Apparatus, arrangement and method for the intrinsically safe supply of current to an appliance, and intrinsically safe appliance

Abstract

The invention relates to an apparatus (4) for providing an intrinsically safe supply of current to an appliance (1), in particular an intrinsically safe appliance which is situated in a potentially explosive area and has a recurring briefly high power requirement, the device comprising - a device (5) for detecting a variable (U) which represents an electrical current (I) flowing into the appliance (1) or in the appliance (1), and - at least one monitoring device (10) which is designed to monitor the device (1) with regard a risk of ignition spark formation, and simultaneously with regard to a resulting thermal overload, on the basis of the detected variable (U), and to shut off the current (I) in response to a risk of ignition spark formation, and to limit the current (I) in response to the resulting thermal overload. In this way, a higher functional electrical power can be temporarily made available to the intrinsically safe appliance (1). The invention thus makes it possible to provide appliances, or functions contained therein, which have hitherto not been implementable with intrinsic safety, such as appliances having electrical high-frequency components which cannot be potted and which have a recurringly briefly high power requirement.

Description

[0001] Description

[0002] Device, arrangement and method for intrinsically safe power supply of a device, as well as intrinsically safe device

[0003] The invention relates to a device, an arrangement and a method for the intrinsically safe power supply of a device, in particular a device with a recurring short-term high power requirement, according to claim 1, 9 or 10, as well as an intrinsically safe device according to claim 17.

[0004] IEC 60079-11 defines requirements for intrinsically safe equipment intended for use in potentially explosive atmospheres. It also defines requirements for related equipment intended for connection to intrinsically safe circuits leading into such atmospheres. The intrinsic safety (Ex i) type of protection aims to prevent ignitable sparks and hot surfaces. The advantage of such intrinsically safe devices is that complex housing designs (e.g., enclosures) are unnecessary, maintenance work can be carried out even during operation, and the low voltages and currents allow for safe work, e.g., during troubleshooting.

[0005] In current electronic implementations of IEC 60079-11, essentially two ignition mechanisms must be controlled for explosion protection:

[0006] Spark ignition with excessive energy that could cause an ignitable gas or dust to explode,

[0007] Thermal power, which leads to an excessive surface temperature, which in turn leads to thermal ignition of an ignitable gas or dust.

[0008] The realization of explosion-proof IoT devices with recurring, short-term high power requirements (e.g., pulse-driven data radio or radar applications) presents very difficult-to-manage problems for intrinsic safety implementation, which are often not economically solvable.

[0009] The most common and simplest method to solve this problem is to use an electrical resistor to limit the electric current and the associated electrical power (after prior voltage limiting). Alternatively, current limiters based on electronic components can be used, which have now also been elevated to a practical method with the recently implemented Ed. 7 of IEC 60079-11.

[0010] These two methods, already in use before Edition 7 of IEC 60079-11, have their limitations in that the user must choose a maximum current limit threshold, resulting from a compromise that applies equally to spark ignition and thermal ignition. This leads either to problematic spark ignition behavior at high available functional electrical power, or to low available electrical power with adequate spark protection.

[0011] Since spark ignition behavior must always be guaranteed, the available electrical power is insufficient for some applications (e.g., high-frequency components in IoT devices such as radio / cable radio or radar) and therefore requires very complex solutions – for example, potting the device housing. However, high-frequency components cannot generally be potted due to their inherent limitations, as this would unacceptably affect their high-frequency characteristics. Therefore, implementation using the "intrinsic safety" (Ex-i) type of ignition protection is not possible, and other Ex ignition protection types also offer significant disadvantages with considerable limitations regarding the cost and functionality of the IoT device.

[0012] Document DE 10 2013 223 141 A1 discloses an electronic circuit arrangement for use in potentially explosive atmospheres. The circuit arrangement can be connected on the input side via a supply line to an electrical power supply unit and on the output side to an external electronic device for supplying it with electrical energy. The circuit arrangement detects the current flowing in the supply line and comprises a first electronic circuit for monitoring for glow ignition, a second electronic circuit for monitoring for spark ignition, and a third electronic circuit for monitoring for a short circuit. All three circuits interrupt the current when triggered.

[0013] Document DE 10 2016 113 268 A1 discloses a non-intrinsically safe safety circuit that regulates the electrical power supply of an intrinsically safe assembly in such a way as to prevent the assembly from heating up above a critical temperature. The regulation is based on a clocked interruption of the power supply using a control signal from a higher-level unit. The safety circuit detects the control signal and then sets the maximum transmissible power by a fixed clock rate of the control signal.

[0014] Document DE 43 16 185 A1 discloses the use of a timer (e.g., a capacitor) in a circuit arrangement for switching an electrical load on and off, in order to delay a reaction to a detected overcurrent for a predetermined time. This measure makes it possible to briefly allow a higher current, which can occur, for example, as an inrush current in certain loads.

