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- เผยแพร่เมื่อ 16 ก.ค. 2024
- Everything you ever wanted to know about how Multimeter input protection works.
Using the Fluke 27 as a baseline example.
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I like how you've manage to keep the same content quality over +700 videos!
This was really informative without being too simplified or complicated!
I've been watching your videos since I started my studies. I've learned so much from watching your videos over 5 years, there's only so much you can learn at school and there's only so many cases you can get at work :)
This is one of the best EEVblog episodes. A lot of this stuff in the previousones, but now I can understand everything finally! Thanks for that!
you're videos are addicting Dave, I work from home and just have your stuff running all day, love the new stuff, and the old videos are great to re-review.
Great video one of my faves yet. I take it that one must also look at the I^2T rating of the fuse and make sure that it's guaranteed to pop first before the diode bridge goes up in flames?
Hi! Usually that's fast or ultrafast blowing fuse.
Dave, your white board stuff clears up so many doubts I have on things I'm not used to. Thanks for sorting MOVs out for me.
Thanks, Dave for making all of these videos on how stuff works. You always manage to explain these advanced circuits and functions in a way that a beginner like myself can understand.
Love your enthusiasm! Almost as if it's transmitted trough the screen, because every time I watch one of your videos my fingers start to itch for either creating something or tearing something apart!
This is one of the best channels on TH-cam.
Dave you are awesome!
Excellent, as usual! Your video's are the best!
I am also an E.E. & E. hobbyist and still gain knowledge every time I watch one of your videos! I just can't acquire Science/Electronic knowledge fast enough, but you help a lot. There is so much fun stuff out there.
Thank you very much!
Thank you, Dave! I was very keen to learn more about this exact subject! You are the best!
Hi Dave, just wanted to say this video looks great and very informative. Just subscribed and look forward to seeing more of your videos.
Really good one Dave! ... And reading the automated transcript is hillarious poetry...
8:16isolation slots in the typically between input jacks between components
28:20southern white physically have a barrier between the vote is jack
28:24and ground all the at current jackson might physically have
29:56dammit sucked westphal at a certain and say will get his elbow teaching put
30:00jacket
30:01ceremony gently jack is going to get through a three point five kind while
YESS! Excellent video Dave!
Beautiful Video Dave! Thank you.
Thumbs way up! Best video series I've seen. Thank you very much.
It's 100% gut busting humour every time it tries to interpret an Aussie accent!
I'll be sure to check them all out.
Thanks for this. I knew my meter was only good for CAT I (not the claimed CAT IV) but now I can see that despite the fuses, rectifier and PTCs, there's no MOVs or isolation, and fairly wimpy PCB tracks. Good to know exactly what's wrong.
Great video as always!
Great Video Dave
This was very informative and fun to watch! Thanks!
great video, thanks Dave!
5:06
Been there, done that.
Was measuring a 3F engine current (with a primitive switch per phase arrangement) and shunted 400V mains with the meter by mistake (NEVER TRY TO DO YOUR WORK TOO FAST!). Awful bang, lots of fear and a dead meter. Thankfully it didn't catch fire. And thankfully I didn't catch any amps.
Brilliant explanation!
That really deserved the thumbs up. Idol!
15:55 is where the voltage, resistance, capacitance measurement part starts.
Thankyou Dave, watched half of this Vid and had a fluke 789 diagnosed in minutes! (input MOV X2 faulty)..
Epic vid, these type videos are the best! :)
Awesome! More stuff like this (schematic walkthroughs for, well, anything)!
Great video, love it when you do vieeos like this
CTIMEPRODUCTIONS
It will certainly help out the overall safety of the meter as a whole, but if the meter originally came with a glass fuse in it, chances are it's a lower quality meter anyways. If the fuse goes on a cheap meter because you connected it across the mains, chances are the meter is going to be toast. Using an HRC fuse instead of a glass fuse won't prevent that, but it will prevent that fuse from throwing arc plasma and/or shrapnel around the inside of the meter case. That could mean the difference between a startled but unharmed meter user, and a crispy critter!
Still very useful even a decade later
That extra 1M tap measures the voltage drop.
Well, there is the recommended fuse of course. If you don't buy the "approved" one, then you are of course on your own and should consider stuff like that. But all quality brand HRC fuses should have a very similar rating in that respect.
A fellow engineer had borrowed my DMM to calibrate an transducer of 4-20ma. He left the leads plugged into the milliamp jacks, I used this same meter later without checking the lead configuration, across the mains of a 575VAC buss. ...Yeah B O O M !!! The meter exploded in my hands. This was a Greenlee meter, not the highest quality but a decent meter.
Good video, very well explained = very well understood!
Once I threw a 10A unfused range right across the mains... I kicked off two 16A breakers in series. Fun stuff.
3 times :s and a 180v motor while running.
