Advice on a new DMM - Page 1
Forum section: electronics / beginners

author: jaimeroldan
author_rank: Newbie
timestamp: September 19, 2011, 03:35:36 am
content: Hi guysThis is my first post here, and would like to say "Hola" to everyone.I'm an undergraduated Electronic Eng. , and i would like to buy a new multimeter.My budget is about a 100-120 bucks.Features in order of magnitud are:- Micro-Amps and Mili-Volts- Decent accuracy for dc volts and ohms- Relative Mode- Autoraging- Acceptable Capacitance acuraccy- Freq. measurement to at least 1Khz- Temp measurement (no a must, but a big plus)Pluses:- Computer Interface- True RMS- AC+DC (volts or/and amps)- Inductance or Transistor gain (hFE) measurementThank you all for advice

author: EEVblog
author_rank: Unknown
timestamp: September 19, 2011, 03:42:57 am
content: If you want PC interface for $100 or so, you'd be looking at the Chinese brands like Uni-TDave.

author: IanB
author_rank: Super Contributor
timestamp: September 19, 2011, 04:10:01 am
content: If you are on a budget you might put the Radio Shack 22-812 on your shortlist, details here:http://support.radioshack.com/productinfo/DocumentResults.asp?sku_id=22-812&Name=Search+Results&Reuse=NIt costs about $70 in Radio Shack stores typically, but it has in the past been offered at $50 for limited periods. It doesn't tick all of your boxes, but it hits many of them.You can either use the computer interface software provided, or I wrote a simple logging program for Windows you can get here:http://www.candlepowerforums.com/vb/showthread.php?261833-Playing-with-the-RadioShack-22-812-Meter&p=3326583&viewfull=1#post3326583My code will work fine on Windows 7, but the Radio Shack software may not. The interface protocol is documented so if you feel like it you can modify my code or write your own.

author: Tony R
author_rank: Regular Contributor
timestamp: September 21, 2011, 02:22:37 am
content: I once wanted a DMM with a computer interface, and i got one it cost me $80 or so after shipping, and i loved it for a while, but i found i never really used the computer interface part of it that much. and then it broke shortly after a year.I looked at the radio shack one, i ended up getting one online fromwww.circuitspecialists.com, and looking back i would not recommend them anymore.The radio shack one does not have an isolated PC connection, and it being a cheep DMM i would not trust it not to take out your computer.ultimately, i reconsider the PC interface requirement, its good if you want to test how a battery drains, but i don't think you will find any use for it any time soon. Im not sure how many low end DMM will have a uA range.I am a big fan of Fluke, the 89 is a good meter and hits everything in the required section (i got mine new for 314.44 on amazon.) No PC interface, is True RMS, does not have a AC+DC but its not hard to get that without the feature built in, and idk about anyone else, i don't trust the hFE tester on DMM, are you really going to use it that much anyways, plus what is hFE? its Ic/Ie, nothing you cant find without itYou may also find a used 189 or 187 on ebay for under or a little over 300, i know its above your budget, but it will do data logging and everything else you require.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 21, 2011, 03:24:40 am
content: Quote from: Tony R on September 21, 2011, 02:22:37 amAre you talking about the IRDA to USB modem ?If yes, some latest Mastech ones uses this too.

author: IanB
author_rank: Super Contributor
timestamp: September 21, 2011, 05:47:54 am
content: Quote from: Tony R on September 21, 2011, 02:22:37 amThat is not true. The 22-812 has an optically isolated serial port with a thick plastic shield separating the serial port module from the rest of the meter. There is no electrical connection between the two parts of the meter.Also the PC interface cable is included with the meter. I just looked at the (admittedly nice) Amprobe AM-270 and the PC interface is a $50 extra cost option.QuoteDoes it go tweet tweet then?I think you are being rather unfair. It is not an expensive meter compared to some, but the construction is tidy and the case is solid. For instance all the case screws are captive so you can't lose them and they screw into metal inserts. And it comes with spare fuses for the mA and A ranges included inside the case.Another thing, the meter uses a 9 V battery and the battery lasts forever. I just measured the current draw at 0.95 mA. I've had the same battery in there for months and taken hours of computer logging measurements and it still reads 9 V.

