Older style Multimeters v Newer ones

[Fungus]

Was any thought at all given to input protection, etc., in those old meters?

I always got the impression they were just bare circuitry and you were supposed to know what you were doing.

[BravoV]

Was any thought at all given to input protection, etc., in those old meters?

I always got the impression they were just bare circuitry and you were supposed to know what you were doing.

For example Simpson Series 7 has 2 (two) fuses in series, one is quick acting Bussman fuse, and also a varistor (MOV) parallel with the meter. Schematic and BOM at last page -> Simpson 260 Series 7 Manual (PDF)

[Neomys Sapiens]

As I indicated in the 'show your multimeters' thread, I tend to tailor my multimeters in use to the task at hand. There's some I like to use for circuits work and some that are suitable for systems&installations. Then of course it is a question of the secondary capabilities, like min/max etc. Basically, I like to have always an analogue meter and a DMM at hand. Often I go for a passive analogue one, as the lower impedance can come handy to avoid falling for spurious signals. That can range from a Soar pen DMM + the diminutive ICE when to my standard fit of the 'T&M-kit' of a Fluke87 and a Metravo 4H. My main toolcase holds a 78-III and a Metravo 2. My Unigor A43 is currently at my working place, as they had only digital meters and it is a instrument made for radio electronics and communications stuff. I could have taken the 6e, but this one being away more than short-term is akin to asking me if you could borrow my significant other!
And while the Metravo 'Gang of Fours' (4S, 4H, 4E) and my Unigors aren't exactly new, they are quite well protected electrically.
And I already told of the definite high-tech company, where veritable herds of the old, black! Siemens Multizet's are kept and used as secondary instruments in complex setups. They are class 1, completely passive and they won't die. When used with the necessary knowledge, any instrument can do valuable work as long as it is not derelict.

[Dwaine]

For DMM, CAT rating basically defined what is safe from unsafe for particular usage.  It doesn't mean the DMM is non-functional, but in the USA if a workplace injury can be traced to the use of a DMM without CAT rating or  improper use of a CAT rated device, the contractor can be held accountable by the Federal gov't.

As for using old equipment, reduced safety beyond CAT ratings vary quite a bit because components age at different rates, it roughly depends on how often its used, to usage that causes wear and tear [ heat generators, as well as high voltage and current] and to what environment its exposed too.  For example, a lot of metrology grade equipment remains useful despite its age, as there are few wear tear elements its exposed too, e.g. the HP3458A.

In the USA, 'useful life' determines the lifespan of most gear to an organization and hence a practical definition of lifespan, here as example:

https://georgewbush-whitehouse.archives.gov/omb/circulars/a076/a076sa3.html

Which differs from its real life as a useful tool:

http://www.businessdictionary.com/definition/useful-life.html


Of if you or your gov't are concerned about whether hazmats exists in your device, then the China RoHS EFUP labels act as guide to its life to the user:

As someone that has worked at Workplace Safety organization.  I want everyone to use the most modern and safety certified DMM. I 100% support Dave on his teardowns and completely regard a meter as utter garbage after 1 second of looking at the piss poor input protection and leads.  Once you see the impact of injuries on people lives.  Safety design, ratings and certifications are the only thing that matters.  Accuracy and resolution important?  No. Great display and black light important?   No. Cheap price with lots of functionality?  No.

You have to assume that any existing DMM will someday be hooked up to mains power at some point of time.

[cjs]

If you had to pay out that much today to replace a meter each time it got destroyed, I think you would think twice about what you was doing and take more care?

Nope. A lot of the people I meet wouldn't be taking any care of a multimeter at all because if I told them they need to spend $400 on a meter to get started in electronics they'd just go find another hobby.

So whenver you're giving advice like this, just ask yourself, what's the price point where you're going to tell someone interested in trying out Arduino or whatever that he shouldn't do so because he doesn't want to pony up the minimum amount of cash for the equipment you feel is necessary?

[kalel]

If you had to pay out that much today to replace a meter each time it got destroyed, I think you would think twice about what you was doing and take more care?

Nope. A lot of the people I meet wouldn't be taking any care of a multimeter at all because if I told them they need to spend $400 on a meter to get started in electronics they'd just go find another hobby.

So whenver you're giving advice like this, just ask yourself, what's the price point where you're going to tell someone interested in trying out Arduino or whatever that he shouldn't do so because he doesn't want to pony up the minimum amount of cash for the equipment you feel is necessary?

