Help with new DMM - Page 1
Forum section: electronics / beginners

author: zorthgo
author_rank: Regular Contributor
timestamp: July 08, 2013, 09:07:39 pm
content: Hi guys, recently it was brought to my attention that I can't keep relying on my little $20 Radio Shack DMM, and I need to shell out the money for a proper DMM. At my level of electronics involvement the only things I've been using the DMM for is to measure Volts, Amps, Ohms, and Capacitance. I know DMMs are used for more advanced things but I haven't reached there yet. I would like to get a DMM that I won't surpass it's abilities pretty quickly, but also that it isn't super overkill. I have 3 in mind but I don't quite know how to choose (or if there are better options for a beginner like me). Below are the DMMs I was looking at:Manufacture Model Price ResolutionRigol DM3058 $695 240,000B&K PRECISION 5491B $409 50,000Agilent U3402A $641 120,000Please let me know what you think. Also if you have any alternatives!

author: zorthgo
author_rank: Regular Contributor
timestamp: July 08, 2013, 09:15:27 pm
content: Also, theRigol DM3058E $449 240,000Frankly I don't know the difference between the DM3058E and the DM3058.

author: Lightages
author_rank: Unknown
timestamp: July 08, 2013, 09:21:27 pm
content: Yes, overkill unless you really need a bench meter. I would suggest you read the following:https://www.eevblog.com/forum/reviews/a-list-of-recommended-multimeters/https://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/But in general I would recommend an Agilent U1272A, or a Brymen BM869 or BM525 or BM257, or Fluke 87V. These would be the best bets in a good higher end handheld meter. If you can get one I would seriously consider the BM869 as it really is the best bang for the buck. It can be purchased fromwww.tme.eufor around $240 plus shipping which is around $30 I think by UPS. You can't go wrong with the Fluke or Agilent but they cost much more.Is there a specific reason you are only looking at bench meters?

author: IanB
author_rank: Super Contributor
timestamp: July 08, 2013, 09:43:43 pm
content: Quote from: zorthgo on July 08, 2013, 09:07:39 pmI am more than happy to use my $50 Radio Shack DMM on my electronics bench (the model 22-812). I have two of them.If you are just starting out and you don't go sticking the probes in a mains socket, then you really don't need to spend more than $50 on a DMM, and even $25 would probably do fine. Just like if you were starting out at tennis you wouldn't spend $300 on a tennis racket.

author: c4757p
author_rank: Super Contributor
timestamp: July 08, 2013, 09:49:41 pm
content: Extech EX-430, $70Extech EX-330, $53B&K Precision 2704C, $56Many others...I've seen some pretty shameful crap for $20 at RadioShack, but that doesn't mean you need to start looking at 20x that price and above for something good!BTW, I own the B&K 2712 (twice the cost), and my only complaint about it is the nonstandard input impedance (seriously, what the hell is 2.3 Meg?). It's an excellent meter. I suspect the 2704C is similar.

author: madshaman
author_rank: Frequent Contributor
timestamp: July 08, 2013, 10:07:47 pm
content: All I'd say is, know what additional features you'll be shelling out money for and if you'll use those features.If you have the need for a 250,000 count meter, then you'll know it.May I ask what your radio shack meter is unable to do for you in the here and now or in the near future?Also, if you *do* need a ridculously accurate bench meter, consider a used HP3457 or something. They are *exactly* as good as a new meter (could even argue "better" in some cases).

author: zorthgo
author_rank: Regular Contributor
timestamp: July 08, 2013, 10:33:50 pm
content: @madshaman, basically the only thing that my little DMM doesn't do (that I am aware of) is that it doesn't have the ability to measure capacitance. I also, don't really trust it's voltage measurements (psychologically I trust the bench DMM better). @IanB, I not really planning on probing any main!I am actually going to use it for low power analog/digital circuits (such as microprocessors, transistors, opamps, sensors, etc). @Lightages, I guess I don't actually need a bench DMM. It's just that at school all out DMMs were bench, so I feel more comfortable with them.. I guess!

author: c4757p
author_rank: Super Contributor
timestamp: July 08, 2013, 10:44:25 pm
content: You can easily find used bench DMMs for a good price that are often still accurate. I buy, sell and repair used DMMs and scopes quite frequently, and with both types of instrument, I very rarely see anything that still works and isn't still spot-on. After a few cal cycles, it's pretty much done drifting around. It's only the broken stuff that often has to be adjusted after parts are replaced. If you really like bench meters, I suggest that. The old Flukes are great, just watch out for failing LCDs.

author: c4757p
author_rank: Super Contributor
timestamp: July 08, 2013, 10:48:28 pm
content: Quote from: zorthgo on July 08, 2013, 10:33:50 pmBah.... the last time I measured capacitance on a DMM was... hmm... well, I think I was testing a meter to see if it worked right! Caps rarely fail by changing in capacitance. 99% of the time, its value is on the label.As for voltage accuracy, in my experience the cheap ones are a gamble. Some are very accurate and some are not. I've seen more than one that was clearly adjusted incorrectly in the factory. Many people are just fine with using a $20 RadioShack meter, I am not.You can get higher accuracy specs in a bench DMM, but a decent handheld will be more than enough for almost all uses. (Still, as I mentioned above, I do understand the desire to have one for other purposes.)

