DE102009029307A1 - Device for transmitting a control signal - Google Patents

Abstract

The invention relates to a device for the galvanic transmission of a control signal from a primary unit (1) to a secondary unit (2), the primary side (1) generating two complementary control signals S, for controlling a switching contact (3), the secondary unit (2) Switching contact (3) and a control unit (4), wherein at least a first capacitor (51) and a second capacitor (52) are provided, the first capacitor (51) transmitting the control signal Szum Schl (4), the second capacitor (52) transmits the control signal Szum opening the switch contact (3) to the control unit (4) and the control unit (4) closes or opens the switch contact (3) depending on the control signal S, S present.

Description

The present invention relates to a device for galvanically separated transmission of a control signal from a primary unit to a secondary unit. The device is integrated, for example, in a field device of process automation, which monitors a process parameter and provides a switching signal at a signal output for transmission to an actuator, for example a valve. The primary unit comprises, for example, a sensor element and a control / evaluation unit and the secondary side represents, for example, the interface to a higher-level control unit.

Often it is desirable for safety reasons that the signal transmission from a primary side to a secondary side via a galvanically isolated interface is possible. For example, this is the case when a high voltage is applied to the primary side, but the secondary side may only have a low voltage-for example because it is located in a potentially explosive environment-and the danger is to be prevented from contacting the high voltage from the secondary side the primary side can be made.

Various configurations of galvanically separated interfaces are known from the prior art. In the case of an optocoupler, a light signal is emitted from the primary side to the secondary side, as a result of which the switching process is activated on the secondary side. With this principle, a signal can be transmitted, but no energy, so that in the event that on the secondary side energy is needed, it must be provided via a separate interface. In addition, an opto-coupler requires a lot of energy, so that these systems are only used when the high energy consumption of the optical transmission system plays no role. If not much energy is available, alternative methods for galvanically separated signal transmission are preferred.

One of these alternative implementations of a galvanically isolated switch includes a transformer. Transformers or inductive interfaces require little energy. However, they have some disadvantages. For one, they are expensive and take up a relatively large amount of space. The latter is a major disadvantage in many systems. On the other hand, additional voltage-limiting components are usually necessary, which limit voltage peaks that occur when switching off or in the event of a fault. This is especially important for applications in potentially explosive areas.

Another conceivable method is the use of a capacitor for transmitting a control signal. However, this has the considerable disadvantage that electromagnetic interference influences the control signal during transmission in such a way that the state of the switch, which is regulated by the control signal, can not be reliably adjusted. For example, low voltages induced by interfering fields on the capacitor lead to unwanted signals, which cause an undesirable change in the switching state.

The object of the invention is to provide a device for galvanically isolated signal transmission, which is inexpensive and robust against electromagnetic interference.

The object is achieved by a device for galvanically separated transmission of a control signal from a primary unit to a secondary unit, wherein the primary side generates two complementary control signals S ₊ , S _- for controlling a switching contact, wherein the secondary unit has the switching contact and a control unit, wherein at least one first capacitor and a second capacitor are provided, wherein the first capacitor transmits the control signal S ₊ to close the switch contact to the control unit, the second capacitor, the control signal S _- to open the switch contact to the control unit transmits and wherein the control unit in response to the adjacent Control signal S ₊ , S _- the switching contact closes or opens.

By concern of a control signal S ₊ , S _- is here to be understood that a non-zero voltage value is applied. If the voltage value of the control signal is zero, this is equivalent to the fact that no control signal is present.

The device according to the invention consists of a few components, which are also standard components. This makes the device inexpensive and space-saving.

The fact that both the closing of the switch and the opening of the switch is controlled by an active signal, the device is robust against electromagnetic interference and thus works very reliable.

Another advantage of the device according to the invention is that it has only a low energy requirement. In addition to the lower energy costs for the device, this leads to the advantage that it can also be used in potentially explosive environments.

Compared with an optical interface, as known from the prior art, the device offers a further advantage. Due to the capacitors, in addition to the signal transmission, the transmission of energy to the secondary side is possible, so that it does not require a separate power supply. This saves space and is very cost effective.

In a first embodiment of the solution according to the invention, the primary side has a processing unit for generating the control signals S ₊ , S _- from a primary switching signal S ₁ . The primary switching signal is, for example, a square-wave voltage. In the simplest case, the conditioning unit inverts the primary switching signal S ₁ and forwards the unchanged primary switching signal S ₁ as the control signal S ₊ to the first capacitor and the inverted primary switching signal S ₁ as the control signal S _- to the second capacitor. As a result, the one capacitor is charged to which a non-zero voltage value is applied, while no voltage is applied to the other capacitor.

