Radiometric measuring device and method for operating a radiometric measuring device

Abstract

The invention relates to a radiometric measuring device comprising a scintillation counter, having at least one semiconductor photomultiplier (10) which can be optically coupled to a scintillator (3) for generating electrical signals on the basis of the light signals, a signal evaluation unit electrically coupled to the semiconductor photomultiplier (10) for generating a measurement signal on the basis of the electrical signals, and measuring device electronics for controlling the measuring device, wherein the measuring device electronics have an activation device (17) and a time measuring device, wherein the semiconductor photomultiplier (10) can be activated and deactivated by means of the activation device (17) and a time interval is provided between an activation of the semiconductor photomultiplier (10) and a first event by means of the time measuring device, wherein the measuring device electronics are designed in such a way that the semiconductor photomultiplier (10) is deactivated for a predefined time period immediately after detection of the event and a measurement result is determined from the time interval.

Description

[0001] Radiometric measuring device and method for operating a radiometric measuring device

[0002] The invention relates to a radiometric measuring device, in particular for level measurement, limit level measurement, density measurement or flow measurement according to the preamble of claim 1, and to a method for operating such a radiometric measuring device according to the preamble of claim 7.

[0003] A variety of radiometric measuring devices with so-called scintillation counters are known from the state of the art. Radiometric measuring devices with scintillators have been used for decades in radiation physics and in industry. They exploit the property of scintillating materials to convert incoming gamma radiation into light. These pulses last a few nanoseconds for plastic scintillators and several tens of nanoseconds to microseconds for sodium iodide scintillators. These light pulses are evaluated using scintillation counters, i.e. light detectors that convert the optical pulses into an electrical signal. A measured value can be determined by simply counting the number of pulses per unit of time. Photomultipliers or avalanche photodiodes, for example, can serve as light detectors. A further development of avalanche photodiodes are so-called semiconductor photomultipliers, e.g.Silicon photomultipliers, which are arrays of avalanche photodiodes.

[0004] The basic structure and operation of such a radiometric measuring device are shown in Figure 4 and are explained below.

[0005] Figure 4 shows the schematic structure of a scintillation counter 1, as known from the prior art. The scintillation counter 1 has a scintillator 3 as a material sensitive to ionizing radiation. The scintillator 3 is excited, for example, by y-radiation, with the excitation energy from the collision processes being re-emitted in the form of light. By measuring the amount of light, the energy deposited in the scintillator 3 by the radiation can be determined, and by measuring the number of light flashes per unit time (counting rate), the intensity of the radiation can be determined. For this purpose, the scintillation counter 1 has a photomultiplier tube 20, or photomultiplier for short, connected downstream of the scintillator 3.In the photomultiplier 20, photons arriving from the scintillator 3 release electrons from the surface of a photocathode, which are then accelerated and multiplied several times in an electron multiplier in an electric field between several electrodes until a measurable electrical signal is present at the end of the electron multiplier. The number and optionally also the amplitude of the electrical signals thus generated are recorded in a counter 13 connected downstream of the photomultiplier 20 and can be further processed in electronics not shown in detail here.

[0006] Measuring instruments in industrial environments, especially radiometric instruments for level measurement, point level measurement, density measurement, or flow measurement, can be exposed to highly fluctuating temperatures. To prevent damage to the measuring instrument, robust and well-insulated housings can be used. However, these are complex to manufacture and have increased weight.

[0007] DE 10 2017 205 738 A1 therefore proposes a radiometric level gauge with a scintillator and a photodetector, which is cooled or heated as needed via an active cooling element within the gauge. This allows the application range of the radiometric gauge to be expanded and the housing manufacturing costs to be reduced.

[0008] Also known in the state of the art are so-called silicon photomultipliers, which are intended to serve as a replacement for the photomultiplier tubes commonly used to date.

[0009] A silicon photomultiplier is an array of multiple avalanche photodiodes (APDs). They typically measure a few square millimeters, housing several hundred avalanche photodiodes. These are also referred to as pixels.