[0015] Based on this, the object of the present invention is to provide a device, an arrangement and a method that enable an intrinsically safe power supply of a device with a high available functional electrical power, in particular for an intrinsically safe device in an explosion-hazardous area with a recurring short-term high power requirement.

[0016] This problem is solved by a device according to claim 1, an arrangement according to claim 9, and a method according to claim 10. An intrinsically safe device is the subject of claim 17. Advantageous embodiments are the subject of the dependent claims.

[0017] An inventive device for the intrinsically safe power supply of a device, in particular an intrinsically safe device in an explosion-hazardous area with a recurring short-term high power requirement, comprises a device for detecting a quantity that represents an electric current flowing into or in the device,

[0018] - at least one monitoring device which, based on the detected quantity, is designed to simultaneously monitor the device for both a risk of ignition sparking and a developing thermal overload, and to switch off the electric current in response to a risk of ignition sparking and to limit the current in response to a developing thermal overload.

[0019] The invention is based on the idea of ​​addressing the aspects of preventing spark ignition (for example, by preventing an impermissibly high current that could lead to or generate a spark) and thermal limitation, i.e., limiting the surface temperature, by means of separate and individual monitoring, and optionally also fault response, with respect to the electric current flowing into or within the device. Since the individual monitoring is based on a measured quantity representing an electric current flowing into or within the device, these are "active" measures, in contrast to "passive" measures such as the known current limiting using an electrical resistor. By providing separate monitoring for spark ignition prevention and monitoring for thermal stress, i.e.,Due to the surface temperature, a significantly higher functional electrical power can now be provided, at least temporarily, which can even reach the maximum power allowed by a safety standard such as IEC 60079-11.

[0020] This also makes it technically possible to achieve peak performance levels that temporarily exceed the thermal limit, as long as they remain sufficiently below the ignition energy of the spark limiter. This allows, for example, the power supply of electrical devices that require several times the thermal limit current for time-limited data transmission or power-intensive sensors.

[0021] The invention thus enables the implementation of devices and their functions that were previously not possible with intrinsic safety. This applies, for example, to non-encapsulated high-frequency electrical components, such as a mobile phone modem or radar sensor, which repeatedly require high power for short periods of transmission and where encapsulation is not possible due to the high-frequency conditions ("detuning"). Therefore, for example, it is now possible to implement an IoT device with radio connectivity (radio technology) in an explosion-proof manner (with higher levels of protection, e.g., Zone 0 / 1).

[0022] The invention is therefore fundamentally suitable in particular for intrinsically safe devices in an explosion-hazardous area with a recurring, short-term high power requirement, such as field devices with radio communication or field devices for radar-based liquid level measurement.

[0023] Especially in battery- or accumulator-powered devices that require a constant standby current (e.g., battery-powered IoT devices), current limiting elements (e.g., electrical resistors or electronic current limiters) previously had to be significantly oversized thermally, resulting in corresponding power losses that reduced the operating time of the devices. The invention reduces such oversizing and the associated power losses, thereby increasing the operating time of the devices. For example, the invention can act as a current limiter to prevent the risk of ignition sparks and as a power limiter to prevent thermal overload.

[0024] The device according to the invention can be an integral part of the device. However, the device according to the invention can also be physically separate from the device and connected to it for power supply via an electrical cable. For example, the device can be located in a potentially explosive atmosphere and the device at a boundary between a non-hazardous area and the potentially explosive atmosphere.

[0025] The quantity representing an electric current flowing into or through the device could, for example, be the voltage across a measuring resistor (shunt) through which the current flows. However, other quantities are also possible, such as the electromagnetic field or the magnetic flux density of the current.

[0026] According to the invention, the monitoring device is designed to switch off the current in response to a risk of ignition sparks and to limit the current in response to an emerging thermal overload. These individually differentiated reactions allow the device to remain operational for a longer period.

[0027] Since ignition sparks are more critical and faster-acting processes than thermal overloads, the monitoring device is preferably designed in such a way that, in the event of a simultaneous risk of ignition sparks and a developing thermal overload, it prioritizes the response to the risk of ignition sparks over the response to the developing thermal overload, in particular by switching off the current.

[0028] To ensure that the risk of ignition sparks subsides sufficiently, the monitoring device is preferably designed to only lift the shutdown or current limitation after a delay period following a reaction to a risk of ignition sparks.

[0029] According to a simple and readily implementable design, the monitoring device is configured to monitor the detected quantity for reaching or exceeding a first threshold value in order to monitor the device for the risk of ignition spark formation. The threshold value is preferably selected such that, within the reaction time of the monitoring device for switching off the current (e.g., 1 microsecond), the energy in the ignition spark is limited to a value specified in a protection standard such as IEC 60079-11 (depending on the respective gas groups, e.g., HB, HC).

