DE102018205824B4 - Capacitor arrangement with voltage-dependent switchable capacitor units, level gauge and power supply unit with this capacitor arrangement and use of the power supply unit in a level gauge, a flowmeter or a point level sensor. - Google Patents

Abstract

Capacitor arrangement comprising a capacitor unit K1, with a capacitor C1 and a control element Reg1 with a switch S1. In this case, the capacitor C1 and the switch S1 of the control element Reg1 are connected in series and to the capacitor unit K1 is an operating voltage U (B). Furthermore, the control element Reg1 is designed to close the switch S1 when the operating voltage U (B) is equal to or less than a maximum voltage Ulmax of the capacitor, and to open the switch when the operating voltage U (B) the maximum voltage Ulmax of the capacitor C1 exceeds. Furthermore, the capacitor arrangement has a capacitor C0, wherein the capacitor unit K1 is connected in parallel with the capacitor C0, so that the capacitor unit K1 and the capacitor C0 form a total capacitance C (total) of the capacitor arrangement.

Description

Capacitor arrangement with voltage-dependent switchable capacitor units, level gauge and power supply unit with this capacitor arrangement and use of the power supply unit in a level gauge, a flowmeter or a point level sensor.

Technical area

The present invention relates to power supply assemblies for level measuring devices, for example for measuring levels in containers. In particular, the invention relates to a capacitor arrangement for a power supply unit of a level gauge, a level gauge, a power supply unit and a use.

Background of the invention

Level measurement devices require a supply voltage or operating voltage for stable operation and for supplying the electrical and electronic components, which can be provided separately via, for example, a power supply or a separate power supply device. In many cases, to simplify the construction and to reduce the necessary number of connection lines, an operating voltage is provided together with other control signals or measuring signals, for example on a two-wire or four-wire line. In many cases, this input voltage U (E) is an alternating voltage which is converted into a DC voltage via rectifiers, for example via diode arrangements. At the output of this rectifier, a ripple DC voltage is generated, which is smoothed by means of buffer capacitors. This means that the buffer effect of the capacitors reduces or ideally eliminates voltage fluctuations so that the DC voltage is as constant as possible. Furthermore, capacitors are used to store energy for subsequent circuit parts with limited input power, which may have a temporarily higher than the input power power consumption.

Often, the input voltages U (E) at which a level gauge is operated in practical use are not known in advance or may be subject to large variations. For example, two-wire devices can be operated in an input voltage range of 10-36 VDC (DC voltage). Four-wire devices are often operated with alternating voltages of up to 230 VAC. Consequently, in the level measuring device, the components of the power supply units must be designed for the maximum possible input voltages U (E). This concerns in particular a dielectric strength of the components. Exceeding a maximum allowable voltage may cause destruction or damage to these components.

Solutions are known in the prior art where, for example, the input voltage U (E) is first converted to a constant higher operating voltage U (B), which lies above the maximum input voltage U (E). The subsequent circuit in the power supply unit can then operate with a constant, known operating voltage U (B). For lower input voltages U (E), however, this can have disadvantages since, in particular, the capacitors can not provide sufficient capacity to smooth the undulating voltage or to compensate for fluctuations in the power consumption. The reason for this is that at the higher voltages present here, assuming the same assumed capacitance, a size of the capacitor increases significantly. Since, for example, fill level measuring devices should be designed to be as small and space-saving as possible, it is accordingly desirable to make the power supply units spatially smaller, in particular.

The document DE 198 57 540 A1 describes a mobile radio communication device with a capacitor which is connectable via a first switch to a power supply.

The document DE 10 2015 225 297 A1 describes a level gauge with at least two functional units. Furthermore, the document discloses capacitor arrangement with a first and a second capacitor, between which a switch of a decoupling circuit is arranged.

The document WO 2008 125 527 A1 describes a field device with a sensor and a communication unit, for transferring a current measured value to the respective network.

