Voltage limiting circuit and field device comprising such voltage limiting circuit

Abstract

The invention relates to a voltage limiting circuit (1, 201) for protection type'ia ', comprising exactly two monolithic voltage limiting modules (40a, 40b, 240a, 240b), each voltage limiting module (40a, 40b, 240a, 240b) having: a supply voltage connection (50, 252); the circuit is grounded; a voltage divider (46a, 46b, 246a, 246b) for providing a voltage divider voltage, the voltage divider (46a, 46b, 246a, 246b) being arranged between a supply voltage connection and a circuit ground; a controller (48a, 48b; 248a, 248b) having a control signal output unit for outputting a control signal; and an actuator (45a, 45b, 245a, 245b) having an actuator signal input and a current channel, a resistance value of the actuator being based on a control signal applied to the actuator signal input, in which the current channel extends in parallel with the voltage divider between a supply voltage connection and a circuit ground, and an input of the controller (48a, 48b, 248a, 248b) is supplied with a voltage divider voltage of the voltage divider (46a, 46b, 246a, 246b). The control signal output portion is connected to the actuator signal input portion. In particular, the supply voltage connection (252) and the circuit ground connection of the two voltage limiting modules (40a, 40b; 248a, 248b) should be arranged in parallel with the supply voltage source (250).

Description

Field of the Invention

[0001] The present invention relates to a voltage limiting circuit and a field device for process automation technology comprising such a voltage limiting circuit. Background Art

[0002] Field devices for recording and / or modifying process variables are frequently used in process automation technology. Sensors, such as level measurement devices, flow meters, pressure and temperature measurement devices, pH redox potentiometers, conductivity meters, etc., are used to record corresponding process variables, such as level, flow, pressure, temperature, pH level, and conductivity. Actuators, such as for example valves or pumps, are used to influence the process variables. Thus, it is possible to change the flow rate of a fluid in a pipe section or the level in a container by means of an actuator. In principle, all devices that are used in a process and provide or process process-related information are referred to as field devices. In the context of the present invention, field devices also include remote I / O, radio adapters, and / or devices that are generally arranged at the field level. Many field devices are so-called 2-wire devices. The field device is powered via the same pair of lines (two-wire line) for communication (in particular for measured values). In process automation technology, physical or technical parameters often have to be measured or determined by field devices in potentially explosive areas, which have an explosion risk due to process media. By means of appropriate measures in the field device and the evaluation system (for example, voltage and current limitation), the electrical power of the signal to be transmitted can be limited so that it does not trigger an explosion under any circumstances (short circuit, interruption, thermal effects, etc.). For this purpose, for example, corresponding protection principles are defined in IEC EN DIN60079-ff. According to this standard, the design and circuit measures of field devices used in potentially explosive areas are defined based on the type of ignition protection to be applied. One of these types of ignition protection represents the ignition protection type "intrinsic safety" (identification code Ex-i, IEC EN DIN 60079-11, published in June 2012). The ignition protection type "intrinsic safety" is based on the principle of limiting current and voltage in the circuit. The power in the circuit that can ignite the explosive environment is limited, so that the surrounding explosive environment is not ignited by sparks or inadmissible heating of electrical components.

[0003] The ignition protection type "intrinsic safety" defines three protection levels: Ex-ia, Ex-ib, and Ex-ic. In this case, the highest level is defined by level a, where two countable fault combinations do not cause the device to malfunction and thus cause ignition (2-fault safety). Level b defines that one countable fault does not cause the device to malfunction and thus cause ignition (1-fault safety). In the case of level c, no fault safety is defined, so ignition can already be triggered in the event of a single device malfunction (0-fault safety). Circuit-related measures for implementing intrinsic safety usually include current limitation, voltage limitation, and associated power limitation, which are typically achieved by limiting the circuit in a triple-redundancy configuration. For example, such a voltage-limiting circuit is disclosed in DE 10 2006 056 591 A1.

[0004] The disadvantage of triple-redundancy limiting circuits is that, on the one hand, they increase the space requirements, and on the other hand, the power consumption is relatively high. The object of the present invention is to make up for this. Summary of the Invention

[0005] According to the present invention, this object is achieved by a voltage-limiting circuit according to claim 1 and a field device according to claim 10.

