Digital multimeter

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On Wednesday, December 11, 2013 11:10:52 PM UTC-5, nestork wrote:

I agree. I have a nice Simpson, but it's kind of a pain to drag that case around and untangle the leads. The cheap Radio Shack is what I usually reach for, unless I'm getting weird readings.
Just a warning though, about being concerned whether voltage is there or not. That's a great use for a meter, and can save you the occasional miserable oops. But the proper technique is Live-Dead-Live.
Check on a known live voltage to be sure the meter is working.
Check the wire you're about to touch to confirm you've disonnected it.
Then check AGAIN on a live source. Meters have been known to fail at just the wrong time, and your dead wire might not be really dead.
Okay, it's rare to have that problem. But that's the way I was taught to test.
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Yep. Mine died once while trying to check resistance/continuity. The battery was low and did not bring the meter out of 0L even while there was a circuit established. The screen worked and all, but that was a cursing TSR moment. Luckily I figured out what was going on and had my expensive meter handy to finish the job in a few minutes. Yes, a hundred feet of wire is enough to defeat the meter with a low battery.
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Not caring about true RMS at the time, I got this meter.

http://www.youtube.com/watch?v=UtmtSyx5Yjg

I scored price wise on it (under 30). Would have preferred replacing my fried Fluke, but spur of the moment need and almost 400 bucks difference in price made the decision easy. I miss the milliamp driver, but cannot say that I have a true need for that any time soon.
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Led display ?
Greg
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that I have a true need for that any time soon.

Um, fatal voltage input. So, sort of. :-)
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On 12/11/2013 10:10 PM, nestork wrote:

A lot of the cost is making the meter safe if you make a mistake on high capacity circuits, as in one of Ralph's posts. A real good idea if you are working in service panels or somewhere other than on the end of a 20A branch circuit.
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Fluke recommends that their meters be calibrated annually. They used to do it for free. Just pay for all of the shipping. If it is the oops, I dropped it again meter, no one cares. Those are a proof of concept tool and are meant to be kicked around, unlike the $300 plus meters that generally stay in their hard cases. Ever drop a Meger? That's an expensive oh sh#t! :-)
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On Wed, 11 Dec 2013 17:48:53 -0500, Stormin Mormon

I forgot that I'd given one to two or three friends, just because I thought they should have one.
I also gave even more of them the HF headlamp when it was on sale real cheap, but that might not have been such a good idea. If they don't use it, the batteries will leak. (and I don't even use mine.) And a few years later, LEDs got good enough to make a better light (still with batteries that might leak.)
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On 12/12/2013 5:05 AM, micky wrote:

Years ago, Nite Ize had LED conversions for mini mag flash light. They fit nicely into the black and yellow HF head lamp. The one that takes two AA cells. Makes for a good light, with AA cells that last longer than AAA cells. Just have to pull out the bi pin bulb, and break out the provided reflector. Fits nicely into the lamp with the Nite Ize reflector inside the HF plastic lens.
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On 12/11/2013 2:42 PM, Larry W wrote:

