although such transducers are particularly specified for determining low differential air pressure conditions such as that found in so called 34 clean room 34 applications it has been discovered that this transducer is also useful to detect modulating air pressure in one of the pockets of a paper manufacturing dryer where flutter frequency is believed not to exceed approximately 100 hz this transducer is also preferred because of its ability to withstand not only the environment in a paper manufacturing operation but also its believed ability to withstand the consequences of a web break for a more detailed description of the specific structure of the sensors reference is again made to copending application ser no 192 255 referring again to fig2 the signal generated by sensor 30 from which the signal from sensor 36 is subtracted is a modulated electrical signal which is connected to demodulator 40 which demodulates the difference sensor signal thus the signal from demodulator 40 is a real time analog signal which represents the time varying air pressure produced by the web flutter pocket 24 in the preferred embodiment demodulator 40 is a cd12 transducer indicator sold by validyne engineering corporation of northridge calif in order to inspect the characteristics of the demodulator output circuit i have analyzed it with the diagnostic processing equipment indicated at blocks 42 44 of fig3 interface 42 is a r300 digital signal processor interface board sold by rapid systems inc of seattle wash such interface boards are designed for insertion into so called 34 desk top 34 computers such as those made.