Patent ID: 8213016

Claim:
A turbidity measuring device with a four-beam, alternating light arrangement for registering the turbidity of a measured medium, comprising: a first light source L 1 and a second light source L 2 ; and a first receiver R 1 and a second receiver R 2 , wherein: a first direct measuring path extends from said first light source L 1 , through a measured medium, to said first receiver R 1 ; a second direct measuring path extends from said second light source L 2 to said second receiver R 2 ; a first indirect measuring path extends from said light source L 1 , through the measured medium, to said second receiver R 2 ; a second indirect measuring path extends from said second light source L 2 , through the measured medium, to said first receiver R 1 ; the turbidity measuring device has an evaluation circuit, with which turbidity can be ascertained as a function of a quotient A/B; one of the terms A or B is a function at least of the signals registered via the direct measuring paths; the respectively other term is a function at least of the signals registered via the indirect measuring paths; and at least a first monitor signal, which is dependent on the intensity of the first light source, enters into one of the two terms A or B; wherein light from the first light source reaches the monitor without interaction with the measured medium; and the monitor signal is added to at least one of the signals registered via the measuring path and entering into the term A or B.