author: IanB
author_rank: Super Contributor
timestamp: July 08, 2013, 10:55:22 pm
content: Quote from: zorthgo on July 08, 2013, 10:33:50 pmThen learn how to verify them using some standard resources. Get two different $25 meters and compare them. How close are they? The difference between their readings will give you an estimate of the accuracy of either.Test a brand new alkaline AA cell (should be about 1.6 V). Test a new 9 V alkaline (should be about 9.6 V). Test a new 9 V heavy duty cell (should be about 10.0 V). Measure the forward voltage drop on some known LEDs (the Vf will often be given on the data sheet or packaging).Learn to "feel" what voltages should be what, don't just put blind faith in instruments.Also remember that a DMM is a luxury not known to hobbyists of the past. A few decades ago we made do with analog meters and we got on fine with those.

author: IanB
author_rank: Super Contributor
timestamp: July 08, 2013, 10:59:23 pm
content: Quote from: c4757p on July 08, 2013, 10:48:28 pmMost of my inexpensive meters have been that way, but on the plus side I learned how to adjust them to my satisfaction. Mostly they seem quite stable and they don't appear to drift after I have adjusted them.On the other hand, if your meter is 0.5% out from the factory are any of your circuits going to fail to work?

author: cthree
author_rank: Frequent Contributor
timestamp: July 08, 2013, 11:30:10 pm
content: Damn. You can get a used Agilent 5 1/2 digit bench meter for under $100. A Fluke 87-3 for about the same price. Don't spend more than $100, you won't get your moneys worth. Buy two $100 meters so you can measure amps and volts simultaneously and cross check for confidence.http://www.ebay.com/itm/Hewlett-Packard-HP-Agilent-3478A-3478-Multimeter-4-wire-Ohm-Measurement-/221249524148?pt=LH_DefaultDomain_0&hash=item33837fd1b4http://www.ebay.com/itm/HP-Hewlett-Packard-Agilent-3468B-Multimeter-106-126V-/280901319461?pt=LH_DefaultDomain_0&hash=item416705fb25I bought two good condition HP3468B meters for $70 and $80 each. Watch for them, don't pay the screw me now prices. You can buy for half at auction. All you need for these are some shielded banana jack adapters, these use standard 4mm banana jacks so won't accept dmm probes without adapters.http://www.ebay.com/itm/Fluke-Meter-87-III-/221248994561?pt=LH_DefaultDomain_0&hash=item338377bd01http://www.ebay.com/itm/FLUKE-87-III-TRUE-RMS-MULTIMETER-WITH-CASE-VERY-GOOD-CONDITION-/141009730905?pt=LH_DefaultDomain_0&hash=item20d4d5bd59&vxp=mtrhttp://www.ebay.com/itm/FLUKE-87-III-Excellent-Condition-TRUE-RMS-INDUSTRIAL-MULTIMETER-/111113594830?pt=LH_DefaultDomain_0&hash=item19dee2e7ceDifference between 87-3 and 87-v is thermocouple temperature support. Lifetime warrant, waterproof, indestructible. Don't let dirt throw you. These meters are the kind of kit that is used in dirty places. Clean it. You'll use it for life.

author: Lightages
author_rank: Unknown
timestamp: July 08, 2013, 11:38:15 pm
content: Based on what you have said so far zorthgo, I Think you should consider the Brymen BM869. It will do everything you need, and still be safe for high energy circuits in the future. If you prefer to spend less, then the BM257 or the Amprobe AM-270 which is available in the US directly fromwww.testequipmentdepot.comfor around $90 plus shipping. The only bad thing on AM-270 meter is its back light.

author: madshaman
author_rank: Frequent Contributor
timestamp: July 09, 2013, 12:54:03 am
content: If capacitance it what you need, you might also consider an LCR meter.I do on occasion end up measuring capacitance, it *is* useful, but only you know if it's useful to you.I second the recommendation of the Brymens and another choice is the BM867, compare to the 869 and you might find the extra money for the 869 isn't worth it for you.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 01:23:32 am
content: @madshaman & Lightages, looks like the BM869 is in the lead with two votes!@cthree, I thought about looking at ebay for a used one. But since I am a newb still, I would rather get something new that I am sure is calibrated and working correctly. Because I would not be able to spot a faulty meter and it would only confuse me when doing my studies. But thanks for the suggestion!

author: c4757p
author_rank: Super Contributor
timestamp: July 09, 2013, 01:39:15 am
content: Quote from: IanB on July 08, 2013, 10:59:23 pmNo, of course not, but the more precise it is, the more you can do. Many circuits could be successfully built with a meter out by 20%. OTOH, one of my biggest hobby interest areas is test and measurement, and I like to build things to a decent level of accuracy because 1) I'm a perfectionist, and 2) I want to be able to rely on the things I've built just as much as the things I've bought.I also repair a lot of test equipment for resale, and I like to be able to get it within its specs. I personally consider it false advertising to sell something as "working" if it doesn't meet its spec sheet.Obviously, though, you only need as much accuracy as (or slightly more than) the circuits you plan to build or work with. The problem I have with these cheap multimeters is that they oftendo not meet their spec, so a beginner with an interest in measurement accuracy could easily be misled by reading the spec sheet and making the somewhat reasonable assumption that the brand-new meter would match it.

