A PHOTOMETRIC PROCESS MEASUREMENT ARRANGEMENT AND A METHOD FOR PERFORMING A PHOTOMETRIC MEASUREMENT

Abstract

The invention refers to a photometric process measurement arrangement (10) with a photometric immersion probe (20). The photometric immersion probe (20) comprises a photometer flashlight source (61) for providing photometric light impulses, a photometric detector arrangement (70) comprising at least two separate wavelength-selective detection elements (71, 72, 73), and a photometer control (80) controlling the photometer flashlight source (61) and the detector arrangement (70). The photometer control (80) comprises several impulse signal integrators (819, 829, 839) for integrating the electric impulses generated by the detection elements (71, 72, 73), several A/D-converters (81, 82, 83) for converting the voltages of the impulse signal integrators (819, 829, 839) when high-precision-converting trigger ports (H) of the A/D-converters (81, 82, 83) are triggered, and a measuring cycle control (90) with an integration target memory (94) memorizing an integration target voltage value (Ut). The photometer control (80) is provided with a high-precision-request port (93) for synchronously triggering the high-precision-converting trigger ports (H) of all A/D-converters (81, 82, 83) after the voltage of the first of all impulse signal integrators (819, 829, 839) has exceeded the memorized integration target voltage value (Ut).

Claims

1-9. (canceled)

10. A photometric process measurement arrangement with a photometric immersion probe; the photometric immersion probe comprising a photometer flashlight source for providing photometric light impulses; a photometric detector arrangement comprising at least two separate wavelength-selective detection elements; and a photometer control controlling the photometer flashlight source and the detector arrangement; the photometer control, comprising: impulse signal integrators for integrating the electric impulses generated by the detection elements; A/D-converters for converting the voltages of the impulse signal integrators when high-precision-converting trigger ports of the A/D-converters are triggered; and a measuring cycle control with an integration target memory memorizing an integration target voltage value; wherein the photometer control is provided with a high-precision-request port for synchronously triggering the high-precision-converting trigger ports of all A/D-converters after the voltage of the first of all impulse signal integrators has exceeded the memorized integration target voltage value.

11. The photometric process measurement arrangement of claim 10, wherein the A/D converters are provided with low-precision-conversion trigger ports, respectively, which are synchronously triggered by a corresponding low-precision request port of the photometer control, if the voltages of all impulse signal integrators are below the memorized integration target value.

12. The photometric process measurement arrangement of claim 10, wherein the photometer control is provided with a flash counter counting the number of flashes of a measurement cycle and with a maximum flash number memory memorizing a maximum flash number of a measurement cycle, and the photometer control triggers the high-precision-converting trigger ports of all A/D-converters when the number of flashes counted by the flash counter equals the maximum flash number.

13. The photometric process measurement arrangement of claim 10, wherein the photometer control is provided with an integrator reset switch for synchronously resetting all impulse signal integrators before a new measurement cycle starts.

14. The photometric process measurement arrangement of claim 10, wherein the integration target voltage value is at least 20% below the saturation voltage of the impulse signal integrators.

15. A photometric measurement method provided by the photometric process measurement arrangement of claim 10, with the following measurement cycle method steps controlled by the photometer control: generating light impulses with the photometer flashlight source; monitoring all impulse signal integrators of the wavelength-selective detection elements; when the voltage of the first of all impulse signal integrators has exceeded a memorized integration target voltage value; synchronously triggering the high-precision-converting trigger ports of all A/D-converters to determine the final voltage all impulse signal integrators; resetting all impulse signal integrators; and starting a new measurement cycle.

16. The photometric measurement method of claim 15, wherein the monitoring step is provided by the photometer control by triggering the low-precision-converting trigger ports of all A/D converters.

17. The photometric measurement method of claim 16, wherein the photometer control schedules the total number of flashes of the full measurement cycle before the fourth flash of the measurement cycle.

18. The photometric measurement method of claim 15, wherein the photometer control triggers the high-precision-converting trigger ports of all A/D-converters and starts a new measurement cycle when the number of flashes of a measurement cycle is equal to the maximum flash number.

Description

[0030] One embodiment of the invention is described with reference to the enclosed drawings, wherein

[0031] FIG. 1 schematically shows a photometric process measurement arrangement with a photometric immersion probe comprising a photometric detector arrangement and a photometer control,

[0032] FIG. 2 schematically shows the photometric detector arrangement and the photometer control of FIG. 1 in more detail, and

[0033] FIGS. 3a to 3d show diagrams of the voltage versus time of the impulse signal integrator with the highest received light impulse intensity of the photometer control of FIGS. 1 and 2 for different sample water absorptions and turbidities.