[0010] In this application, semiconductor photomultipliers are generally referred to below. In this application, the term "semiconductor photomultipliers" generally refers to photodetectors with avalanche photodiodes as sensitive elements, which can be manufactured from various substrates, in particular from silicon, germanium, or other suitable substrates.

[0011] The avalanche photodiodes used in a semiconductor photomultiplier operate in the Geiger range. They achieve a short-term amplification of up to 10 8 , since an electron-hole pair created by a single photon can generate several million charge carriers due to the acceleration in the multiplication zone caused by the high electric field strength.

[0012] Since an avalanche photodiode operating in the Geiger range delivers pulses of fixed height, the signal height of a semiconductor photomultiplier tube is proportional to the number of triggered pixels. The signal height can be specified in pe (pixel equivalent). One pe corresponds to the signal amplitude of a single pixel. Compared to conventional photomultiplier tubes, semiconductor photomultipliers offer several advantages.

[0013] Semiconductor photomultipliers are inexpensive, space-saving, and relatively mechanically robust. They also require a significantly lower supply voltage than photomultiplier tubes. Semiconductor photomultipliers are not affected by magnetic fields, which is another advantage for use in large detectors.

[0014] A major disadvantage is the strong temperature dependence of semiconductor photomultipliers. The photodiodes used in semiconductor photomultipliers often have a relatively narrow temperature range in which they can deliver good measurement results, and tend to generate a dark current at excessively high temperatures, which can negatively impact the measurement accuracy of the radiometric measuring device. Due to the strong temperature dependence of the thermal noise of semiconductor photodiodes and thus semiconductor photomultipliers, their use in combination with a scintillator in a radiometric measuring device at higher temperatures, e.g., 60°C, is difficult. The dark noise of a silicon photomultiplier doubles approximately every 10 K. Thus, the dark noise at 60°C is approximately 16 times higher than at 20°C. The resulting dark current can be so large that the use in a two-wire field device, i.e.for a measuring device operated in a two-wire current loop, is not possible due to the high additional power consumption.

[0015] For example, a current consumption of 0.5 mA was measured at an ambient temperature of 80°C with a supply voltage of 27 V. This results in an additional power loss of 13.5 mW due to the dark current. This power loss corresponds to the total power consumption of a state-of-the-art measuring device with a conventional photomultiplier tube, including the necessary high-voltage generation, an analog amplifier unit, and evaluation by a microcontroller.

[0016] As temperatures rise, the breakdown voltage of avalanche photodiodes also increases, thus decreasing the gain. At the same time, the dark rate—that is, the number of pulses per unit time that occur without optical excitation—increases. In this context, dark current refers to the spontaneous formation of free charge carriers due to heat in a light-sensitive semiconductor, such as a photodiode.

[0017] Semiconductor photomultipliers consist of a multitude of microcells (pixels). The signal amplitude generated by a microcell due to the absorption of a photon is defined as 1 pe. The sum signal generated by the silicon photomultiplier due to the parallel-connected microcells is thus proportional to the number of excited cells. Statistically, it is possible for m microcells to simultaneously generate a first signal S1 as a dark current due to thermal noise, where

[0018] S1 = mx pe

[0019] Another characteristic property of semiconductor photomultipliers is so-called crosstalk. In this case, electron-hole pairs recombine in an avalanche photodiode, and the resulting photons can generate a signal in neighboring pixels. This optical crosstalk from one microcell to n neighboring cells can cause a second signal S2, where

[0020] S2 = (n + 1) x pe Thus, a semiconductor photomultiplier tube can deliver pulses with amplitudes of several pe without optical excitation. Due to the increase in dark current with temperature, the number of dark pulses per unit time, as well as their amplitude, increases. Since large-amplitude dark pulses cannot be distinguished from a countable event based on their amplitude alone, the counting rate of such a photodetector can change significantly with temperature.

