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

[floobydust]

That shunt measures about 0.015 ohms.
If I turn the rotary switch back and forth a few times, it can go down to less than 0.2 ohms but after a month it goes back up to several ohms or worse. Once it was over 50 ohms.
It seems to be the chinesium copper alloy the wipers are made of, with it's dull brown look and high sulphur content. The PCB has good gold ENIG finish still.
For the meter I bought it from the ANENG store, it seems the metals are such low quality I consider it too unreliable.  I could try electroplate the wipers with something.

[HKJ]

That shunt measures about 0.015 ohms.
If I turn the rotary switch back and forth a few times, it can go down to less than 0.2 ohms but after a month it goes back up to several ohms or worse. Once it was over 50 ohms.

You are definitely doing something wrong, the shunt is not switched but permanently connected to the input terminals.

[The Soulman]

That shunt measures about 0.015 ohms.
If I turn the rotary switch back and forth a few times, it can go down to less than 0.2 ohms but after a month it goes back up to several ohms or worse. Once it was over 50 ohms.

You are definitely doing something wrong, the shunt is not switched but permanently connected to the input terminals.

Read the post on the previous page. 

Edit: I cant get the link to work, but its a couple of posts back.

[001]

For the meter I bought it from the ANENG store, it seems the metals are such low quality I consider it too unreliable.  I could try electroplate the wipers with something.

Try to add simple solder bloob
Why not?

[ebastler]

Read the post on the previous page. 
Edit: I cant get the link to work, but its a couple of posts back.

Hmm, which post? Could you indicate the reply number please?

[HKJ]

Hmm, which post? Could you indicate the reply number please?

It looks like he is not talking about the internal current shunt, but about measuring sub-ohm resistors with the meter.

[BravoV]

... about measuring sub-ohm resistors with the meter.

Sub-ohm measuring with 2 wires only meter ? Reliably ? 

[HKJ]

... about measuring sub-ohm resistors with the meter.

Sub-ohm measuring with 2 wires only meter ? Reliably ? 

Most of the better meters uses separate paths for current source and measurement to the connector, i.e. the switch resistance will not affect the result. That is not always the case on cheap meters.

[BravoV]

... about measuring sub-ohm resistors with the meter.

Sub-ohm measuring with 2 wires only meter ? Reliably ? 

Most of the better meters uses separate paths for current source and measurement to the connector, i.e. the switch resistance will not affect the result. That is not always the case on cheap meters.

Yeah, most bench top meters has 4-W capability, but never seen at "handheld" DMMs, except for LCR meter, but its different animal by it self.

[HKJ]

Most of the better meters uses separate paths for current source and measurement to the connector, i.e. the switch resistance will not affect the result. That is not always the case on cheap meters.

Yeah, most bench top meters has 4-W capability, but never seen at "handheld" DMMs, except for LCR meter, but its different animal by it self.

I did not talk about bench meters, but standard hand held meters with two terminals where the current source and voltage measurement do not share a switch terminal.
And yes benchmeters is something else and considerable better at low ohmic measurement.
Handheld multimeter with 4 terminal ohm do exist: METRAHIT IM XTRA but it is probably just as expensive as a bench meter.

[rafik23]

moved to new topic

[Gandalf_Sr]

@rafik23
I'm confused, does your post have anything to do with the AN8008?

[rafik23]

hi
my post is for dtm1106EN i want to analyse data

[ebastler]

hi
my post is for dtm1106EN i want to analyse data

Then please open a new thread, with a descriptive title. (It should mention the model of meter you are actually talking about.) Thanks!

[djos]

Noobs!

[001]

Noobs!

I`m noob for at last 56 years, is it a problem? Why do You discriminate noobs?

[djos]

Noobs!

I`m noob for at last 56 years, is it a problem? Why do You discriminate noobs?

I was referring to his post count, all 3 posts were in this topic.

[tigrou]

Hello. I have one question related to this multimeter (and other multimeters in general) :

When measuring voltage (eg : 220V AC) with probes endings plugged into socket 2 and 3 (the last two sockets, starting from left), is there safe rotary switch positions other than "V" and "mV" ?. AFAIK "A"and "mA" positions are a big no-no (since it's basically a short-circuit) but what about others ? (eg : ohms measurement or continuity test) ?

[Fungus]

When measuring voltage (eg : 220V AC) with probes endings plugged into socket 2 and 3 (the last two sockets, starting from left), is there safe rotary switch positions other than "V" and "mV" ?

No.

(and I have doubts about the mV position)

nb. Even if the switch is on 'V' the leads can still be in an unsafe position... be sure to triple-check everything.

[bobale]

Hello guys 

So, anyway, I've stupidly managed to burn input divider 5MΩ resistor (R30) on my AN870 by trying to measure output of a (unloaded) CCFL backlight driver  .

Since 5MΩ is not really a standard value, and as far as I've managed to find out, this resistor is MELF 0.25%, the best I could manage to find locally was two in parallel 10MΩ 1% metal film resistors. Voltage measurement works now, but it is showing a little bit low. Before it would be almost bang on 10.000V when I feed it AD584 10V voltage reference. Now it reads something like 9.954.

Question is: will I ever be able to get back the accuracy with 1% resistors (can't really find any better locally), should i try calibration procedure, or should I scrap the multimeter?

[Fungus]

Question is: will I ever be able to get back the accuracy with 1% resistors (can't really find any better locally), should i try calibration procedure, or should I scrap the multimeter?

You could buy a load of cheap 1% 4.7M resistors and pick out the two that are best matched.

OTOH the calibration will probably be done with of error so you might have to find two that are slightly mismatched, by just the right amount to make it work (put a pot in series with one of them and dial it in to find the exact ratio needed).

Also think about getting a Fluke 101 for measuring things like that in the future.

[bobale]

I rarely need to measure that high voltage, CCLF backlit monitors are on the way out anyway.

Thanks for the suggestion. I have 4.7M, 5.1M and 10M, 10pcs each, and will combine them in some way to get the it to measure correctly. As far as I'm aware, those two 5M resistors (R29 and R30) are only for measuring voltage, right? Other things shouldn't be affected?

[Fungus]

As far as I'm aware, those two 5M resistors (R29 and R30) are only for measuring voltage, right? Other things shouldn't be affected?

Hang on...

Looking at your photo closely I see they're the input protection resistors (leading to the PTC). It's not a voltage divider at all, it's just a 10M (approx) resistance to give a high impedance input and I don't think they're high precision at all. Maybe your problem is simply that you put in a much higher value.

[bobale]

Here's higher res photo in the attachment. This should be diveder as it is going straight to the chip, not to the PTC.

[HKJ]

Hang on...

Looking at your photo closely I see they're the input protection resistors (leading to the PTC). It's not a voltage divider at all, it's just a 10M (approx) resistance to give a high impedance input and I don't think they're high precision at all. Maybe your problem is simply that you put in a much higher value.

The 10Mohm resistors are always part of the input voltage divider and is used in volt AC/DC, it can also be used in other ranges, but usually a about 1Mohm input resistor is used for them and that resistor is not used in a voltage divider only as protection.