fellow Canadians, do not buy Mastercraft DMM - Page 1
Forum section: electronics / general

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: March 04, 2013, 04:41:51 am
content: Well,Its the waveform and frequency of the ac this meter is not understanding .Its not TRMs i hope .Check AC Mains Voltage in the house it will work .Sometimes Knowledge sucks more then the meter

author: Lightages
author_rank: Unknown
timestamp: March 04, 2013, 05:04:26 am
content: Sorry AmirTheGreat, but your demonstration really is meaningless. You are using some crap meter to verify the reading of another meter using source of unknown voltage and frequency.

author: GeoffS
author_rank: Unknown
timestamp: March 04, 2013, 05:04:40 am
content: Did you consider that perhaps you just have a faulty meter?

author: amspire
author_rank: Super Contributor
timestamp: March 04, 2013, 05:22:53 am
content: Did you manually set the Ac range to the top range and try it? The waveform from that oscillator might be pretty bad. It may be that the waveform had a voltage spike that meant that the meter could not successfully autorange - on the top range the reading was too low so it switches down. On the lower range, the voltage spike causes the active rectifier to saturate and it switches up again.This sort of problem is one of the reasons that every decent autorange meter needs an ability to manually set the range. You can probably find ways to mess up the autorange of the best multimeters.Both are averaging AC meters and they only claim any accuracy up to about 1KHz and that is only with a sinewave. I doubt if either would be vaguely accurate in measuring that oscillator output. It probably runs at over 20KHz.If you want to measure a voltage like that oscillator output, you will need a good quality RMS meter.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 04, 2013, 06:31:13 am
content: A few comments about the Canadian Tire 52-0052-2.The regular price is $59.99 CDN, but when it is on sale (about every 2 months), it can be as low as $14.99 or $19.99. In Canada, we don't have a lot of choices for multimeters at the "big box" stores like Wal-Mart, Home Depot and Canadian Tire. At the Canadian electronics stores, $14.99 will buy you a 830 like multimeter (much like the Cen-tech in the video).I have seen the same behaviour of the AC auto ranging "hunting" with an Extech EX430.Try putting it in manual range as amspire suggests.PS. Mastercraft doesn't make any multimeters. They get some company to put the Mastercraft label on it. I also used the earlier incarnation of this model and it wasn't a bad multimeter for $20. I didn't take it apart as it belonged to my friend.

author: AmirTheGreat
author_rank: Unknown
timestamp: March 04, 2013, 10:41:14 pm
content: I may have a faulty unit. Still annoying though.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 04, 2013, 11:20:50 pm
content: Quote from: AmirTheGreat on March 04, 2013, 10:41:14 pmIf you bought from a store and still have the receipt, they will generally take it back for exchange or refund usually no questions asked. I have returned a couple of non working items and never had a problem.

author: amspire
author_rank: Super Contributor
timestamp: March 05, 2013, 12:52:34 am
content: Quote from: AmirTheGreat on March 04, 2013, 10:41:14 pmThe point is if the problem is only with that oscillator, but it usually works fine, I wouldn't be annoyed in the slightest. Autorange is only useful for fairly constant voltages and for AC, that means not too ugly a waveform. For an ugly waveform, I would not expect an autorange to work reliably. It is even possible that the cheaper meter does not have a problem because it has a much simpler rectifier.You may have a faulty unit, but failing to autorange on a totally unknown waveform that may include spikes or pulsing amplitudes is not a way to detect a faulty unit.Have you tried it yet with a manually set range instead of autorange?Does the autorange work fine if you measure the mains voltage?

author: KuchateK
author_rank: Regular Contributor
timestamp: March 05, 2013, 02:14:33 am
content: There is no AC voltage in this thing! Use DC range to measure it as you should.Cheap disposable flash circuit takes 1.5V DC from battery, generates square wave using transistor (or whatever pulsating waveform it can generate from cheapest parts they used), puts that into primary side of a transformer and gets high voltage from the secondary to charge a capacitor. Such transformer usually has few turns on primary and a 1-3k on secondary. In addition to a xenon tube it has trigger transformer, small trigger cap with ~mega ohm current limiting resistor (otherwise trigger transformer would discharge main cap as well), trigger contacts and few parts to detect and show that big cap is charged (ready light).Here are examples:http://repairfaq.cis.upenn.edu/sam/uc350vc.gifProbably all battery (DC) powered flashes work this way. AC powered units replace that transistor-transformer combo with voltage doubler/triplerto convert AC to sufficent DC voltage, the rest is basically the same.Autorange and fancier measuring techniques will get lost on such unstable and noisy circuit like that. Frequency in this circuit (few kHz, you always hear them charging) might be part of the problem.Here is a good flash circuit resource:http://donklipstein.com/samflash.htmlhttp://repairfaq.cis.upenn.edu/sam/strbfil.htm