According to one development of the invention, at least one third capacitor is connected in series with the first capacitor, and at least one fourth capacitor is connected in series with the second capacitor, so that their respective insulation voltages add up to a total voltage U. In this way, a higher electrical isolation can be achieved.

In a further development of the invention, a feedback device is provided on the secondary side, which serves to control the switching state of the switching contact. In this way, a diagnostic function is feasible, which is for devices that must meet certain safety specifications, a great advantage.

In one embodiment, the feedback device transmits the information about the switching state of the switching contact via a capacitive interface to the primary side. As a result, the information transmission of the feedback device is also galvanically separated. The capacitive interface can also be constructed of several capacitors.

In an advantageous embodiment of the invention, the capacitors in addition to the control signal S ₊ , S _- also transfer energy to the secondary side. The control signals S ₊ , S _- can be superimposed in this case, for example, a fundamental voltage as modulations. This embodiment is particularly advantageous since no further interface for energy transmission has to be provided.

A development of the solution according to the invention consists in that the switching contact has the function of a pulse generator for transmitting the information contained in the primary switching signal S ₁ .

The device is part of a measuring device, for example. In this case, the switching contact serves, for example, to pass on a measuring signal determined by a measuring instrument to a field device for displaying the measured value.

According to one embodiment, the switching contact is connected to a device which is switched on or off depending on the switching state of the switching contact. In this way, z. B. an actuator in response to a process variable, which forms the basis of the primary switching signal control. An application example is a limit switch with a valve.

In an advantageous embodiment, the device according to the invention is part of a measuring device for determining and / or monitoring a physical, biological or chemical process variable, a transmitter or a field indicator. Such measuring and field devices are offered and distributed by the applicant in a wide variety.

The invention will be explained in more detail with reference to the following figures.

1 shows a galvanically isolated switch with two capacitors;

2 shows a galvanically isolated switch with two capacitors and a feedback device.

In 1 is a galvanically isolated switch with two capacitors 51 . 52 shown. This consists of a primary page 1 where a switching signal is generated, and a secondary side 2 with a switching contact 3 whose switching state is regulated according to the switching signal. For example, the switch is part of a process automation or monitoring field device, such as a transmitter, a display element, or a limit switch.

On the primary side 1 For example, there are a sensor for determining a process variable and an evaluation unit which compares the determined process variable with a desired value and generates a primary switching signal S _{1 as a} function of this. In response to this primary switching signal S ₁ , the switching contact changes 3 on the secondary side 2 its switching state. The switching contact 3 this can be the function of an on / off switch or have a pulse generator. In one embodiment, the switching contact 3 the power supply to the secondary side 2 controlled device so that the device through the switching contact 3 can be switched on and off. In an alternative embodiment, the switch contact 3 a pulse generator, which forwards the primary switching signal S ₁ in the form of a pulse to an interface, and thus makes available, for example, a further field device connected to the interface.

The primary side 1 is galvanic from the secondary side 2 separated, wherein the interface for transmitting the primary switching signal S ₁ from the primary side 1 to the secondary side 2 through two capacitors 51 . 52 is realized. Lies on the first capacitor 51 a control signal S ₊ in the form of a voltage, so the switching contact 3 closed. Lies on the second capacitor 52 a control signal S _- in the form of a voltage, then the switching contact 3 open. In that both to close and to open the switch contact 3 an active signal is required, the switching device is insensitive to electromagnetic interference. A random switching of the switching contact 3 is thereby avoided. To increase the galvanic isolation, the separation voltage can be increased by adding the first capacitor 51 or the second capacitor 52 each connected in series with a third and fourth capacitor. The number of capacitors connected in series can also be further increased in this case.

In order to adapt the switching signal to the interfaces so that an active control signal S ₊ for opening and a second active control signal S _{- is} generated for closing, which are suitable to from the two capacitors 51 . 52 To be transferred is the capacitors 51 . 52 a processing unit 6 prefixed. This generates two complementary control signals S ₊ , S _- and acts on the capacitors 51 . 52 with same. For example, the original primary switching signal S ₁ is a rectangular signal. This is amplified unchanged or with a certain amplification factor to the first capacitor 51 forwarded. The second capacitor 52 receives the inverted control signal S _- . On the secondary side 2 there is a control unit 4 which are connected to the two capacitors 51 . 52 processed applied voltages, it generates a secondary switching signal S ₂ and the secondary switching signal S ₂ to the switching contact 3 transfers.

