The high precision KOBOLD single-beam turbidity sensor ATA-K measures the degradation of light (in the near infrared range, NIR) passing through the process medium. The sensor has been manufactured from stainless steel and designed for fitting in the process piping. The process medium is penetrated by a suitably focussed, constant beam of light. The intensity of the incoming light is measured by a silicon photodiode and routed to the transmitter as a photoelectric current. The changes of intensity in this light, caused by absorption and/or scattering by substances (dissolved and undissolved) in the medium, is measured and outputed by the transmitter.