Electronics > Beginners
Yet another what DMM should I get thread
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rsjsouza:

--- Quote from: Discotech on June 01, 2018, 01:56:55 pm ---
--- Quote from: rsjsouza on June 01, 2018, 11:47:57 am ---Depending on the frequencies you are measuring on the synthesizers, the Amprobe may be very limiting as its AC can go up to 400Hz only. You can find a bit of a discussion on the multimeter spreadsheet discussion starting at the following post:
https://www.eevblog.com/forum/testgear/multimeter-spreadsheet/msg1420559/#msg1420559

--- End quote ---

With measuring frequencies though wouldn't I be better off with an actual scope ?

--- End quote ---
I guess my previous sentence was quite bad. I meant to say that, "Depending on the circuits you are measuring on the synthesizers, the Amprobe's maximum frequency may be very limiting..."

Although oscilloscopes can show the entire waveform and help uncover distortions and other artifacts, a DMM is much more accurate than a typical oscilloscope to perform the actual voltage measurement - after all, the typical oscilloscope does not have the same amount of ADC accuracy a DMM has (8 bits versus 12, 14 bits). A DMM with a cutoff frequency of, say, 400Hz, will show a 1VRMS@400Hz as 0,707VRMS (-3dB), while another with a roll off at 10kHz or 100khz will show the actual 1VRMS. Since audio typically goes to 20kHz, this may impact your work depending on what you are trying to accomplish.

On a side note, a frequency meter can also be much more accurate than the one built into an oscilloscope. Certain DMMs also have that feature, although careful reading of its manual is required to know its limitations - mostly involving DC offsets and minimum voltage that is actually detected (sensitivity).   
exe:

--- Quote from: rsjsouza on June 01, 2018, 02:15:44 pm ---On a side note, a frequency meter can also be much more accurate than the one built into an oscilloscope.

--- End quote ---

Why so? Anyway, I don't think this applies to cheap DMMs in this thread.
rstofer:
Look for Dave's review of the Aneng AN8008

Pay attention to the bit where he says to stay away from mains but this comment applies to just about every inexpensive meter.  CAT ratings aren't necessarily proven by a certified testing laboratory.  Mostly, they are bull-winkle.

The BM235 is a nice meter at a good price.

The Fluke 289 is even nicer but costs a lot of money.  I have the predecessor 189 and it's a great meter.  I leave it on the shelf and have the AN8008, the BM235 and Dave's new 121GW on my bench.  I haven't really had a chance to use the 121GW but the other two work fine.  I have great hopes for the 121GW.

Again, look for the review!  The AN8008 is amazingly accurate and only around 20 USD.  Buy a couple!

exe:

--- Quote from: rstofer on June 01, 2018, 02:32:18 pm ---Pay attention to the bit where he says to stay away from mains but this comment applies to just about every inexpensive meter.  CAT ratings aren't necessarily proven by a certified testing laboratory.  Mostly, they are bull-winkle.

--- End quote ---

I know, I read a lot about the topic. Here are some examples why meters don't meet safety specs: https://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/ . I don't encourage using "unsafe" meters, but 1) I don't measure mains current 2) to me using 250V fuses for mains work is adequate 3) voltage range often not protected with fuse, so irrelevant. The only danger I see is a voltage spike and DMM explosion. Anyway, it's just my personal opinion. If someone tells a story how a cheap multimeter killed someone I may change my opinion.
Discotech:

--- Quote from: exe on June 01, 2018, 02:52:41 pm ---
--- Quote from: rstofer on June 01, 2018, 02:32:18 pm ---Pay attention to the bit where he says to stay away from mains but this comment applies to just about every inexpensive meter.  CAT ratings aren't necessarily proven by a certified testing laboratory.  Mostly, they are bull-winkle.

--- End quote ---

I know, I read a lot about the topic. Here are some examples why meters don't meet safety specs: https://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/ . I don't encourage using "unsafe" meters, but 1) I don't measure mains current 2) to me using 250V fuses for mains work is adequate 3) voltage range often not protected with fuse, so irrelevant. The only danger I see is a voltage spike and DMM explosion. Anyway, it's just my personal opinion. If someone tells a story how a cheap multimeter killed someone I may change my opinion.

--- End quote ---

The Cat 1 & 2 confuses me on grey areas

Obviously PC components are Cat 1 apart from the PSU which becomes Cat 2 due to being the part attached to the wall

What about Synths though ? Say for instance the 5v plugs do does the plug itself count as the power supply meaning the Synth itself is Cat 1 ?

Like this https://www.amazon.co.uk/2000mah-charger-Adapter-Charger-myGadgetsandGames/dp/B00WGC2ZOO I understand the plug itself is Cat 2 as it plugs into the mains but is whatever circuit it connects to Cat 1 or Cat 2 ?
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