[0006] The voltage-limiting circuit according to the present invention is a voltage-limiting circuit for the ignition protection type "ia", which includes exactly two monolithic voltage-limiting modules. Each voltage-limiting module has: a supply voltage connection; a circuit ground connection; a voltage divider for providing a voltage-divider voltage, where the voltage divider is arranged between the supply voltage connection and the circuit ground; a controller having a control signal output for outputting a control signal; an actuator having an actuator signal input and a current path, the resistance value of the actuator being based on the control signal applied to the actuator signal input, where the current path extends parallel to the voltage divider between the supply voltage connection and the circuit ground, where the input of the controller is supplied with the voltage-divider voltage of the voltage divider, and where the control signal output is connected to the actuator signal input. In particular, the supply voltage connections and the circuit ground connections of the two voltage-limiting modules are arranged in parallel with a supply voltage source.

[0007] In a further development of the present invention, the actuator includes a transistor, and the actuator signal input includes the base connection of a bipolar transistor or the gate connection of a field-effect transistor.

[0008] In a further development of the present invention, each voltage-limiting module further has a freewheeling diode, which is connected in parallel with the current path of the actuator.

[0009] In a further development of the invention, the controller comprises an operational amplifier and a reference voltage source, in particular a bandgap voltage reference, wherein a first input of the operational amplifier is supplied with the voltage of a voltage divider, wherein a second input of the operational amplifier is connected to the reference voltage source, and wherein an output of the operational amplifier is a control signal output.

[0010] In a further development of the invention, the voltage limiting modules each also have a resistive element which is arranged between the control signal output and the supply voltage connection.

[0011] In a further development of the invention, the voltage limiting modules each have a base area of not more than 18 mm 2 , in particular not more than 12 mm 2 in area.

[0012] In a further development of the invention, the actuator has the largest area share among all the functional elements of the voltage limiting module.

[0013] In a further development of the invention, the transistors of the voltage limiting module each have a barrier layer, wherein the temperature of the barrier layer does not exceed 150 °C when the ambient temperature of the voltage limiting circuit is up to 85 °C and the power consumption of the voltage limiting component is up to 1.4 W each.

[0014] In a further development of the invention, the transistors of the voltage limiting module each have a barrier layer, wherein the power-related temperature rise of the barrier layer does not exceed 60 °C / W, in particular not more than 45 °C / W, when the ambient temperature of the voltage limiting circuit is up to 85 °C and the power consumption of the voltage limiting module is up to 1.4 W each.

[0015] A field device for process automation technology according to the invention comprises: a sensor; a measurement and operation circuit for operating the sensor and for processing signals from the sensor; and a power supply circuit having a supply voltage source for supplying power to the measurement and operation circuit and a voltage limiting circuit according to any one of the preceding claims, wherein the voltage limiting module is connected in parallel with the supply voltage source. Description of the Drawings

[0016] The invention will now be explained in more detail on the basis of exemplary embodiments shown in the drawings. In the drawings:

[0017] Figure 1 is a schematic representation of a field device having a voltage control circuit according to the prior art;

[0018] Figure 2 is a schematic representation of an exemplary embodiment of a field device according to a first exemplary embodiment of a voltage control circuit according to the invention; and

[0019] Figure 3 It is a schematic representation of an exemplary embodiment of a field device according to a second exemplary embodiment of a voltage control circuit according to the present invention. Detailed Description

[0020] Figure 1 The prior art field device shown in the figure includes a power supply circuit 150, a voltage limiting circuit 140, a measurement and operation circuit 170, and a sensor 180, which is operated by the measurement and operation circuit 170, where the latter receives and processes the measurement signal from the sensor 180. The voltage limiting circuit 140 includes three discretely structured voltage limiting modules 140a, 140b, 140c, which are connected in parallel with the measurement and operation circuit to the power supply voltage connection 152 of the power supply circuit 150. The discrete structure of the voltage limiting modules requires a triple redundant configuration to comply with the explosion protection class "ia". Each of the voltage limiting modules 140a, 140b, 140c includes transistors 145a, 145b, 145c as actuators, the current channels of which extend between the power supply voltage connection 152 and the circuit ground. The base of the power supply voltage is connected to the output of controllers 148a, 148b, 148c via resistance elements 160a, 160b, 160c, and the controllers here have controllable voltage sources 142a, 142b, 142c. The control signal of the voltage source is provided from the output or center tap of voltage dividers 146a, 146b, 146c. The voltage limiting circuit 140 achieves its purpose, but the disadvantage is that the discretely structured voltage limiting modules 140a, 140b, 140c with an area of 36 mm each result in a large total space requirement of 108 mm. 2 The discretely structured voltage limiting modules 140a, 140b, 140c of which each has an area of 36 mm result in a large total space requirement of 108 mm. 2 In addition, the resistance elements 160a, 160b, 160c help to limit the base current of the transistors 145a, 145b, 145c within the power consumption range of the voltage limiting circuit 140.