author: amspire
author_rank: Super Contributor
timestamp: March 05, 2013, 03:15:05 am
content: Quote from: KuchateK on March 05, 2013, 02:14:33 amOf course the board has AC voltage on it. It wouldn't work otherwise.

author: KuchateK
author_rank: Regular Contributor
timestamp: March 05, 2013, 03:26:05 am
content: It works. Check out the circuits I've attached.The transformer is actually used more like an ignition coil in the car. Changes in voltage (impulses) on the primary side generate response on the secondary, but no AC voltage is actually generated on any side of the transformer. There is no swing around zero anywhere in the circuit.If there would be AC voltage then rectification would be required to block or invert negative voltage to charge that big electrolytic capacitor.

author: amspire
author_rank: Super Contributor
timestamp: March 05, 2013, 03:42:26 am
content: Quote from: KuchateK on March 05, 2013, 03:26:05 amNormal transformers can only transform if there is a varying flux in the core, so they have to be driven by AC. That is why a diode in needed to rectify the secondary. The voltage on the transformer secondary is pure AC voltage.It is only possible to make DC transformers using superconductors at extremely low temperatures.

author: KuchateK
author_rank: Regular Contributor
timestamp: March 05, 2013, 04:05:41 am
content: DC pulses are generating varying magnetic flux. It is not normal AC transformer. It is a pulse transformer. You feed primary with pulses. You get pulses of different amplitude on the output.Short definition of the difference is:"The magnetic flux in a typical AC transformer core alternates between positive and negative values. The magnetic flux in the typical pulse transformer does not."http://en.wikipedia.org/wiki/Transformer_types#Pulse_transformerhttp://www.butlerwinding.com/store.asp?pid=28355

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 05, 2013, 04:10:40 am
content: Hi,The manual for this meter can be found here:http://sitebuilder.tradeeasy.com/shopimages/9359/html/enus/hardpages/images/52-0052EN.docIt contains the specifications for the meter. In the AC section there is no mention of frequency. I would therefore assume that this meter is only good for measuring line frequency. It is not true RMS.The test with the capacitor charger from a disposable camera is pretty meaningless. I have some very good meters and I am sure that they would all give different and wrong answers.I would check the meter on a AC outlet, it will probably read fine. The topic on which meter is best has been discussed many times on this forum. Most of the time I use older flukes, 8060A, these are are very accurate and readily available used. I suggest you read the archived messages. The UT61D is very popular. I have never owned one of these.I suggest you take the meter back to Canadian Tire, because it not a good choice for electronics.Jay_Diddy_B

author: BMac
author_rank: Contributor
timestamp: March 07, 2013, 06:50:38 pm
content: Yep, that's where I'd go if I was looking for a good meter, a tire store!,,, NOT!

author: Len
author_rank: Frequent Contributor
timestamp: March 07, 2013, 07:10:18 pm
content: Quote from: BMac on March 07, 2013, 06:50:38 pmCanadian Tire is as much a tire store as Wall Drug is a drugstore. Their Mastercraft line of tools are known for their superb mediocrity.

author: Ferroto
author_rank: Frequent Contributor
timestamp: March 07, 2013, 09:12:57 pm
content: I had a manual ranging mastercraft DMM that looked similar. Most of the pads didn't have enough solder on them and when I picked it up a surface mount capacitor was rattling around inside. Funny thing is that it had a UL sticker on it.The 1 Megaohm resistor is soldered to a through hole joint on one end and a surface mount pad on the other, also check out how thin the leads are going up to it.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 08, 2013, 08:29:10 am
content: @Ferroto, thanks for the internal pictures. I believe that multimeter model is part of a "kit" that includes needlenose pliers and wire stripper? The kit usually goes on sale for $10.For some rural Canadians, Candian Tire/Wal-Mart are the only choices for multimeters. Most probably won't use ebay or wait 30+ days for shipping.

