Enzo said:
Most of the very old Fluke's I've dealt with, fail due to increasingly brittle plastic parts. Those plastics do not age well after 25+ years.
These have mostly been Fluke 75s with a grey plastic housing.
I've seen the outer case of one of these old Fluke 77s shatter as the meter was plopped gently onto a desk. A raw egg wouldn't have been damaged by the same slight impact.
Many other Flukes from the same era had corners or chunks of the plastic case broken off, often around the LCD window opening, whose sharp corners provide stress risers that facilitate breakage.
Another typical failure mode in old Fluke's occurs when the internal plastic parts of the rotary selector switch become brittle with age, and and break off during normal switch operation.
The first obvious external symptom is usually that the switch will now click through a full 360 degrees - the internal end-stops don't work any more. Usually electrical problems (some ranges won't work) will soon follow.
This is not a criticism of these old meters - they've long exceeded any reasonable service life by the time the brittleness issues appear. But I am surprised that Enzo and WOTech haven't had their ancient Fluke's crumble to bits, like the one's I've dealt with.
"Were", not "are". Cadillacs were once considered the best cars you could buy in America, but not any more. Tektronix 22xx series analogue oscilloscopes were the bee's knees in the 1980s, but forty years later, that's not true any more.
Decades ago, a Fluke DMM was the best you could buy. Today, buying a Fluke meter usually only means that you've paid ten times the price, for a meter that, for 99% of users, 99% of the time, is no better than the numerous other alternatives. It's like those $100 Snap On screwdrivers apprentice mechanics like to waste their paycheques on.
-Gnobuddy
That's interesting - I've only seen this on few really, really old Flukes - and never the handhelds. I've got a whole pile of 77s and 77 series II meters at home, plus about two dozen of the 73 Series II meters at work, and the only issues I've had are with the zebrastrips for the display. Never really noticed any issues with deteriorating plastic.
Now on the other hand, just about every plastic part on the inside of my Fluke 8506 is literally crumbling...
That said, Fluke 77 Series I and Series II meters usually fetch more than they really should. I got mine for about $15 each at industrial surplus auctions, and that's about what an old 77 is worth in the real world.
In general, you pay a lot of money for the Fluke name. They're great meters, but really no better than the competition. The one good thing about Flukes is that they sell a lot of them, so they're reasonably common at industrial surplus auctions.
If you open them up, the circuits are around the same bought out chips, Intersil 7106/7107, and similar.
The difference is in the quality of the rest of the components, the housing, switch, display quality and so on.
Here sometimes I get mails from a seller, new Fluke meters from $60 or so, but I fear they may be made for Fluke in China.
That said, as an occasional repair man, I do not need extreme accuracy, my cheap meters are within 0.1 V at 12 V against a Fluke.
My meter was a Mastech 830B, $6.
Decide first what you need to do, for design and complicated work and for professional use, buy the best you can afford.
But for hobby use, not really needed.
The difference is in the quality of the rest of the components, the housing, switch, display quality and so on.
Here sometimes I get mails from a seller, new Fluke meters from $60 or so, but I fear they may be made for Fluke in China.
That said, as an occasional repair man, I do not need extreme accuracy, my cheap meters are within 0.1 V at 12 V against a Fluke.
My meter was a Mastech 830B, $6.
Decide first what you need to do, for design and complicated work and for professional use, buy the best you can afford.
But for hobby use, not really needed.
Crumbling plastic is common in hot areas, keeping things in a car on sunny days will cause rapid ageing,
Here we have 45 degree C -113 F - temperatures for 2 months in April and May, and October we exceed 100 F sometimes, and AC is needed.
What that does to plastic kept inside is left to your imagination, as the in car temperature can easily exceed 70 C - 158 F, with closed windows.
So your personal experience will be dependent on the climate where you live and work.
Here we have 45 degree C -113 F - temperatures for 2 months in April and May, and October we exceed 100 F sometimes, and AC is needed.
What that does to plastic kept inside is left to your imagination, as the in car temperature can easily exceed 70 C - 158 F, with closed windows.
