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SaltiDawg

MD suburbs of DC

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Posted: 02/11/18 04:54pm Link  |  Quote  |  Print  |  Notify Moderator

Deleted by SaltiDawg as not adding value.

* This post was edited 02/12/18 06:55am by SaltiDawg *

MEXICOWANDERER

las peñas, michoacan, mexico

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Posted: 02/11/18 05:34pm Link  |  Quote  |  Print  |  Notify Moderator

+ - 5 LSD

Better the Least Significant Digit be in the thousandths of a volt column than the hundredths.

I know of DOZENS of different digital 3-1/2 meters that were so laughably inaccurate (three tenths of a volt in error plus or minus)

And one DROK 3-3/4 digit meter that hunted yes HUNTED +4 -3 TENTHS of a volt when connected to a nine volt alkaline battery sitting on my bench.

Just bought a round digital 2-3/4 digit volt meter for a friend. He chose it because of the colored arc of lights which may or may not help him get a rough idea of charger voltage at a distance. Error = .2 volt low. Yes. two-TENTHS.

The 5.0 digit panels meters I checked were qualified by lab calibration. If you doubt the continuity of accuracy in this line, the URL was given. If you test one and find error, please notify along with giving modality of your qualification -- the more testing and verification, the better.

SaltiDawg

MD suburbs of DC

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Posted: 02/11/18 06:28pm Link  |  Quote  |  Print  |  Notify Moderator

Deleted by SaltiDawg as not bringing added value and not being appropriate.

* This post was edited 02/12/18 06:57am by SaltiDawg *

mike-s

Michigan

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Posted: 02/11/18 06:59pm Link  |  Quote  |  Print  |  Notify Moderator

SaltiDawg wrote:

However if you think that having a meter that is a) Calibrated and b) Displays to five decimals is accurate to five places - which presumably requires a round off for at least the final digit - you would be sadly mistaken.
Sometimes you want resolution for precision, not accuracy. e.g. relative measurements.

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BFL13

Victoria, BC

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Posted: 02/11/18 07:23pm Link  |  Quote  |  Print  |  Notify Moderator

What you want is a meter that may be off, but is consistent. You can use that with confidence. Doesn't matter what it says-- if you know the "index error", just apply that each time. What really matters is to observe any change from last time.

I have no problem with my cheapo hydrometer eg. It does not need to be accurate and temp compensated. It just has to tell me if anything is out of whack since the last reading.

Same thing with the multimeter. Only thing there is the battery getting low makes the voltage reading wrong. It happens slowly, so you can be fooled for a while until you catch on that it is the battery.


1991 Oakland 28DB Class C
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SaltiDawg

MD suburbs of DC

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Posted: 02/11/18 07:34pm Link  |  Quote  |  Print  |  Notify Moderator

Deleted by SaltiDawg as simply being of no value.

* This post was edited 02/12/18 06:59am by SaltiDawg *

MEXICOWANDERER

las peñas, michoacan, mexico

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Posted: 02/11/18 07:55pm Link  |  Quote  |  Print  |  Notify Moderator

When I am pre-sorting resisance or voltage for power supplies "almost" doesn't cut it. You didn't ruffle any feathers, and I had hoped that I made it clear that seeking accuracy was my own personal objective - solely. You are quite correct about resolution versus comprehensibility by the user. I choose 5.0 digit meters for my customers. Then black out the least significant digit with an ultra-heavy duty marker whose medium actually melts the tint into the meter's plastic lens.

The value of hundredths?

If the voltage is creeping up in the hundredths scale, there is no guarantee it will not impact the tenths to as much as 1 or 2 tenths. Yes a person can stand by a meter for 15 minutes to hope the tenths will not trip, but by seeing the hundredths ascend (or not), there is no guesswork. And if the voltage is hunting, a person had better be interested in finding out why.

A meter that reads 13.96 volts rather than 14.2 is intrinsically tricky.

If a person should reverse engineer some of these cheapo panel meters, they should find the same thing as I did, the comparator circuits are a world different between garden variety 2-1/2 - 3-3/4 digit meters and the 5.0 digit.

RC racers are demanding LSD accuracy much greater than what the general market demands.

People with batteries can have at their fingertips a qualifier for voltage that costs disproportionately to its accuracy. I choose to use these meters for my power supply products because they simply do not cost but pennies more than lesser meters. And Magic Marker scrawls are worth a small fraction of a cent.

I have a 3-1/2 lb box of bad NEW meters that can your's for the asking. Simply pay postage [emoticon]

An aside: Late 1960's...
"Say, did you know your speedometer reads seven miles per hour slow?"

"Does not"

"I checked it against the 4 mile-markers last week and a mile takes a hair under 53 seconds" I didn't continue that his 20 mpg mileage did not work for me -- I got 14.

Several miles later, a siren. A half-hour on the shoulder, and a scowling acquaintance got in and slammed the door.

It turned out it was all my fault because I had brought up the subject. We continued on in silence.

Any argument should be taken up with the battery. I'm easy going -- it isn't...

mike-s

Michigan

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Posted: 02/11/18 08:15pm Link  |  Quote  |  Print  |  Notify Moderator

MEXICOWANDERER wrote:

If a person should reverse engineer some of these cheapo panel meters, they should find the same thing as I did, the comparator circuits are a world different between garden variety 2-1/2 - 3-3/4 digit meters and the 5.0 digit.
Which of those panel meters has a comparator? Op-amp(s) and A/D, sure, but what would those cheapo ones use a comparator for? They're certainly not doing A/D with discreet comparators. Most likely a cheap integrated 16 bit A/D.

It's not clear what you mean by "2-1/2 - 3-3/4 digit meters and the 5.0 digit" The meter you showed is a 4 3/4 digit one. What's a "5.0 digit" display?

bucky

Chattahoochee Bend Newnan GA

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Posted: 02/12/18 05:27am Link  |  Quote  |  Print  |  Notify Moderator

I think that most of us on here could use a test light most times we reach for a MM. On DC related RV issues anyway.
As a result my favorite MM is the one I find first.


2005 Cummins 2500 2WD LB quad cab pulling a 2007 Jayco 345bhs. It pulls better than Marcell Ledbetter's mule.

Bumpyroad

Virginia

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Posted: 02/12/18 06:39am Link  |  Quote  |  Print  |  Notify Moderator

out of curiosity, what normal reading related to RV maintenance really requires a precise reading? ego, rocket science? or dueling meters, "My meter is bigger than yours?" I'm trying to find that 480 volt source in my TT and can't locate it.
bumpy





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