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Multimeter

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Dr.EM

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Yes, I finally got me one :lol:

I've already managed to blow the fuse, mere hours after getting it! Of course, current is measured in series with the circuit :oops: . It was a 200ma 250v, luckily I had some 250ma ones around, they will do till I get the suitable one, I am only measuring on low voltages anyhow.

**broken link removed**

I found out what some of that random assportent of resistors I had were. Some bizzarre values, 3.3ohm, 5ohm, 35k etc. A useful device anyhow.
 
When I got my first multimeter, I wanted to measure line voltage, so I switched it to 1000V AC range. Everything went OK and I measured ~230V. Then I "wondered" what would happen if I connected the Lead to 20A plug on the multimeter. Boom! Fuses (and lights) went out. When I could see what happened I was shocked. Multimeter is OK (with 0.5A blown fuse), but one Lead was WELDED to the socket!

That was very dangerous (I was 15 yrs old), but I am still live and kicking :D
 
I also blown the fuse once by forgeting to change it to the 20A socket.

I have ann 10 pack of 200mA fast fuses.So in case i burn one i just stick annother one in.

Anyway i didnt blow a fuse in my new multimeter yet.
 
:lol: , not the only one then. Didn't cause any damage myself, but did wonder why the current measure wasn't working afterwards. I'll have to get a pack of 200ma quick blow, the 250ma I have in there is a slow blow so needs changing really. How come some multimeters cost £500? I know autoranging costs more, but not that much!
 
Dr.EM said:
How come some multimeters cost £500? I know autoranging costs more, but not that much!

Auto-ranging probably costs LESS, it saves on the cost of range switching.

Expensive meters cost lots more money for a number of reasons?:

1) Paying for the name!.

2) Slightly higher spec.

3) Slightly better built.

4) May be slightly better protected?.

Generally the differences are pretty slight though, it would be unusual to notice any difference for almost all uses. Like anything though, it can cost a LOT more to make something slightly better, there are certain levels of performance which are easy to achieve, and pushing past that barrier costs money!.

I don't think anyone would argue that a £500 meter is 100 times better than a £5 one :lol:
 
Nigel Goodwin said:
Dr.EM said:
How come some multimeters cost £500? I know autoranging costs more, but not that much!

Auto-ranging probably costs LESS, it saves on the cost of range switching.

Expensive meters cost lots more money for a number of reasons?:

1) Paying for the name!.

2) Slightly higher spec.

3) Slightly better built.

4) May be slightly better protected?.

Generally the differences are pretty slight though, it would be unusual to notice any difference for almost all uses. Like anything though, it can cost a LOT more to make something slightly better, there are certain levels of performance which are easy to achieve, and pushing past that barrier costs money!.

I don't think anyone would argue that a £500 meter is 100 times better than a £5 one :lol:

Keithley Model 2000.
6-1/2 Digit meter. Cost $999 USD

That's 10 times the cost of a typical 3-1/2 digit meter. (about 11 bits worth of resolution)
6-1/2 digits is about 21 bits of resolution. Twice the number of bits of resolution! Which is about 1024 times better.

10x the cost yields 1000x "better" performance wise. So in this case, you do get a proportionately better meter for the cost..

:-D :-D

But you are "mostly" correct.. :-D
 
Optikon said:
That's 10 times the cost of a typical 3-1/2 digit meter. (about 11 bits worth of resolution)
6-1/2 digits is about 21 bits of resolution. Twice the number of bits of resolution! Which is about 1024 times better.

So do Keithley claim this meter is 0.00005% accurate?, I rather doubt it :lol:

Just checked :lol: they claim "(with 0.002% 90-day basic accuracy)", which although extremely impressive, is well short of 6-1/2 digits! - and the "90 day" accuracy makes it rather academic?.
 
At work there was a crappy DVM that they wouldn't replace. So I bought for myself an expensive Fluke one with fantastic accuracy, a frequency counter, auto-ranging and extra sensitivity.