author: Tony R
author_rank: Regular Contributor
timestamp: September 21, 2011, 12:15:23 pm
content: Quote from: IanB on September 21, 2011, 05:47:54 amIt is always possible i am wrong, i do not see any documentation saying it is isolated, the serial cable hooks directly up to a standard dsub 9 connector, unless they have internal isolation which they should state if they do. Every other DMM i have found had a optical coupling between he meter and the computer. As far as i can see, this does not, and it is still going to take out a computer if that meter experiences any high transients. Can you please show me documentation as to this being electronically isolated?Quote from: IanB on September 21, 2011, 05:47:54 amYou know its one thing to debate and disprove on the facts of ones arguments, its another to point out simple spelling errors, yes I make a lot of spelling errors.

author: elliott
author_rank: Regular Contributor
timestamp: September 21, 2011, 01:38:38 pm
content: Quote from: Tony R on September 21, 2011, 12:15:23 pmI have one that is 10 years old, it is definitely optically isolated, I've had the thing apart numerous times to change fuses. The main board stays with the front half of the case, the serial port stays with the back half and there are no wires connecting them, just an LED.

author: IanB
author_rank: Super Contributor
timestamp: September 21, 2011, 03:23:35 pm
content: Quote from: Tony R on September 21, 2011, 12:15:23 pmYou can either go by my first hand knowledge stated above, having taken the meter apart and examined it, or you can believe some sales blurb found on the net somewhere. I am telling you it is isolated. The serial port module is on the back case of the meter, surrounded by a plastic shield, and connected only with an LED through the transparent plastic window. There is no electrical connection between the two halves of the meter.

author: SgtRock
author_rank: Unknown
timestamp: September 21, 2011, 06:45:48 pm
content: Dear IanB and Tony R:--It may be that your are both right. I am not inclined to disbelieve IanB's eye witness testimony. In as much as IanB's unit is 10 years old, perhaps Radios Hack has changed the design. Check out this current picture:http://www.bz1-img.com/images_customers/04/41/4972737_46353_raw.jpg--I have not yet figured out how to post a picture. If someone could point me to a post which explains how, I would appreciate it. In any case, it seems the current model 22-812 does not have optical, isolation. See the below link for the current manual:http://support.radioshack.com/productinfo/DocumentResults.asp?sku_id=22-812&Name=Search+Results&Reuse=NTo IanB:--In this case I have chosen to believe you and "my lying eyes"."Three weeks in the lab will save you a day in the library every time" Stanley Williams, HP LabsBest RegardsClear Ether

author: IanB
author_rank: Super Contributor
timestamp: September 21, 2011, 07:16:22 pm
content: Quote from: SgtRock on September 21, 2011, 06:45:48 pmIt is elliot's unit that is 10 years old. Both of my units are new.QuoteI can find nothing in any of the documents linked there that say "the 22-812 does not have optical isolation". In fact, as Tony points out above, optical isolation is a standard feature that you expect to find in a meter.QuoteIf you look at the exploded diagram at that link, the serial interface module is part 21 and the plastic insulating shield is part 6. There are no wires or connectors going to the serial interface module.QuoteYour confidence is heart warming, but unnecessary. It is widely documented across the Internet by owners of this meter that it has optical isolation. I am not the first to report it.

author: SgtRock
author_rank: Unknown
timestamp: September 21, 2011, 07:21:48 pm
content: Dear IanB:--Your answer is a nonsequitur. Sir, would you please look at the picture link I posted and tell me what you see?"Three weeks in the lab will save you a day in the library every time" Stanley Williams, HP LabsBest RegardsClear Ether

author: IanB
author_rank: Super Contributor
timestamp: September 21, 2011, 07:50:44 pm
content: Quote from: SgtRock on September 21, 2011, 07:21:48 pmI did look at the picture. It shows a meter that looks rather similar to the one I own alongside a collection of USB and Bluetooth adapters.You need to be more specific with your comments. What conclusion would you like me to draw from that picture?

