Analog Multimeter Readings

[platinumsteel]

Hi guys I asked a friend of mine to give me the resistance measurements on a 3V Rail on a Macbook Pro 2017. He doesn't have any digital multimeter at the moment. Do any of you have experience with this analog multimeter and can be able to tell me what is the reading in ohms being displayed ? Just need to know if this line is shorted.Thanks

[R_J]

Re: Analog Multimeter Readings

Resistance X10 range should be about 32Ω, if it was zeroed correctly and omitting any lead resistance

[platinumsteel]

Re: Analog Multimeter Readings

Okay thanks a lot for this information. Definitely helped.

[eccerr0r]

Re: Analog Multimeter Readings

less and less people can read analog multimeters likewise analog clocks...

TBH I was a bit dumbfounded for a bit when I hadn't used a multiscale analog VOM for a few years. So maybe it isn't so bad people have trouble reading them, but it came back in a few moments.

Speaking of scales, after looking at a few digital multimeters, likewise analog meters, scales are kind of annoying. My B&K 4½ digit DMM fortunately is not autoranging, but my HP 4½ digit DMM, being autoranging, I have to carefully check which LED is lit to tell mV vs V. I had the meter in autorange and measured the primary cap of a SMPS, and read 140.42. It had been unplugged for several minutes, and was kind of surprised that much holdup and still 140.42V... until I saw it was actually 140.42mV as the mV LED was on. Kind of dangerous IMHO.

I also have a Micronta autoranging analog multimeter. This is even more disturbing to read as the multiplier (meaning, the particular scale, which are NOT multiples of 10) needs to be changed depending on which range was chosen.

A recent acquisition was a Dana 4½ digit DMM which likewise is autoranging. This I think is a bit better, this time it moves the decimal point so the display will always display volts or milliamps, and never have to worry about millivolts or microamps (never mind the ohms scale!), alas the resolution on the Dana is no better than 100µV where the HP has a 10µV resolution. Likewise the Dana will only go down to 10mΩ where the HP has 1mΩ resolution.

[redwire]

Re: Analog Multimeter Readings

I think OP's analog multimeter is OK as it uses an AA battery for ohms and I think the test current would be low. It's only 2k/V meter movement.
You have to be careful with analog multimeters because they can have a high (ohms) test voltage or high current.

Example is Simpson 260 on Rx1 range is using 125mA at 1.5V which people love because it really punches through corrosion and oxide etc. but could damage small semiconductors from the high current.
The higher ohms ranges are 9V, so backwards you can hurt some semi's because of the high voltage although it's 75uA.

[megaraider]

Re: Analog Multimeter Readings

less and less people can read analog multimeters likewise analog clocks...
TBH I was a bit dumbfounded for a bit when I hadn't used a multiscale analog VOM for a few years. So maybe it isn't so bad people have trouble reading them, but it came back in a few moments.
Speaking of scales, after looking at a few digital multimeters, likewise analog meters, scales are kind of annoying.

It all comes down to basic stuff, much like riding a bike...
Of course digital tends to be more direct forward making readings because we don't have to pay attention to the multiply knob factor and match with the appropriate scale. But analog meters are still the best when it comes to detect fast breaking joins and connections (both Ohm, V, or A)

I think OP's analog multimeter is OK as it uses an AA battery for ohms and I think the test current would be low. It's only 2k/V meter movement.
You have to be careful with analog multimeters because they can have a high (ohms) test voltage or high current.
The higher ohms ranges are 9V, so backwards you can hurt some semi's because of the high voltage although it's 75uA.

Again we fall back to basic stuff...
But if we're somehow distracted disaster can strike
Reading V or A we start with the knob in max. factor and walk our way down. Unlike reading Ohm we do the opposite.
Nowadays with 1.8V devices even with AA powered meter we have to be careful enough...

[eccerr0r]

Re: Analog Multimeter Readings

But analog meters are still the best when it comes to detect fast breaking joins and connections (both Ohm, V, or A)

I have not needed to use an analog meter since forever. I only used it because I can leave it attached without worrying about wasting electricity since the meter is powered by the DUT...

Unfortunately my autoranging/FETVM requires batteries so this multimeter is quite useless for me, more of the annoyance of the autoranging, but then power consumption is next...

[eccerr0r]

Re: Analog Multimeter Readings

BTW, if reading the 1/(X+1) scale is hard enough on battery powered VOMs, anyone use VTVOMs where the scale is reversed where the full scale reading is infinite ohms... the natural way someone would read a meter?

I learned using battery powered VOMs so the 0 as full scale is "normal" for me, but I suppose the VTVOMs would look more "natural" to people who've used DMMs forever...

[stj]

Re: Analog Multimeter Readings

i expect the next generation of meters to use colour lcd displays,
they have better viewing angle and backlighting than the old black type and as new meters are all mcu controlled, it just needs a 3wire spi bus and not a big load of segment drivers

big boys are already on it.
https://www.tme.eu/en/details/ca-529...x/c-a-5293-bt/

but the flood of cheap displays in china makes it cheap enough to start using them on $20 meters

[megaraider]

Re: Analog Multimeter Readings

I learned using battery powered VOMs so the 0 as full scale is "normal" for me, but I suppose the VTVOMs would look more "natural" to people who've used DMMs forever...

