Author Topic: EEVBlog 121GW Discussion thread  (Read 247215 times)

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Offline 1anX

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Re: EEVBlog 121GW Discussion thread
« Reply #1625 on: November 07, 2019, 12:22:06 am »
Joe Smith has got a youtube vid up with 2 new meters he just bought from the EEVBlog shop being put through their paces.

 


 
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Offline CDaniel

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Re: EEVBlog 121GW Discussion thread
« Reply #1626 on: November 08, 2019, 08:32:16 pm »
The resistance settling time is definitly not caused by debris  ;D , its the firmware . Every firmware is somewhat different . Of course this is just a part of the problem ...
Those 2 meters are very bad refusing to measure 150pF and 1nF showing less ... at least mine is just drifting about 50pF as we discused some time ago . Maybe this a hardware issue after all , not firmware  :-//
 

Online chronos42

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Re: EEVBlog 121GW Discussion thread
« Reply #1627 on: November 08, 2019, 09:13:19 pm »
I wrote this before several month:

"A 220pF NP0 ceramic capacitor is shown as 0.160nF at the first time, after switching off and on again as 0.180nF, after another power cycling as 0.200nF... The more often I switch the meter off and on, the closer the reading comes to the actual value. Also if I first use a small capacity, then a bigger one (e.g. several hundred nF) and then again the small capacity, the 121GW every time shows a different reading. I am not able to get a steady reading of small capacities with the 121GW."
This is one of the most weird issue I have ever seen with a multimeter. The fact that Joe's prototype seems not affected from this issue shows that this probably can't be fixed with a firmware update and is hardware related.
« Last Edit: November 08, 2019, 10:37:13 pm by chronos42 »
 

Offline CDaniel

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Re: EEVBlog 121GW Discussion thread
« Reply #1628 on: November 08, 2019, 09:56:47 pm »
The prototipe is affected too , Joe confirmed later .

My meter is behaving like yours , but if you leave it on you should also see the value drifting slowly .
« Last Edit: November 12, 2019, 08:05:17 am by CDaniel »
 

Offline 1anX

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Re: EEVBlog 121GW Discussion thread
« Reply #1629 on: November 08, 2019, 10:28:06 pm »
I think Joe will reveal the real issues with this meter once and for all. He has planned a number of vids and will be running one on firmware version differences. Facts and data are always appreciated along with his unbiased assessment.
Might put an end to the fanboy and troll comments this meter seems to attract?
 

Offline joeqsmith

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Re: EEVBlog 121GW Discussion thread
« Reply #1630 on: November 09, 2019, 07:50:35 pm »
I think Joe will reveal the real issues with this meter once and for all. He has planned a number of vids and will be running one on firmware version differences. Facts and data are always appreciated along with his unbiased assessment.
Might put an end to the fanboy and troll comments this meter seems to attract?

That's a tall order!!   :-DD :-DD 

I wouldn't read too much into the unboxing video beyond that it does appear that the mechanical stack up between the prototype and production meters appears the same (except for the added preload caused by the shim).   Not being able to read the 150pF was a bit of a surprise but I am sure I could add enough capacitance to the fixture to get the meter to read something, then null it out and try again.  It's not like we have not seen this with other meters but I wouldn't have expected the 121 to be this far out.   

I don't recall the prototype ever having problems reading a 1M resistor.   Actually, I don't think I have seen ANY meter exhibiting a problem like this.   After cycling the switch a few times, the readings continued to get tighter and I never saw the meter hunt like that again.    It can be difficult to track down problems like this that are not reproducible. 

Obviously the settling time has been a hot topic.  I'm sure a few of you remember me posting a fair amount of data on the firmware changes to the filters which I expect was an attempt to get the meter to settle faster.  I removed most of that data to help clean up the "issues" area.   Personally, I will take slow, accurate measurements any day over fast inaccurate ones.   While I had installed 1.57 in the prototype, I don't appear to have any notes about testing it.  I suspect the upgrade was part of sorting out the BLE / LabView interface.   

