Position control for the MSL Kibble balance coil using a syringe pump

Abstract

The position of the coil in a Kibble balance must be finely controlled. In weighing mode, the coil remains stationary to maintain a constant magnetic field. In calibration mode, the coil is moved in the magnetic field to induce a voltage. The MSL Kibble balance design is based on a twin pressure balance where the coil is attached to the piston of one of the pressure balances. Here we investigate how the piston (and therefore coil) position may be controlled through careful manipulation of the gas column under the piston. We demonstrate the use of a syringe pump as a programmable volume regulator which can provide fall rate compensation as well as controlled motion of the piston. We show that the damped harmonic oscillator response of the pressure balance must be considered when moving the coil. From this initial investigation, we discuss the implications for use in the MSL Kibble balance.