[0030] According to another easily implemented embodiment, the monitoring device is designed to monitor for the resulting thermal overload and determine the level of utilization of the device's thermal capacity or thermal reserve by the current, based on the measured value, particularly by means of a timer or a counter. The timer preferably comprises a capacitor, in particular a capacitor of a capacitor-based integrating controller.

[0031] The monitoring device can then be designed to limit the current to a defined value when the level of utilization of the thermal capacity or thermal reserve of the device meets a predetermined condition (e.g., reaches, exceeds, or falls below a threshold).

[0032] The monitoring device is preferably designed to determine the utilization of the thermal capacity or thermal reserve based on the measured values ​​and the duration of these values ​​within different value ranges. Using such value ranges, it can be particularly easy to define whether a specific measured value indicates a thermal load (heating) or a cooling load (discharging) of the device. For example, a first value range can be above a value corresponding to the device's rated current, and a second value range can be below this value.

[0033] If the monitoring device includes a timer that incorporates a capacitor (e.g., a capacitor in a capacitor-based integrating controller), it is preferably configured to charge the capacitor when the values ​​exceed a second threshold and to discharge it when the values ​​fall below this threshold. Alternatively, in the sense of hysteresis, discharge can also occur only when the values ​​fall below a third threshold. The electrical voltage across the capacitor then represents a thermal load or thermal reserve of the device. The threshold(s) can be used to easily define the value ranges described above. The monitoring device can then be configured to limit the current to a defined value when a voltage across the capacitor meets a predetermined condition (e.g., reaches or exceeds a threshold).

[0034] If the monitoring device includes a counter, it is preferably configured to count in a first direction when the detected values ​​exceed a second threshold, and in a second direction, opposite to the first, when the detected values ​​are less than the second threshold or, alternatively, less than a third threshold. The counter value then represents the thermal load or thermal reserve of the device. Here, too, the value ranges described above can be easily defined based on the threshold(s).

[0035] The monitoring device can then be designed to limit the current to a defined value when a meter reading meets a predetermined condition (e.g., reaches or exceeds a predetermined value).

[0036] According to a further advantageous embodiment, the monitoring device includes at least one semiconductor switch for limiting and / or switching off the current.

[0037] The device for detecting the quantity representing an electric current flowing into or within the device preferably consists of a measuring resistor (shunt) through which the electric current flows, with taps for a voltage applied to the measuring resistor.

[0038] Depending on the safety requirements, the device may also include several of the monitoring devices described above, each designed to monitor the device simultaneously for both a risk of ignition sparking and a developing thermal overload, based on the detected quantity, and to switch off the current in response to a risk of ignition sparking and to limit the current in response to a developing thermal overload.

[0039] An arrangement according to the invention for the intrinsically safe power supply of a device, in particular an intrinsically safe device in a potentially explosive atmosphere with a recurring, short-term high power demand, comprises several devices according to the invention as described above, each of which includes a device for detecting a quantity that represents the electric current flowing into or within the device. This also allows for the fulfillment of increased safety requirements.

[0040] An inventive method for the intrinsically safe power supply of a device, in particular an intrinsically safe device in an explosion-hazardous area with a recurring short-term high power requirement, comprises:

[0041] Detecting a quantity that represents an electric current flowing into or through the device,

[0042] Monitoring the device based on the detected quantity simultaneously for both the formation of an ignition spark and a thermal overload, switching off the electrical current in response to a risk of ignition spark formation and limiting the current in response to a thermal overload.

[0043] According to a further advantageous embodiment of the method, in the event of a simultaneous risk of ignition spark formation and resulting thermal overload, the reaction to the risk of ignition spark formation has priority over the reaction to the resulting thermal overload; in particular, the current is switched off.

[0044] Following a reaction to the risk of sparking, the power is preferably only switched off after a delay period.

[0045] To monitor the device for the risk of spark formation, the detected quantity can be monitored to see if a first threshold value is exceeded.

[0046] To monitor the device for the resulting thermal overload, the level of utilization of a thermal capacity or thermal reserve of the device by the current can be determined based on values ​​of the recorded quantity, in particular by means of a timer or a counter.

[0047] The current can then be limited to a defined value if the utilization of the device's thermal capacity or thermal reserve meets a predefined condition (e.g., reaches, exceeds, or falls below a threshold). The utilization of the thermal capacity or thermal reserve can be determined particularly easily based on the values ​​and the duration of these values ​​within different value ranges.

[0048] If a timer with a capacitor is used to monitor the device for the resulting thermal overload, the capacitor can be charged when the values ​​are greater than a second threshold, and discharged when the detected values ​​are less than the second threshold or alternatively less than a third threshold.

