Method for developing circuit capacitance measurements corrected for

Abstract

Accuracy of capacitance measurements taken with flying probes--probes that are movable relative to each other and surfaces of an object containing circuits being tested (e.g. a printed circuit board)--is improved by dynamically applying corrections for stray capacitance as individual probes are selected for measurements. Measuring circuitry to which the probes are linked includes multiplexor circuitry. The latter stray capacitance encompassing the stray capacitance between the one movable probe and the other movable probes as well as the cabling between the latter probes and the multiplexor circuitry. For these measurements, the reference point is contacted either by a fixed conductor or another one of the movable probes (other than the probe aligned with the test point) that is currently usable for that purpose. As the one movable probe is moved into alignment with the test point, while out of contact with the object, a first capacitance measurement is taken and saved; that measurement representing the stray capacitance between that one probe and both the reference point and the other probes. The one probe is then moved into contact with the respective test point and a second capacitance measurement is taken and saved; that measurement representing capacitance between the respective test point and the reference point. The saved first measurement is subtracted from the saved second measurement, and the result is saved as a corrected measurement; i.e. a measure of the capacitance between the respective test point and reference point, corrected for all relevant stray capacitances.