Digital subtraction circuit for a centrifugal chemical analyzer of the rotating spectrophotometer type

Claim 1

In combination with a photometric analyzer for the substantially simultaneous determination of the light transmission of plurality of discrete samples, comprising: a. a power-driven rotor assembly including: (1) a plurality of sample analysis chambers at a common radial position in said rotor assembly, each of said sample analysis chambers having at least one light-transmitting means for permitting the passage of light therethrough; and (2) at least one storage chamber communicating with each of said sample analysis chambers to retain liquid when said rotor assembly is at rest, and to release said liquid to said sample analysis chamber when said rotor assembly is rotated; b. a light source for providing a beam of light incident on said rotor assembly at a location station on said common radial position whereby said beam of light passes through each of said sample analysis chamber individually as the sample analysis chambers pass said location station during rotation of said rotor assembly; c. detecting means for measuring the intensity of said beam after it has passed through said sample analysis chamber individually, said detecting means including means for generating an electrical pulse each time one of said sample analysis chamber passes said location, each said electrical pulse being proportional to the measured intensity of said beam, and d. means for converting each of said electrical pulses into electrical pulses corresponding to the light absorbance for each sample analysis chamber, the improvement which comprises i. means for converting each of said electrical pulses corresponding to light absorbance to an electrical signal in binary form and provide a serial sequence of binary input data signals corresponding to light absorbance ii. means for providing an electrical revolution pulse for each revolution of said rotor assembly iii. serial storage means arranged to receive said revolution pulse and store a predetermined binary number value in response thereto iv. subtraction means arranged to receive a predetermined binary input data signal in said sequence of binary input data signals concurrently with a binary electrical signal from said serial storage means corresponding to the predetermined binary number value stored therein and provide a first output binary electrical signal equal to the difference of said input data signal and said signal from said serial storage means, v. first gating means arranged to transmit said first output binary signal to said serial storage means, vi. means arranged to transmit said first difference signal from said serial storage means to said subtraction means concurrently with each subsequent binary input data signal and provide a binary output data signal for each said subsequent binary input data signal equal to the difference between such input data signal and said first difference signal and vii. second gating means for re-circulating said first difference signal to said serial storage means.