Reactive power - Reactive Generator research from GotoLuc - discussion thread

[poynt99]

Hi poynt and all,

here is a video update with the scope set to DC coupling. I'm still questioning the channel 2 Inversion.
Can you please confirm which way it is and what is Watts used

Video: http://www.youtube.com/watch?v=gTJ8i5unIwQ&feature=youtu.be

Thanks

Luc

EXCELLENT VIDEO LUC!

- Glad to see the power is much closer when switching between inverted and non-inverted. They should be the same however, and hopefully a channel calibrate will take care of that problem (see next point).

- Please run a "cal" on the scope from the "Utility->DoSelfCal" and check your measurements again. Run scope for 20 min. then disconnect all probes before you run the cal. Check your measurement again, as any offset in the channels should now be compensated. It takes about 5 minutes to run its course.

- DC Coupling on both channels...all good.

- Tip1: For low frequency measurements such as these, it may be beneficial to reduce the scope bandwidth limit (BW) to 20MHz on both channels. This is what I usually do and have done for my measurements here. You will get a slightly cleaner trace and triggering is sometimes less jittery (when traces are spiky).

- Tip2: If you haven't already, set the trigger source to "line".

- I am a little confused about your current probe scaling. I am using a x1 probe, 0.1 Ohm CSR, and scaling is 100mV/A. You sure that making it x10 is correct? The 100mV/A scaling already accounts for the fact that the resistor is 0.1 Ohms, so no need to multiply by 10. Also, I noticed your MATH does not read in Watts anymore; I thought it did before.

- CH2 inverted is (still) the correct way. Sources compute to a NEGATIVE MEAN power. But I will be making a video to explain all this. So yeah, you should have about -20W (CH2 inverted and the current scale setting is correct) GRID power. And a negative GRID power (with CH2 inverted) does not mean power is going back to the grid. A positive power would however mean power is going back to the grid (with CH2 inverted).

- I'm not sure why your MEAN value did not change much when increasing the number of MATH samples on the display, but it does make a marked difference with my measurement. But it is quite dependent on the wave shape. Sometimes it makes a great difference, others not, but the bottom line is that for an accurate MEAN power measurement, you should always use at least 10 MATH cycles (5 voltage cycles) on the display.

- Your power reading on the DC Wattmeter fluctuates when you remove the batteries because the meter would be seeing a FWR signal rather than a relatively steady DC.

.99

[barbosi]

I determined that using a 0.1 Ohm CSR, one can select current for probe CH2, and one can also set the scaling for 100mV/A so that CH2 will read directly in the correct mA.

Yes, the measurement is sufficiently accurate for these measurements at 60Hz. If that CSR was replaced with a good non-inductive resistor, we could do high frequency measurements as well. Actual Current probes are non-intrusive, but they produce a voltage output just as a voltage probe across a CSR does.

No need to lecture me, I know for many years how to use a scope.
Are you sales rep for Tek? ask them for a group discount because all should be buying Tek. Or you want to keep this as a 2 people thread with Luc which I doubt?

A propos: What happened with polarities and DVM usage and all that theory you fought for? It was just an insertion tool?
Man, in my life I met hundreds of sales reps, but you are... Don't bother to respond, I won't read, I'm out!

[poynt99]

No need to lecture me, I know for many years how to use a scope.
Are you sales rep for Tek? ask them for a group discount because all should be buying Tek. Or you want to keep this as a 2 people thread with Luc which I doubt?

What's your problem fella? You asked a question, and I answered it appropriately. Sorry that you take offense so easily.

A propos: What happened with polarities and DVM usage and all that theory you fought for? It was just an insertion tool?

The video to explain the proper channel invert selections when using the common probe placement is coming. I first needed to determine why I was not getting the negative MEAN measurement Luc was, and now that I have resolved that, I can move on. But who are you to be making demands on my schedule and method of approach?

I'm not sure what you are inferring with "DVM usage".

Man, in my life I met hundreds of sales reps, but you are... Don't bother to respond, I won't read, I'm out!

Happy trails! 

[gotoluc]

EXCELLENT VIDEO LUC!

- Glad to see the power is much closer when switching between inverted and non-inverted. They should be the same however, and hopefully a channel calibrate will take care of that problem (see next point).

- Please run a "cal" on the scope from the "Utility->DoSelfCal" and check your measurements again. Run scope for 20 min. then disconnect all probes before you run the cal. Check your measurement again, as any offset in the channels should now be compensated. It takes about 5 minutes to run its course.

- DC Coupling on both channels...all good.

- Tip1: For low frequency measurements such as these, it may be beneficial to reduce the scope bandwidth limit (BW) to 20MHz on both channels. This is what I usually do and have done for my measurements here. You will get a slightly cleaner trace and triggering is sometimes less jittery (when traces are spiky).

- Tip2: If you haven't already, set the trigger source to "line".

- I am a little confused about your current probe scaling. I am using a x1 probe, 0.1 Ohm CSR, and scaling is 100mV/A. You sure that making it x10 is correct? The 100mV/A scaling already accounts for the fact that the resistor is 0.1 Ohms, so no need to multiply by 10. Also, I noticed your MATH does not read in Watts anymore; I thought it did before.

- CH2 inverted is (still) the correct way. Sources compute to a NEGATIVE MEAN power. But I will be making a video to explain all this. So yeah, you should have about -20W (CH2 inverted and the current scale setting is correct) GRID power. And a negative GRID power (with CH2 inverted) does not mean power is going back to the grid. A positive power would however mean power is going back to the grid (with CH2 inverted).

- I'm not sure why your MEAN value did not change much when increasing the number of MATH samples on the display, but it does make a marked difference with my measurement. But it is quite dependent on the wave shape. Sometimes it makes a great difference, others not, but the bottom line is that for an accurate measurement, you should always use at least 10 MATH cycles (5 voltage cycles) on the display.

- Your power reading on the DC  Wattmeter fluctuates when you remove the batteries because the meter would be seeing a FWR signal rather than mostly DC.

.99

Thanks for all the details. I will do them all.

How about in the Acquire menu... what should be selected there?

Luc

[poynt99]

Luc, to summarize:

Channel Settings:
- Coupling = DC
- BW = 20MHz
- Termination = 1M
- Offset: 0.0V, 0.0A
- Leave the vertical scaling to default for now. i.e. don't adjust the fine scale to make the traces the same on the display. This shouldn't have any effect, but just in case for now.
- Current scaling with 0.1 Ohm = 100mV/A (or 10A/V) and x1 attenuation.

Acquire Menu:
- Mode = Sample (for now)
- Record Length = 10k (increasing to 100k did not make any difference for me)
- Delay = don't care


btw, I changed the horizontal scale to see what difference the number of cycles makes for my measurements, and it was as follows:

5 MATH cycles, MEAN=2.37W
12 MATH cycles, MEAN=3.59W

So even if it doesn't seem to make a difference, please make it a habit of using 10 or so MATH cycles when making the critical MEAN power measurement. After you get the measurement, you can always decrease the horizontal to see the wave forms better if you wish.