[0049] The current can then be limited to a defined value if a voltage across the capacitor meets a predetermined condition (e.g., reaches or exceeds a threshold).

[0050] If a counter is used to monitor the device for the resulting thermal overload, the counter can count in a first direction when the values ​​are greater than a second threshold, and in a second direction, opposite to the first direction, when the detected values ​​are less than the second threshold or alternatively less than a third threshold.

[0051] The current can then be limited to a defined value if a meter reading meets a predefined condition (e.g., reaches or exceeds a predefined value).

[0052] The advantages mentioned for the device according to the invention apply accordingly to the method according to the invention.

[0053] An intrinsically safe device according to the invention, in particular an intrinsically safe field device for measuring or influencing a process variable, comprises a power supply device (in particular a battery, an accumulator, a capacitor or a supercapacitor), an electrical load and a device or arrangement as described above according to the invention, wherein the device or arrangement is connected in an electrical connection between the power supply device and the electrical load.

[0054] The invention and further advantageous embodiments of the invention according to features of the dependent claims are explained in more detail below with reference to exemplary embodiments in the figures; therein: FIG 1 shows a first exemplary embodiment of a device according to the invention in an intrinsically safe device,

[0055] FIG 2 shows a second embodiment of a device according to the invention in an intrinsically safe device,

[0056] FIG 3 shows a third embodiment of a device according to the invention in an intrinsically safe device,

[0057] FIG 4 shows an embodiment of an arrangement according to the invention comprising several devices according to FIGS 1 to 3,

[0058] FIG 5 shows a first exemplary time course of a current for supplying the devices according to FIG 1 - 3,

[0059] FIG 6 shows the time course of the current from FIG 5 with first examples of threshold values ​​and time windows based on the device according to the invention,

[0060] FIG 7 shows a second exemplary time course of a current for supplying the devices according to FIGS. 1-3 with the first examples of threshold values ​​and with time windows due to the device according to the invention.

[0061] FIG 8 shows the time course of the current from FIG 5 with second examples of threshold values ​​of the device according to the invention,

[0062] FIG 9 shows an example of a first monitoring unit for the danger of ignition spark formation,

[0063] FIG 10 shows an example of a second monitoring unit for an emerging thermal overload,

[0064] FIG 11 shows an exemplary process sequence according to the invention, FIG 12 shows an example of an arrangement of a device according to the invention at a boundary between a non-explosion-hazardous and an explosion-hazardous area.

[0065] FIG 1 shows a simplified and schematic representation of an intrinsically safe device 1 suitable for use in a potentially explosive atmosphere. The device 1 comprises an electrical energy storage device 2, an electrical load 3 supplied with an electric current I from the energy storage device 2, and a device 4, described in more detail below, for the intrinsically safe power supply of the load 3 or the device 1, which is connected in an electrical connection 8 between the energy storage device 2 and the load 3. Supplying the load 3 from the energy storage device 2 is only an example. Alternatively, the load 3 can also be supplied with power from a power supply network.

[0066] Device 1 is, for example, a field device for measuring or influencing a process variable, such as a field device for measuring level, flow rate, pressure, temperature, vibrations and / or field strengths, a field device for positioning a valve (e.g. a valve positioner) or a gas quality sensor (e.g. for CO2).

[0067] Preferably, device 1 is an IoT device, i.e., a device with a communication connection to the Internet of Things (IoT).

[0068] Preferably, the device 1 is also a device with a recurring, short-term high electrical power demand. Examples include field devices with a transmitter for radio communication or radar-based distance measurement. FIG 5 shows an example of the current I over time t. The load 3, or the device 1, consumes a current IR in a standby state and, at time intervals, a maximum current IM for current or power pulses 17 with a duration λ. In the case of a radar IoT device, for example, l M = 600 mA, IR = 5 - 10 mA, T = 200 ms and the interval between the current pulses 17 can, for example, be in the range of hours to days in the case of radio communication and in the case of a sensor such as a radar sensor, for example, in the range of seconds to hours.

[0069] In the embodiments shown in FIGS. 1-4, the device 1 is energy-autonomous, but this is not a limitation of the invention. The energy storage device 2 is, for example, a (rechargeable) battery, an accumulator, a capacitor, or a supercapacitor. The energy storage device 2 can be kept charged, for example, by means of a battery or another external power supply and an electronic charge controller, in a manner not shown in detail. To ensure explosion protection, the energy storage device 2 can be encased in a potting compound.

[0070] Load 3, for example, consists of electronics for controlling and communicating with the device, as well as electrical components for performing the device's actual functions (e.g., sensors, actuators). Load 3 can include, for example, transmitters for radio communication or radar-based distance measurements.