[0021] The present invention is based on Section 7.5.2, parallel voltage limiter circuit, of the IEC EN DIN 60079-11 standard published in June 2012. According to this section, a dual redundant configuration of the voltage limiting circuit is acceptable if, in each case, there are two voltage limiting modules of a monolithic design fully implemented using semiconductor technology. This allows minimizing both the space requirement and the power consumption of the voltage limiting circuit.

[0022] Figure 2An exemplary embodiment of a field device 1 according to the invention with a voltage limiting circuit 40 according to the invention as shown includes a power supply circuit 50, a voltage limiting circuit 40, a measurement and operation circuit 70, and a sensor 80, which is operated by the measurement and operation circuit 70, where the latter receives and processes measurement signals from the sensor 80. The voltage limiting circuit 40 includes only two monolithic voltage limiting modules 40a, 40b using semiconductor technology, which are connected in parallel with the measurement and operation circuit to the power supply voltage connection 52 of the power supply circuit 50. The monolithic implementation of the voltage limiting module enables a dual redundant configuration to meet the explosion protection class "ia". The voltage limiting modules 40a, 40b each include transistors 45a, 45b as actuators, whose current channels extend in parallel between the power supply voltage connection 52 and the circuit ground, and whose bases are connected to the outputs of controllers 48a, 48b, which here have adjustable parallel voltage controllers 42a, 42b. The control signals for the parallel voltage controllers are provided by the outputs or center taps 47a, 47b of voltage dividers 46a, 46b, which are also connected in parallel between the power supply voltage and the circuit ground. In the case of the voltage rising above the target value, the current flowing through the transistors 45a, 45b is increased by controlling the bases of the transistors until the voltage drops back to the target value again.

[0023] Here, the voltage limiting modules 40a, 40b are designed such that at a power consumption of 1.4 W (which corresponds to 1.5 times the maximum possible power to be disposed of), and at an ambient temperature of 85 °C, the barrier layer of the transistors does not exceed a temperature of 150 °C. In addition, the voltage limiting modules 40a, 40b are designed such that the current channels can carry a current of 150 mA, which corresponds to 1.5 times the maximum possible current. This is achieved in particular by the fact that the transistors 45a, 45b each have a relatively large area share in the total area of the voltage limiting modules 40a, 40b. The voltage limiting modules 40a, 40b can each be implemented with a substrate area of 9 mm². Since only two such voltage limiting modules are required, the substrate area of the entire voltage limiting circuit 40 is only 18 mm 2 , which corresponds to one-sixth of the substrate area of a discrete structured voltage limiting circuit according to the prior art. The voltage limiting modules each further include freewheeling diodes 60a, 60b, which can reduce voltage surges opposite to the polarity of the power supply voltage, such as voltage surges caused by inductance.

[0024] Figure 3An exemplary embodiment of the field device 201 according to the invention with a voltage limiting circuit 240 according to the invention as shown includes a power supply circuit 250, a voltage limiting circuit 240, a measurement and operation circuit 270, and a sensor 280, which is operated by the measurement and operation circuit 270, where the latter receives and processes the measurement signal from the sensor 280. The voltage limiting circuit 240 includes only two monolithic voltage limiting modules 240a, 240b using semiconductor technology, which are connected in parallel with the measurement and operation circuit to the power supply voltage connection 252 of the power supply circuit 250. The monolithic implementation of the voltage limiting module enables a dual redundant configuration to meet the explosion protection class "ia". Each of the voltage limiting modules 240a, 40b includes field effect transistors 245a, 245b as actuators, whose current channels extend in parallel between the power supply voltage connection 252 and the circuit ground, and whose gates are connected to the output parts of controllers 248a, 248b, which here have operational amplifiers 242a, 42b. The input signal of the first input part of the operational amplifier is provided by the output part or the center tap 247a, 247b of voltage dividers 246a, 246b, which are also connected in parallel between the power supply voltage and the circuit ground. At the second input part of the operational amplifiers 248a, 248b, there are voltage reference signals 244a, 244b, which are particularly provided by a bandgap voltage reference. In the case where the voltage rises above the target value, the current flowing through the field effect 245a, 245b is increased by controlling the gates of the transistors until the voltage drops back to the target value again.

