Development of a 125 g quartz flexure accelerometer for the RIMU program

The AlliedSignal Q-Flex(R) accelerometer is widely recognized for its value in terms of performance delivered per dollar invested. The model QA-2000, in particular, which features temperature modeling for performance from -54°C to +95°C, has become the de facto standard for many applications, including inertial navigation of commercial aircraft, and spaceborne microgravity measurements. The design has long been recognized as one of those technical devices which dominates its market by offering an unusually well balanced set of design parameters. The factors which limit the useful g range of Q-Flex accelerometers have been identified, but not understood in detail, for many years. RIMU provided an occasion to refine that understanding. A design investigation was undertaken, based on both classical physics and modern statistical design techniques. Several refinements were identified and implemented, but the dominant contributor to the useful acceleration limit was confirmed as insufficient coincidence of two centers: the center of mass of the pendulum which comprises the sensor proofmass, and the center of force of the electromagnetic torquer which is used to effect servo-loop closure. For the unmodified baseline accelerometer design, the yield rate for 125 g was typically about 40%. After fine-tuning the design and certain key production processes, the yield increased to 88% for two lots and 100% for a third, with other aspects of performance remaining equal or better. This improved capability is expected to open new areas of application for the Q-Flex design