[0071] The device 4 comprises a device 5 for detecting a quantity that represents the electric current I flowing into the load 3 in the device 1. For this purpose, the device 5 includes a measuring resistor (shunt) 6 and two voltage taps 7 for detecting a voltage drop U across the measuring resistor 6. The measuring resistor 6 is connected in an electrical connection 8 between the energy storage device 2 and the load 3 and is thus traversed by the load current I. The voltage U applied to the voltage taps 7 is proportional to the current I flowing into the load and thus represents this current I. The maximum current l M This corresponds to a maximum voltage UM across the measuring resistor 6 and the quiescent current l. R This corresponds to a resting voltage UR across the measuring resistor 6 (see FIG 4).

[0072] The device 4 further comprises a monitoring device 10, which in turn includes a first monitoring unit 11, a second monitoring unit 12, a semiconductor switch 13, and an electrical resistor 14. Both monitoring units 11 and 12 are connected to the voltage taps 7 on their input side, so that the voltage U is applied to them on the input side. On the output side, monitoring unit 11 is directly connected to a control input of the semiconductor switch 13. Monitoring unit 12 is connected to the control input of the semiconductor switch 13 via the electrical resistor 14. In the exemplary embodiment, the semiconductor switch is a p-channel MOSFET whose gate represents the control input, which is connected to the monitoring units 11 and 12.

[0073] The first monitoring unit 11 is configured to monitor the device 1 for the risk of ignition sparks based on the detected voltage U. The second monitoring unit 12 is configured to monitor the device 1 for thermal overloads based on detected voltage U values. Thus, by means of the monitoring units 11 and 12, the device 1 is simultaneously monitored for both the risk of ignition sparks and the risk of thermal overload.

[0074] The monitoring unit 11 is designed to control the semiconductor switch 13 via its control input (gate) in such a way as to switch off the current I in response to a danger of ignition spark formation.

[0075] The monitoring unit 12 is designed to control the semiconductor switch 13 via its control input (gate) in response to an emerging thermal overload, such that it limits the current I.

[0076] The resistor 14 ensures that a shutdown attempt generated by the monitoring unit 11 has a higher priority in controlling the control input (gate) of the semiconductor switch 13 than a control attempt by the monitoring unit 12. In the event of a simultaneous risk of ignition sparking and thermal overload, the response to the risk of ignition sparking, i.e., shutdown, has priority over the response to the thermal overload, in this case, current limiting.

[0077] The monitoring unit 11 is designed to monitor the detected voltage U for exceeding a first threshold value Ui, which corresponds to a first threshold value h for the current I (see FIG. 6), in order to monitor the device 1 for the risk of ignition spark formation. The threshold value h is defined such that the energy of the current I is limited to a value specified by a protection standard such as IEC 60079-11 (depending on the ignitability of the respective gas groups, e.g., HB, HC).

[0078] The monitoring unit 11 can, for example, comprise – as simplified in FIG. 9 – a comparator 21, an RS flip-flop 22, a delay element 23, and a diode 24. The voltage U is applied to the input of the comparator 21. The output of the comparator 21 is connected to the Set (S) input of the RS flip-flop 22. The output Q of the RS flip-flop 22 is connected via the diode 24 to the control input (Gate) of the semiconductor switch 13. The output Q is also connected via the delay element 23 to the Reset (R) input of the RS flip-flop 22. The comparator 21 compares the voltage U with the first threshold value Ui for the voltage U. If the voltage U is below the threshold value Ui, the comparator 21 generates a low signal (S = 0) at the set input of the RS flip-flop 22, which in turn generates a low signal (Q = 0) at its output Q.This generates a control signal for the control input (gate) of the semiconductor switch 13 such that the semiconductor switch 13 is switched on or switched to allow current flow and thus allows the current I to pass through.

[0079] When the voltage U is above the threshold Ui, comparator 21 generates a high signal (S = 1) at the set input of RS flip-flop 22, which in turn generates a high signal (Q = 1) at its output Q. This creates a drive signal for the control input (gate) of semiconductor switch 13, causing the semiconductor switch 13 to switch off the current I. With the current switched off, the voltage U at the input of comparator 21 drops below the threshold Ui again. Comparator 21 then generates a low signal (S = 0) at the set input of RS flip-flop 22, and RS flip-flop 22 stores the previously set state. At the same time the current flow is switched off, the delay element 23 is started. Only after a delay time defined by the delay element 23 has elapsed is the RS flip-flop 22 reset, i.e. a low signal (Q = 0) is generated again at the output Q and as a result the semiconductor switch 13 is switched on again.In practice, turn-off times of 1 ps and less are possible in the case of a p-channel MOSFET.

[0080] The monitoring unit 12 is designed to monitor for thermal overload by determining the level of utilization of the thermal capacity or thermal reserve of device 1 by the current I, based on the voltage U. The monitoring unit 12 determines the utilization of the thermal capacity or thermal reserve using the measured voltage U values ​​and the duration of these values ​​within two different value ranges. In principle, however, more value ranges are also possible.

