poynt99's Testing of Rosemary Ainslie's Circuit 2013-06

[poynt99]

The following video clearly demonstrates how parasitic circuit inductance can and will skew the battery power measurement "Pbat" when taken using a DSO oscilloscope.

Of note to remember for the video:

-  A "positive" indicated Pbat  tells us that the battery energy is depleting.

-  A "negative" indicated Pbat  tells us that the battery energy is increasing.

http://www.youtube.com/watch?v=pnZLwA2Uohs

[poynt99]

The following segment "4" video illustrates essentially the same as segment 3 did, in that parasitic inductance between CSR probe tip and probe ref will significantly skew the Pbat measurement. There was concern expressed that I did not have the Vbat probe reference connected, and therefore it is connected in this redo. In this segment I only compare the CSR probe measurement in two positions rather than 5. The variance is dramatic still and changes from roughly -1.02 to +0.91 by simply moving the probe tip and ref 1" away on either side of the CSR body.

Video Link: http://www.youtube.com/watch?v=SietCns2r-M

The two attached pictures relate to those two probe positions and their resulting Pbat values.

[poynt99]

Here again is the same test as segment 4 but with 20 cycles in the scope display. There is no significant difference in the measured Pbat values.

http://www.youtube.com/watch?v=CGDzic26qQs

[poynt99]

Here I've done a video segment illustrating an often-encountered problem when doing power measurements on switching type circuits...GROUNDING!

A test involving a function generator and an oscilloscope is going to be troublesome, particularly when wanting to measure multiple components in the circuit. The two pieces of equipment must be isolated by some means; either by lifting the earth ground on the FG or using differential scope probes. I chose the former as will most folks attempting these measurements.

With the FG reference lead isolated from the oscilloscope's reference leads, the scope probes can be placed anywhere in the circuit in order to accurately and safely perform specific power measurements.

http://www.youtube.com/watch?v=0rtuSwfs-90

[poynt99]

This next segment illustrates the correct location for the FG's reference lead. Previously it was connected in such a way to bypass the CSR and would therefore not capture any current the FG may be passing through the circuit.

http://www.youtube.com/watch?v=e_ZK6OPJLl4