DMM accuracy question

[emoze]

i have a older Fluke 88; after zero'ing on mV, mA, or ohms; when i attach leads, the readings get a bit erratic & don't hold zero even after i re-zero;

is this normal?

the variation ("bouncing" readings) is a problem especially when trying to read parasite draw or when using both eis & innova amp-clamps with mV output

- i've tried both oem Fluke leads & aftermarket leads with same results; my 88 was factory re-calibrated in 2014 & has not been used much since then

(if a new 88V behaves the same, there's no reason to upgrade; but if it always holds on steady zero's then i'm ready to order one)

 

[minke]

My Fluke 115 is the same. My inference has always been that with auto-ranging it is presenting small voltages from induction in the leads. I never pursued it further. It doesn't diminish my confidence in the meter.

 

[theoldwizard1]

My experience is that most bouncing is caused by the way the probes are connecting to the source or movement. Use alligator clips or pieces probes.

 

[minke]

To clarify: with the leads plugged into the meter and not yet attached to what I will measure, I experience the numbers flying around.

… I just went to actually look instead of relying on me geriatric memory. Reading DC volts with the test leads in the meter but not connected to anything and making no effort to keep the leads separate what I read was ±5 millivolts. To my mind that is noise.

 

[Wrench97]

Mine does that, but if you touch the leads to each other it goes to 0.

 

[BukitCase]

If you're looking at parasitic levels you're probably on the most sensitive scale - these days an open lead is enough of an antenna to pick up all kinds of airborne noise that can cause the readout to wander - easy way to see if it's the meter is just short your leads together (as Wiz pointed out, alligators or other clips will remove your personal "jitter" factor.

If you're in a REAL "dirty" area electronically, you might STILL see some fluctuation but it should be a LOT less than with open leads... Steve

I gotta learn to type faster; between Wrench and me, you got the simple answer and the not so much simple one

 

[unslow1]

I have had a Fluke for many years but I don't really use it because the way it bounces drives me crazy. Not all brands do that.

 

[BukitCase]

BTW Minke - I've worked in industrial control panels where a wire I was tracing had 60 volts AC on it, and was NOT CONNECTED to ANYTHING (just an abandoned wire, about 8 feet long, picking up inductively. Hooking a Wiggie to it caused my DMM to drop back down near ZERO (Wiggies are pretty low impedance with a coil and a neon light, most DMM's are several MEGohms so don't load things... Steve

 

[minke]

BTW Minke - I've worked in industrial control panels where a wire I was tracing had 60 volts AC on it, and was NOT CONNECTED to ANYTHING (just an abandoned wire, about 8 feet long, picking up inductively. Hooking a Wiggie to it caused my DMM to drop back down near ZERO (Wiggies are pretty low impedance with a coil and a neon light, most DMM's are several MEGohms so don't load things... Steve

I haven't seen that but I do indeed believe you. You reminded me that I learned with my old man's Simpson 260 and I just looked up it's sensitivity: DC: 20KΩ/volt and AC: 5KΩ/volt!

 

[BukitCase]

I still have a Tripplet 630, I think I even remember where it is - IIRC, those took a really weird battery, if I get a bit more curious I might dig it out and see if it still works - I'm kinda "DMM poor", 3 or 4 flukes, couple Keithleys, a Tektronix TX3, plus several clamp-on's, HV probes, etc - Some of the electrostatic scrubbers at work had plate voltages around 50KV

Been awhile, can't forget that analog meters aren't quite as idiot-proof as digital - they last longer if you remember what voltage (and polarity, if DC) you expect

 

[oldmachinenut]

I had a student ask about this one day in the classroom. I laid the leads straight out on a bench and the meter was fluctuating. I had the class gather around the meter then turned the fluorescent lights off and shined a flashlight on the now stable meter display.

 

[2ndGearRubber]

I had a student ask about this one day in the classroom. I laid the leads straight out on a bench and the meter was fluctuating. I had the class gather around the meter then turned the fluorescent lights off and shined a flashlight on the now stable meter display.

