Light-guiding element arrangement for optical drop detection

Abstract

A drop-detection device detects a drop that escapes from a metering valve. The drop-detection device includes a light guide with first and second light-guiding elements that are arranged opposite each other at an intermediate space. A drop trajectory runs through the intermediate space such that a light beam sent out by the first light-guiding element crosses the drop trajectory and is subsequently coupled into the second light-guiding element. In addition, the drop-detection device includes a light-signal generation device that couples a pulsed light beam with a carrier frequency into the first light-guiding element. Furthermore, the drop-detection device also has a light evaluation device for evaluating the light beam coupled into the second light-guiding element to determine if a drop has been dispensed by the metering valve. A method of detecting a drop is also described.

Claims

1. A drop-detection device comprising: a light-guiding element arrangement with a first light-guiding element and a second light-guiding element, which are located opposite to each other at an intermediate space, through which, the trajectory of the drop passes, in such a way that a light beam guided by the first light-guiding element crosses the trajectory of the drop and is subsequently coupled into the second light-guiding element arrangement so that drops escaping from a nozzle of a metering valve moving along a trajectory may be detected for application of a defined amount of a metering medium over a distance without any contact to the component to be processed, a light-signal generation device in order to couple a pulsed light beam with a carrier signal with a carrier frequency into the first light-guiding element, and a light evaluation device in order to evaluate the light beam coupled into the second light-guiding element in order to determine if a drop has been dispensed by the metering valve based on a modulation of the carrier signal by the drop.

2. The drop-detection device according to claim 1, wherein the first light-guiding element as a first and a second end and the first end of the first light-guiding element is coupled with a light-emission device of the light-signal generation device and the second end of the first light-guiding element forms an emission window to the intermediate space to be monitored, and the second light-guiding element has a first and a second end and the first end of the second light-guiding element forms an detection window to the intermediate space to be monitored and the second end of the second light-guiding element is coupled with a sensor device of the light evaluation device.

3. The drop-detection device according to claim 1, wherein the light-guiding elements are arranged at the metering valve in such a way that the pulsed light beam from the first light-guiding element hits the drop directly, is then modulated by the drop and directly coupled into the second light-guiding element.

4. The drop-detection device according to claim 1, wherein the first light-guiding element and the second light-guiding element comprise plastic fibres.

5. The drop-detection device according to claim 1, wherein the light-guiding elements are positioned relative to the metering valve in such a way that a defined effective cross-section surface of the first and/or second light-guiding element results depending on the respective metering process, in particular depending on a drop size to be expected.

6. The drop-detection device according to claim 1, wherein the light evaluation unit is configured to determine if a drop has been dispensed by the metering valve taking a defined carrier frequency of the pulsed light into account.

7. The drop-detection device according to claim 1 with a demodulation unit that is configured to carry out an amplitude modulation or a quadrature modulation of a captured modulated measurement signal based on the pulsed light.

8. The drop-detection device according to claim 1, wherein the light evaluation device comprises a modulation valuation unit, which is configured, preferably based upon an in-phase component and a quadrature component, to determine the amount of amplitude and/or the phase of the modulation signal based on the modulated measurement signal.

9. The drop-detection device according to claim 1, wherein the light-emission device is configured to convert a pulsed electrical signal into a light wave without changing the carrier frequency and phase of the pulsed signal.

10. The drop-detection device according to claim 1, wherein the light-signal generation device is designed in such a way that the brightness of the pulsed light beam is set via the selection of a pulse width of light pulses of the pulsed light beam.

11. A method of detecting a drop, which escapes from a metering valve, wherein a pulsed light beam with a carrier frequency is guided from a first light-guiding element in such a way that it passes through an intermediate space between the first light-guiding element and a second light-guiding element, and thereby crosses a trajectory of the drop, which passes between the intermediate space between the first light-guiding element and the second light-guiding element, and then is coupled into a second light-guiding element, and, on the basis of a modulation of the carrier signal by the drop of the light beam coupled into the second light-guiding element, it is determined if a drop has been dispensed by the metering valve such that there is application of a defined amount of a metering medium over a distance without any contact to the component to be processed.