Maybe...but I'd shy away from the free ones if it's your only meter. I picked up one free. I was gonna throw it into the car, but decided to check it out. Shorted the probes on ohms. Reading varied around 500 ohms. OOPS!! Took it back. "sorry, it was free, not guaranteed." "I guess I got what I paid for, GRRRR!" "OK, go get another one."
This one is much better, but still crap. there are a lot of much better ones on sale at sears, home depot etc. for under $50.
One handy feature missing on cheap meters is the temperature function. Make sure it comes with the temperature probe.
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Start with the Harbor Freight - freebee or very low cost - under $10.00
A lot will depend on what you want to measure. I have a farily expensive H P multimeter, but use the HF cheapie 00% of the time, I don't need the incr eased accuracy very much. Just, is the circuit activated, is it 6V or 9V o r 12V? For these levels of sophistication, you don't need more than a HF.
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My opinion:
Must-haves: AC volts to at least 300 V DC volts to at least 100 V AC and DC amps to 10 A, 15 A, or 20 A Ohms Continuity beeper (might be part of the Ohms function) Detachable test leads
Nice-to-haves: Auto-ranging "Smart" ohms mode that will flip over into volts mode if you accidentally probe a live circuit Backlit LCD Easy-to-get fuses Easy-to-get batteries Rubber case or holster Hooks, straps, stands, etc. Extra test leads, alligator clip attachments, etc.
Rationale: Those voltage and current ranges will handle anything that a mild- mannered homeowner will want to measure.
The continuity beeper is useful to figure out if a wire is broken or shorted to another wire, or if an (unpowered) switch is closed or open, without having to look at the meter.
The detachable test leads are because the leads *will* get beat up if you use it a lot. 99% of meters use standard "banana" plugs on the test leads, so any set of replacement leads will fit. This is kind of an advanced use, but if you have a situation where you want to wire the meter in for a while, you can buy banana plugs on your own and make a custom set of leads.
However, detachable leads do make the meter more bulky; the "pocket" meters tend not to have detachable leads. If you only use it once a month or less, detachable leads are not such a big deal.
Auto-ranging means you just have to pick (say) "AC Volts" or "Ohms" and the meter figures out the rest. Manual ranging means you have to choose between (say) 4 V AC, 40 V AC, and 400 V AC ranges. It will say on the package if it's auto-ranging, and also the big round switch on the front will be simpler (fewer positions).
The backlit display is easier to read in the dark, which includes the nooks and crannies of your furnace or washing machine. It uses a little bit of battery life, though.
"Smart" ohms mode is because if you try to measure resistance on a powered circuit, at best you'll get the wrong answer and at worst you'll blow up the meter. Some meters detect this, beep, and flip themselves over into measuring volts instead (which is safe for the meter).
Most all meters will have at least one internal fuse and a lot of them have two. Eventually you *will* blow one of them, probably the amps one. If it is a 15 A or 20 A ceramic 0.25" x 1.25" fuse, every Radio Shack, hardware store, and electronics store in the US can supply them (those fuses also get used in microwave ovens). If it's some weird size of fuse, you'll have to go to an electronics store or order online. You may have to look this up online; the packaging will say "fused for protection", but the fuse *size* is probably only in the owner's manual. Sometimes you get a spare fuse with the meter when new.
Most meters take a 9 V battery, but some take AAs or AAAs, and a few take oddballs. In general the battery will last for at least several months, and probably several years, so this isn't a super big deal. But it's nice to be able to scrounge a battery from something else if the meter goes dead at an inopportune time.
The case, holster, extra test leads just make it nicer to use, but aren't *required*.
Tips:
If the test probes aren't already like this, it can help to cover all but the last 1/8" (3 mm) or so of the metal probe tip, to avoid shorting it out on nearby wires. You can use electrical tape, heat-shrink tubing, or even stripped wire insulation if you can find some that is a good force fit.
When you first get it, practice on some stuff you know the voltages of, like flashlight batteries, a car battery, wall adapters for small electronics, and stuff like that. You can even (very carefully) measure your line voltage by sticking the probes in an electrical outlet.
If you get a manual-ranging one, and you have no idea what the answer is going to be, always start on the highest range and work down. This is less important than it was for an analog meter, but it's still nicer for the meter to not ask it to measure something out of range.
A lot of time, the amps ranges will require that you move the red lead over to a different socket. This is fine, but the *SECOND* you get done using that range, move the red lead back over to its regular socket - don't wait until later to move it back. The reason is that in the amps range, the meter is nearly a dead short. It's *easy* to measure current and then try to measure voltage without moving the lead back, and blow the fuse in the meter. I've watched it being done and I've even done it myself.

The one I use around the house is a Radio Shack 22-805, which I bought around 1999 or 2000 because of its computer connection, but I don't use that feature much now. It is a rebadged Metex meter. In Radio Shack's current lineup, the 22-813 ($40) or 22-075 ($45) might do what you want. Their 22-182 is a "pocket meter" style that is on sale for $20; that one will get you through a lot, but if I was going to buy only one meter from Radio Shack, I'd go for one of the other two.
My "daily driver" in my field toolbox for a long time has been a Sperry DM8400, which I bought probably at Home Depot in about 1997. The closest meter to that in their current lineup is probably the DM5300, which is about $80. Their lower-priced meters may be worth a look if they are easily available in your area.
I used to work with college students and they were unable to kill the two Fluke 12 multimeters we had, even though they tried. The only odd thing I ever noticed about these was that when the "low battery" indicator came on, the calibration would be off; replacing the 9 V battery made everything work right again. The closest current model is the Fluke 113, but it sells for about $120; I don't think they have any meters under this price.
I hope this helps!
Matt Roberds
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On Thu, 12 Dec 2013 09:17:33 +0000 (UTC), snipped-for-privacy@att.net wrote:

I would lower this to Nice to Have. In 45 years, I've measured current 4 or 5 times.

