You provide some of the best quick, simple explanations on these topics. While I knew about RMS measurements (both sine and square wave), I completely forgot about square wave DC offset and needed to verify that my two meters did not measure RMS voltage correctly. Great pointer!
I am a new subscriber and love your videos, but I couldn't help but note a math error at 4:04. The square of 0.500 is 0.250, not 0.500 as written. I hate nit-picking, but this confused me (a little) the first time I watched the video and might have confused others. Again, thank you for your clear, concise explanations of complex topics.
I thought your first video of this topic was excellent, but this one was even better. I watched the first video twice over, and got the message after thinking about it for a while. The video today was more logically and clearly presented -- you're a very good speaker.
The square value written for your 150 degree increment is written as .500 vs .250 although i believe you summed it correctly. Thanks for the great tutorials. 👍
Yeah I noticed that too, I just think he forgot to square the voltage at that point, but no biggie I still got the gist of what he was doing. Great Video.
AWESOME Video! Your simplistic approach makes me wonder why the RMS subject was not explained to me like that back in the days of my electronic classes... Thanks a lot for verifying my reasons for spending the extra twenty dollars into the procurement of a True RMS DMM…Cheers!
You refer several times to the 0.7071 factor which is the ratio of the RMS to peak value of a sine wave. However, in the comparison of the true RMS and non-true RMS meters on a square wave, what counts is the "form factor" of the waveforms, which is 1.111 for a sine wave, and 1 exactly for a square wave. Thus the non-true RMS meter (which is almost certainly responding to the average modulus of the waveform) reads high by a factor os 1.111, because it is calibrated to rad correctly for a sine wave.
Was going along with your notes - minor mistake at phase angle=150 degrees where the amplitude is .5V and the Vsquare corresponding reads .5V rather than .25V. With this correction the math comes out as it should. *Supplemental: Clearly others have made the same comment and I neglected to show my appreciation for the video content, for which I thank you!
@w2aew Thanks, once again, for these videos; This particular video helped to remind me that a True RMS meter (without the designation of True RMS AC + DC) would read incorrectly if a DC bias was applied to the signal - hope this makes sense.
Awesomely lucid and clear presentation-as usual- Alan. Would love to see your take on PEP vs peak vs average input and output power in regards to amateur radio as the rules have changed over the years, in term of the various modulation modes and lastly how manufactures talk about these things. Seems like your discussion of RMS voltage could be a good entry point to what I see as a mildly confusing topic to new hams, generating debates on various forums tens of pages long! lol!
Thanks again - watched this as a refresher as I just bought a Fluke 17B+ (non RMS) DMM. You always add a bit more than I thought I knew (ie: duty cycles, etc...). Now I feel better about spending a bundle on my other meter B&K Precision 393 (True RMS AC+DC). Can never have too much info or too many meters :) Just need to make sure you know what they can do!
Some of the DMM's I've seen will give a voltage rating plus the duty cycle at the same time on the display. So if you are making a quick check of a chips output to see if its faulty it gives a better picture of what is happening in circuit without bringing out your scope.
Ah, I see. That explains it. :) Thank you for taking the time to make all these videos. Your channel is truely a wonderful resource for anyone interested in electronics. And I have never really understood the concept of RMS voltage, so I was very happy to see a video from you on this topic. May I perhaps request a little follow up video where you deal with RMS for triangle waves and maybe even more complex waveforms as well?
You could have gotten the correct RMS voltages at 8:35 by switching the meters to DC mode. This would have correctly determined the DC offset. Your "true" RMS reading would then be sqrt(AC-RMS^2 + DC-RMS^2). It's a 2 step process for any DIMM that filters out the DC offset.
Hello! I played a little with a FG and 2x true rms DMMs. I tried square wave of different freq and duty cycle. At 50% I get ~Vp value on both, but if I increase or decrease the duty cycle, the dmm readings go lower instead of maintaining the Vp value. What can be wrong? The DMMs are fluke 175 and uni-t ut139.
Hi .. I just have a basic question. Why is everyone using the RMS ( which is a quadratic mean [ power of 2 ] ) ? Why not use a normal average ? I'm not quite convinced by the fact that because of the direction changes in AC voltage, the value will sum up to zero in a single cycle ( from 0:2*pi, say ), for an answer here. That's a theorotical answer. Practically, why not always take a Modulus(-ve value) and do a normal average. Since what we mean here is literally "voltage means work done", we can always ignore the -ve sign and flip the voltages which are below x-axis to the top of the x-axis and do a normal integral over the period of relevance. For a sine. this happens to be 2 square units from 0:pi [ 1 square unit ( 0 : pi/2 ) + 1 square unit ( pi/2 : pi ) ]. Converting the area of 2 from the sine curve to a rectangle, we get an amplitude of 0.6366 ( considering the rectangle width as pi ), which is infact the Vavg ( which is < Vrms ). This looks perfectly corrrect for me. In this case, why is Vrms preferred over Vavg ? Thanks !!
