To open the contacts, a magnet of opposite polarity is brought into the existing magnetic field, canceling the field from the existing permanent magnet. This in turn opens the contacts. The magnet must be carefully chosen so that its strength is strong enough to cancel the field from the permanent magnet, but not too strong that it overpowers the permanent magnet’s field, which could re-close the contacts. Furthermore, care must be taken in selecting the physical operate and release points. There are typically three magnetic lobes to deal with. Knowing where these lobes are is essential for proper operation. For normally closed sensors, it is best done working closely with Standex Electronics application engineers.