Description

(1) The invention is explained once again below with reference to the enclosed figures on the basis of exemplary embodiments. Thereby, identical components in the various figures are provided with identical reference numbers. The figures are generally not to scale. The figures show:

(2) FIG. 1 is a schematic representation of a drop-detection device according to an exemplary embodiment of the invention,

(3) FIG. 2 a cross-sectional view of a drop-detection device according to the invention as well as a plurality of variations with different active light-guiding element heights,

(4) FIG. 3 is a detailed representation of a drop-detection device according to an exemplary embodiment of the invention,

(5) FIG. 4 is a detailed representation of a mixer unit of a demodulation unit of a drop-detection device in accordance with an exemplary embodiment of the invention,

(6) FIG. 5 a schematic representation of a control unit of a drop-detection device according to an exemplary embodiment of the invention.

(7) FIG. 6 a flowchart, with which a method to detect a drop is illustrated,

(8) FIG. 7 a flow chart, with which the functional principle of the modulation valuation unit shown in FIG. 3 is illustrated,

(9) FIG. 8 a flow chart, with which the functional principle of the detection filter unit shown in FIG. 3 is illustrated in detail.

(10) In FIG. 1, a drop-detection device 11 according to an exemplary embodiment of the invention is shown. In the exemplary embodiment shown in FIG. 1, the drop-detection device 11 comprises a light-signal-generation device 70, a light-guiding element arrangement L and a light evaluation device 80. The light-signal-generation device 70 comprises a signal-generation unit 20, which generates a pulsed electrical carrier signal TS. The electrical carrier signal TS is transmitted to a light-emission unit 31, for example a light diode, which converts the electrical signal TS into a light beam LS pulsed with the carrier signal TS. The pulsed light LS generated by the light-emission unit 31 is transmitted to the light-guiding element arrangement. In the exemplary embodiment shown in FIG. 1, a first light-guiding element L1 of the light-guiding element arrangement is connected to the light-emission unit 31 in such a way, that the light beam LS emitted by the light-emission unit 31 is directly coupled into the first light-guiding element L1 of the light-guiding element arrangement L.

(11) With the aid the first light-guiding element L1, the pulsed light beam LS is supplied to the intermediate space ZR through an emission window 14, in which a trajectory T of a drop TR emitted by a metering valve DV (with a nozzle adjusting nut DEM). The light of the light beam LS is modulated by the drop TR in such a way that it then comprises information corresponding to a modulated light signal MS. Then, the light beam LS comprising the modulated light signal MS is coupled into a second light-guiding element L2 out to via a detection window 15.

(12) The light beam LS comprising the modulated light signal MS is transmitted to a light evaluation device 80 by the second light-guiding element L2. The light evaluation device 80 comprises a light sensor 32 and a signal evaluation device 50.

(13) Since the drop-detection device 11, in particular due to the use of the pulsed light beam, is very sensitive to scattered light and other disturbances, however extremely sensitive to the useful signal, it is favourably not required to use additional optical elements, such as lens systems or the like, at the emission window 14 of the first light-guiding element L1 or at the detection window 15 of the second light-guiding element L2. The exit and entry sides of the light-guiding elements must be level and vertical to the longitudinal axis of the light-guiding elements. Since the light sensor 32 in the light-emission unit 31 are located outside of operating range of the metering valve DV, this sensor 32 and the emitter 31 can be dimensioned independently of the confined space conditions that are predominant within the range of the nozzle adjusting nut DEM of the metering valve DV. The emitter 31 serves as a signal converter, which converts the unmodulated electrical carrier signal into an unmodulated light signal LS. The light sensor 32 serves as a signal converter, which converts the modulated light signal MS in a modulated electrical measuring signal EMS.

(14) The subsequent processing of the modulated electrical measurement signal EMS is described in more detail in relation to FIGS. 3, 6 and 7.

(15) In FIG. 2, in the upper detailed drawing, a cross-section of a drop-detection device according to an exemplary embodiment of the invention is shown. Furthermore, in FIG. 2 in the lower detailed drawing, a plurality of variations of the arrangement of the light-guiding elements L1, L2 are illustrated with different active light-guiding element heights h.sub.a. The arrangement of the light-guiding elements L1, L2 are determined with the aid of distance spacers DS, that are attached between a light-guiding element holder LH and the metering valve DV. In the case shown in the upper detailed drawing, the active height beyond the nozzle adjusting nut DEM of the metering valve is approximately half of the light-guiding element diameter, which, in the case of a light-guiding element diameter of 1 mm, corresponds to an effective height h.sub.a of 500 m. The height of the section of the light-guiding elements L1, L2 should be understood as an active height, which is open toward the intermediate space, in which the trajectory T of the drop runs. That means that the section is the part of the cross-section of the light-guiding elements L1, L2 which is not covered by the nozzle adjusting nut DEM of the metering valve DV. However, this height can be adapted to the respective circumstances, which are determined by the respective metering process by means of approximately 100-m thick distance spacers.