author: Fsck
author_rank: Super Contributor
timestamp: July 09, 2013, 02:06:26 am
content: Quote from: madshaman on July 09, 2013, 12:54:03 amDitto. BM869 is an excellent value. Though the BM867 is actually an even better value if you don't need the additional features of the 869.I use my 869 the most out of all my meters, especially when I don't want to wait for my 3457 to stabilize completely.

author: cthree
author_rank: Frequent Contributor
timestamp: July 09, 2013, 02:28:11 am
content: Fair choice, but still, don't spend too much. The recommendation about sounds reasonable and they are both knowledgeable users. I'm sure you would be happy with it. Still, buy two meters. I use two all the time.

author: Fsck
author_rank: Super Contributor
timestamp: July 09, 2013, 02:44:45 am
content: If he can do the 400-700 for those bench dmms, he can grab an 869 and another meter (like an 867, possible 869 depending on shipping and such)

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 03:08:26 am
content: Good Idea Fsck, for the second DMM I think I am getting the EXTECH EX430 as c4757p suggested!Thanks for the help guys! Much appreciated!

author: Rick Law
author_rank: Super Contributor
timestamp: July 09, 2013, 03:43:37 am
content: Quote from: zorthgo on July 09, 2013, 03:08:26 amMay be get two of equal quality?Let me explain my frustration and see if that annoying feeling may get you too.What I found most annoying with multiple DMM is: I am always temped and switch to my better DMM to "there" and see what the reading really is "there". So it is like as if I have just one.I have 4, a cheap DT830B (2000 count), a cheap 2000 count Radio Shack, a 4000 count Radio Shack, and a 22000 count UT61E.I rarely swap out the DT830B because I calibrate it to be +-1 digit from my UT61E for the ranges I use. The two RShack are not calibratable. I know from experience both are +- 3 to 5 mV (and +- 3 to 5 count whichever is larger). So, when I have a four-meter arrangement such as: In-Volt, In-mA, out-Volt, out-mA. I often end up thinking: what really is the In-Volt exactly, let me switch my 22000 count meter to there and put the RShack here. Wait, what is really is the current, let me switch my 22000 count meter there and put the RS there. So I am swapping back and forth as if I have only one DMM. Well, actually as if I have just two. After I calibrated the DT830B, it tracks the UT61E well and I feel I get the "right reading" even while it has only 2000 count. So what really bugs me is not the accuracy or precision but the inconsistency when the two RS are not consistent with itself, and not consistent with the other meters. Small delta at merely +- 3-5 counts but it bugs me enough that I don't feel I have a reading.A bit silly to be bothered by consistency so much, I admit.

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 04:12:33 am
content: Quote from: c4757p on July 09, 2013, 01:39:15 amAs a perfectionist, I also like to see things looking right:But to be reasonable, after the fourth digit or so I can accept a small amount of deviation

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 04:22:06 am
content: @IanB, now I get why you didn't mind you Radio Shack DMMs! After seeing the picture you will understand why I need a real DMM!

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 04:24:54 am
content: @IanB, Question... Did you make your own banana plug cables for you power supply? Where did you get the banana end clips? Do they work as well as the store bought ones? I need some cables fast would be cool to make them!

author: c4757p
author_rank: Super Contributor
timestamp: July 09, 2013, 04:26:07 am
content: That one might not be too bad, actually, just don't use it on high energy circuits. (A general rule is this: If you can't afford a proper name-brand electrician's meter to work on high energy circuits, you can't afford the hospital bill when you screw up either. Stay away. - Might not be applicable in countries with real health care.) Unless I'm mistaken, from that picture it appears to be one of those little "pocket" meters? They're kind of cool, even "Hooray for Fluke" Dave said he recommends one, and from what I've seen they're usually not total pieces of shit.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 04:40:30 am
content: @c4757p, your right, that is one of those pocket meters. They are convenient, because I just toss them in my electronics bin and take them to school (or wherever I am working on a project). Don't worry, I don't plan on doing anything with high voltage. I just want to work with low voltage electronics... you know, your average analog sensors feeding into a Pic, Ardunino, etc. You know, basic electronics!But I think it's time I should get a decent DMM. (And I totally understand the Health care remark!)

author: Lightages
author_rank: Unknown
timestamp: July 09, 2013, 04:44:42 am
content: Quote from: zorthgo on July 09, 2013, 03:08:26 amI have a much different opinion of Extech EX series meters. They rather unreliably built. Parts falling out because they weren't soldered correctly, easily broken selector dials, etc. I seriously would never buy an Extech EX series meter. Please consider the Brymen BM869 and the BM257 if you want two meters, or the BM525 to have as an alternative. The BM525 does internal logging up to 20 times a second with a memory of up to 87000 points. Of course to read back all that you would need the data cable. The BM257 makes a nice compact rugged meter with the addition of a non-contact voltage detector to let you know if you have a live wire without touching it.Or if you are willing to never use it on anything other than electronics then another consideration could be a Uni-T UT71D. It also has internal logging for a low price but it has some other poor qualities.Search for reviews for all of these here, including the Extech EX series and you will learn quite a bit.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 04:52:55 am
content: @Lightages, I know, I probably should have waited a little bit more. But I already bought the Extech EX 430 on ebay (it was only $48). At that price, if it breaks, I can just get another! As long as it is accurate!

