Maybe on Vulcan, but here they typically block DC. What you get is the RMS value of the AC component of the waveform only. A clue is when you see the AC bandwidth specified with a low frequency of 40 Hz or so. Attached is a page from the old 8050a TRMS meter, back when they put such things in the manual. Note the difference between readings and the last calculated column for half rectified waveforms.
Both are valid. If you will make sound, a DC-blocked reading is appropriate. But an odd but real-world problem is heating tube heaters with rectified (full or half-sine) AC. While very nasty, sometimes it is expedient for simple 115VAC line-power instruments. But what is the heating value? Both the AC and the DC matter. The math is hard to keep straight. As recently as the 1970s it was wise to check the answer with a #47 pilot light on both a 6V battery and (a fraction of) the rectified AC, going for equal brightness.
No, certainly not. If you try to measure the voltage of the mains panel in an industrial site with your cheap multimeter in the 10A position, you risk serious injuries, sometimes your life. I have seen the scenario in real life, it is not pretty.
What I mean is that you should always be extra careful, even with a properly fused multimeter, because any mistake will cause damages. The high-end multimeter will protect your eyes and body, but it still may end up damaged, and there will also be collateral damages.
Check your CAT safety ratings- https://www.digikey.com/en/blog/what-are-multimeter-cat-safety-ratings
Then pick your meter!
Then pick your meter!
Even my dirt cheap Topcraft TDM 600 multimeter is claimed to be 600 V CAT II. Does that mean you can safely plug the leads in its 10 A sockets and connect it to the mains, just as long as you stay well clear from anything with a three-phase connection? (Not that I have the intention to try it.)
Most high-end multimeters (that means a good number of true RMS ones) have the provision to be configured to measure the complete RMS value, including DC. That's the case with my huge, late seventies Datron, and at work even my handheld Fluke 83 could also be configured that way. The default setting is always DC-ignore though.
That said, I completely agree with Conrad: true RMS capability is rarely needed in real life, and it can be misleading: for many people, if you make the product of the RMS voltage with the RMS current into a load, you get the so-called "RMS power" (which can be calculated theoretically but has little physical relevance). What those people mean is in fact the average power, which is the result of calculations on RMS values, but making a scalar operation on just the magnitude of the variables only yields the right (average) result for a purely resistive, linear load.
In many cases, the average value has more sense and usefulness: saturation in transformers and inductive components is governed by the average voltage, not the RMS one.
The current output of a capacitive supply is also determined by the average value. This is why my home-made instruments have the ability to measure both (with the average value displayed as RMS, as in old-style instruments)
Yes, and when you want to know whether your amplifier or recorder has enough headroom to handle a signal without clipping, it's the peak value that matters, rather than the RMS, the average or the average absolute value. True RMS can be handy for noise measurements or to figure out the power dissipation of a resistor, but that's about it (and most multimeters are not sensitive enough for noise measurements anyway).
By the way, I did the battery test with my cheap TDM 600 multimeter. When I connect an old 9 V battery, it indicates 8.45 V in its DC mode, and in its AC mode, 17.8 V in one direction and 0.0 V in the other direction. Clearly half-wave rectification with a single diode.
By the way, I did the battery test with my cheap TDM 600 multimeter. When I connect an old 9 V battery, it indicates 8.45 V in its DC mode, and in its AC mode, 17.8 V in one direction and 0.0 V in the other direction. Clearly half-wave rectification with a single diode.
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Since I once worked in a job where mistakes cost a lot of money I got to know “voltage only” DMM’s. The well known mistake that OP made (we practically all have done it at least once) could then not be made. Measuring current was only allowed with clamp type meters.
Grarea, all the true RMS Fluke DMMs I owned the last 20 years or so measured ripple. FWIW I work with expensive Fluke DMMs on a daily basis but like my own 117 most of all. Affordable and can take abuse. It really pays off to buy good stuff at once.
Grarea, all the true RMS Fluke DMMs I owned the last 20 years or so measured ripple. FWIW I work with expensive Fluke DMMs on a daily basis but like my own 117 most of all. Affordable and can take abuse. It really pays off to buy good stuff at once.
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The first (and so far only) multimeter I blew up, some two weeks after buying it, was subjected to too much voltage. Using a meter with a 1200 V DC range, I wanted to measure a DC bias voltage in a high voltage amplifier that should be about 1100 V. Unfortunately the amplifier oscillated, so the voltage was going up and down with peaks well above 2 kV. After cleaning its PCB, the meter became more or less usable again.
It certainly scared me: the current that the power supply could deliver wasn't even close to that of a power distribution transformer, but it was enough for a lethal shock.
I haven't a clue how 10 kV transformers are measured. I guess from a safe distance.
Yes and with quite long measurement sticks. I think it is a good experience for many to view such an environment, the avoidance of risks and the way all are involved with safety. Only after having witnessed a few high power incidents I really learned to respect electrical power. It can be VERY scary.
It is a good thing that the HV DMM does not have an Ampère position
It is a good thing that the HV DMM does not have an Ampère position
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Years ago at the Dayton Hamvention the power company put on a demonstration. Maybe they still do. They set up a stage with a reversed "pole pig" to generate the feed voltage you'd find on the pole. Then they proceeded to show how far the arc can go, using long poles. They put a hot dog on the end of one and ran the arc through that. Not appetizing! Various other demos, but the bottom line is high voltage cooking is a very bad way to die. Me and my meters stay far away from industrial grade power. Also, look up Arc Flash. Another thing to avoid like the plague.