(16) In the lower detailed drawing, three variations of the arrangement of the light-guiding elements L1, L2 are shown with different active light-guiding element heights h.sub.a. In the detailed drawing on the left, the entire light-guiding element surface is used, meaning the active height h.sub.a corresponds to the diameter of the light-guiding elements L1, L2. By means of this, a long transit time of the drop is achieved due to the detection range between both light-guiding elements L1, L2. This is beneficial for drop detection since more sampled signal values can be acquired.

(17) In the lower middle detailed drawing, half of the light-guiding element surface is used, meaning the active height h.sub.a corresponds to half of the diameter of the light-guiding elements L1, L2. The active width b.sub.a of the light-guiding elements corresponds to the diameter of the light-guiding elements L1, L2. Although, in the case of this variation, the transit time of the drop is somewhat shorter due to the detection range between both light-guiding elements L1, L2, however this variation represents a good compromise between the required installation space, meaning the minimum distance to the workpiece that the drop is being applied to and the achieved transit time.

(18) In the lower right partial drawing, only a fraction of the entire light-guiding element surface is used. Such an arrangement can, for example, in the case of very small drops, be advantageous since, in the case of this variation, there is a more favourable ratio between active surface and a surface shadowed by the drop. This results in a stronger signal amplitude modulation signal, which contributes to an improved signal-to noise ratio.

(19) In FIG. 3, a drop-detection device 11a in accordance with an especially preferred exemplary embodiment of the invention is shown. The drop-detection device 11a also comprises the units shown in FIG. 1, such as a light-signal generation device 70, a light-guiding element arrangement L and a light evaluation unit 80 which is marked with a dotted line in FIG. 3. The light-signal generation device 70 as well as the light evaluation device 80 are shown in detail in FIG. 3. The light-signal generation device 70 comprises, as shown in the light-signal generation device in FIG. 1, a signal-generation unit 20, which is been drawn into FIG. 1 using a dotted line. In this exemplary embodiment, the signal-generation unit 20 comprises a transmission signal-generation unit 21, which generates a transmission signal PWM_5 with a defined specifiable pulse frequency, for example, as a pulsed square wave signal. The generated transmission signal PWM_5 is transmitted to a power amplifier of 24, which amplifies the transmission signal PWM_5 to a carrier signal TS. In addition, the signal-generation unit 20 comprises a signal-generation unit 23, which is configured to transmit pulsed control signals PWM_1, . . . , PWM_4, which are phase-shifted with relation to the carrier signal, to a mixer unit 43 of a demodulation unit 40. The signal-generation unit 23, is part of the signal-generation unit 20, however, it serves to evaluate a detected modulated signal EMS and is therefore not part of the light-signal generation device 70, but considered a part of the light evaluation device 80.

(20) Furthermore, the signal-generation unit 20 has a control signal output 22 to control amplifier switches 44, 45 of the light evaluation device 80, which are also not part of the light-signal generation device 70 but deemed to be part of the light evaluation device 80 since the control signal generated by the control signal output 22 serves to evaluate the modulated signal MS.

(21) The pulse frequency of the control signals PWM_1, . . . , PWM_4 for the mixer 43 is always equal to the frequency of the transmission signal PWM_5. The phase shift between the control signals PWM_1, . . . , PWM_4 and the transmission signal is variable. The pulse frequency is preferably 450 kHz+15 kHz. The determination of the frequency of the carrier signal serves to ensure that the received signal (the carrier signal and sidebands resulting from the amplitude modulation caused by the drop) can optimally run through the bandpass filter.

(22) By the setting of the phase position between the carrier signal and the control signals of the demodulation unit, a sideband is then selected. The carrier frequency must be higher than two times the frequency resulting from the drop transit time through the modulation unit 30 in accordance with the sampling theorem.

(23) The carrier signal TS generated by the transmission signal-generation unit 21 is transmitted by the amplifier 24 to a light-emission unit 31. The light-emission unit 31 may be, for example, a light-emitting diode, which lights up TS according to the carrier signal TS adjacent to the LED. In other words, the carrier signal, which is initially occurs as pulsed electrical current, is converted into a pulsed light signal. The light-emission unit 31 is connected to the light-guiding element arrangement L. In detail, the light-emission unit 31 emits the pulsed light signal TS into a first light-guiding element L one of the light-guiding element arrangement L1, which supplies the pulsed light signal TS to an intermediate space ZR, in which a trajectory of a drop TR to be detected of a metering valve (see FIG. 1) runs. A second light-guiding element L2 to is arranged opposite the first light-guiding element L1, as has been already explained in association with FIG. 1.

