Amplification and Electrical Systems for a Double Beam Recording Infra-Red Spectrophotometer
Max D. Liston, John U. White · Journal of the Optical Society of America · 1950
A detection and amplification system for a recording infra-red spectrophotometer has been designed and built around a pin-type thermocouple, 13-cycle chopper, 13-cycle amplifier and synchronous rectifier. The subsequent circuits modulate the rectified output to 60 cycles for operation of a 2-phase servo balance motor and automatic suppression of the wave-length scanning speed whenever a pen servo error exists. An independent circuit employs a tapped potentiometer as an electrical cam to control the monochromator slit width to give relatively constant energy output at seven energy levels. A total of eighteen tubes are employed, with three of them in the 13-cycle amplifier. The first tube is operated at reduced voltage with a floating grid following a 300:1 gain transformer. Special construction of the preamplifier greatly reduces the susceptibility to 60-cycle pick-up over previous amplifiers.