Digital Multimeters

dcaster wrote

On recommendation of somebody here I bought a bunch of these:

At that time 3 for AU $10,47 including batteries.

I still use those, calibrated those (trimpots inside) and apart from the rotary switch needing precise positioning to set a range I am happy with those.

The other useful instrument I bought on ebay is this (type in ebay search window): MASTECH MS2108 DIGITAL TRUE RMS CLAMP MULTIMETER AC DC VOLTAGE FREQUENCY TESTER Was about 36$, won a bid for one.

Very useful in cars, boats, battery chargers and anywhere where you want to measure current without having to cut connections and insert a multimeter.

I do not see the point of USB interfaces etc.. I do not see the point of a zillion digits, remember that 1% is plenty for normal circuits. Anything better for WHAT?

And I do not need, or even want, autoranging. If you really have no clue what range to select, then autoranging will not help you either :-)

The rest of the instrumentarium is home made here. Frequency counters, SWR meters, spectrum analyzer (RTL_SDR)

RFconverters, RF generator (raspberry pi) antenna analyser SARK100, nuclear stuff, a long list really.

It is the accuracy that counts, especially when you charge special types of batteries, more than the number of counts, always check the meters you bought against some known reference. That reference for calibration is important to have, I use a Microchip reference chip that I know the exact voltage of as reference. I have seen cheap meters with large errors.

It all depends on what you want to do. If you build things yourself or write the code, then you can have a lot for a few dollars.

Jeff,

I agree with your list above except for Autoranging. I find that to be a major pain when checking power where you are trying to trace intermittents. Typically it takes a few seconds for autoranging to settle on a voltage, whereas switched range meters settle typically well under a second. Faster probing results.

For the ESR meter I like Bob Parker's - we've sold 700 or so of those since 1999 and they are a great tool. Of course tech has moved on and the FPGA based component testers are accurate (and very cheap), but Bob's is still the fastest ESR meter!

For talking meters the MOOSHIMETER is handy (have you phone read out the screen)...you can add Wi-Fi with that tool for logging to your list.

John ;-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup) 
                      John's Jukes Ltd. 
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 
          (604)872-5757 (Pinballs, Jukes, Video Games) 
                      www.flippers.com 
        "Old pinballers never die, they just flip out."

My BM235 is mostly used to measure loose SMT capacitors. It's also used when a second DMM is needed to size up a circuit. My primary meter is a Q1126 from down-under. The Q1126 lacks most modern features. But there's just something that's handier about it that's hard for me to put my finger on. It's the DMM that's most useful to me. It uses alkaline batteries and doesn't even power off automatically. As for my other DMMs, they mostly remain in the pouch or in the box on the shelf. They seldom get used at all.

73,

--
Don Kuenz, KB7RPU

Ok, that's fair, but I beg to differ. I took the trouble to learn what the extra buttons on the front of my various DMM operate. One is typically a "range hold" button. If I want a specific range, I just set the DMM to (for example) DC Volts, and push the range hold button until the decimal point lands in the correct voltage range. It's an extra step, but it offers a bonus for me. I tend to blow up my DMM's less often this way. Without autoranging, the meter can be set on any full scale value, some of which tend to blow fuses or other sensitive components. For reasons I refuse to admit, I tend to apply the probes to the device under test first, and then set the range. Autoranging and button pushing has largely eliminated this problem (but not completely).

Other problems with non-autoranging DMM's is that the rotary switch keeps getting bigger and bigger as more functions are added to the dial. A few manufacturers have recognized the problem and placed two or more of these functions on a single switch position. That works, but only after the requisite cursing and suggestions of eternal damnation for the designer of the DMM user interface. The big dial feels like I'm winding up the DMM. That's not a problem, it just feels odd. The bigger dial tends to crowd the front panel lettering, which has become too small for me to easily read without my glasses (or a magnifier).