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 04:54:19 am
content: @IanB, you like everything to look right... You probably would die if you worked with the equipment I have right now! lol!I am guessing it is the power supply that is showing the wrong reading.

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 04:54:25 am
content: Quote from: zorthgo on July 09, 2013, 04:22:06 amYeah, that's a $2.99 DMM. At some point there is a price to pay for cost cutting. Even so, such bargain basement meters can still be serviceable as long as you check them against a known reference before you use them:We see here that 10.0072 V is between 10.00 and 10.01, so the lower resolution meters are undecided and they split the difference.(Note: I adjust my meters to make them read that well. They won't necessarily do that right out of the box.)

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 04:59:00 am
content: Quote from: IanB on July 09, 2013, 04:54:25 amYou said you adjust the meters yourself. Are there any tutorials online that I can learn to calibrate them? Is it something that a beginner could do?

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 05:00:33 am
content: Quote from: IanB on July 09, 2013, 04:54:25 amAlso, I last adjusted all those meters at least a year ago. Even a $2.99 Harbor Freight special will hold its calibration without much drift once correctly adjusted. The main problem with the HF cheapies (and it's a big one) is the rotary switch. The contacts oxidize over time and make the meter reading go wild unless you turn the dial regularly to keep the contacts clean.

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 05:11:41 am
content: Quote from: zorthgo on July 09, 2013, 04:59:00 amYes, adjusting inexpensive meters is easy and is something anyone can do. If you open them up you will usually find a trim pot inside marked "DC V" or something similar. You need a reliable voltage reference such as theDMMCheckor another meter of known accuracy. You just adjust the trim pot until the reading matches expectation. (Careful with the adjustment, it only needs tiny movements.)The advantage of inexpensive meters is you can do this adjustment without much fear, whereas you wouldn't dare touch the adjustments on an expensive meter like a Fluke or an Agilent.When you play with meters you will find that 3.5 digits of accuracy is stable and readily achieved. It's the 5th, 6th and more digits that start becoming a challenge. Luckily most inexpensive meters don't have so many digits to worry about, and neither do normal circuits care about such accuracy.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 05:30:17 am
content: @IanB, cool! Thanks for the instructions. I can't wait till I get the DMMs so I can mess with this one!

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 05:34:16 am
content: Quote from: zorthgo on July 09, 2013, 05:30:17 amNote, I'm not suggesting you try to adjust a brand new meter away from its factory settings unless (a) you know the readings are inaccurate, and (b) you consider the meter expendable in the event you mess it up. I'm talking aboutinexpensivemeters here.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 05:37:01 am
content: lol! I was talking about tinkering with my Radio Shack meter. I will leave the new ones alone for now!

author: Lightages
author_rank: Unknown
timestamp: July 09, 2013, 05:38:54 am
content: I would also recommend getting a DMM Check Plus fromwww.voltagestandard.comIt is well worth the investment.

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 05:55:18 am
content: Quote from: zorthgo on July 09, 2013, 04:54:19 amOK, 2.3 V vs 2.58 V. That's bad, about 10% off. Nothing should be that far out. Even basic meters should read within about 1% or so.What is the power supply? Do you have a third reference to check against? A borrowed more accurate meter perhaps? You really need to know whether it is your DMM or the power supply that is wrong.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 05:59:38 am
content: Well, basically, the only option I have is to wait until my new meter/ DMM tester to arrive. Everyone I know are programmers.so nobody has a meter. Unless I take the power supply to school and measure it with one of the trektronix DMM that we have there! If it is the power supply is there any way I can adjust it?

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 05:59:57 am
content: Quote from: zorthgo on July 09, 2013, 04:24:54 amYes I make my own power supply patch cables. I use 14 AWG speaker cable as it is nice and flexible and has fat copper inside it for low resistance. Banana plugs and alligator clips come from my local Fry's. A bit more expensive than an online merchant, but I can examine them before I buy so I know exactly what I'm getting.Soldering such items can be tricky, so expect a few retries before you get it right.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 09, 2013, 06:03:23 am
content: Cool, I have 14 AWG speaker wire here at the house, and I'll look for banana plugs at my local Radio Shack (we don't have a Fry's here in Boca Raton). I'll take any excuse to fire up my soldering station! OH YEAH!

