01 December 2011

App Note 65 part 4

Sixty-four total pages of appendices!

Appendices A and B are reprinted directly from App Note 55 (and App Note 49). Appendices C and D both have significant updates.

Appendix C discusses instrumentation for electrical measurements. In App Note 55, this discussion was six pages long, but here it has been expanded to twenty-four pages. His instrumentation suggestion are much more detailed. Figures C1 and C2 illustrate the problem: the necessary measurements need to be made with wide-band tools. For example, a new 10-MHz current-probe amplifier is detailed in Figures C3 through C7, and Figures C8 and C9 show a Wien-bridge oscillator used for its calibration and demonstrate its use.

Voltage probes and RMS voltmeters are discussed starting with Figure C10, with a calibration circuit shown in Figure C13. With the new emphasis on floating-lamp circuits in the main text, a new section on "Voltage Probes for Floating Lamp Circuits" starts on page 72. "Measuring voltage of floating lamp circuits requires a nearly heroic effort." Figure C14 shows a wide-band differential amplifier for use with high-voltage probes and a single-ended RMS voltmeter. Calibration of this fully differential RMS voltmeter apparatus is a significant challenge. Jim explains the difficulties, starting with first principles and a detailed schematic of a high-voltage probe in Figure C15. "No less than seven user adjustments are required to compensate the probe to any individual instrument input." And the warning in footnote 10, "Allow at least six hours for the entire session. You’ll need it."

A fully floating, differential, high-voltage calibrator is shown in Figure C16 (schematic in Figure C19). Photos of the details and internals are shown in Figures C17 through C23. The calibrator produces a 500-VRMS waveform to check the calibration of the probes. "Those who construct and trim the differential probe and calibrator will experience the unmitigated joy that breaks loose when they agree within 1%."

RMS voltmeters are discussed starting on page 82. Much of this discussion is copied from App Note 55, with the addition of Figures C25 and C26 (which are mostly borrowed from App Note 61 Figures 22 and 23). The appendix ends with the discussion of calorimetric measurements from App Note 55.

Appendix D discusses instrumentation for photometric measurements. In App Note 55, this discussion was less than two pages long, but here it has been expanded to six pages. He again starts with a picture of his "glometer" tube in Figure D1, which has been modified to allow variable-frequency drive to test individual lamps. The drive schematic is shown in Figure D2, and the measurement schematic is shown in Figure D5.

Finally, Figure D7 shows his complete "CCFL test set", including current probe, differential RMS voltmeter, calibrators, and photometer. Compare to the CCFL test set in App Note 55 (Figure C6). He has also upgraded his computer to a slide rule!

I'll discuss the rest of the appendices next time.


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