MULTI-WAVELENGTH PROCESS PHOTOMETER

Abstract

The invention is directed to a multi-wavelength process photometer (20) for quasi-continuously determining the absorption of a liquid sample, comprising a continuous-spectrum flashlight source (24), a transparent liquid sample measurement cell (40) which is radiated by the flashlight source (24), a translucent light diffusor element (50) behind the measurement cell (40) for homogenously diffusing the light of the flashlight source (24) coming from the liquid sample measurement cell (40), and at least two different wavelength-selective light detectors (61, 62, 63) behind the light diffusor element (50), wherein the light detectors (61, 62, 63) have substantially the same distance (X4) to the light diffusor element (50).

Claims

1-8. (canceled)

9. A multi-wavelength process photometer for quasi-continuously determining an absorption of a liquid sample, the multi-wavelength process photometer comprising: a continuous-spectrum flashlight source; a transparent liquid sample measurement cell which is radiated by the continuous-spectrum flashlight source; a translucent light diffusor element which is arranged behind the transparent liquid sample measurement cell for homogenously diffusing the light of the continuous-spectrum flashlight source coming from the transparent liquid sample measurement cell; and at least two different wavelength-selective light detectors which are arranged behind the translucent light diffusor element, the at least two different wavelength-selective light detectors having substantially a same distance (X4) to the translucent light diffusor element.

10. The multi-wavelength process photometer of claim 9, further comprising: a converging lens which is arranged between the continuous-spectrum flashlight source and the transparent liquid sample measurement cell, the converging lens focusing the light of the continuous-spectrum flashlight source at a measuring section of the transparent liquid sample measurement cell.

11. The multi-wavelength process photometer of claim 9, wherein the translucent light diffusor element is defined by a translucent diffusor body with micro-inclusions of less than 30 m diameter, preferably of less than 8,0 m diameter.

12. The multi-wavelength process photometer of claim 9, wherein the translucent light diffusor element is defined by a translucent diffusor body with a concentration of micro-inclusions of more than 100 mio/cm.sup.3 and less than 5000 mio/cm.sup.3, preferably less than 2500 mio/cm.sup.3, and with an effective optical thickness (W2) of 0.5 to mm.

13. The multi-wavelength process photometer of claim 9, wherein the translucent light diffusor element has a detector-facing surface which has a light scattering surface structure.

14. The multi-wavelength process photometer of claim 9, further comprising: an electronic photometer control with a summarizing module for summarizing measurement signals of the at least two different wavelength-selective light detectors of at least 10 light flashes of the continuous-spectrum flashlight source.

15. The multi-wavelength process photometer of claim 9, wherein at least three of the at least two different wavelength-selective light detectors are provided, each of which have a filtering wavelength of between 195 and 240 nm.

16. A wastewater measurement arrangement comprising an immersion probe which is immersed into wastewater of a wastewater tank, the immersion probe comprising the multi-wavelength process photometer of claim 9.

Description

[0020] FIG. 1 schematically shows a wastewater measurement arrangement with an immersion probe immersed into wastewater, the immersion probe comprising a multi-wavelength process photometer according to the invention; and

[0021] FIG. 2 schematically shows in more detail the multi-wavelength process photometer of FIG. 1.

[0022] FIG. 1 schematically shows a wastewater measurement arrangement 10 being a part of a wastewater treatment plant for cleaning wastewater. The wastewater measurement arrangement 10 is provided with a large wastewater tank 12 with wastewater 13. The wastewater tank 12 is a tank in a series of wastewater treatment tanks (which is not shown). The is wastewater measurement arrangement 10 comprises an immersion probe 21 which is immersed into the wastewater 13 and which is held by a stationary holding arm 16. The immersion probe 21 comprises a multi-wavelength process photometer 20 which quasi-continuously determines, in real-time, the nitrite quantity of the wastewater 13 and which is electrically connected to a land-based control device 14 via suitable energy lines and signal lines.

[0023] The process photometer 20 is provided with a continuous-spectrum flashlight source 24 which comprises a flashlight energy generator 26 for generating electric energy pulses and a xenon illuminant 28. The xenon illuminant 28 generally has a long life and generates a continuous wavelength spectrum. The flashlight energy generator 26 can generate electric energy pulses with a frequency of up to 20 Hz. The flashlight source 24 generates light pulses with a sufficiently continuous wavelength spectrum, in particular in the ultraviolet range of 150 to 300 nm.

[0024] The process photometer 20 is provided with a converging lens 30 which is arranged in-line with and between the flashlight source 24 and a transparent sample measurement cell 40 which is a flow cell. The lens body 32 of the converging lens 30 is bi-convex and concentrates the light of the flashlight source 24 within a measuring section 42 of the sample measurement cell 40. The axial optical length W1 of the measuring section 42, which is the transverse diameter of the liquid line, is 2.0 mm in the present embodiment. The measurement cell 40 can be provided with a wiper for cleaning the inner surfaces of the liquid line in the measuring section 42. A liquid sample of the wastewater 13 is continuously pumped by an electric sample pump 48 to the measuring section 42 of the measurement cell 40. The body of the measurement cell 40 is substantially transparent for the light radiated by the flashlight source 24 and is concentrated by the converging lens 30 at the measuring section 42.

[0025] A translucent light diffusor element 50 is provided, as seen from the flashlight source 24, behind the sample measurement cell 40. The light diffusor element 50 is defined by a translucent and plate-like diffusor body 52 with micro-inclusions with a typical inclusion diameter of 3-4 m, with an inclusions concentration of 300 mio/cm.sup.3 and with an axial optical thickness W2 of about 1.0 mm. The diffusor element 50 generates a spatially homogeneous light cone with a total cone angle of approximately 30. The detector-facing surface 52 of the light diffusor element 50 has a light scattering surface.

[0026] Three different wavelength-selective light detectors 61,62,63 are arranged behind the light diffusor element 50. The three light detectors 61,62,63 all have substantially the same distance X4 to the light diffusor element 50. Every light detector 61,62,63 is provided with a silicon photo sensor 65 and with an individual interference filter 61,62,63 of filter wavelengths of 215 nm, 205 nm and 230 nm, respectively. The present light detector arrangement allows a precise determination the concentration of nitrate to be made, whereas the 215 nm detector 61 determines the absorption caused by nitrite, the 205 nm detector 62 determines the absorption caused by nitrate and nitrite, and the 230 nm-detector 63 determines the general light intensity of the flashlight source 24 and, if given, other components of the absorption matrix.

[0027] The signals of the photo sensors 65 are amplified by three signal amplifier modules 71, and 50 consecutive amplified signals are summarized by three summarizing modules 72 to thereby provide a measurement result with a high signal to noise ratio. The light detectors 61,62,63 are part of an electronic photometer control 70 which also controls and synchronizes the flashlight source 24, which controls the sample pump 48, and which communicates with the land-based control device 14.

[0028] In the present embodiment of the process photometer 20, the distance X1 between an aperture of the flashlight source 24 and the convex light inlet surface of the converging lens 30 is about 17 mm, the distance X2 between the convex outlet surface of the converging lens 30 and the plane inlet surface of the measurement cell 40 is about 7.5 mm, the distance X3 between the outlet surface of the measurement cell 40 and the light diffusor element 50 is 13.5 mm, and the distance X4 between the light diffusor element 50 and the light detectors is 17.1 mm. The focal length of the converging lens 30 is about 9 mm so that the focus of the light generated by the flashlight source 24 lies in the center of the measuring section 42.