Presentation of the invention

The object of the invention is defined by the independent claims. Embodiments of the invention may advantageously reduce the size and cost of a power supply unit of a level gauge. The invention described below is based on the following considerations: The size of a power supply unit is determined in particular by the size of the buffer capacitors. These are often designed as electrolytic capacitors, wherein the storable energy is proportional to the capacitance and the square of the voltage. A Minimum capacity of the buffer capacitor must therefore be designed for the lowest operating voltage U (B). This means that a lower capacitance of the capacitor increases, the lower the operating voltage U (B).

At the same time, the size of a capacitor results in capacity and maximum operating voltage. In other words, with the same capacitor technology, the capacitor volume is approximately proportional to the storable electrical energy. Due to their design, capacitors are designed for a certain maximum dielectric strength, referred to below as the maximum voltage. Here, a doubling of the maximum voltage means about a quadrupling of the volume at the same capacity. This is of particular importance for the space requirement of the capacitor and consequently for the size of the power supply unit.

One aspect relates to a fill level measuring device for detecting a fill level in a container that has a power supply unit with a capacitor unit K1 having. The condenser unit K1 has a capacitor C1 with a maximum voltage U1max and a rule element reg1 with a switch S1 on. Here are the capacitor C1 and the switch S1 of the control element reg1 connected in series. At the switch S1 It may be both an electronic switch, as well as a continuously controllable electronic component or an actuator. Over the entire capacitor unit, so the capacitor C1 and the switch S1 , is an operating voltage U (B) at. The rule element reg1 is executed, the switch S1 close when the operating voltage U (B) is equal to or less than the maximum voltage U1max of the capacitor C1 , Furthermore, the control element opens reg1 the switch S1 when the operating voltage U (B) the maximum voltage U1max of the capacitor C1 exceeds. The capacitor C1 may be embodied in various ways, for example as an electrolytic capacitor, but also in any other embodiments. The desk S1 has the function to separate the capacitor circuitry from the operating voltage or another power supply or power supply. The purpose here is primarily to prevent a possible destruction or damage to the capacitor due to excessive voltages.

The rule element reg1 is executed, the switch S1 to close or open. In this case, the control element detects or measures reg1 an absolute or relative level of the operating voltage U (B) , This can be for example the direct measurement or detection of the operating voltage U (B) mean, but also an indirect measurement, for example via voltage dividers or similar mechanisms. As an advantage can be seen here that the operating voltage U (B) when the maximum voltage is exceeded U1max from the condenser C1 is disconnected. As a result, the capacitor is protected from excessive voltages and thus from damage or destruction. In other words, an operating voltage U (B) a withstand voltage of a capacitor implemented in, for example, a power supply unit C1 exceed and still a capacitor C1 be used with lower dielectric strength.

Remains the operating voltage U (B) under the maximum voltage U1max , is the capacitor C1 thus by the closed switch S1 connected to the operating voltage and can contribute as a buffer capacitor for smoothing the DC voltage. In case of exceeding the capacity of the capacitor C1 disconnected from the circuit and thus does not contribute further to the smoothing of the DC voltage. According to one example, the rule element is reg1 and the switch S1 in the condenser C1 structurally or spatially integrated. Advantage of this arrangement can be a space-saving design and simplified implementation in a circuit.

According to one embodiment, the capacitor unit K1 the power supply unit of the level gauge on a pre-charging voltage source. This precharge voltage source provides a precharge voltage U (VL) to charge the capacitor C1 ready. This precharge voltage U (VL) is less than or equal to the maximum voltage U1max of the capacitor C1 , This precharge voltage source can be designed, for example, independently of the operating voltage U (B). In one example, the precharge voltage source is configured as a capacitor or back-up battery that may be powered, for example, via a two-wire or four-wire line of a field bus. Advantage of a pre-charge voltage source may be, for example, that the capacitor C1 can be brought into a charged state, even if this example by an open switch S1 not with the operating voltage U (B) connected is. This can be done when closing the switch S1 the stored energy in the capacitor C1 immediately available to a connected consumer.

In one embodiment, the switch S1 of the control element reg1 designed as a field effect transistor in open-drain circuit. Such metal oxide field effect transistors can be a very simple and inexpensive implementation, especially as they can approach in their electrical properties of an actual physical separation, for example by a mechanical switch, by high ohmic resistance in the locked state. At the same time they have Transistors in a conductive state in the source-drain direction has an advantageously low on resistance.

