12V lighting track ghost voltage?

[ELA]

220416-0832 EDT

Whereas my Fluke 27 goes to about 400 to 500 kHz, then just drops. What other meters do I don't know.

Gar,
I believe the Fluke 27 is good to around 30Khz when talking True RMS readings?

My BK 391A reads a square wave RMS value fairly accurately up to around 10Khz and drops off rapidly after 20Khz.

It will be interesting to hear the Frequency the transformer in question operates at.

 

[gar]

220417-1600 EDT

ELA:

The Fluke 27 is not an RMS meter, but rather a rectified sine wave which when full wave rectified and averaged would read 0.636 of the sine wave peak. However, average measuring AC instruments are usually calibrated to read the RMS value of a sine wave. That means on other waveforms, for example gaussian noise, the reading will need a correction factor from the labeled RMS reading.

From memory I had in my mind that the RMS values dropped off around your 30 kHz on the typical DVM.

But that is not the case for the Fluke 27 or my Beckman 4410 ( which is an RMS meter ). I don't have a Fluke 87 at home. Simpson below is in Output mode ( meaning an internal series capacitor ), all of the others are inherently built with a series capacitor in all AC voltage modes. Really the AC current modes also have that series capacitor, except in this case there is a resistive shunt external to the capacitor.

Some measurements today using a Tektronix CFG250 function generator in sine wave mode and no adjustment of its amplitude were:

Freq ........ Simp ...... Fluke ..... Beckman
kHz

000.1 ...... 4.60 ....... 5.06 ....... 5.06

001.0 ...... 4.85 ....... 5.06 ....... 5.06

010.0 ...... 4.90 ....... 5.05 ....... 5.43
020.0 ...... 4.90 ....... 5.04 ....... 5.88

100.0 ...... 4.80 ....... 5.41 ....... 6.26
200.0 ...... 4.80 ....... 4.94 ....... 2.42
300.0 ...... 4.60 ....... 1.71 ....... 2.20
400.0 ...... 4.40 ....... 1.36 ....... 0.05
500.0 ...... 4.35 ....... 1.16 ....... 0.001

600.0 ...... 4.20 ....... 1.07
700.0 ...... 4.10 ....... 0.78
800.0 ...... 3.95 ....... 0.02
999.9 ...... 3.70 ....... 0.005

.

 

[tortuga]

Some measurements today using a Tektronix CFG250 function generator in sine wave mode and no adjustment of its amplitude

What was the Peak to Peak voltage set at?
Did you have it connected to a 50 ohm load?

 

[gar]

220417-2324 EDT

tortuga:

When you have a sine and know the RMS voltage, then you multiply by 1.414 to get the peak value.

If you have a high impedance parallel resonant circuit and parallel a 50 ohm source across that resonant circuit you will virtually see no resonant peaking. The 50 ohm source is relatively a zero impedance source connected in parallel with the coil and capacitor.

In my test looking for resonance I used a separate inductor to create an approximate constant magnetic field vs frequency to my inductor in the resonant circuit, and swept the frequency thru the resonant point.

.

 

[gar]

220417-2345 EDT

tortuga:

If you wanted to use a 50 ohm impedance voltage source to check for resonance you would connect that source in series with the inductor, and caacitor. And of course there is series resistance internal to the inductor, and that is why its Q is low.

.

 

[ELA]

220417-1600 EDT


.

Gar,

I thought we were interested in the square wave performance of a meter and not sine wave for this discussion?

 

[gar]

220418-1433 EDT

ELA:

I don't know that there is any identification or definition of what the waveform is in this discussion. Whether it is DC, a sine wave, square wave, or something else is really of little importance. The voltage reading is so far from any likely value that at this point waveform is of no importance, except as possibly related to frequency.

A useful experiment to run at this point is to excite one of the bulbs with 12 V DC from a car battery, and measure the light output from the bulb.

This measurement can be done in a dark room with one of the bulbs, and a light meter at a determined distance. Then repeat the same experiment with the strip bus as the power source. Essentially this will be using the bulb as a voltmeter..

If you do not want to work in a dark room, then use a tube of X feet with the bulb at one end and the meter at the other end.

This is a relative type of experiment. It is also a way to perform power measurements up into the many megahertz frequency range.

.

 

[gar]

220418-1513 EDT

Another experiment that relates to AC measurement.

I set my function generator sine wave to output a reading of 5 V AC on the 10 V range at 1 kHz. This is high enough in frequency to avoid rolloff of the AC reading on the Simpson.

