Digital multimeter question

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  #1  
Old 05-01-13, 09:14 AM
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Digital multimeter question

Seems like a decent thread to hijack, since OP might want to know too;

Why all the hate for digital multimeters from everyone here? Are they inaccurate or is it that they aren't as easy to read?
 
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Old 05-01-13, 11:47 AM
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Digital meters respond to voltage with very little current flow. They will show power when there really isn't any. An analog meter like a solenoid type Wiggy places a load on the conductors and does not respond to the phantom voltage.
 
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Old 05-01-13, 12:44 PM
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Seems like a decent thread to hijack
Guess not.

Digital meters respond to voltage with very little current flow
So the only issue is that they will show something it hot when it isn't?
 
  #4  
Old 05-01-13, 12:45 PM
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They each have their places where they are better than the other. When I need precise readings on a circuit board I go for one of my digital meters. But the more common home owner use of measuring ac power, like pcboss is explaining, the analog meter is less susceptible to induced readings. In other cases, like watching a dc voltage jump and decay, an analog will give you more than just a final reading.

9 out of 10 times I will grab my analog meter. Digital displays look neat, but you will need to know what they are telling you.

Bud
 
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Old 05-01-13, 01:01 PM
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High end digitals are as good as analog for most home uses...but few people want to spend $100 or more. I have one that somehow found it's way into my toolbox when I left the Navy...(I think it was a retirement gift) and it sometimes gives me very low fluctuating readings at times on household AC circuits and I just ignore them.

An analog is great for a quick test of power or not when troubleshooting since people register a visual movement of a needle faster than they do a number on a display. Proven fact.

I have 2 digital and 2 analog and if I need a precise measurement..I grab the digital. Troubleshooting...9 times out of 10 it's the analog.

EDIT...Oops...guess I just duplicated Buds post...lol.
 
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Old 05-01-13, 02:08 PM
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The problem is in the field a pro will know when to question a digital reading. Here we often don't know the background how a reading posted as fact was made. We may give the wrong advice or be stumped for an answer because we are relying on false facts.
 
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Old 05-01-13, 04:58 PM
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Vic, that meter doesn't have a Navy METCAL Lab sticker on the back, does it?
 
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Old 05-01-13, 07:43 PM
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Most homeowners never need a voltage tester any more sophisticated than a Square D Wiggy and only need to identify a votage and not actually measure it.

http://static.schneider-electric.us/...013-100-17.pdf

Ideal has a similar solenoid tester that I like.

IDEAL INDUSTRIES, INC. - Vol-ConŽ Elite Voltage Testers

There are occasions, however, when a more accurate test is required. That can be done with an analog meter or a good quality digital meter. There again, most homeowners don't want to spend the dollars required to buy a good quality digital meter.
 
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Old 05-01-13, 08:41 PM
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Vic - As a one time Navy Cal tech and lab supervisor, I hope the retirement gift was a Fluke.

I have a Simpson 260-6XLP analog that I've had forever. IMO one of the better analogs made. I seldom, if ever, use it. DVM's have unfortunately gotten a bad rep for use around the house because of "phantom" voltage. Supposedly its an induced voltage that is swamped by analogs, but lingers on a digital because of its high input Z. I've never encountered phantom voltage although I don't dispute that it might exist.
 
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Old 05-01-13, 09:13 PM
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Joe, both of the testers you linked to actually show the voltage that's present, which is a definite step up from a non-contact voltage tester. The thing is, they show it crudely, without either an analog scale or a digital readout.

The one from Square D hasn't been made in more than 5 years. Klein appears to have discontinued theirs. That leaves Ideal.

Before recommending that a homeowner spend $65 for an Ideal Vol-Con - which I have, somewhere - I would suggest an nice, cheap analog meter. Much more intuitive, as well as less expensive, IMO.
 
