Weird Meter Problem!

[Arnak]

Hi,

I have the strangest problem with 2 meters that I have ever seen.

Meter 1 is a Fluke with a new battery, Meter 2 is an older digital Meter with a new battery.

Using the Fluke to test a circuit it reads a voltage, yet when I use the older meter it does not show a voltage at the same points!

The older meter works fine on other test points and a 9v battery.

The Fluke is showing a voltage between a 4.7k resistor and ground where there should not be any voltage.

So to sum up Test point 2 - 3.6v, Test point 1 - 1.3v (Should be 0v) .Using the Fluke.

Test point 2 - 0v, (should be 3.6v), Test point 1 - 0v (Should be 0v), Using the older meter.

Any ideas what is going on please?

Martin

 

[Minder]

I know with Fluke meters in general, the reading go crazy when the battery is low and before the low batt comes on.
I had one maintenance electrician come to me with the problem, he was measuring 230vac where it should be 120vac max.
I changed the battery and solved his problem!
M.

 

[Harald Kapp]

What kind of voltage (AC, DC, mixed) are you trying to measure?
What ranges on the meters do you use and whcih types are the meters (especially the "old" one you haven't told us anything about)?
What are the input specs (mainly input resistance) of the meters in the ranges used?
Can you show us a schematic of the circuit you are measuring?

Chances are that an AC component superimposed on a supposedly DC signal together with different input resistance (and/or filtering within the instrument) confound the measurements.

 

[Harald Kapp]

I know with Fluke meters in general, the reading go crazy when the battery is low and before the low batt comes on.

Supposedly the batteries are new.
However, it's a good idea to check the batteries, too.

 

[Tha fios agaibh]

When I'm getting strange readings, I like to switch to an analog meter that can show ac or pulsing dc signals. A dvm will flash random unreadable numbers, while the needle of an analog will jump around giving you some idea of what you have.

 

[Arnak]

Hi Folks,

Thanks for the replies.

From my further testing I would say that it is picking up ac and thinks that it is a dc voltage as Harald suggested, that is the problem with this type of meter, I don't know how you eliminate that problem?

Martin

 

[Minder]

The problem with electronic VOM's is they are relatively high impedance and often induced or stray currents /ground currents etc can make them show a reading, if this is experienced in a circuit that should normally be off or dead, then applying a low value resistor across the meter will usually remove the reading, IOW make the meter a low impedance device, This should of course be done with the knowledge of the nature of the circuit being read.
M.

 

[duke37]

With a high input impedance meter, a broken input lead can give all sorts of funny readings. Measure something you know to check.

 

[Arnak]

Hi,

It's not a broken lead as I checked the meter on a 9v battery.)

Thanks for the advice, what value do you suggest for the resistor please?

Martin

 

[BobK]

Well, the errant reading was across a 4.7K resistor, so the high input impedance answer is moot.

Bob

 

[Arnak]

Hi Bob,

OK, thanks for the help.

Martin

 

[Martaine2005]

Not another Martin!!!!
I have similar issues with my fluke 7-600. It wont acknowledge resistors below 2k.
Yet my cheap china DVM will go right down to 1 ohm.
My Fluke is not an electronics tool. It is for the electrician. And also the auto ranging doesn't help with component level measurements.

Martin

 

[Tha fios agaibh]

When I get differing answers, I always ask for a third opinion.

Might want to ask a Fluke 87, or another prominent opinion.

 

[Arnak]

Hi,

Yep, another one of us...!

I agree that the auto ranging can be a problem, I'd like a better Fluke but the prices... ouch!

Martin

 

[BobK]

If it is accurate it's a fluke!

Bob

 

[Martaine2005]

I agree that the auto ranging can be a problem, I'd like a better Fluke but the prices... ouch!

Touche'

 

[Arnak]

Hi Bob...)

It's an even bigger Fluke if I circuit I built actually works.!

Martin