Exactly, ghost voltage.

 

[engineer2]

to put it simply, your meter leads act like an antenna. They will pick up any stray voltages and display it.

 

[tool_scrounge]

Have you swapped the battery? I was getting odd readings on my Fluke 87 III. After doing some research, I installed a new battery and all was fixed. The low battery indicator was never on.

 

[cvairwerks]

Analog meters are becoming a lost tool for troubleshooting these days. There are areas where the analog shines and is a much better tool. For example, doing continuity checks, I can ring thru a huge wire bundle that terminates in a few branches, significantly faster than using a digital. Unless you need the line resistance, you only need to see a meter deflection to determine continuity. You don’t have to wait for the display to settle and stabilize on a reading. The beep function is not much of a help in high noise environments, or where the meter has to be placed at a significant distance from a user, but within eyesight.

How about just needing to see if there is any voltage on a wire... Same thing, a meter deflection is all you need. Chasing a variable voltage... Peak hold is great on the digital. Same for taking timed readings and downloading them into graphing software.

VTVM’s still out shine DMM’s for some things. One needs to select the best type tool for the need at hand.

 

[Citation]

Have you swapped the battery? I was getting odd readings on my Fluke 87 III. After doing some research, I installed a new battery and all was fixed. The low battery indicator was never on.

That's very odd. Part of Fluke's safety is that the meter is accurate so long as the battery indicator isn't on. The idea being, if the battery is low enough to affect accuracy it could result in a safety issue. The newer meters refuse to display a measurement if the battery level is low. I don't recall how the 87-3 did it (it's been a decade since mine went away - damn good meter).

 

[Citation]

i have a older Fluke 88; after zero'ing on mV, mA, or ohms; when i attach leads, the readings get a bit erratic & don't hold zero even after i re-zero;

is this normal?

the variation ("bouncing" readings) is a problem especially when trying to read parasite draw or when using both eis & innova amp-clamps with mV output

- i've tried both oem Fluke leads & aftermarket leads with same results; my 88 was factory re-calibrated in 2014 & has not been used much since then

(if a new 88V behaves the same, there's no reason to upgrade; but if it always holds on steady zero's then i'm ready to order one)

As others said, the leads act like antennas so high impedance inputs (voltage, mA) can/will move around when the leads are plugged in but not connected. The bouncing should decrease if you short the leads but it should be basically zero. The same is true of the mA range. The behavior between AC and DC will be different and AC is likely to dance around more than DC. The resistance range is different. It should read out of range/over range or similar when the leads are open. That's because open leads is a very high resistance.

 

[tool_scrounge]

That's very odd. Part of Fluke's safety is that the meter is accurate so long as the battery indicator isn't on. The idea being, if the battery is low enough to affect accuracy it could result in a safety issue. The newer meters refuse to display a measurement if the battery level is low. I don't recall how the 87-3 did it (it's been a decade since mine went away - damn good meter).

I agree. Very odd. I only tried the swap battery solution after seeing other posts of the same problem and that fix online. Never saw that with my original Fluke 87. Still a nice meter though.

 

[Iridium rand]

Mine is stable on the resistance setting, but all meters I’ve ever used display minute fluctuating ghost voltage when on that setting

 

[Bad Habit]

Analog meters are becoming a lost tool for troubleshooting these days. There are areas where the analog shines and is a much better tool. For example, doing continuity checks, I can ring thru a huge wire bundle that terminates in a few branches, significantly faster than using a digital. Unless you need the line resistance, you only need to see a meter deflection to determine continuity. You don’t have to wait for the display to settle and stabilize on a reading. The beep function is not much of a help in high noise environments, or where the meter has to be placed at a significant distance from a user, but within eyesight.

How about just needing to see if there is any voltage on a wire... Same thing, a meter deflection is all you need. Chasing a variable voltage... Peak hold is great on the digital. Same for taking timed readings and downloading them into graphing software.

VTVM’s still out shine DMM’s for some things. One needs to select the best type tool for the need at hand.

