Multimeters: Which one?

[Kesh]

VC97

http://www.ebay.com/itm/VC97-3999-Auto-range-multimeter-vs-FLUKE-15B-tester-DC-V-AC-V-Resistance-Frequen-/300774399328?pt=LH_DefaultDomain_0&hash=item46078d1d60

30 bucks ?

tell me a lil more about this , presntly i have a cheap 17 dollar one , but it has lasted forever . i got a 10 dollar super cheapo to do hfe but the sockets dont work .

is the vc97 quality ? does the hfe test work well ?

it does capacitance measurement well too ?

i have the vc99, it's fine except the auto shut-down is a bit too keen, once it has warned you that it's going to turn off in a few seconds, using it doesn't prevent it turning off. maybe there's a way i haven't figured out yet. you can turn the auto shut-down off though. cap test seems accurate (but it won't go down to pico) as does hfe for non leaky silicon.

i have used it for amps, between a psu and a chip amp, where you don't want a resistor. but i can't see the point of micro amps.

[Perrow]

Mainly, when checking collector current / leakage on germanium transistors (to work out the hfe).
Paul

http://www.geofex.com/Article_Folders/ffselect.htm

[chromesphere]

Hey Perrow, thanks for the link, I have seen it a few times before.  I've already built the small bear hfe tester though which measures current. 

its ok though, im thinking the B K Precision is the way to go anyway and it does uA so all good.

Cheers.
Paul

[Perrow]

What I would love for the Geofex tester is a DMM with relative measures, measure the leakage, push a button on the DMM and switch the tester and voila the hfe without the math  Not that I can't do subtractions in my head, it just would be that much easier when you want to measure 100 transistors. I've thought about buying an Arduino board and programming it for germanium testing.

[greaser_au]

Paul

After 20+ years on the road,   I think the MY-68  is great. A good pair of 1000V silicone leads - which cost at least as much as the meter) and I'm set. Wish I could find another one for the same $26 I paid at the auto parts shop!!!  AND it agrees down to uA  with  the lab calibrated fluke 87 at work (as far as I can read on the 87's display with the faint & missing segments, anyway)!!!    

Personally, unless I needed a yearly laboratory calibration certificate  to earn my daily bread with it, I'd stick with sub-$100  meters. If nothing else they are disposable

david

[Perrow]

TWO of these will set you back less that $120 

http://www.ebay.com/itm/Brand-New-UNI-T-UT61D-AC-DC-Modern-Digital-Auto-Ranging-Multimeters-True-RMS-/300827395683?pt=LH_DefaultDomain_0&hash=item460ab5c663

http://www.uni-trend.com/UT61D.html

True RMS, uA, 4000uF, 60M ohm, 10Hz - 10MHz.

[lonewolf]

I just bought a amprobe 38xr-a meter for about 160.00 that handles most everything I would need to measure (resistance up to 40 meg/dc amps from 100ua up to 10 amps/capacitance from 40nf to 400uf/ frequency from 100hz up to 10mhz/dc/ac volts 1000mv to1000v/temp ranges from-20c -1300c/-4f to 2372f/dbm range -13 to +50 dbm/duty cycle range0 to 90% rs232 data output/analog bar graph/backlit display/auto range..etc..has a 3 year warranty..pretty good meter for the money..this is teir top of the line model..plus got it in town so I was able to look at it first...

[kodiakklub]

fluke will always have your back. no one stands by their product (in DMM's) the way fluke does. expensive yes. if that china crap dies or you nuke it, it goes in the garbage. buy crap, buy twice. its also my line of work so i have a 337 amp clamp as well for balancing loads. i cant suggest fluke enough. and the 77, which i own, is perfect for anything as far as music electronics. as a stocking stuffer for another 100bux, ask santa for the fluke lead kit. i think its 6 diff kind of lead heads. comes in a rollup pouch. true RMS is also mandatory.

[greaser_au]

In any target market beyond basic commercial, a 'test schedule' is used to confirm a device meets specification, the cover page or appendix usually contains a place to record types/serials of devices used for testing so that they can be tracked back to  a calibration register in the event of problems later - or for trend analysis. very few brands of DMM are calibratable and respected like a Fluke especially in this sort of environment. Their support is excellent, but as usual with premium gear,  I found the service agent repair costs were in keeping  with the purchase price...   I could have bought 6 or more whole MY68s for the cost of a single F'87 display replacement (ours went back for this several times over it's operational life). 

I've read the words 'true RMS' a few times in this thread, I know it's a necessary thing in a few occupations and if you need a true RMS reading for your test schedule, you'll have a calibrated true RMS capable meter on the test bench. However I have to admit that I struggle with the importance placed on it in this context,  any technician worth his salt will know the limitations of the tool he is using and will (*if* it's ever necessary) mentally correct the reading from average to RMS in his head  based on the operation of the stage he is working on.  It's a nice thing to have- like display backlighting or max/min hold-    but I personally wouldn't spend heaps more on a meter just for frills like these in a general use environment.

david

[reveal]

https://www.sparkfun.com/products/9485   Does anyone have any experience with JYE kits? 

[PRR]

> 'true RMS' ... I struggle with the importance placed on it in this context

Me too. But I disagree on....

