Studies of beam position monitor stability

We present the results from two studies of the time stability between the mechanical center of a beam position monitor (BPM) and its electrical/electronic center. In the first study, a group of 93 BPM processors was calibrated via a test pulse generator once per hour, in order to measure the contribution of the readout electronics to offset drifts. In the second study, a triplet of stripline BPMs in the Final Focus Test Beam, separated only by drift spaces, was read out every six minutes during one week of beam operation. In both cases offset stability was observed to be on the order of microns over time spans ranging from hours to days, although during the beam study much worse performance was also observed. Implications for the BPM system of future linear collider systems are discussed.