AC or DC

[Mark-VA]

Measured the output from my TDI on the TX side and noticed three main things.
Out put voltage is about half the battery voltage
There is DC voltage when my meter is set to DC
There is AC voltage when my meter is set to AC
So which would be used to measure the current entering the coil

V=IR
V = DC voltage is 3.22
R 3.3 ohms
I = .97 amp

V=IR
V = AC voltage is 5.74
R = 3.3 ohms
I = 1.74

I guess the question is which voltage is to be used.
AC or DC

[dbanner]

AC. Meter measure RMS in sine(AC). For square, Vpeak=Vrms=Vavrg

[dbanner]

Wait a minute, that's not right. Tx is pulses and pulse width can vary. I am not sure.

Vrms is the value indicated by the vast majority of AC voltmeters. It is the value that, when applied across a resistance, produces that same amount of heat that a direct current (DC) voltage of the same magnitude would produce. But for square pulses? What would be its Vrms? Don't know.
Of course the peak current would be Vpk/R. But this is not the same thing.
Can AC meter accurately measure Vrms of non sinus pulses? No. They are calibrated to measure true RMS only for sinusoidal, and they will read incorrectly if the wave is not sinusoidal.

[dbanner]

I think only way is to measure peak voltage on scope along with two different points, then use math to calculate RMS voltage.
Or measure the on time/off time ratio of TX pulse as a percentage of Vpeak to obtain Vavrg. Then use Vavrg/R, provided that Vavrg=Vrms.

[waltr]

Correct, due to TDI outputting a Pulse of around 10% duty a meter can NOT be used.
This must be measured with a O'scope and only during the TX pulse.

[Carl-NC]

TDI is ~30% duty cycle and the TX-on voltage is a rising exponential. Trying to measure anything with a voltmeter is useless, you gotta use a 'scope. BTW, unless the meter says "true RMS" it is likely RMS only for sinusoids, not valid for any other waveform.

[Mark-VA]

Thanks everyone. Just curiously experimenting. For sure the TX on a PI is totally different from the TX on a VLF. I was actually studying the TX output in relation to increasing the system voltage.
All very intriguing.
Several years ago I read numerous posts from Reg maybe Carl and many others about the relationship of voltage and depth on the TDI. Just studying the subject.

[kt315]

i do not think Carl could write about increasing the system voltage. thats is weird idea to get more depth.

[Mark-VA]

Like I said, "maybe Carl", it's been so long ago and White's dropped the find mall forum, so I can't access the posts that pertained to the voltage. The increased depth capability is a proven fact according to Reg.
I can ascertain an increase in the increased voltage, which actually increased the current in the coil but only in small increments.
I had the pleasure of seeing some of Reg's results but been curious as to the SL version in particular. Since I work for a printed circuit board producer I'll check on the true RMS meter Carl mentioned.

[Mark-VA]

meter

TDI is ~30% duty cycle and the TX-on voltage is a rising exponential. Trying to measure anything with a voltmeter is useless, you gotta use a 'scope. BTW, unless the meter says "true RMS" it is likely RMS only for sinusoids, not valid for any other waveform.

Work just happens to use this meter.

[kt315]

this fluke is better. take it.

[Mark-VA]

I don't know if they have one that nice.
I was borrowing from work.

[dbanner]

Work just happens to use this meter.

By the way, that Fluke Meter says "True RMS" . I wonder if it can measure non-sinusoidal waveform accurately? Maybe it can.
Try downloading the user manual for it, there you can see specifications for AC measurements.

[Mark-VA]

The only thing the meter would do is give me:
AC voltage
Average 4.426 volt
Max 4.449 volt
min 4.406 volt


I got this information in the manual about the True RMS meter.

Understanding AC Zero Input Behavior of True RMS Meters Unlike averaging meters, which can accurately measure only pure sinewaves, True RMS meters accurately measure distorted waveforms. Calculating True RMS converters require a certain level of input voltage to make a measurement. This is why AC voltage and current ranges are specified from 5% of range to 100% of range. Non-zero digits that are displayed on a True RMS meter when the test leads are open or are shorted are normal. They do not affect the specified AC accuracy above 5% of range. The input levels that are unspecified are: • AC voltage: below 5% of 6000 mV AC, or 300 mV AC • AC current: below 5% of 60 A AC, or 3.00 A AC

I think I wasted my time borrowing the meter!

[dbanner]

No, not at all. Once the voltage measured is above a certain level, you get a true RMS reading of waveform(non sinus). This is exactly what you want. Unless I'm interpreting the manual incorrectly.
Even if you have true RMS value of tx pulses, I don't think the calculation is simply to divide by R. That only works for DC voltage.
With AC or alternating pulses, the coil presents an inductive reactance. The calculation become more complicated.
It is XL= 2πLF where L is inductance in Henries and F is frequency in Hertz. But this is for waveforms, not sure about pulses which have field collapsing to zero then there is period of off before next pulse.
Divide true RMS voltage by XL to get current(I). I am not sure about pulses like the on in pi detectors, maybe some calculus required for XL.
I wonder what experts have to say.