A fiber‐optic retroreflective turbidimeter for continuously monitoring cell concentration during fermentation

A fiber‐optic retroreflective turbidimeter has been developed to automatically and continuously assay the cell concentration in a fermentor by measuring the turbidity of the solution as a function of the light scattered at 180° to the incident light. The output signal is nearly directly proportional to the cell concentration in a fermentor when the sample stream contains from 0 to more than 50 g of cells per liter (wet weight). The device consists of a bifurcated fiber‐optics light pipe with its distal end inserted into a flow cell through which the material to be analyzed passes. A light source on one proximal branch of the light pipe illuminates the sample stream; light that is back‐scattered from participates in the stream re‐enters the light pipe and is returned to a photodetector on the other proximal branch of the light pipe. A signal conditioning system connected to the optical head by a cable provides gain and zero adjustment.