author: gregariz
author_rank: Frequent Contributor
timestamp: September 21, 2011, 08:12:15 pm
content: I use the serial function rarely to log temperature over time but I have one of these when I dohttp://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_117373_-1It is also optically isolated, the aquisition rate is slow - but for my purposes that is fine.

author: SgtRock
author_rank: Unknown
timestamp: September 21, 2011, 08:38:17 pm
content: Dear IanB:I would expect you to draw the conclusion that I am an ass, and you would be correct. I was confused by the fact that your link to the manual is a dead link. The one I provided is working, but their is no legend explaining the parts in the exploded diagram. Also I can find no place in the manual where it says anything about optical isolation. But I did finally find a sale listing (see below) where it officially mentions optical isolation.http://milo.com/pc-interface-46-range-digital-multimeter--I am very glad I keep a civil tongue in my mouth as it makes eating crow so much easier. Finding no mention of isolation in the manual I assumed there was none. It it kind of an important feature to neglect mentioning.--"If it weren't for Philo T. Farnsworth, we'd still be eating frozen radio dinners. Johnny CarsonBest RegardsClear Ether

author: ziq8tsi
author_rank: Regular Contributor
timestamp: September 21, 2011, 08:49:55 pm
content: Quote from: Tony R on September 21, 2011, 12:15:23 pmQuite the reverse. Anyone buying a handheld DMM with PC interface should be entitled to assume that it is optoisolated. In the extremely unlikely event that the design is an accident waiting to happen then there should be very stark warnings to that effect all over the documentation. ("Keep hands clear of the lethal Dsub during use. Never attach the PC interface when the common probe is at any non-ground potential.")

author: IanB
author_rank: Super Contributor
timestamp: September 21, 2011, 09:37:39 pm
content: Quote from: SgtRock on September 21, 2011, 08:38:17 pmI didn't know it was a dead link, I've fixed it now. Thanks for pointing that out.QuoteIt is true there is no legend, but as I have taken the meter apart I was able to describe in my post which items on the diagram are the computer interface as an aid to the viewer.

author: Tony R
author_rank: Regular Contributor
timestamp: September 21, 2011, 10:12:53 pm
content: I shall admit that they it is optically isolated, it is not your standard isolation that most DMM have. I still stand by what i said earlier though. I would save the money and go for a good brand.

author: SgtRock
author_rank: Unknown
timestamp: September 21, 2011, 10:39:53 pm
content: To All:--Ding, ding, ding...The winner and still standing after ten rounds, by a KO, the Battling Brit from California, Ian the Bruiser B."Marconi invented the radio but he had to wait years and years till anything decent was on." Johnny CarsonBest RegardsClear Ether

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 21, 2011, 10:50:13 pm
content: Quote from: SgtRock on September 21, 2011, 10:39:53 pmAdd in the losses the original thread starter ... LOL

author: jaimeroldan
author_rank: Newbie
timestamp: September 23, 2011, 12:39:50 am
content: Well i'm here.But i didn't like how this thread turn out ...On topic ...I saw yesterday the Uni-Trend UT61C, for about 69 USD. Keep in mind that i live in Colombia (South America)It meets almost every single criteria, the downside is that it doesnt have true RMS, but well i can live without it.Theres a second hand fluke 189, for 320 USD, but its wayyyyyyyyy over my budget.I will keep searching!

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 23, 2011, 01:08:03 am
content: Well if you plan to work with battery powered devices, yes you do not need True RMS.

