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AN8008 US $19, 9999count, 1uV, 0.01uA, 0.01Ohm, 1pF resolution meter

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Mr. Scram:

--- Quote from: flywheelz on September 20, 2017, 07:11:31 pm ---Could someone compare the frequency the buzzers are running at?  Loud vs Quite.  Perhaps they started using different batch of buzzers that require a different frequency, even 500Hz off make a huge difference.


--- End quote ---
The frequency seems to be exactly the same, with the main frequencies being slightly under 2 KHz and 4 KHz. The first figure shows both waveforms overlaid. This shows the frequencies to be the same, but the amplitude very different. The waveform may be slightly different too, but to my ear with voided calibration, they sound very close. The two other plots show the spectrum of both beeps separately.




flywheelz:
@Mr. Scram, nice work!  Then the problem is lack of power.  Perhaps they've used a higher value current limiting resistor for the buzzer, if there is one.

ceut:

--- Quote from: flywheelz on September 21, 2017, 04:53:56 am ---@Mr. Scram, nice work!  Then the problem is lack of power.  Perhaps they've used a higher value current limiting resistor for the buzzer, if there is one.

--- End quote ---


I've put a 39 Ohms in series with the buzzer, because it was too loud for me  ;D
The buzzer is driven by Q2 directly from the MCU, at a fixed frequency of 1.95kHz (datasheet of the DTM).
My buzzer has 50 Ohms impedance - Maybe the impendance can be a little different from DMM to DMM.

I have also put another 39 Ohms in series with backlight Led.

So I think my mod are a little battery-saver  :-+

Also I've done all my calibrations manually in the Eeprom (moving the hexa values) and now I find it nearly perfect for me  8)

Crumble:

--- Quote from: Fungus on September 17, 2017, 03:53:01 pm ---[...]

a) If it's always used correctly on the AC setting then probably nothing spectacular will happen. Safety features are for when you mess up, right?

b) If it simply dies a quiet death then "Crappy China" will be blamed, not the person who chose the meter.

--- End quote ---
I wouldn't be too sure about that.

a) Yes and no, when you are measuring mains, there is probably something going on there. Let's say a contactor is malfunctioning intermittently and creates inductive peaks upon disconnecting. Despite the high voltages possible these are usually quite innocent in energy content. They may however be able to initiate an arc within your meter (if the internal clearances are too small) that is then fed by the mains current which is capable of 1000s of Amps before any safety trips. That is why the CAT ratings require testing with voltage transients way beyond the voltage rating they test for (8kV for a CAT IV 600V meter for example). These occurrences aren't actually that likely, but only one such an event is able to kill you so I'd try to prevent it when feasible. Fluke has published a document with a simplified explanation of the things that can go wrong. You might like the explanation of mjlorton too.

b) If not, you will die a loud one, and then it might be less relevant who is to blame. You should watch the older videoblogs of Dave's if you have the time. I can recommend EEVblog #6 part 2. I do disagree with Dave in his crusade against anything cheap, but in this episode he does elaborate quite well (but not too long) about why a cheap multimeter would not suffice and makes some excellent points that hold today (8 years later). There was one with him emphasising about the UL listing, but I could not find it in the 1220 odd blogs he made. Bottom-line is that a CAT rating is only worth anything if it is independently tested, else it is no more than a claim of the manufacturer.

GreyWoolfe:
Sorry if I annoy anyone with this question, but I don't have the patience to delve into 27 pages.  What I am looking for is a cheap meter for some low resistance measurements.  I need to fairly reliably measure 15 \$\Omega\$ and less than 1 \$\Omega\$ on an FRU for a piece of deployed company equipment.  My cheap Velleman meter(with Brymen leads) does it but it is bigger than I want to carry in my toolbag and I would rather not pay $50 for a Fluke 101 if this meter will do what I need.  This isn't going to be a constant use meter but just for this specific field application.  I have better meters at home when I rebuild the FRU.  It won't even be used for V or A measurement of any kind, just the resistance measurements.  If anyone can test their AN-8008 and let me know, that would be awesome.  It's even cheap enough, if it works, to buy 2 in case I leave one behind on a service call and don't get it back and it would still be cheaper than a 101.

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