GB1036647A - Seismic amplifier - Google Patents

Abstract

1,036,647. Amplifier with automatic gain control; seismic prospecting. JERSEY PRODUCTION RESEARCH CO. July 1, 1964 [July 26, 1963], No. 27175/64. Headings H4D and H4R. A seismic amplifier is provided with automatic gain control by attenuator sections 18, 36, 50, 64, and 78, Fig. 1, inserted between amplifier stages in which the attenuators are normally in circuit but are short-circuited by switches 26, 44, 56, 70, and 84, when the amplifier output falls below a predetermined level. The arrangement is such that the gain of the amplifier is successively doubled by the operation of the switches in an order determined by the counter circuit 93 and the gates 97 and 98 to give sixteen different gain conditions. The control circuit 92 is shown in Fig. 4 and is such that whenever the output signal level of the amplifier fed to the Schmitt triggers 85 and 89 exceeds a predetermined positive or negative value one or other of triggers 85 or 89 operates and charges capacitor 104 to a negative potential. The potential on capacitor 104 leaks away through resistor 106 and, if the predetermined signal level is not again exceeded within the appropriate discharge time of the capacitor resistor circuit, the triggering potential of trigger 110 is exceeded and the trigger operates to send a counting pulse to the counter circuit 93, Fig. 1. At the same time the trigger circuit 110, Fig. 4, provides an enabling input to gate 122 and so allows the following pulse from clock 124 to trigger the monostable circuit 126. The output from circuit 126 is fed to the capacitor circuit 102 to maintain this circuit's output below the triggering level of trigger 110 for a predetermined time so that only one pulse is sent to the counter during the time which is required for the system to react. The sequence of inserting the various attenuator stages obtained by the gating system shown with the counter in Fig. 1, and the gain of the amplifier, each stage of which has a gain of 8 x, with attenuator stages of specified losses is indicated in a table, Fig. 2 (not shown).