If the internal current control feedback mechanism is slow to act, then the output current might indeed change significantly. I have never put a constant current supply under careful supervision before but assumed that the guys designing them would go to lengths to ensure that they in fact maintain the output DC current constant under varying loads. Have you performed this measurement on a high quality constant current supply?
We also would need to assume that McKubre was not aware of the possible problems that have been pointed out. Perhaps we should get feedback from him to answer that question. If the current does not remain fixed and DC, then there are many possible errors to follow up on. On the other hand, if the source really does keep the current constant with adequate feedback control then the input power can be accurately determined by only taking into account the average DC voltage appearing across the supply terminals. AC signal voltages generated due to bubbles, etc. should not enter into the power input measurement unless they force the supply to go into operation outside of its normal range. Bob, I would be somewhat surprised to find that an expert of McKubre's caliber would not have a good handle upon the input power and energy levels after chasing that sort of problem for many years. Surely he would have seen the significant variation in current flowing through his test system at some time and attempted to rectify the situation with a better constant current system. Perhaps something as simple as a large capacitor across the supply output terminals would smooth out the current pulses. How confident are you that he missed this issue? Dave -----Original Message----- From: Bob Higgins <rj.bob.higg...@gmail.com> To: vortex-l <vortex-l@eskimo.com> Sent: Mon, Oct 27, 2014 11:05 am Subject: Re: [Vo]:questions on McKubre cells and AC component What you say, Dave, is entirely true and always pragmatically wrong. Most DAQ systems do not sample simultaneously and have an input capacitance that provides averaging. Thus, you will always be reading average current between samples and average voltage. Computing power from average current and average voltage will always be in error if there is any variation. As the sampling period approaches zero, the sampled average current times the sampled average voltage will approach the sampled average power. Unfortunately many DAQ systems have sampling periods of 1-3 seconds to sample many channels and provide best an most accurate readings (of the average) and to filter out 60 Hz and its harmonics. This means that short scale current variation will be averaged (not RMS'ed). It may be better to create a calibrated analog multiplier and feed that into a DAQ channel. Then you would be reading average power which would be OK. If you had an analog RMS function, that would also be OK to be averaged. Still, for bubble current/voltage noise, this represents only a small error bar in his experiment and does not invalidate the results. Bob On Sun, Oct 26, 2014 at 9:50 PM, David Roberson <dlrober...@aol.com> wrote: The total instantaneous power into the system can be calculated by taking the instantaneous source voltage and multiplying it by the instantaneous source current. It does not matter whether you want to call it AC or DC since this is the total that is being delivered. There is no more, regardless of how the load changes resistance. If you then integrate the instantaneous power over the time period of interest, you get the total energy delivered by that source. The requirement is that you must accurately measure the voltage and current waveforms during the period of interest. If someone can show that the measuring system used by McKubre was not capable of following the waveforms then they might have a valid point. I suspect the Mike knew how to make these measurements in an accurate manner. The skeptics need to demonstrate otherwise. Dave