[0081] The monitoring unit 12 can include a timer with a capacitor and charges the capacitor when a voltage value U is greater than a second threshold U2, which corresponds to a second threshold I2 (see FIG. 6) for the current I, and discharges the capacitor when a voltage value U is less than the second threshold U2 (see FIG. 6), or alternatively, in the sense of hysteresis, less than a third threshold U3 for the voltage U, which corresponds to a third threshold l3 (see FIG. 8) for the current I. The monitoring unit 12 is also configured to limit the current I to a defined value, for example l2, when a voltage across the capacitor meets a predefined condition (e.g., reaches or exceeds a threshold).

[0082] As simplified in FIG. 10, the monitoring unit 12 can, for example, comprise a capacitor-based integrating controller. This controller includes, for example, a differential amplifier 31 and an integrator 32. The integrator 32, in turn, comprises a capacitor 33 and an electrical resistor 34 connected in parallel. The measurement voltage U is applied to the input of the differential amplifier 31. On the output side, the monitoring unit 12, i.e., the differential amplifier 31 in combination with the integrator 32, generates an output voltage that is proportional to the integral of the measurement voltage U.

[0083] The monitoring unit 12 thus behaves like an integrating controller. When the second threshold U2 for the voltage U (or the second threshold l2 for the current I) across the measuring resistor 6 is exceeded, the integration process begins. This manifests itself as the charging of the capacitor 33, a consequent slow increase in the voltage across the capacitor 33, and consequently a slow increase in the output voltage of the monitoring unit 12. Above a defined threshold, the rising output voltage causes the semiconductor switch 13 to limit the current I. The monitoring unit 12 then controls the semiconductor switch 13 in such a way that the current I is regulated or limited to exactly the second threshold l2 for the current I. This prevents a permanent thermal overload of the connected load 3.

[0084] The slow increase in the output voltage of the monitoring unit 12 described here ensures that short-term currents of the load 3 are not subject to current limiting up to the defined threshold of the output voltage. The currents only need to be below the first threshold h of the current I of the monitoring unit 11.

[0085] The tolerable time during which such short-term currents do not cause a limitation by the monitoring unit 12 can now be selected so that it corresponds to the thermal capacity of the components involved in the load 3 or the device 1, which therefore never heat up impermissibly.

[0086] As soon as the second threshold value l2 for the current (or the second threshold value U2 for the voltage) across the measuring resistor 6 falls below the threshold value again, the capacitor 33 is discharged. A slow decrease in the voltage across capacitor 33 begins, and thus a decrease in the output voltage of the monitoring unit 12. Once a defined threshold value for the output voltage is reached, the control input (gate) of the semiconductor switch 13 is activated such that the semiconductor switch 13 completely removes the current limit and switches to unlimited current flow.

[0087] The second threshold U2 thus divides the voltage U range into two value ranges: a first range with U < U2 and a second range with U >= U2. As long as the voltage U remains in the first value range, the capacitor 33 is not charged, or, in the case of an existing pre-charge, is even discharged via the resistor 34.

[0088] However, as soon as the voltage U reaches or exceeds the threshold value U2, the capacitor 33 is charged for a subsequent period of time in which the voltage U remains in the second value range.

[0089] As a result, depending on the magnitude of the current I or the voltage U and any pre-charge of the capacitor 33, which represents a thermal pre-load of the device 1, there are different time windows within which the current I can flow without limitation by the monitoring unit 12 due to thermal overload of the device 1.

[0090] In FIG. 6, it is assumed by way of example that all current pulses 17 have the same maximum current IM and the same duration T. It is also assumed that the capacitor 33 is completely discharged between two successive current pulses 17, i.e., that there is no thermal preload on the device 1 for each current pulse. This results in time windows of equal length Tm. If a thermal preload on the device 1 already exists for a current pulse 17, i.e., the capacitor 33 already has a precharge, the time window is correspondingly shorter.

[0091] FIG. 7 shows, by way of example, that in addition to the current pulses 17 with maximum current IM, there are also current pulses 18 with a different maximum current l. M' (corresponding to a voltage UM' across the measuring resistor 6) and of different durations. Furthermore, it is assumed that the capacitor 33 is not fully discharged at the beginning of the second current pulse 17, i.e., that the device 1 is already under thermal stress. This results in time windows of different lengths for the current pulses 17 and 18: For the first current pulse, a first time window T results. T Hi, for the second current pulse, an already smaller time window T T h2 and for the third current pulse due to the lower maximum current l M 'an even larger time window T T h3-

[0092] As an alternative to a timer, the second monitoring unit 12, in a digital (microcontroller-based) implementation, can also include a counter (or multiple counters) and be configured to count in a first direction when the voltage values ​​U are equal to or greater than the second threshold U2, and in a second direction, opposite to the first, when the detected voltage values ​​U are less than the second threshold U2 (see FIG. 7), or alternatively less than a third threshold U3 (see FIG. 8). The counting speed increases with the current I and thus the voltage U across the measuring resistor. The second monitoring unit 12 then limits the current I to the defined value when a counter reading meets a predefined condition (e.g., reaches or exceeds a predefined value).