[0021] By combining the measurement signals from at least two semiconductor photomultipliers and a suitable signal acquisition / signal analysis system, dark noise can be significantly reduced or eliminated, thus minimizing the distortion (increase) of the counting rate due to the increase in dark pulses at higher temperatures. This can be solved by detecting signals occurring within a specified time interval, which are recorded simultaneously, i.e., coincidentally, by both semiconductor photodiodes. Thus, statistically distributed dark pulses contribute only a minor amount to the counting rate to be measured.

[0022] The semiconductor photomultipliers are ideally arranged directly adjacent, for example, in an array at one end of a scintillator. This ensures that the light pulses generated by y-quanta or particles in the scintillator material generate electrical signals of comparable amplitude, whose amplitude or signal shape is not distorted by absorption in the scintillator material due to different signal propagation paths. Due to the spatial proximity of the at least two semiconductor photodetectors, they also have approximately the same temperature, so that their dark noise changes to a comparable extent during operation.

[0023] However, these measures do not eliminate all dark pulses, and the power loss caused by the dark current increases even further.

[0024] To save power, the state of the art also proposes the possibility of cyclically switching the semiconductor photomultiplier and the associated signal processing on and off. However, cyclically switching the aforementioned components on and off has the disadvantage of reducing measurement accuracy and / or speed, since no pulses are recorded when the device is switched off.

[0025] Semiconductor photomultipliers operate in the so-called "Geiger mode." In this operating mode, semiconductor photomultipliers exhibit an avalanche effect that, once triggered, must be interrupted by an external force. The current flow caused by the avalanche effect can only be interrupted by reducing the voltage applied to the semiconductor photomultiplier below the breakdown voltage, thus returning the semiconductor photomultiplier to the blocking state.

[0026] In avalanche diodes and semiconductor photomultipliers, this can be achieved by a so-called quenching resistor, which is connected in series with the avalanche diode or semiconductor photomultiplier. The current flow through the avalanche diode or semiconductor photomultiplier causes a voltage drop across the quenching resistor, so that the voltage across the diode drops below the pinch-off voltage and the avalanche diode or semiconductor photomultiplier is blocked again.

[0027] To detect the next pulse, the avalanche diode must return to blocking mode, meaning the junction capacitance must be discharged. This also occurs via the quenching resistor. The time it takes for the avalanche photodiode or semiconductor photomultiplier to be ready for the next radiating event determines the maximum possible measurement speed. This time is also referred to as the decay time. The larger the quenching resistor, the faster the avalanche effect is terminated, but the longer it takes until the diode capacitance is discharged and a new radiating event can be detected.

[0028] It is the object of the present invention to improve the known devices and methods so that a higher measuring speed and / or a reduced energy consumption is achieved.

[0029] This object is achieved by a radiometric measuring device having the features of patent claim 1 and a method having the features of patent claim 7. Preferred embodiments, features, and properties of the proposed field device correspond to those of the proposed method, and vice versa.

[0030] Advantageous embodiments and variants of the invention emerge from the dependent claims and the following description. The features listed individually in the dependent claims can be combined with each other in any technically reasonable manner, as well as with the features explained in more detail in the following description, and represent other advantageous embodiments of the invention. It should be noted that the features listed individually in the claims can be combined with each other in any technically reasonable manner (even across category boundaries, for example, between method and device) and demonstrate further embodiments of the invention. The description further characterizes and specifies the invention, particularly in conjunction with the figures.

[0031] A radiometric measuring device according to the invention with a scintillation counter, has at least one semiconductor photomultiplier that can be optically coupled to a scintillator, for generating electrical signals based on light signals, a signal evaluation that is electrically coupled to the semiconductor photomultiplier, for generating a measurement signal based on the electrical signals and a measuring device electronics for controlling the measuring device and is characterized in that the measuring device electronics has an activation device and a time measuring device, wherein the semiconductor photomultiplier can be activated and deactivated by means of the activation device, and a time period between an activation of the semiconductor photomultiplier and a first event can be determined by means of the time measuring device, wherein the measuring device electronics is designed in such a way thatthat the semiconductor photomultiplier is deactivated for a predetermined period of time immediately after detection of the event and a measurement result is determined from the time period.,

