Automatic photomultiplier tube voltage controller

Claim 1

In an analytical photometer device including a multicuvet rotor provided with a plurality of cuvets for receiving respective samples and reagents thereinto for mixing and reacting, means for rotating said rotor at a desired selected high speed, a stationary photometer system for scanning all of said cuvets during rotation of said rotor, at least one of said cuvets containing a water blank to provide an output signal for reference purposes, and an on-line computer connected to the output of said photometer system for evaluating the signal received from each of said cuvets during oPeration of said system, said photometer system including a photomultiplier tube and a source of photomultiplier high voltage supply, the improvement comprising a feedback circuit for maintaining said water blank cuvet output voltage signal at a desired constant value during operation of said photometer system, said feedback circuit including a first fast-acting solid state switch, a second fast-acting solid state switch, a well regulated power supply, a potentiometer connected between the output of said regulated power supply and said first switch to supply a desired reference voltage thereto corresponding to said desired water blank output voltage signal, the output of said photomultiplier tube connected to said second switch, means connected to both of said switches for gating them ON in response to rotor position and at the instant the water blank output signal from said photometer system is at its peak value, a sample-and-hold unit connected to the output of said first switch, a peak-followerand-holder unit connected to the output of said second switch and in turn providing an output having a polarity opposite to the output of said sample-and-hold unit, an inverter, circuit means for combining the signal outputs of said sample-and-hold unit and said peak-follower-and-holder unit and feeding such a combined output signal as an input to said inverter, a diode connected as a feedback across said inverter, a three-mode controller connected to the output of said inverter, a control transistor connected in the input circuit of said photomultiplier high voltage supply, and circuit means for connecting the output of said controller to said control transistor, whereby said feedback circuit maintains said water blank output voltage signal at a desired constant value even in the event of photomultiplier gain changes or power supply drift during operation of said photometer system.