> any technician worth his salt will know the limitations of the tool he is using and will (*if* it's ever necessary) mentally correct the reading from average to RMS in his head

But is it Average? Never! Many meters do detect average but display "RMS" (assuming Sine) because that's how all AC power distribution is specified, and AC power is generally sine-like.

However my VTVM actually detects Peak-To-Peak (then divides by 2.8 to display "RMS"). I have seen VTVMs with two scales: P-P and RMS. OTOH some lesser VTVMs only detected Peak (half-wave).

If the wave is very Sine-like, these 0.9 and 2.8 factors give the right answer.

If not, not.

Here's an audio example how the type of detection matters. Bring an amplifier up into clipping on a custoomary sine-wave. With a Peak or P2P detector, reading stops rising when you hit clipping. With Average or RMS, the reading keeps rising far into clipping.

If you are heating light-bulbs with odd wave-forms, RMS is for-sure the way to go. (As long as we can still get incandescent lamps.) Triac dimmer calibration is generally done with an RMS meter. However because the very-odd waveform is consistent for every %-dim, you can also use an Averaging meter which has been re-marked with "triac RMS". You can not use a Peak meter because everything from 100% down to 50% has the same peak (50% is about a quarter wave so includes the peak of a sine).

In "clean" audio we usually design amplifiers to handle the peaks of the audio. Here a peak meter is appropriate for reading any wave-shape to confirm it is not clipping.

(OTOH loudspeakers burn-out from RMS, so knowing the RMS of your signal seems appropriate. However reading RMS Voltage is insufficient information, because speaker impedance varies with frequency and thermal history. You could combine RMS Voltage and RMS Current then multiply for Watts. Phase-shift gives error, typically small, but it is the untypical cases where you want the best measurement. Additionally large excustion cools the coil, and this is not easily corrected. {The usual best-practices include micro-thermocouples and resistance-rise techniques.})

To me (more a clean guy), THE key spec is Frequency Response.

Many classic lineman digi-meters are specced to 400Hz (to cover old aircraft systems) and some fade quite alarmingly past 1KHz. As an audio-guy, this omits half the spectrum I need.

The better old needle-meters are quite flat past 10KHz, but you have to know that the droop at 20KHz is probably in the meter not the system under test.

Better VTVMs are flat past 500KHz *if* source impedance is low. (That's why there were dedicated ACVMs, flat past 100KHz with very low input loading.)

In hi-fi (and even some guitar amps) it can be useful to go to very low frequency. Where do you draw the line between "AC" and "DC"? Arbitrary. For low error at 50/60Hz most meters extend to 10Hz. Going lower costs more. (Except the old cheap needle-meters which did not distinguish AC from DC!) I used to run plots down below 1Hz. 33RPM record-warp is half-Hz, some old phono preamps had a bump in this area, which would cause distortion "for no reason". Bootstrapping also tends to subsonic bumps which can lead to unexpected interactions.

Min/Max hold recently became quite useful to me for quantifying the way my lights flutter (dim and bright) when the pump or furnace cycle on my too-long power line. (However I suspect a dumb old needle-meter would have told me enough.)

I think we agree that knowing the tool (and its limits) is more fruitful than buying buzz-words.

[amptramp]

If waveform is important, use a scope.

There are meters that have the correct RMS conversion because they contain one of the chips that were designed to do the mathematical operations to determine true RMS, but these are expensive and scopes are getting cheaper and more portable all the time.  There are older meters that use heater/thermocouple methods of determining RMS voltage with lesser accuracy and a large number that say RMS on the outside but are really peak-reading meters.  I can't think of any signal measurement you can do better with a meter than with a scope and most scopes have at least a DC to 1 megahertz bandwidth whereas you may never be able to get information on a meter's bandwidth.  A lot of scopes are going on the used market because companies are ceasing operations or moving them to third-world hellholes.  You can find scopes on auction sites or classified listing sites and there were two at the last vintage radio club meeting - a two-channel 25 MHz scope that was offered for $25 (but sold for less) and a two-channel 50 MHz scope that didn't sell because it was offered for $50 and it is a buyer's market.

[Rob Strand]

Re: averaging vs true-rms.   When the waveform is a sine-wave the measurement is *always* correct in both cases.   It's not as if the averaging meter is wrong in some way.

It's when you measure a waveform that isn't a sine-wave that measurements start to deviate.

For example an averaging meter will measure about 10% high on a square wave and about % low for a triangle-wave.
If you measure sine-wave that are distorted by a non-linear process generally the results are in good agreement.

However some of the waveforms that come about in power electronics the results start to deviate a lot - that's where a true-rms meter holds it's own.  Pulse type waveforms are another of waveform where you get problems.

See,
http://www.analog.com/static/imported-files/application_notes/AN-268.pdf
http://ave.dee.isep.ipp.pt/~mjf/PubDid/TRMS.PDF

If you want to measure frequency you need a wide band-width meter, and virtually none of the low end meters.
True-rms meters are better for measuring noise levels, but here the largest error is the filtering effect of the meter's frequency response (or that you haven't limited the bandwidth yourself.)

You have to ask yourself what you are going to use it for.    Most people will be fine with an averaging meter.