I have a Bob Parker design ESR meter that I purchased from Dick Smith long ago. I had some complaints about the PCB quality, flimsy probes, lack of a push button shield, awkward sandwich style construction, difficulties measuring ESR of batteries, inaccurate chart on the front panel, etc. I also hate 9V batteries. Still, I managed to build it in one evening, and haven't blown it up in the last 17(?) years. It measures very low resistances better than anything else I own. Today, an ESR meter can be integrated into the DMM firmware, which is what I want.

I dunno. Talking data loggers are so 20th century. If a 21st century meter is going to talk to me while I'm trying to get some work done, I want the ability to talk back, complain, argue, and ask questions. For example, I want to command: OK Dummy. What's is the battery voltage and power drain now, and how long is the battery going to last before shutdown.

OK Dummy. Measure and log the coulombs going in and out of the battery and estimate if the battery will still work when the warranty expires.

OK Dummy. Measure and log the performance statistics at TP1 through TP 20. Link to the Sonic Screwdriver option and adjust everything so that it meets spec.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

It's election season in Wyoming and today's mail brought a multitude of political fliers. One candidate's mailer is folded in half and sealed. Voters break the seal to get at the goodies inside. Anyhow, there's a photo of said candidate on the front, above the fold, and yet another photo under the fold, on the rear when the mailer's still sealed up. The front photo shows the candidate busy at work, wielding a DMM in the great outdoors and using it to measure a uncovered breaker on his irrigation system. The rear photo shows the candidate prominently brandishing his DMM in one hand as he leans up against one of the wheeled arms of his irrigation with the other hand. His DMM is one of those where the insulated end of the positive probe can be seated into the housing, and the whole housing is moved to position the positive, business end of the probe. That's apparently the best type of DMM to use when you run for public office.

73,

--
Don Kuenz, KB7RPU

Well now I know. But... what are counterfeit PCBs? How does UV detect them?

NT

essential IME. How some people claim to manage without them I don't know.

NT

A live case 1920s meter would have gotten him more airtime

NT

Some companies mark their PCB's with invisible UV dots to indicate that the boards have been inspected and tested. If the products is returned for repair and is lacking those markings, it's likely that the PCB is a counterfeit. If the markings are there, but show the wrong pattern, it is likely that the board was exchanged with one from a different device and probably out of warranty. We used this system because it was fast, easy to apply, and fairly easy to read. Scribbling on labels was messy, required some time to prepare, sometimes rubbed off, and was generally illegible.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

what does that mean practically? The whole product is counterfeit, or someone has gone to great lengths to repair something?

Like. I've never done that.

NT

I've never seen an autorange meter that you couldn't use in single range mode. You are aware of that, no?

Rick C.

Irrigation? Wyoming? Only the rich can afford water! A vulgar display of wealth inequality! Amass the proletariat!!!... :^)

(No, I don't think it's actually that bad... They do say we're going to run out of ground water in the next century or so, though, which will be... interesting.)

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

Neither. The company had some of the boards made offshore by a contract house. The boards were all in a card cage and were easily removed and inserted. We expected some manner of counterfeiting problem, so we took measures to discourage it. We rationed some key components and had the boards delivered untested. When they arrived in the US, we touched up the soldering, inserted the missing components, tuned the boards in a fixture, and marked them as tested with inspection stickers and phosphorescent dots.

Of course, that didn't stop the contract house from making "extra" boards, filling them with whatever components they had left over, claiming shortages on the components used, and then selling the boards as "spares" to our dealers at very low prices. The dealers knew how to add the missing parts and tune the boards. They would later sell them to customers for out of warranty repairs at full list price. Meanwhile, marketing didn't really understand what was happening and gave the contract house a complete set of plans so that they could quote on building the entire product. There were other things happening included a very good clone of the entire product. Fortunately, that didn't last very long. I don't want to discuss the mess beyond that point.

I've seen the phosphorescent dots on a small number of PCB's over the years. I would guess(tm) that they were there for the same reasons we had them. It's just one of many ways to identify if a product is genuine. They may also have been added by a refurbisher, to identify boards that they had repaired and tested.