So your personal experience will be dependent on the climate where you live and work.
I've dropped my Fluke 77 more times than I can remember over the decades.
Not a crack or problem ever.
I blew the MA fuse a few times, no biggie.
This is more or less what I observed also.
I remember another diyAudio user posting that he had compared various DMMs against a calibrated lab-grade digital meter, and found the cheapies as accurate as the Flukes he tried. He is very well qualified to pronounce judgement, have a Master's degree in electrical engineering.
This is not really surprising, when you consider that these days we find excellent 16-bit A/D converters in $15 USB audio soundcards. By contrast, in the early 1980s, when the original Phillips / Sony Compact Disc players came out, the 16-bit / 44.1 kHz converters inside were a truly revolutionary technological advance, one that pushed semiconductor technology to its limits.
For a DMM, you also don't need the sort of speeds necessary for 44.1 kHz audio sampling - in fact, you only need a few samples per second for DC measurements.
For a DMM, you also don't need a 16 bit A/D, or anything close to it. To achieve a resolution of 0.1% of full-scale, you only need a 10-bit A/D converter - a far, far simpler device to manufacture than a 16-bit one.
In fact, these days, 10-bit A/D converters are dirt cheap and extremely common. For example, you can find one built into the $2.34 Atmega 328P chip used in the Arduino Uno.
Here are $2.34 Atmega 328P chips at Digikey (if you buy 100 or more, as a DMM manufacturer would): Blocked
Here's an extremely simple DIY digital voltmeter using an Arduino, achieving errors around +/- 10 mV on a 5V full-scale range: Accuracy of an Arduino voltmeter - #5 by GolamMostafa - Sensors - Arduino Forum
Note that this is not a usable replacement for a DMM, but illustrates the point that a chip costing a few bucks and a few lines of code is all it takes to make a surprisingly good single-range digital voltmeter. These guys didn't even use an external voltage reference, and still got +/- 10 mV accuracy!
Naresh is right, these days the electronic guts of a typical hand-held DMM are almost trivially easy. Most of the design effort must go into the case, switches, connectors, electrical certifications, and so on.
-Gnobuddy
A good chunk of what differentiates meters is the front-end. Those of us who have designed front-ends for instrumentation know that designing precision amplifiers / attenuators (that don't drift excessively with temperature) and robust input protection is not trivial.
One other area that does separate meters is in the AC voltage measurement. Accuracy isn't the most important thing in the world, but reasonably wide bandwidth is really nice to have. Having a good true-RMS meter with bandwidths beyond 20 kHz is very useful for audio work, and some handhelds DO have this capability.
A good capacitance range is very useful. Nobody cares if it can measure 10,000 uF, but how accurate is it? How low in capacitance can it go? A lot of diyers don't have real LCR meters, so this is really important.
Another consideration, which really doesn't seem to be all that price-dependant, is how fast it autoranges. I've used some pretty expensive meters with dog-slow autoranging speeds, which is a huge PITA.
There are really two areas where the old Fluke 77s really fall apart. They don't have a capacitance range at all, and they aren't true-RMS. That's why I wouldn't pay more than about $20 for one.
I wouldn't waste my time on a meter below about $30, but I also don't see a point to spending more than about $200, unless it's a bench meter.
One other area that does separate meters is in the AC voltage measurement. Accuracy isn't the most important thing in the world, but reasonably wide bandwidth is really nice to have. Having a good true-RMS meter with bandwidths beyond 20 kHz is very useful for audio work, and some handhelds DO have this capability.
A good capacitance range is very useful. Nobody cares if it can measure 10,000 uF, but how accurate is it? How low in capacitance can it go? A lot of diyers don't have real LCR meters, so this is really important.
Another consideration, which really doesn't seem to be all that price-dependant, is how fast it autoranges. I've used some pretty expensive meters with dog-slow autoranging speeds, which is a huge PITA.
There are really two areas where the old Fluke 77s really fall apart. They don't have a capacitance range at all, and they aren't true-RMS. That's why I wouldn't pay more than about $20 for one.