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Old 05-02-13, 05:32 AM
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I would also add the analog meters are dummy proof I never have any problems using my analog meter but I have a cheap digital that was given to me that confuses me more than it helps
 
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Old 05-02-13, 06:37 AM
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Great information to have. I personally just use a digital because that's what I have (bought because it folds up nicely to store in my former motorcycle). Since I mainly use it for DC or continuity, I've never noticed phantom readings.
 
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Old 05-02-13, 06:57 AM
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Ironically, what we refer to as a phantom reading isn't imaginary, it really is there. Static electricity can be 20,000 volts or more, but lacks the energy to do more than snap us. The reading we see on a digital meter exist due to the high sensitivity of those instruments. If we places a 50,000 (maybe 100,000) ohm resistor across our meter input, that induced voltage would disappear and we would have a bit more stable reading.

Bud
 
  #14  
Old 05-02-13, 07:00 AM
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The cheap analog meters have a plastic face over the meter which will get charged with static and upset the reading (even zero). Nice thing about the VOM is you don't need a battery only for reading ohms.
 
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Old 05-02-13, 07:52 AM
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Jeweled meter movements & the need for highly accurate components make analog meters more expensive than digitals. Analogs are also more sensitive to overload (smoked resistors in the range switch) & physical damage. I have several of both at home & calibrate dozens of digitals yearly. In my experience the quality of digitals has gone up & prices have gone down--just the opposite with analog. Digitals often have many more features than analog. Frequency, RPMs, temperature are common on digitals and are very handy features for a homeowner.

IMO for occasional use a homeowner won't spend the money to get a good analog and the cheapies aren't worth having. You can get a $30 digital from Sears or a big box store that will have the same accuracy & functions as a $200 Fluke DMM. Some even have a bargraph display under the digits for a quick visual indication like you get from a moving analog needle.
 
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Old 05-02-13, 09:42 AM
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I don't have an analog anymore, they all died but the one thing I found it indispensable for was tracing audio through a circuit but I haven't done any of that work in a long time.
 
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Old 05-02-13, 11:03 AM
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Bud - The phantom voltages that show up on digital meters is not a static charge on the conductor. It's an actual AC voltage (stray voltage) induced/coupled on the conductor by nearby current carrying wires. I'm not clear about which reactive component is responsible. In my mind it would be more likely to be inductive, but I have read other reports that attribute the voltage to distributed capacitance.

Analog meters have a low input impedence that provide a leakage path for this voltage. The hi input impedence of DVMs does not.
 
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Old 05-02-13, 11:27 AM
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I know one big disadvantage to an analog meter is that the scale often baffles a new or inexperienced user, especially if is a full featured meter.
Nothing requires less effort than a simple auto-ranging digital meter.
 
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Old 05-02-13, 11:44 AM
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This is what I use when great accuracy is not needed. Never had any "phantom" problems or false indications.

Knopp K-60 Voltage Tester

I have several as they were freely distributed at my former employer. I never thought about their cost, thinking maybe twenty bucks or less but a quick Google shows them to be currently between $40 and $70 depending on where you buy.
 
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Old 05-02-13, 12:40 PM
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"Wiggys" are good and I use to include them in my recommendations but the price will make them unattractive to some posters. Actually what my father used would be fine in most cases and could be built for $5 or less but that is probably a little too DIY. (Two edison base lamp holders in series with equal wattage 120v incandescent bulbs.)
 
  #21  
Old 05-02-13, 12:43 PM
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IMO for occasional use a homeowner won't spend the money to get a good analog and the cheapies aren't worth having.
Differences in opinions is why horses still race and bookies still make the skim! IMO an average homeowner doesn't need to spend additional money to get anything better, or more fully-featured, than a basic analog multimeter. That will give him or her the visual clue of the needle sweep without having to mentally adjust for any low readings from induced voltage, for less than $15.

