With a budget of $400 - Rigol or Siglent scope?

[kcbrown]

Why is it okay for you to get accidentlay zapped and not students?

Because we got zapped alone at home out of stupidity+ignorance, not in a classroom with somebody there to guide us and tell us not to do whatever stupid thing we were doing.

Ahhhh and you think just because students are at school under the supervision of an teacher they are smarter than you at home.  See that's the problem we are teaching these kids to be smart, but that doesn't mean they still don't do dumb thinks.  (Notice I did not use the word stupid.)  They would remain stupid if they did not go to school.

I certainly agree with the sentiment that kids are far too shielded from the real world, to their detriment.  Your intentions here are commendable.  The problem is the approach.

In essence, what you're saying is that you want the kids to learn from their mistakes.  But what you really want is for them to learn, whether through their mistakes, through the mistakes of others, or through direct instruction.

But you also want to keep your job, keep your assets, and retain your freedom, all within an environment which is highly litigious and in which people apparently desire their kids to be overly sheltered.

This means that, if you need to set up an environment in which making mistakes is both possible and part of the learning process, you'll want to set it up such that there is no real possibility of actual injury arising from such mistakes.  This means limiting the voltage and available current in anything the students might play with.  You'll want both to be high enough to make the mistakes apparent and at least mildly unpleasant, but nothing more than that.

Of course, prior to even that exposure, you'd want to instruct them in safe handling practices, etc., and perhaps even show them some videos that illustrate the dangers of getting it wrong.   Which is to say, you give them the opportunity to learn from direct instruction first, then indirect experience (the videos) and then, only after that has been given, direct experience.


Exposing the students to experimentation with mains voltages and available currents is needless exposure to risk, both for them and for you.

[DougSpindler]

One more story.  Had a boss who was wearing safety glasses.  Somethign arced sending motlen metal in the air.  One small spec of molten metal hit him in the face buring him.  The trajectory of the meal was such that the path was beween the top of safety glasses and the skin of his forehead.  As I reacl it hit hin in the eye causign a minor burn.

Moral of the story - Never rely on safey equipment to protect you.

In other news: Smoking doesn't cause cancer. I know this because I had an uncle who smoked until he was 90.

What about the millions who did smoke and died very young from lung cancers, and pulmonary diseases?   You might be interested to know tobacco is fertilized with radio-active Polonium and radio-active lead.
https://www.reddit.com/r/askscience/comments/3jaitj/why_is_radioactive_fertilizer_used_on_tobacco/

A smokers lungs receive far more nuclear ionizing radiation from tobacco smoke than people at Fukushima or Chernobyl. 

https://www.youtube.com/watch?v=TRL7o2kPqw0&feature=youtu.be&t=9m55s






 

[IAmBack]

One more story.  Had a boss who was wearing safety glasses.  Somethign arced sending motlen metal in the air.  One small spec of molten metal hit him in the face buring him.  The trajectory of the meal was such that the path was beween the top of safety glasses and the skin of his forehead.  As I reacl it hit hin in the eye causign a minor burn.

Moral of the story - Never rely on safey equipment to protect you.

In other news: Smoking doesn't cause cancer. I know this because I had an uncle who smoked until he was 90.

What about the millions who did smoke and died very young from lung cancers, and pulmonary diseases?   You might be interested to know tobacco is fertilized with radio-active Polonium and radio-active lead.
https://www.reddit.com/r/askscience/comments/3jaitj/why_is_radioactive_fertilizer_used_on_tobacco/

A smokers lungs receive far more nuclear ionizing radiation from tobacco smoke than people at Fukushima or Chernobyl. 

https://www.youtube.com/watch?v=TRL7o2kPqw0&feature=youtu.be&t=9m55s

Funny thing, I've read somewhere that tobacco industry is the first victim of nuclear (weapon) industry (and tests)...

[DougSpindler]

One more story.  Had a boss who was wearing safety glasses.  Somethign arced sending motlen metal in the air.  One small spec of molten metal hit him in the face buring him.  The trajectory of the meal was such that the path was beween the top of safety glasses and the skin of his forehead.  As I reacl it hit hin in the eye causign a minor burn.

Moral of the story - Never rely on safey equipment to protect you.

In other news: Smoking doesn't cause cancer. I know this because I had an uncle who smoked until he was 90.