Switching the generator to square wave and the reading jumps to 7.65 V. That is ratio of 1.53, but remember the Simpson is really reading the average AC voltage and is calibrated in RMS. So if 1.63 is divided by 1.1 ( the ratio of 0.707 to 0.636 ), then the value is 1.39 which is close 1.414 the expected ratio.

Now, if I use my Beckman which is an RMS measuring device calibrated in RMS my values are 6.83 / 5 = 1.36, and this is moderately close to 1.414 .

.

 

[hbiss]

The only way we are going to know what the voltage is in that track is to take a quick look at it with a scope. Then you can figure out why you can't measure it or what you are doing wrong.

-Hal

 

[LarryFine]

Can you hide a low-value, high-wattage resistor somewhere, and wire it in series with the load?

I withdraw my resistor suggestion. How about a pair (for AC) of diodes, which will drop 0.6v?

 

[gar]

220419-2000 EDT

Larryfine:

Nothing wrong with your series resistor idea, actually better than back to back diodes. The problem is still back to the measuring instrument, and whatever the signal is, its frequency, and how the instrument responds to the signal.

.

.

 

[tortuga]

Just a little update, since the light was provided by a GC they are ordering a replacement one before they send us back out there. When I do go back ill bring the faulty light to the shop and put a scope on it and do some messing around.

 

[hbiss]

If I get a chance I want to see how my Fluke 87 responds to a square wave. With years of audio work I have never noticed a problem like this. One thing I did notice in that video made by the power supply supplier, that little Fluke 7-300 that they used was auto function and auto ranging. It didn't look like it could figure out what was connected to it in order to know whether to measure VAC, VDC or resistance.

-Hal

 

[hbiss]

Ok. With a Fluke 87 (which Fluke hasn't changed in better than 30 years):

Sine wave= 1.008 vac
Square wave= 1.014 vac

Neither reading changed from 65 Hz to 400Hz.

So, I submit that what you are using to measure the voltage is junk and that guy in the video is all wet.

-Hal

 

[ELA]

The only way we are going to know what the voltage is in that track is to take a quick look at it with a scope. Then you can figure out why you can't measure it or what you are doing wrong.

-Hal

As you pointed out what is needed is an oscilloscope reading to determine the wave shape involved in the transformer.
All DVM's AC-RMS readings will fall off and become inaccurate at some frequency specification. 400hz is not a high enough frequency to exhibit a roll off for most meters.

Assuming a Sine Wave reading of 1V RMS wouldn't the equivalent Square Wave reading be 1.414?
Or was the input amplitude purposely adjusted when changing between sine and square modes?
When evaluating data is is helpful to understand what the test setup was?

 

[gar]

220421-0931 EDT

hbiss:

My results of of various measurements are somewhat different than yours.

I will repeat my previous data with some additions to the data, and this includes the Fluke 87. Also I created a test that included an RC low pass filter that has a rolloff much below the frequency capability of the meters. The additional data is the addition of a calculated column that is the ratio of the sq-wave to sine wave measured values. Also, it should be noted that all these meters have a much lower low pass filter relating to their display mechanism.

The Fluke 27 is electrically very much like the Simpson. Both use a bridge rectifier or equivalent to convert AC to DC, and have AC calibration based on RMS of a sine which is the factor 0.707 / 0.636 = 1.11 . Whereas, the Beckman and Fluke 87 use some kind of converter from AC to DC that does the RMS calculation.


Some measurements today using a Tektronix CFG250 function generator in sine wave mode and no adjustment of its amplitude were:

Freq ........ Simp ........................................... Fluke ........................................... Beckman ..................................... Fluke
kHz ........ 270 ............................................. 27 ................................................ 4410 ............................................ 87
................ Sine ..... Sq-W ..... Ratio ............ Sine ..... Sq-W ..... Ratio .............. Sine ..... Sq-W ..... Ratio ............. Sine ..... Sq-W ..... Ratio

000.1 ...... 4.60 ............................................ 5.06 ............................................. 5.06 ....................................................................................

