Inch per second

Abstract: The ambient ground‐noise level is one of the most important factors in determining sensitivity requirements for a seismograph system. This paper, on the basis of eighty‐one measurements in three areas in Texas, concludes that for these areas minimum ambient noise levels (in terms of particle velocity) of the order of 3 to 5 millionths of an inch per second are common. Assuming a seismometer sensitivity of 2 volts per inch per second and an oscillograph sensitivity of 5 inches per volt, an overall gain of 20,000 from the output of the seismometer to the input of the oscillograph would be required to give a one‐half‐inch peak‐to‐peak deflection from a noise signal with a peak‐to‐peak particle velocity of 2 1/2 millionths of an inch per second.

Abstract: The wide signal bandwidth attainable with the 960 inch per second longitudinal tape transport, combined with high density recording at about 20,000 bits per inch provide a multichannel 20 Megabit/second recorder with a 64:1 time expansion capability. The tape transport mechanism consists of two solid, flangeless tape packs placed in direct contact with a large capstan. Stability of the tape movement is achieved by use of a control system which provides instantaneousadjustment of the pack contact forces as a function of direction, velocity, acceleration and pack diameter. This results in full versatility when programming the transport motion. The high density digital signal is phase encoded and processed through the recorder as an analog signal, then is demodulated using a phase lock loop to recover the clock. The sample and hold phase comparator controls a VCO at a fixed nominal frequency, followed by a divider. This configuration permits operation at all bit frequencies in a 128:1 range and allows the clock to coast through a 50 bit dropout without bit slip. Demonstrated bit error rate is 10 maximum.