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Variable Gain Control for Photomultiplier Tubes

IP.com Disclosure Number: IPCOM000088919D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Culver, JV: AUTHOR [+3]

Abstract

PMTs (photomultiplier tubes) are commonly used in spectrophotometers for providing an electrical output proportional to the intensity of light received by the PMT. In some applications, there is a need to be able to select a gain-setting over a range of potential gain-settings, whereby the PMT will operate in the linear portion of its characteristic curve without exceeding the recommended cathode current. The drawing schematically shows one way of accomplishing this.

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Variable Gain Control for Photomultiplier Tubes

PMTs (photomultiplier tubes) are commonly used in spectrophotometers for providing an electrical output proportional to the intensity of light received by the PMT. In some applications, there is a need to be able to select a gain-setting over a range of potential gain-settings, whereby the PMT will operate in the linear portion of its characteristic curve without exceeding the recommended cathode current. The drawing schematically shows one way of accomplishing this.

As shown, a PMT includes a light-activated cathode C, an anode A and a plurality of dynodes D1-D10. A Zener diode 3 is connected between cathode C and the first dynode D1, and acts as a current stabilizer. A plurality of resistors R1-R10 are connected between succeeding dynodes. An output resistor R(L) is connected between anode A and a high voltage source and resistor R10. The PMT thus far described is of conventional construction and operates in the normal manner where electrons are emitted from cathode C upon photo- excitation thereof, the electrons being multiplied by the addition of secondary electrons added to the electron stream from the dynodes.

A series of different valued potentiometers P1-P4 have one side connected between resistors R8 and R9 and have the other sides thereof selectively connectable through the rotary arm 1 of a rotary switch to the other side of R8, whereby such potentiometers may be connected in parallel with resistor R8 dep...