(24) The light-guiding element L2 is connected to the light evaluation device 80, which is also marked with dashes in FIG. 3. The light evaluation device 80 comprises a sensor unit 32 which records a light signal modulated by the drop TR, provided that a drop has been dispensed. The sensor unit 32 comprises, for example, a photodetector, which receives the modulated light signal MS and converts it again into an electrically modulated signal EMS that can be transported by an electrical line.

(25) The electrical modulated signal EMS is then transmitted to an evaluation unit 50 (also marked with a dotted line in FIG. 3), which is part of the light evaluation unit 80 and also has a demodulation unit 40. The demodulation unit 40 comprises an amplifier unit 41, which amplifies the modulated electrical signals. The amplifier unit 41 is controlled via a control signal output 22 of the signal-generation unit 20 and, on the one hand, serves to pre-amplify the modulated signal EMS detected by the photodetector 32 and, on the other hand, as a transimpedance amplifier. Thereby, the photo detector 32 is pretensioned in the blocking direction and operated in a quasi-short-circuit. By means of this, only the emission of a linear current from the photodetector 32 depending on the lighting strength across many factors without voltage fluctuation still takes place. By means of this, the bandwidth of the detector, which is normally limited due to the terminal capacitance, is considerably higher since no reversal of the capacitance takes place. Due to the pretensioning, in addition, a further reduction of the capacitance is achieved with which another increase in the achievable bandwidth goes hand in hand. In addition, a transfer of the power signal takes place into a voltage signal due to the transimpedance amplifier. The amplification factor of this implementation is adjustable. By means of this, a maximum voltage-driven signal modulation is achieved, which is dependent on the drop shadowing.

(26) Furthermore, the demodulation unit 40 comprises a filter unit 42. The filter unit 42 can, for example, comprise a bandpass filter, which only lets through both sidebands and the carrier frequency of the modulated signal EMS. The filter unit 42 furthermore removes possible disruptive signals caused by an external light incidents with frequencies far away from the pulse frequency of the carrier signal TS. In addition, the filter unit 42, preferably a deep-edged bandpass filter, also removes the harmonic waves generated by the pulse width modulation. The modulated measurement signal EMS filtered in this way is then sent onto a mixer 43, which mixes the modulated and filtered measurement signal EMS with the pulsed control signals PWM_1, . . . , PWM_4, hereinafter also referred to as PWM signals, which are phase-shifted with relation to the carrier signal and generated by the second signal-generation unit 23 and an in-phase signal or an in-phase component I is transmitted to an in-phase signal amplifier 44 and a quadrature signal or a quadrature component Q is transmitted to a quadrature signal amplifier 45. The in-phase signal amplifier 44 and the quadrature signal amplifier 45 are controlled by a control signal output 22 of the signal-generation unit 20. The amplifiers 41, 44, 45 are controlled separately from each other. They are set via a varying resistor (rheostat) that can be programmed via a data bus (e.g. 120 bus). Thereby, each rheostat (and thus amplifier) is adjusted individually. Thereby, the setting of the amplifier 41 with regard to the value is completely independent of the amplifiers 44 and 45. However, the amplifiers 44 and 45 always have the same value in order not to change the relation between the I and the Q signal. However, also these are controlled separately from each other. The function of the mixer unit 43 is explained in FIG. 4 in detail and will be explained in further detail later on. The in-phase component I and the quadrature component of Q form the modulation signal MOD.

(27) After the amplification of both signal components I, Q has taken place within the amplifiers 44, 45, within the evaluation unit 50, both components I, Q are transferred to the subunits of the evaluation unit 50, which are part of a control unit 60 in the exemplary embodiment shown in FIG. 2. The control unit 60 comprises corresponding inputs 53, 54 for the signal components I, Q. The A-D converters (not shown), which convert the analogue signal components I, Q into digital signals, are connected downstream from the inputs 53, 54. The amplifiers 44, 45 of the demodulation unit 40 can be adjusted with regard to their amplification factor and serve to increase the signal components I, Q of the modulation signal MOD generated by the mixer unit 43 to an optimal voltage level for the A-D converter. This ensures maximum utilisation of converter resolution. In order not to take the A-D converters to their voltage limit specified by a reference voltage due to their steady components available in the components I, Q, only the alternating parts caused by a drop will be amplified.