Because the goal is to find the equivalent voltage that would do the same *work*. Work is equivalent to power. Power is proportional to volts squared. Thus, the instantaneous power produced at the halfway point up the sinewave is not half of the power produced at the peak. To get the equivalent dc power producing result, we have to take the root of the average of the square values over time.
Something not right at 6:02. If the non true-RMS meter is just assuming a factor of 0.707 (as if it were a sine wave) then it should be reading 0.707*1 volt = 0.707 V (on a 2 V peak to peak square wave) and not 1.113 volts. I just happened to do a series of tests just like this on my "true RMS" meter and on a 4 V peak to peak signal my meter read 1.394 V which is 2/sqrt(2). So my meter IS making the 0.707 assumption regardless of the shape of the waveform. The other things I discovered (as you mentioned) is that the meter gives identical readings whether or not there is an offset suggesting it is AC coupling the signal. Finally I found that at any frequency above about 1 kHz the readings become progressively more inaccurate. E.g., with a 4 V peak to peak sine wave at 1 K Hz meter reads 1.395 (2/sqrt(2)) but at 3 K Hz reads only 1 volt and at 5 k Hz reads a mere 0.268 volts. In all cases my oscilloscope calculates and displays the correct RMS voltage regardless of wave type, frequency or offset.
Fantastic video, I really liked it. However, I am a bit confused on the bit at 5:43. You said that "RMS voltage, on a square wave, is equal to the peak voltage for any duty cycle" and I was a bit surprised to hear that. Can you please explain why "for any duty cycle"? Thanks. Regards.
This statement applies when the squarewave is balanced around ground, such it's high and low voltage levels are +Vp and -Vp. Thus, regardless of duty cycle, a voltage of Vp is always applied to the load. The polarity changes, but the power dissipation in the load is the same.
Great video! But I don't get it - I watched a very similar video from you a few days ago. However, this one is just a few hours old and now I can't find the old one. Did you delete the other one and made a new one with the same content? How come? Was there something you were not happy with? To me the previous one was just as great as this one. Keep up the good work.
I'm curious why the non true rms meter wouldn't read .707V for the 1V PK square wave? I was expecting 1 x .7071 = .7071. My non-true rms Fluke 79 reads 1.110V, about the same as the non true rms meter in the video.
I'm confused when the DVM specs say RMS with a crest factor of 10, what do they mean by this crest factor of 10 what does it do or if you didn't have a crest factor of 10 how would your RMS measurement be affected?
difference brands of meters has different input protection circuits some have poly fuses and MOVs and others don't have much at all. How can you protect your DVM DMM meters by knowing what input protection you have or don't have on your meters? without opening the meters up what are the most common input protection circuits in meters?
Thank you for the help, I'm guessing GFCI have comparator circuits, a differential amplifier, phase lock loop to compare the hot and neutral currents? Normal Regular Circuit breakers don't compare the hot and neutral currents, they just trip at a certain threshold. I thought GFCI outlets were went only for connecting plugging in equipment like sterilzers machines, dishwashing machines, autoclave machines, etc that uses water, water tubes, electronic circuits boards because if the water gets on the circuit boards or on the AC wires the GFCI will trip or if you had your hand on the sink which is grounded and the units chassis was hot live chassis the GFCI will trip.
They have some kind of current comparison circuitry. No PLL involved. They’re used whenever there’s a possibility of a person touching a wet surface and the equipment.
Hello , what is the type of the oscilloscope you are using ? I'm guessing its Tektronix also as the AFG 3252 function generator you are using , I am getting started in the repair of marine electronic business and realy need to simulate the signals that coming out of sensors to verify the integrity of the systems , what is your recommendation to buy signal generator and oscilloscope? Thanks in advance
The scope I used in this video is a Tektronix MDO3000 series. Nice feature with this scope is that it has a optional built-in arbitrary function generator. One cool feature with this is that you can take a measured waveform on the scope and copy it to the function generator so that you can replay it later. Handy for replaying a signal from a sensor or other device later.
The RMS value of a waveform is essentially the same as the DC value that would produce the same power dissipation. For a square wave balanced around ground, the peak voltages are +Vp and -Vp where the value of |Vp| is the same. So, even thought he polarity switches, the load still sees Vp volts across it at all times. So, the power dissipation is the same as if the polarity *didn't* change. Thus, the RMS voltage is equal to Vp in this special case.
(sin(x))^2+(cos(x))^2=1 (Pythagoras). Cos and Sin are identical except for phase shift so the average of sin^2 is the same as the average of cos^2 on a full cycle. So the average of sin^2 is 1/2. So the average power of a sin voltage of peak 1v is half the power of a constant 1v dc. So it's the same as 1/sqrt(2) v dc.
