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AN8002 Digital multimeter

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LAN_403

Conundrum

Sat Aug 26 2017, 06:07PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Feel free to send me any "dead" meters, I would enjoy the challenge.

Still have to make a proper insulation test rig, 1KV module from Geiger counter is incredibly small.

Dr. Slack

Tue Sept 05 2017, 05:36AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Inspired by your investigations, and intrigued by other meters in that series (like the 8008 with 9999 counts and an audio square wave output, but no 10/100mA ranges as you point out), I took to google and youtube, where I found a tear-down.

He was reasonably impressed by the functions and accuracy, but pointed at the CAT ratings on the front, and said that they were probably BS. Then opened the meter and fished out a tiny fuse with 250v stamped on it, saying that you can't have a rating of 600 or 1000v with a 250v fuse! He wasn't impressed with the apparent lack of decent protection devices on the board, but reckoned it was par for the course for the price.

Longevity of the meter is one thing, but my longevity is another. I do measure mains from time to time, and then realised that the other cheap 'CAT rated' meters I have may well be similarly 'optimistically labelled', and on internal investigation found that they too were similarly BS.

The issue with an inadequately rated meter is that a voltage transient on the supply can cause the meter to short internally, and then the fault current can vapourise the test leads, leading to a channel which arcs until upstream fuses blow. What that means is that adequately fused test leads can protect the user from any meter, even if the meter ends up as toast.

While RS does have fused test leads, in the Â£15 to Â£80 range, it also sells the bare fuses for about Â£1. They carry 500mA, rated to break 50kA at 1kV. Interestingly the blurb with them says 'low resistance, doesn't disturb resistor measurements when used in meter leads', so that's obviously the application. I've now made up some fused leads, though whether I remember to switch to them to measure mains is another matter.

Yet one more question on the 8002, which isn't answered in their data, and wasn't in the youtube teardown. What's the input resistance of the meter? It used to be that 10M was the norm for DMMs, though I have a cheap meter that presents 1M, obviously loading the circuit much more. Would you measure it please?

Sulaiman

Tue Sept 05 2017, 09:27AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Just using my Fluke87 on Ohms range;
Range, Manual, Measured
V, 10 MOhm, 10.97 MOhm
mV, 10 MOhm, 2.6 MOhm ... could be 'clamped' as over-renge input ?
Hz, ???, 2.1 MOhm

the readings are inconclusive as;
. input resistance may change due to autoranging ?
. possible protection acting on mV range
. the input resistances stated in the manual are 10 MOhm for volts and >60 MOhm for ac 600mV range.

As I have no intention to measure anything high power at greater than 240Vac I'm not too worried about the hv/energy ratings.
The one feature that I miss is manual range setting,
auto-ranging is great, but can be distracting at times so a manual range selection helps.

I had considered (ordered even) an AN8008 because I like 0000 - 9999 display, and the low voltage and current ranges interested me. When the purchase failed I bought an AN8002, mainly for the 'missing' current ranges and the thermocouple, so far I am more than satisfied with its performance - and it is so cute !

At these prices I can't complain.

hen918

Tue Sept 05 2017, 11:30AM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

CAT rating is very important if you are working on high current mains voltage or above.

I one read a report of a case in an American city in a factory where there had been a power cut (or so they thought).
Someone (a qualified electrician contracting to the company he was at) opened up the covers on the main incomer to check the voltage at the source. He was accompanied by two employees of the company he was visiting.

Unfortunately, he had left his professional multimeter in his van, so he asked one of the employees if they had one he could borrow. They supplied him with a cheap unrated multi-meter which he used to check the voltages phase to ground. Finding that they were all powered at the right voltage, he checked them phase to phase (I don't know why, but it seems to be a habit amongst electricians to test all possible combinations of conductors).

All this was taking place during a thunderstorm, and whilst the electrician has his multimeter probes between phases, lighting struck the local transformer sub-station. The resulting voltage spike caused arcing inside the multimeter, between PCB traces. The underrated fuse blew and then arced over.

The instinctive reaction to a loud bang is to jump backward. The electrician's multimeter probes left the busbars, and arcs started between the probe tips and busbars.
As you can probably guess, the arc flashed over between busbars. The explosion killed the electrician and one of the employees. The other got away with third-degree burns.

Hydron

Tue Sept 05 2017, 01:09PM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

I grabbed a AN8008 for the low voltage/current etc ranges and it's small size. Worth the price for a special-purpose meter and it's never going to get anywhere near mains - that's what my Fluke 87V is for!

Sulaiman

Tue Sept 05 2017, 04:39PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

aside:
At work my Fluke 87 got replaced with a Fluke 287 ... I want my 87 back !

the 287 has a heavier 6x AA cells, that last nowhere near as long as in the 87
but worse
who wants to wait whilst an operating system boots up, just to measure a voltage ?
(not me !)

Sulaiman

Sat Sept 09 2017, 06:07AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Banggod are having their 11th aniversary sale;

AN8002 = Â£08.63

AN8008 = Â£12.08

incl. p&p

Dr. Slack

Sat Sept 09 2017, 01:42PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Thanks for the heads-up. Finally placed my order.

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