Like what? Scribble your initials, the date, or a serial number on a cloth label? I think we're all guilty of writing those in a sloppy manner at some time. Even rubber stamps can be used in a manner that renders the printing unreadable.

Drivel: The same company decided that it would look cool if the final inspection checklist had the inspection stamp of a responsible FCC 1st class (now GROL) licensee. There was no legal reason to supply that, but since most every company in the industry did it, we decided to follow the herd. The problem was that it was my name and license that was on the rubber stamp. So, my rubber stamp appeared with every shipped product for about 7 years. After I changed jobs, they continued to use my rubber stamp for another 5 years. I saw one of the later stampings. The stamp, my name, and my license number were all illegible after 12 years of use.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

What's wrong with the chart? I have one of those here. It's usually pretty obvious if a capacitor needs to be replaced, but I still refer to the chart on occasion.

Mooshimeters are pretty handy because they can be left unattended in hard-to-reach spots, behind racks, under the hood of your car, etc. and read remotely. The name also tends to make Germans laugh, which is a minor technical achievement in itself.

-- john, KE5FX

Bob Parker posted a revised chart some time in the distant past. I seem to recall that it was more representative of low-ESR electrolytics. Here's my text copy: and Bob's PDF version: or the latest on Pg 14 of the "blue" ESR meter user manual: which includes higher voltage caps.

In my neighborhood, if I left anything unattended, it would soon be stolen. I guess adding an alarm function where the meter yells "Help. help. I'm being stolen" might be useful.

I was born in Munich, Germany and I laughed, so I guess that part works. I suspect that my problem might be congenital. In 1986, my father bought a 1986 Cadillac Seville, which included seat belt interlocks and a talking alert system. Everyone in my family hated both of these features. However, friends and associates thought they were amazing, marvelous, wonderful, cute, impressive, etc. We held a vote and decided to have the dealer disarm the monster. Driving was less stressful after that. 30 years later, I have a Baofeng UV-7 that tries to talk to me whenever I press a button. I disabled that mis-feature on arrival and don't even remember what it was trying to tell me. Children and test equipment should be seen and not heard.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

** As with scopes and most other test equipment, a threshold of usefulness is achieved when the operator has acquired a good mental image of what display output he/she is expecting. If that image pops up, one quickly moves on.

Unsurprisingly, that threshold is reached sooner in the mind of the operator with test gear that only outputs a moving needle and dial reading or a few digits of info compared to multiple signal cope traces.

** Bob's ESR meter is damn fast !!!

With only 3, 2 digit, 1:10 wide impedance ranges one can zip around a familiar PCB checking every electro at a furious rate.

My rules are:

1. Find one bad electro = replace it.

1. Find 2 identical, bad electros = replace all like ones.

2. Find more and its probably time for a complete re-cap.

Using Bob's meter allows that decision to confidently be made in about 2 minutes. It takes a tad longer to find replacements & quickly test them before installation.

.... Phil

Ok, I mostly looked at Murata.

Yup and the AC magnetic field they make is usually awful too. That can be fixed with a metal can, in the process ruining whatever creepage and clearance they did have between input and output.

No, of course not; those are fire and shock safety standards that don't apply to low-power low-voltage circuitry, but to AC mains powered items. The Ethernet magnetics are tested according to different criteria entirely .

USB, because there's a master-side power source, can be optically isolated, with a bit of active circuitry on both sides.

I have a bunch of scopes for examination and/or repair/replace. But they were all stored vertically with the control panels facing upwards and an

*awful* lot of dust has settled on them. This is how long it take me to get around to doing stuff. Sometimes I even accumulate dust myself I'm so slow. If you were faced with this problem (the dust on the scopes I mean) would you hoover it off or blow it off with compressed air? I can see pros and cons both ways and am somewhat undecided as to the best approach.

Just be grateful you don't have a squirrel problem. Squirrels are substantially smarter than rats. And smarter than *I* am in many respects. :(

--
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
protocols, whether for profit or not, is conditional upon a charge of  
GBP10.00 per reproduction. Publication in this manner via non-Usenet  
protocols constitutes acceptance of this condition.