Frequency, RPMs, temperature are common on digitals and are very handy features for a homeowner.
I've been doing this work for a while now. I own three meters. None of them has those features and I've never missed having them, frankly. I'm sure they're great to have when you actually have a need for them, but I wouldn't know what to do with them if I did have them, even at work - let alone around the house. It's certainly not something I'm willing to ask a homeowner to invest in just to troubleshoot their electrical system, phone line or doorbell circuit.

Originally Posted by Wayne Mitchell
The phantom voltages that show up on digital meters is not a static charge on the conductor. It's an actual AC voltage (stray voltage) induced/coupled on the conductor by nearby current carrying wires. I'm not clear about which reactive component is responsible. In my mind it would be more likely to be inductive, but I have read other reports that attribute the voltage to distributed capacitance.
Exactly. It's a real, induced current which can be felt. I never heard it referred to as "phantom voltage" before coming to this forum. To me, that's a misnomer, possibly slopped over from referring to the readings as "phantom readings."

Referring to this current as "stray voltage," OTOH, is the misapplication of a term that might not be widely known or understood, and therefore easy to stick in somewhere it doesn't apply. Stray voltage is a very real, and sometimes deadly, occurrence. It is encountered outdoors and in association with pools, not within wiring. If it was in the wiring, it wouldn't have "strayed." The best work I've seen on the subject has been done by Mike Holt and his team. Anyone who would like to know more can check out Mike Holt discusses Stray Voltage or Stray Voltage Articles.

Finally, connecting a high-capacity resistor across the two conductors we're seeing induced voltage on didn't make it vanish. It's still there, just shunted to a different path. So in that sense, it did "disappear," because then we can't "see" it."
 

Last edited by Nashkat1; 05-03-13 at 01:26 PM. Reason: Correction
  #22  
Old 05-02-13, 02:18 PM
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NashKat - I don't know who Mike Holt is, and there are certainly differing definitions of "stray voltage" but the differing definitions I have read (I just broke out a Navy basic electricity book from the 60's) all have one common thread.

Stray voltage is a charge between two objects that would not normally be there. Here's the IEE working definition from WIKI -

Stray voltage is defined as "A voltage resulting from the normal delivery and/or use of electricity (usually smaller than 10 volts) that may be present between two conductive surfaces that can be simultaneously contacted by members of the general public and/or their animals. Stray voltage is caused by primary and/or secondary return current, and power system induced currents, as these currents flow through the impedance of the intended return pathway, its parallel conductive pathways, and conductive loops in close proximity to the power system. Stray voltage is not related to power system faults, and is generally not considered hazardous."[1]

IEEE should have interviewed John McCain before making that last statement. McCain was neary toast when his bomb laden A-4 was hit by a Zuni rocket accidently fired by "stray voltage." That stray voltage accident cost 134 lives and nearly sank the ship.

NEMA uses the term "phantom voltage" and that may be where most posters here got it.

I have had occasion where I would have liked to have an RPM or frequency function on my home multimeter. RPM for tuning small engines and F for checking my generator.
 
  #23  
Old 05-02-13, 07:42 PM
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Before recommending that a homeowner spend $65 for an Ideal Vol-Con - which I have, somewhere - I would suggest an nice, cheap analog meter. Much more intuitive, as well as less expensive, IMO.
I guess it shows how long it's been since I bought a solenoid type voltage tester.

I still contend that most homeowners never need an accurate voltage measurement, but only need to identify what voltage they are working with.
 
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Old 05-03-13, 03:25 PM
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I don't know who Mike Holt is,
That's OK. You don't work in our field. FYI, everyone, Mike Holt is one the most respected and best-known experts and educators in the field of electrical work. He has probably had a hand in training more licensed and working electricians than any other person. He's also one of the the elite group that oversees the evolution of the National Electrical Core. But y'all can follow the link and let him speak for himself and Mike Holt Enterprises.

