Review: £10 multimeters - Now includes the new RS-14!

[radioman]

My AN8008 arrived in the post this afternoon but I've not had time to check it out thoroughly.
This was the first meter I've bought that wasn't supplied in a box - just some of the usual Bang-good thin white foam wrap plus some bubble-wrap but seems to have survived it's journey OK.
Quality of the leads seems alright to me - no worse than the leads on any of my other meters - however, I wish they were 2-3cm longer then I could wrap them round the meter.
The continuity test buzzer is not 'instant' to operate but I've seen worse.
The extra digit on the ranges is very nice to have. See the attached picture measuring a battery on the 0-9.999V range, with the backlight ON.
Can't tell how accurate it is as I don't have a reference voltage source.
Maybe I should calibrate all my old meters to read the same as this one ?
Also, as has already been mentioned it is really small and fits in the palm of your hand !

Overall very pleased with it and the extra leads supplied look very useful too.

Andy
       

[Murphyv310]

Hi.
If you add the Banggood app to your phone you get a discount. I have ordered a second AN8002 for the princely sum of £8.80 with the discount and have contacted Banggood re the non arrival of the first AN8002 and I am getting refunded as it's now over their delivery date window, I did add insurance to the new order for 18 pence. So in the end I'm going to save money.

[jimmc101]

I've had my AN8008 for a few days now and I have to say I am most impressed with its performance.
As far as I can tell well within specification for all ranges. (Capacity above 10uF not verified.)

I can add little to Mark's excellent review, except to add a couple of measurements on my sample...

Auto-range shifts up above 9999 and down below 8500.

Input current on mV ranges -16pA (-1.6mV across 100Mohm)

Open circuit voltage on all Ohms ranges  1.018v
Full scale voltage 99.99ohm  41mV
                        999.9           82mV
                       9.999k          91mV
                     99.99k            92mV
                   999.9k              92mV
                 9.999M             510mV

Capacity ranges (Shunted by 1Mohm 'Scope input resistance)
Test voltage approximately -1.5v +1v at 100pF  (20kHz)
                                          -800mV +400mV at 10nF (750Hz)
                                           0 +400mV at 1uF (1Hz)
                                           0 +400mV at 1000uF (0.5Hz)
(see attached waveforms)

Jim

[Mark Hennessy]

Glad you're pleased with it

I gave up trying to measuring the input impedance in mV range - with the AN8002 (and the AN860B+) I estimated 20GΩ, but the AN8008 was even higher. I was using a 33M resistor. Funnily enough, I tried the same test with the Uni-T UT61E earlier today, and the voltage doesn't change at all! Once upon a time, such high input impedances were the preserve of bench multimeters - it's really quite remarkable what you can get today.

There's a couple more points to add to the reviews - hopefully I'll update them next week.

[Nick]

I gave up trying to measuring the input impedance in mV range - with the AN8002 (and the AN860B+) I estimated 20GΩ, but the AN8008 was even higher. I was using a 33M resistor. Funnily enough, I tried the same test with the Uni-T UT61E earlier today, and the voltage doesn't change at all! Once upon a time, such high input impedances were the preserve of bench multimeters - it's really quite remarkable what you can get today.

The thing is, with impedances like that, environmental conditions come into play. A humid day can change everything

[ppppenguin]

I'm wondering how DMMs achieve a very high input impedance on the mV range while being a standard 10M on all other voltage ranges. I suppose that the basic meter has a very high input impedance from a FET input opamp. Higher voltage ranges need multiplier resistors and so must have a defined impedance. I also wonder how well protected the mV range is against overvoltage. A thousand volts, or the maximum allowed for the meter, applied to any normal voltage or resistance range shouldn't bother the mater at all. Is the Hi Z mV input likely to suffer?

As Nick says, when you're dealing with picoamps, humidity and cleanliness are everything.

[Nick]

... when you're dealing with picoamps, humidity and cleanliness are everything.

Absolutely - the soldering on these is "OK" at best, and there is no conformal coating, though you could add one easily enough.

If one was added, I'd like to think it wouldn't affect the calibration if done when the meter is fairly new - leave it (opened up) in the airing cupboard for a day or so, then spray the PCB...

[Mark Hennessy]

I'm wondering how DMMs achieve a very high input impedance on the mV range while being a standard 10M on all other voltage ranges. I suppose that the basic meter has a very high input impedance from a FET input opamp. Higher voltage ranges need multiplier resistors and so must have a defined impedance. I also wonder how well protected the mV range is against overvoltage. A thousand volts, or the maximum allowed for the meter, applied to any normal voltage or resistance range shouldn't bother the mater at all. Is the Hi Z mV input likely to suffer?

The input travels via a 10M resistance straight to to the IC. Inside the IC, that signal goes straight to an amplifier, but at the input to the amplifier are a bunch of FET switches that are used to connect external resistors to form a potential divider with the 10M, according to the required range. In mV, none of these resistors are engaged, hence the high input impedance. The fact there are two millivolt ranges for both the AN8002 and AN8008 is because of the ability to switch the input amplifier between x1 and x10.

In terms of input protection, you have that 10M in series with the IC, and the spec for the IC states ±2mA max via the body diodes. So that's pretty good. Remember Joe Smith's tests, where the AN8002 survived transients of 2.5kV - these transients were applied to the meter at all settings of the dial apart from the current ranges. The breakdown, when it happened at 3kV, was between the PCB tracks that form the range switch. Dave Jones has subsequently done some similar tests on the AN8008: https://www.youtube.com/watch?v=Ru2rb7bFhag

The input impedance spec is given as "larger than 60MΩ" for the AN8002 (the other Aneng meters don't mention it in the manuals I have). So that fact we're getting results in the GΩ region is pretty nice, but well beyond the spec.

As to humidity, this is low-voltage, so providing there's no condensation, I really doubt it would be a big problem here - certainly not enough to make it fail the 60MΩ spec. It's 60% in my cellar where I've done my tests - but the dew point is 12 degrees, and nothing down here is that cold apart from the occasional glass of beer

Better meters use guard traces and similar techniques to mitigate against leakage on the surface of the PCB (contamination from handling being an obvious issue), but these cheap meters are an interesting study of what can be achieved for minimal cost and effort. The really interesting test will be how they perform long-term. If anything, they might expose other meters as being over-engineered, which is just as bad as under-engineering in a capitalist world.

[Murphyv310]

Wow. For a ten quid meter to survive that punishment well it makes you wonder why it's worth a spending so much on quality stuff.
It's got to be very electrically robust for that punishment.

[Mark Hennessy]

It passed tests that apparently the Fluke 87V did not. That was a surprise, given that the £450 87V is regarded as something of a "gold standard" in industrial multimeters.

But on the upside, the Fluke 101 passed all of his tests (13kV IIRC), and it's less than £40 delivered. It might be basic, but for jobs where safety is critical, it's got more than enough functionality, and I'd have no worries about using it inside my consumer unit or worse. In case you haven't seen it, my review is here: http://www.markhennessy.co.uk/budget_mul...ke_101.htm