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 06:04:03 am
content: Quote from: zorthgo on July 09, 2013, 05:59:38 amI've no idea if the power supply can be adjusted. But usually it would not be worth trying. Just check the readings against a good DMM and make a note of the differences. Then when you set the power supply you can compensate for the error accordingly.

author: c4757p
author_rank: Super Contributor
timestamp: July 09, 2013, 06:22:44 am
content: I had a similar one and it had easily accessible trimmers on the back of the display board.

author: IanB
author_rank: Super Contributor
timestamp: July 09, 2013, 03:01:22 pm
content: Quote from: mojo-chan on July 09, 2013, 10:31:50 amIn America all temperatures are in Fahrenheit. (All measurements are in feet and inches and all weights are in pounds and ounces. You get used to it.)

author: Fsck
author_rank: Super Contributor
timestamp: July 10, 2013, 12:53:46 am
content: Quote from: IanB on July 09, 2013, 03:01:22 pmNot if you're a scientist.Every american academic journal/paper/etc that I've ever read uses SI.

author: c4757p
author_rank: Super Contributor
timestamp: July 10, 2013, 01:02:00 am
content: Quote from: IanB on July 09, 2013, 03:01:22 pmThis "X and Y" thing is retarded. I had a good laugh back when my dad was remodeling our old house, and he'd always struggle with simple addition and subtraction of measurements in feet, inches and sixteenth-inches, and then he refused my suggestion to just measure everything in decimal inches because it'd be "too confusing".The fact that we don't measure in feet, inches and bees' dicks shows that people can handle fractional inches. So why do they think they need this idiotic mishmash of units??We do thiseverywhere, too. I also remember my mom scurrying around the house once looking for a tablespoon to measure with because a recipe called for "1 tablespoon plus 1 teaspoon". (Why there was none to be found in a kitchen is beyond me...) 1T + 1t = 4t....

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 01:02:55 am
content: I agree with Fsck, In college we also use the SI unit. I am a CE major and have never used anything other then the SI unit in school.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 01:22:09 am
content: Hey IanB, I just couldn't wait until I got the DMM I bough online, so I went out and got one of the same DMM as you have on your picture. My question is, does it have a back light for the screen? I couldn't find anywhere to turn it on.

author: IanB
author_rank: Super Contributor
timestamp: July 10, 2013, 02:24:55 am
content: Quote from: zorthgo on July 10, 2013, 01:22:09 amYou got the 22-812 with the PC interface? That's a nice meter.It has no backlight, but I have never needed one for electronics. If my workbench is too dark to see the meter it is too dark to see what I'm doing...

author: ahnuts72
author_rank: Regular Contributor
timestamp: July 10, 2013, 02:30:53 am
content: Zorthgo no backlight I have 2 just like Ian's and I have no prob with them seem like solid meters of you recognize their limitations.I also have 1 of the pocket meterslike yours as well.Sent from my Milestone X using Tapatalk 2

author: IanB
author_rank: Super Contributor
timestamp: July 10, 2013, 02:39:14 am
content: Quote from: Fsck on July 10, 2013, 12:53:46 amYes the scientific community has to use SI because of the international readership, but the engineering world plows its own furrow. Interestingly enough, precision engineering is done in metric inches. You can get an engineer's rule marked in tenths of an inch, and accurate measurements are done in thousandths of an inch ("thou" in Commonwealth countries and "mil" in America).

author: mtdoc
author_rank: Super Contributor
timestamp: July 10, 2013, 03:51:24 am
content: Quote from: Fsck on July 10, 2013, 12:53:46 amAnd in medicine as well. Vital signs - temperature in degrees C, weight in Kg (though often translated into F and lbs for patients), blood pressure in mm Hg and lab test results reported in SI units.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 03:59:50 am
content: No backlight, not biggie. I was just wondering if it did have it but I just couldn't find that feature.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 04:02:30 am
content: @IanB, By the way, thanks for the instructions on how to adjust the meter. My pocket meter was just a tad off from the reading of the new meter. So, I adjusted it to match the new meter. Now I'm just waiting for the other meter to come in the mail, so I can match it with these two, and see if everything lines up!

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 04:31:14 am
content: Can someone tell me how to check if the meter's fuse got blown? I was trying to measure the amps with the new meter but instead of switching to mA (the actual reading was 65mA), I was reading it set to uA. At first it kept giving me some wierd numbers, but now it just stays at 00.00. Is there a way to pull the fuse and test it? Thanks!

author: ahnuts72
author_rank: Regular Contributor
timestamp: July 10, 2013, 04:56:46 am
content: Remove the back cover have to remove the fuses check for continuity.Watch out when u remove the back the extra fuses are at the top of the meter and will fall out.They are hrc in mine if I remember so can't tell if blown visually.Sent from my Milestone X using Tapatalk 2

author: IanB
author_rank: Super Contributor
timestamp: July 10, 2013, 05:01:11 am
content: Gosh, you're clumsyBut yes, you can open up the meter and see the two fuses inside it. You can pull them and test with the meter on the continuity setting. Luckily for you there are spare fuses included inside the case. Don't blow the other oneA good safety rule is always to measure current on the 10 A range (using the separate 10 A socket). Only switch to mA if you are sure you will be within the maximum current limit of that range.

