Rms

Root Mean Square

Want a mathematical explination or would you rather leave it alone?

 

Take it away Ranger, Your the man for this one!!!!!!

 

I must learn to engage brain before putting mouth into gear.


Because AC is a varing quantity, (always changing ) the ability of a speaker to handle power also changes with the frequency.

A speaker that can handle 100 watts at 200Hz may only be able to handle 50 watts at 50 Hz.

RMS is a Statistical Method of averaging the constantly changing values. First we need to realize that it is possible to add an infinite series of numbers. But first we will square that infinite series so that we have no negative values. Then we average (take the mean) the result and then take the square root. We now have a reliable average power handling.

 

After staring at the equation, I just realized that there is a mistake.

There is more than one x, so x subscipt 1 is wrong. It should read x subscript i

 

A speaker that can handle 100 watts at 200Hz may only be able to handle 50 watts at 50 Hz.

RMS is a Statistical Method of averaging the constantly changing values. First we need to realize that it is possible to add an infinite series of numbers. But first we will square that infinite series so that we have no negative values. Then we average (take the mean) the result and then take the square root. We now have a reliable average power handling.[/QUOTE]

100watts 200hz ok, 50watts 50 hz fine,x max and peak power don't like each other. but as far as that equation goes may I quote Homer Simpson "Duhhh,mmmm beer"

 

I love this place.

 

yea i do too ranger i learned so much being here these last 2 months its crazy lol and every post it seems like u teach me more and more thanks

 

rms is the amount of continues power something can take dont exceed it unless you know what ur doing

 

What if there was 3 bananas 2 pears , an apple and a grapefruit. They were put in a bowl and on a bus to chicago, the bus travels at 68mph and gets 12 mpg and it's 100 miles to the destination. x=? and y=3 , How long would it take the apples to get to chicago if jenny eats 2 bananas 2 pears and throws the other banana at jimmy who is sleeping for 10 minutes. and if x = y x 100.

 

Hope you don't mind if I jump in here.

Many of the digital volt ohm meters (DVOM) use the same formula built in. In simple terms, it will "average" the signal according to the equation Ranger put up. Granted, Ranger can use the equation to get to the sum of the signal, and I will most certainly admit I have no clue as to how to even come close to using it. But, I can sort of put it in simple terms.

Say you were measuring a frequency signal which goes to 10 volts at it's high part of the square wave, and 0 at the off part, the meter would "average" the voltage to 5 volts. I know I am speaking in DC volts here, but the principle is the same, in a sense. Again, this is simplifying it to the most basic sense there is. The only way you would be able to know if it really was hitting the actual high and low would be to turn on the Min/Max graph that most DVOM's have that runs along the bottom.

Thing is, I haven't had to turn on my DVOM in many moons. Seems each time I do, I eat a 9 volt battery because I fail to turn the dang thing off. Using a scope to measure AC volts is so much more eye opening to me, at least. But, I can certainly understand the use of RMS in the audio field.

Please feel free to correct me if I passed on any untruths.

 

LOL!!!!!!!!!!!!!



Throttle, that pretty much sums it up in a very basic way

 

I think you've got it. In household AC, 110 is the RMS measure. By working my equation in reverse (I wont bother you with the details) you should see that it actually peaks around 155-volts.

Throttletune, I bet you have access to an Oscilloscope. Look at the AC from the wall plug and see where it peaks.

Sound is AC, same rules apply.

 

Interesesting thought on the line voltage of our outlets Ranger.

Now, i am not a mathmetician such as yourself, but I find your staement of the line voltage reaching 155 volts a bit high. ( I may be wrong and am NOT saying you are wrong)..but line voltage from a transformer is usually from 108 volts up to 125 volts, give or take, depending on load of the main grid. Many times i have used my DMM and its record function to monitor my line voltage. (issues I wont get into right now).....

The highest i ever saw was about 123 volts and the lowest was 118 volts. Give or take from what i remember. If an AC waveform spikes at 155 volts, consistantly, this would be detrimental to some sensitive AC motors and non regulated devices. Most all home equipemtn can take this voiltage without a probelm, even computers and the likes.

I have a few O scopes, and I have never hooked them up here at the house on line voltage. Maybe i should one of these days.


BUT, now that i thnk of it, my meter does do RMS readings........ BUT the min/max setting should at least be fast enough to pick up the high spikes.....

You have made me curious!!!! If the continuous output of an outlet spikes at 155 volts or so, then what is the lowest voltage that can happen by your formulations?

Educate me!!! Please!!! I am serious, what am i missing on this?

 

Hi Ranger,

A 6-7 years ago when I first got into scoping, I hooked my Fluke 98 to a wall socket. And yes, peak to peak was a heck of a lot more than I suspected. I will try to upload some captures I have of the type of AC I deal with.

Basically, in we use Hall Effect, Analog, and we use Variable Reluctance. The VR sensors make AC then it is converted in the ECM, or the Ignition Control Module to a digital signal. Same with a wheel speed sensor in ABS brake systems. Where the signal rides in relation to 0 is dependent on how I hook up. If I hook up positive to sensor high, and ground to sensor low, it should be equally above and below. But, if I use the engine ground on negative, and the positive lead on sensor high, it will read more above 0 than below. But, I am more interested in peak to peak than where it rides, so I generally hook up to a common ground, and scope a couple signals.

If I used an RMS DVOM, it would skew the readings in a non favorable way. Hence my statement using a scope is far better in the stuff I deal with.

Thanks Viking. I deal in basics. Best way I know to wrap my head around stuff.

And thanks Ranger for the lesson. Very well put, and your patience is very much appreciated.

 

I have Mucho Respect for that Ranger guy, he knows his stuff!

 

All meters, with the exception of some high end units, read RMS. Remember that RMS is a Statistical Averaging Method. Unless you have an upper end Fluke or Simpson, you cannot read the actual peak.

When you say that 123 is the highest that you've seen, you are talking about an RMS measurement. The actual peak for that RMS measurement will be around 178- volts. And its not a spike, this is happening 60 times per second.

What we need to realize is that it is spending so little time at this extreme that its not important. When equipment is built to work at 110 RMS these peaks are taken into account. But in many cases these peaks are ignored.

Again try to get access to an Oscilloscope and look at the AC wave form, you'll be suprised

 

I would locate some grapes and have a fruit salad.

 

Very interesting!!!!

I never really knew that the line voltages were so high in the peaks. I have 3 O-scopes sitting in the shop, wait, make that 2 O scopes, the old tube unit is dead and tubes are almost impossible to find!!!

I wil play around with the line voltage next time i get them out.

This makes me think though. If say, our line voltage peaks at 170 volts or so, then when the high tension lines on the grid leading to my transformer on this trunk line are rated at say, 18Kv, wonder what the actual peaks are!!!