My plan is to dedicate one full segment just to the firmware.   I plan to repeat my previous noise testing on the production meter which will include all the same firmware plus the latest versions.   For now I will stay focused on the hardware differences between the current production meters and the prototype. 
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 
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Offline bicycleguy

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Re: EEVBlog 121GW Discussion thread
« Reply #1631 on: November 10, 2019, 02:21:30 am »
Joe
The rotary switch contact holder has a 3 split shaft with little tangs that grab the back of the PCB.  The height of these tabs minus the PCB thickness was probably what determined the compression of the contacts in the original design.  I think the idea of the shim was to provide more compression without having to remold the plastic contact holder.  You didn't measure the height of the tabs, but since the shim is still present one can conclude that the new meters are same as old except with shim pre-installed.

The shim is not necessarily a bad idea, although a tolerance analysis of the resulting stack-up would surely prove otherwise, but maybe proper height tabs caused too much friction and subsequent debris or since the contact load is in a straight line perhaps the assembly would cock off axis which the shim would prevent.

« Last Edit: November 10, 2019, 02:23:57 am by bicycleguy »
 

Offline joeqsmith

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Re: EEVBlog 121GW Discussion thread
« Reply #1632 on: November 10, 2019, 03:08:27 am »
Joe
The rotary switch contact holder has a 3 split shaft with little tangs that grab the back of the PCB.  The height of these tabs minus the PCB thickness was probably what determined the compression of the contacts in the original design. 

I agree and stated that in the video. 

I think the idea of the shim was to provide more compression without having to remold the plastic contact holder.

Per Dave, they want to use a thicker PCB.   Personally, I don't think they have a clear understanding of the root problem.  The original prototype had some major wear problems so when they added a shim after the release, I wasn't all that surprised to hear they were still fighting a mechanical problem.

You didn't measure the height of the tabs, but since the shim is still present one can conclude that the new meters ae same as old except with shim pre-installed.

I measure the PCB thickness and the height of the contact holder to the bottom of the PCB.  I also measured the resting height of the contacts dimple to the bottom of the contact holder.  None of these have changed.   From a mechanical standpoint in regards to the switch, the contacts are now plated, the contacts now use a single dimple rather than two and there is an addition of a shim. 

The shim is not necessarily a bad idea, although a tolerance analysis of the resulting stack-up would surely prove otherwise, but maybe proper height tabs caused too much friction and subsequent debris or since the contact load is in a straight line perhaps the assembly would cock off axis which the shim would prevent.

On most meters I have looked at where they use a hole in the PCB as part of a bearing surface, they have it plated.  In the case of the prototype without the shim, the debris was not from this area but from the contacts and pads.   Until I run it, it's just a guess on how it will hold up to the 50,000 cycle test.   I understand what you are saying about it going off axis.  The center of the plastic contact holder is locked in place by the hex shaft.  Of course that could go off axis as well.     

As far as the shim idea, having looked at the prototype and seeing the wear first hand, I have been concerned about the switch design ever since.   After hearing they added this shim as a last minute fix did nothing to improve my confidence.   I openly stated that the reason I did not buy a production meter was in hope that they would address the problems that caused them to add the shim.   Per Dave, a thicker PCB.  I think the last time I saw an update on this was during one of the Amp Hour shows.  That's been several months ago.    I felt allowing them two years to sort out these problems was more than fair enough.   So, what happens when I try some simple tests to check out the meter?  As you saw, it appears as though the shimmed switch is still having problems. 

I wouldn't be at all surprised to hear about a new revision once I finish this series.
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 
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Offline CDaniel

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Re: EEVBlog 121GW Discussion thread
« Reply #1633 on: November 10, 2019, 11:25:53 am »
The materials and the optimal contact preasure for long life shouldn't be "rocket sience" if you are in the industry , but ... when we see how difficult it is for them to do a decent firmware the trust is not very high .
 

Offline joeqsmith

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Re: EEVBlog 121GW Discussion thread
« Reply #1634 on: November 10, 2019, 04:12:31 pm »
The materials and the optimal contact preasure for long life shouldn't be "rocket sience" if you are in the industry , but ... when we see how difficult it is for them to do a decent firmware the trust is not very high .

When we have looked at low cost meters like the ANENGs, we can see that designing a reliable switch is not in everyone's wheelhouse.  Even Keysight seems to have problems designing a reliable detent spring.  We know Brymen tests their products as part of the design process.  We have seen their test setups.   I suspect Fluke does something similar as their meters have done very well in this test as well. 

I also didn't think designing an electrically robust meter would be rocket science for those skilled in the art. 