What about the millions who did smoke and died very young from lung cancers, and pulmonary diseases?   You might be interested to know tobacco is fertilized with radio-active Polonium and radio-active lead.
https://www.reddit.com/r/askscience/comments/3jaitj/why_is_radioactive_fertilizer_used_on_tobacco/

A smokers lungs receive far more nuclear ionizing radiation from tobacco smoke than people at Fukushima or Chernobyl. 

https://www.youtube.com/watch?v=TRL7o2kPqw0&feature=youtu.be&t=9m55s

Funny thing, I've read somewhere that tobacco industry is the first victim of nuclear (weapon) industry (and tests)...

I don't think so.....  But if you have additional information I would like to consider it.

[donkey77]

Have you killed off any of the students yet? Oh, and how's the scope going?

[DougSpindler]

Have you killed off any of the students yet? Oh, and how's the scope going?

Thanks for asking.  Class is going really well.  I've been trying to zap a student here and there but so far no success.  Nest week I'll be talking about relays and solenoids so I'm increasing my odds someone will get zapped.

I'd like to say this again.  I really want to thank Dave for his videos and everyone here in the forums who helped me in deciding what scope to buy.  I am very pleased with the Rigol DS1054Z.  My only gripe is the text is a bit small for my eyes.  But I think that would be the case with all of the scopes.

 

[Gandalf_Sr]

Doug,

1. Buying the DS1054Z for the class - great idea.
2. Suggesting your students use the scope to probe 115V from an outlet - terrible idea.

If you are teaching an electrical safety class then there is a lot of ground to cover, lethal voltages, arc flash, grounding, etc. and I don't think you have time to do all that.  The best reason of all not to let them do that is that, if one of your students managed to kill themselves (a definite possibility IMHO), your ass would be in the fryer and you could lose everything - house, 401k, etc.

So now you're thinking that I'm a do-it-by-the-rules boring old git eh?  Try this, if you want to probe high voltages with your scope, cut the ground pin off your mains lead; now the ground on your scope will be floating. You could then fasten the live side of the 115 V to the ground on your scope and there will be no explosion, no fried PCB, no smoke from the ventilation holes    It works because the SMPS bricks are (almost always) isolated so there's no connection from input to output - you can prove this to yourself with an ohms meter.

I do this all the time but I have a note on the front of my scopes reminding me that they're not grounded.

[DougSpindler]

Doug,

1. Buying the DS1054Z for the class - great idea.
2. Suggesting your students use the scope to probe 115V from an outlet - terrible idea.

If you are teaching an electrical safety class then there is a lot of ground to cover, lethal voltages, arc flash, grounding, etc. and I don't think you have time to do all that.  The best reason of all not to let them do that is that, if one of your students managed to kill themselves (a definite possibility IMHO), your ass would be in the fryer and you could lose everything - house, 401k, etc.

So now you're thinking that I'm a do-it-by-the-rules boring old git eh?  Try this, if you want to probe high voltages with your scope, cut the ground pin off your mains lead; now the ground on your scope will be floating. You could then fasten the live side of the 115 V to the ground on your scope and there will be no explosion, no fried PCB, no smoke from the ventilation holes    It works because the SMPS bricks are (almost always) isolated so there's no connection from input to output - you can prove this to yourself with an ohms meter.

I do this all the time but I have a note on the front of my scopes reminding me that they're not grounded.

I am a college professor who teaches computer networking, server administration, virtualization security and digital forensic investigations. .  All of the classes I teach are advanced level classes.

This semester I was asked to teach a college level class to high school students.  (I actually have an 8th grader.). These kids are smart and are eager to learn.  The class is an introduction to computers class and is suppose to teach them  how to solve “business” problems with computers.

I am taking the liberty since the course does not specifying what type of computer or programming language is to be taught in the class to use Arduino.  Right now I have the studnets going through the standard labs.  The business problem they are going to solve is to build a replica of an arcade game and learn how to hack it.  (Actually the real arcade game is “rigged” so players who win only actually win 1 in 30 plays.  The business problem I’m teaching them is games of skill may not....  They are rigged.

So why the scope?  It’s a real stretch for what I’m teaching.  But these kids are smart and I am teaching them networking and computer protocols.  I’ve already taught them how to use a multimeter (HarborFreight) to measure DC voltages and currents to determine the DC voltage and current of one mini-Christmas light from a string of 100 which is spec’d at 120 VAC,  We actually found the bulbs could be run at 220vac.

Since our college doen’t have the budget for every student to blow a channel in a scope I’m the only one that will be using it.  I did watch Dave’s video on scope gnd fully understand what he’s talking about.  The Arduino when connected with USB to a computer I’m sure are earth grounded.  Something I’m always thinking about.

I want to use the scope to show students the scope show voltages a multimeter can’t display.  And then I would like to show them how to use a scope to “see” a protocol and to my +1 the Rigol has a decoder for the protocols Arduino uses.  It would be really neat if it had the ability to decode an Ethernet frame.  (But for that I have Wireshark.)