For example I would definitely not be doing anything at all if it was required to have a $400 multimeter. Thankfully, it's not. But the necessary equipment also depends on the project you're trying to make. So, only when you notice you need a function that only exists in an expensive piece of equipment - or the specific accuracy level only provided by such equipment - you have a need to at least think whether or not you could find a way to afford it.

[joeqsmith]

Was any thought at all given to input protection, etc., in those old meters?

I always got the impression they were just bare circuitry and you were supposed to know what you were doing.

For example Simpson Series 7 has 2 (two) fuses in series, one is quick acting Bussman fuse, and also a varistor (MOV) parallel with the meter. Schematic and BOM at last page -> Simpson 260 Series 7 Manual (PDF)

At a quick glance of the schematic, connect leads to the +10A and -10A inputs.  Apply high energy source....

One lead on the 50uA, switch range to 1mA.  Set function switch to DC.  Second lead to Positive.  Apply high energy source....

One lead on -10A, switch range to Rx10K.  Set function switch to FC+ and attach second lead to Positive.  Make sure battery B2 is installed.  Apply high energy source....

[Fungus]

The chances of a fused $15 multimeter (eg. the new AN8008) being directly responsible for serious injury in a CAT II environment are very small. Probably smaller than driving a car. If you're mostly working with Arduinos and stuff the risk from such a meter is negligible.

There's always people who want to try to eliminate all risk at any cost but they usually aren't spending their own money.

That said, if I see you working with mains electricity on a regular basis I'd try to convince you to get a $42 Fluke 101 instead of a $15 meter.

$400? That's a luxury meter, not an essential meter.

[Specmaster]

If you had to pay out that much today to replace a meter each time it got destroyed, I think you would think twice about what you was doing and take more care?

Nope. A lot of the people I meet wouldn't be taking any care of a multimeter at all because if I told them they need to spend $400 on a meter to get started in electronics they'd just go find another hobby.

So whenever you're giving advice like this, just ask yourself, what's the price point where you're going to tell someone interested in trying out Arduino or whatever that he shouldn't do so because he doesn't want to pony up the minimum amount of cash for the equipment you feel is necessary?

You need to read this in conjunction with post #23, to which I was referring. Would you not agree then that a Simpson meter is a class act? Class acts cost lots of money and would you really require an expensive piece of equipment just dabble with some Arduinos that are really cheap and do not pose any threats of likely high energy faults. Therefore you could get away comfortably with a cheap $25 meter or maybe less than that in reality.

I would love to own and drive a Bentley car, I'd also love to surround myself with the very latest and best in test gear, full of functions that I'd never need or use and of course by their very nature would be the safest on the market, except for one thing, I couldn't afford to pay for it all so I can't.

Dave has a blog on setting up a basic electronics lab for $350 and that includes meters and everything else required to get started, you wont find any high end or high safety rated devices there but with care will get anyone started in electronics and then they can replace with better items as they can afford to do so. I'm perfectly sure that Dave and these other people with these well equipped labs had start off with very basic items in the first instance?

[Elf]

As someone that has worked at Workplace Safety organization. [...] Safety design, ratings and certifications are the only thing that matters.  Accuracy and resolution important?  No. Great display and black light important?   No. Cheap price with lots of functionality?  No.

Well, that's a perspective. For a commercial electrician who rarely sees anything under 100 Vac or circuits smaller than 15 A, it's applicable.

For someone that works on digital logic where 5Vdc is considered a high voltage and sub-watt power is the norm, it is not applicable, and accuracy and resolution are much more important than safety. I'm not sure what an unsafe multimeter would look like at 3.3V; maybe one with sharp edges?

You have to assume that any existing DMM will someday be hooked up to mains power at some point of time.

Being safety focused is a laudable goal and I am not trying to discourage an active consideration of safety where electricity is concerned, but I think a lot of people go too far and make residential CAT II 120-240Vac out to be some sort of boogeyman. I think it is great that modern multimeters have all this built in protection, but in a non-commercial hobbyist setting, even a somewhat inexpensive multimeter is most likely the safest device in the room compared to all the cheap USB chargers, questionably "double insulated" DVD players, toaster ovens with "value engineered" cords, etc. Most consumer devices have little to no concept of input protection beyond a (usually non-HRC, in North America) fuse, and from design to assembly a lot of the decisions made are not exactly safety centric. According to the multimeter-universe rules people should be dying left and right.

Treated respectfully, residential mains isn't too bad; certainly not the monster people make it out to be. With AFCIs and "tamper resistant" outlets now being mandated in code, you even have to go through some effort to scorch things.