The difference between a GFI ground fault interrupt compared to a circuit breaker is that the GFI ground is connected reference to the water sink pipe ground? Equipment that uses water and electronic circuit boards in a piece of equipment should be "always" connected to a GFI AC outlet because if the water or tubing leaks water onto the electronic circuit boards or AC power internal inside the unit the GFI will trip? If the piece of equipment is "not" connected to a GFI AC outlet and the water or tubing leaks water onto the electronic circuit boards internally the AC outlet doesn't have an GFI to trip the water will leak onto the circuit boards and AC wiring which will blow the internal fuses of the unit but the "time delay" of the fuses are much later compared to a GFI tripping?
No. A GFI, or more accurately, a GFCI (ground fault circuit interrupter) is a circuit breaker that trips when the there is an imbalance between the current on the "hot" lead and the "neutral" lead. Normally, these two currents are equal and opposite. If there is an imbalance between these two, this could mean that the circuit is taking a improper path to ground (possibly through a person!), so it then breaks the circuit. GFCI devices are used and required for any circuits that are used around wet locations because this is the most likely place where someone could accidentally get shocked.
I think your comment about "using the 0.7071 factor" is a bit vague and doesn't quite tell the story as pertains to RMS meters that are not "true" RMS. I think it is important to introduce the concept of the average value, because that is exactly what the meter does. The average of the peak voltage is easy to obtain electrically with not much more than a capacitor. And the average of a sine wave is 0.637 of peak. The meter (analog ir simple digital meter) simply scales this up by the ratio of 0.7071 / 0.637 = 1.11. That is, of course, where that scaling factor really exactly comes from. And this is why a square wave on such meters will read about 11% too high. It isn't quite the "0.7071" factor, but the 1.11 factor.
Hey Alan, great tutorial as always, I wish I had more professors like you... Why is your Tek reading higher the square wave? Shouldn't it be reading the same value as for AC, since it is applying a factor of 0.707? At least, my meter works like that.
w2aew Obviously I need to read more, because I still have the wrong perception on AC signals interpretation. In my mind, an AC square signal with amplitude ptp of -1V to +1V will show 1V on the TRMS meter and 0.707 on the non-TRMS. Thank you for your answer, I am looking forward for your videos, Octavian.
Non True-RMS DMMs measure AC signals by first rectifying them, then measuring them (usually their average/filtered value, then they apply a scaling factor to give you the result. Since a rectified square wave has a higher average value than a rectified sine wave, it reads higher than the sine wave on a non-true-RMS meter.
Does an Average-responding DMM have RMS? Is it dangerous for AC beginner DIY electronics to use such a meter without RMS or true RMS? What's the difference between RMS and true RMS, or is it just a marketing term? Also, is there some sort of way to reverse engineer what a non-true RMS DMM displays by using a formula for an accurate reading? Aren't most basic electronics DC anyways? Sorry for all the questions!
+Dark Seid An average-responding DMM will only show an accurate RMS value of a sinewave input, and only if it is at a frequency below the maximum frequency rating for the meter. The difference is that True-RMS will give an accurate RMS voltage reading for various waveforms. Without true-RMS, the reading will only be correct for sine waves. Different waveform types would have difference equations to calculate the true RMS value. No danger, just getting incorrect readings. And yes, most measurements for basic electronics are DC.
thanks for your vídeo. but do you know how get current value? this from a multimeter I've been trying but for example the read is 188mA and the real current most be 200mA how I can make an approximation
Well that's true, I'm using a Fluke 179, when I change the frequency nothing change, but sometimes when I'm read 10mA the error is more bigger like 21% . I'm looking for a solution. Thanks w2aew!
+w2aew Yes, my TrueRms say for no sinusoidal wave, add 2%measure +2%scale. So my Scale is 400 mA, and my measure is 188mA . Do you know something about High impedance in a signal generator? Thanks for you answer. I tried with a R circuit. of 50 and 100 Ohm. of 5 W.
How do you know it will Sink and Source the same amount of wattage/power? How do you tell if the power supply is going to sink and source the power/wattage. I'm confused about the sinking and sourcing because some power supplies might source but can't sink. What is the difference between Sourcing current and Sinking Current?
I thought a power supply is the power source, what else would the device be connect to that has its own power source? How do you know if the Sourcing and Sinking is "equal ratio" or is every circuit sourcing and sinking have different currents of sourcing and sinking?Because I thought that every circuit has to have an equal ratio of sourcing and sinking current has to match the sourcing current and sinking current has to match from the current laws of theory?
Digital Oscopes have a MEAN measurement not sure when would you use the MEAN measure what in a circuit? The mean value for an AC sinewave is in the millivolts value which is the difference between the positive forward voltage compared to the negative reverse voltage of the AC sinewave? When measuring a DC voltage the MEAN value is always the same as the peak dc voltage, but in AC voltages the MEAN value is in the millivolts compared to a DC voltages the mean value is the same as the DC peak voltage, any reasons why?