author: BMac
author_rank: Contributor
timestamp: March 08, 2013, 03:14:44 pm
content: Yeah, I was born and raised in Canada, we used to call it "mastercrap".As for waiting 30 days for an ebay shipment, I still have stuff delivered up there and I don't notice any appreciable delay in shipping to Canada, (UPS or Fedex), at least not Ontario, I cant comment on deliveries to the Yukon or North Bay. I have ask my relatives on that.BMac

author: Ferroto
author_rank: Frequent Contributor
timestamp: March 08, 2013, 05:09:10 pm
content: Quote from: retiredcaps on March 08, 2013, 08:29:10 amI had my suspicions since the PCB was plated through hole however the soldering was crap.Quote from: retiredcaps on March 08, 2013, 08:29:10 amYa I live in rural newfoundland anything worth having you have to order in.

author: AmirTheGreat
author_rank: Unknown
timestamp: March 10, 2013, 02:16:49 am
content: Quote from: KuchateK on March 05, 2013, 02:14:33 amI looked at the waveform with a scope and sure enough it is AC at about 360Vp-pwhich is about 130 Vrms

author: AmirTheGreat
author_rank: Unknown
timestamp: March 10, 2013, 02:20:28 am
content: Quote from: Jay_Diddy_B on March 05, 2013, 04:10:40 amI would love to but it was given to me as a part of a First Year Kit at my school.

author: Monkeh
author_rank: Super Contributor
timestamp: March 10, 2013, 03:31:29 am
content: Quote from: AmirTheGreat on March 10, 2013, 02:16:49 amDoesn't mean it's suitable for an averaging meter designed to look at sine waves.Quote from: AmirTheGreat on March 10, 2013, 02:20:28 amWhat're you complaining about, then? It may not be perfect, but there are much worse around. Operator error isn't the fault of the meter.

author: Frollard
author_rank: Newbie
timestamp: March 11, 2013, 10:47:46 pm
content: I've got an older generation manual selection mastercrap - and while I've never bothered with anything non-dc. It recently just went haywire with dc measurements being out by a good 40% on the low side; fresh batteries, just random readings on the screen. My cheap china 'power fist' from princess auto may be cheap crap but it knows it from the get-go; not mascarading as an expensive meter. I need to pick me up an entry level fluke or one of the cheaper options Dave recently reviewed.

author: Ratib
author_rank: Newbie
timestamp: March 13, 2013, 08:47:29 pm
content: While I do not know the quality of the meter, I can tell you that you have just learned why NOT to use auto-ranging on a meter! With the cheap meter on a fixed voltage, you proved that the readings were all over the place. Look at the video! Of course the auto-ranging will not work when the voltage does not settle down. If you had put the condemned meter on a fixed voltage the outcome would have been different.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 14, 2013, 01:13:08 am
content: Interestingly though, they do go for UL or CSA certification, for whatever that's worth.I noticed that when I went looking for a cheap DC clamp meter, only to find out it had been recalled:http://www.esasafe.com/pdf/Recall_Notices/RCL11-64.pdfDammit.(No apologies for Canadian Tire though; for all their flag waving they don't seem to have any sort of mandate to support Canadian manufacturers.)Additional: I think they're the same OEM though:http://www.colluck.com.hk/diyhp/9359/enus/c-25520/p-AAAV+EAAhAAAMdxAAS/Mini_Digital_Multimeter.htmlBullet Point: "Very Competitive": one wonders against whom?Must have a no compete agreement with CT:http://www.colluck.hk/catagory.asp?cls_code=00001&grp_code=00003

author: AmirTheGreat
author_rank: Unknown
timestamp: March 16, 2013, 11:39:14 pm
content: Quote from: Ratib on March 13, 2013, 08:47:29 pmI have also tried it on manual. none of the scales work.tried it with three other units (everyone in my course got the same DMM) and the same thing happened.

author: Monkeh
author_rank: Super Contributor
timestamp: March 16, 2013, 11:40:20 pm
content: And what waveform are you attempting to measure?

author: AmirTheGreat
author_rank: Unknown
timestamp: March 16, 2013, 11:58:30 pm
content: Quote from: Monkeh on March 16, 2013, 11:40:20 pmI'm not sure If I understand your question clearly, so excuse the (probably wrong) answerwhen I looked at it with a scope at school a few weeks back, It was a very sinusoidal wave with no spikes or irregularities.I could take a picture sometime in the next few days.