Control of a Physical Parameter Down to the Noise Level

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Contents of the Talk

To control a magnetic field inside the large magnetically shielded room (BMSR-2) at PTB in Berlin, attempts with “standard” regulation technology was unsatisfying. The presented Stepwise Immediate Follower (SIF) was so successful that PTB applied for a patent. The SIF assumes that the reaction of the system due to a controller intervention is reproducible and can be measured even for a small interaction. The prediction of the reaction allows to separate deviations from the requested set point value due to the controller from changes caused by disturbances. This allows the controller to compensate the disturbances independent from previous controller interventions. The output of the SIF thus follows the disturbance. The optimal SIF parameter settings can be determined automatically by measurements without additional equipment. SIF will keep the controlled parameter in the order of the noise on the measured parameter unless a finite resolution of equipment in the decision loop limits the accuracy. An additional magnetic field of 2 µT inside BMSR-2 for spin precession experiments was stabilized with SIF inside BMSR-2. The stability of the magnetic field was found to be limited already after 150 s not by the SIF control, but by the uncertainty of the used magnetic field detector, a SQUID. Presently a SQUID is the most accurate magnetic field detector. The long-time magnetic field stability is the best achieved for such a setup so far.

Short CV

Allard Schnabel received his Diploma in Electrical Engineering from Rhein-Main University, Germany, in 1978. He furthered his education with a second Diploma in Physics from Goethe University Frankfurt, Germany, in 1984. In 1988, he completed his Ph.D. in Theoretical Physics at the University of Cape Town, South Africa. Following his academic pursuits, Schnabel joined PTB Berlin, Germany's national metrology institute. He retired as a Senior Scientist from PTB Berlin in 2022, where he specialized in magnetic shielding. Despite his retirement, he remains actively involved in enhancing magnetic shields, including developing magnetically shielded rooms. Additionally, Schnabel plays a significant role in the national and international standardization of medical electric equipment.