@@w2aew But Oscopes have the Average mode also or is Mean always averaging the measured value? I see on Oscope they have an average setting and also a Means setting. Not sure to use Mean when measuring Non-linear loads I have heard that its when to use it for non linear loads but I'm guessing the Mean is just averaging the output of the non linear load?
@@waynegram8907 The scope averaging mode is an acquisition mode (averaging successive traces together). The Mean function is a measurement is computed across a single trace.
@@w2aew yes true they are but do you use the averaging mode when the non-linear load or sensor is varying up and down the voltage? because the averaging mode is an acquisition mode that will average all the sample voltages so its kind of doing the same as the mean function. Not sure when to use the Average mode and when to use the mean mode
@@waynegram8907 it’s apples and oranges. Average acquisition mode gives you a waveform that is averaged over multiple acquisitions. The Mean is a measurement that gives you a single numeric result from a given waveform.
Hello Alan. I have been doing my own investigation into RMS measurement and trying to use cycle RMS on my old TEK TDS 2022. Anyway I cannot get readout to stabilise it’s all over the place. I’m measuring a current wave form that’s a bit noise I have the BW limit enabled and also used the averaging function but the reading are still inconsistent. Just wondered if you could advise limitations on using cycle RMS function on the scope and why the reading are so bad. ruclips.net/video/xVAmzbBv5sg/видео.html. I’m hoping to try to measure the RMS current delivered into a capacitive load in the next video and try to work out the rms long hand using the square mean route approach. I would be interested to know what the correct instrument is for the job as I found True RMS meters don’t necessary give the correct answers. Thanks for sharing learned something today. Regards Chris
I think the problem might be that the scope is having difficulty determining duration of one cycle. The measurement computes the Cycle RMS over the *first* cycle it finds in the waveform. With the waveform beginning at the trough where the noise variation is, it is possible that it is finding the first cycle very quickly where the noise is bouncing up and down. I wonder if you re-position the waveform horizontally so that it starts near the mid-point, if that will help. I don't know what algorithm the scope is using to determine a "cycle", so give it a go to see if this works.
Thanks for the reply I will give that a try. Its kind of interresting to find that even high end so called True RMS meters dont work to well for fast rise time or short interval pulses. Not something i had really considered before as we are so used to dealling with sign waves and perhapstrusting what the meter indicates. Im sat at kitchen table now looking at the current pulses coming out the inverter and trying to take a number of readings square them work out the mean and square root them. I loosing the will to live I need a magic RMS meter that works on any waveform ? Best regards Chris
your awsome but the multi meter is for automotive repair duty cycle would be how long your egr or evap stays open and closed . and hz square wave ocilloscope type signal is the computor signal for like low res signal would be dc 0-2 volts high res signal dc 2-4 volts on optispark distributor .r then on ac amps between cpu and ignition modual to tell if its open or shorted. continuity impedence milliseconds hold min max freeze time frames to look at ramps and tails of square waves. picoscope is the bomb that can compare freeze frame ocilloscope to others you just looked at after fix. watch scanner danner on youtube youl get a kick out of him . its just a get byable way to fix auto electrical problems . Im just learning it my self. rookie talking. the dmms will take temperatures. my luk 77 died rest in peace now im trying a innova autometer 3340a itsure isnt a snapon picoscope scanner. watch the scanner danner videos so far I havent got a square wave yet lol on my scanner I Can graff my fuel trimms and advance on disributor. nice video thankyou some are averages because dmms dont move as fas as ocilloscope
You provide some of the best quick, simple explanations on these topics. While I knew about RMS measurements (both sine and square wave), I completely forgot about square wave DC offset and needed to verify that my two meters did not measure RMS voltage correctly. Great pointer!
I am a new subscriber and love your videos, but I couldn't help but note a math error at 4:04. The square of 0.500 is 0.250, not 0.500 as written. I hate nit-picking, but this confused me (a little) the first time I watched the video and might have confused others. Again, thank you for your clear, concise explanations of complex topics.
I thought your first video of this topic was excellent, but this one was even better. I watched the first video twice over, and got the message after thinking about it for a while. The video today was more logically and clearly presented -- you're a very good speaker.
The square value written for your 150 degree increment is written as .500 vs .250 although i believe you summed it correctly.
Thanks for the great tutorials. 👍
Yeah I noticed that too, I just think he forgot to square the voltage at that point, but no biggie I still got the gist of what he was doing. Great Video.
AWESOME Video!
Your simplistic approach makes me wonder why the RMS subject was not explained to me like that back in the days of my electronic classes...
Thanks a lot for verifying my reasons for spending the extra twenty dollars into the procurement of a True RMS DMM…Cheers!
Again, sorry for the nit-picking. I really appreciate your videos. IMHO, no one does it better.
You refer several times to the 0.7071 factor which is the ratio of the RMS to peak value of a sine wave. However, in the comparison of the true RMS and non-true RMS meters on a square wave, what counts is the "form factor" of the waveforms, which is 1.111 for a sine wave, and 1 exactly for a square wave. Thus the non-true RMS meter (which is almost certainly responding to the average modulus of the waveform) reads high by a factor os 1.111, because it is calibrated to rad correctly for a sine wave.