author: c4757p
author_rank: Super Contributor
timestamp: July 10, 2013, 05:13:25 am
content: Quote from: IanB on July 10, 2013, 05:01:11 amI've blown DMM fuses exactly twice: once when I was ten years old and dicking around, I thought I'd measure the mains current. I distinctly remember intending to do that - not sure what ten-year-old me thought would happen, but whatdidhappen was that I came very, very close to pissing myself. That was when I learned to double-check around mains.(A sub-lesson about cheapass DMMs: the breaker tripped when I did that. This means that the circuit breaker, inherently a time-delay device, and a 15A one at that, cut out before a multimeter supposedly protected by a 10A fast-blow fuse. This should not happen.)The second time was more recently, when I had just bought my first "good" multimeter, with good fuses. (Not on mains this time.) My lesson was learned when I had to buy the replacement fuse. Not only are those damn sand-filled fuses pretty expensive as it is, but they used an uncommon type in that meter. And I was broke as hell, being a student and having just spent a large chunk of my moneyon that meter.Every time I switch a multimeter onto the current range I think of experience #2.Moral of the story: don't blow the second...

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 05:18:31 am
content: Thanks! I replaced the fuse and it is working fine... And to my defense, I am mainly a programmer (not counting the theoretical shit that I learned in school for CE). Working with these things on your own is way different than following the labs or solving the problems the teacher gives you in class. For example, I bought this RGB LED at radio shack, and I've spent the last 3 hours trying to get it to work, and the only thing I've accomplished was to blow my fuse! Pun not intended!

author: mtdoc
author_rank: Super Contributor
timestamp: July 10, 2013, 05:25:17 am
content: Quote from: c4757p on July 10, 2013, 05:13:25 amWhen my oldest son was about 4 and dicking around, he thought he'd measure the mains current with a bent fork. I'm not sure what he thought would happen but he did in fact piss himself.Thank goodness for the breaker.He's 7 now and whenever he is curious and starts poking around my lab equipment all I have to say is " remember what happened last time you .....? He immediately drops whatever he's picked up and takes a step back.

author: c4757p
author_rank: Super Contributor
timestamp: July 10, 2013, 05:26:50 am
content: Don't feel too bad, there are people in myEE class at school right now who probably couldn't figure out how to light an RGB LED. You'll get it eventually.Does it look like this?Connect the longest lead to the negative terminal of a 9V battery (or a variable power supply set to at least 5V), then connect the positive terminal to a resistor between 200 and 2000 ohms. Then when you connect the loose end of the resistor to one of the loose leads of the LED, it will light up.If the leads are all the same length, compare your LED to that picture (especially look at the size of the metal elements inside the dome) and figure out which one matches.When you connect multiple colors at once, they'll each need their own resistor.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 05:27:23 am
content: @mtdoc, that is so funny! I did the same thing when I was a little kid. The only difference is that I gave the fork to my little sister and told her to stick it in the socket. Good thing no one got hurt! lol!

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 05:35:17 am
content: @c4757p, Are you sure? I get it to light up (but only red), by connecting the positive voltage to the longest leg (the anode), and the other 3 legs to ground. I would think that as a diode, if you plug it the wrong way it doesn't work.The problem that I am having right now, is that I can't get the other colors to light up. The voltage at the LED only increase to a certain voltage (roughly 2.8V), after that only the amps increase. I set one of my resistors on fire by increasing the power supply voltage to high, when attempting to get the voltage past the resistor going into the LED past 2.8V. Driving me crazy!

author: c4757p
author_rank: Super Contributor
timestamp: July 10, 2013, 05:35:29 am
content: Quote from: mtdoc on July 10, 2013, 05:25:17 amI've always been completely unteachable with things like that... To this day, I still routinely burn myself on the soldering iron, cut myself on knives, and occasionally zap myself on HV-ish circuits. (Interestingly, all three feel exactly the same when they catch you off guard.) I am, however, an insufferable cheap ass, so I do learn from experiences that make me spend money.Considering stupid things we do when we're kids, I've also burned my lip on a light bulb and my knuckle on a toaster oven (still have the scar on my knuckle), shocked myself on a light socket, shocked myself on a half exposed plug, shocked myself on a damaged VCR that my dad warned me not to touch.... on and on...And now that I've grown up and I actually understand what was going on, I can remember even more situations that wereextremelyclose, in some cases to more than a little zap. I was one reckless child...And after all that, my parents still let me work on electronics. Possibly because I was too embarrassed by my idiocy to ever tell them what happened...

author: c4757p
author_rank: Super Contributor
timestamp: July 10, 2013, 05:38:47 am
content: Quote from: zorthgo on July 10, 2013, 05:35:17 amIt could be backwards from that.QuoteThey smell good, don't they?I just set one on fire too, so you're among friends. Are you connecting all three leads together? Like I said, they'll need their own resistors. If you connect them together directly, only the LED with the lowest voltage threshold (red) will light, because it'll keep the voltage from going above that to the next LED's threshold.Also - LEDs arenothappy with overcurrent. There's a possibility that you blew it.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 05:43:20 am
content: Are you telling me I might have killed my LED??? So that makes An LED, a fuse, and a resistor. All in under 5 hours? I must be setting a record. lol!