How come...? Take an example where the test leads are unconnected: both VOMs and DMMs will read 0 in V & A and 'infinite' or 'OL' in Ohm > Correct.
Unlike Vacuum Tube VOMs (VTVOMs) that will read 0 in Ohms > Incorrect

i expect the next generation of meters to use colour lcd displays, they have better viewing angle and backlighting than the old black type (...)

Yes, even the 'inverted' B&W display (white over black) is better than the traditional black over gray...

[eccerr0r]

Re: Analog Multimeter Readings

No... If you short the leads on a VTVOM, VOM, and DMM, they will all say 0 ohms... Likewise leave them open, it will say infinite. However:

VOM:
0Ω -- Full scale deflection (meter points to the right)
∞Ω -- No deflection (meter points to the left at rest location)

VTVOM:
0Ω -- deflects back to 0 (meter points to the left)
∞Ω -- full scale deflection pointing to ∞ - circuit passes current to make default location pointing to the right

DMM:
0Ω -- Displays 0
∞Ω -- Displays overload (OL or 1)

So the VTVOM (at least the Heathkits and a lot of other VTVOMs) the behavior sort of matches DMM operation whereas battery VOMs it looks kind of reversed...

[megaraider]

Re: Analog Multimeter Readings

No... Likewise leave them open, it will say infinite.

The pictures may help...
Test leads are unconnected (Needle in rest position):

• VOM: ∞Ω -> Correct
• VTCOM: 0Ω -> Incorrect
• DMM: 'OL' = ∞Ω -> Correct

[eccerr0r]

Re: Analog Multimeter Readings

Not sure what you're trying to help here, but the key aspect of some VTVOMs is that they pass current to swing the meter "full scale" and point to infinity ohms when you're in resistance mode and have nothing connected to the probes.

The only reason why they do this is for people who must have 0 on the left hand of the scale for volts, amps, AND ohms. Having 0 ohms on the same side of the scale as 0 volts is of course impossible without requiring current to pass through at all times to support ∞Ω on the right hand of the scale with the other full scale readings. For battery operation this would kill batteries in no time, but with wall powered VTVOMs this is not as serious of an issue when vacuum tube heaters will use up many more watts anyway.

[redwire]

Re: Analog Multimeter Readings

i expect the next generation of meters to use colour lcd displays,
they have better viewing angle and backlighting than the old black type and as new meters are all mcu controlled, it just needs a 3wire spi bus and not a big load of segment drivers

big boys are already on it.
https://www.tme.eu/en/details/ca-529...x/c-a-5293-bt/

but the flood of cheap displays in china makes it cheap enough to start using them on $20 meters

I really wanted to make a DMM with an LED display, some 14-seg alphanumerics but that is too hard to support menus etc.
Have to augment it with an OLED or maybe LCD is mature enough now. LCD are used on every phone, tablet, monitor, TV so going to stay cheap.

The Chauvin Arnoux is 320x240 (and $750 ouch) and look how meh it is, next to an LED meter in the flyer. They're using a small font and the screen layout is poor.

Character LCD's are crap, especially if there is a bar-graph the mux ratio is too much. I am fixing an old handheld DMM with huge 3/4" 21mm LCD 9V direct-drive display. I was going to bin it but the display has great contrast and you can easily read it outdoors, in the sun etc. An AN8008 looks washed out and faded in comparison.

[stj]

Re: Analog Multimeter Readings

i have a collection of interesting displays,
maybe i'll put an arduino between my uni-t 61e and a 14digit BIG vfd from a gambling machine - to see how it looks

i'd like to use a graphic vfd, but i have not managed to write functioning code for those yet
the industrial displays from gambling/vending gear are dirt cheap on ebay, but there are no datasheets public
i also have 4inch 7segment red led displays!!
(and maybe some 6 inch ones!!!)

[eccerr0r]

Re: Analog Multimeter Readings

Should make a DMM frontend to AVRTransistortester... Ha...

[redwire]

Re: Analog Multimeter Readings

I haven't seen the big gambling VFD's on eBay but they need around 5W.
What about the Bluetooth-only multimeters, a remote display head or like Mooshimeter or Pokit Meter that use your phone as the display? Or maybe a large display for readings and a second smaller one for menus and extra info.

pokit looks a bit kickstarter hokey though 60VDC/42VAC 1MEGohm max it's kinda crappy, ha the Pokit Pro Nov. 2019 and still not shipping.... and Mooshimeter died out after their kickstarter.

[megaraider]

Re: Analog Multimeter Readings

the industrial displays from gambling/vending gear are dirt cheap on ebay, but there are no datasheets public

As i recall they used a multiplex scan circuitry IC (maxim i believe) connect to a µC. You might get better luck disassembling it and walking your way thru.

pokit looks a bit kickstarter hokey though 60VDC/42VAC 1MEGohm max it's kinda crappy, ha the Pokit Pro Nov. 2019 and still not shipping.... and Mooshimeter died out after their kickstarter.

imo it's to expensive for the specs, unless the smallest size matters.

[stj]

Re: Analog Multimeter Readings

the vfd's arent multiplexed, they have onboard microcontrollers that handle ASCII conversion and mapping from a syncronous serial interface.
https://www.fruitmachinesales.co.uk/...chine-displays

[stj]

Re: Analog Multimeter Readings

I haven't seen the big gambling VFD's on eBay but they need around 5W.

12v @ average of 300-500mA depending on how much stuff is displayed.

https://www.ebay.co.uk/sch/i.html?_f...y&_osacat=3944