SC20 Magnetic Field Cancelling System     The SC20 is the latest magnetic field cancelling system from Spicer Consulting, introduced in 2004. The SC20 is the recommended system for cancelling DC fields, large fields and, as the SC20FAST, the 9kHz fields generated by wafer transport robots in 300mm fabs.      The SC20 has been designed to be largely backwards compatible with the SC12. The systems use the same operating principle and installations as described on the SC12 Product Description page. The SC20 is plug compatible with the SC12 field cancelling cables to enable easy upgrade of SC12 installations to the SC20.The SC20 control unit is not plug compatible with the SC12 magnetic field sensors. The SC20 case is larger than the SC12 enabling more powerful amplifiers, more cancelling range and easier rack mounting. It will install into a standard 19inch rack 3U space with the rack mount brackets fitted. The SC20 output amplifiers provide 60% more cancelling range than the SC12 and they will withstand an output short circuit or full scale overload indefinitely without degradation. (The SC12 amplifiers are protected with thermal fuses which may degrade if subjected to long term overload.) The front panel display has been simplified and upgraded to display the magnetic field amplitude of all three field axes continuously as well as the magnitude of the total field vector. The display units are switchable between milligauss and microtesla and the display can be AC-RMS or Incremental DC when the SC20 wideband sensor is used. The BNC connectors for monitoring the realtime field with a scope have been moved to the front panel for easier access. To futher enhance the "set and forget" performance, the set up controls which affect cancelling have been located behind a secure drop down front panel. This is to prevent tampering or accidental adjustment of the controls in unattended installations. The system can provide AC or DC cancelling depending on the sensors installed. It recognises the sensors used and selects the internal filters to use. The sensor mixer function (an add-on box with the SC12) is built into the SC20 and becomes active when two sensors are plugged in. The SC20 includes a system interface (not available on the SC12) enabling the SC20 monitor to be connected, allowing remote monitoring of the SC20 status and measured field levels.