Handheld meter robustness testing

[EEVblog]

In the mean time, someone was asking about how Dave could justify the 121GW as a $200 class meter.   The meter has a lot of unique features.    Here is a sneak peek of the VA feature being used to measure the power dissipation of the 400mA ASTM fuse.  Don't tell Dave I posted this. 

There was an error in your system setup here.
The error you are seeing was because you are not taking into account the insertion of the 121GW (and hence the small burden voltage of the 121GW) into your measurement. Your UT181 is not measuring at the same ground node a the 121GW is.
So it's a system connection error, not a meter error.
The 121GW can display it's own burden voltage (unique feature), but not in power measurement mode. But if you added that burden voltage and added to the voltage on the UT181 you should find that the two reading should match.?
Or of course simply connect the UT181 ground to 121GW ground.
This is why it was spot on at the low voltage, and then got progressively more error as you increased the current.?

[joeqsmith]

In the mean time, someone was asking about how Dave could justify the 121GW as a $200 class meter.   The meter has a lot of unique features.    Here is a sneak peek of the VA feature being used to measure the power dissipation of the 400mA ASTM fuse.  Don't tell Dave I posted this. 

There was an error in your system setup here.
The error you are seeing was because you are not taking into account the insertion of the 121GW (and hence the small burden voltage of the 121GW) into your measurement. Your UT181 is not measuring at the same ground node a the 121GW is.
So it's a system connection error, not a meter error.
The 121GW can display it's own burden voltage (unique feature), but not in power measurement mode. But if you added that burden voltage and added to the voltage on the UT181 you should find that the two reading should match.?
Or of course simply connect the UT181 ground to 121GW ground.
This is why it was spot on at the low voltage, and then got progressively more error as you increased the current.?

Funny, what you are calling an error in my setup, I was calling an error in the calculations.  Thanks for jumping in as I did not want to answer oh2hyt because I knew they were correct.  I just assumed this was a missing firmware calc.   

I was expecting the meter to measure the power at the load and would include the burden voltage as part of that calculation which is why it is connected this way.  Yes, if I wanted to measure the power dissipated by the load plus the meter, you are both correct and the three meters read very close.   I had tested it up to around 50 Watts (5A 10V sort of range).   I have not looked at AC.   

So, to be clear this is really what the plan is?  Not to display load power by compensating for the burden? 

[EEVblog]

Funny, what you are calling an error in my setup, I was calling an error in the calculations.  Thanks for jumping in as I did not want to answer oh2hyt because I knew they were correct.  I just assumed this was a missing firmware calc.   

I was expecting the meter to measure the power at the load and would include the burden voltage as part of that calculation which is why it is connected this way.  Yes, if I wanted to measure the power dissipated by the load plus the meter, you are both correct and the three meters read very close.   I had tested it up to around 50 Watts (5A 10V sort of range).   I have not looked at AC.   

So, to be clear this is really what the plan is?  Not to display load power by compensating for the burden?

I don't recall when we discussed this way back, but IIRC it wasn't possible to measure the burden voltage in power measurement mode for some reason, hence there was no data to compensate.
You could of course guess and fudge in a number and do it that way, but is guessing better than not including it?
What if you actually want the entire power consumption? e.g. for PSU efficiency testing, which is a major use I envisaged for this function.
Ideally you'd want to select between the two modes.
I'll take another look at it though.
The second display can show the volts or amps BTW, just keep pressing SETUP to get to it, yes confusing, need to fix this in the firmware.
And IIRC the Gossen Energy doesn't compensate, but it's been a long time since I used it.

[oh2hyt]

The 121GW can display it's own burden voltage (unique feature), but not in power measurement mode.

Sounds really cool feature.

Should power measurement have setting to include or exclude power used by meter? Sometimes you want measure power coming from supply, sometimes power consumed by device under test. There is ofc problem of test leads and connections wasting some power that meter can't exclude from measurement.

[joeqsmith]

I don't recall when we discussed this way back, but IIRC it wasn't possible to measure the burden voltage in power measurement mode for some reason, hence there was no data to compensate.
You could of course guess and fudge in a number and do it that way, but is guessing better than not including it?
I'll take another look at it though.
The second display can show the volts or amps BTW, just keep pressing SETUP to get to it, yes confusing, need to fix this in the firmware.

That seems like a bit of a miss or maybe that's just my perception.  If I need to make a separate measurement and hand calculate, the feature becomes less useful.   Maybe most people are interested in wanting the total power rather than at the load.  Both would be my preference.     

I had no idea about being able to read the current/voltage.  Just tried it and seems to work.  Really, UI is not too bad.  Needs a little polish is all.   

Also,  I'm curious what your thoughts are on the 400mA ASTM fuses.  If you have some that are out of a different lot, I would be interested in knowing if their cold resistance changes a fair amount.   That 2 ohms I measured seems a bit high.   

[EEVblog]

I had no idea about being able to read the current/voltage.  Just tried it and seems to work.  Really, UI is not too bad.  Needs a little polish is all.   

The UI has had very little spit'n'polish added yet.

Also,  I'm curious what your thoughts are on the 400mA ASTM fuses.  If you have some that are out of a different lot, I would be interested in knowing if their cold resistance changes a fair amount.   That 2 ohms I measured seems a bit high.

I have many boxes of them, will need to do some measurements.

