Digital multimeters, should we trust them?

mcgivor · November 2016

During an EQ set to 30.2v, the remote meter of my charge controller read 30.2v at the battery, I grabbed my UEI clamp on and connected it to the battery terminals and it measures 29.98v, so to make sure it was correct I connect a Fluke 179, it reads 30.22v, so I connect all the meters I have, here is the result. The UEI was the cheapest at $120, Fluke 12 $130, Ideal $220 and the Fluke 179 $350, not sure if it's a case of you get what you pay for but got me wondering what a $20 meter would read. Despite the fact the Ideal reading 30.2 as it only measures tenths, it is still more accurate of a reading. Measuring current, UEI measured 6.55A and Ideal 5.2A , although I've never fully trusted clamp on DC meters and consider the readings a rough estimate, in line is best though impractical.

softdown · November 2016

I'd be very encouraged by the accuracy of those readings. My suspicion is that the health of a meters battery may effect readings. I also like to get readouts beyond tenths. I have three clamp meters that rarely work as designed.

Four good meters? Wow.

softdown · November 2016

I just ordered the Ideal 61-766. Was interested in the Ideal 61-768 but it had no reviews at Amazon where I often buy. I like to see a couple reviews. Got a used one...on a very tight budget. Will need a manual I am sure.

Wish I would have noticed that you have the 61-768 when evaluating it.

Cheaper clamp meters don't seem to work worth a hoot.

mcgivor · November 2016

The 61-766 is basically the same as the 61-768 but lacks the DC amp feature, manual attached.

softdown · November 2016

Awesome...thanks!

People have a hard time believing that 9 volt batteries are actually 6 unsleeved AAA batteries. My dad was a medical electrician for over 40 years. He always swore by 9 volt batteries. Obviously did not know what they are made of.

I still prefer a 9 volt instead of some AA's or AAA's for some reason.

mike95490 · November 2016

softdown said:

Awesome...thanks!

People have a hard time believing that 9 volt batteries are actually 6 unsleeved AAA batteries. My dad was a medical electrician for over 40 years. He always swore by 9 volt batteries. Obviously did not know what they are made of.

I still prefer a 9 volt instead of some AA's or AAA's for some reason.

Huh ? All the rectangular 9V rectangular batteries I took apart, were a stack of little rectangular cells
I've seen some 6V spring top lantern batteries made up of a dozen or more, AA cells stacked in double layers.

softdown · November 2016

I don't take many apart. That is what I have seen.

BB. · November 2016

https://en.wikipedia.org/wiki/Nine-volt_battery

Image: https://qph.ec.quoracdn.net/main-qimg-f741a27cef72e9f13a39c0785f08d159-c?convert_to_webp=true

I used to see the left battery about 50+ years ago (carbon-zinc stacked cell "rectangles" also seen in 45 and 90 volt tube type radio batteries for "portable" radios)... The one on the right is what I have seen (alkaline) over the last few decades--the few I have taken apart. The center rectangular stacked battery is Alkaline too.

Guess I have not bought a carbon zinc battery in a long time...

-Bill

oil pan 4 · November 2016

I only use fluke meters too and they can give weird reading when the battery gets low. If the low battery light comes on, don't trust the readings just change the battery.

mcgivor · November 2016

Changed all batteries, same reading, perhaps the UEI needs calibration.

softdown · November 2016

Should we trust multimeters? A properly used and high quality multimeter......then yes. It is too easy to get bad readings with a low quality meter and grabbing a single reading.

MichaelK · November 2016

Are there NIST standards for voltage and amperage? I assume there are.

I've been shopping for clamp meters recently because I wanted to determine the draw on my 240VAC well pump. I started out with an inexpensive Chinese meter, the Uni-T 203. It measured the running AC amperage at 9.9 to 10.0. It does not measure in-rush (start-up current). For that I subsequently bought an expensive Fluke 326. The in-rush for the pump was 36-38 amps, while the running current was 10.0. These two running readings are accurate to within 1% of each other. Subsequently I spotted another inexpensive Chinese meter, the Uni-T 216 that does have in-rush capability. Again, the readings of 37.6/10.1 match the Fluke within 1% for both in-rush and running amps.

Going further I compared the running voltages (this is with my generator powering the well pump). The Fluke reads 240.2, while the 216 reads 240.6VAC.That's accuracy better than 99.5%. The question is, is the Fluke more accurate than the Uni-T, or is the Uni-T more accurate than the Fluke? Assuming that because the Fluke costs 5X as much, the quality should be 5 times higher, right? So, who is actually in charge of guaranting the accuracy of these meters? Here is the 216...

http://www.ebay.com/itm/UNI-T-UT216C-RMS-600A-Digital-Clamp-Meter-Frequency-Cap-Temp-NCV-Tester-S7A0-/141981828468?hash=item210ec6c574:g:~yYAAOSwKfVXKXia

BTW, my wellpump is a 240VAC three-wire capacitor-start Grunfos 1.5hp pump. Its insightful that the startup current is almost 4X the running current.

jonr · November 2016

I have a Mastech MS2108 - measures inrush current and uses RMS.

mcgivor · November 2016

Not all meters are created equal, there are category ratings which determine where a meter may be used, this will determine price to a large degree. As an electrican working on distribution systems I had to choose higher ratings but for the purposes of working on most solar systems a cheap meter will suffice however the higher voltage systems such as the 600V Morningstar systems may require a higher category rating. See PDF for details.