Was going along with your notes - minor mistake at phase angle=150 degrees where the amplitude is .5V and the Vsquare corresponding reads .5V rather than .25V. With this correction the math comes out as it should.
*Supplemental: Clearly others have made the same comment and I neglected to show my appreciation for the video content, for which I thank you!
@w2aew Thanks, once again, for these videos; This particular video helped to remind me that a True RMS meter (without the designation of True RMS AC + DC) would read incorrectly if a DC bias was applied to the signal - hope this makes sense.
Yes, makes sense. Many True-RMS meters don't give you the choice, or even tell you whether the measurement includes the DC content or not.
Awesomely lucid and clear presentation-as usual- Alan. Would love to see your take on PEP vs peak vs average input and output power in regards to amateur radio as the rules have changed over the years, in term of the various modulation modes and lastly how manufactures talk about these things. Seems like your discussion of RMS voltage could be a good entry point to what I see as a mildly confusing topic to new hams, generating debates on various forums tens of pages long! lol!
Thanks again - watched this as a refresher as I just bought a Fluke 17B+ (non RMS) DMM. You always add a bit more than I thought I knew (ie: duty cycles, etc...). Now I feel better about spending a bundle on my other meter B&K Precision 393 (True RMS AC+DC). Can never have too much info or too many meters :) Just need to make sure you know what they can do!
Some of the DMM's I've seen will give a voltage rating plus the duty cycle at the same time on the display. So if you are making a quick check of a chips output to see if its faulty it gives a better picture of what is happening in circuit without bringing out your scope.
Ah, I see. That explains it. :) Thank you for taking the time to make all these videos. Your channel is truely a wonderful resource for anyone interested in electronics. And I have never really understood the concept of RMS voltage, so I was very happy to see a video from you on this topic. May I perhaps request a little follow up video where you deal with RMS for triangle waves and maybe even more complex waveforms as well?
Excellent explanation without using calculus. I learned that even rms meter can be wrong becuase of the ac coupling.
Well Done !!! Meter examples and explaining the math for the sine values helped "see" it. I'm still a little stuck on understand PWM, though.
Thank you!! This video greatly helped with my lab readings!
Very cool, I had a hard time explaining RMS to an apprentice a while ago, I'll have to get them to check out this video.
You could have gotten the correct RMS voltages at 8:35 by switching the meters to DC mode. This would have correctly determined the DC offset. Your "true" RMS reading would then be sqrt(AC-RMS^2 + DC-RMS^2). It's a 2 step process for any DIMM that filters out the DC offset.
Hello! I played a little with a FG and 2x true rms DMMs. I tried square wave of different freq and duty cycle. At 50% I get ~Vp value on both, but if I increase or decrease the duty cycle, the dmm readings go lower instead of maintaining the Vp value. What can be wrong? The DMMs are fluke 175 and uni-t ut139.
Thanks for your effort in making this simple to understand video.
Hi .. I just have a basic question. Why is everyone using the RMS ( which is a quadratic mean [ power of 2 ] ) ? Why not use a normal average ? I'm not quite convinced by the fact that because of the direction changes in AC voltage, the value will sum up to zero in a single cycle ( from 0:2*pi, say ), for an answer here. That's a theorotical answer. Practically, why not always take a Modulus(-ve value) and do a normal average. Since what we mean here is literally "voltage means work done", we can always ignore the -ve sign and flip the voltages which are below x-axis to the top of the x-axis and do a normal integral over the period of relevance. For a sine. this happens to be 2 square units from 0:pi [ 1 square unit ( 0 : pi/2 ) + 1 square unit ( pi/2 : pi ) ]. Converting the area of 2 from the sine curve to a rectangle, we get an amplitude of 0.6366 ( considering the rectangle width as pi ), which is infact the Vavg ( which is < Vrms ). This looks perfectly corrrect for me. In this case, why is Vrms preferred over Vavg ? Thanks !!
Because the goal is to find the equivalent voltage that would do the same *work*. Work is equivalent to power. Power is proportional to volts squared. Thus, the instantaneous power produced at the halfway point up the sinewave is not half of the power produced at the peak. To get the equivalent dc power producing result, we have to take the root of the average of the square values over time.
Something not right at 6:02. If the non true-RMS meter is just assuming a factor of 0.707 (as if it were a sine wave) then it should be reading 0.707*1 volt = 0.707 V (on a 2 V peak to peak square wave) and not 1.113 volts. I just happened to do a series of tests just like this on my "true RMS" meter and on a 4 V peak to peak signal my meter read 1.394 V which is 2/sqrt(2). So my meter IS making the 0.707 assumption regardless of the shape of the waveform. The other things I discovered (as you mentioned) is that the meter gives identical readings whether or not there is an offset suggesting it is AC coupling the signal. Finally I found that at any frequency above about 1 kHz the readings become progressively more inaccurate. E.g., with a 4 V peak to peak sine wave at 1 K Hz meter reads 1.395 (2/sqrt(2)) but at 3 K Hz reads only 1 volt and at 5 k Hz reads a mere 0.268 volts. In all cases my oscilloscope calculates and displays the correct RMS voltage regardless of wave type, frequency or offset.
