fellow Canadians, do not buy Mastercraft DMM

[AmirTheGreat]

[Amarbir[Lynx-India]]

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

[Lightages]

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.

[GeoffS]

Did you consider that perhaps you just have a faulty meter?

[amspire]

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.

[retiredcaps]

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.

[AmirTheGreat]

I may have a faulty unit. Still annoying though.

[retiredcaps]

I may have a faulty unit. Still annoying though.

If 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.

[amspire]

I may have a faulty unit. Still annoying though.

The 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?

[KuchateK]

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.gif

Probably 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.html
http://repairfaq.cis.upenn.edu/sam/strbfil.htm

[amspire]

There is no AC voltage in this thing! Use DC range to measure it as you should.

   Of course the board has AC voltage on it. It wouldn't work otherwise.

[KuchateK]

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.

[amspire]

It works. Check out the circuits I've attached.

Normal 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. 

[KuchateK]

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_transformer
http://www.butlerwinding.com/store.asp?pid=28355

[Jay_Diddy_B]

Hi,
The manual for this meter can be found here:

http://sitebuilder.tradeeasy.com/shopimages/9359/html/enus/hardpages/images/52-0052EN.doc
It 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

[BMac]

Yep, that's where I'd go if I was looking for a good meter, a tire store!,,, NOT!

[Len]

Yep, that's where I'd go if I was looking for a good meter, a tire store!,,, NOT!

Canadian Tire is as much a tire store as Wall Drug is a drugstore. Their Mastercraft line of tools are known for their superb mediocrity.

[Ferroto]

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.

[retiredcaps]

@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.

[BMac]

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

[Ferroto]

@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.

I had my suspicions since the PCB was plated through hole however the soldering was crap.

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.

Ya I live in rural newfoundland anything worth having you have to order in.

[AmirTheGreat]

There is no AC voltage in this thing! Use DC range to measure it as you should.

I looked at the waveform with a scope and sure enough it is AC at about 360V_p-p which is about 130 V _rms

[AmirTheGreat]

I suggest you take the meter back to Canadian Tire, because it not a good choice for electronics.

I would love to but it was given to me as a part of a First Year Kit at my school. 

[Monkeh]

There is no AC voltage in this thing! Use DC range to measure it as you should.

I looked at the waveform with a scope and sure enough it is AC at about 360V_p-p which is about 130 V _rms

Doesn't mean it's suitable for an averaging meter designed to look at sine waves.

I suggest you take the meter back to Canadian Tire, because it not a good choice for electronics.

I would love to but it was given to me as a part of a First Year Kit at my school. 

What'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.

[Frollard]

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.