Patent Description:
A photometric process measurement arrangement comprises a land-based control unit and a separate photometric immersion probe being immersed into the water of a water basin. The water basin can be a part of a water treatment plant for controlling drinking water or for controlling a process step of a wastewater treatment process. A typical photometric immersion probe is disclosed in <CIT> and comprises a spectroscopic UV light source and a corresponding photometric detector detecting at least two wavelengths for photometrically determining, for example, the concentration of nitrate and nitrite.

The UV light source is preferably a high voltage UV xenon lamp which is ignited, for example, every <NUM> with a high temporary electric energy which is accumulated and stored in an impulse energy capacitor. A typical ignition voltage is <NUM> V. The immersion probe comprises a probe electronics comprising a flyback-converter for stepwisely increasing the voltage of the impulse energy capacitor with numerous charging voltage quantums having a quantum voltage of a few Volt until the ignition voltage of, for example, <NUM> V is reached.

The flyback-converter is provided with a converter switch between a converter supply voltage port having the actual probe supply voltage and a transformer. The converter switch is driven by a signal generator generating a switching signal having a constant a switching frequency and having a constant duty cycle. The transformer, the duty cycle length and the switching frequency are designed to guarantee that a maximum duration of a complete charging cycle for completely charging the impulse energy capacitor up to the ignition voltage is not exceeded. When designing the converter, it is assumed that the actual supply voltage will not fall to less than, for example, <NUM>% of the nominal supply voltage of, for example, <NUM> V.

The immersion probe is supplied with the supply voltage of a land-based control unit having a typical nominal operating voltage level of, for example, <NUM> V. However, since the land-based control unit of the process measurement arrangement is arranged generally remote and occasionally with a relatively large distance of up to <NUM> from the photometric immersion probe, the voltage loss between the land-based control unit and the photometric immersion probe can be considerable and can be fluctuating as well so that the actual probe supply voltage at the flyback-converter can fall, under adverse conditions, to less than <NUM>% of the nominal supply voltage. Such a voltage drop at the flyback-converter is not generally a problem because the number of charging voltage quantums is automatically increased proportionally to arrive at the target ignition voltage, but the charging procedure is prolongated accordingly.

It is an object of the invention to provide a photometric process measurement arrangement and a method for controlling the photometric process measurement arrangement with a constant charging procedure.

This object is, according to the invention, solved with a photometric process measurement arrangement with the features of apparatus claim <NUM>, and is solved with a method for controlling the photometric process measurement arrangement with the features of method claim <NUM>.

The photometric process measurement arrangement according to the invention comprises a photometric immersion probe which is continuously and completely immersed into water. The immersion probe comprises a photometer flashlight source for providing photometric light impulses with a continuous optical spectrum, preferably with an optical spectrum focused on the ultraviolet spectrum for the determination of the concentration of, for example, nitrate and nitrite. Preferably, the flashlight source is a high voltage xenon lamp with a preferred ignition voltage of <NUM> to <NUM> V.

The immersion probe comprises an impulse energy capacitor for storing the electric impulse energy. The immersion probe comprises an impulse ignition switch being electrically arranged electrically in-line and between the impulse energy capacitor and the photometer flashlight source. When the impulse ignition switch is closed, the electric energy stored in the impulse energy capacitor flows to the photometer flashlight source so that a photometric light impulse with a continuous frequency spectrum is generated. In practice, a period length of charging the impulse energy capacitor and initiating a photometric light impulse is in the range of <NUM> to <NUM>.

The immersion probe is provided with an electronic flyback- converter for successively electrically charging the impulse energy capacitor with numerous charging voltage quantums. The flyback-converter is provided with a converter switch between a converter supply voltage port having the actual probe supply voltage and a transformer. The immersion probe is provided with a switching signal generator for driving the converter switch with a switching signal having a preferably constant switching frequency of, for example, <NUM> to <NUM>. The switching signal generator comprises a standard duty cycle signal generator for driving the converter switch with a standard duty cycle value which can be, for example, <NUM>, which corresponds, for example with <NUM>% of one period of a switching frequency signal of <NUM>. The impulse energy capacitor is charged with a charging voltage quantum at every period of the switching signal and, typically, is in a range of <NUM> V to <NUM> V. The charging voltage quantum substantially depends on the duty cycle length and on the probe supply voltage.

The switching signal generator also comprises a boost duty cycle signal generator for alternatively driving the converter switch with a boost duty cycle value when the boost duty cycle signal generator is activated. The boost duty cycle value is higher/longer than the standard duty cycle value, and is, for example <NUM> to <NUM>% higher/longer than the standard duty cycle value. Referring to a standard duty cycle value of <NUM>, the boost duty cycle value can typically be <NUM> to <NUM>.

The switching signal generator is provided with a supply voltage comparator and a boost voltage memory memorizing a boost voltage value. The supply voltage comparator continuously compares the actual probe supply voltage at the converter supply voltage part and the boost voltage value memorized in the boost voltage memory. The switching signal generator activates the boost duty cycle signal generator if the supply voltage comparator determines that the supply probe supply voltage is below the boost voltage value. As long as the probe supply voltage is equal or above the boost voltage value, the standard duty cycle signal generator is and remains active.

