GENERATION OF A HIGH VOLTAGE TO SUPPLY A PHOTOMULTIPLIER

Abstract

A power supply for a photomultiplier is provided, the power supply including: a charge pump configured to generate a first high voltage for the photomultiplier; a DC/DC converter configured to generate a second high voltage for the charge pump; a first control loop configured to control the charge pump and/or the DC/DC converter, the first control loop being controlled by the first high voltage; and a second control circuit configured to control the DC/DC converter, the second control circuit being controlled by the second high voltage. A radiometric measuring device for measuring a filling level and/or a limit level of a product in a container is also provided. A method of supplying power to the photomultiplier is also provided.

Claims

1. A power supply for a photomultiplier, the power supply comprising: a charge pump configured to generate a first high voltage for the photomultiplier; a DC/DC converter configured to generate a second high voltage for the charge pump; a first control loop configured to control the charge pump and/or the DC/DC converter, wherein the first control loop is controlled by the first high voltage; and a second control circuit configured to control the DC/DC converter, the second control circuit being controlled by the second high voltage.

2. The power supply according to claim 1, wherein the first control circuit has a slower reaction speed than the second control circuit.

3. The power supply according to claim 1, wherein dynodes of the photomultiplier are operated with stepped high voltages, which are parts of the first high voltage.

4. The power supply according to claim 1, wherein the DC/DC converter is operated with a variable frequency.

5. The power supply according to claim 1, wherein the DC/DC converter and/or the charge pump is operated at a frequency between 0.1 Hz and 10000 Hz.

6. The power supply according to claim 1, wherein the DC/DC converter and/or the charge pump is operated at a frequency between 1 Hz and 1000 Hz.

7. The power supply according to claim 1, wherein the second control circuit is activated periodically and/or event-driven.

8. The power supply according to claim 1, wherein the photomultiplier is supplied with a voltage of between 500 V and 1000 V.

9. The power supply according to claim 1, wherein the photomultiplier is supplied with a voltage of between 700 V and 900 V.

10. The power supply according to claim 1, wherein the first control loop and/or the second control loop is realized by means of a microcontroller.

11. The power supply according to claim 1, wherein the power supply is supplied with energy by a two-wire loop.

12. A radiometric measuring device for measuring a filling level and/or a limit level of a product in a container, wherein the radiometric measuring device comprises a photomultiplier and a power supply according to claim 1.

13. A method of supplying power to a photomultiplier comprising a power supply according to claim 1, the method comprising the steps of: detecting a first high voltage of the photomultiplier, which is generated by a charge pump; detecting a second high voltage for the charge pump, which is generated by a DC/DC converter; controlling the first high voltage of the photomultiplier by means of a first control circuit; and controlling the second high voltage for the charge pump by means of a second control circuit.

14. The method according to claim 13, wherein the first control circuit has a slower reaction speed than the second control circuit.

15. The method according to claim 13, wherein the DC/DC converter is operated with a variable frequency.

16. A nonvolatile computer-readable storage medium having a program stored therein which, when executed on a microcontroller, instructs a power supply to perform the steps of the method according to claim 13, the power supply comprising: a charge pump configured to generate a first high voltage for the photomultiplier; a DC/DC converter configured to generate a second high voltage for the charge pump; a first control loop configured to control the charge pump and/or the DC/DC converter, wherein the first control loop is controlled by the first high voltage; and a second control circuit configured to control the DC/DC converter, the second control circuit being controlled by the second high voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] This shows:

[0028] FIG. 1 schematically a power supply according to an embodiment;

[0029] FIG. 2 schematically a charge pump according to an embodiment;

[0030] FIG. 3 schematically a start phase of a charge pump according to an embodiment; and

[0031] FIG. 4 a flow chart showing a method according to an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032] FIG. 1 schematically shows a power supply 100 for a photomultiplier 300 according to an embodiment. The photomultiplier 300 is supplied by a high voltage U.sub.out, which is generated by a charge pump 190. The high voltage U.sub.out has partial voltages U1 to U4, each of which is fed to the dynodes of the photomultiplier 300. The highest partial voltage U4 may be identical to the output voltage, the high voltage U.sub.out. The number of partial voltages may be significantly higher for a real photomultiplier; for example, a photomultiplier may contain 10 or more dynodes, which makes 10 or more partial voltages necessary. The power supply 100 also has a DC/DC converter 200, which is configured to generate a second high voltage U.sub.in for the charge pump 190 and provides the second high voltage U.sub.in.

[0033] As can be clearly seen in FIG. 1, the power supply 100 has two separate control circuits: a first control circuit 110, which is configured to control the charge pump 190, and a second control circuit 120, which is configured to control the DC/DC converter 200. The first control circuit 110 is controlled by the first high voltage U.sub.out and acts on the terminal Ctrl of the charge pump 190. The second control circuit 120 is controlled by the second high voltage U.sub.in and acts on a switch 205, which, for example, controls the duration and frequency of PWM signals for controlling the DC/DC converter 200. The first control circuit 110 may have a slower response speed than the second control circuit 120. Both control circuits may be realized by a single microcontroller 150. The microcontroller 150 may have further components, e.g., one ADC at each of the inputs 111, 121 of the first and the second control loops 110 and 120 respectively. Instead of two ADCs, there may also be a single ADC, which multiplexes the inputs 111, 121.

[0034] The power supply 100 is connected to a two-wire loop 250, which supplies the power supply 100 with energy. The power supply 100 may optionally have an energy storage 220, e.g., a rechargeable battery or capacitor.

