Author Topic: EEVblog #832 - Keysight U1282A Multimeter Teardown  (Read 26279 times)

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Offline EEVblog

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EEVblog #832 - Keysight U1282A Multimeter Teardown
« on: December 21, 2015, 10:48:19 pm »
« Last Edit: December 21, 2015, 10:51:25 pm by EEVblog »
 

Offline kaadam

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #1 on: December 21, 2015, 11:14:40 pm »
"BD" may be stands for bead, so i suppose it will be a ferrite bead, although i don't know why it's necessary.
« Last Edit: December 21, 2015, 11:17:10 pm by kaadam »
 

Online Fungus

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #2 on: December 21, 2015, 11:21:32 pm »
I like the Anti-Batteriser sheilding under the battery compartment.


Heat shrunk thermistors? Because they turn to green dust when you zap them. I'm guessing the heatshrink is to hold them together.
« Last Edit: December 21, 2015, 11:26:53 pm by Fungus »
 

Offline ECEdesign

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #3 on: December 21, 2015, 11:39:53 pm »
What is the difference between autohold and trig hold? 
 

Offline EEVblog

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #4 on: December 21, 2015, 11:47:51 pm »
"BD" may be stands for bead, so i suppose it will be a ferrite bead, although i don't know why it's necessary.

Yes, I think it's a bead too.
Can't say I've ever seen one in this application.
Possibly a last minute addition to pass EMC compliance?
They do have a awful lot of shielding, even going right up the side of the already shielded ceramic resistor divider.
 

Online Fungus

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #5 on: December 21, 2015, 11:48:16 pm »
What is the difference between autohold and trig hold?

So long as it displays the number then it's the same, isn't it? The only difference is that it goes into memory as well.
 

Offline EEVblog

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #6 on: December 21, 2015, 11:49:47 pm »
What is the difference between autohold and trig hold?

Trigger hold allows you to log into memory, but it's not automatic, you have to push the button.

 

Offline EEVblog

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #7 on: December 21, 2015, 11:50:18 pm »
What is the difference between autohold and trig hold?
So long as it displays the number then it's the same, isn't it? The only difference is that it goes into memory as well.

In this case it is not the same as auto hold.
 

Online Fungus

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #8 on: December 21, 2015, 11:57:10 pm »
What is the difference between autohold and trig hold?

Trigger hold allows you to log into memory, but it's not automatic, you have to push the button.

Ew!
 

Offline hayatepilot

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #9 on: December 22, 2015, 12:17:53 am »
Just saw in the manual that this meter does indeed have a setup menu and Auto-Hold.
Setup is accessed by holding Shift while turning it on. There, one can activate the Auto-Hold function instead of Trig-Hold.

Greetings
 

Offline AlxDroidDev

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #10 on: December 22, 2015, 12:51:46 am »
The Agilent DMMs where a lot prettier.
"The nice thing about standards is that you have so many to choose from." (Andrew S. Tanenbaum)
 

Online blueskull

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #11 on: December 22, 2015, 01:03:05 am »
The inductor with silastic gunk is to prevent acoustic noise. They chose the wrong DC/DC converter that operate in burst mode or skipping mode, instead of PWM mode (or deliberately for low power consumption), so there will be hiccup noise falling into acoustic range at light load. A simple bulge will be simply gunk it up and damp any mechanical vibration in acoustic range.
 

Offline gslick

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #12 on: December 22, 2015, 01:31:04 am »
Did you get a U5404A Remote Switch Probe with your review unit?

http://www.keysight.com/en/pd-2615346-pn-U5404A/remote-switch-probe

The current promotion for the U1281A / U1282A includes the U5404A Remote Switch Probe for "free", normally listed at $60 separately.
 

Offline joeqsmith

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #13 on: December 22, 2015, 02:13:24 am »
GDTs are slow and if there is nothing else in there for a clamp, I wonder how that thing would handle a transient with a fast edge.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 
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Offline brutester

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #14 on: December 22, 2015, 07:47:43 am »
To get the 60000 count from a 50000 count chipset they must use more than one ADC. Luckily they have 3 sigma-delta ADC chips built into HY3131 .

They must use the data from the fast SD-ADC to get the base value and then use the slow SD-ADC to get a more-precise value by moving the FTN pin  up with a DAC or controllable voltage divider from the reference voltage.
 