Fantastic video, I really liked it. However, I am a bit confused on the bit at 5:43. You said that "RMS voltage, on a square wave, is equal to the peak voltage for any duty cycle" and I was a bit surprised to hear that. Can you please explain why "for any duty cycle"? Thanks. Regards.
This statement applies when the squarewave is balanced around ground, such it's high and low voltage levels are +Vp and -Vp. Thus, regardless of duty cycle, a voltage of Vp is always applied to the load. The polarity changes, but the power dissipation in the load is the same.
*****
Thanks for the explanation and my confusion is no longer. Just got back in to electronics after many years. Regards.
YOU EXPLAINED THIS VERY WELL..TY!
Great video! But I don't get it - I watched a very similar video from you a few days ago. However, this one is just a few hours old and now I can't find the old one. Did you delete the other one and made a new one with the same content? How come? Was there something you were not happy with? To me the previous one was just as great as this one. Keep up the good work.
This is one reason I had to measure using db signal on DC output PWM when troubleshooting car electronics.
Thanks for uploading this video. Very helpful.
I'm curious why the non true rms meter wouldn't read .707V for the 1V PK square wave? I was expecting 1 x .7071 = .7071. My non-true rms Fluke 79 reads 1.110V, about the same as the non true rms meter in the video.
I'm confused when the DVM specs say RMS with a crest factor of 10, what do they mean by this crest factor of 10 what does it do or if you didn't have a crest factor of 10 how would your RMS measurement be affected?
difference brands of meters has different input protection circuits some have poly fuses and MOVs and others don't have much at all. How can you protect your DVM DMM meters by knowing what input protection you have or don't have on your meters? without opening the meters up what are the most common input protection circuits in meters?
Nice video Alan.
Clear as crystal.
Excellent explanation. Thanks for uploading
Excellent class.
Very helpul explanation of the problem. Quick ans smart.
Thank you for the help, I'm guessing GFCI have comparator circuits, a differential amplifier, phase lock loop to compare the hot and neutral currents? Normal Regular Circuit breakers don't compare the hot and neutral currents, they just trip at a certain threshold. I thought GFCI outlets were went only for connecting plugging in equipment like sterilzers machines, dishwashing machines, autoclave machines, etc that uses water, water tubes, electronic circuits boards because if the water gets on the circuit boards or on the AC wires the GFCI will trip or if you had your hand on the sink which is grounded and the units chassis was hot live chassis the GFCI will trip.
They have some kind of current comparison circuitry. No PLL involved. They’re used whenever there’s a possibility of a person touching a wet surface and the equipment.
@@w2aew ok thanks for the help
Hello , what is the type of the oscilloscope you are using ? I'm guessing its Tektronix also as the AFG 3252 function generator you are using , I am getting started in the repair of marine electronic business and realy need to simulate the signals that coming out of sensors to verify the integrity of the systems , what is your recommendation to buy signal generator and oscilloscope? Thanks in advance
The scope I used in this video is a Tektronix MDO3000 series. Nice feature with this scope is that it has a optional built-in arbitrary function generator. One cool feature with this is that you can take a measured waveform on the scope and copy it to the function generator so that you can replay it later. Handy for replaying a signal from a sensor or other device later.
I just have to say that is some DAMN sexy equipment you've got there! Very helpful video too :)
Very Nice.
Thanks for taking the time to do this.
Truly awesome video.
I need a meter with True-er RMS then :)
Thx again for another great lesson.
Regards
Francisco
👍Thank you sir.
Nice and informative. Thanks!
@5:30. This isn't clicking for some reason. The Vp =Vrms. How ?
The RMS value of a waveform is essentially the same as the DC value that would produce the same power dissipation. For a square wave balanced around ground, the peak voltages are +Vp and -Vp where the value of |Vp| is the same. So, even thought he polarity switches, the load still sees Vp volts across it at all times. So, the power dissipation is the same as if the polarity *didn't* change. Thus, the RMS voltage is equal to Vp in this special case.
(sin(x))^2+(cos(x))^2=1 (Pythagoras). Cos and Sin are identical except for phase shift so the average of sin^2 is the same as the average of cos^2 on a full cycle. So the average of sin^2 is 1/2. So the average power of a sin voltage of peak 1v is half the power of a constant 1v dc. So it's the same as 1/sqrt(2) v dc.