PNjunction · December 2016

Measuring battery terminal voltages is one thing, but if you are doing systems-type work, or measuring voltages across long cable runs, or next to other wiring, that's another.

If you are doing more than just measuring battery terminal voltages, give some thought to a multimeter with a "Low-Z", or low impedance to avoid reading phantom induced voltages. The Fluke 114 comes to mind as an inexpensive example. Check your own meter to see if it has a low-impedance option.

Generally, when choosing a multimeter, it is best to decide upon an "electrician's" multimeter, or an "electronics" multimeter. That is, if you are doing mostly electrical work (systems wiring and such), vs circuit-board type measurements (electronics work), the electrician's multimeter, with a Low-Z option, is something to consider. Or course get a "true-rms" meter to make ac measurements more accurately.

Using the Fluke 114 as an example, it will do *both* low-impedance or high-impedance measurements - manually selected of course. Choose the right mode for the type of work you are doing.

Dave Angelini · December 2016

Adding here to the excellent previous post that if the meter is over 1 year old it needs a calibration.
For critical measurement, either calibrate or buy a new meter.
Most corporations calibrate new equipment also.

mike95490 · December 2016

Any ideas to avoid a $200 calib fee for a $90 meter ? What about using some sort of primary lithium 9V battery as a voltage reference to set your meter with.

jonr · December 2016

You can buy voltage references like this one:

http://www.voltagestandard.com/Home_Page_JO2U.html

PNjunction · December 2016

Recalibration for a second-hand 1980's vintage Fluke? Sure. New, single-owner, and for about a decade afterwards, not so much.

Ask yourself how much accuracy do you REALLY need? Can you tolerate setting your lead-acid CV parameters 0.1 to 0.2v off? Quite possibly. Working with lithium? You want that tight, as a 0.1v inaccuracy can prove disastrous.

Recalibration yearly under our non-manufacturing environment, would be total overkill for a Fluke.

There are MANY fine meters out there, not just Fluke. BUT, the thing here is a level of out-of-the-box trust. And something which you can rely upon as your reference for everything else. At the very least, it will put your mind to rest if your existing meters have been in or out of the ballpark.

Note that even my 87V is total overkill for basic solar maintanance duties. When I picked up additional Flukes, I went inexpensive with the 11x line. They lined right up with the 87-V. Even good enough for lithium work.

So unless one is a manufacturer, or for some reason their calibration needs to be 0.0001v accurate, or swinging their multimeter from the bottom of a 4x4 off road race, recalibration of a Fluke is total overkill.

PNjunction · December 2016

Um, that last sentence should read "yearly recalibration of a well-cared for Fluke" is total overkill. 10 years if you are an average consumer with high-calibration needs working with lithium or just a total stickler going beyond your application's need for accuracy.

mcgivor · December 2016

To add to the whole equation the calibration must take place at a certain temperature, say 20 deg.C for example, so the readings outside these parameters would be erroneous, so perhaps we shouldn't get to serious about the slight deviations and just accept the readings as a close representation of what it actually is.Calibration may well be the manufacturer's way to reap in some extra income, post sales, or to price the calibration high enough to promote the sale of the next generation meter, which too will need calibration, and on and on.

softdown · December 2016

I'll guess that most of the regular posters here own about 1/2 dozen multimeters.....of varying quality. If four meters deliver the same read-out, I would have confidence in that measurement.

$200 for calibration is a complete rip-off. I'll bet that a lot of variances can be explained by the health of the multimeter battery. What if someone jammed lithium batteries in their multimeter? They deliver quite a bit more voltage in those I have tested.

Dave Angelini · December 2016

mike95490 said:

Any ideas to avoid a $200 calib fee for a $90 meter ? What about using some sort of primary lithium 9V battery as a voltage reference to set your meter with.

There is a cal lab in Santa Clara I use that will do a DC range or 2 for $45. Most do not need this but I do as I sometimes have to show the data. Embarrassing to be wrong. If you look at the pix you can see that a good calibrated meter is needed. The other way is just buy a new meter which (the good makes) have the Cert.

softdown · December 2016

mcgivor said:

The 61-766 is basically the same as the 61-768 but lacks the DC amp feature, manual attached.

The 766 provides another decimal point of reading. For example: 12.64 volts rather than 12.6 volts. The 768 is built for 1000 volts instead of the usual 600 volts.....or perhaps that is 1000 amps. The trade-off is losing a decimal point in the read-out.

I now have both. I keep looking for a clamp meter that works on low output DC lines. Perhaps I am doing something wrong....

Digital multimeters, should we trust them?

Comments

Categories