Fluke 289 mysterious metering

[Viagra Berlusconi]

As you all probably know, the Fluke 289 has a switch position to measure Volt at LoZ.

Mine shows 2.0 Volt AC when the inputs are shorted, and I can't make sense of that. Shouldn't that be 0.0 Volt instead?

[Simon]

well I assume that by loZ mode you mean the meter has a low input impedence so putting a load on the circuit under test, I assume this is done by putting a resistor in parallel with the probes, in that case there should be 0V without even shorting the probes

[Viagra Berlusconi]

Hi Simon,

by LoZ mode I mean the leftmost position (counterclockwise) of the rotary switch  Unfortunately I have no information how Fluke implemented this mode in their hardware.

I thought there might be something I'm missing because I called their support hotline, whose gentleman assured me that his 289 shows exactly the same Voltage under this condition, so it oughta be correct. I just don't understand the logic behind that, I'm afraid.

[alm]

You don't mention the range. AC voltage accuracy is usually specified from 10% of full scale or so, so 2V on the 1000 VAC range might be in spec, 2V on the 20 VAC definitely not. Are the measurements in spec for a low AC voltage (eg. 20 VAC on the 1000 VAC range, or 200 mV AC on the 2 VAC range) correct?

A small offset on the bottom of the range is normal for True RMS converters. Their linearity drops off at the bottom of the range, so correcting for this offset would reduce the accuracy of the higher part of the range. See this Keithley FAQ for more info.

[Richard W.]

I think it's a PTC resistor in parallel.
With another multimeter you can measure 3,14kOhm, but if the 289 is connected to mains voltage it draws initially 75mA and then drops.

My 289 shows 0,0 VAC and 0,0VDC at LoZ.

If you have a look at the specs it says miniumum 2%+40 digit tolerance. These 40 digits mean 4 Volts.

@alm: in LoZ it's fixed to 1000V range.

[Viagra Berlusconi]

Hi Richard,

if I understand correctly, you're saying that my 289 is well within specs when it shows 2.0 V that aren't there. Right?

[Richard W.]

if I understand correctly, you're saying that my 289 is well within specs when it shows 2.0 V that aren't there. Right?

in my opinion, yes.

alm already described the reason for this behaviour. (nonlinearity below a few percent of the range)

[IanB]

In another thread I have previously asked about my Protek meter reading about -0.0004 V when the probes are shorted on the DC volts range, since none of my other meters read other than 0 when the probes are shorted. However, none of my other meters have 50,000 count displays.

I am trying to determine by how much I should be surprised by this offset voltage and how much it is normal. Do other high precision meters ever display a small offset at zero like this?

[Viagra Berlusconi]

Thanks to all, I think I'm starting to understand how that Accuracy Table works: When there's an entry, say,

2% + 40 (digits)

then it means that the reading can deviate from reality by 2% of the true value (not 2% of the range) plus 40 times the resolution (i.e., whatever-the-smallest-unit-on-that-scale-is). Therefore, if the true value is 0, then 2% of that is also 0, but 40 digits means 40 times 0.1 Volt (if 0.1 Volt is the resolution) ergo 4 Volt.

Hmm. If this is true, then the Fluke 289 (with shorted leads) should also not give a reading of more than 0.06 mV when set to AC mV, since the resolution in that setting is 0.001 mV and the accuracy is (at worst) 1.5% + 60.

Right?

[samgab]

In another thread I have previously asked about my Protek meter reading about -0.0004 V when the probes are shorted on the DC volts range, since none of my other meters read other than 0 when the probes are shorted. However, none of my other meters have 50,000 count displays.

I am trying to determine by how much I should be surprised by this offset voltage and how much it is normal. Do other high precision meters display a small offset at zero like this?

My Fluke 87V has no DC V offset, but it does have a small DC A offset.
In the mA range I get a reading of 0.006 with the leads shorted. And 0.0006 in the A range, and 0.2 in the µA range.
Another 87V I previously had read 0.020mA with the leads shorted from new.

[samgab]

Thanks to all, I think I'm starting to understand how that Accuracy Table works: When there's an entry, say,

2% + 40 (digits)

then it means that the reading can deviate from reality by 2% of the true value (not 2% of the range) plus 40 times the resolution (i.e., whatever-the-smallest-unit-on-that-scale-is). Therefore, if the true value is 0, then 2% of that is also 0, but 40 digits means 40 times 0.1 Volt (if 0.1 Volt is the resolution) ergo 4 Volt.

Hmm. If this is true, then the Fluke 289 (with shorted leads) should also not give a reading of more than 0.06 mV when set to AC mV, since the resolution in that setting is 0.001 mV and the accuracy is (at worst) 1.5% + 60.

Right?

Regarding zero measurements with a True RMS meter on AC this is what Fluke state:

"True Rms Meters accurately measure distorted waveforms, but when the input leads are shorted together in the AC functions, the meter displays a residual reading between 1 and 30 counts. When the test leads are open, the display readings may fluctuate due to interference. These offset readings are normal. They do not affect the Meter’s AC measurement accuracy over the specified measurement ranges. "

[Viagra Berlusconi]

Regarding zero measurements with a True RMS meter on AC this is what Fluke state:

"True Rms Meters accurately measure distorted waveforms, but when the input leads are shorted together in the AC functions, the meter displays a residual reading between 1 and 30 counts. When the test leads are open, the display readings may fluctuate due to interference. These offset readings are normal. They do not affect the Meter’s AC measurement accuracy over the specified measurement ranges. "

Thanks. Provided that I understand the concept of "counts" correctly, my Fluke 289 doesn't seem to work according to specs then. With shorted leads it reads 0.02 V, and 0.2 mV, respectively. That's both off by 200 counts. 