Two topics that firmware is never going to address.  It's the main reason I am more interested in how the hardware has changed from the prototype to the production release. 
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline e0ne199

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Re: EEVBlog 121GW Discussion thread
« Reply #1635 on: November 11, 2019, 04:36:58 am »
I wrote this before several month:

"A 220pF NP0 ceramic capacitor is shown as 0.160nF at the first time, after switching off and on again as 0.180nF, after another power cycling as 0.200nF... The more often I switch the meter off and on, the closer the reading comes to the actual value. Also if I first use a small capacity, then a bigger one (e.g. several hundred nF) and then again the small capacity, the 121GW every time shows a different reading. I am not able to get a steady reading of small capacities with the 121GW."
This is one of the most weird issue I have ever seen with a multimeter. The fact that Joe's prototype seems not affected from this issue shows that this probably can't be fixed with a firmware update and is hardware related.

what type of batteries are you using?
 

Offline e0ne199

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Re: EEVBlog 121GW Discussion thread
« Reply #1636 on: November 11, 2019, 05:38:02 am »
I think Joe will reveal the real issues with this meter once and for all. He has planned a number of vids and will be running one on firmware version differences. Facts and data are always appreciated along with his unbiased assessment.
Might put an end to the fanboy and troll comments this meter seems to attract?

That's a tall order!!   :-DD :-DD 

I wouldn't read too much into the unboxing video beyond that it does appear that the mechanical stack up between the prototype and production meters appears the same (except for the added preload caused by the shim).   Not being able to read the 150pF was a bit of a surprise but I am sure I could add enough capacitance to the fixture to get the meter to read something, then null it out and try again.  It's not like we have not seen this with other meters but I wouldn't have expected the 121 to be this far out.   

I don't recall the prototype ever having problems reading a 1M resistor.   Actually, I don't think I have seen ANY meter exhibiting a problem like this.   After cycling the switch a few times, the readings continued to get tighter and I never saw the meter hunt like that again.    It can be difficult to track down problems like this that are not reproducible. 

Obviously the settling time has been a hot topic.  I'm sure a few of you remember me posting a fair amount of data on the firmware changes to the filters which I expect was an attempt to get the meter to settle faster.  I removed most of that data to help clean up the "issues" area.   Personally, I will take slow, accurate measurements any day over fast inaccurate ones.   While I had installed 1.57 in the prototype, I don't appear to have any notes about testing it.  I suspect the upgrade was part of sorting out the BLE / LabView interface.   

My plan is to dedicate one full segment just to the firmware.   I plan to repeat my previous noise testing on the production meter which will include all the same firmware plus the latest versions.   For now I will stay focused on the hardware differences between the current production meters and the prototype.
if it cannot measure pF then it will be useless for me... and if firmware update cannot fix this issue then looks like i need to sell my 121GW...seeing that even chinese cheap crap multimeters can measure pF range accurately really makes 121GW look like a stupid purchase
« Last Edit: November 11, 2019, 05:44:09 am by e0ne199 »
 

Offline beanflying

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Re: EEVBlog 121GW Discussion thread
« Reply #1637 on: November 11, 2019, 06:07:26 am »

if it cannot measure pF then it will be useless for me... and if firmware update cannot fix this issue then looks like i need to sell my 121GW...seeing that even chinese cheap crap multimeters can measure pF range accurately really makes 121GW look like a stupid purchase

Not sure about the current firmware or if it is an issue but I ran a fairly broad range test against my HP/Yokagowa Capacitance Decade box a while ago https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg2051194/#msg2051194

No smoke no trolling bs from the peanut gallery just what I found.

Low end range is 10 nF 0.01 nF ±2.5%+5counts if you want lower or better accuracy then you may need something else.
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Offline tautech

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Re: EEVBlog 121GW Discussion thread
« Reply #1638 on: November 11, 2019, 06:36:07 am »
See a recent post from Joe and watch the vid linked for further info on low capacitance measurements:
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg2778872/#msg2778872
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Offline 1anX

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Re: EEVBlog 121GW Discussion thread
« Reply #1639 on: November 11, 2019, 09:45:34 pm »
It seems the two 121GW meters Joe's just purchased from the EEVBlog store are not the latest revision!
Looks like the meter has been revised and some people have them but not Joe Smith who is about to put the meters under a complete range of tests.
I imagine he is pretty pissed  :palm:

Maybe Dave can advise us all on what the current revision is for the meters and if he plans to sell a revised PCB to those who already have the meter?
A discounted replacement PCB for early adopters would be much appreciated! (Providing its actually an improvement of course).
 