author: c4757p
author_rank: Super Contributor
timestamp: July 10, 2013, 05:49:47 am
content: When you're still trying to figure out the LED, stick to a 1k resistor and nine volts. That will definitely be enough (both voltage and current) to light it, and never be enough to kill it (or the resistor). There's no reason to drive it harder to get it to turn on, only do that once you have it working and it's not bright enough.When you finally want to choose resistor values, measure the voltage across the LED when it's lit (separately for each color). The current it takes will be (Vsupply- VLED)/R - don't let it go above 10mA or 15mA or so (even better, the datasheet maximum, if you have a datasheet). Then just choose by trial and error. You'll find you need different values per color for even brightness.Some multimeters can measure that voltage VLEDdirectly on diode mode, but some don't go high enough to measure LEDs (especially blue and white ones).

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 06:08:53 am
content: Thanks I got it working. YAY! I replaced the single resistor between the power supply and the cathode, with 3 separate resistors between the 3 anode and ground. By varying the resistor values I can vary the light color. I guess, that if I can replace the 3 resistors with 3 potentiometers I can vary the color on the fly! Is there any other way besides with a potentiometer? I would guess I could use transistors to turn the different legs on and off. Oh well, at least I can go to sleep. That LED was going to keep me awake all night if you hadn't helped me get it to work. THANKS!

author: AndrejaKo
author_rank: Frequent Contributor
timestamp: July 10, 2013, 09:26:26 am
content: Don't feel bad about burning (relatively cheap) components! You at least managed to set a resistor on fire.Last time I tried to do that, the damn thing was still within 5% of resistance value after being cooked at 25 V for 30 minutes and it was a 0.25 W 100 ohm 1% resistor! At least I managed to get it out of spec.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 12:44:52 pm
content: @AndrejaKo: Thanks! I am just chucking it up to growing pains. lol!@Everybody: By what I've heard so far from several people, apparently I shouldn't stick my multimeter in the wall socket to measure the "main" current. But why? If my circuit breaker is 20A and the multimeter is rated at 20A, in my mind the worst that could happen would be to trip the circuit breaker. Am I wrong?

author: AndrejaKo
author_rank: Frequent Contributor
timestamp: July 10, 2013, 02:34:15 pm
content: This is one of the things that come up a lot for no good reason.First, think what would you gain by measuring the mains current in the described manner? Assuming that you actually get a measurement (and that's a big assumption), all you'd get would be the short-circuit current of that single plug, which isn't going to be very helpful.Now time to scare you straight!First, let's think a bit about realistic system: Your multimeter is rated for 20 A, but under what conditions? Did you completely read the manual? Did you fully understand the specifications there? are you 100% sure that you did, if the answer to previous question is yes? Would you bet your life and lives of people around you on that?Let's take a look at what happens when you're measuring current: First, your multimeter is definitely using some sort of resistive element and when measuring current is actually measuring voltage across that element. That may be a precise resistor or it could be even just a metal bar of (more or less) known resistance.When I stick one my meter's probes into amperes socket of my other meter (also rated for 20 A), I get around 0.5 ohms as resistance. Do that experiment yourself! Now let's assume for a second that the reading is correct and that resistance of my probes and my meter's socket is zero. If I were in the US and I connected that meter to mains socket to "measure the current", in world of ideal voltage sources, I'd have say 220 A flowing through that meter. That's 11 times the current it's rated for. If the probes had resistance of say 0.01 ohm, then they'd be dissipating around 485 W of heat just from that connection. The meter would be dissipating around 24 kW! You can of course see that in such conditions it would momentarily melt.On the other hand, you have circuit-breakers and hopefully fuses in the meter. That's all fine and nice, but!! the circuit-breakers have minimal time it takes them to respond and that time might be too long for your hands or whatever you're using to connect the probes. Next, we have the fuse in the meter. If that fuse is safe (and that's a big, great, huge and extremely dangerous assumption), it should burn out very quickly and open the circuit, hopefully before the rest of the meter vaporizes. Those fuses have maximum breaking current and maximum breaking voltage. You need to be sure that those numbers are realistic and that they will be sufficient for your case. There's a reason why you can buy a whole multimeter (or maybe even more than one) just for a price of a Fluke fuse.Next, you have all the imperfections along the way. I won't go too much into them, there are other members of this forum who are much more capable of providing relevant information. I'll just mention that in this case, you can expect lots o sparking when making connection, you can expect the multimeter fuse to explode, maybe even eat bits of the PCB with it. Good quality multimeters will often have some sort of blast walls inside, especially around fuses that are meant to prevent the explosion from escaping the meter's enclosure. They will also have specially designed seams, so as to reduce the possibility of explosion getting outside of the meter.And keep in mind: The time it takes for the circuit breaker to react is short, but the time it takes for the meter to turn you into a cripple is even shorter. And yes, I've heard of a guy who was scratching his head trying to understand why appliances work from a plug whose current reads as zero. You really don't want to try to find out if you're as lucky as he was.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 04:35:46 pm
content: Thanks for the explanation AndrejaKo! You painted a very understandable picture. It answered my question. I guess I won't go around sticking my probes into any sockets!