[0093] As shown in FIG. 2, the monitoring device 10 can also have a separate semiconductor switch 13', 13" for each of the monitoring units 11, 12, wherein the semiconductor switches 13', 13" are connected in series in the line 8 in which the current I flows. The monitoring unit 11 controls a control input (gate) of the semiconductor switch 13' and the monitoring unit 12 controls a control input (gate) of the semiconductor switch 13" in the same manner as in the embodiment of FIG. 1.Since the monitoring unit 11, in response to a risk of ignition spark formation, causes the current I to be switched off by means of the semiconductor switch 13', and the monitoring unit 12, in response to an emerging thermal overload, only causes the current I to be limited by means of the semiconductor switch 13", the reaction of the first monitoring unit 11 automatically has priority over the reaction of the second monitoring unit 12 due to the series connection of the semiconductor switches 13', 13".

[0094] As shown in FIG 3, the device 4 for increased safety requirements can also include several monitoring devices 10 described above, at the input of which the voltage U measured at the measuring resistor 6 is applied and whose semiconductor switches 13 or 13', 13" are electrically connected in series in the line connection 8 in which the electric current I flows.

[0095] As shown in FIG 4, increased safety requirements can also be met by an arrangement 15 comprising several devices 4 according to FIG 1-3, each having a device 5 for detecting a quantity representing the electric current I flowing into or in the device 1.

[0096] Further advantages of the invention will now be explained by comparing a prior art solution with a series resistor and a solution using the invention, specifically in the case where device 1 is a battery-operated IoT liquid level meter with a radar sensor and radio-based data transmission in an explosion-proof zone. Key functional parameters:

[0097] Battery nominal voltage 3.6V / lifespan several years

[0098] Continuous power consumption: 2mW (~6mA); short-term power consumption: 2W (~600mA); short-term power consumption (< 1 s), e.g., for radio or radar.

[0099] The following values ​​result for the parameters according to FIG 5-7: T < 1 sl M = 600 mA h = 1 A l2 = 100 mA

[0100] With a monitoring device 10 according to FIG. 1 with monitoring units 11, 12 according to FIG. 9 and 10, a current cut-off can be carried out within a few microseconds in the event of a risk of ignition spark formation. The IoT liquid level meter can therefore also meet the requirements of the ATEX ignition protection type "ia" and be used in ATEX Zone 0.

[0101] The invention thus allows an intrinsically safe power supply for the IoT liquid level measuring device with radar sensor and radio-based data transmission in an explosion-proof zone, whereby, compared to the prior art, only half the battery cells are required, a longer battery life is enabled and smaller components can be used.

[0102] FIG 11 illustrates an exemplary process sequence 40 according to the invention for the intrinsically safe power supply of the device 1 according to FIG 1 :

[0103] In a first step 41, the monitoring device 10 detects the voltage U across the measuring resistor 6 as a quantity that represents the electric current I flowing in the device 1.

[0104] In a second step 42, the device 1 is monitored by the monitoring device 10, based on the detected voltage U, simultaneously for both a risk of ignition spark formation and a developing thermal overload.

[0105] In a third step 43, the monitoring device 10 switches off the current I by means of the semiconductor switch 13 in response to a risk of ignition sparking, or limits the current I by means of the semiconductor switch 13 in response to an emerging thermal overload. The response to the risk of ignition sparking takes priority over the response to the emerging thermal overload.

[0106] In a fourth step 44, after a reaction to the risk of ignition sparking, possibly after a delay time, the shutdown of the semiconductor switch 13 can be lifted, i.e., the semiconductor switch 13 is switched back to current flow, or, after a reaction to the resulting thermal overload and its elimination, the current limiting of the semiconductor switch 13 can be lifted. FIG 12 shows an example of an arrangement of a device 4 according to the invention at a boundary 50 between a non-hazardous area 51 and an hazardous area 52. The device 4 is connected on its input side to a power supply device, here the energy storage device 2. The energy storage device 2 is arranged in the non-hazardous area 51. The load 3 and a load-accepting device 2 are located in the non-hazardous area 51.

[0107] Device 53, on the other hand, is located in the potentially explosive atmosphere 52. The device 4 is connected on its output side to the load 3 or device 53 via electrical connecting lines 54 and supplies it intrinsically safely with the electrical current I from the energy storage device 2.