[0034] FIG. 1 schematically shows a photometric process measurement arrangement 10 substantially consisting of a land-based control unit 12 and a photometric immersion probe 20 being arranged remote from the land-based control unit 12. The immersion probe 20 is arranged below a water surface 18 and is completely immersed into water 17 of a water basin 16. The water basin 16 can be a part of a wastewater treatment plant. Alternatively, the immersion probe 20 can be used in a laboratory application.

[0035] The measurement arrangement 10 is generally suitable for quasi-continuously photometrically determine the concentration of at least one water parameter. In the present embodiment, the photometric process measurement arrangement 10 determines the concentration of nitrite and nitrate in the sample water 17 with a measurement frequency of a few seconds.

[0036] The photometric immersion probe 20 comprises, within a fluidtight probe housing 22, an electronic flyback-converter 30 for energizing an impulse energy capacitor 33, comprises an impulse ignition switch 36 and a photometer flashlight source 61 being a xenon flash lamp for providing photometric light impulses with a sufficiently quasi-continuous spectrum in the ultraviolet range. The flyback-converter 30 is supplied by the land-based control unit 12 with electric energy via an electric supply line 52, and comprises a converter switch 31, a transformer 32 and a blocking diode 35. The charging duration for charging a completely empty impulse energy capacitor 33 is about 10 ms until the impulse energy capacitor's voltage reaches a defined ignition voltage value.

[0037] The photometric immersion probe 20 comprises a photometric detector arrangement 70 with an optical beam splitter 78 and three separate wavelength-selective detection elements 71, 72, 73. Every wavelength-selective detection element 71, 72, 73 comprises an interference bandpass filter 71,72,73 and a corresponding photocell 71,72,73. The detection elements 71, 72, 73 detect the light impulses generated by the flashlight source 61 at wavelengths of 218 nm, 225 nm and 245 nm. The 218 nm and the 225 nm detection elements 71, 72 are used for the direct detection of the extinction/absorption caused by the nitrite and the nitrate concentration in the probe water. The 245 nm detection element 73 is a reference detector for supervising the general constitution and performance of the flashlight source 61 and of the optical path between the flashlight source 61 and the detection elements 71,72,73. The photometer flashlight source 60 one and the photometric detector arrangement 70 define a photometer device for detecting the light absorption of sample water in a photometric measuring section 64 defined between a measuring section light inlet window 65 and a measuring section light outlet window 66.

[0038] The photometric immersion probe 20 comprises a photometer control 80 with three impulse signal integrators 81,82,83, three corresponding A/D-converters 81,82,83, an integrator reset switch 86 and a measuring cycle control 90. The impulse signal integrators 81,82,83 technically are capacitor elements and accumulate the electric voltage impulses generated by the photometric detection unit 70 until the integrator reset switch 86 is closed and all impulse signal integrators 81, 82 83 are discharged. The impulse signal integrators 81, 82 83 have a saturation voltage Us of, for example, 2600 mV.

[0039] The three A/D-converters 81,82,83 each have a high-precision-converting trigger port H and a low-precision-converting trigger port L. When the low-precision-converting trigger ports L of the three A/D-converters 81, 82, 83 are synchronously triggered, low-precision A/D conversions of the actual voltages of the three corresponding impulse signal integrators 81, 82 83 are provided which takes only a about 2 ms. The low-precision-conversion takes less time than the charging of the impulse energy capacitor 33.

[0040] When the high-precision-converting trigger ports of the three A/D converters 81, 82, 83 are synchronously triggered, very precise and high-precision A/D-conversions of the actual voltages of the three corresponding impulse signal integrators 81, 82, 83 are provided by the corresponding A/D converters 81, 82, 83 which takes about 65 ms. The high-precision-conversion takes much more time than the charging of the impulse energy capacitor 33.

[0041] The measuring cycle control 90 comprises a reset port 91 for activating the integrator reset switch 86, comprises a low-precision request port 92 for synchronously requesting a fast low-precision A/D conversion via the low-precision-converting trigger ports L of the A/D converters 81, 82, 83, and comprises a high-precision-request port 93 for synchronously requesting a high-precision A/D conversion via the high-precision-converting trigger ports H of the three A/D converters 81, 82, 83.

[0042] The measuring cycle control 90 further comprises an integration target memory 94 memorizing an integration target voltage value Ut and comprises an evaluation module 95 for continuously evaluating the digital A/D-converter results in relation to the integration target voltage value Ut. The integration target voltage value Ut is, in the present embodiment, 2000 mV.

[0043] The measuring cycle control 90 comprises a flash counter 99 counting the cycle flashes F generated by the flashlight source 61 within one measurement cycle and comprises a maximum flashing number memory 99 memorizing a maximum flash number Fmax of, in this embodiment, 64 flashes.