(28) Furthermore, the evaluation unit 50 includes a modulation valuation unit 51 and a detection filter unit 52. These subunits of the evaluation unit 50 are part of the control unit 60 shown in FIG. 2. In the modulation valuation unit 51, the digitised signal components I, Q are mathematically prepared and transformed into amplitude and phase information, for example, with the aid of a polar-coordinate transformation process. The detection filter unit 52, for example can be designed as a parametrizable filter, with which, using the collected information, it can be determined whether a drop has passed through the intermediate space ZR between the first light-guiding element L1 and the second light-guiding element L2. Before the system 11a begins regular operation, it must be set by two ongoing initialization operations that are separate from one another.

(29) On the one hand all hardware assemblies must be set on a working point that is optimal for detection. These settings comprise the determination of the operating point of the light sensor 32 by the carrier signal duty cycle, the frequency tuning of the carrier signal TS on the filter characteristic of the bandpass filter 42, the setting of the phase position of the mixer signals PWM_1 . . . PWM_4 in relation to the carrier signal to the exact sideband selection, the determination of the optimal amplification factor of the transimpedance amplifier 41 and signal adapting of the I and Q signals to the A-D converter of inputs 53, 54 by the A-D preamplifier 44, 45. On the other hand, all parameters of the detection filter unit 52 are adjusted with reference to the target drops to be expected TR. This comprises the time window for searching for the derivative maxima for the amplitude and phase values, the permitted relative variances of the comparative values of the reference values of the amplitude and phase values as well as the permitted absolute ranges of the reference values of the amplitude and phase values. Both the hardware and the filter settings can be set manually or by automatic training processes. These settings are required for the acquiring the modulation value, as well as the signal evaluation with regard to the detection of a drop of TR.

(30) In FIG. 4, a mixer unit 43, in this embodiment a quadrature modulator, is shown in detail. The quadrature demodulator 43 comprises a transmitter 431, a switch unit 432 with parallel switches 432a, 432, 432 c, 432d, an integrator unit 433 with parallel switches 432a, 432, 432c, 432d, each with downstream integrators 433a, 433b, 433c, 433d, as well as a first and a second differential amplifier 434a, 434b, which are each electrically connected to two integrators. The quadrature demodulator 43 acts as a single-sideband mixer and again sets the electrical modulated measurement signal EMS back into the baseband. The sideband used for the modulation is selected by a passing choice of the phase position of the modulated measurement signal EMS with relation to for control signals PWM_1, . . . , PWM_4, which control the switches 432a, 432b, 432c, 432d of the mixer 43 via the differential amplifiers 434a, 434b, which are connected downstream from integrators 433a, 433b, 433c, 433d. As output signals of the differential amplifiers 434a, 434 (b), in-phase signals I and quadrature signals Q are generated, from which a modulation signal MOD can be derived, which is correlated with the disturbance of the carrier signal TS by a drop TR of the metering valve.

(31) In particular, the mixer unit 43 works as follows: A measurement signal EMS is transferred from the transmitter 431 to the input of the mixer unit 43. The transmitter 431 serves to adapt the performance between various components as well as to balance signals and remove existing offsets. Furthermore, the mixer 43 comprises a resistor R which is connected in series to the output of the transmitter and forms a filter together with the integrators 433a, 433b, 433c, 433d. Control signals PWM_1, . . . , PWM_4 are applied to the switches 432a, 432b, 432c, 432d and incremented by the signal-generation unit 23, which interconnect one of the switches 432a, 432b, 432c, 432d for a fourth of the period T.sub.PWM or a quarter wave of the carrier signal TS. The control signals PWM_1, . . . , PWM_4 are synchronised with the carrier signal TS. If one of the switches 432a, 432b, 432c, 432d is closed, the measurement signal EMS for the time interval, in which the respective switch 432a, 432b, 432c, 432d is closed, is integrated into an average value by the assigned integrator 433a, 433b, 433c, 433d. The integrators 433a, 433b, 433c, 433d can, for example, comprise parallelly connected capacitors and generate average values of the sections of the modulated electrical measurement signal EMS assigned to the individual quarter waves of the carrier signal TS. An average value integrated into the first quarter wave is at the positive input of the first differentiator 434a marked with a + and an average value integrated into the third quarter wave is at the negative input of the first differentiator 434a marked with an . An average value integrated into the second quarter wave is at the positive input of the first differentiator 434b and an average value integrated into the fourth quarter wave is at the negative input of the second differentiator 434b marked with an . In-phase signal I in the baseband is generated at the output of the first differentiator 434a and a quadrature signal in the baseband is generated at the output of the second differentiator. Details about the functionality of such mixed units are described in U.S. Pat. No. 6,230,000 B1

