Fluke 87v non-zero current reading

[nack]

Hi all,

I've recently bought a second-hand Fluke 87v. Cosmetically in brand new condition. Including recent calibration stickers up to June 2013.
Now I have discovered something rather strange on the current measurement ranges. On the AC and DC range the meter shows a non-zero reading without the meter being connected to a current source.



Off course I can Null it out, but is this normal? It is really an offset as it read continuously high if I apply a constant current trough the meter with my bench power supply.
Should a proper calibration cancel for this offset or is the meter faulty?

[nack]

Anyone having similar experiences with their Fluke 87v?
My Agilent u1241a reads dead zero on the current ranges if no load is connected, which is should right?!

[tom66]

I think something is wrong with the cal. I had a 179 at work and it read 0.002A with no current, so a small offset might be acceptable, but one that large looks bad.

[Neilm]

It might be noise pick up as the terminals are open circuit. What do you get if you short the terminals together?

Neil

[tom66]

It might be noise pick up as the terminals are open circuit. What do you get if you short the terminals together?

Neil

That doesn't make much sense, there's a 0.005 ohm shunt inside the meter, so I can't see what shorting the leads together would do.

[Baliszoft]

dc A is .0005 on mine in hi res mode and 0.000-0.001 in normal mode. dc uA 0.06 in hi res, 0.2 normal.

[nack]

Thanks for the replies 

Indeed, shorting the probes doesn't do that much. Another closed loop circuit in parallel to the current sense resistor won't change anything. It reads a steady 0.0022 A on the amps DC range as well as 0.22 uA in the microamps DC range. Sure it is something I can REL but its quite annoying and not something I would expect from a quality brand like Fluke.

The only option to fix it will be an official calibration I believe? I don't think I am willing to spend money on that just to fix this current offset issue... Also I've checked the CAL menu, and it reads n001, so it is still on its factory calibration settings.

[d0ss]

Just thought I'd add my readings.

Leads unplugged:
DC A: 0.002 or .0019 hi res
DC uA: 0.3 or 0.22 hi res

Leads plugged in:
DC A: 0.002 or .0019 hi res
DC uA: 0.1 or -0.01 hi res

Accuracy on both the ranges is 0.2% + 4 counts, so the readings are correct with the leads are plugged in. When in hi resolution mode counts are to be multiplied by 10 so 0.2% + 40 counts.

Having the leads in for the uA range does appear to make a difference I'd be interested to see if you have the same results and hope this helps. Although it is a little annoying having to zero readings.

[nack]

@d0ss

Your measurements correspond closely to mine, so there shouldn't be a problem I guess. And yes the specified accuracy corresponds as per the manual...

[Baliszoft]

I should be pretty happy with my .0005 reading then. To be the honest i prefer my U1252B on the bench, a lot faster, more precise (with no offsets), but i would not take it to the field.

[nack]

About the Agilent meter, that's why is was surprised by the readings on the Fluke as my Agilent 'cheapy' U1241A reads spot-on 0.0 at the current ranges.

A rather annoying thing on the u1241a I found was the contrast and small digits on the LCD. Especially the way the LCD is mounted deep underneath the window. That's really one of the aspects why I purchased the Fluke as the large digits and LCD contrast seems way beter (and it is).

However the speedy update rate on the u1252b as well as the accuracy and resolution (50.000 cnts) seems tempting. From pictures on the internets the LCD on the u1252b seems a big improvement over the u1241a/b models. What's your thoughts about it?

[Baliszoft]

I got the old 87v. Although the numbers are smaller on the u1252b (due to the dual display), its contrast is better than the old lcd in the 87. Viewing from the side, it is nealy the same, but viewing from top or bottom it is far more visible on the agilent. I like its backlight, too (complete even "warm" orange light, the 87 has darker/ligher spots in it).

[Robomeds]

I know this is an old thread but I thought I was seeing the same thing and thought I would ask.

The other day I noticed the AC current offset on my 87V was around .014 on the display.  I mean the last two digits were consitently 14 regardless of range (0.014 A, 0.014 mA, 00.14 mA, 1.4 uA).  The fact that the offset was always the same number of counts got me thinking there was something wrong with the meter.  I couldn't seem to find anything to cause it.  Shorting the leads, as was mentioned above, didn't take care of it.  Moving closer or farther from power cords didn't seem to mater. 

My first thought was perhaps something was wrong (I previously repaired this meter after an over voltage event).  I checked with some other meters I could get my hands on as points of reference.  A Fluke 27-II shows 1 count in the AC amps range, 2 counts in the AC-mA range. 

I also checked a Fluke 189 (series 1).  It shows a 45 count offset (it's a 50000 count meter). 

Does anyone know what the story is here?  It seems this is not a failure of the meter.  Any thoughts?

[ModemHead]

RMS-responding AC converters have a residual offset which cause non-zero readings with no input. This residual has negligible effect above a certain small percentage of full-scale, so it's not a good idea to use REL or Delta functions.

From Table 14 in the 87V user manual:

[Robomeds]

Thanks!  That answers the question.

Now if I could get you to help me with that bench power supply that isn't cooperating....