I wouldn't waste my time on a meter below about $30, but I also don't see a point to spending more than about $200, unless it's a bench meter.
I inherited the care and feeding of a pool of about forty Fluke 75s when I got my present job. They were being used to teach introductory physics classes at a local junior college.
Quite a few of those old meters had one or more of the problems I mentioned above, due to brittle and crumbling plastic. The pool of good meters kept shrinking, as the remaining ones continued to break.
Another issue was the black nubs (feet) on the bottom of the cases - some of these had turned into sticky black goo that made a mess and was very hard to clean up.
As I said earlier, I do not consider this to be a flaw in these old Flukes. These old meters had already given good service for a very long time, and had clearly outlived any reasonable expectation of service life for a complex electronic device.
When the pandemic hit in early 2020, our classes went online. In an attempt to shore up just some of the enormous learning deficits that come with solitary, isolated, online learning, it was decided to mail out DMMs (and a custom-assembled kit of other bits and pieces) to students in some of our courses, so they could still do actual labs at home.
The old Fluke 75s were too fragile, and the risk/cost balance of sending out expensive new Fluke meters - to already discouraged and unmotivated students untethered to the campus - didn't look good.
I found a $35 (CAD) DMM model on Amazon Canada that met all our requirements (and provided several useful features the old Fluke 75s didn't have), and those are the meters we mailed off to our students.
We did lose a few meters, as some students dropped out and disappeared without a trace. But at $35 a pop, we could afford to eat the loss. The hope is that the benefits to our students outweighed the small fiscal loss we incurred.
The $35 meters proved to be entirely satisfactory, and the remaining unbroken Fluke 75s are now slumbering quietly in storage somewhere.
I have nothing against Fluke meters. They are excellent products. The problem is that there are now alternative equally excellent products available at one-tenth the price, which IMO makes Flukes an overpriced and useless luxury in most use cases.
-Gnobuddy
I just did a search for 'meter ic', and found Maxim or Renesas 7107 at $1, and energy meter IC at $2, from reputed sellers.
7107 is the classic Intersil (later Harris) A/D LED meter IC, and its twin is the 7106 (LCD version), I have seen them in temperature controller displays also.
Chinese blob chip carriers, and later Chinese blob meter boards also I have seen. Blob means the IC is bonded to the PCB, covered with a blob of black goop.
If the reading seems odd, change the cell, or the meter, cheap ones (830B) are $2 here. Cells are 10 cents for Chinese 9V (HiWatt or Gold Peak makes).
Energy meters today display many many parameters, among them voltage, current, frequency, power factor, kVA, kWh, kVAR and so on.
They are required to be able to retain their memory for a long time in case of outages, and the daily readings for up to a year (in case you have a dispute with the power company).
$2 is almost a prank price, but we do now get these assembled meters here for $6 and up for single phase models.
3 phase ones are from $12 or so.
Some can be modified to add data communication, so meter reading can be done as NFC all the way to wireless modem, ranges up to miles are there.
Also IOT, of course, which makes the data processing available anywhere you have Internet.
In sum, the expensive meters use the same basic circuits, the switches and resistors are better quality, maybe they use a Wheatstone Bridge in the input. Or something to improve the measurement accuracy. Maybe shielded housings, earth planes on the PCB.
But all those are not so expensive.
But until the extreme accuracy or rugged build is vital, a waste of money.
7107 is the classic Intersil (later Harris) A/D LED meter IC, and its twin is the 7106 (LCD version), I have seen them in temperature controller displays also.
Chinese blob chip carriers, and later Chinese blob meter boards also I have seen. Blob means the IC is bonded to the PCB, covered with a blob of black goop.
If the reading seems odd, change the cell, or the meter, cheap ones (830B) are $2 here. Cells are 10 cents for Chinese 9V (HiWatt or Gold Peak makes).
Energy meters today display many many parameters, among them voltage, current, frequency, power factor, kVA, kWh, kVAR and so on.
They are required to be able to retain their memory for a long time in case of outages, and the daily readings for up to a year (in case you have a dispute with the power company).