I Thought I understood multimeters lol
Great job!, I enjoyed this video! 🙂
l have several pieces of junk that have served me well thank you very much and have never blown anything up but did like the video in your teardowns you point things out put do not always explain in detail why they are there as you did here
Superb!
Dave, you underestimate dramatically how addictive your videos are, or how addictive is knowledge for that matter. It's 0009 here, so there is some time :P
Good video
you're good Dave :D
thanks for the nice video ...
very very good video this one thumbs up
No, it goes through the mA shunt
Yes, provided you don't exceed their energy limit and destroy them. They are designed to reset.
My DMM got a combined V,Ohm, Hz,Capacitance, mA and µA jack. and it was 250 bucks! :P So there are some midrange DMMs that still got combined jacks. I'm not a HUGE fan of the combined jacks. But by now i'm used to it. So it's ok. The DMM is a APPA 82 btw. Very nice and solid DMM for the money.
that particular ADC can handle voltages up to ( 0.5~0.7V x 6 ) = 3~4.2V on the input, so it clamps at that level. If it couldn't (needn't) handle more than 2V, they would have put 3 diodes (bridge+1 extra).
Excellent video covering something I've wanted to better understand, which this video definitely did for me. Would the input protection circuit on a 'scope look pretty much the same as on a multimeter voltage input or are there other considerations involved?
If you want to measure current in the negative/grounded output wire from an isolated dc/dc converter, but by misstake puts the range switch to volt instead of current... The fluke will burn... My friend tried that on a 1 Amp, 100 kV dc/dc :-D
Very good discussion. I am wondering if MOVs have supplanted crow bars with SCRs as the fastest type of protection?
Dave Jones does multimeter input protection. AKA Unsafe at any voltage :D
On the mA range, at 440mA the voltage could be 2.2V at the input to the ADC. 2 diodes wouldn't be enough.
Hi Dave, interesting video, thank you.
A few weeks back I needed to come up with transient-proof voltage input stage, and what did I use for reference? Fluke 87 schematic of course from the service manual :P
I was referring to my own meter, 200mA scale. I'd have to measure it's impedance on mA, but if it's below 0.7V / 200mA = 3.5ohm, than it looks ok.
I've directed many people to Dave's videos who ask me about such things.
Thank you for teaching us this stuff! How is the ADC reading the voltage drop on the amps range? Is the drawing incomplete?
I have never blown a fuse. Check the meter and input jacks used before measuring.
*****
You haven't measured enough, or you are really, really careful :)
Hi,
Is there any way to upgrade input protection on UNI-T UT61E?
Maybe by upgrading some of components, or adding som extra?
If there is a way please guide me to it.
Thanks
How does the ohms range protection work agains external voltage? How can it measure low resistance values like 0.1ohm across this several kilo-ohm input circuit?
Great video Dave! Now I know that my crap Radio Shack multimeter doesn't have input protection or fuses. I guess that's what I get for $14.99.
Speaking of blowing the crap out of your meter, I remember I used to blow up electrolytic capacitors.
EEVblog , question for you. Can you build the circuit at 22.11 for the ptc and mov's etc in a seperate box with leads to go into your DMM that you can then plug your leads into externaly and still be protected so it is between your leads and the DMM ?. Retro fitting is ok I guess if you want extra protection and surety IF it would work.
How do you measure amps? Switch to mA range?
Please do Polyfuse tutorial. Thanks
Here we see the damage from high voltage/current on the Volts setting (so most fuses and diode bridges not in play). "EEVblog #84 - High Energy Multimeter Destruction" th-cam.com/video/M-FZP1U2dkM/w-d-xo.html
im curious about what will hapen if you stick it in mains at ohm range
Do they do anything different for Megger meters (megaohm meters)? I'm interested in measuring moisture in wood which is in the 1-20,000 megaohm range.
How does the meter measure ohms accurately if there is a 1k PTC and 3.5k wirewound resistor in series with the input?
Porque tengo problema con un multiters UN-T58C, no mide VAC en ninguna escala. Gracias
Hello
I want to ask, i have measured current by connect multimeter with wall outlet in parallel instead of series, so i replaced one fuse and still not working 😐😐
Wens 52 multimeter
Awesome video, I have a question , why not use 3.6v 2 zener diode inspite of using those 8 diode ?
A zener is not as fast.
The Zener diode will not clamp in time, and therefore it does not protect well.
Why in current protection circuit is there bridge + 4 diodes and not just 2 reverse zener diodes ?
How is the A range shunt voltage connected to the internal voltage meter? Your range switch has no position for the A range. If you want to measure few mikro amps, the current through the diode bridge will add error.
If a DMM has glass fuses will putting a HRC fuse in it work?