[EEVblog]

Also,  I'm curious what your thoughts are on the 400mA ASTM fuses.  If you have some that are out of a different lot, I would be interested in knowing if their cold resistance changes a fair amount.   That 2 ohms I measured seems a bit high.

I have many boxes of them, will need to do some measurements.

I had a 600mA version here and measured that at a smidge under 1ohm. Above the 0.75ohm typical datasheet value.

[Wytnucls]

The 121GW can display it's own burden voltage (unique feature), but not in power measurement mode.

Sounds really cool feature.

The Fluke 867B does something similar, displaying the value of the shunt for the mA and uA ranges. No power measurement though.

[EEVblog]

20 units from the same box:



Datasheet spec is 1.65. So seems they are specifying the lowest typical measured value, and it can be higher based on contact and wire tolerance etc. But not really lower.

[SeanB]

Betting the cold resistance relates in some way to the radial position of a spool of wire that supply the fuse elements before cutting. Looks like there is a slight stretch in the wire with it having some cyclic change in either width of slitting or thickness in the original sheet, and this is carried through to the order in which they were packed in the box with some faithfulness. No other way to get that cyclic curve in resistance with them coming out the box in order.

When using film that subtle cyclic change can be a real problem at times, if the tolerance is tight or just enough to get you out of the one end of the tolerance window.

[EEVblog]

Betting the cold resistance relates in some way to the radial position of a spool of wire that supply the fuse elements before cutting. Looks like there is a slight stretch in the wire with it having some cyclic change in either width of slitting or thickness in the original sheet, and this is carried through to the order in which they were packed in the box with some faithfulness. No other way to get that cyclic curve in resistance with them coming out the box in order.

Can't guarantee that I tested them in order, took out the first row of 10, then the second row. Some shuffling may have happened.
Interesting hypothesis, and something like that wouldn't surprise me.

I almost see two distinct value levels with some tolerance around each one. Wasn't really one smack in the middle.

[Fungus]

Anyone else watch bigclive's last video and think it was going to be the end of that CEM meter?

Love the serial number!

[joeqsmith]

Datasheet spec is 1.65. So seems they are specifying the lowest typical measured value, and it can be higher based on contact and wire tolerance etc. But not really lower.

That's interesting.  If I look at the 2014 document, they do indeed show 1.65 typical.  However, the document I show in the video from 2016 shows 1.5.   See attached. 

[EEVblog]

Datasheet spec is 1.65. So seems they are specifying the lowest typical measured value, and it can be higher based on contact and wire tolerance etc. But not really lower.

That's interesting.  If I look at the 2014 document, they do indeed show 1.65 typical.  However, the document I show in the video from 2016 shows 1.5.   See attached.

Interesting.
I've asked them to explain why our measurements are higher than the datasheet "typical".

[EEVblog]

Reply from ASTM:

Sorry for the mistake.
I checked our internal spec, the spec of HV620.0.4 had been 1.5-2.2Ohms since 2015, and we had submit to and approved by the DMI manufacturer by that time.
Since the HV620 series fuse sold to DMI manufacturer only, I believe the mistake caused by forgot to updated the public datasheet after approval by DMI manufacturer internally.
 
Anyway, the fuses we sold to you are correct and the electrical performance meet spec.
Here I attached the updated datasheet with correct resistance value.

[Crumble]

[...] I tend to look for the more obvious answers.   
[...]

Well, that seems to have been the proper thing to do. Once again I love it when a company returns proper info when asked about some strange behaviour/result. Credits to them!

[joeqsmith]

Reply from ASTM:

Sorry for the mistake.
I checked our internal spec, the spec of HV620.0.4 had been 1.5-2.2Ohms since 2015, and we had submit to and approved by the DMI manufacturer by that time.
Since the HV620 series fuse sold to DMI manufacturer only, I believe the mistake caused by forgot to updated the public datasheet after approval by DMI manufacturer internally.
 
Anyway, the fuses we sold to you are correct and the electrical performance meet spec.
Here I attached the updated datasheet with correct resistance value.

Thanks for checking into this. 

[bitseeker]

Is len = 0 the reason the spreadsheet shows the interval to be zero seconds?

[bitseeker]

Ah, I guess they have the wait at the beginning of the loop.

@EEVBlog: Dave, it'd be good to have the actual interval, instead of 0, output to the file when setting len = 0.

[joeqsmith]

@EEVBlog: Dave, it'd be good to have the actual interval, instead of 0, output to the file when setting len = 0.

I agree.  Being a pre-production unit and knowing they are working on the UI, they may have already changed it. 

[Fungus]

@EEVBlog: Dave, it'd be good to have the actual interval, instead of 0, output to the file when setting len = 0.

I agree.  Being a pre-production unit and knowing they are working on the UI, they may have already changed it.

And if not, it's a suggestion. 

[bitseeker]

Yep, figured I'd post it, just in case.

[bitseeker]

It also sounds like it may be dying before it can unload its buffer. Either way, something for the 121 team to check out. Good pre-release testing.

[bitseeker]

Thanks for the update, Joe. I agree it's too early for videos and probably best to just continue reporting the findings to Dave so they can take care of them.

[Fungus]

With the right firmware ... this meter looks like a winner!

Who needs a Fluke 87V?

(apart from people who want to get past building security guards)