My goal is to show these kids how hackers can hack ther Arduino projects by converts injecting traffic on the network buss.  One of the projects I think I might have them make with the Arduinos because we have the IR module is the TV-B-Gone.  Push a button and the Arduino sends out all TV off IR codes.  (Nice little hacking project.)

Will the kids be touching the mains?  No, but them I’m not watching them 24 hours a day.  Will I teach them mains safety?  Yup.

Will I be attaching the scope to the mains?  I was thinking about it.  But in my “junk” box I remember I have a doorbell transformer.  120 VAC to 24 VAC.  Perfect for displaying a sine wave.  Transformer not only steps downl, but isolates.  Thank you some one in the forums who suggested that.

Quick question on the scope.  I seem to remember being taught that scope can display current over time.  With the Rigol scope I have can I display current?  (Or am I mistaken?)

Thanks.
 

 



 

 

[Fungus]

Quick question on the scope.  I seem to remember being taught that scope can display current over time.  With the Rigol scope I have can I display current?  (Or am I mistaken?)

The 'scope can't measure current directly, only voltage.

You can see current if you pass it through (eg.) a 1 Ohm resistor then measure the voltage across the resistor.

(aka a "current shunt")

[DougSpindler]

Quick question on the scope.  I seem to remember being taught that scope can display current over time.  With the Rigol scope I have can I display current?  (Or am I mistaken?)

The 'scope can't measure current directly, only voltage.

You can see current if you pass it through (eg.) a 1 Ohm resistor then measure the voltage across the resistor.

(aka a "current shunt")

Is a special probe needed?  For AC you could use an inductive coil.  But for DC?

[Fungus]

Is a special probe needed?

No, it's just Ohm's law.

[DougSpindler]

Is a special probe needed?

No, it's just Ohm's law.

Underrdtood.  Somthing I'm going to need to researh if I ever need to do it.

[Fungus]

Is a special probe needed?

No, it's just Ohm's law.

Underrdtood.  Somthing I'm going to need to researh if I ever need to do it.

You need to research Ohm's law?

[ebastler]

Try this, if you want to probe high voltages with your scope, cut the ground pin off your mains lead; now the ground on your scope will be floating. You could then fasten the live side of the 115 V to the ground on your scope and there will be no explosion, no fried PCB, no smoke from the ventilation holes

And all those exposed ground shields on the scope's BNC connectors, and your probes' ground clips which are dangling around, would be at what potential exactly?

 

[Gandalf_Sr]

Try this, if you want to probe high voltages with your scope, cut the ground pin off your mains lead; now the ground on your scope will be floating. You could then fasten the live side of the 115 V to the ground on your scope and there will be no explosion, no fried PCB, no smoke from the ventilation holes

And all those exposed ground shields on the scope's BNC connectors, and your probes' ground clips which are dangling around, would be at what potential exactly?

 

I didn't say that you couldn't kill yourself, I said you wouldn't let the magic smoke out of your scope.  Pay attention.

[ebastler]

I didn't say that you couldn't kill yourself, I said you wouldn't let the magic smoke out of your scope.  Pay attention.

As it happens, a large part of this thread is about how to avoid killing yourself, and even more importantly, avoid killing your students. And your post was giving advice on that matter, it appears.

And to make sure everybody realizes how cool you are, you had to point out this dare-devil approach you are taking to scope measurements. I am pretty sure you are not a teenager, but this behavior is worthy of one. Or maybe, if they ever produce a "Jackass" episode for nerds...

[DougSpindler]

I didn't say that you couldn't kill yourself, I said you wouldn't let the magic smoke out of your scope.  Pay attention.

As it happens, a large part of this thread is about how to avoid killing yourself, and even more importantly, avoid killing your students. And your post was giving advice on that matter, it appears.

And to make sure everybody realizes how cool you are, you had to point out this dare-devil approach you are taking to scope measurements. I am pretty sure you are not a teenager, but this behavior is worthy of one. Or maybe, if they ever produce a "Jackass" episode for nerds...

You folks keep saying I or one of my studnets is going to get killed.  Yet no one can site even one case where a student school was killed in an electronics class.  Or for that matter even seriously injured.

[Gandalf_Sr]

I didn't say that you couldn't kill yourself, I said you wouldn't let the magic smoke out of your scope.  Pay attention.

As it happens, a large part of this thread is about how to avoid killing yourself, and even more importantly, avoid killing your students. And your post was giving advice on that matter, it appears.