[0032] Activation and deactivation of the semiconductor photomultiplier are understood as follows in this application: Upon activation, the semiconductor photomultiplier is active, i.e., it is ready to detect photons and provide an electrical signal on the output side by utilizing the avalanche effect. Activation in this context means operation of the semiconductor photomultiplier in the Geiger range, i.e., with a voltage that exceeds the breakdown voltage of the avalanche photodiodes used. In the Geiger range, even a single photon can trigger a complete avalanche breakdown, which spreads across the entire activated photodiode and generates a current pulse, regardless of the number of incident photons.

[0033] When deactivated, the semiconductor photomultiplier is inactive, meaning that incoming photons are not detected and, in contrast to the previously described operating mode, do not trigger an avalanche breakdown. For this purpose, the semiconductor photomultiplier is preferably operated with a voltage below the breakdown voltage. By lowering the voltage below the breakdown voltage, the avalanche effect is quenched. Preferably, the semiconductor photomultiplier is disconnected from the supply voltage, or the resistance of a connection to the supply voltage is significantly increased, so that the voltage applied to the semiconductor photomultiplier drops, or the applied voltage is reduced.

[0034] The radiometric measuring device may also include a scintillator for generating light signals based on radiative events. Scintillators can be plastic scintillators or sodium iodide scintillators, for example.

[0035] In a further development, the radiometric measuring device is designed in such a way that the signal evaluation can be activated and deactivated by means of the activation device or can be put into a standby mode and woken up again.

[0036] In the context of signal processing, enabling and disabling also means turning the signal processing unit on or off. Alternatively, the signal processing unit can be disconnected from and reconnected to a power supply, or the supply voltage of the signal processing unit can be reduced below the operating voltage of the signal processing unit. Alternatively, the signal processing unit can be put into a standby mode with reduced power consumption and then woken up from this mode.

[0037] If the signal evaluation unit is disconnected from the power supply, it may take some time to become operational again. This can be due, for example, to the fact that resonant circuits require a settling time to reach a stable state. For this reason, in these situations, it is often preferable to place the signal evaluation unit in a standby or sleep mode with reduced power consumption, as this can significantly reduce the time required until the signal evaluation unit is ready for operation.

[0038] In a further embodiment of the radiometric measuring device, the activation device can comprise a switching device for varying a supply voltage of the semiconductor photomultiplier. This switching device allows two different supply voltages to be applied to the semiconductor photomultiplier, so that in one switching position, it is operated with a first voltage above the breakdown voltage of the semiconductor photomultiplier, particularly in Geiger mode, and in another switching position with a second voltage below the breakdown voltage of the semiconductor photomultiplier.

[0039] In one embodiment of the radiometric measuring device, the switching device is designed as a MOSFET, which can be used to disconnect the semiconductor photomultiplier from a supply voltage. Disconnecting the semiconductor photomultiplier from the supply voltage immediately stops the current flow, and any avalanche breakdown is extinguished. In this way, in a semiconductor photomultiplier operating in Geiger mode, an avalanche breakdown can be stopped very quickly due to a detected event. Once the avalanche breakdown is stopped, charge carriers can flow away, making the semiconductor photomultiplier ready for use again, i.e., ready to detect photons.

[0040] Additionally or alternatively, the switching device can comprise a changeover switch, by means of which a supply voltage of the silicon photomultiplier can be switched between a first supply voltage above a breakdown voltage and a second supply voltage below a breakdown voltage of the silicon photomultiplier. As already described, an avalanche breakdown can also be extinguished in this way. Furthermore, charge carriers can flow out of the semiconductor photomultiplier in a voltage range below the breakdown voltage, so that it is subsequently ready for use again.