author: olsenn
author_rank: Frequent Contributor
timestamp: July 10, 2013, 06:00:46 pm
content: I would recommend the Rigol DM3058E. The only difference between the 'E' model and the regular DM3058 (apart from the price) is that the DM3058E lacks some of the connectivity options like LAN and GBIB (but USB is still present).Don't listen to people suggesting to buy a handheld meter. If you are an engineer and not a technician or a repair man, then you don't need portability. Bench meters are MUCH more precise and accurate, offer more features, and you can leave them on as much as you'd like without worrying about batteries dying. They support 4-wire resistance measurements and in many cases offer data-logging and remote connectivity.With the Agilent meters you are paying for the brand name; the Rigols are no worse spec wise (in fact they're often better), and they will last just as long (decades).

author: c4757p
author_rank: Super Contributor
timestamp: July 10, 2013, 06:04:34 pm
content: He will know when he needs a $450 multimeter.

author: olsenn
author_rank: Frequent Contributor
timestamp: July 10, 2013, 06:19:38 pm
content: QuoteAnd when he does know he needs one, he won't have one! A good engineer makes due with what he/she has to work with, but that's not an escuse to not acquire quality equipment to work with. If he is paying $10,000/year tuition for an EE program, then I think he is committed enough that a $450 lab purchase is reasonable. That being said, if you are just a kid who wants to muck around with blinking LEDs and that's it, stick with you cheap RadioShack POS

author: c4757p
author_rank: Super Contributor
timestamp: July 10, 2013, 06:26:17 pm
content: The Rigol's specs aren't even all that impressive, for a new bench DMM. If you really need that much accuracy and precision, buy a used-in-good-condition Fluke or HP and ask permission to bring it to school and compare it to the good ones in the lab.

author: IanB
author_rank: Super Contributor
timestamp: July 10, 2013, 06:31:57 pm
content: As I recall, our friend is not in an EE program, he is studying Computer Engineering and doing the electronics side as more of a hobby.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 06:40:02 pm
content: @IanB, you are correct. I am finishing both my CE and CS programs this fall. But the reason I took up this hobby is because I wan't to work with digital hardware (where I can use my programming skills as well as working with HW), so I've decided to change my master's enrollment to EE. Correct me if I am wrong, but from all I've read, most of the designing jobs (even digital one) usually goes to EE majors.

author: IanB
author_rank: Super Contributor
timestamp: July 10, 2013, 06:51:50 pm
content: @zorthgo: Don't take this the wrong way, but based on where you are now and where you want to go, you have quite a mountain to climb. Your technical knowledge evidenced in this thread is very weak for a college student.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 10, 2013, 07:06:09 pm
content: I understand what you are saying. That is because as a CE student the only time I have come in contact with analog circuits was when I took Electronics Lab I. We don't need to take all those other classes. But I've spoken to the E.E. advisor, and I will have to take anadditional4 classes to be able to get an EE masters degree. If I remember correctly they are Electronics II, Electromagnetic Fields and Waves, Control Systems 1, and I can't remember the other. Right now, my specialty is not analog circuits. Put me in front of a MP and some digital sensors and I am gold; ask me to program you a game, or a simulation no problem; as me to make RGB lights light up, and I might set something on fire (for now). Like everything else, I just need to play around with this stuff so I can match the theory with actual hands on practice (at least that is my theory).

author: Lightages
author_rank: Unknown
timestamp: July 10, 2013, 08:00:44 pm
content: A bench meter is nice if everything you want to measure is on the bench..... They also cost much more than a handheld. You can by to really nice handheld meters, safe ones, for the price of a decent bench meter.Want to measure the power rails on a computer sitting in a room? Well you disconnect everything can drag the computer out to the bench or you can just carry you handheld meter over to the computer. Need to measure something in your car? Something in your home theatre wiring? You get the idea. I am not saying that bench meters don't have their place but the name implies what they are for.It is better to have two reliable meters so that you can measure voltage and current too. Seeing as the OP doesn't have a good handle on some safety aspects of using meter the meter better help out and be a very safe meter. My previous recommendations take care of this consideration.

author: zorthgo
author_rank: Regular Contributor
timestamp: July 11, 2013, 02:25:12 am
content: @Lightages: Yeah, I've bought the two handheld already anyways. Too late to go back even if I wanted to. Besides, from what I've gathered from you guys for now I won't be needing anything that it can't do!

author: c4757p
author_rank: Super Contributor
timestamp: July 11, 2013, 03:00:57 am
content: Quote from: Lightages on July 10, 2013, 08:00:44 pmI guess it depends on what you do, but I generally find that it works well enough for me to just keep one handheld DMM around for the rare time when I want to move it. Otherwise my bench is stocked with a number of bench DMMs, which I find much more convenient for bench use to just keep on the shelf and use in place.I wouldn't buy one new, though, at least for home use. Mine are all used.