Offline EEVblog

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Re: EEVBlog 121GW Discussion thread
« Reply #1640 on: November 11, 2019, 11:17:25 pm »
Maybe Dave can advise us all on what the current revision is for the meters and if he plans to sell a revised PCB to those who already have the meter?
A discounted replacement PCB for early adopters would be much appreciated! (Providing its actually an improvement of course).

No plans for replacement boards to be made available, there is no functional difference, it's just a normal process of refining the design over time, happens regularly to all meters. Existing customers are not missing out on anything.
 

Offline J-R

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Re: EEVBlog 121GW Discussion thread
« Reply #1641 on: November 11, 2019, 11:30:08 pm »
Random 68pF cap:
121GW - 68-70pF (drifted upward over a 10 second period)
Homebuilt cap meter - 66.2pF
Roman Black Kit- 71.10pF

If I let the 121GW sit overnight, it displays ~25pF at power on.  If I use REL it drifts around a bit, but shorting the leads instead for 10 seconds and retrying makes it spot on.

Bought my unit about a year ago, running v2.00 firmware.


The homebuilt unit was made by my grandfather about 35 years ago and can measure 0.1pf up to 9.99F within 1 second.  So naturally I use it 99% of the time with an occasional check on other meters for sanity.

More history, my grandfather worked for the Air Force and his primary job was checking test equipment.  I remember some of his stories about the National Bureau of Standards (of course now called NIST) and how the various test processes worked.  My primary take-away was for sure never trust a single piece of equipment...  Just to clarify, I don't mean any disrespect to the 121GW, it's just a good idea to verify measurements!
« Last Edit: November 12, 2019, 12:08:10 am by J-R »
 
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Offline 1anX

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Re: EEVBlog 121GW Discussion thread
« Reply #1642 on: November 12, 2019, 08:22:52 pm »
Maybe Dave can advise us all on what the current revision is for the meters and if he plans to sell a revised PCB to those who already have the meter?
A discounted replacement PCB for early adopters would be much appreciated! (Providing its actually an improvement of course).

No plans for replacement boards to be made available, there is no functional difference, it's just a normal process of refining the design over time, happens regularly to all meters. Existing customers are not missing out on anything.

Hey Dave it would be nice if you could provide an update on what hardware revisions the "most current" version of the 121GW has had installed.
It would also be appreciated to know what the revised hardware has been fitted to achieve in the meter's function or protection.

It seems the EEVBLog store is selling older versions of the 121GW meter as Joe Smith found with his latest purchase of 2 new meters from your store. Can you supply from your store the current version meter? Will you discount the old meters or continue to sell old revision meters at full price?

How about sending Joe Smith 2 current version meters so we can see the results of comprehensive and unbiased testing of the current 121GW meter!!!!!!!!!!!!!!!!!!!
« Last Edit: November 12, 2019, 08:35:29 pm by 1anX »
 

Offline Terry01

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Re: EEVBlog 121GW Discussion thread
« Reply #1643 on: November 13, 2019, 07:41:48 am »
I brought this up when I bought my 121 GW and was steam rolled by the same people moaning now that the meter was great and upgrades meant nothing and the meter I got was the same as the revised ones  so no different. In fact it wasn't new so it was no different yada yada yada....!

Too funny  ;D
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Offline joeqsmith

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Re: EEVBlog 121GW Discussion thread
« Reply #1644 on: November 13, 2019, 12:46:41 pm »
I brought this up when I bought my 121 GW and was steam rolled by the same people moaning now that the meter was great and upgrades meant nothing and the meter I got was the same as the revised ones  so no different. In fact it wasn't new so it was no different yada yada yada....!

Too funny  ;D

Link?
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline joeqsmith

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Re: EEVBlog 121GW Discussion thread
« Reply #1645 on: November 13, 2019, 01:10:19 pm »
Maybe Dave can advise us all on what the current revision is for the meters and if he plans to sell a revised PCB to those who already have the meter?
A discounted replacement PCB for early adopters would be much appreciated! (Providing its actually an improvement of course).

No plans for replacement boards to be made available, there is no functional difference, it's just a normal process of refining the design over time, happens regularly to all meters. Existing customers are not missing out on anything.

