Finally got a clamp DMM

Do you have a link for the RMS DMM ?

Sound level meter: mic, opamp, filter. Connect dmm

NT

Add: - Wind screen for microphone. - Measure -3dB points for microphone directionality. - Measure mic and opamp bandwidth and flatness. - A and C weighting compensation. - Range switch (op amp gain switch). - Rectifier and filter, so that the meter can read peak or average SPL (sound pressure level) - Calibrate DMM reading in decibels SPL. - Battery, battery charger. - Automatic power off, on/off switch, power on LED. - Calibration:

But how do you calibrate it? Calibrated microphones are $$$$.

--sp

A pistonphone[1] tone generator at 250Hz and 124dB SPL, or an acoustic coupled tone generator running at 1KHz and 94dB SPL. Assorted acoustic calibrators: Yes, they're expensive, but can be rented or borrowed.

design, consists of two pistons mounted on opposite sides of a cam disc. The rotation of the cam disc forces the pistons to move, in phase, in and out of the coupler cavity. The design reduces cam disc eccentricity and harmonic distortion, and ensures maximum level stability."

------------------------

If the OP can borrow a high quality SPL meter, just place it alongside the $10 one and then have someone sound a nearby car horn.

If the $10 meter has a "cal" adjustment, set it to match the other meter otherwise note the difference and add or subtract it as appropriate.

The true condenser capsules used on quality SPL meters are inherently flat so need no further testing. The $10 job will likely have an electret capsule which will be flat up to 10kHz or so - then rise a few dB.

.... Phil

That's what I did to calibrate my various Android smartphone SPL meters: I like this one, mostly because the classic panel meter looks cool: Calibration is easy:

Unfortunately, most smartphone apps are not very accurate: "A representative sample of smartphones and tablets on various platforms were acquired, more than 130 iOS apps were evaluated but only 10 apps met our selection criteria. Only 4 out of 62 Android apps were tested." A later version of the study, but using external microphones.

I've also compared my two analog Radio Shack sound level meters with several Android smartphones and apps. There was about a 1.5dB difference between the Radio Shack meters and my smartphone (Samsung S6). Not very accurate, but maybe good enough for some applications.

For orders from AliExpress you can usually choose from several shipping options. I always go for free or nominally paid shipping because shipping cost with couriers like FedEx and DHL are insanely high compared to the price of an inexpensive gadget. Estimated delivery times vary for different items and the destination country. If you're in the US, it's 12-20 days for this particular item with free shipping which is about half that for India.

The *claimed* specs for this unit are - Accuracy +/-1.5 dB. A weighting

I don't expect it to perform like those costing hundreds of dollars. It's actually for my budding architect son who at this point needs only indicative measurements.

That seems pretty good from my perspective. I never had my RS analog calibrated, but I had someone measure response in a large sound room. Larger element not accurate like little ones like Panasonic. I have a Harbor Freight do-all VOM, has SLM, light meter, capacitance, maybe frequency. I have yet to compare sound pressure.

I have infrasonic energy around my house and river valley, been monitoring pulses on analog meter. It around 8 Hz I'm guessing. Need to measure.

Greg

I just bought a 9999-count version of that DMM, the ANENG AN8008, and it was shipped to the Netherlands in 8 days. Cost me 21 euro at the "official ANENG shop", I think it can be found slightly cheaper even in other shops.

Recently an agreement has been made between AliExpress and our local postal service which appears to speed up shipping/handling a lot. (2 other orders also arrive within 10 days, that used to be more like

I envy you. If I had that kind of service I'd place a lot more orders from AliExpress and I wouldn't have to stock up on things I *may* need in the future. I live in a remote area and even orders from Indian sites generally take 5 to 10 days.

The long transit times for orders from AliExpress to India are probably caused by the inefficiency and don't-care attitude of our customs people. Some of my recent orders were delivered in 3 weeks or less. I don't know if they're flukes or a sign of things to come. I sure hope it's the latter.

Well, as of now we have quite some webshops that can deliver orders made before 20:00 or 21:00 on the next business day. That is not by special (and expensive) courier but using a special service of the regular postal service. Of course our country is much smaller.

It could be due to batching of shipments too. Previously, when I ordered at AliExpress it sometimes was very slow and sometimes a little faster. I heard that the postal service in China filled air shipping containers for each country and when the container was full it got underway. So when your package was amongst the last to go in it would ship faster than when it was the first in the new, empty, container. Don't know if that was or is true, but of course when the volume of shipments increases (as it apparently does), the effect of this batching would diminish.

EEVBlog did a video review of a meter *very* similar to that one:

Right, same here. I remember having blown the mA range of my first multimeter (analog of course) and feeling bad about it, but it is not something happening regularly.

I would not leave the probe in the 10A connection after a measurement, in fact I normally don't use the probes for current measurement, certainly not for amps.

When measuring current, I plug one of the leads from the power supply in the 10A input, and use a spare 4mm lead from the negative to the device under test. After the measurement, I unplug everything and put the probes in the voltage input.

The probes are only used to measure voltages and resistance/capacitance during normal use. Besides, I only use my DMM on low-voltage equipment, not on mains circuits. If I would, I would spend more on a well protected DMM.

On 7/27/2017 12:31 AM, Jeff Liebermann wrote: ...

Damn ... that is cool! From the photo can't tell that it's not hardware.

That's because it's made from a photo. That how you do these things.

I made an HP calculator emulator around 1991, by scanning a photo of an actual HP calculator. We had a comparatively crappy scanner, so I had to greatly enlarge it and edit it at the level of single pixels (to remove dithering and noise), but even in fairly low resolution, you could see not just the angulation of the key top and the altkey front, but the little molding ridges around the key front. HP's attention to detail was apparent in the curvature of those little plastic buttons.

It really felt three-dimensional to look at and to use.

The thing you couldn't do with a meter is to simulate the parallax mirror behind the needle - that would need to know where the viewer's head is :).

Clifford Heath.