[0025] Here, the voltage limiting modules 240a, 240b are designed such that at a power consumption of 1.4 W (which corresponds to 1.5 times the maximum possible power to be handled), and at an ambient temperature of 85 °C, the barrier layer of the transistors does not exceed a temperature of 150 °C. In addition, the voltage limiting modules 240a, 240b are designed such that the current channels can carry a current of 150 mA, which corresponds to 1.5 times the maximum possible current. This is achieved in particular by the case where each of the transistors 245a, 245b has a relatively large area share in the total area of the voltage limiting modules 240a, 240b.

[0026] Each of the voltage limiting modules 240a, 240b can be implemented with a substrate area of 9 mm². Since only two such voltage limiting modules are required, the substrate area of the entire voltage limiting circuit 240 is only 18 mm 2 , which is approximately one-sixth of the substrate area of the voltage limiting circuit according to the prior art. Each of the voltage limiting modules also includes freewheeling diodes 260a, 260b, which can reduce voltage surges opposite to the power supply voltage polarity, such as voltage surges caused by inductance.

Claims

1. A voltage limiting circuit (1; 201) for an ignition protection type "ia", comprising exactly two monolithic voltage limiting modules (40a, 40b; 240a, 240b), Among them, Each voltage limiting module (40a, 40b; 240a, 240b) has: A supply voltage connection (52; 252); A circuit ground connection; A voltage divider (46a, 46b; 246a, 246b) for providing a voltage divider voltage, wherein the voltage divider (46a, 46b; 246a, 246b) is arranged between the supply voltage connection and the circuit ground; A controller (48a, 48b; 248a, 248b) having a control signal output for outputting a control signal; An actuator (45a, 45b; 245a, 245b) having an actuator signal input and a current path, the resistance value of the actuator being based on the control signal applied to the actuator signal input, Wherein the current path extends parallel to the voltage divider between the supply voltage connection and the circuit ground, Wherein the input of the controller (48a, 48b; 248a, 248b) is provided with the voltage divider voltage of the voltage divider (46a, 46b; 246a, 246b), Wherein the control signal output is connected to the actuator signal input, Wherein, in particular, the supply voltage connection (252) and the circuit ground connection of the two voltage limiting modules (40a, 40b; 248a, 248b) are arranged in parallel with a supply voltage source (250).

2. The voltage limiting circuit according to claim 1, Among them, The actuator includes a transistor, Wherein the actuator signal input includes the base connection of a bipolar transistor or the gate connection of a field effect transistor.

3. The voltage limiting circuit according to claim 1 or claim 2, wherein, Each of the voltage limiting modules further has a freewheeling diode connected in parallel with the current path of the actuator.

4. The voltage limiting circuit according to claim 1, 2 or 3, wherein The controller includes an operational amplifier and a reference voltage source, Wherein the first input of the operational amplifier is provided with the voltage divider voltage of the voltage divider, Wherein the second input of the operational amplifier is connected to the reference voltage source, and Wherein the output of the operational amplifier is the control signal output.

5. The voltage limiting circuit according to claim 1 or claim 2, wherein, Each of the voltage limiting modules further has a resistive element arranged between the control signal output and the supply voltage connection.

6. The voltage limiting circuit according to any one of the preceding claims, wherein, The voltage limiting modules each have a base area not exceeding 18 mm 2 , in particular not exceeding 12 mm 2 in size.

7. The voltage limiting circuit according to claim 6, wherein The actuator has the largest area share among all the functional elements of the voltage limiting module.

8. The voltage limiting circuit according to any one of the preceding claims, wherein, Each transistor of the voltage limiting module has a barrier layer, wherein when the ambient temperature of the voltage limiting circuit is up to 85 °C and the power consumption of the voltage limiting module is up to 1.4 W, the temperature of the barrier layer does not exceed 150 °C.

9. The voltage limiting circuit according to any one of the preceding claims, wherein, The transistors of the voltage limiting module each have a barrier layer, wherein, when the ambient temperature of the voltage limiting circuit is as high as 85 °C and the power consumption of the voltage limiting module is as high as 1.4 W, the power-related temperature rise of the barrier layer does not exceed 60 °C / W, in particular does not exceed 45 °C / W.

10. A field device for process automation technology, comprising: a sensor; a measurement and operation circuit for operating the sensor and for processing signals from the sensor; and a power supply circuit having a power supply voltage source for supplying power to the measurement and operation circuit and a voltage limiting circuit according to any one of the preceding claims, wherein the voltage limiting module is connected in parallel with the power supply voltage source.

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