Not to be outdone, my boss bought a cheap one from RadioShack with about the same functions as mine, except even at RadioShack's inflated price it was half the cost of mine. It wasn't very accurate and even caused an argument about which meter was correct. It broke within a week but mine is like new about 8 years later.
You do get what you pay for! :shock:

Except the cheap one I bought a couple of years ago for my toolbox is accurate, and still works fine. It was 10 bucks. :lol:
 
Nigel Goodwin said:
Optikon said:
That's 10 times the cost of a typical 3-1/2 digit meter. (about 11 bits worth of resolution)
6-1/2 digits is about 21 bits of resolution. Twice the number of bits of resolution! Which is about 1024 times better.

So do Keithley claim this meter is 0.00005% accurate?, I rather doubt it :lol:

Just checked :lol: they claim "(with 0.002% 90-day basic accuracy)", which although extremely impressive, is well short of 6-1/2 digits! - and the "90 day" accuracy makes it rather academic?.

LOL.. .I doubt anything is 0.00005% accurate. That's half of 1 ppm!


Accuracy and resolution are not the same thing!! The meter is 6-1/2 digits of resolution at very slow sampling (mostly to filter out noise) but accuracy as you can see is a different spec. I really dont know of what use a 90 day spec is though... Presumably for planning calibration cycles?
 
Value for money ?

audioguru said:
You do get what you pay for! :shock:

I think there is lots of scope for argument here ... I agree that my 20 year old Fluke is still working fine and so has probably justified its high cost but I also have some second-hand bench meters (maybe 20 years old ?) that I have bought for £5 or £10 that have also given excellent service.


Optikon said:
Keithley Model 2000.
6-1/2 Digit meter. Cost $999 USD
...
10x the cost yields 1000x "better" performance wise. So in this case, you do get a proportionately better meter for the cost..
But how many times a millenium do you actually NEED that resoluton ?
 
audioguru said:
At work there was a crappy DVM that they wouldn't replace. So I bought for myself an expensive Fluke one with fantastic accuracy, a frequency counter, auto-ranging and extra sensitivity.

Not to be outdone, my boss bought a cheap one from RadioShack with about the same functions as mine, except even at RadioShack's inflated price it was half the cost of mine. It wasn't very accurate and even caused an argument about which meter was correct. It broke within a week but mine is like new about 8 years later.
You do get what you pay for! :shock:

Except the cheap one I bought a couple of years ago for my toolbox is accurate, and still works fine. It was 10 bucks. :lol:

The radioshack crap broke or was it......

sabotaged!

Yeah, sometimes the "cheap" ones end up outliving everything... don't know why that is really other than good quality design practice..kinda makes me think those companies are selling themselves short.
 
Optikon said:
The radioshack crap broke or was it......

sabotaged!
I didn't touch it. Its selector switch fell to pieces from being used, not dropped. Its umpteen million battery connectors came loose from its pcb (it used a bunch of AA cells while mine uses a little 9V battery). :lol:
 
Re: Value for money ?

mechie said:
audioguru said:
You do get what you pay for! :shock:

I think there is lots of scope for argument here ... I agree that my 20 year old Fluke is still working fine and so has probably justified its high cost but I also have some second-hand bench meters (maybe 20 years old ?) that I have bought for £5 or £10 that have also given excellent service.


Optikon said:
Keithley Model 2000.
6-1/2 Digit meter. Cost $999 USD
...
10x the cost yields 1000x "better" performance wise. So in this case, you do get a proportionately better meter for the cost..
But how many times a millenium do you actually NEED that resoluton ?

Yeah, I agree for the casual tinkerer/hobbyist you probably never need it.. but all the manufacturers of all the opamps we've come to love and enjoy certainly need it. For example, to measure 10uV output offset on a precision opamp one needs orders of magnitude better resolution. Having good resolution helps to characterize components as well as noise floor in a circuit design. It's also arguable that capability is worth the cost but I guess if you need it, you need it...
 
Re: Value for money ?

Optikon said:
to measure 10uV output offset on a precision opamp one needs orders of magnitude better resolution.
I think you mean input offset voltage, which is nice to have extremely low if you are using the opamp in a circuit with lots of DC gain.

Hey, isn't that how opamp manufacturers measure input offset voltage of an opamp? Just like how you and me would measure it. Set the opamp under test with a DC gain of 1000, then amplify it with another opamp circuit with a DC gain of 1000. Then if you filter out the noise it will be easy for any old meter to measure the resulting 10V. :lol:
 
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