author: Tony R
author_rank: Regular Contributor
timestamp: September 23, 2011, 02:48:36 am
content: Quote from: ziq8tsi on September 21, 2011, 08:49:55 pmExcuse me for not assuming things are isolated, I for one do not assume the power is turned off because I want to cut a high voltage line, why would i assume its isolated? People get hurt all the time because they assume things.but on topic again, you mentioned the UT61C for 69 found one for cheaper...http://www.dealexcel.com/unit-modern-digital-multimeters-ut61c-dmm-dvm-dtm_p368.htmland if i am reading it right it will be $15 to ship it to Colombia so that makes about 65... so not much cheaperThis one is like the cheap one i used to havehttp://www.radiolabs.com/products/electronics/meters/digitalmultimeter.php,one thing with the one i used to have the continuity buzzer started to fail and the buttons lost there sensitivity, but maybe they fixed it in this one...Even cheaper:http://www.amazon.com/TekPower-TP4000ZC-RS232-Interaced-Ranging-Multimeter/dp/B000OPDFLMbut i do not see anything about optical isolation, and i don't want to assume that it is. On the plus side it gives a pretty good documentation if you wanted to write your own data collection software.http://www.amazon.com/Tekpower-Digital-Multimeter-Interface-DT9602R/dp/B000E2422Gis another one, but i do not see that it comes with software, and i do not see anything saying how it transmits the data.

author: Wartex
author_rank: Frequent Contributor
timestamp: September 23, 2011, 03:00:10 am
content: Quote from: jaimeroldan on September 19, 2011, 03:35:36 amAmprobe 38XR has ALL that (except hfe).

author: Lightages
author_rank: Unknown
timestamp: September 23, 2011, 02:23:58 pm
content: Based on my experience with UNI-T, I would not recommend them without reservation. I have a UT71E, their supposedly top of the line at around $200, and its accuracy was worse out of the box than my UT33C which cost me $16.I have no experience with Protek, but this one:http://www.tequipment.net/Protek608.aspis only $9 more than your budget and meets everything you want as far as I can see. It also seems to get some positive comments where I have been able to find any reviews. As far as its build quality and safety I cannot comment. If it actually meets its specifications and has decent build quality, it is a bargain.Oops: I see it does not have transistor HFE, but otherwise it has everything I think.

author: Unknown
author_rank: Unknown
timestamp: September 23, 2011, 10:15:53 pm
content: Note that searching for meters with hFE measurements will give you the lower quality meters with many features. The hFE sockets are rarely isolated very well, if you're measuring dangerous voltage, this voltage is also likely on the transistor socket. Few, if any, high-quality meters are able to measure hFE. Since the DC current gain is a function of collector current and temperature, it's not a very useful measurements. About the only thing it's good in my opinion for is figuring out the polarity, pin-out and if it's shorted. Two or three diode measurements will tell you the same, however, and will work with a much wider range of devices and packages (eg. TO-220, or SOT-23).

author: SgtRock
author_rank: Unknown
timestamp: September 23, 2011, 10:45:30 pm
content: Dear Alm:--Thanks for the spot on comments. I have always wondered why hFE was only on the cheaper meters.“I do believe that it's the first time in history that fire has ever melted steel." Rosie O'DonnellBest RegardsClear Ether

author: IanB
author_rank: Super Contributor
timestamp: September 23, 2011, 10:47:51 pm
content: Quote from: alm on September 23, 2011, 10:15:53 pmWith the RS 22-812 meter I mentioned above the transistor test socket is closed off with a locking shutter when the meter probes are inserted, so it is impossible for this socket to be exposed when measuring voltages. Likewise the meter probes cannot be inserted when the transistor test function is being used. It's pleasing they considered that in the design.On the utility of hFE sockets in general, I imagine they can help to get a ball park estimate, and also could help if trying to match two transistors with similar gains?

author: Lightages
author_rank: Unknown
timestamp: September 23, 2011, 11:54:49 pm
content: Quote from: IanB on September 23, 2011, 10:47:51 pmI too think that hFE measurement features are rather pointless and usually indicate a poorer quality meters. They can be useful however for matching and sorting transistors of certain types but I would have a separate meter to do that and not as my main and safe meter. A meter with hFE can be purchase for only a few dollars.But, as the original poster specified hFE as a plus for his meter, it is his choice.