Muy bureno sus videos!!! una pregunta que proteccion tiene un multimetro al medir continuidad a un fusible presumiblemente quemado y con tension??? gracias y saludos
En principio, el modo de continuidad de un multímetro es el mismo que el de resistencia, pero con un distinto modo del ADC (velocidad en vez de precisión).
Aún así, si estás midiendo un fusible, en principio no hay ningún problema. Aunque el fusible esté conectado a 220v, no vas a medir ningun voltaje (= diferencial) grande. Sería igual que meter las dos sondas en el mismo conector de un enchufe, casi 0V. Ya esté quemado el fusible o no.
What about TVS diodes? How would they help/hinder input circuitry?
What happens if i conect probes between Amps input jack and Volts input jack ,and try to measure something on Amps scale?
I will damage the multimeter?
Did you forget to add the link to the manual?
Hi Dave, does a Mov act like a Surge Arrester ? (without reset functionality)
can i assume that a Mov is doing the opposite function of a fuse ?
great Video btw :)
You only have 370 vids to catch up on!
It's kind of scary some of the crazy unsafe stuff out there that sometimes even falsely labels itself as having some kind of rating, when in reality, it probably would blow up or start on fire just connected to an electrical outlet.
Hi! I'm little confused about this monster protection diode bridge with many diodes... Why they can't simply connect bidirection TVS , couple of power zeners or something like that? OK TVS might be not a very good idea for long time pulses but it looks like very cheap way to solve the same problem...
excelent, I don´t speak english but I understand everyting
When would one use MOVs instead of zeners?
So by that chart of cat ratings, is cat III better than cat 4? It said it handles 1000v working voltage and the peak impulse transient is 8000v (same as cat 4). Or am i missing something?
I am working on an HP E2378A DVM. It was dropped and now the Resistance measurements only indicate OL or 0.00 when the leads are shorted. All other measurements of resistance indicate 0.00 Inspecting the internals show a section of the PCB that has something labeled "PTC" The connections to the PCB are about 3/8" apart and there appears to be residue on the leads. Do you have any idea what the PTC is and a replacement part?
Thank you in advance for replying.
Why can't a zener diodes in back to back configuration be used instead of the diode bridge for the current protection. Is it because the diode bridges have a greater PIV(Peak Inverse Voltage) than the Zener Diodes?
Great Tutorial by the way !
Same Question asked here (10 questions above). But I will add to answers.
1. Obviously Zener is not as fast a signal-diode or even a rectfiier-diode.
2. More imporantly the knee is not as sharp as diode for the zener V-I characteristic.
So it leaks current very much before it reaches its breakdown voltage.
This affects uA range reading , since some uA from probe is not flowing thru shunt resistor.
Whereas for diode practically no current (or nA/pA) flows at V< 0.5V.
current and temperature (if meter has one)
Awesome! And just in time too: I need a new multimeter for current measurements... I'll be scanning eBay for those old yellow Flukes (; Also, could anyone suggest a cheap (or better yet DIY) inductor meter?
Nice, video, good to know there are techies out there, In a age of does not work, throw away (yeah change the fuse, get something for free, lol)
Where you've labelled mA on the whiteboard should say mA and A then?
El video esta bueno. que posibilidad de coclocar video con subtítulo en ESPAÑOL.( BARQUISIMETO - VENEZUELA)
Yeah, get some sleep, it'll be there tomorrow!
OK. What do we do,now, with our" captured" solar power...?
do MOVs reset themselves?
I've got a great cheap china made multimeter with "cat II" rating, 10A current range is unfused, all input jacks go through less than 10mm wide pcb (3 jacks in a row) and the pcb quality is horrible,
I might send it to you for teardown and some other stuff for review.
5:08 well, it caused a big bang all right lol i forgot to change the plus probe to the volts plug PUFFF
37:17 bang! it blows your damn hand off!! :D
Damn, i LOL with that one! :D
Dave, nothing to do with the vid (sorry), I've told to buy some EXPENSIVE period/freq counter from Standford Research, the 620 model. Can these succkers cost as much as 5K dollars ????. Its to fine adjust a fork xtal to get below below 4ppm. The only signal coming from the IC is 1s and 4s pulse, that's why plenty of digits are need. Woud you recommend me another way and more importan .... less expensive. This price IS MADDDD. Cheers.
I didn't understand the bridge explanation. If it's there to take some load off of the the resistor, why not just use another resistor instead of a bridge?
If u wrongly apply, Voltage directly to Current-jack, especially uA/mA current jack, it takes a few milliseconds or even few seconds for the fuse to blow, depending on the strength of voltage & resistor-shunt value. Two things can happen before that. The sensing electronics directly feels full voltage & can get damaged, Or/and the shunt resistor get damaged/smoked or vaporized. The diode bridge prevents this. It limits voltage across the shunt to (N*0.6V). Also to sense electronics inside.