The difference between a GFI ground fault interrupt compared to a circuit breaker is that the GFI ground is connected reference to the water sink pipe ground? Equipment that uses water and electronic circuit boards in a piece of equipment should be "always" connected to a GFI AC outlet because if the water or tubing leaks water onto the electronic circuit boards or AC power internal inside the unit the GFI will trip? If the piece of equipment is "not" connected to a GFI AC outlet and the water or tubing leaks water onto the electronic circuit boards internally the AC outlet doesn't have an GFI to trip the water will leak onto the circuit boards and AC wiring which will blow the internal fuses of the unit but the "time delay" of the fuses are much later compared to a GFI tripping?
No. A GFI, or more accurately, a GFCI (ground fault circuit interrupter) is a circuit breaker that trips when the there is an imbalance between the current on the "hot" lead and the "neutral" lead. Normally, these two currents are equal and opposite. If there is an imbalance between these two, this could mean that the circuit is taking a improper path to ground (possibly through a person!), so it then breaks the circuit. GFCI devices are used and required for any circuits that are used around wet locations because this is the most likely place where someone could accidentally get shocked.
Wonderful video
I think your comment about "using the 0.7071 factor" is a bit vague and doesn't quite tell the story as pertains to RMS meters that are not "true" RMS. I think it is important to introduce the concept of the average value, because that is exactly what the meter does. The average of the peak voltage is easy to obtain electrically with not much more than a capacitor. And the average of a sine wave is 0.637 of peak. The meter (analog ir simple digital meter) simply scales this up by the ratio of 0.7071 / 0.637 = 1.11. That is, of course, where that scaling factor really exactly comes from. And this is why a square wave on such meters will read about 11% too high. It isn't quite the "0.7071" factor, but the 1.11 factor.
Hey Alan, great tutorial as always, I wish I had more professors like you... Why is your Tek reading higher the square wave? Shouldn't it be reading the same value as for AC, since it is applying a factor of 0.707? At least, my meter works like that.
The Tek meter reads high (incorrect) on the square wave *because* it is using the 0.707 factor on the signal, which *only* applies to sine waves.
w2aew Obviously I need to read more, because I still have the wrong perception on AC signals interpretation. In my mind, an AC square signal with amplitude ptp of -1V to +1V will show 1V on the TRMS meter and 0.707 on the non-TRMS. Thank you for your answer, I am looking forward for your videos, Octavian.
Non True-RMS DMMs measure AC signals by first rectifying them, then measuring them (usually their average/filtered value, then they apply a scaling factor to give you the result. Since a rectified square wave has a higher average value than a rectified sine wave, it reads higher than the sine wave on a non-true-RMS meter.
w2aew I did not know about the rectification! Thank you, makes sense
Does an Average-responding DMM have RMS? Is it dangerous for AC beginner DIY electronics to use such a meter without RMS or true RMS? What's the difference between RMS and true RMS, or is it just a marketing term? Also, is there some sort of way to reverse engineer what a non-true RMS DMM displays by using a formula for an accurate reading? Aren't most basic electronics DC anyways? Sorry for all the questions!
+Dark Seid An average-responding DMM will only show an accurate RMS value of a sinewave input, and only if it is at a frequency below the maximum frequency rating for the meter. The difference is that True-RMS will give an accurate RMS voltage reading for various waveforms. Without true-RMS, the reading will only be correct for sine waves. Different waveform types would have difference equations to calculate the true RMS value. No danger, just getting incorrect readings. And yes, most measurements for basic electronics are DC.
***** Thank you so much!
Thank you
thanks for your vídeo. but do you know how get current value? this from a multimeter I've been trying but for example the read is 188mA and the real current most be 200mA how I can make an approximation
Depends on many things including the particular DMM you're using, the frequency of the signal, the wave shape of the signal, etc.
Well that's true, I'm using a Fluke 179, when I change the frequency nothing change, but sometimes when I'm read 10mA the error is more bigger like 21% . I'm looking for a solution. Thanks w2aew!
How do you know there is an error? Have you accounted for the affect of the burden voltage of the ammeter?
+w2aew Yes, my TrueRms say for no sinusoidal wave, add 2%measure +2%scale.
So my Scale is 400 mA, and my measure is 188mA . Do you know something about High impedance in a signal generator? Thanks for you answer. I tried with a R circuit. of 50 and 100 Ohm. of 5 W.
+jay lord frama I have an Agilent 33220a using no high impedance just 50 ohm of load that it has internal. The current is more stable.
there is an error in your V^2 calculation for 150 phase angle
w2aew, when you measure the AC outlet using an RMS DVM it measures 120vac RMS this means its equal to 120vdc? 120vac RMS = 120Vdc?
120vac RMS will deliver the same amount of power to a circuit as 120Vdc.
How do you know it will Sink and Source the same amount of wattage/power? How do you tell if the power supply is going to sink and source the power/wattage. I'm confused about the sinking and sourcing because some power supplies might source but can't sink. What is the difference between Sourcing current and Sinking Current?
@@waynegram8907 A power supply will only have to sink current if the device you're connecting to has it's own power source.