In one embodiment, the control element reg1 for evaluating the operating voltage U (B) a comparator circuit. A comparator circuit is characterized in that an output variable can be controlled in dependence on a comparison between two voltages. In the present case, the comparator circuit compares directly or indirectly the operating voltage U (B) with a reference value. This reference value can be, for example, the maximum voltage U1max of the capacitor C1 be. For example, if the comparator circuit detects that the operating voltage U (B) above the maximum voltage U1max is located, the comparator circuit controls the switch S1 to open and thus separates the capacitor from the excessively high operating voltage U (B) , In one embodiment, the control element Reg1l and the switch S1 configured to charge and / or discharge the capacitor C1 to regulate.

According to one aspect of the invention, a capacitor unit K1 proposed that a capacitor C1 with a maximum voltage U1max and a rule element reg1 with a switch S1 having. Here are the capacitor C1 and the switch S1 of the control element reg1 connected in series. Over the entire capacitor unit, so the capacitor C1 and the switch S1 , is an operating voltage U (B) at. The rule element reg1 is executed, the switch S1 close when the operating voltage U (B) is equal to or less than the maximum voltage U1max of the capacitor C1 , Furthermore, the control element opens reg1 the switch S1 when the operating voltage U (B) the maximum voltage U1max of the capacitor C1 exceeds. The embodiments described above and below with regard to the condenser unit of the power supply unit of the level measuring device also apply correspondingly to the condenser unit described here.

According to one aspect of the invention, a capacitor arrangement is proposed which comprises at least one capacitor unit K1 and another capacitor C0 with a maximum voltage U0max having. The condenser unit K1 is to the capacitor C0 connected in parallel, so that the capacitor unit K1 and the capacitor C0 form a total capacitance C (total) of the capacitor array. This is true in the event that U (B) Smaller or equal U1max is. is U (B) greater than U1max that's just how it is C0 effective. The maximum voltage U1max of the capacitor C1 the condenser unit K1 is chosen smaller than the maximum voltage U0max of the capacitor C0 , By means of this exemplary embodiment, for example, a cascade of capacitors connected in parallel can be made possible, whereby depending on the level of the operating voltage U (B) one or more capacitor units K1 . K2 , .. switch on or switch off. This is especially in the range of higher operating voltages U (B) interesting, where even smaller capacities can cause sufficient smoothing / buffering of the DC voltage. This means that smaller designs can be used. In the range of lower voltages, for example in the range of 10-16 VDC, is the capacity C1 the parallel connected capacitor unit K1 Active and thus allows effective buffering and smoothing of the DC voltage. In the range of for example 16-24VDC is the capacity C2 the parallel connected capacitor unit K2 Active and thus allows effective buffering and smoothing of the DC voltage. In the range of voltages greater than 24VDC is only the capacity C0 active. The preceding and subsequently described embodiments with regard to the condenser unit of the level measuring device also apply correspondingly to the capacitor arrangement described here.

Another aspect relates to a power supply unit comprising a capacitor arrangement of one or more capacitor elements K1 . K2 , ... and one or more parallel capacitors C0 . C1 . C2 , .... having.

Another aspect relates to a use of the power supply unit in a level gauge, a pressure gauge, a flowmeter or a point level sensor.

list of figures

• 1 zeigt in vereinfachter Darstellung ein Füllstandmessgerät mit einer Stromversorgungseinheit und einer Zweidrahtleitung.
• 2 zeigt eine Stromversorgungseinheit mit einem Pufferkondensator und Verbraucher.
• 3 zeigt eine Kondensatoreinheit K1 mit einem Regelelement Reg1 und einem Pufferkondensator gemäß der Erfindung.
• 4 zeigt eine Kondensatoranordnung mit mehreren Kondensatoreinheiten und einem parallel geschalteten Pufferkondensator.
• 5 zeigt ein Ausführungsbeispiel einer Stromversorgungseinheit eines Füllstandmessgerätes mit einer Vorladespannungsquelle und Diode.

Embodiments will now be described in detail with reference to the accompanying drawings. Neither the description nor the figures are to be construed restrictively.

