Effects of Mechanical Tolerances on QMF Performance for Operation in the Third Stability Zone

Abstract

Our previously reported method of accurately simulating the performance of a quadrupole mass filter (QMF) has been applied to the investigation of the effects of electrode positional tolerance on the performance of a QMF when operated in stability zone 3 ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> ≈ 3.16 and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> ≈ 3.23). Simulations for single- and dual-electrode positional errors have been undertaken. Single-axis errors produced changes in mass peak shape that are similar to those previously reported for zone 1. Compound errors produce changes in mass peak shape that are approximately a summation of the effects obtained from individual single-axis errors. Our results show that the direction of the electrode displacement, not the electrode, is the important factor in determining the effect on QMF performance. We also show that the effects of an individual electrode radius tolerance result in changes to the mass peak shape that are similar to those produced by individual electrode positional errors. Simulations also show the suitability of unbalanced excitation voltages as a method of compensating for mechanical tolerance when operating in zone 3. From these results, we are able to provide suitable limits for the voltage accuracy and stability when employing this method of compensation.