Hey Dave it would be nice if you could provide an update on what hardware revisions the "most current" version of the 121GW has had installed.
It would also be appreciated to know what the revised hardware has been fitted to achieve in the meter's function or protection.

It seems the EEVBLog store is selling older versions of the 121GW meter as Joe Smith found with his latest purchase of 2 new meters from your store. Can you supply from your store the current version meter? Will you discount the old meters or continue to sell old revision meters at full price?

How about sending Joe Smith 2 current version meters so we can see the results of comprehensive and unbiased testing of the current 121GW meter!!!!!!!!!!!!!!!!!!!

I assumed buying the meters from Dave's store of all places would yield the latest hardware.  If he had both new and old stock, I would have just paid the difference for the latest.   If Germany has been selling the new one for months prior to me placing an order, I wonder if this is part of the EU approval.  Maybe the revisions are tied to that.  If the changes make no difference, they are stupid for making them in the first place.  Your just pissing money away at that point.     

Someone had suggested I just cut my losses and sell the meters.  After cycling the switches the readings have improved but seeing that one brand new, out of the box unit hunt the way it did,  to be honest, I wouldn't give them away.   I have no confidence in them and I see them is more a novelty than anything.   CEM quality with an EEVBLOG name on it.  I don't know many people who want to play with firmware loads.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline daveyk

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Re: EEVBlog 121GW Discussion thread
« Reply #1646 on: November 13, 2019, 08:43:30 pm »
"Someone had suggested I just cut my losses and sell the meters.  After cycling the switches the readings have improved but seeing that one brand new, out of the box unit hunt the way it did,  to be honest, I wouldn't give them away.   I have no confidence in them and I see them is more a novelty than anything.   CEM quality with an EEVBLOG name on it.  I don't know many people who want to play with firmware loads."

Quite honestly I was expecting a super meter, better than anything I have ever used before.  The resistance function on the free harbor freight meters work better.  Putting the two leads together on the `121GE still takes 2-2.5 seconds to come up with a reading less than zero and then that reading fluctuates so much that it make the REL function irrelevant.  Readings voltages has been fine.  When I am trouble-shooting, I use my scope to read voltages and my DVM to read resistance and the 121GW, with 2.02 code is still not usable for resistance measurement.  Yes, you have the range switch, but I can not tell what range I am putting it in, nor when I cycled through all the ranges.

I think the 121GW is a cool piece of hardware, and it may be very accurate in numerous modes, but it is a very difficult device to use for trouble-shooting.  Perhaps my 121GW isn't good, but I wouldn't know how to tell.  I do need to purchase a new Fluke 87 or something for trouble-shooting.

I hope it doesn't end up in my storage closet with other useless test equipment such as that Siglent scope I bought last year.
 

Offline CDaniel

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Re: EEVBlog 121GW Discussion thread
« Reply #1647 on: November 13, 2019, 10:23:20 pm »
All the meters are like yours with slow resistance autorange . The 50ohm range  is not stable because they design it with very low measurement current and insanely high ADC gain .  This can't be fixed in firmware .
« Last Edit: November 13, 2019, 10:33:38 pm by CDaniel »
 

Offline exe

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Re: EEVBlog 121GW Discussion thread
« Reply #1648 on: November 14, 2019, 07:56:47 am »
Is it possible to modify that diode clamp so it doesn't disturb resistance measurements? I'm actually willing to sacrifice meter's survivability if it improves usability and doesn't degrade my safety.
 

Offline J-R

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Re: EEVBlog 121GW Discussion thread
« Reply #1649 on: November 14, 2019, 10:43:27 am »
Dug up some resistors to test with my 121GW using the UEI leads:
0.1 - 0.094 (two in series was 0.208)
2 - 1.918
10 - 9.985
27 - 27.743

Values from a sub-$50 meter:
0.10
2.01
10.3
28.5


Also revisited capacitance, with four 68pF caps in parallel (individually, they measure between approximately 60pF and 70pF, as mentioned previously)
121GW - 244pF
BM235 - 260pF (0.26nF)
Home built - 270pf
Roman Black - 284.18pF


The 121GW performed these measurements reasonably well.  Keep in the mind the published accuracy for this meter.

For accurately measuring small pF caps I believe I would primarily use the Roman Black unit as it is accurate to within 0.01pF and designed specifically for this.

 


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