Mike needs no introduction to those in the electrical field. There's no reason I should have assumed that to be the case here, and I regret that I didn't introduce him earlier.

there are certainly differing definitions of "stray voltage"
There may be. What I find interesting is that the definition you quoted, from the former Institution of Electrical Engineers, is congruent with what I said earlier. It is, as your quote states, "A voltage... that may be present between two conductive surfaces that can be simultaneously contacted by members of the general public and/or their animals." It isn't the current induced on a non-energized conductor as it runs in parallel with an energized conductor in a closed (until opened for working on it) electrical system. Maybe I'm being picky, but I don't think it applies (I think it shouldn't be applied) to the induced voltage that can confuse people when it appears on an inexpensive digital multimeter being used to test between two conductors in the same raceway.

(I just broke out a Navy basic electricity book from the 60's)
Thank you for your service to our country, particularly if you served, as it sounds like you may have, in our unfortunate and ill-fated involvement in a civil war in southeast Asia. (Off topic, so I'll just leave it at that in this discussion. Just wanted to say it.)

Most of us reach for reference materials that are less than 50 years old, as thinking in any field, especially a technical one, may have changed or evolved over the years. But that's no reason to discard the classics.

IEEE should have interviewed John McCain before making that last statement. McCain was neary toast when his bomb laden A-4 was hit by a Zuni rocket accidently fired by "stray voltage." That stray voltage accident cost 134 lives and nearly sank the ship.
While McCaim was extremely fortunate to have escaped the fire and explosions that severely damaged the USS Forrestal, I don't think that the cause of that disaster was "stray voltage" in the sense that it's sometimes used here. There are varying accounts (and urban legends) about the cause. The one that seems most reliable to me, and involves electricity, is that "an unguided 5.0 in (127.0 mm) Mk-32 "Zuni" rocket, one of four contained in a LAU-10 underwing rocket pod mounted on an F-4B Phantom II, was accidentally fired due to an electrical power surge during the switch from external power to internal power. The surge originated from the fact that high winds had blown free the safety pin, which would have prevented the fail surge, as well as a decision to plug in the "pigtail" system early to increase the number of takeoffs from the carrier." That's neither stray voltage nor induced voltage. That's the real juice getting to somewhere it shouldn't have been, due to a malfunction in the system.

NEMA uses the term "phantom voltage" and that may be where most posters here got it.
Interesting! However, I don't think that NEMA, or the National Electrical Manufacturers Association, actually uses the term "phantom voltage" in any technical or meaningful way. I think what they did do in 1998, in their Bulletin No. 88 (reaffirmed in 2011) was explain what was being referred to as "phantom voltage." It does show, though, that the term has been floating around (sorry, couldn't resist ) for some time.

I still don't like the phrase and won't use it. As a poster said in a forum frequented by professional electricians, "I personally don't believe in phantom voltages. "PHANTOM" indicates that there is no reason for it to be there."

I have had occasion where I would have liked to have an RPM or frequency function on my home multimeter. RPM for tuning small engines and F for checking my generator.
Then you could invest in those capabilities. It sounds like you've chosen not to. Yes, they'd be nice to have on hand sometimes, but it's hard to justify the expense for someone who just needs a bit of accuracy when they're troubleshooting their wiring.
 
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Old 05-06-13, 01:35 PM
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Wow! I could start by asking why you felt the need to insert the irrelevant and unneccesary Vietnam comment and the gratuitious and meaningless "thank you for your service".

As for McCain, my source was his biography "Faith of My Fathers" On page 178 McCain states "stray voltage from an electrical charge(r) used to start a nearby F-4 had somehow fired the 6 foot Zuni from under the Phantom's wing . . ." I also had a face to face with a longtime friend and survivor that was badly burned fighting the deadly fire. I also watched the training film developed following the disaster at least a half dozen times. It too uses the words "stray voltage." Its most likely that the stray voltage was initiated by a power surge but the fact that the firing voltage wasn't supposed to be there makes it a stray voltage.

I won't even get into the swimming pool thing. Or current vs voltage or the terminology. I had never heard it from anywhere except here. As for a reference more than 50 years old - do you think that electricity behaves differently now than it did 50 years ago?
 
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