Claims

Patent claims 1. Device (4) for the intrinsically safe power supply of a device (1), in particular an intrinsically safe device in an explosion-hazardous area with a recurring short-term high power demand, comprising a device (5) for detecting a quantity (II) that is present in the device (1) or in the Device (1) representing flowing electric current (I), at least one monitoring device (10) which is configured, based on the detected quantity (U), to simultaneously monitor the device (1) for both a risk of ignition spark formation and a developing thermal overload and to switch off the electric current (I) in response to a risk of ignition spark formation, characterized in that the monitoring device (10) is configured to limit the current (I) in response to a developing thermal overload.

2. Device (4) according to claim 1, wherein the monitoring device (10) is designed such that, in the event of a simultaneous risk of ignition spark formation and resulting thermal overload, it gives priority to the reaction to the risk of ignition spark formation over the reaction to the resulting thermal overload, in particular by switching off the current.

3. Device (4) according to one of the preceding claims, wherein the monitoring device (10) is configured to monitor the detected quantity (II) for reaching or exceeding a first threshold value (Ui) in order to monitor the device (1) for the risk of ignition spark formation.

4. Device (4) according to one of the preceding claims, wherein the monitoring device (10) is configured to monitor for the resulting thermal overload based on the detected quantity to determine a utilization of a thermal capacity or thermal reserve of the device (1) by the current (I), in particular by means of a timer or a counter.

5. Device (4) according to claim 4, wherein the monitoring device (10) is configured to determine the utilization of the thermal capacity or thermal reserve based on values ​​of the detected quantity (II) and on the dwell times of these values ​​in different value ranges.

6. Device (4) according to claim 4 or 5, wherein the monitoring device (10) comprises a timer with a capacitor (33) and is configured to charge the capacitor (33) when the values ​​are greater than a second threshold (U2) and to discharge it when the values ​​are less than the second threshold (U2) or less than a third threshold (U3).

7. Device (4) according to claim 6, wherein the monitoring device (10) is configured to limit the current (I) to a defined value when a voltage across the capacitor (33) meets a predetermined condition.

8. Device (4) according to one of the preceding claims, comprising several monitoring devices (10), each configured, based on the detected quantity (II), to simultaneously monitor the device (1) for both a risk of ignition spark formation and a developing thermal overload, and to switch off the current (I) in response to a risk of ignition spark formation and to limit the current (I) in response to a developing thermal overload.

9. Arrangement for the intrinsically safe power supply of a device (1), in particular an intrinsically safe device in an explosion-hazardous area with a recurring short-term high power requirement, comprising several devices (4) according to one of the preceding claims, each comprising a device (5) for detecting a quantity (II) that represents the electric current (I) flowing into or in the device (1).

10. Method for the intrinsically safe power supply of a device (1), in particular an intrinsically safe device in an explosion-hazardous area with a recurring short-term high power demand, comprising: Detecting a quantity (U) representing an electric current (I) flowing into or through the device (1), Monitoring the device (1) based on the detected quantity (U) simultaneously for both a risk of ignition spark formation and a developing thermal overload, switching off the current (I) in response to a risk of ignition spark formation and limiting the current (I) in response to a developing thermal overload.

11. Method according to claim 10, wherein, in the event of a simultaneous risk of ignition spark formation and resulting thermal overload, the reaction to the risk of ignition spark formation has priority over the reaction to the resulting thermal overload, in particular the current is switched off.

12. Method according to one of claims 10 to 11, wherein, in order to monitor the device (1) for the risk of ignition spark formation, the detected quantity (II) is monitored to reach or exceed a first threshold value (Ui).

13. Method according to one of claims 10 to 12, wherein, for monitoring the device (1) for the resulting thermal overload, the utilization of a thermal capacity or thermal reserve of the device (1) is determined by the current (I) based on values ​​of the detected quantity (II), in particular by means of a timer or a counter.

14. Method according to claim 13, wherein the utilization of the thermal capacity or thermal reserve is determined based on the values ​​and on the dwell times of the values ​​in different value ranges.

15. Method according to claim 13 or 14, wherein a timer with a capacitor (33) is used to monitor the device (1) for the resulting thermal overload, wherein the capacitor (33) is charged when the values ​​are greater than a second threshold (U2) and discharged when the values ​​are less than the second threshold (U2) or less than a third threshold (U3).

16. Method according to claim 15, wherein the current (I) is limited to a defined value when a voltage across the capacitor (33) satisfies a predetermined condition.

17. Intrinsically safe device (1), in particular an intrinsically safe field device for measuring or influencing a process variable, comprising a power supply device (2), an electrical load (3) and a device (4) according to one of claims 1 to 8 or an arrangement (15) according to claim 9, wherein the device (4) or the arrangement (15) is connected in an electrical connection (8) between the power supply device (2) and the electrical load (3).

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