Electron microscopes have to operate in an ambient magnetic field comprising the earth’s field (DC magnetic fields) and fields radiated by electric power networks and electrical machines (AC magnetic fields). The SC24 with DC/AC sensor is the premier magnetic field cancelling system both types of fields. When the ambient field changes due to trains, elevators, trucks, metal doors, etc. (DC EMI), the electron beam deflects. This results in a loss of resolution and image distortion. The SC24 with DC/AC sensor rapidly detects field changes and dynamically creating equal and opposite field to stabilize the image. The result is an image that is clear, stable, and free of distortion. In addition, the SC24 is equally effective in cancelling AC magnetic fields from transformers, electrical wiring, and electrical equipment.
The SC24 system comprises a magnetic field control unit, one or two magnetic field sensors and three orthogonal axis multicore cables. A VEC engineer will install these cables in the room where the field is to be cancelled. The SC24 can drive single loop and double loop room size cables. It also works with Helmholtz cables that are attached to a frame around the column or a specially designed Octagon frame for optimal AC and DC field cancellation. Three power amplifiers in the control unit drive currents through the cables to create a field of the opposite sign to the change in ambient field. The magnetic field sensor measures the resulting field and real time negative feedback reduces the ambient field by the loop gain of the system. The system is dynamic, automatically responding to field changes within 100 µs.