Logger "peak max" vs "RMS max"

[electrofelon]

What is the difference between these two? The definitions are provided by the manual. Mainly interested in current.

1. RMS max
- Greatest, maximum value of the RMS voltage or current which occurred during the recording time.

2. PEAK max
- The greatest instantaneous value of voltage or current (the highest point of the sinusoid)

 

[wwhitney]

For a pure sine wave, PEAK = RMS * sqrt(2). If you have a current that's basically always a sine wave over any given cycle, but it may increase or decrease in magnitude, then it follows that PEAK max = RMS max * sqrt(2) over a recording time.

If instead you have distortion or spikes that show up within a cycle, then the relation between the two will differ. Say your machine samples 100 times a cycle and you sample for 1 second, so 6,000 samples for 60 Hz power. RMS max should divide those 6,000 data points into 60 groups of 100, calculate the RMS average for each of the 60 groups, and then tell you the maximum of those 60 computations. While PEAK max should just give you the biggest number of the 6,000 samples.

At least, that's what I would expect the terms to mean. I don't have any actual experience with loggers.

Cheers, Wayne

 

[gar]

230128-0021EST

electrofelon:

In most applications for RMS to be a useful measurement it needs to be averaged over an integral number of full cycles. Most RMS meters that you would encounter probably have an averaging time of at least a half second to several seconds. So many cycles of 60 Hz ( really 120 ) will go into that average, and therefore an integral number of cycles is not very important.

Peak max is just what you wrote. It is the highest instantaneous voltage ( + or - ) that occurred during whatever time period you monitored. Does not matter whether the waveform is a sine wave or not. If we have a stationary process ( all different values are unchanged with time ), then for a sine wave the RMS value is 0.707 times the peak, and the average is 0.636 of the peak. For non sine waves these constants may be different

Suppose you have a waveform that is zero most of the time and only 1 % of the time is it a square positive pulse of 100 V. Then the average value is 1 V positive. And its RMS value is square 100*100 = 10,000: average of square = 100; sq-root of 100 = 10. So RMS is much greater than the average of 1 V.

,

 

[electrofelon]

Ok thanks guys. I get peak vs RMS, I guess I was just confused because peak current just seems like a rather useless measurement no? Maybe if you are measuring very distorted waveforms it would be useful.

 

[cadpoint]

First remember you got to let the water in for the current to flow. Current Lags voltage.

Second thing one has to realize is that a meter displays the Average Voltage value of any AC sign wave but it's all based
of the peak voltage. I know that most modern hand meters say right on it states "True RMS meter", well I hate to tell ya, they do it with
a memory chip! One wouldn't want to buy a meter that stated: True Average Voltage, but they display average voltage.

So given 120 V (av)

V Peak 120_av /.637 = 188.38

V_rms = V_PK X 0.707 188.38 X 0.707 = 133.18 | from link below
V_av = V_PK X 0.637 188.38 X 0.637 = 119.99 |

https://www.electricaltechnology.or...elated-Terms-to-AC-Circuits-and-Sine-wave.png

The drawing is incorrect the length of one cycle should stop at 360^ and not be to the V_pp Line which is another dimension line, Bad Drafting!

Consider RMS to be a Cube inside a sine wave, the cube of the RMS elevations is a little higher than the Average (V_av).
So the work of the Cube repeats 60 times a second. Bang Work!

With three phase power, each phase is 120^ out of phase to each other. The 2nd phase or cube of RMS is starting up as the first sign wave is finishing. There is no gap in power. As I recall the phases never drop below the RMS line.

Well that's the way I learned it, maybe I'm remembering it wrong.

 

[gar]

230128-0623 EST

Half-wave average of a sine wave has a value of 0.318 of the peak, Full wave average of a sine wave is 0.636 of the peak. RMS of full sine wave is 0.707 of peak. Average or RMS of a rectified full square wave is 1.0 times peak.

A Simpson 260/270 measures full wave average, but is calibrated as RMS with the assumption of a sine wave input. The output of a full wave bridge rectifier will read 0.636 of the peak of a sine wave. Thus, the actual measured current is multiplied by 1.1116 to produce the displayed value.

