Hach NITRATAX plus sc, User Manual

Page: 11 / 42

9
General Information
2.3 Theory of operation
Nitrate dissolved in water absorbs UV light with wavelengths below 250 nm. This inherent
absorption by nitrate makes it possible to photometrically determine the nitrate
concentration without reagents by using a sensor positioned directly in the medium. As the
measuring principle (
Figure 3 ) is based on the evaluation of (invisible) UV light, the color
of the medium has no effect.
The sensor contains a two-beam absorption photometer with turbidity compensation. The
measuring window is mechanically cleaned using a wiper.
The measuring and cleaning intervals can be entered using the related controller. The
measured value is displayed as NO
x
-nitrogen in mg/L NO
x
–N (NO
2
–N is included in the
measured result as nitrite nitrogen) and provided on current outputs. Various operating
modes for the outputs permit local regulation without further process data processing.
Figure 3 Measurement principle of the NITRATAX sc
1 Receiver, Reference Element 3 UV Lamp 5 Mirror
2 Two-sided Wiper 4 Measurement Slit 6 Receiver, Measuring Element