The boost voltage value a minimum voltage value which still guarantees that the impulse energy capacitor is completely charged in a maximum charging time interval so that the frequentness of the photometric measurements is not affected. Even if the probe supply voltage falls below the boost voltage value, a maximum charging time interval is not exceeded. However, the boost duty cycle value must not be used if the probe supply voltage is above the boost voltage value to avoid an overheating and damage of the transformer of the flyback-converter.

Preferably, the switching signal generator drives the converter switch always with a constant switching frequency in the standard and in the boost mode. The constant switching frequency is in the range of <NUM> to <NUM>. Preferably, the boost duty cycle value is <NUM>% to <NUM>% higher than the standard duty cycle value.

The immersion probe comprises an ignition voltage memory memorizing an ignition voltage value defining the impulse energy capacitor's voltage when the ignition switch is closed to cause the flashlight source to provide a photometric light impulse. A typical ignition voltage value is in the range of <NUM> V, and can be, for example, exactly <NUM> V.

Preferably, the photometric immersion probe comprises a voltage comparator comparing the actual electric capacitor's voltage with the memorized ignition voltage value. The voltage comparator preferably is an analogue electronic element which is fast and does not need any processor capacity. The ignition voltage memory is preferably defined by a constant analogue reference voltage source applied to the analog voltage comparator. If a general impulse command has been issued, the impulse ignition switch is closed and a photometric light impulse is caused as soon as the actual electric capacitor's voltage equals the memorized ignition voltage value.

Preferably, a land-based control unit for controlling the photometric immersion probe is provided. The land-based control unit provides a supply voltage for the photometric immersion probe of less than <NUM> V, preferably of less than <NUM> V, and typically of <NUM> V. The supply voltage provided by the land-based control unit can be identically with the general supply voltage of the electronics of the land-based control unit which is typically in the range of <NUM> to <NUM> V. Since the land-based control unit is arranged remote and often with a relatively large distance of up to <NUM> from the photometric immersion probe, the supply voltage loss between the land-based control unit and the photometric immersion probe can be considerable so that the actual probe supply voltage at the converter supply voltage port can be considerably lower than the land-based control unit's supply voltage.

Preferably, the photometric immersion probe is provided with a photometric detector arrangement comprising at least two wavelength-selective detection elements. Since the photometric process measurement arrangement is designed to photometrically detect at least two different wavelengths, a flashlight source with a continuous spectrum is advantageous. However, this concept makes it necessary to reliably provide a perfect lifetime consistency of the photometric spectrum generated by the photometer flashlight source.

According to the independent method claim for controlling a photometer flashlight source of a photometric process measurement arrangement according to one of the apparatus claims, the following method steps are provided:.

An embodiment of the invention is explained with reference to the enclosed drawings, wherein.

<FIG> schematically shows a photometric process measurement arrangement <NUM> substantially consisting of a land-based control unit <NUM> and a photometric immersion probe <NUM> being arranged remote from the land-based control unit <NUM>. The immersion probe <NUM> is arranged below a water surface <NUM> and is completely immersed into water <NUM> of a water basin <NUM>. The water basin <NUM> can be a part of a wastewater treatment plant. The photometric process measurement arrangement <NUM> determines the concentration of nitrite and nitrate in the water <NUM>.

The photometric immersion probe <NUM> comprises, within a fluidtight probe housing <NUM>, a photometer flashlight source <NUM> and a photometric detector arrangement <NUM> with three different photometric detector elements <NUM>, <NUM>, <NUM> with three different detection wavelengths. The photometer flashlight source <NUM> and the photometric detector arrangement <NUM> together define a photometer device for detecting the light absorption of a water sample in a photometric measuring section <NUM> defined between a light inlet window <NUM> and a light outlet window <NUM>.

Alternatively, the probe <NUM> could be used in a laboratory by means of a suitable adapter fluidically closing the photometric measuring section <NUM> which is fed with the water by a suitable water feeding arrangement.

The photometric immersion probe <NUM> also comprises an electronic flyback-converter <NUM> for generating charging voltage quantums Uq, comprises an impulse energy capacitor <NUM> having an actual electric capacitor's voltage U and accumulating the charging voltage quantums Uq, comprises an impulse ignition switch <NUM>, comprises an electronic ignition control unit <NUM> for controlling the ignition switch <NUM>, and comprises an electronic probe control <NUM> for controlling a switching signal generator <NUM>, the photometric detector <NUM>, the ignition control unit <NUM> and the communication with a control electronics <NUM> of the land-based control unit <NUM> via a signal line <NUM>.

