New Zoyi multimeter+oscilloscopes - ZT-70xS, up to 50MHz/250MSps (nov 2022)

[eljjc]

I agree, it would be something amazing!

[nikbry]

The 701, just never even made it to market I guess in favor of the 702, the 702 isn't significantly cheaper than the 703 anymore, and when the next model, my guess is in the sub 100MHz hits the market for a similar price, the 703 will be history too.

Might the 702 or 703 have it's firmware modded by some coding guru? Wish it was open-sourced. Seems the hardware is worthy, but it's the programming that could be improved in a few key areas. 

That would be sweet. Meanwhile we can continue betatesting for Zotek hoping they read this and fix things 

[xfint34]

What fuse rating do you all have on the mA plug?
Mine came with a 600mA fuse. Is that correct? Isn't it too high?

[xKertx]

What fuse rating do you all have on the mA plug?
Mine came with a 600mA fuse. Is that correct? Isn't it too high?

Mine has 250mA written on it (don't know what the actual fuse is).
That's odd. If you google the zt-703s and zoom in at the photos, there are atleast three versions, 200mA, 250mA and 600mA.
So, are they using whatever fuses they can find cheaply?

[nikbry]

What fuse rating do you all have on the mA plug?
Mine came with a 600mA fuse. Is that correct? Isn't it too high?

Mine says 250mA next to the plug, but don't know the rating of the actual fuse inside.

[xfint34]

What fuse rating do you all have on the mA plug?
Mine came with a 600mA fuse. Is that correct? Isn't it too high?

If you google the zt-703s and zoom in at the photos, there are atleast three versions, 200mA, 250mA and 600mA.

Oh I didn't even notice the label on the front is different in photos online. The Zoyi website shows photos of all three different labels.

Mine says 250mA on the front of the device. It has 600mA fuse inside. It's got a v2.2 PCB.

[Astur_TorQue]

2.0

600 mA 250V in my case

But this is an ANENG instead of zoyi

[apollo11fan]

My understanding of fusing is rather incomplete. Mostly recommendations are, follow manufacturer's recommendations, or that of the designer.
Well, there seems to be a good deal of variation in the fusing that has been supplied by the manufacturer, and to top that off, the manual (outdated) doesn't specify the fuses for replacement.

I was always of the understanding (mis-understanding?) that fusing existed to protect the circuitry in an electronics device. Further, that you'd want to use a fuse just slightly higher rated in current carrying capability than that consumed by the circuit it protects. And if one wished to provide some additional margin in that fusing, one could go to a rating as high as that which could be tolerated by the wiring, traces, and other components in the current flow-path.

If the device were to read mA current up to the spec of 250.00mA (from the outdated manual), then I could imagine the ideal fuse to use for the mA input path on the scope to be rated somewhere between 1.5x to 2.0x of this value, therefore between 370 to 500mA.
So I could see the manufacturer (or rebrander) utilizing a fuse of 600mA. I would imagine 200mA or 250mA to be too small.

Can someone provide the size / rating of the fuse that should be used in the circuit should it fail, and a source to acquire them?
My PCB is V2.2 and has a 250mA ceramic fuse that is 20mm long. I was thinking of replacing it with a 500mA rated fuse.
Perhaps the following (as an example):https://www.amazon.com/ZUPAYIPA-F0-5AL-Fast-Blow-0-5amp-Ceramic/dp/B07KZRR3GL/ref=sr_1_1?crid=SVXYPSC429GV&dib=eyJ2IjoiMSJ9.6vzKtaZjL9er9MqtA5o3gyBfOyZWQ22wWwdENLgskL1Hc6u5LKPXXUuEOk6xCvi8yTe44QZUXv-69vCTIcWFHFy6l_oVDFzmUHaQj9l89Kh_WXwFdTjRRgwl1LgeT-q2bNj38QeeZp6kdhplAR7JuRiuqZiomZboXPLww_4WQjO2n2tF4DxmO-4vGTdi4D36z-dKvMgeEvmUobCV66Rw2d3TKYIM4WAGgEN1dmiIbzi68-w798Jn0PVBmmm5_ur_3lyr1NcInvCrWjfC-UvwYcHfXofguqXTQvZb8UjIoZ4.CnWMkbGIyzco43HT6R9PxAj8rVGLU_lSpNcFX7I6mAY&dib_tag=se&keywords=Busmann%2Blow-current%2Bceramic%2Bfuses&qid=1725285390&s=industrial&sprefix=busmann%2Blow-current%2Bceramic%2Bfuses%2Cindustrial%2C84&sr=1-1&th=1

