a sensor , such as a mass spectrometer , capable of detecting the presence of materials in a sampled gas is interconnected with a processing chamber of a vacuum manufacturing tool . the sensor includes a timing circuit which is activated only if certain levels of specific materials are detected . furthermore , the timer is set to run a predetermined time interval after activation so as to discriminate between known transient processing conditions and the presence of impurities which can greatly influence the manufacturing process . when the timer exceeds the predetermined time duration , an output signal can alert the process operator or automatically shutdown the manufacturing tool .