EEVblog #10 Part 1 of 2 – More cheap Chinese MultimetersPosted on May 24th, 2009 10 comments
More on cheap Chinese Multimeters, how a rubber band cost millions of dollars, and the Fluke 87-V Multimeter reviewed.
I totally agree with your judgment about cheap Chinese multimeters. There is one additional aspect I don’t like about them: safety, or the lack of safety.
I have seen such multimeters rated, let’s say, up to 600 V working environment. OK, fine. But when you open them, you find that the current ranges are protected by a bog standard fuse, rated 250 V. Such a fuse is supposed to reliably cut off up to 250 V. But the multimeter is spec’ed to be used in an environment with up to 600 V. There might be some margin what a 250 V fuse can do, but using a 250 V fuse in a multimeter to cut off up to 600 V? That doesn’t make sense to me.
Another example. In my multimeter collection I have a particular multimeter with a transistor test mode. This is a simple socket where hfe is “measured”. When you switch the multimeter to AC or any other range this socket isn’t completely cut off from the test leads. One pin of the socket is permanently connected to the multimeter’s internal ground, and so is on test lead.
If you have a trough hole transistor plugged into that socket, if you forget to remove it when you switch to AC and, for example, measure a wall wart, there is a risk of electrical shock, since one of the transistor leads, sticking out of the multimeter can carry the live phase.
By the way, having to unscrew the battery compartment of a quality multimeter is also a safety measure. Depending on the schematics, the battery contact can have connection to a test lead. So there is a risk of electrical shock if you touch it while the multimeter leads are still connected to some dangerous voltage. The screws prevent the compartment from accidentally becoming open in normal operation. And they s serve as a hurdle hopefully making you think twice when you intentionally change the battery.
It’s good that you do acknowledge your procedures were partly to blame in the first part of your video. Looks like there’s a pattern of bad procedures in the companies you work for. What I got out of your rubber band story is that until there was a problem with the rubber band, you had no procedures for evaluating the performance of your product, and had to cobble together some stuff in panic mode (which is EXPENSIVE). Sounds like there are some deep systemic problems at your company, and if it wasn’t a rubber band bringing you down it would’ve been something else.
By the way, “Cheap Chinese Multimeter” doesn’t really roll off the tongue that well, why do you insist on repeating it over and over???
Actually, that’s not entirely correct. The company in fact had *extensive* procedures for evaluating the performance of every product manufactured. It’s just that this problem took months to manifest *after* assembly and extensive performance testing (it took a long time in the oil to swell this rubber). I do believe the rubber band change was made through a formal ECO process, but obviously the engineer who signed off on it did not factor in long term rubber swelling. Hindsight is 20-20.
Why do I keep repeating Cheap Chinese Multimeter? because that’s what *I* have always called them. Sorry if you don’t like that. I’ve already said I’ll call them “cheap no-name multimeters” for those who got their nickers in a knot over over the Chinese implication. Care to offer up your own suggestion?
It’s good that you at least acknowledge that faulty procedures might’ve been in play in the first part of your video. Seems like at least two of the companies you worked for had deep systemic problems. Like not having a way of evaluating your own product’s performance until a customer reports an issue, and then having to scramble in panic mode (which always becomes EXPENSIVE) to cobble together some tests and procedures. If it wasn’t the rubber band, it was bound to be something else. But go ahead and blame the cheap chinese multimeter or the rubber band if it makes you feel better.
Great post! Just wanted to let you know you have a new subscriber- me!
rubber band story: company is not to be blamed, they just try to make money, except if they dont listen to their engineer. engineer that working on it that should be blamed except for some constraint. why? it is he who knows or should knows the procedure. but things can get mixed up. some time engineer advice the company to put more time to test the product but the company just doesnt have such time and forced to comply with client time requirement. thats why the company, engineer and the client will go in the deep shit later on. i called it “politics in engineering”. engineer just dont have a power to control it.
cheap DMM: i just posted a comment on the older cheap DMM video. my comment here is still same. The cheap DMM is a total useless for PROFESSIONAL, yes. BUT it is a usefull for NON-PRO like me. even for a (pro) company mostly, buying many PRO DMM is a pain. so that why they sorted out to buying many cheap DMM. but for budget pro like them, my advice is to buy more cheap DMMs, but u must buy one expensive super accurate DMM as a master, just as “in-housely” calibrator and double check all those cheappoo reading in case of such problem arise.
the fluke DMM u showed. is it really LCD screen as you mentioned? liquid charged display? or it is just a classic polarized glass panel or something as i can see it in the video? i dont know and not sure, sorry i got no detail knowledge on it, just asking.
ps: love your videos. u ar the master!
Was at harbor freight the other day and came across a new Cen-Tech DMM .. Model P99674
Its about twice the cost of the model ( or similiar ) talked about on the blog. Does a boat load of different things along with some
operational features I have never seen in a DMM before.
I removed the back cover and was pleasantly surprised at the difference in quality compared to the cheaper model. I also took my cheaper one apart and it looked like something soldered at a toy factory ..
But truly this one wasnt as bad ..
I think it would be worth looking into and reviewing ..
The ONLY bad thing is the battery pack is connected to the circuit board via springs ..
Have seen this design on other things before
but do not prefer it .. and it makes it a bear to get the cover back on.
I compared some DC and AC volt readings against my Rigol DS1102e scope and they are within 2% .. Repeatability ?? dunno, havent had it long enough to give the rotary switch a good workout ..
Thought I would toss it your way and see what you thought..
I have a picture of the front and circuit board if you ( or anyone ) wants them ..
Randy – N2CUA
This is actually my very first time i visit here. I discovered so many fascinating things within your blog especially it’s discussion. From the tons of comments on your articles, I suppose I’m not the only one having all the enjoyment here! keep up the good work.
Was it a cable of hydrophones? And as you have worked for Sercel it was probably them;)
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