Some meters actually directly measure the RMS value ( electrodynamometer type ), others measure RMS by rapidly sampling the input squaring the samples, averaging this, and taking the sq-root of the average.

There are also peak reading meters. A diode and capacitor will do this.

.

 

[electrofelon]

Second thing one has to realize is that a meter displays the Average Voltage value of any AC sign wave .

Can you expand on this? Why couldn't a meter display peak voltage or current?

 

[gar]

230128-1023 EST

electrofelon:

cadpoint's statement is incorrect when applied to a broad range of different meters.

In fact seldom will you find an AC meter that displays the average value of an AC waveform. When an AC meter is based on an average measurement it is usually calibrated in the RMS value of a sine wave when a sine wave is applied.

A Simpson 260/270 is an average reading meter, but calibrated in RMS for a sine wave.

.

 

[kwired]

First remember you got to let the water in for the current to flow. Current Lags voltage.

Second thing one has to realize is that a meter displays the Average Voltage value of any AC sign wave but it's all based
of the peak voltage. I know that most modern hand meters say right on it states "True RMS meter", well I hate to tell ya, they do it with
a memory chip! One wouldn't want to buy a meter that stated: True Average Voltage, but they display average voltage.

So given 120 V (av)

V Peak 120_av /.637 = 188.38

V_rms = V_PK X 0.707 188.38 X 0.707 = 133.18 | from link below
V_av = V_PK X 0.637 188.38 X 0.637 = 119.99 |

https://www.electricaltechnology.or...elated-Terms-to-AC-Circuits-and-Sine-wave.png

The drawing is incorrect the length of one cycle should stop at 360^ and not be to the V_pp Line which is another dimension line, Bad Drafting!

Consider RMS to be a Cube inside a sine wave, the cube of the RMS elevations is a little higher than the Average (V_av).
So the work of the Cube repeats 60 times a second. Bang Work!

With three phase power, each phase is 120^ out of phase to each other. The 2nd phase or cube of RMS is starting up as the first sign wave is finishing. There is no gap in power. As I recall the phases never drop below the RMS line.

Well that's the way I learned it, maybe I'm remembering it wrong.

Thread title suggests OP is using a data logger though where your description is probably for the displayed value on typical DMM's.

 

[cadpoint]

230128-1023 EST

electrofelon:

cadpoint's statement is incorrect when applied to a broad range of different meters.

In fact seldom will you find an AC meter that displays the average value of an AC waveform. When an AC meter is based on an average measurement it is usually calibrated in the RMS value of a sine wave when a sine wave is applied.

A Simpson 260/270 is an average reading meter, but calibrated in RMS for a sine wave.

.

Gar:

First off the standard digital hand held meter doesn't hold a candle to a The Simpson 260/270 !

I was trying to say that. The RMS is used to calibrate the value it will display.

I believe we both said the same thing differently, although mine might have been presented less descriptive than yours.
Maybe I shouldn't post overnight!

kwire:

I realized that my presentation was a little off thread but that in fact if a data logger is used that some expose for understand the
fundamentals of what one is looking at, as in a display, would be no less than prudent.

electrofelon
Can you expand on this? Why couldn't a meter display peak voltage or current?

In the link up in the corner is www.electricaltechnology.org One can thoroughly get lost in why things are electrically!
I will worn everyone that it's heavy in ADS.

Because the chips inside handle the math inside of a RMS meter takes care of it. Consider this: we build everything to be 120V AC
compatible in the US. But, the power was created from the Circular motion of a turbine it creates the sine wave. This act alone creates
all sorts of usage of math to measure at any point in that rotation.

The average person thinks ok I got 120V at point of usage, I'm good. But the average person doesn't think about the on and off of a sine wave.
much less that that sine wave was created by the rotation of the turbine at 60 times in a Second.

One doesn't want it to display 133.83 RMS Volts (back to the math is handled with chips) ((electronfelon does )) they want to see 120V.
We are trained to read for 120V.