Well, the cute little meters, maybe 1/2 inch thick by 3 x 4 inches, that one can carry in a shirt pocket while viisting friends have permenently attached leads. It's worth it to me so if I'm there for dinnner and they have electrical problems, I can whip out my meter, before my host can even get his from the workshop (if he even has a workshop). This hasn't happened often, actually never, so the leads aren't close to wearing out yet, but like my horse Trigger, I like having it with me.

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I usually end up measuring current when I'm messing around with cars - watching a battery charge, seeing how much current some accessory is drawing, stuff like that. That's why I spec'd the "high" current range. I haven't done it much on line-voltage AC; the times I have, I either used a clamp meter, or a Kill-a-Watt portable kWh meter. As others have noted, line-voltage AC stuff is more of a "it works or it doesn't" thing.

I firmly believe that as long as you have a tool with you, nothing that you can fix with that tool will ever break.
Matt Roberds
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I was trouble shooting a car. Battery kept discharging. I attached ammeter into battery connection. After computer sleep, everything was good for a while. Then it would keep drawing current at intervals. After sitting in car I heard clicks. Click found to be coming from trunk. Bad radio antenna contacts trying to pull down antenna. Solution, pull relay with antenna extended.
Greg
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On Wed, 11 Dec 2013 05:22:12 -0800, Jennifer Murphy

BTW, afaik all meters cheap or expensive, unless maybe it was home-built, have a clever circuit, (whose name I forget. It looks like a 4-sided diamond) , that makes the read-out the same, even when the voltage of the battery inside is going down. When the battery is almost dead (1.3 or 1.4 volts for a nominal 1.5 volt battery) it won't work but if it's 1.47, which might be 80% discharged, the reading should be the same as with a new battery.
Meters don't use much current, so they might work with batteries that don't work in a portable radio with an actual speaker. (radios that drive headphones don't need so much power so I'm not comparing with them.)
I'm sure some people here will take issue with some of this. It's true that my numbers are only educated guesses.
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wrote:

It took 4 1/2 hours but it came to me. It's called a Wheatstone bridge. http://en.wikipedia.org/wiki/Wheatstone_bridge
A) It uses the values and ratios of 3 known resistors to measure an unknown resistance, and in a meter, since the ratios don't change with voltage, the value of an unknown (external) resistance, is not dependant on the votage of the battery.
However the url above only says "Variations on the Wheatstone bridge can be used to measure capacitance, inductance, impedance and other quantities," and "The concept was extended to alternating current measurements" and doesn't mention voltage or DC current.
In fact, a few lines up it says "If all four resistor values and the supply voltage (VS) are known, ....the voltage across the bridge (VG) can be found by working out the voltage from each potential divider and subtracting one from the other. " which implies that voltage measurements are dependant on knowing the battery voltage.
So maybe I was wrong, except wrt resistance and AC current (and very few meters measure AC current.)
^^Impedance is much like resistance, measured in ohms, but it's used for coils and caps, where it depends on frequency. If the frequency is 0, like it is with a battery, caps will have infinited impedance, but coils will have the impedance of a resistor made with the same length of the same wire.
Still, I've never read a warning that measurements are inaccurate as the battery weakens, and the guys who design these things are pretty clever, so I'm not giving up on the notion that, until the battery is almost dead, the voltage of the battery doesn't matter. Anyone know?

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On 12/12/2013 10:34 AM, micky wrote:

For what it's worth, I'm using NiMH rechargeable batteries in my Fluke meters (1.2V nominal/cell as opposed to 1.5V/cell for alkaline) I'm using a Tenergy Centura brand 7 cell/8.4V "9V" battery instead of the 6 cell 9V alkaline specified; I have noticed no inaccuracies in resistance readings.
I'm also using a Tenergy Centura D cell and similar "9V" battery in my Simpson 260 with no issues, but on the 260 you need to zero the meter every time you change resistance ranges anyway. However I suspect that it uses a similar circuit as the relative knob position ends up about the same for both alkalines and NiMH.
As an aside I've been happy after switching over to NiMH; hopefully I will not buy any more cells/batteries unless I buy more devices for a good long time.
nate
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Jennifer,
Most cheap digitals work fairly well. Look at the leads. You want robust leads and good probes. I also favor auto-ranging. Spend around $30.
Dave M.
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to

if

Digital is easy to read but unless I'm doing hi spec work, I prefer the old analog type. For one think, it's easier to see changes in reading with the needle swinging back and forth. If you every want to check the engine error codes, I can be difficult to do it with a digital meter.
$5-30 should get you something decent. I bought one at Radio Shack about 10 years ago for $25 that I could connect to a computer and record a time trace.
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