Or

https://www.amazon.com/Ceramic-HV510-600VAC-5x20mm-Multimeters/dp/B0BMWZMLF4/ref=sr_1_4?crid=3SE1WK2J9K2SB&dib=eyJ2IjoiMSJ9.8TcWDUFwbS8ofL-IB-a4igh2FHRnIzEZHG0ohdPuukEWaYUTB_uYaUAWkaYxiBo35UQcM13RSdUjRqvAmZTQdedRsaAKz_bq6l6dykaenaolWyr7xuF_VjrStKXxTYMCG_UjeRDt2lUJLkic3C6obx_hC6tIvSshZA30gkqYssjpa7tcQBYtfyLLX33TEWu7pzJNFNAosklzV_ErVQTv0ifzDnvgBsV1jdgbijj3sav4N2X3ZULlGN8B62VnpNZDkRx0bIRn6A3Cowtsohl9G7opGnprtMF3_Nn4MNrx9so.AuqZ3yOdMPQ7heMT4mxCuNjJBjVeI46mcaSH2DsqhsQ&dib_tag=se&keywords=500mA+20mm+ceramic&qid=1725286194&s=industrial&sprefix=500ma+20mm+ceramic%2Cindustrial%2C83&sr=1-4

[nikbry]

Are you sure you read the current rating of the fuse correctly? It's easy to confuse with the 250V.

In my case PCB 2.2, I have a 20mm ceramic fuse rated for 600mA, 250V. And the print next to the plug says 250mA.

[ArdWar]

When manufacturers do this kind of stuff with fusing, they usually either use I_F=I_max but with slow blow, or I_F≈2I_max but with fast blow.

[indman]

What fuse rating do you all have on the mA plug?
Mine came with a 600mA fuse. Is that correct? Isn't it too high?

This is wrong. There must be a 250mA fast-blow fuse - this is the upper current limit for this range, which is indicated in the technical specifications. It is unacceptable to install fuses with a higher trip current, you risk damaging the device!!! Chinese friends install the cheapest fuses and are not very concerned about this.

[nikbry]

What fuse rating do you all have on the mA plug?
Mine came with a 600mA fuse. Is that correct? Isn't it too high?

This is wrong. There must be a 250mA fast-blow fuse - this is the upper current limit for this range, which is indicated in the technical specifications. It is unacceptable to install fuses with a higher trip current, you risk damaging the device!!! Chinese friends install the cheapest fuses and are not very concerned about this.

How do you know a current >250mA will blow the device? Where did you get the specifications from?

[indman]

How do you know a current >250mA will blow the device? Where did you get the specifications from?

I say this because I have many years of experience using various multimeters. Do you have such experience?
The technical characteristics of the ZT-703S are indicated in its manual on the last pages.

[nikbry]

How do you know a current >250mA will blow the device? Where did you get the specifications from?

I say this because I have many years of experience using various multimeters. Do you have such experience?
The technical characteristics of the ZT-703S are indicated in its manual on the last pages.

Well, I have been owning and using multimeters, since the 1980s...so that should give me some experience, but you may be right, that doesn't mean I'm technically competent... lol...
Anyway I just checked a Fluke in my endless collection of multimeters and it has a 440mA fuse....So, not all multimeters are limited to 250mA in their low current plugs. I'm also not aware of any standard that specifies such a limitation.

However, I totally agree that anything above 250mA should probably be measured using the 10A plug.

p.s.: those specifications are for measuring ranges, but don't specify the fuse rating nor the current limit of the circuitry.

[indman]

p.s.: those specifications are for measuring ranges, but don't specify the fuse rating nor the current limit of the circuitry.

This is not indicated, but is implied by the number counts of readings on the multimeter(25000) and the OL readings if the current allowed for a given limit has exceeded its value.

[xfint34]

Dave has covered this already. (Of course! )



Looks like if your meter has a 600mA then better get a proper rated fuse of 250mA.