$2 is almost a prank price, but we do now get these assembled meters here for $6 and up for single phase models.
3 phase ones are from $12 or so.
Some can be modified to add data communication, so meter reading can be done as NFC all the way to wireless modem, ranges up to miles are there.
Also IOT, of course, which makes the data processing available anywhere you have Internet.
In sum, the expensive meters use the same basic circuits, the switches and resistors are better quality, maybe they use a Wheatstone Bridge in the input. Or something to improve the measurement accuracy. Maybe shielded housings, earth planes on the PCB.
But all those are not so expensive.
But until the extreme accuracy or rugged build is vital, a waste of money.
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A trick I've used for years is to use a precision resistor to make an RC high-pass or low-pass filter with the unknown capacitor under test, apply a sinewave from a function generator, look at the waveform on my 'scope, and twiddle the frequency until I find the -3 dB point.
This then lets you calculate C very simply, as C = 1/(2 Pi R f).
If you remember that 1/(2 Pi) is very close to 0.16, this becomes even simpler, a quick mental calculation. For instance, if C is in nF, and f in kHz, and R in kilo ohms, then C = 160/(R f). The formula is accurate to a fraction of a percent, better than most caps or resistors we use in DIY electronics.
This is too crude a technique to actually measure the value of a capacitor, but it is sufficient to catch any gross errors, such as accidentally using a 47nF capacitor where a 4.7nF one was intended.
-Gnobuddy
That's a good trick, and is one I use fairly regularly at work, since all of our LCR meters have a lenghthy setup process before they're usable. Still useful to have a cap range on meters though.
By the way, I don't disagree that Flukes are an overpriced luxury in most cases. Even from the perspective of my day job, it is rare that I'd ever grab something like an 87 or a 289, even though we have them. Most of the time I use my "backpack meter" (a 77 Series II, because we've got piles of them), and when that's not good enough, I probably need something closer to an 8842A or a 34401A than a 289.
Also, props to you / your institution for trying to have students do actual labs from home. I know a lot of students who did all of their "labs" in a simulator, or worse still, not at all.
Thanks for the kind remarks. Sadly, my experience is the same as yours.H713 said:
My wife and I are both involved in education, and at this point in the pandemic, we're finding that a huge fraction of today's students, from little kids in 2nd grade all the way up to young adults in junior college, have fallen two or more years behind grade level.
Electronics is one of many areas where online learning is a very poor substitute. An online student whose circuit doesn't work simply because she mis-wired a pushbutton, will give up after hours of solitary frustration.
But in a conventional face-to-face in-person lab, the instructor would have helped her find and fix the problem within minutes, and she would have stayed engaged and continued learning.
-Gnobuddy
OK.....
Who put the JINX on me about Fluke Meters????
Tonight, I had to repair (minor) my Fluke 23.
The tiny plastic "stop" projection nub that keeps the knob from going PAST "off" must have chipped off, allowing the knob to go past "off".
So...
I drilled a tiny hole (1.5mm) and put a teeny tiny screw in the spot - all fixed now, good as new!
Who put the JINX on me about Fluke Meters????
Tonight, I had to repair (minor) my Fluke 23.
The tiny plastic "stop" projection nub that keeps the knob from going PAST "off" must have chipped off, allowing the knob to go past "off".
So...
I drilled a tiny hole (1.5mm) and put a teeny tiny screw in the spot - all fixed now, good as new!
I'm not sure.
The model 23 must be at least from the 1990's.
Well-used, but works perfectly otherwise.
It's the beginning of the end for that meter, my brother in electronics!
-Gnobuddy
It's still nice to have those functions in a multimeter, but yes, it is sort of redundant.
Jeez, that's kind of a lot of effort to put into a Fluke 23...
Well, it's kind of sentimental.
I aquired it when we closed the shop in 2016, it once belonged to one of the old techs there who passed away.
And besides that, it's in great shape, look new, functions like new, has the outer travel case.
Popping the dial knob off is easy, drilling a tiny hole with a Dremel 1.5mm bit is easy.
And... it's a Fluke!