• 1 shows a simplified representation of a level measuring device with a power supply unit and a two-wire line.
• 2 shows a power supply unit with a buffer capacitor and consumer.
• 3 shows a capacitor unit K1 with a rule element reg1 and a buffer capacitor according to the invention.
• 4 shows a capacitor arrangement with a plurality of capacitor units and a parallel-connected buffer capacitor.
• 5 shows an embodiment of a power supply unit of a level measuring device with a pre-charging voltage source and diode.

The drawings are only schematic and not to scale. Basically, identical or similar parts are provided with the same reference numerals.

Detailed description of the figures

In 1 is in a simplified way a level gauge 10 for measuring a level 12 in a container 14 shown. In the example shown here is a radar-based level gauge 10 shown radiating high-frequency electromagnetic waves in the direction of a surface of a product, which receives reflected signals and by running time measurement a level 12 in the container 14 determined. For operating the level gauge 10 is a power supply unit 16 intended. An input voltage U (E) or supply voltage for the level gauge 10 is over a two-wire line 18 provided. In addition to the supply voltage, other control data or measurement data can also be transmitted via this two-wire cable. For example, these may be implemented via the known 4-20mA standard.

In 2 is a power supply or power supply unit 16 shown. An input voltage U (E) For example, it may be an alternating voltage that is connected to the diodes via a rectifier circuit D1 to D4 is converted into a DC voltage. This DC voltage usually has a wavy shape at the output of a rectifier circuit over time. However, this wavy shape is unfavorable for subsequent components and assemblies, since a DC voltage as constant as possible is needed for error-free operation. This is usually a capacitor C0 between a positive pole 20 the circuit and a negative pole 22 or ground connected. This may be, for example, an electrolytic capacitor which, depending on the application, has a correspondingly adequate capacitance in the microfarad region. The at the output of the power supply unit 16 available smoothed operating voltage U (B) is a consumer R , shown here as resistance available.

With regard to the dimensioning of the buffer capacitor C are due to the physical relationship between capacitance and voltage for the same stored energy at lower operating voltages U (B) provide higher capacities for buffering and smoothing. In contrast, at higher input voltages U (B) , For example, in the range of 200-250 V smaller capacity sufficient, but they must have sufficient dielectric strength for this voltage range. However, this dielectric strength requires a higher volume of the capacitor C , In order to cover the entire expected voltage range, so must in previous solutions, the dielectric strength of the capacitor C0 to the maximum operating voltage U (B) be interpreted. Furthermore, in previous solutions, the capacitance of the capacitor C0 to the minimum operating voltage U (B) be interpreted.

In 3 becomes an embodiment of a capacitor unit K1 shown at the one load resistor R is switched as a consumer. A rule element reg1 with a switch S1 is in series with a buffer capacitor C1 connected. The rule element reg1 is executed, an operating voltage U (B) to detect or to measure their height. For this purpose, for example, on the control element reg1 separate taps to the positive pole 20 and to the negative pole 22 be provided. The rule element reg1 closes the switch S1 if an operating voltage U (B ) less than or equal to a maximum voltage U1max of the capacitor C1 is recognized. The control element opens accordingly reg1 the switch S1 when the operating voltage U (B) is greater than the maximum voltage U1max of the capacitor C1 , In other words, the capacitor C1 from the operating voltage U (B) separated, which is advantageous damage to the capacitor C1 can be prevented by excessive voltage. This can, even if the operating voltage U (B) is higher than the dielectric strength of the capacitor C1 structurally smaller design variants of the capacitor C1 be used at the same capacity.

In 4 is a capacitor arrangement of a capacitor unit K1 , a parallel connected capacitor unit K2 and a capacity connected in parallel thereto C0 shown. The condenser unit K1 has a capacitor C1 up, correspondingly, the condenser unit points K2 a capacitor C2 on. A load resistor R at which the operating voltage U (B) is intended to clarify a consumer. The capacitor arrangement is supplemented by an optional power source SR1 , which regulates and limits the load current or the charging currents for the capacitors C0 to C2 can cause. With the capacitor units K1 and K2 are the respective dielectric strength or maximum voltages U1max and U2max in each case on the operating voltage-dependent switching times of the control elements reg1 and reg2 Voted.