On the other hand, commercial electric work with CAT III sources and up is a completely different story. 480Vac arc flash is an incredible force, and I've seen the results in person. Not something to play around with. ElectroBOOM wouldn't be able to get away with what he does at 480V; if someone did that sort of thing at 480V or above I think about the best they could hope for would be to lose an arm. But is that really what we are talking about here? I can't see an entry level hobbyist buying their first multimeter and finding some 3 phase bus bar to go probe or trying to grappling hook an overhead power line.

I think we're at the level of safety now, more or less across the board, where danger comes from bad decision making rather than unexpected equipment failures. That's the point at which I would call equipment "safe," for my own purposes. Companies can and do make multimeters that protect people from bad decision making (e.g. sweeping across the dial while still connected), which I think is an amazing feat of design. But the only way that would make people safe is if all they ever did was probe things with a multimeter. I have to expect that people interested in electronics (or working in an electrical profession) do more than just probe things all day. You aren't going to make a wire that protects itself from becoming a short, or a capacitor that stops someone from soldering it in backwards. If people can't be trusted not to try and measure across two 480Vac bus bars on the 10A range, even if it's just because they're tired and having a bad day, I think something is going to get them sooner or later even if it isn't their meter.

In the case of 480Vac arc flash I saw, someone just wired a short into a piece of switchgear because they misunderstood the diagram. It blew the 5' front panel off of the switch, and if they had been standing a foot closer it would have taken them with it. They had a perfectly safe modern multimeter, but neither the terminals nor the wire said "sorry Dave, I can't do that" when they were being torqued down.

In my opinion, equipment free from unexpected failures and a working mind are what are necessary for safety, and I think many analog meters are capable of serving in that role. If I were doing commercial electric work professionally, of course I would use something explicitly CAT rated for the purpose from a reputable manufacturer. But low voltage hobbyists are in the position of reasonably being able to use whatever they want or can afford.

Oddly enough I do have a safety rated analog multimeter, the Simpson 260-9SP, CAT III 600V rated. Orange meter in the orange case below:

I would comfortably use anything in that photo to measure up to 240Vac mains, including the small Triplett pocket meter, although it's probably not one I would recommend to someone else for the purpose. I would only use the 87V or the orange Simpson for CAT III work above 240V. The yellow banana in front of the meters is a Fluke C9970 (formerly known as the Western Electric 188A) for checking whether something is live (up to 20kVAC) which is something I prefer not to use a meter for if I can avoid it.

[Specmaster]

You have to assume that any existing DMM will someday be hooked up to mains power at some point of time.

No, thats like saying that you have to assume that every car will at some point in its life be driven flat out on a race track and so has to be built so that it can survive being driven like a racecar.

Before starting work on anything, you should do a risk assessment and part of that assessment is making sure that you have the right equipment for the job and the right skill set.

[David Hess]

I would compare it to modern cars and classic cars. Both will get you from A to B.
A modern car is more fuel efficient, more comfortable, have more features and has significant safety features over the classic cars.

This analogy falls apart because many newer meters cannot make measurements that old meters make just fine.  I keep my old TM500 Tektronix meters around and in good repair because their linear JFET input stages produce no charge pumping making them very useful as a sanity check when my more modern meters return funny results like showing a 10 megohm shunt resistance as a drifty 1 megohm.

Are they a safety risk?
Modern dmm have better safety. What will happen to one of those old meters if you leave it on Ohms and measure mains voltage?

My old DMMs handle line voltage overload on the ohms modes just fine.  Obviously old meters are not certified to the CAT standards but the CAT standards did not exist then.  They may or may not meet them just like modern meters may or may not meet them despite what they say.

I miss having exposed binding posts which could directly attach wires and parts on bench meters.  Is that safer than having the user attach an external banana plug which can pull lose?

[David Hess]

Was any thought at all given to input protection, etc., in those old meters?

I always got the impression they were just bare circuitry and you were supposed to know what you were doing.

For analog meters there is not much that could be done simply because their input impedance is so much lower.  I was trained to make unknown voltage measurements starting from the high ranges to prevent meter damage.

Old DMMs mostly have the same input protection that modern DMMs have.  Vacuum tube and JFET input voltmeters can also be well protected for the same reason; the high input impedance input stage allows it.

[switcher]

I really cannot understand why people are so obsessive over CAT ratings, for meters for hobby use.

Most DMMs and DVMs, that are used by both hobbyists, and electronic engineers (I count myself in both categories) are used to make DC voltage and resistance checks on low voltage, low energy equipment. 