author: IanB
author_rank: Super Contributor
timestamp: September 24, 2011, 12:26:42 am
content: Quote from: Lightages on September 23, 2011, 11:54:49 pmI'm not sure about the reference to "main and safe meter". Surely one should buy the right tools for the job? I have two of the 22-812 meters (among other meters) that live on my home workbench as electronics lab tools to measure low energy circuits and I'm thinking about getting a third. The 22-812 is CAT II rated, and considering the highest energy circuit I am ever likely to measure is the domestic mains, that is quite sufficient. A CAT III or CAT IV meter would be entirely pointless and would involve paying for features I don't need. Better for my purposes that I have two multi-featured meters with data logging facilities than one more expensive meter without.The transistor test socket is a bonus that comes with the meter along with the other features like capacitance, frequency, duty cycle, pulse width, logic level, max/min, rel, hold, uA, diode test--all of which indicate suitability as a lab meter.Various people seem to be turning their nose up at this meter because it comes from "Radio Shack", but more fool them, they are missing a bargain.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 24, 2011, 01:19:03 am
content: Quote from: IanB on September 24, 2011, 12:26:42 amWell you had wrote few lines of software about it, and probably you have emotional ties with it,but every one makes his own decisions, and your advertising method does not help any.

author: IanB
author_rank: Super Contributor
timestamp: September 24, 2011, 02:03:40 am
content: Quote from: Kiriakos-GR on September 24, 2011, 01:19:03 amDon't be silly. All I did was make one post suggesting it was worth a look, and someone came along and made bullshit claims out of their ass saying it had no isolation and would blow up your computer, without any knowledge or evidence to back it up. That's a good way to derail a thread but it's not very enlightening.

author: Unknown
author_rank: Unknown
timestamp: September 24, 2011, 02:56:46 am
content: Quote from: IanB on September 24, 2011, 02:03:40 amadvertising? emotional ties.Must be on drugs! Ignore the static, your comment about selecting a device appropriate for intended use has been the most sensible advice offered in this thread.

author: Lightages
author_rank: Unknown
timestamp: September 24, 2011, 06:55:25 am
content: Quote from: IanB on September 24, 2011, 12:26:42 amMy statement was "usually indicate" and that my personal opinion was that hFE was not that useful. If it is to you and you have a meter with this feature and it meets your needs, then all is good. I am not a brand snob. I have a Radio Shack pen style multimeter that performs well and is rather accurate.As far as insults from other people about your posts, ignore them.

author: EEVblog
author_rank: Unknown
timestamp: September 24, 2011, 12:08:29 pm
content: Quote from: alm on September 23, 2011, 10:15:53 pmCorrect.In fact I'd go as far to say that no high quality reputable meter has a hFE function.I think I mentioned in my multimeter tutorial video that a hFE feature feature is a basic way to differentiate a good quality meter from a OneHungLow cheapie.But granted, hFE may be useful to some people in some circumstances, but if so, you can just use $5 cheapie for that.And a meter having hFE does not of course automatically mean it is crap of course, you have to weight up each meter on it merits. But it obvious which way to betDave.

author: EEVblog
author_rank: Unknown
timestamp: September 24, 2011, 12:40:20 pm
content: Quote from: Lightages on September 23, 2011, 02:23:58 pmThe Protek 506 was a classic RS-232 interface meter, and had a very long product life and was very popular.I can't recall the internal quality, but it was a pretty decent meter for the money.Off hand, the Protek 608 does look hard to beat at that price point, and I'd probably agree that it looks like a bargain.How many other 0.05% 50,000 count class meters for $120 are there?The Uni-T UT71 series is one.Did someone do a teardown on the UT71 on the forum?I haven't touched either, but my money would be on the Protek being the better quality unit.Dave.

author: Lightages
author_rank: Unknown
timestamp: September 24, 2011, 03:40:53 pm
content: I have a UT71E, and for the price at the time and the semi-good reputation of UniTrend I thought I would give one a try. It did not meet any of its specs out of the box.I will be doing a teardown sometime and a mini-review. I would not recommend a UT71 series at this point. I have taken the UT71E apart and it has OK construction inside but very little input protection. I did not take any pictures yet.I might just order one of those Protecs to see for myself too.

author: jaimeroldan
author_rank: Newbie
timestamp: September 24, 2011, 06:50:55 pm
content: Yep, i was no expecting to pay more than 70 for a Uni-T. They are an okay option. In the other hand, the protek looks promising. I'm going to research a little more.BTW i have a fluke 110 right now, but the lack of amps is just ... lame.