I have a ~40yo Amprobe that I use quite a bit because of that, postive indication of voltage, etc. Had a Greenlee DMM that didn't indicate voltage on a hot circuit, haven't really trusted DMMs since.

 

[theoldwizard1]

Contact Fluke. They can recalibrate the meter. Not going to be cheap !

 

[ddawg16]

Contact Fluke. They can recalibrate the meter. Not going to be cheap !

Almost cheaper to buy a new meter.

Those Flukes have a real high input impedance.
I just checked my Fluke 179.
On AC with the leads open....voltage is all over the place. When I short them, it slowly works it's way to 'almost' 0. Stopped at 0.4mv
On DC, pretty much near 0 Vdc. Short the leads...0.0000

The 60 Hz AC noise in the typical house/garage is a lot. Near a car running? Even more noise from the ignition.
Want to see it really get noisy? Put it close to your wife.

 

[RPH]

Try twisting the leads together. This helps cancel the noise you are seeing.

 

[theoldwizard1]

Those Flukes have a real high input impedance.

For a low impedance meter, you can't beat an analog Simpson 260 !

 

[ddawg16]

For a low impedance meter, you can't beat an analog Simpson 260 !

I still have a 260
Nothing beats an analog meter when trying to set up an SCR

 

[emoze]

Contact Fluke. They can recalibrate the meter. Not going to be cheap !

NO THEY CAN'T - WON'T - too old - they offered a 20% discount on a new 88V; it was re-calibrated in 2014

 

[emoze]

great comments above from y'all who use these things regularly - many thanks -

'yep - touching the leads together halts the fluctuation on mV - will also try the twisted leads idea -
haven't tried the other scales yet

this was never a "problem" { until i tried using the meter with an amp-clamp for parasitic draw on mV scale) - turns out the 88 is simply not suited for that purpose

see post #18 here
https://www.garagejournal.com/forum/threads/dmm-amp-probes-for-parasite-draw.496286/#post-9545384

"Your 88 Fluke's lowest mV range (for reading amp clamp results) is 600.0mV, which is just too high. Your Innova 3347 clamp has a setting for 10mV/1A which means that 30mA of actual current flow would show up on your multimeter as 0.3mV. That means any low value you measure using an amp clamp is going to be completely lost in the error and slight fluctuations of your meter when at the lowest range setting.

You really need a meter capable of measuring at least to the second digit after the decimal point for the mV function. "

sure enuf - when i use the 88 in series i read 22mA draw on my current parasite gremlin issue, but using the clamp gets me anywhere from 1.8-5.3 mV reading (before conversion) which is not confidence building - i just want to avoid having to disconnect batteries for parasite diagnostics

S0 - ?? anybody got a recommendation for a new meter that can do this?

 

[cvairwerks]

A VTVM or scope if you want reliable capability.

 

[minke]

A VTVM or scope if you want reliable capability.

I can see a new thread here on GJ in six months: "Who on ETSY makes the best replacement vacuum tubes?"

 

[cvairwerks]

I can see a new thread here on GJ in six months: "Who on ETSY makes the best replacement vacuum tubes?"

LOL...you would be surprised at how many manufacturers are making tubes these days. The Nixie is back in production, Western Electric is producing again, there is a guy in Japan making some high end audio power tubes....

 

[BukitCase]

Amazing what die-hard tube sound afficionados, psychotic oligarchs and threats of EMP's can resurrect

 

[ddawg16]

great comments above from y'all who use these things regularly - many thanks -

'yep - touching the leads together halts the fluctuation on mV - will also try the twisted leads idea -
haven't tried the other scales yet

this was never a "problem" { until i tried using the meter with an amp-clamp for parasitic draw on mV scale) - turns out the 88 is simply not suited for that purpose

see post #18 here
https://www.garagejournal.com/forum/threads/dmm-amp-probes-for-parasite-draw.496286/#post-9545384

"Your 88 Fluke's lowest mV range (for reading amp clamp results) is 600.0mV, which is just too high. Your Innova 3347 clamp has a setting for 10mV/1A which means that 30mA of actual current flow would show up on your multimeter as 0.3mV. That means any low value you measure using an amp clamp is going to be completely lost in the error and slight fluctuations of your meter when at the lowest range setting.

