The present invention is directed to phosphorus containing flame retardant photoimagable compositions useful as a coverlay material in a flexible electronic circuitry package. The pre-sealing unit includes bellows unit and partition unit which surrounds the sealing mechanism from within the working tank. The first semiconductor controlled rectifier includes a first semiconductor region and a second semiconductor region, and the second semiconductor controlled rectifier includes the first semiconductor region and the second semiconductor region. A plurality of monitors is included, each of which monitors the voltage across a respective one of the plurality of disk drive elements in response to the direct current and the alternating magnetic field.