[0041] In a further development, the radiometric measuring device is designed such that the period for which the semiconductor photomultiplier and / or the signal evaluation is deactivated or put into a standby mode is at least 50 ps, ​​preferably at least 75 ps, particularly preferably at least 100 ps.

[0042] The longer the duration, the greater the energy savings that can be achieved. For example, if 10,000 pulses per second are expected, this means that there is an average of 100 ps between two pulses. If signal processing is deactivated or put into standby mode for 100 ps after an event is detected, the average waiting time for the next event is 100 ps. However, only half of the pulses are recorded. [In the technical literature, this situation is described with randomly distributed pulses. The corresponding formulas are quite complex. Should this description still be included?]

[0043] The method of shortening the dead time of a detector, during which no further pulses can be detected, by lowering the supply voltage below the breakdown voltage, was originally developed for Geiger-Müller counter tubes and is called the "time-to-first-count method." By shortening the dead time, more pulses can be measured per unit of time, thus improving measurement accuracy and / or speed. However, since the detector's dead time is still unknown, a defined waiting time is introduced between deactivation and activation of the detector, which must be longer than the current detector dead time. This method can be used to determine a measured value because a measurement of a time interval until the next event can be converted into the usual measurement of pulses per time interval by calculating the inverse.During the waiting time, no pulses can be detected, so parts of the signal processing can be switched off during this time, thus saving energy. This option can be particularly advantageous with two-wire devices.

[0044] Using the above numerical example we get:

[0045] Pulse rate = 10,000 pulses per second

[0046] Average active time until the next pulse = lOOps

[0047] Waiting time (passive time) = lOOps

[0048] Ratio of passive time to active time = 100ps / 100ps

[0049] Proportionate active time lOOps / (100ps+100ps) = 50%

[0050] Proportional passive time (lOOps / 100ps+100ps) = 50% = Energy savings

[0051] At 10 times the pulse rate, the following calculation results:

[0052] Pulse rate = 100,000 pulses per second

[0053] Average active time until the next pulse = lOps

[0054] Waiting time (passive time) = lOOps

[0055] Ratio of passive time to active time = 100ps / 10ps

[0056] Proportional active time lOps / (10ps+100ps) = 9.1%

[0057] Proportional passive time (lOOps / 10ps+100ps) = 90.9% = Energy savings

[0058] A method according to the invention for operating a radiometric measuring device according to the above description is characterized by the following method steps:

[0059] - Activating the semiconductor photomultiplier,

[0060] - Determining a time period between the activation of the semiconductor photomultiplier and the detection of a first event,

[0061] - Deactivating at least the semiconductor photomultiplier immediately after detection for a predetermined period of time and

[0062] - Determining a measurement result based on the time duration.

[0063] In a further development of the method, a signal evaluation unit of the semiconductor photomultiplier is activated and deactivated, or placed in standby mode and then reactivated. By activating and deactivating the signal evaluation unit, or placing it in standby mode and then reactivated, the energy consumption of the radiometric measurement setup can be significantly reduced.

[0064] To activate and deactivate the semiconductor photomultiplier, for example, the supply voltage of the semiconductor photomultiplier can be changed. By changing the supply voltage of the semiconductor photomultiplier, it can be achieved that it operates with a supply voltage above the breakdown voltage when activated, and with a supply voltage below the breakdown voltage when deactivated. This has the effect of achieving Geiger mode operation in the active state, and extinguishing an avalanche breakdown in the inactive state, clearing the semiconductor photomultiplier of generated charge carriers.

[0065] Additionally or alternatively, the semiconductor photomultiplier can be deactivated by disconnecting it from the supply voltage. Disconnecting the semiconductor photomultiplier from the supply voltage results in an avalanche breakdown being extinguished very quickly, thus minimizing the dead time of the semiconductor photomultiplier.

[0066] Changing the supply voltage of the semiconductor photomultiplier can be achieved, for example, by switching between a first voltage above the breakdown voltage and a second voltage below the breakdown voltage of the semiconductor photomultiplier.