You really need a meter capable of measuring at least to the second digit after the decimal point for the mV function. "

sure enuf - when i use the 88 in series i read 22mA draw on my current parasite gremlin issue, but using the clamp gets me anywhere from 1.8-5.3 mV reading (before conversion) which is not confidence building - i just want to avoid having to disconnect batteries for parasite diagnostics

S0 - ?? anybody got a recommendation for a new meter that can do this?

Assuming you're measuring DC....and chasing a very small current draw....try putting a 10 ohm 5w resistor in series. Then measure across the resister. A 20ma current will show up as 0.200 Vdc.

 

[mrjaw14]

Sounds like you're describe ghost voltage. This is actually a useful phenomenon. Ghost voltage = open circuit. If you went to ground it should be true 0.00 volts, and anything else is source voltage.

On ohms scale you do have to take lead resistance into account if you are testing a very low resistance widget.

 

[richfinn]

I answered in your other thread, the "ghost voltage" on the DCV setting is a great asset for automotive diagnostics, it saves a lot of time switching to ohms or disabling circuits when looking for basic continuity.

As long as it reads 0.00v or 0.000v with the probes shorted your good to go!!!

 

[BukitCase]

"On ohms scale you do have to take lead resistance into account"

A few of my DMM's have a "delta" button, clip the leads together and push the button, this becomes your new zero "reference" -

I got curious about how much effect twisting the leads has - it's a LOT. Sitting in my studio, 6' leads on the Tektronix TX 3 - held the leads out straight, no twist, AC only - 55-60 mV. Twist the leads (fairly loose, about 1 twist in 4" - readings bounced between 4-6 mV with leads essentially in the same location/orientation. Switching to DC only, no twist - open leads still below 1 mV. About what I expected.

No surprise to me, been dealing with mostly shielded (grounded ONLY on one end, AKA "telescoping shield") twisted pair for years.

For un-balanced gear one of my most looked at specs is CAPACITANCE, normally spec'd in pF per foot - with the high impedance connections used in semi-pro gear, that impedance can SERIOUSLY affect high frequency response, because it teams with inter-electrode capacitance to form a low pass filter (as in, LESS HIGHS)

I have a couple of condenser mics (old term, should be updated to "capacitor" but hasn't been) that I had to rig a small Faraday cage around 'em before I could get rid of the local FM radio station - just proper shielded cables made ZERO difference. With all the **** that's floating around in the air, it's hard to believe ANYTHING works any more... Steve

 

[dogdog]

Does it matter if it is within a 1% 5% measurement range for you? Unless you are in that scientif-ma-testicle lab group of people that needs their instruments certified every year or two, most of the DMM is good enough accuracy for trouble shooting many of the things. It is dependent on how you use your tools at this point. I know some one will jump in and say yeah **** if that 1% off will completely F-ed my troubleshooting... well buddy, you needed a new skill or brain more than a new 99.999% accurate tool.

 

[Citation]

great comments above from y'all who use these things regularly - many thanks -

'yep - touching the leads together halts the fluctuation on mV - will also try the twisted leads idea -
haven't tried the other scales yet

this was never a "problem" { until i tried using the meter with an amp-clamp for parasitic draw on mV scale) - turns out the 88 is simply not suited for that purpose

see post #18 here
https://www.garagejournal.com/forum/threads/dmm-amp-probes-for-parasite-draw.496286/#post-9545384

"Your 88 Fluke's lowest mV range (for reading amp clamp results) is 600.0mV, which is just too high. Your Innova 3347 clamp has a setting for 10mV/1A which means that 30mA of actual current flow would show up on your multimeter as 0.3mV. That means any low value you measure using an amp clamp is going to be completely lost in the error and slight fluctuations of your meter when at the lowest range setting.

