanks for this check. I looked at the data again, applied a little formatting, and all data up until record 12120 is real. From 12121 on, it is a repetition of the previous 60 records. If I log data once per second, I'll hit this same bug at 202 minutes and 1 second, if the bug is with the counter. I'll be asleep by then so I'll have it log once every two seconds to see if it'll reproduce as such.

The original, but zipped, CSV file is attached and a trimmed Excel file are attached.
 

Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #765 on: September 13, 2018, 02:36:42 am »
The test done yesterday was for just a few minutes at 1 per second.  Previously, July 18th, in Fahrenheit, I had 23690 records at 10 second intervals with no problems with whatever version was the latest at the time.
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #766 on: September 13, 2018, 09:11:13 am »
Didn't happen after 19K records. Trying again to see if it is time-based so I'll report back in a few days.
 

Offline CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #767 on: September 15, 2018, 01:12:52 am »
Probably it is known by now , just in case , DC+AC is autoranging endlenssly if DC voltage is greater than 5V . I used just an adjustable power supply . Latest firmware .


In AC mode , last measured frequency on secondary display stay there for about 15sec , way too long , even with shorted leads ...  Could be very misleading if you measure some small voltage around 0.15Vac , at the threshold of frequency sensitivity  .
« Last Edit: September 15, 2018, 02:25:03 am by CDaniel »
 

Offline CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #768 on: September 21, 2018, 08:46:47 pm »
As other people mentioned , it is very susceptible to mains noise through probes , especially in resistance mode ... I wonder what can be done , maybe changing some switching resistors around HY3131 to increase the measuring current ? 

Also , when using LowZ voltage input , the heat dissipated inside by the 2 thermistors makes resistance mode to be inaccurate for many minutes ...
as nearby thermistors that are in measurement path are heating too ...
« Last Edit: September 21, 2018, 08:49:52 pm by CDaniel »
 

Offline Seppy

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Re: EEVblog 121GW Multimeter Issues
« Reply #769 on: September 24, 2018, 02:29:29 pm »
Probably it is known by now , just in case , DC+AC is autoranging endlenssly if DC voltage is greater than 5V . I used just an adjustable power supply . Latest firmware .


In AC mode , last measured frequency on secondary display stay there for about 15sec , way too long , even with shorted leads ...  Could be very misleading if you measure some small voltage around 0.15Vac , at the threshold of frequency sensitivity  .

This issue should be resolved in latest firmware 1.51.
 

Offline Seppy

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Re: EEVblog 121GW Multimeter Issues
« Reply #770 on: September 24, 2018, 02:30:19 pm »
Both date and time is on the first row in the file, then it says what interval is used. So it is not impossible, just somehwat cumbersome. Add another column, copy the time from the top row, then next row is the one above+(interval in seconds)*(1/86400). If using excel or the like. Otherwise I suppose a script could be used...
But it would be very easy codewise to implement the timestamp into the log file, so we don't have to mess around like that.

The default setting is to sample and save points as fast as the ADC allows, hence the interval is not fixed but depends on the mode, range, etc. It is therefore impossible to calculate the time for each point using the default setting.

However it is true that if you change the settings and limit yourself to a slower sampling speed, i.e. not using the full potential of the meter, it does seem like the timing is consistent so that can assume a fixed number of seconds between each point. I tried it over 4 minutes using a stopwatch and I could not detect any drift or dropped points by eye at least. Hence I guess this is the recommended method for now.

In order to allow for faster sampling I guess you need the actual time in a column (seconds since start is probably easiest), as it would make analysis much easier without having to process the time manually every time. Also as a separate improvement I would remove the "mode" from being printed on every row, either print it once in the header or only print it when it changes (if you intend to include mode switching during logging in the future). This would save approx 10-30 % in space depending on the mode used.

I also noticed that the meter does not autorange during logging (it goes into manual ranging when starting the logging process). This is definitely a feature that I would like to see in future updates.

Edit:
More issues I noticed today:
  • The claimed "update rate" is 5 samples/s nominal, however my display only updates 1-2 times/s, hence the meter feels slow and unresponsive, is this an error in the manual or is the meter supposed to be faster?
  • When manually selecting the 10 A current range, the display tells you that you are in the 1000 A range. Perhaps there is no 10 indicator in the LCD and this is intended, if that is the case please update the manual.
  • There is a 1000 V range, however the manual specifies maximum 600 V for the input protection. Perhaps this is the same issue as above? Please update the manual.
  • There are no range indicators in the display for Frequency, Period, Capacitance. Perhaps indicators is lacking in the LCD? In that case I suggest to always show leading zeros in these modes when in a manual range. For example the 100 nF range, write 07.6 nF, instead of just 7.6 nF in order to indicate the amount of headroom available.
Additionally, all log files are dated 2006.09.02 (yyyy.mm.dd format used) @ 21:30:00. Yes, a timestamp is in the actual file, but that doesn't help things if you go searching through the files for one at a specific time. Timestamps for the actual sample should be trivial to do since there is a hardware RTC in the DMM. A solution some other logging packages takes is to either log the absolute time or even using a relative time in thousandths of a second. I've well enough versed in Excel to add fractional second timestamps if I have at least 1 second resolution added in, but when you are using the fastest ADC output, and given that there is no "end" timestamp in the log file, it is not possible to determine the duration of a logged session.

The timestamps meta information issue should be resolved in the latest firmware.
 

Offline CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #771 on: September 25, 2018, 03:07:41 am »
Thx for update , is much better now  :D , the only big issue left that I can see is the resistance mode instability when mains noise is present .
https://streamable.com/e4kfa

If you really work with a multimeter is certain that you will touch the probes and  tips all the time . For now is picking the "hum" like a bad shielded audio amplifier  :P
I will investigate if the capacitor C21 27nF in the schematic is switched across input to form a low pass filter , as it should be when measuring a DC voltage ( resistance is just a DC voltage ) .
« Last Edit: September 25, 2018, 03:51:41 am by CDaniel »
 

Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #772 on: September 25, 2018, 03:19:04 am »
Slight regression in Ver 1.51     In AUTO DC, AUTO AC or AUTO DC+AC:

After hitting the range button the range button will no longer cycle back to AUTO.  You must hit the mode button to get back to AUTO xx, but it will be the next mode.
 
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #773 on: September 25, 2018, 03:21:49 am »
After hitting the range button the range button will no longer cycle back to AUTO.  You must hit the mode button to get back to AUTO xx, but it will be the next mode.

To get back to AUTO, shouldn't you press and hold the range button?
I'm not an EE--what am I doing here?
 
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Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #774 on: September 25, 2018, 03:28:50 am »
To get back to AUTO, shouldn't you press and hold the range button?

Thanks IanB,  that seems to work.  Need to add this to the manual.
 


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