The flyback-converter <NUM> of the immersion probe <NUM> is supplied with electric energy having a nominal supply voltage Un of <NUM> V at the land-based control unit <NUM> via an electric supply line <NUM>. Due to a considerable length of the electric supply line <NUM>, the effective actual probe supply voltage Up at a converter supply voltage port <NUM> can be substantially reduced and temporarily or constantly can be less than <NUM> V, or even can be less than <NUM> V. The flyback-converter <NUM> comprises a converter switch <NUM>, a transformer <NUM> and a blocking diode <NUM>. The converter switch <NUM> is a MOSFET and is opened and closed with a constant switching frequency of, for example, <NUM>. A totally empty impulse energy capacitor <NUM> is loaded with about <NUM> charging voltage quantums Uq of a few Volts each, which results in a total charging duration of about <NUM> until the capacitor's voltage U arrives at the ignition voltage value Ui.

The switching signal generator <NUM> comprises a duty cycle control <NUM> with a supply voltage comparator <NUM>, comprises a boost voltage memory <NUM> memorizing a boost voltage value Ub, comprises a standard duty cycle signal generator <NUM> memorizing and generating a standard duty cycle value d1 and comprises a boost duty cycle signal generator <NUM> memorizing and generating an elongated boost duty cycle value d2.

During a charging process for electrically charging the impulse energy capacitor <NUM>, the supply voltage comparator <NUM> continuously controls if the probe supply voltage Us at the converter supply voltage port <NUM> falls or is below the boost voltage value Ub memorized in the boost voltage memory <NUM>. As long as the actual probe supply voltage Us is not below the boost voltage value Ub, the duty cycle control <NUM> continuously activates the standard duty cycle signal generator <NUM> which generates a squarewave- signal having a switching frequency f of <NUM> and a duty cycle length of <NUM>. The switching frequency is the number of full periods per second. If the actual probe supply voltage Us is below the boost voltage value Ub of <NUM> V, the duty cycle control <NUM> activates the boost duty cycle signal generator <NUM> which generates a signal having the same unchanged switching frequency f of <NUM> but having an elongated duty cycle length of <NUM>. As soon as the energy of each charging voltage quantum generated by the flyback-converter <NUM> substantially decreases due to a drop of the actual probe supply voltage Us, this energy drop is compensated by increasing the duty cycle of the switching signal generated by the switching signal generator <NUM>, as shown in <FIG>.

The supply voltage comparator <NUM> comprises a hysteresis element defining a hysteresis difference of <NUM> V to avoid unwanted unsteadiness in the selection and activation of the duty cycles.

<FIG> shows the time-related correlations between the actual probe supply voltage Us, the corresponding duty cycle d and the resulting voltage of a charging quantum Uq. As long as the actual probe supply voltage Us is above the boost voltage value Ub, the duty cycle d is the standard duty cycle d1, as during the standard periods ts. As soon as and as long as the actual probe supply voltage Us is below the boost voltage value Ub, the duty cycle d is the boost duty cycle d2, as during the boost periods tb. The resulting voltage Uq of a charging quantum is substantially increased during the boost cycle periods tb.

The ignition of the flashlight source <NUM> is controlled by the ignition control <NUM>. The ignition control <NUM> comprises a voltage comparator for comparing the actual electric capacitor's voltage U with a memorized ignition voltage value Ui, comprises an ignition voltage memory memorizing the ignition voltage value Ui, and comprises an ignition trigger controlling the ignition switch <NUM>. The control of the immersion probe <NUM> and the communication with the land-based control unit is provided by the electronic probe control <NUM>.

Claim 1:
A photometric process measurement arrangement (<NUM>) with a photometric immersion probe (<NUM>), the photometric immersion probe (<NUM>) being electrically supplied with a probe supply voltage (Us) comprising:
a photometer flashlight source (<NUM>) configured for providing photometric light impulses with a continuous spectrum,
an impulse energy capacitor (<NUM>) configured for storing the electric impulse energy,
an electronic flyback-converter (<NUM>) configured for successively electrically charging the impulse energy capacitor (<NUM>) with numerous charging voltage quantums (Uq), wherein the flyback-converter (<NUM>) is provided with a converter switch (<NUM>) between a converter supply voltage port (<NUM>) and a transformer (<NUM>),
a switching signal generator (<NUM>) configured for driving the converter switch (<NUM>) with a switching signal having a switching frequency (f), the switching signal generator (<NUM>) comprising a standard duty cycle signal generator (<NUM>) configured for driving the converter switch (<NUM>) with a standard duty cycle value (D1) and comprising a boost duty cycle signal generator (<NUM>) configured for alternatively driving the converter switch (<NUM>) with a higher boost duty cycle value (D2), when the boost duty cycle signal generator (<NUM>) is activated,
the switching signal generator (<NUM>) being provided with a supply voltage comparator (<NUM>) and a boost voltage memory (<NUM>) memorizing a boost voltage value (Ub), the supply voltage comparator (<NUM>) continuously comparing the probe supply voltage (Us) at the converter supply voltage port (<NUM>) and the boost voltage value (Ub),
the switching signal generator (<NUM>) activating the boost duty cycle signal generator (<NUM>) if the supply voltage comparator (<NUM>) determines that the supply voltage (Us) is below the boost voltage value (Ub).