EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Bobson on July 02, 2016, 02:40:07 pm
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Is (was) there any international standards on analog meters precision?
Most of meters from my collection have 0.2-0.5% precision (mostly dedicated V- and A-meters), some have 0.1%. Do they count as lab grade meters?
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I don't think there's an agreed definition of "lab grade" even for modern digital meters.
Real precision comes from low drift, low temperature coefficients, etc.
The main difference between a lab/bench multimeter and a handheld is that the internals are temperature controlled, ie. You have to let it reach working temperature before you take a measurement.
Your meters can't really be classed as "lab grade" unless they do that. The accuracy printed on them will only be true under a specific range of temperatures.
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Best wiggle meters were made by Sensitive Research in New York followed by Weston.
Bernice
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i dont think there is any precision in analog meters smiply because you need to read the scale properly.
i used to use one, and remember the anoyance of having to look at the needle and it's reflection in the mirror to get the value from the center-point.
good riddance to moving-coil meters.
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Any meter can be lab grade, because labs do a very wide range of things, and have a very wide range of performance requirements.
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i dont think there is any precision in analog meters smiply because you need to read the scale properly.
i used to use one, and remeber the anoyance of having to look at the needle and it's reflection in the mirror to get the value from the center-point.
good riddance to moving-coil meters.
Please, not another analogue vs digital thread! |O
The meters are readable to their stated accuracy using the scale marking and anti-parallax mirror, that's all that is needed.
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Most analogue meters I've used (before switching to digital) are not better than 1.5 or 2.5% For me that was good enough in most cases.
I still have one large analogue meter instrument saved, that is class 0.5, so 0.5% full scale (100uA).
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The other thing that separates the men from the boys in analog meters is while feeding in a half scale voltage, rotate it in various orientations and notice if the reading moves, as someone who can balance a meter movement to 0.1% I know most of them will drift when not in there vertical mounting hole orientation
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Analog meters are only precise or accurate when you consider gravity and maybe external magnetic fields as well, and a mirrored scale may reduce parallax. Take an AVO 8 for example, it has to be used horizontal, tip it up to vertical and get a different reading. Gravity pulls your needle and you need to compensate for that and also for friction in the bearings. Probably the only class of accurate analog meters are old school galvanometers because they have a leveling bubble and screws to get them horizontal, it's simple physics which most people either ignore or don't understand. The forces on your indicator needle are very small and can be easilly influenced.
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The other thing that separates the men from the boys
Try building a control system for laser deflection galvos then you might understand physics and mechanics.
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I got some 0.2% analog meters.
There is one with 30A AC current range(0.2%) that rivals the best digital meter today.
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The best analog meter I have is this 0.1% mV meter ranging from 45mV to 3000mV with reflective mirror reading.
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Analogue scale or analogue meter? The former is clearly quite limited, although some tricks have been performed with light (pre laser -- nowadays that should be much easier and precise) pointers via a moving mirror etc., the latter can be arbitrarily precise -- I'm thinking of null meters and their cousins the differential volt meters (although you could consider those digital, even if they don't use ICs).
Analogue scales might be quicker to read, but digital displays are much quicker to read precisely and log their data. I'd think anybody who looks for precision today (or the last thirty years), goes digital.
If you have a nice null meter for sale though, I'm quite interested 8)
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Null the Null meter , codswallop on the digital meter though , i have given up on using it to peak circuits (oscillators/IF's and the likes) , go past the peak and is down go back up to a peak oooop's past it again and going down go up to the peak and >>>>>>>>> loop
Using the Analog side and watching the needle is so easy and immediate no matter which way it swings , visually instantaneous and floats my boat , then I'll go to the digital meter , take a reading and see if it correlates with the needle pointer
Many digital meters have a bar graph display at the bottom for watching voltage swings like that.
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Many digital meters have a bar graph display at the bottom for watching voltage swings like that.
Not my old Gadget (post near up the top) , that's what I'm on about , 2 meters in one gadget .
DMMs with bar graph are also "2 meters in one gadget". :)
(DMM bar graph displays are a recognition of the fact that watching needles swing is useful)
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Sadly those bargraphs are aimed at speed of response (using a separate fast low-res A/D), while waiting for the main A/D to update the digital display, rather than useful resolution. Maybe someone should introduce one with a log scaled bargraph for use in nulling.
Edit: Do I mean log scale? :-\
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Sadly those bargraphs are aimed at speed of response (using a separate fast low-res A/D), while waiting for the main A/D to update the digital display, rather than useful resolution. Maybe someone should introduce one with a log scaled bargraph for use in nulling.
They're mostly there to show you if a signal is wiggling or not.
If it isn't wiggling then you can read the numbers on the DMM screen to 3 or more digits of precision very quickly.
If it's wiggling then your analog meter won't give an accurate reading either. :-//
(and any DMM with a bar graph usually has min/max mode for following the wigglers)
Analog meters are pretty, but better than a decent DMM? In very few circumstances.
The main one I can think of is where you need to measure several similar items. Once you get your eye in on how the needle is supposed to move for a given voltage or resistance then it's very quick to take other measurements for similar values (eg. a row of equal-value resistors).
Then again, a bar-graph DMM might be just as good. I've never actually tried doing that. :popcorn:
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Analog meters are pretty, but better than a decent DMM? In very few circumstances.
Whoa, I'm not going there! :palm:
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Then again, a bar-graph DMM might be just as good. I've never actually tried doing that. :popcorn:
Update: I just tried it and it works perfectly.
You can measure one resistor to get your eye in and set the range of the meter.
After that you can quickly go down a line of resistors using just the bar graph. There's no need to look at the numbers (which take a second or two to catch up).
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Now if someone could come up with a decent bargraph meter that would be perfect... I'm thinking 100 segments 1%, 500 segments 0.5%,... 1000 segments?
That would have all the benefits of both worlds, clear speed readable display with decent precision, robust, low light readable etc. You could have variable attack and decay times, simultaneous peak and average readings etc. (like studio ppm meters). I wonder what display technology could deliver it though, might be a bit fine for LCD (maybe not), OLED?
I think a meter like that could find application in many settings. Could certainly be a fun project.
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Just got some from garage.
The first two (A-meter and mirror W-meter) are shielded electrodynamic type, so should be TRMS.
The third one (DC mV-meter), is magnetoelectric.
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That first one is an interesting take on the pointer width problem. Maybe a bit more robust than the normal hair width pointer tip. :-\