[0044] The measuring cycle control 90 also comprises a signal ramp pattern table memory 96 and a cycle pattern table memory 98.

[0045] The photometer control 80 controls the complete measurement process and adapts the length of a measurement cycle to the intensity level of the light impulses received by the photometric detection unit 70 and accumulated by the impulse signal integrators 81, 82, 83.

[0046] The immersion probe 20 comprises an electronic probe control 50 for controlling the communication between the photometer control 80 of the immersion probe 20 and a control electronics 14 of the land-based control unit 12 via a signal line 51.

[0047] When the photometer control 80 starts a new measurement cycle CY, the impulse ignition switch 36 is electronically caused to provide photometric light impulses generated by the photometer flashlight source 61 with a flashing interval of, for example, about 20 ms. After the third single flash, the photometer control 80 requests after every following single flash a low-precision-conversion via the low-precision request port 91 and the connected low-precision-conversion trigger ports L of all A/D-converters 81, 82, 83, and compares the digital low-precision voltage values U provided by the A/D-converters 81, 82, 83 with the memorized integration target voltage value Ut memorized in the integration target memory 94. As long as the highest digital voltage value U of all A/D converters 81, 82, 83 is below the memorized integration target voltage value Ut, the measurement cycle CY is continued by continuing the flashing action.

[0048] As soon as the voltage U of the first of all impulse signal integrators 81, 82, 83 has exceeded the memorized integration target voltage value Ut, the flashing action is stopped and the photometer control 80 requests a synchronous high-precision-A/D-conversion via the high-precision request port 93 and the corresponding high-precision-converting trigger ports H of all A/D converters 81, 82, 83 to determine the final digital voltage value of all impulse signal integrators 81, 82, 83. These final digital voltage values are then converted into corresponding concentration values of nitrite and nitrate in the sample water 17 and into a corresponding device condition value. After the high-precision conversion, the reset port 91 of the measuring cycle control 90 causes the integrator reset switch 86 to reset the impulse signal integrators 81, 82 83 to be reset to a voltage value of zero, so that the photometer is a ready for the following measurement cycle.

[0049] FIGS. 3a to 3d show measurement cycles CY for different sample water absorptions for that detector element receiving the highest light intensity of all three detector elements 71, 72, 73. The impulse time interval ti is always constant and is about 20 ms. The high-precision conversion time interval tc of a single high-precision conversion interval 100 is always constant and is about 65 ms.

[0050] FIG. 3a shows, for the detector element receiving the highest light intensity, several identical measurement cycles CY for very clear drinking water causing a very low general light absorption. Every photometric light impulse therefore causes a relatively high impulse voltage Ui at the corresponding impulse signal integrator 81, 82, 83. After the third flashlight source impulse, the measuring cycle control 90 receives the integrated low-precision digital voltage value U of the corresponding A/D converter 81, 82, 83, compares the integrated low-precision voltage value U with the memorized integration target voltage value Ut, detects a non-exceeding and allows a another photometric light impulse generated by the photometer flashlight source 61. After the fourth flashlight source impulse, the measuring cycle control 90 receives again the integrated low-precision voltage value U of the corresponding A/D converter 81, 82, 83, compares the integrated low-precision voltage value U with the memorized integration target voltage value Ut, and detects that the integrated low-precision voltage value U is now higher than the memorized integration target voltage value Ut. The measuring cycle control 90 now stops the flashing action and causes all A/D converters 81, 82, 83 to provide a high-precision conversion with the maximum precision. After the high-precision conversion has been finalized, the integrator reset switch 86 is closed for synchronously resetting and completely discharging all impulse signal integrators 81, 82, 83 so that a new measurement cycle CY can be started successively.

[0051] FIGS. 3b and 3c show measurement cycles CY for more turbid sample water causing less intensive single impulse voltages Ui and causing correspondingly longer measurement cycles CY.

[0052] FIG. 3D finally shows a measurement cycle for a very turbid water sample with a very low single impulse voltage Ui. As soon as the flash counter 99 indicates that the number of flashes F within one measurement cycle CY is equal to the maximum flash number Fmax of 64 memorized in the maximum flashing number memory 99, the measurement cycle CY is finished by causing all A/D converters 81, 82, 83 to provide a high-precision converting and to finalize the measurement cycle CY.

[0053] Generally, after the first few flashes, the measuring cycle control 90 can provide an estimation of the expected number of photometric light impulses until the first of the impulse signal integrators 81, 82, 83 arrives at the integration target voltage value Ut, so that the measuring cycle control 90 does not need to continuously control the real development of the voltages of the impulse signal integrators 81, 82 83.