A maximum voltage U1max the condenser unit K1 is less than a maximum voltage U2max the condenser unit K2 selected. With increasing operating voltage U (B) opens at the voltage U1max first the rule element reg1 the condenser unit K1 the switch S1 , With further increasing operating voltage U (B) then opens the rule element reg2 at the tension U2max the switch S2 , The capacity of the capacitor C0 is available over the entire voltage range due to the fixed connection. In other words, one reduces the load resistance R Total effective capacity C (total) of parallel capacities C0 . C1 . C2 by the gradual shutdown of the individual capacitors C1 and C2 , The parallel connection from the capacitor C0 and the condenser unit K1 and K2 can be used as a capacitor arrangement 26 be understood, with closed switches S1 and S2 the capacities of the capacitors C0 . C1 and C2 to make a total capacity C (total). The control element may be implemented with a comparator IC or may be constructed discretely with diodes and transistors.

5 shows an embodiment of a power supply unit 16 a level gauge 10 with a precharge voltage source 28 , The precharge voltage source 28 delivers at its exit 30 a precharge voltage U (VL) for the capacitor C1 that are below the maximum voltage U1max of the capacitor C1 lies. The rule element reg1 is together with the switch S1 as a diode DS executed. At the exit 30 the precharge voltage source 28 For example, there is a constant precharge voltage U (VL) on the capacitor C1 to disposal. Consequently, over the reverse-biased diode DS the differential voltage to the operating voltage U (B) on, and the diode DS is locked. Now drops the operating voltage U (B) below the value of the precharge voltage U (VL) , opens the diode DS and the capacitor C1 can store its stored energy directly to the consumer R submit. This has the advantage that a stored electrical energy of the capacitor C1 immediately available and no intermediate charging over the positive pole 20 the operating voltage UB must take place.

In the described embodiments are the control elements reg1 . reg2 , ... as a two-position controller and the control elements S1 . S2 , ... each as a switch. The control and adjusting elements can also be designed as continuously or stepwise modifiable assemblies. This would be a continuous or gradual adjustment of the charging and discharging of the capacitors C1 . C2 possible.

Claims (8)

Capacitor assembly comprising: a capacitor unit K1, comprising: a capacitor C1 having a maximum voltage Ulmax; and a control element Reg1 with a switch S1, wherein the capacitor C1 and the switch S1 of the control element Reg1 are connected in series and to the capacitor unit K1 an operating voltage U (B) is applied, wherein the control element Reg1 is designed to close the switch S1 when the operating voltage U (B) is equal to or less than the maximum voltage Ulmax of the capacitor, and to open the switch when the operating voltage U (B) the maximum voltage Ulmax of the capacitor C1 exceed; and a capacitor C0 having a maximum voltage U0max, wherein the capacitor unit K1 is connected in parallel to the capacitor C0 so that the capacitor unit K1 and the capacitor C0 form a total capacitance C (total) of the capacitor arrangement, wherein the maximum voltage Ulmax of the capacitor C1 is set smaller than the maximum voltage U0max of the capacitor C0. Level measuring device (10) with a capacitor arrangement according to Claim 1 for detecting a level (12) in a container (14). Level gauge (10) according to Claim 2 , further comprising - a precharge voltage source (28) arranged to provide a precharge voltage U (VL) for charging the capacitor C1; wherein the precharge voltage U (VL) is less than or equal to the maximum voltage Ulmax of the capacitor C1. Level gauge (10) according to one of Claims 2 or 3 , wherein the switch S1 of the control element Reg1 is designed as a field effect transistor FET in open-drain circuit. Level gauge (10) according to one of Claims 2 to 4 , wherein the control element Reg1 for evaluating the operating voltage U (B) comprises a comparator circuit KS. Level gauge (10) according to one of Claims 2 to 5 wherein the control element Reg1 and the switch S1 are configured to control the charging and / or discharging current of the capacitor C1. Power supply unit, comprising a capacitor arrangement according to Claim 1 , Using the power supply unit according to Claim 7 in a level gauge, a pressure gauge, a flowmeter or a level sensor.

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