[0067] The radiometric measuring device according to the present application is preferably designed as a two-wire field device. The aforementioned energy-saving measures make it possible to operate a semiconductor photomultiplier in a two-wire field device with the limited energy available there.

[0068] A two-wire field device according to the present invention is understood to be a field device that is connected to a higher-level unit via two lines, wherein both a power supply and measured value transmission take place via these two lines. The power and / or signal transmission between the two-wire field device and the higher-level unit occurs according to the well-known 4 mA to 20 mA standard, in which a 4 mA to 20 mA current loop, i.e. a two-wire line, is formed between the field device and the higher-level unit. In addition to the analog transmission of signals, it is possible for the measuring devices to transmit further information to or receive information from the higher-level unit according to various other protocols, in particular digital protocols. Examples of this include the HART protocol or the Profibus PA protocol.

[0069] These field devices are also powered via the 4 mA to 20 mA current signal, eliminating the need for an additional power supply cable besides the two-wire cable. To minimize wiring and installation effort, as well as safety measures, for example, when used in explosion-proof areas, it is also not desirable to provide additional power supply cables.

[0070] With two-wire field devices, the available input power is significantly limited. The electronics in the field device must be designed to operate reliably even with a minimum signal current of 4 mA.

[0071] Two-wire field devices, for example, require significantly less installation and wiring than four-wire field devices. With two-wire field devices, the additional installation and wiring of a supply voltage is completely eliminated, as this is carried out via the two-wire cable, as described above. This offers significant advantages, especially in applications where explosion protection regulations must be observed, since the separate cables for the supply voltage and the additional components required for this can be considered during the planning stage.

[0072] Two-wire field devices can also be designed to be intrinsically safe, thus offering a wider range of applications in explosion-protected (Ex) areas. Maintenance work on field devices in Ex areas is significantly easier and safer with two-wire field devices than with four-wire field devices, for example, because it can be performed safely even while measurements are in progress. With four-wire devices, however, the power supply must first be disconnected and secured against reconnection. This is usually done in the connection compartments, which are often located a considerable distance from the measuring point.

[0073] The present invention will be explained in detail below using exemplary embodiments with reference to the accompanying figures. They show:

[0074] Figure 1 shows an embodiment of a radiometric measuring device according to the present application,

[0075] Figure 2 shows the voltage curve at the output of the discriminator from Figure 1,

[0076] Figure 3 shows an embodiment of a method for operating a radiometric measuring device according to Figure 1 and

[0077] Figure 4 shows the structure of a radiometric measuring device according to the state of the art (already discussed).

[0078] In the figures, unless otherwise stated, the same reference symbols designate the same or corresponding components with the same function.

[0079] It should also be noted that a conjunction "and / or" used herein between two features and linking them together is always to be interpreted in such a way that in a first embodiment of the subject matter according to the invention only the first feature can be present, in a second embodiment only the second feature can be present, and in a third embodiment both the first and the second feature can be present.

[0080] Figure 1 shows an embodiment of a radiometric measuring device 100 according to the present application.

[0081] The radiometric measuring device 100 comprises a semiconductor photomultiplier 10 as a photosensitive element. The semiconductor photomultiplier is optically coupled to a scintillator (not shown in detail), which converts incoming gamma quanta into an optical signal in the form of photons. The semiconductor photomultiplier 10 is formed by an array of parallel-connected avalanche photodiodes and, for the sake of simplicity, is depicted as a photodiode in the circuit diagram shown in Figure 1, since its basic electrical properties are similar to those of a photodiode.

[0082] The semiconductor photomultiplier 10 is operated in reverse bias and is connected to ground on the anode side via a measuring resistor Rmess. On the cathode side, the semiconductor photomultiplier 10 is connected to a supply voltage UB via an element 11 represented as a switch. Depending on the design, the element 11 can be implemented as a variable resistor or switching element, for example, in the form of a field-effect transistor or as a changeover switch.

