Two beam alternating light colorimeter

A two light beam colorimeter, comprising:

• a light source producing a light beam which is directed through a lens system having a shutter means for producing a chopped beam;
• a pivotable mirror which is arranged so that in a first position it does not deflect the light beam and permits the light beam as a first measuring beam to pass through a first measuring cell, and in a second position the pivotable mirror deflects the light beam as a second measuring beam through a second measuring cell;
• fixed position deflecting means for causing the first and second measuring beams to impinge on a common photo sensitive element;
• switch means for connecting a first signal from the photo sensitive element corresponding to the first measuring beam through to an analog memory means when the pivotable mirror is in the non-deflecting position creating the first measuring beam, and for disconnecting the analog memory from a second signal when the pivotable mirror is in the deflecting position creating the second measuring beam;
• and
• a computing means for producing an output voltage which is related to the first and second signals from the photo sensitive element resulting from the first and second measuring beams, said computing means being connected to an output of the analog memory so as to receive the first signal and to a point between the switching means and the photo sensitive element so as to receive the second signal.