Offline tru

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #15 on: December 22, 2015, 08:41:58 am »
To get the 60000 count from a 50000 count chipset they must use more than one ADC. Luckily they have 3 sigma-delta ADC chips built into HY3131 .

They must use the data from the fast SD-ADC to get the base value and then use the slow SD-ADC to get a more-precise value by moving the FTN pin  up with a DAC or controllable voltage divider from the reference voltage.
I understand count as referring to speed not precision, so 60000 count means something like 60000 readings per second.
 

Online Fungus

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #16 on: December 22, 2015, 09:24:57 am »
I understand count as referring to speed not precision, so 60000 count means something like 60000 readings per second.

Nope. It's the maximum value that can be displayed on screen. The reason there's so many cheap "2000" count meters is that the first digit only needs two LCD segments if it can only count to 1999.

(...and why would anybody want 60000 readings per second on a multimeter?)

 

Offline TheSteve

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #17 on: December 22, 2015, 09:36:06 am »
BD is a common reference designator for ferrite beads in radio equipment.
VE7FM
 

Offline mux

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #18 on: December 22, 2015, 10:37:42 am »
Thumbs down to those rubber sealing... things. They're probably well-engineered and soft enough, but the issue with these removable boots is that their sealing is 100% dependent on the user putting them back properly after removing, and it looks like you do have to remove them every time a fuse or battery needs to be swapped.

It's too easy to accidentally get an edge folded over or pinch the fingers, which will result in an almost guaranteed non-watertight seal.

This is why we use greased o-rings, people. They're not meant to be removed, so you have a guarantee that they stay put in the orientation and location you intended them to be.
 

Offline DutchGert

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #19 on: December 22, 2015, 10:43:04 am »
Dave, think u forgot the datasheet for the Multimeter IC :)

Nice teardown!
 

Online Fungus

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #20 on: December 22, 2015, 10:49:50 am »
Thumbs down to those rubber sealing... things. They're probably well-engineered and soft enough, but the issue with these removable boots is that their sealing is 100% dependent on the user putting them back properly after removing, and it looks like you do have to remove them every time a fuse or battery needs to be swapped.

It's too easy to accidentally get an edge folded over or pinch the fingers, which will result in an almost guaranteed non-watertight seal.

I wonder about the long term stability, too. Will that rubber last for many years? I hope they sell spares.

Mind you: If you need a waterproof multimeter then you can probably afford to replace them every ten years or so.
 

Offline NANDBlog

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #21 on: December 22, 2015, 11:10:16 am »
Anyone knows what is the reason for heatshrinking those resistors and PTCs?
BTW 500 dollars is a lot for a meter with these specs. I guess the only reason to buy it if you break meters every now and then due  to water and stuff. But who am I kidding? Are you really going to use it standing in water, hoping for your cat 4 rating? Seems very alien situation to me, the office  dweller.
 

Online Brumby

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #22 on: December 22, 2015, 11:20:37 am »
My guess would be in the case of failure involving physical damage, the heatshrink would limit the dispersal of shrapnel through the meter, possibly creating an alternate current path and shock risk.
 

Offline German_EE

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #23 on: December 22, 2015, 11:29:12 am »
Why is it on almost every multimeter I see there is either no AC current range or AC current mode is selected using a 'shift' function, yet capacitance measurement has it's own position on the knob? It's an industrial meter and in industry there is often a requirement to measure the current drawn in an AC circuit.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

Warren Buffett
 

Online Fungus

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Re: EEVblog #832 - Keysight U1282A Multimeter Teardown
« Reply #24 on: December 22, 2015, 11:29:24 am »
Anyone knows what is the reason for heatshrinking those resistors and PTCs?

joeqsmith managed to turn a few PTCs into green dust over in the "here kitty" thread.  I'm guessing the heatshrink is to stop them messing up the inside of the meter when you zap them too hard.

Although if you're regularly exploding your PTCs you might want to consider a whole new meter just in case, and wrapping them in heatshrink might hide any damage  :-//

On a side note: How fast do PTCs react? Surely they have to physically heat up and that takes a few milliseconds at least. Joe's PTC-destroying pulses are only a few microseconds long.

And MOVs, how fast are they? Presumably a lot faster than PTCs.
 


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