[0083] The anode of semiconductor photomultiplier 10 is connected to the non-inverting input of a discriminator 13, which compares the voltage applied to the node with a reference voltage Uref. It outputs an output signal if the measurement voltage Umess exceeds the reference voltage Uref, and does not output an output signal if the measurement voltage Umess is below the reference voltage Uref. In the simplest case, the discriminator 13 is a comparator constructed with an operational amplifier that compares the measurement voltage Umess with the reference voltage Uref, but it can also be a more complex circuit.

[0084] The output signal of discriminator 13 is fed to an evaluation circuit 15, which, among other things, has a time measuring device by means of which a time period tmess from activation of evaluation circuit 15 until the detection of a first event after activation can be measured. The evaluation is connected to an activation device 17 of the measuring device electronics, which is configured to deactivate evaluation circuit 15 immediately after detection of an event and output of the measured time period tmess for a predetermined or predeterminable standby time Ts. Simultaneously with the deactivation of evaluation circuit 15, element 11 is actuated, thus deactivating semiconductor photomultiplier 10.

[0085] In the context of the semiconductor photomultiplier, this means that an avalanche breakdown triggered by a photon is quenched. As already explained above, this can be achieved by lowering the supply voltage UB of the semiconductor photomultiplier 10 below a breakdown voltage of the semiconductor photomultiplier. This can be achieved, for example, by breaking the connection between the cathode and the supply voltage Ub, by increasing a variable resistance between the supply voltage Ub and the cathode, or by connecting the cathode to a second supply voltage U2 that is below the breakdown voltage of the semiconductor photomultiplier 10.

[0086] From the measured time Tmeas, a measured value processing unit 19 downstream of the evaluation circuit 15 can use statistical methods to determine a counting rate, i.e., the number of radiating events per unit of time, from which, for example, a fill level, a density, or a density profile can be determined. The final measured value is output via a two-wire interface 21 and transmitted to a higher-level unit, e.g., a control room.

[0087] After the standby time Ts has elapsed, the semiconductor photomultiplier 10 and the evaluation circuit 15 are reactivated and a new measurement can be carried out.

[0088] Figure 2 shows the measuring voltage Umess at the measuring resistor Rmess from Figure 1 in three different configurations.

[0089] The output signal labeled 101 shows the measurement voltage Umess when a resistor with a value of 100 kΩ is used as element 11. In this configuration, a decay time of approximately 100 ns results until the measurement voltage Umess drops back to 0 V due to the voltage drop across the resistor.

[0090] The curves labeled 102 and 103 show the output signal 101 when an avalanche breakdown of the semiconductor photomultiplier is actively cancelled, e.g., by interrupting the supply voltage UB. In this configuration, element 13 is designed as a field-effect transistor, which is opened by the activation device 17 after an avalanche breakdown, so that the semiconductor photomultiplier 10 exhibits a reduced current flow.

[0091] The signal labeled 104 would require a discriminator 13 for detection, which has a response time of less than 5 ns. The signal labeled 103 could be detected with a discriminator 13 with a response time of approximately 10 ns. However, due to the high processing speed, such discriminators require a power consumption of 10-15 mW or more, which represents an intolerable power consumption and thus energy consumption in a two-wire field device and therefore cannot be implemented.

[0092] The signal designated 102 can be detected by a discriminator 13 with a response time of approximately 40 ns, which can be achieved with components currently available on the market with a power consumption of less than 1 mW.

[0093] Figure 3 shows an embodiment of a method for operating a radiometric measuring device 100 according to Figure 1.

[0094] The method begins in step 301 with the successful commissioning of the field device, which includes the radiometric measuring device 100. The measuring device electronics are activated at this point, and in step 302, the semiconductor photomultiplier 10 and the evaluation circuit 15 are activated.

[0095] With the activation of the evaluation circuit 15, the time measuring device is activated and begins to measure the time until the detection of a first radiating event or the resulting measurement signal in step 303.

