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

[Murphyv310]

Hi.
On the AN8008 when the meter is off there appears to be a Diode and possibly a resistor across the Common and V/Ohms/Hz connection.
This caught me out on a valve radio repair, (Checking Anode of output valve voltage) fortunately on low HT as it was powered via the variac.
Switched meter off and the audio died. So DON'T switch meter off first....... Remove prods first, i was using croc clips on this occasion.

[Mark Hennessy]

Yes, all the Aneng meters do this - I discovered this a few weeks back during another investigation that I'm in the middle of writing up. It seems that the output path (needed for injecting current into resistors, diodes and capacitors) is switched into circuit when the meter is switched off. This means that the PTC and the two transistors configured as a high speed, low leakage clamp are across the terminals.

That explains why if you try to measure the resistance between the terminals, you'll get different results according to the meter you use to test, and its open-circuit voltage.

As to why they do this, your guess is as good as mine, but one suggestion was to stop static damaging anything (though I don't buy that because the meter is pretty robust in all of its modes, as we know). It could be an intentional feature - lots of DMMs have a low-Z mode - but if so, why is it undocumented?

It's obviously good practice to not change the function switch while connected to a circuit, but one could definitely be forgiven for thinking that switching the meter off ought to be OK

I'll be honest - I let them auto power-down. I figure that the current drain is so small that I might as well save wearing out the switch contacts!

[Refugee]

Thanks for pointing out the switching on the AN8008.
I ordered a couple and they are within 1mv of each other when I compared them.
I have also bought an AN860B for jobs where I am messing about with power supplies that are distant from the test points.
I am impressed.

[Mark Hennessy]

That's good to know. Even with their occasional quirks, they're pretty astonishing for the money

Shame I'm not on commission!

[Murphyv310]

Hi.
Yes I'm still impressed and actually glad I found out this quirk without causing any noticeable damage or doing this with more current available.
TBH I rarely use crock clips and would normally use a prod so very unlikely to have had an issue as the circuit under test would have been disconnected before switching the meter off. Good point though about letting the meter go to sleep.

As yet I've not got the AN8002 banggood have a reference number for me to take to the sorting office but I think that is a waste of time, I'll go though to keep me right.
I was realigning a CR100 yesterday and the frequency readout was really handy to keep my old valve signal generator in check.

Mark I think we should have a whip round for you for your commission

[Murphyv310]

Hi.
Well lo and behold I got two AN8002 meters delivered today and Banggood is sending another one as well!!!! I've not had a chance to have a go with them yet as I'm doing my good deed for today and taking a 90 years old friend for an echocardiogram. Will report back later on.

[Murphyv310]

Hi.
Again what an excellent multimeter. As a frequency counter it works well with my signal generator up to around 18kHz then it reads low and above 21mhz the reading jumps around, a two transistor rf amp restores the readout up to around 50mhz, I'd suspect with more drive then higher frequencies could be measured, a dedicated frequency counter would be more practical though. All other ranges tie in with the AN8008 and my Fluke. The temperature facility is also very accurate, I have my Dads old photographic thermometer and it's within a degree of its range, checking the freezer which is -17c the readout was corresponding to it. I've not checked the current ranges as yet though.
So far so good, no complaints and a terrific purchase.

[radioman]

Trev, if they don't want them sent back, I'll buy one off you to go with my AN8008... after all, as Mark has said above you really need to have both !


Andy

[Murphyv310]

Hi Andy.
You're more than welcome to have one of the AN8002's for nothing, certainly the next one won't have cost me anything anyway, you've been more than generous to me, so let me return the compliment.

[radioman]

Thanks Trevor, that's very good of you.


Andy