[samgab]

Regarding zero measurements with a True RMS meter on AC this is what Fluke state:

"True Rms Meters accurately measure distorted waveforms, but when the input leads are shorted together in the AC functions, the meter displays a residual reading between 1 and 30 counts. When the test leads are open, the display readings may fluctuate due to interference. These offset readings are normal. They do not affect the Meter’s AC measurement accuracy over the specified measurement ranges. "

Thanks. Provided that I understand the concept of "counts" correctly, my Fluke 289 doesn't seem to work according to specs then. With shorted leads it reads 0.02 V, and 0.2 mV, respectively. That's both off by 200 counts. 

I believe what it's saying is that you can't get a true representation of accuracy with a true RMS meter by just shorting the leads. It will read with offset. To find out it's accuracy, you have to be measuring an actual known AC signal, not zero. So just because of the reading you get with the leads shorted, on AC it doesn't mean it's out of spec.

Edit... I don't think you are understanding "counts" correctly. It's the number of least significant digits, depending on the range you have selected.
Have you watched Dave's video on this subject?

[alm]

samgab was probably quoting the manual for a different meter. The 289 manual states 200 counts on page 67 of the English version from Fluke's website.

[samgab]

samgab was probably quoting the manual for a different meter. The 289 manual states 200 counts on page 67 of the English version from Fluke's website.

Yes, I was (87V manual). What I was trying to draw attention to was the part about how with true RMS meters there will be an offset with the leads shorted, rather than the specific number of counts out.

[Richard W.]

In another thread I have previously asked about my Protek meter reading about -0.0004 V when the probes are shorted on the DC volts range, since none of my other meters read other than 0 when the probes are shorted. However, none of my other meters have 50,000 count displays.

I am trying to determine by how much I should be surprised by this offset voltage and how much it is normal. Do other high precision meters ever display a small offset at zero like this?

My Fluke 289 reads 0.0000V in VDC range, and -0,030mV in mVDC and it's approaching to 0.000.
These readings are maybe caused by thermoelectric effects. That would explain the dropping value.
The voltage drops, when the temerature difference of both contacting metals gets lower.

Thanks to all, I think I'm starting to understand how that Accuracy Table works: When there's an entry, say,

2% + 40 (digits)

then it means that the reading can deviate from reality by 2% of the true value (not 2% of the range) plus 40 times the resolution (i.e., whatever-the-smallest-unit-on-that-scale-is). Therefore, if the true value is 0, then 2% of that is also 0, but 40 digits means 40 times 0.1 Volt (if 0.1 Volt is the resolution) ergo 4 Volt.

Hmm. If this is true, then the Fluke 289 (with shorted leads) should also not give a reading of more than 0.06 mV when set to AC mV, since the resolution in that setting is 0.001 mV and the accuracy is (at worst) 1.5% + 60.

Right?

Yes, but you have to add 20 counts because the reading is below 5% of the range.

My Fluke 87V has no DC V offset, but it does have a small DC A offset.
In the mA range I get a reading of 0.006 with the leads shorted. And 0.0006 in the A range, and 0.2 in the µA range.
Another 87V I previously had read 0.020mA with the leads shorted from new.

Similar effects on my 289 and my 177. Mostly 1 or 2 digits above/below 0.

[ipman]

189 show the same non-zero readings. Worried, I went to the Fluke dealer here, which was kind enough to let me use their calibrator for free.
All readings were 1 digit off the real value of the callibrator. That means one least signifiant digit, and the meter was produced in 2002 and tested in 2011.

My advice (i did the same thing): I found here a REF102 precision voltage reference in an electronics shop here. Altough this is not a match for my 189, it's still 0.025% and 2.5ppm/C. My 189 reads 9.9999 from this voltage reference, which is well withing calibration specs. I've spent less than 10euros here for this reference and the two caps needed for it.

[michael09876]

Hello,

Like Viagra Berlusconi many of us are traumatized with this Loz function on fluke 289 what isn't finish from project also. Not anyone mentioned correctly about this Loz and let mathematics away, in this cause the problem what Berlusconi bring here is about unused function because come just with bind software of just 1000V manual mode and do not lets us read in range for a correct resolution, mode, what is necessary in all functions of all tools measurement. Also, many of us whom buy this model have blocked display when try to measure low tension. Then, this is a fail from FLUKE. 

[R005T3r]

Hi,

I have a Fluke 287 and when the inputs are shorted reads:
uA DC : 0.02
mA DC: 0.001
mV DC: -0.010, after 10 min later is -0.015 (going divergent)
V DC: 0.0001
mV AC: 0.000
V AC: 0.0000

I'm shorting it with a 1.2 meter long cables, but adding more cables to the short does not make any difference (as it should be)...
Also, the instrument has 5 years from now...

Actually I won't call it a fail: handheld DMMs are not meant for ultra low "current/voltage/resistance" applications. The 289 was designed for industrial application/general applications It's very useful when you have to do general stuff and you need something that records events.
But for precision analysis that's why you use a bench-top DMM or if the resolution won't suffice and you have to go on extreme low values you use a specialized unit (see keithley A meter: they go down to pA  range )... Also, other factors such as temperature and many other external events will influence your measurement (your neighbor is using an oven or a vacuum cleaner or a bloody POE)...