Clem Clement
Well-known member
It has got to be me: when I try and use a digital volt meter, the reading never seems to stay constant. I have points on the wires, not clips. I seems like my fingers effect the voltage reading.
Readin a digital V/A meter
- Thread starter Clem Clement
- Start date
ian Simpson
Well-known member
Always use clips and keep your fingers well away. Better yet, sell the digital thing and get an old fashioned analogue device.
It has been my experience (based on fifty plus years in electronics) that inexpensive digital devices should be buried at sea. I still use a 1960's Avometer when I need accuracy.
Rex_A_Lott
Well-known member
I like the HF meters for rough stuff....6V or 12 V or maybe 0 ohm or infinity.
Pinpoint accuracy is not where they are good.
I agree the old analog is best for a lot of things, but for most of us , we can get by with a test light or the cheap VOM, YMMV.
Good luck!
Pinpoint accuracy is not where they are good.
I agree the old analog is best for a lot of things, but for most of us , we can get by with a test light or the cheap VOM, YMMV.
Good luck!
Mike V. Florida
Well-known member
With a name like Simpson I would hope so.
As for the original post, if the engine is running you will not get a good reading. An analog (one with a pointer) meter is best with an engine running.
marc hildebrant
Well-known member
A Digital type of meter uses an a\d (analog to digital) converter on the front end. Most of the low cost models are very sensitive to noise and as such, give unstable readings with the high amount of noise present in the Model A.
A "analog" meter doesn't respond to the noise since the meter's metal pointer can't move as fast as the noise.
Marc
A "analog" meter doesn't respond to the noise since the meter's metal pointer can't move as fast as the noise.
Marc
SeaSlugs
Well-known member
all good points, and yes always keep your fingers off the test lead points especially when taking measurements for accuracy and your own safety.
yes cheap DMM's (digital multi meters) are subject to noise and give bouncy readings, im partial to fluke as i use mine daily in an industrial setting from 24vdc to 600vdc and 600 vac. but flukes aint cheap and overkill for a model A and most cars.
it is hard to get a constant reading using the needle points due to such a small contact area. you and everyone else who uses them will wiggle them ever so slightly while measuring and thus changes the amount of contact (thus resistance) to whatever your measuring. clips are great for this (sometimes, be aware they can pop off and fall on hot parts and or get wrapped up in belts/fans/etc...)
analog meters are great and what everyones said are all valid points BUT you must remember to hook them up polarity correct otherwise you can run the risk of snapping the meter needle off when it pegs the other way.
now i agree with whoever said cheap meters are good enough for car stuff as 98% of the time you just want to know if you have voltage at a point or if the circuit is open somewhere.
and yes model A's do have a metric ton of electrical noise associated with them. even my digital camera when taking video within 2 feet of a running engine you can hear the electrical crackle in the sound recording due to it affecting the camera
yes cheap DMM's (digital multi meters) are subject to noise and give bouncy readings, im partial to fluke as i use mine daily in an industrial setting from 24vdc to 600vdc and 600 vac. but flukes aint cheap and overkill for a model A and most cars.
it is hard to get a constant reading using the needle points due to such a small contact area. you and everyone else who uses them will wiggle them ever so slightly while measuring and thus changes the amount of contact (thus resistance) to whatever your measuring. clips are great for this (sometimes, be aware they can pop off and fall on hot parts and or get wrapped up in belts/fans/etc...)
analog meters are great and what everyones said are all valid points BUT you must remember to hook them up polarity correct otherwise you can run the risk of snapping the meter needle off when it pegs the other way.
now i agree with whoever said cheap meters are good enough for car stuff as 98% of the time you just want to know if you have voltage at a point or if the circuit is open somewhere.
and yes model A's do have a metric ton of electrical noise associated with them. even my digital camera when taking video within 2 feet of a running engine you can hear the electrical crackle in the sound recording due to it affecting the camera
Clem Clement
Well-known member
Thanks all. I'm glad it isn't me doing something incorrectly. I have a huge V/A meter from long ago that is steady as a rock. I use it frequently. I was trying to do the electrolysis test on my radiator fluid and thought the digital would be more accurate.
Checking anti-freeze for 0.5 volts huh?
I carried a Tektronix 465 scope and a Fluke 77 DVM for work ... the one with the beige case and push buttons on the side for 30 years. Seems to me that it jumped around a little with Model A engine running.
I recently picked up a Fluke 77 the newer gray colored one with rotary dial. Will have to test it on running Model A.
I use my personal Simpson 260 analog for running Model As.
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My Sears DVOM is not accurate on voltage measurements. I do use it for checking ohms resistance in modern secondary ignition wires, and for continuity testing. I also prefer analog meters. However, they vary one with another. At the school where I taught Mechanics, we would do a comparison of voltage readings off one battery using Snap-on, Marquette, and Allen meters (all meters calibrated or "zero'd"). All gave slightly different readings! The question still remains: which gives you the correct reading?
Accuracy? Who knows? Over the years, I've come to accept "ballpark" as my indicator of what is happening in the electrical system. And I will not accept the voltage readings from my Sears digital!
Accuracy? Who knows? Over the years, I've come to accept "ballpark" as my indicator of what is happening in the electrical system. And I will not accept the voltage readings from my Sears digital!
jrelliott
Well-known member
Noise as an earlier post noted is the main cause of fluctuating readings of a Digital Multi meter on the Model A when it is running. I still use a old analog multi-meter that I purchased in '63 while an Electronics Technician in the Navy and used it for the remainder of my enlistment as my personal meter along with my own tools never loaning it out. It is still very accurate as is a later Radio Shack FET input Multi-meter that a friend gave me. Simpson and Fluke analog meters are some of the most accurate if they are calibrated and kept away from people that do not know how to use them accurately. (i.e. Measuring voltage on a resistance scale). They are precision instruments and treat them as such. Where I worked we had calibration labs that certified all the instruments used to test components were within specifications to certify that the product we produced met the specs.