(32) In FIG. 5, an outer view (a housing) of the control means 60 is shown, with which the control system of individual units of a drop-detection device 11, 11a, the evaluation of measurement signals, the monitoring of the functionality of individual units and the settings and tuning of individual system parameters can be carried out. In this case, all of the electronics are accommodated within this housing. In principle, this concerns the whole drop-detection system including the optoelectronic signal converter (receiver photodiode 32, and transmission LED 31). These represent the border of the optical range, meaning to the transmission light-guiding element L1, to the emission window and to the drop path T, which is located externally.

(33) In future, the data-bus connection DB should, among other things, serve to communicate with the valve control unit. For example, the current status of drop detection or also statistics on the past metering processes (number of detected errors and when these occurred) can be transmitted to this via the data-bus connection DB. Another optional application for this data-bus connection DB entails the drop-detection system being able to prompt the valve control unit to make intentional wrong doses in order to check if the drop detection is functioning properly. The drop detection must then detect these intentional incorrect doses. Part of the control means 60 also includes a communication interface I/O, with which trigger signals from the valve control unit 70 are received and, via which, information on the system status of the drop-detection device in the metering status is indicated.

(34) Furthermore, the control means 60 comprises a serial interface SI, which serves as a connection to a higher-level process control computer 80. The process control computer 80 can control the drop detection via the serial interface SI and/or request status reports on the past doses.

(35) The control means 60 has an input RX, which serves as a connection of the receiving light-guiding element L2 to the photo element. The receiver light-guiding element L2 is connected to the RX input. An output TX serves a connection of the transmission light-guiding element L1 to the transmission light-emitting diode 31. The transmission light-guiding element L1 is connected to the output TX.

(36) Another input U.sub.S serves to supply control means 60 with power. An additional input PGM can be used as a programming socket for transferring firmware.

(37) Beyond this, the control means 60 comprises a display 55 as well as a plurality of control indicator lights 56, . . . , 59. A first indicator light 56 serves to display various system errors. A second control light indicator 57 serves to display the system status and an activity of the system. This status can, for example, concern circumstances in which a light-guiding element L1, L2 is not connected properly, damaged, too long or dirty. A third control light indicator 58 can include a notification that a drop with correct dosage was detected. A fourth control light indicator 59 can comprise a notification that a metering error has occurred, meaning, for example, that no drop has been detected or the detected drop deviates from the target drop too much.

(38) Furthermore, the control means 60 comprises two pressure switches S1 and S2 to coordinate the individual units of a drop-detection device. For example, by pressing the one switch S1 for a defined span of time (here, for example, 2 sec.), a first training mode, a hardware training mode is activated, in which, for example, the settings of a pulse width of the carrier signal TS occur so that an optimum brightness of the light-emission unit 31 with relation to the residual light reaching the light sensor unit of a light beam formed based on the carrier signal TS is reached, the determination of a frequency of the pulse carrier signal TS occurs so that both sidebands of the modulated signal EMS can pass through a filter unit 42 connected downstream from the sensor device occurs, setting the phase position of the carrier signal TS via the signal PWM_5 in relation to the control signals PWM_1, . . . , PWM_4, with which the mixer unit 43 belonging to the demodulation unit is controlled, and the setting of the amplifier units 44 and 45 occurs to adjust voltage and the amplifier unit 41, which acts as a transimpedance amplifier. The hardware training mode is, for example carried out during a first commissioning of the drop-detection device or if hardware components have been replaced.

(39) By pressing the other switch S2 for a defined span of time (also, for example, 2 sec.) a second training mode, namely a software training mode is activated, in which, for example, the detection filter unit 52 as well as the modulation valuation unit 50 one of the evaluation unit 51 is trained for a new type of drop. Here, the relative permitted fluctuation ranges of the compared values in relation to the reference values, the acquisition time window of the values relevant for the detection filter unit 52 as well as the absolute value ranges of the reference values are determined. This software training mode is carried out, for example, when a new test series is pending, meaning a different sort of drop should be detected.

(40) In FIG. 6, a flowchart is shown with which a method 500 of detecting a drop of a metering valve DV is illustrated. At step 6.I, a pulsed carrier signal TS is generated with a defined pulse frequency or carrier frequency and a defined duty cycle.