[0035] FIG. 2 schematically shows a charge pump 190 according to an embodiment. The charge pump 190 is connected via a connection U.sub.in to a high voltage, which is provided, for example, by a DC/DC converter 200 (see, for example, FIG. 1). The charge pump 190 has a plurality of outputs U1-U4, which provide the high voltages for the dynodes of the photomultiplier 300. In FIG. 2, only four outputs U1-U4 are shown for better visualization; a real photomultiplier may contain 10 or more dynodes, which requires 10 or more partial voltages. The charge pump 190 also has an output U.sub.out. A capacitor Cout may be connected to the output U.sub.out. This output U.sub.out may be connected to a control circuit 110, which regulates the high voltage U.sub.in and acts on the control input Ctrl. The control input Ctrl controls the switches S.sub.1 and S.sub.2, by means of which the functionality of the charge pump 190 is realized. Details of this control system are described in the following figures. FIGS. 3-5 use timing diagrams to describe the function of the charge pump 190 as an example. For clarification, the course of the voltages U2a, U3a, U4a are also shown in these figures.

[0036] FIG. 3 schematically shows a start phase of a charge pump 190 according to an embodiment, e.g., based on a circuit as shown in FIG. 2. The interval between two vertical lines is 1 ms. In the steady state, with U.sub.pump=Low (here 0V), the voltages are: U2a=U1=100V, U3a=U2=200V, U4a=U3=300V. In the steady state, with U.sub.pump=High (here 100V): U2a=U2=200V, U3a=U3=300V, U4a=U4=400V. C1, C3, C5 are the pump capacitors whose voltage is added to the rectangular voltage U.sub.pump. The voltages at the capacitors C2, C4, C6 are added to the constant voltage U1.

[0037] In the example shown, the input voltage U.sub.in is quadrupled. In this example, the input voltage U.sub.in is 100 V. [0038] Before the start time (0 ms), all capacitors are discharged, i.e., capacitors C1-C6 have 0 V and switches S.sub.1 and S.sub.2 are open. [0039] At the start time (0 ms), switch S.sub.1 is closed, S.sub.2 remains open, i.e., U.sub.pump=0 V. This charges C1 via a diode D1 to U2a=U.sub.in and the series circuit consisting of C2, C4, C6 is charged to U4=U.sub.in. [0040] Then (time 0.5 ms) switch S.sub.1 is opened and switch S.sub.2 is closed, i.e., U.sub.pump=U.sub.in. This means that U2a=U.sub.pump+U (C1)=2*U.sub.in. The charge of C1 is therefore distributed over C1+C2 up to U2=U2a, for U.sub.pump=U.sub.in, U2a=U.sub.pump+U (C1)=2*U.sub.in. [0041] Then (time 1 ms) switch S.sub.1 is closed again and switch S.sub.2 is opened, i.e., U.sub.pump=0. C1 is charged via D1 to U2a=U.sub.pump+U (C1)=U.sub.in. [0042] Then (time 1.5 ms) switch S.sub.1 is opened again and switch S.sub.2 is closed, i.e., U.sub.pump=U.sub.in. [0043] Then (time 2 ms) switch S.sub.1 is closed again and switch S.sub.2 is opened, i.e., U.sub.pump=0. [0044] This pattern is continued accordingly at the other points in time.

[0045] It becomes clear that the first control loop-due to the operating principle of the charge pump-needs to take into account the time constants for charging the capacitors C1-C6. By separating the control loops, the second control loop may advantageously have a significantly shorter time constant.

[0046] After a run-up phase (not shown), a steady state is reached. In the steady state, the following voltages are applied to C2, C4, and C6:

[00001]$U2-U1=U3-U2=U4-U3=U_{\mathrm{in}}$

[0047] This means thatin this examplethe voltage U.sub.in is applied between each of the dynodes.

[0048] FIG. 4 shows a flow chart with a method 600 for supplying voltage to a photomultiplier 300 (see, e.g., FIG. 1) according to an embodiment. In a step 602, a first high voltage U.sub.out of the photomultiplier 300 is detected. The high voltage U.sub.out is generated by a charge pump 190. In a step 604, a second high voltage U.sub.in is detected for the charge pump 190. The high voltage is generated by a DC/DC converter 200. In a step 606, the first high voltage U.sub.out of the photomultiplier 300 is controlled by means of a first control circuit 110. In a step 608, the second high voltage for the charge pump 190 is controlled by means of a second control circuit 120. Steps 602 to 608 may be repeated several times. Steps 602 and 604 and steps 606 and 608 may be performed substantially in parallel (quasi-parallel if a monoprocessor microcontroller is used for control) or in some other temporal relationship to each other. In particular, the first control loop 110 may have a slower response speed than the second control loop 120. The DC/DC converter 200 may be operated at a variable frequency.

LIST OF REFERENCE SIGNS

[0049] 100 power supply [0050] 110 first control loop [0051] 111 input [0052] 120 second control loop [0053] 121 input [0054] 150 microcontroller [0055] 190 charge pump [0056] 200 up converter [0057] 205 switch [0058] 220 energy storage [0059] 250 two-wire loop [0060] 300 photomultiplier [0061] 600 procedure [0062] 602-608 steps [0063] Ctrl control input of the charge pump [0064] Dy.sub.1-Dy.sub.4 dynodes of the photomultiplier [0065] U1-U4 partial voltages [0066] U2a-U4a partial voltages [0067] U.sub.in input voltage [0068] U.sub.out output voltage