Another good overview that you might enjoy is https://www.electronics-tutorials.ws/accircuits/phase-difference.html .
It's a little high in the math.

Or Google > diagram of peak value to current take you pick

I just wanted to expose the fact that a lot more is present to gain that 120V reading.

 

[Jpflex]

Ok thanks guys. I get peak vs RMS, I guess I was just confused because peak current just seems like a rather useless measurement no? Maybe if you are measuring very distorted waveforms it would be useful.

Could be useful if you could use this feature to measure max voltage spike inductive kick for DC primary or secondary ignition systems

 

[ptonsparky]

Could be useful if you could use this feature to measure max voltage spike inductive kick for DC primary or secondary ignition systems

I've used the min/max voltage on my Fluke 87 for catching the inductive kickback on coils. Peak Min/Max catches a bit more.

 

[gar]

230128-2150 EST

ptonsparky:

I found the min-max mode of the Fluke 87 to be quite useless for my purposes. Its time constant is way too long, 100 milliseconds. However, switching into peak mode is useful. Here the response is nearly 100 % of the value of a pulse duration of 1 millisecond.

My Fluke 27 does not have this 1 millisecond mode.

.

 

[electrofelon]

If I may expand the topic slightly:. Assuming you could choose, what would be a good time interval to measure peak current or power over? I don't think absolute peak is that meaningful as you would catch every bit of Inrush. But on the other hand, typical 15 minute demand always seemed too long to me. Perhaps something like the max 10 second average would be good for general purposes?

 

[ptonsparky]

If I may expand the topic slightly:. Assuming you could choose, what would be a good time interval to measure peak current or power over? I don't think absolute peak is that meaningful as you would catch every bit of Inrush. But on the other hand, typical 15 minute demand always seemed too long to me. Perhaps something like the max 10 second average would be good for general purposes?

I think you comparing apples to oranges here.

I use an HMI to graph demands for my water pump. Current, pressure, HP, etc. Most sensitive is one point every one second. I can average x number of points and plot it on the graph.

Somewhat different than looking for a peak on the sine wave.

 

[gar]

230129-1208 EST

See plots P1 thru P8 at

BETATRONICS&reg, Electrical photos, communication, Long Cable, High Baud Rate, RS-232, fast, I232, vendor, supplier, manufacturer, industrial

Electrical photos.

beta-a2.com

for several turn on currents.

The trip time curve of a fuse or breaker in comparison to a device's ( load ) turn-on curve will determine if the protective device will trip or not.

.

 

[ptonsparky]

I took some 1 ms Peak Min/Max readings for this coil setup. 120 volt coil.
With RCS1A--6: -152/160 respectively
Without: -352/484
The coil is fed via an interface relay to a small PLC (for tire inflation).
It doesn't take much of a coil to give some grief to sensitive equipment.
I can easily trip GFCIs by cycling a small contactor coil. IDK how they affect AFCIs but I could hazard a guess.

I've had the R-K for a bit.

 

[winnie]

If I may expand the topic slightly:. Assuming you could choose, what would be a good time interval to measure peak current or power over? I don't think absolute peak is that meaningful as you would catch every bit of Inrush. But on the other hand, typical 15 minute demand always seemed too long to me. Perhaps something like the max 10 second average would be good for general purposes?

I think that the time interval for averaging depends upon the time constant of why you care.

If you care about a panelboard being ripped apart by magnetic fields during a fault, you probably want to measure peak current at the sub-cycle level.

If you care about a distribution transformer overheating, then peak RMS averaged over a 15 minute period is probably just fine.

For some of these data logging applications it would be nice to have a dial that you could spin and watch the graph change as you adjust the averaging period.

-Jon

 

[ptonsparky]

Well, I didn't mean to post those pictures etc. on this thread, but I managed it.

 

[mtnelect]

Is a "Wiggy" just as accurate as a digital meter when it comes to every day measuring of voltage ?

I use a "Fluke" T+PRO for everyday work.