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So the meters impedance changes what kind of tests or measurements?
it changes the resistance reading of the circuit or component you're measuring? because of the meter loading? and the meter is in parallel with the circuit?
Analog meters are okay with odd waveforms, whereas my digital meters have fits.
Analog meters can be connected longterm for taking readings over a period of hours or days, while using no battery juice. My digital meters will not conduct at all through the mA ranges when turned off.
When measuring mA, I always need to have an idea beforehand as to how much is about to through my digital meters, because they blow an internal fuse if it's over 200mA (unless I'm using the 10A range).
1. The mechanical parts of an analog meter have mass and so make the reading less responsive to instant changes, this makes them show more of an average figure than an instantaneous one.
2. Visually, it also easier to see if the needle is swinging one way or the other so increasing or decreasing readings are more obvious.
3. Most (but not all) analog volt meters are powered from the voltage they measure, DVMs require a power source of their own.
4. Less important: the reading can be anywhere from zero to maximum in the selected range, DVMs read in discrete steps or 1 count in the least significant digit.
As far as I know there are no measurements that ONLY an analog meter can make. You can use both types equally, it's just that in some applications one is easier to read than the other.
Analog meters have virtually been rendered obsolete by digital meters. DMM's have so many advantages.
However there are some setups when I reach for my analog meter.
1.
Such as operations that take hours. For instance, I might periodically look at current going through a battery or capacitor. With a DMM I'd need to go through a lot of motion, turning it on and off, and installing and removing a jumper across its leads because it doesn't conduct while it is off.
2.
It's simple to turn a DMM on and off just to read voltage. But I might fiddle with something, then forget to shut off the DMM as I walk away. It could be left on overnight. Next day, the battery is low.
This won't happen with an analog meter.
3.
I have a few inverters. I tried to read AC voltage from the ones that put out square-ish waves. My inexpensive DMM would not give sensible volt readings. When I tried my analog meter, it showed a consistent reading (though not the correct one). There are higher-priced DMM's that give correct RMS readings, but I didn't have one, and I was only experimenting with the inverter.
4.
If I want to measure current, and I'm not sure if it's under or over 200mA (but is under 1 amp), then I reach for my analog meter. It reads up to 300mA. It won't blow a fuse if current is higher than that. (The DMM will blow an internal fuse.)
I can always use my DMM on the 10A range to be safe, which is not a hardship, but it means I have to move plugs back and forth.
5.
It took a while using my analog meter, for me to learn that the 300mA current range inserts the least resistance. So that's the range I try to use first, because it affects a circuit the least. Then I might switch to a lower range if it doesn't hurt operation.
This has become habit acquired over the decades.
I know I could use the 10A range on a DMM, but then I might want to switch to a lower range. However I have never tried to find out what resistance is inserted by the 200mA range. I suppose I should have determined the resistances in each of the 3 DMM's I've had, but it all gets beyond me, and I'm a creature of habit.
To me, the primary use is for doing RF tuning peaking. Much easier to look at the relative movement of a needle then a DVM number or even the digital bar on some DVM's.
So the meters impedance changes what kind of tests or measurements?
it changes the resistance reading of the circuit or component you're measuring? because of the meter loading? and the meter is in parallel with the circuit?
Voltmeters are put in parallel with the load in order to measure the potential difference between two different points and potential. If they are in parallel with the load, then the first junction the current will split and flow into both paths defined by Kirchhoff's Laws. However, if current is flowing through the voltmeter, then it is not all flowing through the load, and the potential difference across the load would change when the voltmeter is added and removed. Therefore, the voltmeter must have a very high resistance so that current doesn't flow through it. Of course, little amount of current does flow through, but it is insignificant in most cases. Digital voltmeters is better with high impedance, such is case in most pro voltmeters.
If you whant precise measuring you use digital instrument, with analog instruments there is possibility for human factor error. Digital instruments can be very very precise, you see alone what you have in shops, and what people bying, this is not just like that.
As additional comparison:
At digital voltmeters you have digital display with huge digits and with backlight lights, which make easier reading of values, also this eliminate errors durirng readings, what can be situation at analog voltmeter reading of values. Also analog voltmeters are sensitive on shaking and vibrations, like usage in cars, bykes,.... digital dont have nidle and this problems. Because analog have coils they are sensitive to magnets, coils, trafos, they must be far away from this sources, for digital voltmeters that is not the case.
What if engineer have poor vision and use googles (what in case of losing googles), and he is tired after long day, and he should read some value from analog instrument which have thin nidle and small diplay windows? Can you imagine what value will get from reading ?
You can use some nice GLCD and present current measured data on that display like analog instrument with nidle.
Can you imagine analog instrument with nidle in some modern airplane ? Can you tell me why ?
Can you imagine some analog instrument in nuclear plant with stucked nidle on it, and personels reading wrong value, and real value is lots different! About that situation there is one old movie "The China Syndrome" 1979. Or should I mention "Three Mile Island accident" from real life. This is excelent example why should go to digital.
In agreement with the preceding, among the disadvantages to analog meters...
1.
My analog meter moves progressively lower up the scale than it ought to as indicated by the 'calibrated markings'. (I compared it against my DMM.) At the high end the needle reads low by 5 percent. The D'Arsonval movement inside must have a low-quality spring.
2.
There is the ohms per volt spec. Mine is 20,000 ohms/V on DC. Thus the 3V range loads a circuit 60,000 ohms. The .6V range loads it 12,000 ohms. This can throw off readings unless the circuitry is low impedance.
The AC spec is 10,000 ohms/V. It loads a circuit even more. I'm not even sure I can trust AC readings in the lower ranges.
3.
Furthermore the incoming AC is rectified by diodes, which have maybe 1/2 volt threshold. I sometimes check an audio signal coming from an amplifier, but I do not believe it is an accurate figure until it gets to be several volts. At normal audio levels (1 or 2VAC) it can only be good for rough readings.
4.
I need glasses to read a precise value on the minute scale. And if I haven't used the analog meter in a while I need to re-acquaint myself with the many ranges, and the amount per division on each range. It makes it easy to take incorrect readings.
I will say fine look of some instruments, just see newset car instrument table, all digital GLCD, and such things, but analog shape of instruments on it. ;-)
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