12VAC that goes through one diode which is half way rectified to DC. The formula is 12vac X .707 or 12vac X 1.414? to get the DC voltage
I thought a power supply is the power source, what else would the device be connect to that has its own power source? How do you know if the Sourcing and Sinking is "equal ratio" or is every circuit sourcing and sinking have different currents of sourcing and sinking?Because I thought that every circuit has to have an equal ratio of sourcing and sinking current has to match the sourcing current and sinking current has to match from the current laws of theory?
Digital Oscopes have a MEAN measurement not sure when would you use the MEAN measure what in a circuit? The mean value for an AC sinewave is in the millivolts value which is the difference between the positive forward voltage compared to the negative reverse voltage of the AC sinewave? When measuring a DC voltage the MEAN value is always the same as the peak dc voltage, but in AC voltages the MEAN value is in the millivolts compared to a DC voltages the mean value is the same as the DC peak voltage, any reasons why?
Example - let's say you have some sort of sensor who's output is varying up and down a bit - the Mean measurement can give you it's average level.
@@w2aew But Oscopes have the Average mode also or is Mean always averaging the measured value? I see on Oscope they have an average setting and also a Means setting. Not sure to use Mean when measuring Non-linear loads I have heard that its when to use it for non linear loads but I'm guessing the Mean is just averaging the output of the non linear load?
@@waynegram8907 The scope averaging mode is an acquisition mode (averaging successive traces together). The Mean function is a measurement is computed across a single trace.
@@w2aew yes true they are but do you use the averaging mode when the non-linear load or sensor is varying up and down the voltage? because the averaging mode is an acquisition mode that will average all the sample voltages so its kind of doing the same as the mean function. Not sure when to use the Average mode and when to use the mean mode
@@waynegram8907 it’s apples and oranges. Average acquisition mode gives you a waveform that is averaged over multiple acquisitions. The Mean is a measurement that gives you a single numeric result from a given waveform.
excellent
So, not even the Fluke 87 did measure the correct RMS value when there's a DC component there. That's dissapointing.
Ok, I'm not crazy... Thank you for this video!
Hello Alan. I have been doing my own investigation into RMS measurement and trying to use cycle RMS on my old TEK TDS 2022. Anyway I cannot get readout to stabilise it’s all over the place. I’m measuring a current wave form that’s a bit noise I have the BW limit enabled and also used the averaging function but the reading are still inconsistent. Just wondered if you could advise limitations on using cycle RMS function on the scope and why the reading are so bad. ruclips.net/video/xVAmzbBv5sg/видео.html. I’m hoping to try to measure the RMS current delivered into a capacitive load in the next video and try to work out the rms long hand using the square mean route approach. I would be interested to know what the correct instrument is for the job as I found True RMS meters don’t necessary give the correct answers. Thanks for sharing learned something today. Regards Chris
I think the problem might be that the scope is having difficulty determining duration of one cycle. The measurement computes the Cycle RMS over the *first* cycle it finds in the waveform. With the waveform beginning at the trough where the noise variation is, it is possible that it is finding the first cycle very quickly where the noise is bouncing up and down. I wonder if you re-position the waveform horizontally so that it starts near the mid-point, if that will help. I don't know what algorithm the scope is using to determine a "cycle", so give it a go to see if this works.
Thanks for the reply I will give that a try. Its kind of interresting to find that even high end so called True RMS meters dont work to well for fast rise time or short interval pulses. Not something i had really considered before as we are so used to dealling with sign waves and perhapstrusting what the meter indicates. Im sat at kitchen table now looking at the current pulses coming out the inverter and trying to take a number of readings square them work out the mean and square root them. I loosing the will to live I need a magic RMS meter that works on any waveform ? Best regards Chris
DMMs are, by their nature, limited in measurement bandwidth. Fast edges, short pulses, etc. are all made up of higher frequency content.
Thank you!
The real meat & potato's of electronics! Thank You!
your awsome but the multi meter is for automotive repair duty cycle would be how long your egr or evap stays open and closed .
and hz square wave ocilloscope type signal is the computor signal for like low res signal would be
dc 0-2 volts high res signal dc 2-4 volts on optispark distributor .r
then on ac amps between cpu and ignition modual to tell if its open or shorted. continuity impedence
milliseconds hold min max freeze time frames to look at ramps and tails of square waves.
picoscope is the bomb that can compare freeze frame ocilloscope to others you just looked at after fix.
watch scanner danner on youtube youl get a kick out of him .
its just a get byable way to fix auto electrical problems .
Im just learning it my self. rookie talking.
the dmms will take temperatures.
my luk 77 died rest in peace now im trying a innova autometer 3340a
itsure isnt a snapon picoscope scanner.
watch the scanner danner videos
so far I havent got a square wave yet lol on my scanner I Can graff my fuel trimms and advance on disributor.
nice video thankyou some are averages because dmms dont move as fas as ocilloscope
hi, nice job !
Et tu Fluke :)