Help with Reed Multimeter and mV readings - Page 1
Forum section: electronics / beginners

author: SunBeam
author_rank: Newbie
timestamp: April 04, 2021, 02:35:54 am
content: I purchased a REED R5007 TRMS Digital Multimeter with NonContact Voltage Detector yesterday.I find that the milli-volts voltage reading is not working correctly. I turn the dial from Off to mV, and the dial goes all over the place from 0 to 200 mV continuously, never settling down.--Without the leads connected to any equipment, it reads values from -50mV to +200mV, lots of fluctuations.--With the leads connected to my amplifier, same story, there is also a lot of fluctuation in the value, -50mV to +200mV.--With the leads shorted, it reads zero mV, no fluctuationsThe resistance/ohms, and the voltage/V readings are correct. I tested with a speaker driver which read ohms correctly, and with a AA battery and the "V" setting read 1.5V correctly.For reference here is what I'm trying to do: the 7 steps in the first post herehttps://audiokarma.org/forums/index.php?threads/amplifier-distortion-dc-offset-and-you.5634/I purchased this to measure DC offset in an old stereo amplifier I have. i.e. is there any DC voltage coming out through the speaker terminals.My $5 cheap multimeter reads 38mV from the outputs, but the more expensive Reed is all over the place.Did I get a faulty unit? Am I using it incorrectly (which is possible as I don't have much experience here)? I purchased this brand new, it's just 2 days old.

author: wraper
author_rank: Unknown
timestamp: April 04, 2021, 02:42:51 am
content: Without leads connected, it's normal that multimeter shows fluctuating readings. However it shouldn't do so when leads are shorted together. Cheapest multimeters are less likely to show fluctuations with floating leads because they have much lower input resistance.On a side note, it has ridiculous spec on their website and datasheet.https://www.reedinstruments.com/pdfs/cache/www.reedinstruments.com/r5007/datasheet/r5007-datasheet.pdfAC spec is better than DCQuote

author: SunBeam
author_rank: Newbie
timestamp: April 04, 2021, 03:08:17 am
content: Quote from: wraper on April 04, 2021, 02:42:51 amI should add that when leads are shorted together, it reads zero with no fluctuations. So that works!What I meant in my post is when the leads are not connected to any equipment, or even if they are, the readings fluctuate.I mean, I know this isn't a Fluke, but I thought it would at least be better than than the $5 one I have.I'm just trying to figure out if I should exchange it and get a replacement, or if I'm using it incorrectly.

author: wraper
author_rank: Unknown
timestamp: April 04, 2021, 03:38:09 am
content: Quote from: SunBeam on April 04, 2021, 03:08:17 amIt's most likely a problem with your equipment or your setup, not multimeter.

author: sleemanj
author_rank: Super Contributor
timestamp: April 04, 2021, 05:00:29 am
content: I'd hazard a guess that your two multimeters have different input impedence.The details of the REED say it has DCV input impedence up to 1G and that is probably the case in the DC mV mode.https://www.reedinstruments.com/pdfs/cache/www.reedinstruments.com/r5007/manual/r5007-manual.pdfYour cheaper meter might just have 10M (or less) in it's mV range (if it has a mV range).

author: SunBeam
author_rank: Newbie
timestamp: April 04, 2021, 03:37:20 pm
content: Quote from: sleemanj on April 04, 2021, 05:00:29 amDoes this mean I should use the cheaper multimeter (it's the CEN-TECH which you find everywhere) to measure mV? And use the more expensive one for everything else?Cheapo multimeter specshttps://manuals.harborfreight.com/manuals/63000-63999/63759.pdf

author: SunBeam
author_rank: Newbie
timestamp: May 13, 2021, 12:48:32 am
content: Bumping up a thread from a month ago, I still haven't managed to solve this oneI took a short video of what's going on, with the hope that it makes it easier for someone to follow what's happening.LINK.As you can see, the cheap generic multimeter reads DC mV just right (-37.7mv) on the amp outputs I am trying measure off, and the more expensive REED is all over the place, no steady value either before or after I plug it in.I'm beyond the return window for this, so I'm stuck with it for the time being. Am I using this REED multipeter incorrectly? Any help would be appreciated. Thanks!