(41) At step 6.II, a modulated measurement signal MS is generated by a physical interaction of the carrier signal TS with a drop TR to be detected, which has been dispensed by the metering valve DV. To be specific, at sub-step 6.IIa, the carrier signal TS is initially converted into a light signal LS by a light-emission unit. During a sub-step 6.IIb, the light beam LS pulsed with a carrier frequency is coupled into a first light-guiding element L1. Then, the pulsed light beam LS at step 6.IIc is emitted by the first light-guiding element L1 in such a way that it runs through an intermediate space ZR between the first light-guiding element L1 and a second light-guiding element L2, crosses a trajectory of the drop TR, which runs through the intermediate space ZR between the first light-guiding element L1 and the second light-guiding element L2, and thenpossibly comprising a modulated light signalis coupled into the second light-guiding element L2. At step 6.IId, the possible light beam LS comprising a modulated light signal MS is converted into a possibly modulated electrical measurement signal EMS by a light conversion unit, for example, a light sensor.

(42) At step 6.II, a modulation signal MOD is determined based on the possibly modulated electrical measurement signal EMS. The modulation signal MOD corresponds to the information, which is formed via a change in the light beam when a drop TR collides with the light beam LS. Then, at step 6.IV, based on the modulation signal MOD, it is determined if a drop TR is distributed by the metering valve.

(43) In FIG. 7, the functional principle 700 of the modulation valuation unit 51 of an evaluation unit 50 shown in FIG. 3 is illustrated in detail. At step 7.I, the modulation valuation unit 51 records in-phase and quadrature components I, Q from the inputs 53, 54 shown in FIG. 3 of the A-D converters connected downstream to the control means 60 of the evaluation unit 50. The sampling of the in-phase signal I and the quadrature signal Q takes place on a continual basis. Thereby, both values I, Q are preferably acquired at the same time. Before being further processed, the values I, Q go through a median filter in order to remove extreme values caused by irradiation interference, ADC conversion errors, etc. At step 7.III, the signal components I, Q are converted into a signal MOD(A, ) by means of a polar-coordinate transformation process, which comprises information concerning the amplitude A and the phase of the modulation signal MOD. For example, A the amplitude is as follows:
A={square root over (I.sup.2+Q.sup.2)}.(1)

(44) Furthermore, the phase of the modulation signal MOD results from the following equation:

(45) $\begin{array}{cc}=\mathrm{arc}\tan \left(\frac{Q}{I}\right).& \left(2\right)\end{array}$

(46) While I and Q correspond to the amplitudes of the in-phase and quadrature components I, Q of the demodulated signal or the modulation signal MOD. The amplitude A and the phase are time-dependent factors like the signal components I and Q. Due to the high sampling rate and fast value acquisition associated therewith, the calculations according to equation 1 and 2 are calculated via look-up tables with linear intermediate value interpolation.

(47) At step 7.III, a time derivation of the amplitude A and the phase of the modulation signal MOD(A, ) occurs. At step 7.IV, derivative values dA/dt, d/dt are observed at a predetermined time interval I.sub.T and a number of maximum values max(dA/dt), max(d/dt) of the derivative values dA/dt, d/dt determined in advance are selected at a predetermined time interval I.sub.T, for example, the largest 10 values. The predetermined time interval I.sub.T can, for example, be determined in advance when initialising the drop-detection device and during the detection filter training. At step 7.V, modulation values A.sub.M, .sub.M are shown for the amplitude A and phase as a sum of the predetermined number of maximum values.

(48) FIG. 8, the functional principle 800 of the detection filter unit 52 of the evaluation unit 50 shown in FIG. 3 is illustrated in detail. At step 8.I, modulation values A.sub.M, .sub.M for the amplitude A and the phase determined by the modulation valuation unit 51 according to the method shown in FIG. 7, also known comparative values, are received. At step 8.II, these comparative values A.sub.M, .sub.M are saved in an electronic storage system. Furthermore, at step 8.III, the save comparative values are used to calculate reference values. The reference values RW.sub.A, RW.sub., for the amplitude A and the phase are determined. These reference values of RW.sub.A, RW.sub. can be, for example, average values from older amplitude and phase values, i.e. comparison values obtained, for example, during an earlier detection of drops.

