SC22 Product Description
The SC22 is a fourth generation Magnetic Field Cancelling System. It is a replacement for the SC12 system, which has an installed base of over 1000 units world wide. The system is dynamic, automatically responding to field changes within 100 µs and AC Line fields (50/60 Hz) are reduced by 50x. The SC22 does not cancel DC field changes from sources such as elevators, trains and traffic. The more powerful SC20 system is available to cancel both AC and DC fields.
The SC22 controls are much simpler than the SC12 and SC20 and are supervised by the embedded microcomputer. There are just 3 control buttons on the front panel. The “units” button enables choice of the displayed field units. It has no effect on field cancelling. The “setup” button starts a 4 second program that measures and sets the gain and phase of the feedback loop. The “cancel/standby” button turns cancelling on and off.
The amount by which the field is reduced is determined by the loop gain of the system, which is automatically set by the SC22 to 50 times.
The SC22 control unit displays the amplitudes of the X, Y & Z field components and the total vector field on its LCD panel. Tesla and Gauss units, RMS & pk-pk can be selected. The measuring system can resolve 1µG (100 pT) field changes. The real-time measured fields are available on front panel BNC’s as analog voltage levels for oscilloscope display. The magnetic field amplitude is continuously monitored and compared with preset “trip levels” to provide “/NO” indication of the field quality. The LCD panel and a small green LED on the sensor indicate that the field is “OK”.
Cables are normally installed on the walls near the microscope, as shown in the figure to the right but when the room is large or in clean rooms where there are no local walls, a frame around the electron beam tool can be used to mount Helmholtz cables. A frame, however, limits access to the tool so should only be used where room cable installation is not possible. The cancelling performance with a frame may also be inferior to a room cable installation.
For leading edge TEM installations, double loop room sized helmholtz cables are available. These are recommended for TEM’s fitted with Gatan Imaging filters (GIF’s). Customers are advised to consult Spicer Consulting support staff for design and installation of these special field cables.
The SC22 AC field sensor is shown on a sensor mount attached to a column in the figure below. This is the most common configuration with one sensor.
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