2 discloses a feedback device 7 to check the switching state of the switching contact 3 , By such a device, it is possible to the primary side 1 the information about the switching state of the switch contact 3 to make it possible to check whether the control signals S ₊ , S _{- are} correct from the primary side 1 to the secondary side 2 were transferred. This functional test is advantageous, for example, if the device is part of a device which has to meet certain safety requirements. An example of this is compliance with the specifications of a security level after the Standard IEC 61508 or IEC 62061 , a so-called SIL (Safety Integrity Level). For reading out the switching state of the switching contact 3 is a measuring shunt 9 with the switching contact 3 connected.

A transmission unit 10 , which with the measuring shunt 9 and the control unit 4 is connected, reads the switching state of the switch contact 3 off and generates a feedback signal. The feedback signal is preferably via a further capacitive interface 8th to the primary side 1 transfer. On the primary side 1 is a microcontroller 11 arranged, which receives the feedback signal and evaluates, for example by comparing the primary switching signal S ₁ with the feedback signal. The microcontroller may be the same component which commands the switch contact 3 gives. Results in the evaluation of the switching state of the switching contact 3 that this is in the wrong state, for example, an error message is generated and output. Preferably, the measuring device, in which the galvanically isolated switch is integrated, additionally converted into a safe state defined by the manufacturer. Particularly advantageous is a redundant design of the switch contact 3 so that in case of failure of the first switch contact 3 an identical switching contact 3 ' can be switched.

LIST OF REFERENCE NUMBERS

1

primary

2

secondary side

3

switching contact

4

control unit

51

First capacitor

52

Second capacitor

53

Third capacitor

54

Fourth capacitor

6

conditioning unit

7

Feedback device

8th

capacitive interface

9

Shunt

10

transmission unit

11

microcontroller

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Standard IEC 61508 [0029]
• IEC 62061 [0029]

Claims (9)

Device for the isolated transmission of a control signal from a primary unit ( 1 ) to a secondary unit ( 2 ), the primary side ( 1 ) two complementary control signals S ₊ , S _- for controlling a switching contact ( 3 ), the secondary unit ( 2 ) the switching contact ( 3 ) and a control unit ( 4 ), wherein at least one first capacitor ( 51 ) and a second capacitor ( 52 ) are provided, wherein the first capacitor ( 51 ) the control signal S ₊ to close the switch contact ( 3 ) to the control unit ( 4 ), the second capacitor ( 52 ) the control signal S _- to open the switch contact ( 3 ) to the control unit ( 4 ) and wherein the control unit ( 4 ) in dependence of the applied control signal S ₊ , S _- the switching contact ( 3 ) closes or opens. Device according to claim 1, wherein the primary side comprises a processing unit ( 6 ) for generating the control signals S ₊ , S _- from a primary switching signal S ₁ . Device according to claim 1 or 2, wherein at least one third capacitor ( 53 ) with the first capacitor ( 51 ) is connected in series and wherein at least a fourth capacitor ( 54 ) with the second capacitor ( 52 ) is connected in series, so that add their insulation voltages in each case to a total voltage U. Device according to at least one of the preceding claims, wherein on the secondary side ( 2 ) a feedback device ( 7 ) is provided, which for controlling the switching state of the switching contact ( 3 ) serves. Apparatus according to claim 4, wherein the feedback device ( 7 ) the information about the switching state of the switching contact ( 3 ) via a capacitive interface ( 8th ) to the primary side ( 1 ) transmitted. Device according to at least one of the preceding claims, wherein the capacitors ( 51 . 52 ) in addition to the control signal S ₊ , S _- and energy to the secondary side ( 2 ) transfer. Device according to at least one of the preceding claims, wherein the switching contact ( 3 ) has the function of a pulse generator for transmitting the information contained in the primary switching signal S ₁ . Device according to at least one of the preceding claims, wherein the switching contact ( 3 ) is connected to a device which, depending on the switching state of the switching contact ( 3 ) is switched on or off. Device according to at least one of the preceding claims, wherein the device is part of a measuring device for determining and / or monitoring a physical, biological or chemical process variable, a transmitter or a field indicator.

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