(49) At step 8.IV, a deviation AW of the modulation values A.sub.M, .sub.M for the amplitude A and the phase determined by the modulation valuation unit 51 from the reference values RW.sub.A, RW.sub. are calculated. Then, at step 8.V, a comparison between the respectively determined deviation AW and the maximum the permitted relevant deviation upwards AW_up or downwards AW_down takes place. If the deviation is too great, which is marked with a j in FIG. 8, a notification is made at step 8.VI that an faulty drop has been detected. The extent of permitted deviation AW_up or AW_down is determined using one or a plurality of target drops during an initialisation procedure or in the aforementioned software training mode of the drop-detection device.

(50) In order to be able to recognise a gradual error, for example the phenomenon that the size of the drop TR to be detected during a frequently repeated emission of drops from a metering valve DV changes very slowly, the reference values RW.sub.A, RW.sub., meaning, for example, the average values of modulation values A.sub.M, .sub.M from past drops, are also monitored. At step 8.VII, it is determined if the reference values RW.sub.A, RW.sub. for amplitude A and phase are within a predetermined absolute value range ARI, PRI. If the reference values RW.sub.A, RW.sub. are not within a predetermined value range ARI, PRI, which is marked with an n in FIG. 8, a notification is given at step 8.VIII that only a series of faulty drops is present. The resolution to this error only occurs after stabilizing the average value, meaning when a valid reference value of the past drops is present again. If the reference values RW.sub.A, RW.sub. are not within a predetermined value range ARI, PRI and the relation of the values A.sub.M, .sub.M, of the current drops to the reference values RW.sub.A, RW.sub. is within the tolerated relative range, which is marked with a j in FIG. 8, a notification is given at step 9.IX that a correct drop has been detected. The output of the results can occur, for example, via the control light indicators 58, 59 shown in FIG. 5.

(51) In conclusion, it is again pointed out that in the case of the apparatuses described above in detail, these only have to do with exemplary embodiments, which can be modified by the person skilled in the art in various ways without leaving the realm of the invention. Still, the use of the indefinite article a or an does not rule out that several relevant features can also be available. As well, the term unit should comprise components that consist of a plurality, if applicable, also spatially separate subunits. In addition, with the term unit, a conceptual logical unit can be meant, meaning that the same hardware component can comprise a plurality of these logical units. This also particularly applies, for example, to the demodulation unit 40 and, if applicable, also to the signal-generation unit 20 and the evaluation unit 50.

REFERENCE LIST

(52) 11, 11a Drop-detection device 14 Emission window 15 Detection window 20 Signal-generation unit 21 Transmission signal-generation unit 22 Control signal output 23 Second signal-generation unit 24 Power amplifier 30 Modulation unit 31 Light-emission unit/light-emitting diode 32 Light sensor 40 Demodulation unit 41 Amplifier unit 42 Filter unit 43 Mixer/mixer unit 44 In-phase signal amplifier 45 Quadrature signal amplifier 50 Evaluation unit 51 Modulation valuation unit 52 Detection filter unit 53, 54 Inputs 56, . . . , 59 Indicator lights 60 Control unit 70 Light-signal generation device 80 Light evaluation device 431 Transmitter 432 Switch unit 432a, 432, 432c, 432d Switches connected in parallel 433 Integrator unit 433a, 433b, 433c, 433d Integrators 434a, 434b Differential amplifiers A Amplitude A.sub.M Amplitude modulation value ARI Predefined value range of the amplitude reference values AW Deviation AW_up Relative deviation upwards AW_down Relative deviation downwards b.sub.a Active width dA/dt Time variation of the amplitude d/dt Phase derivation value DEM Nozzle adjustment nut DS Distance spacers DV Metering valve EMS Modulated electrical measurement signal h.sub.a Active light-guiding element height I In-phase signal/in-phase component I.sub.T Predefined time interval I/O Communication interface L light-guiding element arrangement LH Light-guide element mount LS Light beam/light signal L1 First light-guiding element L2 Light-guiding element LS Pulsed light beam MOD Modulation signal MOD(A, ) Modulation signal in polar coordinates LS Modulated light signal PGM Programming socket for transferring firmware PRI Predetermined value range of the phase reference values PWM_1, . . . , PWM_4 Phase-shifted pulsed carrier signals PWM_5 Transmission signal Q Quadrature signal/quadrature component R Resistor RX Input RW.sub.A Amplitude reference value for the amplitude RW.sub. Phase reference value S1, S2 Pressure switch SI Serial interface T Trajectory T.sub.PWM Period of the carrier signal TR Drop TS Pulsed light/carrier signal TX Output U.sub.S Input for power supply of the control unit ZR Intermediate space Phase .sub.M Phase modulation value