[0096] The output signal of the discriminator 13 is processed in the evaluation circuit 15 in step 304 and output to the measured value processing unit 19. At the same time, a signal is sent to the activation circuit 17, which then detects a radiation event in step 304, so that the evaluation circuit 15 and the semiconductor photomultiplier 10 are subsequently deactivated in step 305.

[0097] Step 306 represents a delay element that delays the process for the duration of the standby time and then returns to step 302. Reference numeral

[0098] scintillator

[0099] Semiconductor photomultiplier

[0100] element

[0101] Counter / Discriminator

[0102] Evaluation circuit

[0103] Activation device

[0104] Measured value processing

[0105] Photomultiplier tube

[0106] Two-wire interface radiometric measuring device

[0107] Output signal

[0108] signal

[0109] signal

[0110] Signal -306 process steps

Claims

Patent claims 1. A radiometric measuring device with a scintillation counter, comprising at least one semiconductor photomultiplier (10) which can be optically coupled to a scintillator (3) for generating electrical signals based on the light signals, a signal evaluation unit electrically coupled to the semiconductor photomultiplier (10) for generating a measurement signal based on the electrical signals, and measuring device electronics for controlling the measuring device, characterized in that the measuring device electronics has an activation device (17) and a time measuring device, wherein the semiconductor photomultiplier (10) can be activated and deactivated by means of the activation device (17), and has a time period between an activation of the semiconductor photomultiplier (10) and a first event by means of the time measuring device, wherein the measuring device electronics is designed in such a way thatthat the semiconductor photomultiplier (10) is deactivated for a predetermined period of time immediately after detection of the event and a measurement result is determined from the time period., Definition activation / deactivation -> adjust voltage 2. Radiometric measuring device according to claim 1, characterized in that the signal evaluation can be activated and deactivated by means of the activation device (17) or can be put into a standby mode and woken up again.

3. Radiometric measuring device according to one of claims 1 or 2, characterized in that the activation device (17) has a switching device for changing a supply voltage of the silicon photomultiplier.

4. Radiometric measuring device according to one of the preceding claims, characterized in that the switching device is designed as a MOS-FET, by means of which the silicon photomultiplier can be separated from a supply voltage.

5. Radiometric measuring device according to one of the preceding claims, characterized in that the switching device is designed as a changeover switch, by means of which a supply voltage of the semiconductor photomultiplier (10) can be switched between a first supply voltage above a breakdown voltage and a second reference voltage below a breakdown voltage of the semiconductor photomultiplier (10).

6. Radiometric measuring device according to one of the preceding claims, characterized in that the time duration is at least 50 ps, ​​preferably at least 75 ps, particularly preferably at least 100 ps.

7. Method for operating a radiometric measuring device with a scintillation counter, comprising at least [a scintillator (3) for generating light signals due to radiant events, ] a semiconductor photomultiplier (10) which can be optically coupled to a scintillator (3) and for generating electrical signals based on the light signals, a signal evaluation unit which is electrically coupled to the semiconductor photomultiplier (10) and for generating a measurement signal based on the electrical signals, and, measuring device electronics for controlling the measuring device, characterized by the steps: - Activating the semiconductor photomultiplier (10), - Determining a period of time between the activation of the semiconductor Photomultiplier (10) and the detection of a first event, - deactivating at least the semiconductor photomultiplier (10) immediately after the detection for a predetermined period of time and - Determine a measurement result based on the period.

8. Method according to claim 7, characterized in that a signal evaluation of the semiconductor photomultiplier (10) is activated and deactivated or put into a standby mode and woken up again.

9. Method according to one of claims 7 and 8, characterized in that a supply voltage of the silicon photomultiplier is changed to activate and deactivate the semiconductor photomultiplier (10).

10. Method according to one of claims 7 to 9, characterized in that for deactivation the semiconductor photomultiplier (10) is separated from a supply voltage.

11. Method according to one of claims 7 to 10, characterized in that a supply voltage of the semiconductor photomultiplier (10) is switchable between a first voltage above a breakdown voltage and a second voltage below a breakdown voltage of the semiconductor photomultiplier (10).

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