001.0 ...... 5.00 ..... 7.70 ....... 1.51 .............. 5.06 ............................................. 5.14 ..... 7.09 ....... 1.37 .............. 5.19 ...... 7.04 ....... 1.36

010.0 ...... 5.00 ..... 7.65 ....... 1.51 .............. 5.05 ............................................. 5.18 ..... 6.97 ....... 1.35 .............. 5.17 ...... 6.91 ....... 1.34
020.0 ...... 5.00 ..... 7.60 ....... 1.50 .............. 5.04 ............................................. 5.17 ..... 6.82 ....... 1.32 .............. 5.09 ...... 6.76 ....... 1.33
050.0 ...... 5.00 ..... 7.60 ....... 1.52 .................................................................... 5,14 ..... 6.40 ....... 1.25 .............. 4.72 ...... 6.25 ....... 1.33
070.0 ...... 5.00 ..... 7.60 ....... 1.51 .................................................................... 4.98 ..... 6.10 ....... 1.23 .............. 4.36 ...... 6.00 ....... 1.38

100.0 ...... 5.00 ..... 7.55 ....... 1.51 .............. 5.41 ............................................. 4.33 ..... 5.03 ....... 1.22 .............. 3.76 ...... 5.02 ....... 1.34
150.0 ...... 4.95 ..... 7.50 ....... 1.51 .................................................................... 2.26 ..... 3.03 ....... 1.34 .......... 2.40 ...... 4.80 ....... 2.00
200.0 ...... 4.90 ..... 7.40 ....... 1.51 .............. 4.94 ............................................. 0.96 ..... 1.23 ....... 1.28 .............. 0.14 ...... 3.86 ....... 27.6
300.0 ...... 4.70 ..... 7.35 ....... 1.56 .............. 1.71 ............................................. 0.02 ..... 0.04 ....... 2.00 .............. 0.03 ...... 0.02 ....... 0.67

400.0 ...... 4.40 ............................................ 1.36
500.0 ...... 4.35 ............................................ 1.16
600.0 ...... 4.20 ............................................ 1.07
700.0 ...... 4.10 ............................................ 0.78
800.0 ...... 3.95 ............................................ 0.02
999.9 ...... 3.70 ............................................ 0.00

Both the Simpson 260 / 270 and Fluke 27 will use a full wave bridge rectifier for conversion of AC to DC for the meter. Whereas, the RMS meters will some sort of converter from AC to DC.

The low pass filter data I am not presenting now.

.

 

[hbiss]

As you pointed out what is needed is an oscilloscope reading to determine the wave shape involved in the transformer.
All DVM's AC-RMS readings will fall off and become inaccurate at some frequency specification. 400hz is not a high enough frequency to exhibit a roll off for most meters.

We are talking about what's relevant to this discussion. It's extremely doubtful that that power supply provides anything near 400 Hz. so discussion of anything higher really doesn't apply and is the reason I stopped at that frequency.

Any decent DVM should give you an indication in this case of the voltage from that supply regardless of the waveform. Depending on the (quality of the) meter, it may not be 100% accurate but you certainly shouldn't be seeing only 1-2 volts with 12 volts.

If a cheap analog meter will give an accurate reading, you need a better DVM.

-Hal

 

[ELA]

The only way we are going to know what the voltage is in that track is to take a quick look at it with a scope. Then you can figure out why you can't measure it or what you are doing wrong.

-Hal

We are talking about what's relevant to this discussion. It's extremely doubtful that that power supply provides anything near 400 Hz. so discussion of anything higher really doesn't apply and is the reason I stopped at that frequency.


-Hal

Initially you appear to agree that more information is needed on the waveform from a scope. Then you go on to speculate without having data.
Many switching power supplies operate at well above 400hz.

Will you please share your test setup information and what amplitude adjustments may have been made between sine and square modes?

 

[hbiss]

Will you please share your test setup information and what amplitude adjustments may have been made between sine and square modes?

As simple as can be- out of the signal generator and into the meter test leads. Output is the same level for both sine and square and frequency. Signal generator sees to that.

Many switching power supplies operate at well above 400hz.

And they deliver DC voltages by rectifying and filtering the output. I'm going to assume that these work the same way but without the rectifier, delivering straight AC. No way to tell what the frequency and waveshape of the AC is without a scope but I doubt it's up in the Khz range.

BUT the fact remains- if it can be measured with a simple analog meter, a good DVM should work also.

-Hal

 

[ELA]

As simple as can be- out of the signal generator and into the meter test leads. Output is the same level for both sine and square and frequency. Signal generator sees to that.


-Hal

Thank you for that information. How do you explain the data you posted in post #34 based on the signal generator amplitude being the same for both?
If the signal generator was left at the same amplitude and Sine wave = 1.000 then Square wave should be 1.414.
Gars data depicts this fact.