And to make sure everybody realizes how cool you are, you had to point out this dare-devil approach you are taking to scope measurements. I am pretty sure you are not a teenager, but this behavior is worthy of one. Or maybe, if they ever produce a "Jackass" episode for nerds...

Thanks for those kind words oh flawless one. 

With the caveat that you have to know what you're doing, there are some occasions where having no earth on your scope power lead has advantages - as long as you're aware of the pitfalls.  I bet you I'm not the only EE that's ever cut the earth probe off a power leads for scope use.

[ebastler]

Thanks for those kind words oh flawless one. 

I love you too, my daredevil.

[ebastler]

You folks keep saying I or one of my studnets is going to get killed.  Yet no one can site even one case where a student school was killed in an electronics class.  Or for that matter even seriously injured.

That may be due to the fact that such classes are mostly led by teachers with a different approach than yours. 

Seriously: Yes, you have to be unfortunate to kill yourself with 115V. But what if you have a student in that class who has a pre-existing heart condition, probably without even being aware of it? Do you really want to take that risk -- morally, and looking at the impact it might have economically on the remainder of your life?

When doing a proper risk assessment, you multiply probability (very small here) with impact (fatal). I can't find a freely accessible copy of the risk matrix e.g. in IEC 61010, and don't have our copy handy -- maybe someone can help out with the details. But if you have identified a certain risk with a fatal outcome and want to argue that you can simply live with it, the tolerable probability according to that standard is awfully small; certainly less than one in a million, from memory.

When thinking about the probabiity aspect, consider the impact you will have on the way these kids will approach mains electricity for the rest of their life. "Hey, no need to search for an isolated screwdriver. Remember, Doug even showed us how he could quickly touch that life lead with his fingertip!"

The warnings from several different forum members are very much well-intended and heartfelt. Please don't read them as arrogant "I know about electrical safety and you don't" statements. These are serious concerns about a very unlikely, but fatal risk.

[Fungus]

When thinking about the probabiity aspect, consider the impact you will have on the way these kids will approach mains electricity for the rest of their life. "Hey, no need to search for an isolated screwdriver. Remember, Doug even showed us how he could quickly touch that life lead with his fingertip!"

(image should be viewed at full res. to truly appreciate it  )

[DougSpindler]

I'm not saying 120 or 240 can't kill.  I'm just asking if in a classroom environment if it ever has?  Football yes, baseball yes, basketball yes and even auto accidents on school grounds yes.  But an electrocution death in an electronics class?  Don't think so.  I'm more concerned about my students being shot while in the classroom than getting serious hurt or dying from being electrocuted.

[Fungus]

I'm not saying 120 or 240 can't kill.  I'm just asking if in a classroom environment if it ever has?  Football yes, baseball yes, basketball yes and even auto accidents on school grounds yes.  But an electrocution death in an electronics class?  Don't think so.  I'm more concerned about my students being shot while in the classroom than getting serious hurt or dying from being electrocuted.

There was a first football death, a first baseball death, etc. I'm sure the coach wasn't expecting it.

It's also about attitude. Electricity should always be treated with respect, safe practices followed. I don't see how you can justify not doing it.

[DougSpindler]

I'm not saying 120 or 240 can't kill.  I'm just asking if in a classroom environment if it ever has?  Football yes, baseball yes, basketball yes and even auto accidents on school grounds yes.  But an electrocution death in an electronics class?  Don't think so.  I'm more concerned about my students being shot while in the classroom than getting serious hurt or dying from being electrocuted.

There was a first football death, a first baseball death, etc. I'm sure the coach wasn't expecting it.

It's also about attitude. Electricity should always be treated with respect, safe practices followed. I don't see how you can justify not doing it.

When did I ever say I'm not treating electricy with respect or not teaching my studnets electricy safety.  You folks are all saying a kid getting zpped with 120 is going to kill them.  I'm just asking for one exapmle of were it has bapped.

I stated previoully when I was in school, and I'm sure many people in the fourms have been zapped.  It's all just part of learning.  Yes we know what we are doing but accidents do occur sometimes.  Even Dave said he had a multimeter blow-up in his hand.  Is he dead, did he get seriouly hurrt or burned.....  Nope. 

Yes treat electricty with respecct, but no need to scare people about it either?

[Dubbie]

According to this article: http://www.ecmweb.com/content/case-120v-electrocution-mystery

In 1999, 278 workers died from electrocution.
1/3 were high voltage incidents, the remaining were 120V

If you want to contribute to the next generation of statistics, go ahead. I will judge you as a fool though.

The reason there are no readily available examples of students being electrocuted is that there are very few educators moronic enough to expose their students to unnecessary risks.