You really need a meter capable of measuring at least to the second digit after the decimal point for the mV function. "

sure enuf - when i use the 88 in series i read 22mA draw on my current parasite gremlin issue, but using the clamp gets me anywhere from 1.8-5.3 mV reading (before conversion) which is not confidence building - i just want to avoid having to disconnect batteries for parasite diagnostics

S0 - ?? anybody got a recommendation for a new meter that can do this?

What amp clamp are you using. I don't recall the 88 specs (is it an 88-1, 88-3 or 88-5). In general, I doubt the meter is the issue. The clamp may not have the resolution for the job but it may be something else. If the meter were any model of 87 I would say the issue isn't the meter.

 

[dogdog]

S0 - ?? anybody got a recommendation for a new meter that can do this?

not sure what you are doing that needs super accurate reading assuming that your technique is top notch already.. maybe give these guys a call ... I think lots of industrial ppl get stuff from them.

https://www.tequipment.net/

 

[BukitCase]

"Unless you are in that scientif-ma-testicle lab group of people that needs their instruments certified every year or two"

4 decades ago that's EXACTLY where I was; by default I ended up being Svc Mgr of 3 different divisions of the same company - one was consumer level audio/video, second was pro versions of those, third was a NIST certified cal lab (actually NBS traceable, before NIST) that had both industrial and military contracts. 12 techs not including myself. Virtually ALL calibration got done in a 16' x 20' Faraday cage (a REAL one)
Wearing all those hats I got used to ***-u-me-ing that perfection was NOT an option - old habits seem to die hard

I agree though - in a LOT of stuff, perfection is rarely needed (except maybe EMOTIONALLY ) ... Steve

 

[Citation]

great comments above from y'all who use these things regularly - many thanks -

'yep - touching the leads together halts the fluctuation on mV - will also try the twisted leads idea -
haven't tried the other scales yet

this was never a "problem" { until i tried using the meter with an amp-clamp for parasitic draw on mV scale) - turns out the 88 is simply not suited for that purpose

see post #18 here
https://www.garagejournal.com/forum/threads/dmm-amp-probes-for-parasite-draw.496286/#post-9545384

"Your 88 Fluke's lowest mV range (for reading amp clamp results) is 600.0mV, which is just too high. Your Innova 3347 clamp has a setting for 10mV/1A which means that 30mA of actual current flow would show up on your multimeter as 0.3mV. That means any low value you measure using an amp clamp is going to be completely lost in the error and slight fluctuations of your meter when at the lowest range setting.

You really need a meter capable of measuring at least to the second digit after the decimal point for the mV function. "

sure enuf - when i use the 88 in series i read 22mA draw on my current parasite gremlin issue, but using the clamp gets me anywhere from 1.8-5.3 mV reading (before conversion) which is not confidence building - i just want to avoid having to disconnect batteries for parasite diagnostics

S0 - ?? anybody got a recommendation for a new meter that can do this?

OK, I went back and looked at the other thread. The issue isn't that your meter isn't accurate enough. I suspect your Fluke 88 has resolution down to 0.1mV. Your amp clamp in the 20A range is 100mV/A. However a 0.02A signal is 0.2mV so basically just 1 count per 10mA. You basically need an amp clamp with a lower range. Odds even if you had a perfect meter, your amp clamp is getting rather noisy at that low current level as well. One of the things I like about the UniT UT210e is the clamp has a 2A range. The minimum current reading resolution is 1mA thus your 20mA target is an order of magnitude higher. That's good.

Anyway, right now you are doing the equivalent of taking a 12" ruler and a good magnifying glass to try to measure something that should be measured with calipers. The amp clamp is operating right at it's noise floor and the meter isn't far from its own noise floor.

I bet there is nothing wrong with your Fluke.
https://www.amazon.com/dp/B0188WD1NE/?tag=atomicindus08-20
In the 2A range this has a resolution of 1mA. A ~20mA signal is well into it's reasonable range.