Where I work, I am not allowed to work on main switchgear, or on anything 'mains' - I  have no need (nor do I want to). The Techs who are; are suitably equipped (and qualified) to do so. They are not allowed to use multimeters of any sort. They have to use a CAT IV tester, such as a Martindale:-

http://martindale-electric.co.uk/martindale-vi-15000-voltage-indicator-p-1870.html

At home, in my electronics hobby, I have no need, or desire, to measure mains voltage; its either there or its not.

[Specmaster]

Obviously old meters are not certified to the CAT standards but the CAT standards did not exist then.  They may or may not meet them just like modern meters may or may not meet them despite what they say.

Precisely and going back to the car analogy again, this is the same sort of thing regarding the mandatory seat belt, stability control, ABS braking etc etc etc, all of these you expect to have a on a modern car by law but you still see loads of classic cars in use all over the world. I don't believe that you would be able to license these classic cars for things like taxi work for example because they don't meet regulations for carrying fare paying passengers.

[hexreader]

Avo 8 is highly desirable to many older repair technicians. If it is in good condition, then either keep it if you like it, or sell it at a good price (no idea what that might be).

There are a few handy tricks that can be done with Avo 8 that won't work with a digital meter.

Do not bin a working Avo 8.

[David Hess]

Obviously old meters are not certified to the CAT standards but the CAT standards did not exist then.  They may or may not meet them just like modern meters may or may not meet them despite what they say.

Precisely and going back to the car analogy again, this is the same sort of thing regarding the mandatory seat belt, stability control, ABS braking etc etc etc, all of these you expect to have a on a modern car by law but you still see loads of classic cars in use all over the world. I don't believe that you would be able to license these classic cars for things like taxi work for example because they don't meet regulations for carrying fare paying passengers.

I *hate* the ABS brakes on my GMC pickup.  Not only do they not fulfill their purpose by activating when they should not and not improving control when they do activate, but the design compromises made to include them mean that if the engine dies, the brakes fail (1) once the vacuum reservoir is emptied which is practically immediately.  How could that possibly be safer?  I am sure the rent seeking is profitable for GMC though.  The mandatory power steering is not much better.

My previous vehicles which lacked power steering and ABS were much easier to control under adverse conditions.

(1) When I say fail, I mean it is no longer possible to even stop motion on an incline and that is with 200+ pounds pushing on the brake pedal.  Except for the ABS, they work fine when the engine is running and GMC confirmed that this is normal.  WTF?

[David Hess]

I really cannot understand why people are so obsessive over CAT ratings, for meters for hobby use.

The situation reminds me of what did companies did before certified X and Y class line interference suppression capacitors existed.  They voltage derated existing capacitors, qualified them for line applications, and used them.

[Specmaster]

Avo 8 is highly desirable to many older repair technicians. If it is in good condition, then either keep it if you like it, or sell it at a good price (no idea what that might be).

There are a few handy tricks that can be done with Avo 8 that won't work with a digital meter.

Do not bin a working Avo 8.

Thanks, I intend to keep it, although I do feel a bit let down by it after all years of waiting to acquire one, compared to the TMK 700 it seems to so cumbersome and clunky and the lead interface is rather odd and can introduce unnecessary resistance and weak links in the chain compared to most meters.   

[tautech]

Avo 8 is highly desirable to many older repair technicians. If it is in good condition, then either keep it if you like it, or sell it at a good price (no idea what that might be).

There are a few handy tricks that can be done with Avo 8 that won't work with a digital meter.

Do not bin a working Avo 8.

Thanks, I intend to keep it, although I do feel a bit let down by it after all years of waiting to acquire one, compared to the TMK 700 it seems to so cumbersome and clunky and the lead interface is rather odd and can introduce unnecessary resistance and weak links in the chain compared to most meters.

Have you got all the lead types and all the connection accessories ?
The grabber (like a scope probe) is my most valued as it allows hands free use. 
Much better than the bulldog clips which are next to useless for any compact modern DUT.

I've got a few sets of what seem to be pirate leads......stiff PVC, horrible to use compared to the genuine AVO leads which BTW AFAIK were always branded.

[Specmaster]

No I havent, just got the standard leads (push on type) with 2 sets of probes and a set of the bulldog clips which don't seem to fit the bill IMO. It did come with just one of the scope type grabbers, a red one, need a black one to make a pair though.
I think it would be a far better meter if the probes and leads was a single item, but it would make a set of leads so much more expensive but far safer to use.