Author Topic: The Living DMM/Scope Electrical Measurement Thread  (Read 1188 times)

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Offline mkawa

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The Living DMM/Scope Electrical Measurement Thread
« on: Sun, 08 September 2013, 07:52:59 »
I just realized that we haven't had a single thread dedicated to one of my favorite subjects. MEASUREMENT!

digital multimeters come in all shapes and sizes, architectures, and accuracies. you can get meters that cost anywhere between 2$ to 2000$.

however, they are the bread and butter of a hobbyist electronics kit after the iron for joining parts. can't test your joints without a continuity meter!

a couple things i'll mention right now in the OP:

1) this is the 21st century. many multimeters that are surprisingly reasonably priced are now coming with opto-isolated serial outputs. mine has one, although mine was expensive (how expensive? i'll detail everything at the OP end). quite a few cheaper multimeters are starting to come with txrx as well. sigrok: http://sigrok.org/wiki/Supported_hardware is an awesome little software library and set of associated tools for interfacing with DMMs, the new wave of cheap, not entirely accurate ( :) ) scopes, and all kinds of other specialized meters. you can take a meter with no memory that just measures instantaneously, and graph the output literally as fast as the serial interface can give it to you. you can then use all kinds of off the shelf software (excel, even!) to graph the output. it's not as robust as a dedicated scope (although they have serial interfaces for the cheap rignol scopes that are popping up on the market), but it's very very cool. when i was student we had these bench meters that IF YOU WERE LUCKY had a hold button. that was it.

2) want to know what the most reliable featureful, longest lasting durable multimeter is? it's a fluke. fluke is the leader in electrical measurement, period. i have owned nothing but flukes for the past 15 years. actually, that's not true. i have owned other equipment, but i broke it all. my flukes have lasted through multiple fuse pops, me electrocuting myself (MANY TIMES WHEN I WAS YOUNGER), and everything else i've thrown at them. they just work, they're accurate, and they take every bit of beating you can dish out at them. the canonical fluke is the 7xx series. it has everything you need and nothing you don't.

3) there are two types of DMMs, the normal DMM, and the clampmeter. the clampmeter measures VERY HIGH CURRENTS (> 10A) without needing to be inserted into the circuit. they universally work on the hall effect and are specialized devices for measuring high current in circuits. what you want to start out with is a standard dmm and then add a clampmeter only when you need one.

ok, so here's my progression. back when i was a wee lad, i bought a crappy DMM. i immediately fried the thing, and went looking for a reasonable one. i almost bought an extech, but at the last minute i thought better of it and shelled out for a fluke 79 series III. this was in '98 or '99. i used that DMM until earlier this year. let me repeat. i used that DMM FOR > 10 YEARS without a single hiccup, and without needing to calibrate it a single time. it went through god knows how many batteries and 3-4 fuses from measuring current in circuits that were on the borderline of 10A, but it's still accurate and samwisekoi is still using it today. it's still accurate and still taking a beating every single damned day. FLUKE GEAR LASTS.

the only reason i got rid of it was that i got the 79 series III that i bought came without thermocouple support (there was a model that did and i'm still kicking myself for not getting it in the first place), and i realized when i started 3d printing that i really needed to measure temperatures. that was literally the only reason. otherwise i would have used it for another 10 years, easily. frankly, ron's going to use it for another 10 years and be very happy with it.

MY CURRENT METER SETUP: i now own a fluke 287, serial interface cable and a fluke i1010A. let's go over this in parts. the fluke 287 is the lower end of fluke's new line of DMMs that bridges the gap between scopes and DMMs. the DMM itself is powered by a 32-bit arm SoC and has literally ever function you can think of, as well as a built-in memory that will record trends at 1hz. the txrx cable and sigrok allow it to reach 20+hz. this isn't true scope capability (20mhz+), but does the job for now. however, it's still just a basic DMM and cannot measure very high currents (think car starter battery, or 24 FARAD 20v capacitor network). for that i bought a fluke i1010a, which is an add-on clamp meter that translates between very high currents and turns them into very low dc voltages: (1A = 1mv). it can take 1kA DC and 600A AC. and yes, i have tested the bounds of this with the welder. in fact, i killed a 9v battery by clamping it over the welder at ~750A instantaneous  :llama:.

that said, there's now a huge variety of DMMs and scopes on the market, priced from basically free to 20k$+. you can get a 20mhz scope from rignol for 200$. it's a new world out there. let's talk about it!
« Last Edit: Sun, 08 September 2013, 07:56:07 by mkawa »

to all the brilliant friends who have left us, and all the students who climb on their shoulders.