[nikbry]

Dave has covered this already. (Of course! )



Looks like if your meter has a 600mA then better get a proper rated fuse of 250mA.

Lovely, what a can of worms! I specially like the part at 29:30 where the document he's reading says "it's impossible for a fuse to fulfill both standards ratings"
Thanks for sharing.

[xKertx]

This is wrong. There must be a 250mA fast-blow fuse - this is the upper current limit for this range, which is indicated in the technical specifications. It is unacceptable to install fuses with a higher trip current, you risk damaging the device!!!

So, you are saying that if you exeed the 250mA range by 1mA it should blow the fuse?
That doesn't sound normal to me. There must be some margin.

[indman]

So, you are saying that if you exeed the 250mA range by 1mA it should blow the fuse?
That doesn't sound normal to me. There must be some margin.

No, you're wrong! 250mA is the rated current of the fuse. A 250mA fast fuse will blow at 1.5-2 times the rated current. At what current the Chinese 600mA fuse will blow we do not know?

[apollo11fan]

No, unless I'm mistaken, the demonstration (very non-intuitive to me but educational) is that the current rating of the fuse is generally the sustained current the fuse will tolerate flowing through it WITHOUT blowing. Further the demonstration shows that some fuses can tolerate 2x the current rating. And that there is quite a distribution in performance of one make of fuse, on top of, amongst / between manufacturers with the same ratings.

Yikes! I'm both better educated now, AND less sure of what to put in the meter.

I wonder if he repeated his experiment, but with an inductive load what would happen. 

I think I should probably re-think the use of a 2x fuse... 

What we don't know is the current carrying capability of the traces and electronics (ADC ?) performing the sampling on the input path.

[wasedadoc]

How do you know a current >250mA will blow the device? Where did you get the specifications from?

I say this because I have many years of experience using various multimeters. Do you have such experience?
The technical characteristics of the ZT-703S are indicated in its manual on the last pages.

Nothing there about the figures in the range column being warnings such as "do not exceed or damage will be caused".

(60 years and counting of using multimeters.)

[indman]

What we don't know is the current carrying capability of the traces and electronics (ADC ?) performing the sampling on the input path.

Let joesmith check it out if he's interested. I, for example, don't want to risk an appliance that I like for some reason!

Nothing there about the figures in the range column being warnings such as "do not exceed or damage will be caused".
(60 years and counting of using multimeters.)

Does the word MAX on the front of the device in front of the mA socket mean anything to you? 250V MAX 250mA MAX!!!
In your devices you can put any fuses and for any current, nobody forbids it.

[wasedadoc]

What we don't know is the current carrying capability of the traces and electronics (ADC ?) performing the sampling on the input path.

Let joesmith check it out if he's interested. I, for example, don't want to risk an appliance that I like for some reason!

Nothing there about the figures in the range column being warnings such as "do not exceed or damage will be caused".
(60 years and counting of using multimeters.)

Does the word MAX on the front of the device in front of the mA socket mean anything to you? 250V MAX 250mA MAX!!!
In your devices you can put any fuses and for any current, nobody forbids it.

Do you seriously believe that the design and manufacturing tolerances on this meter (or any other DMM) are so tight that the maker can confidently say it will be damaged or some other bad thing will happen if subjected to even 5% beyond the MAX on the front panel?

[indman]

Do you seriously believe that the design and manufacturing tolerances on this meter (or any other DMM) are so tight that the maker can confidently say it will be damaged or some other bad thing will happen if subjected to even 5% beyond the MAX on the front panel?

No, I'm not suggesting that. But usually Chinese multimeters are built on a single chip without any serious protection.
Have you never seen such cheap toys explode inside? The fuse remains intact, but all the measuring circuits are burned out! I've seen it several times.

[wasedadoc]

My interpretation of the 250mA MAX is simply this: If you want to measure more than 250mA, do not use this socket.  Quite probably the meter will come to no harm at 500mA or even more.  What is to be marked on the front panel?  If it is OK at 500mA should the marking say 500mA MAX?  But then customers will try to measure up to 500mA and complain that the reading is invalid.

250mA is the maximum that can be measured using that input. Not the maximum that can be tolerated.  And no I'm not suggesting that the MAX be completely ignored.