Device for intrinsically safe redundant current supply of field devices

Abstract

A device is provided for intrinsically safe redundant current supply of field devices with a common current-limiting resistor in the mesh of the field device and with redundant current supply units. A current sensor can be provided in the mesh of the field device, the output signal of which sensor is connected to a controllable voltage source in the redundant current supply units.

Claims

1. A device for intrinsically safe redundant current supply of a field device, the device comprising: a common current-limiting resistor in a mesh of the field device; redundant current supply units; and a current sensor, provided in the mesh of the field device, wherein an output signal of the current sensor is connected to a controllable voltage source in the redundant current supply units.

2. The device of claim 1, wherein the current sensor is configured in analog input assemblies to acquire a measured value transferred by the field device as imprinted current.

3. The device of claim 1, wherein the current sensor includes a diode in a forward direction.

4. The device of claim 1, wherein the current sensor includes a resistor.

5. The device of claim 2, wherein the current sensor includes a diode in a forward direction.

6. The device of claim 1, wherein the current sensor is a diode in a forward direction.

7. The device of claim 2, wherein the current sensor includes a resistor.

8. The device of claim 1, wherein the current sensor is a resistor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be described in even greater detail below based on the exemplary figure. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawing which illustrates the following:

(2) FIG. 1 shows a device for intrinsically safe redundant current supply of field devices.

DETAILED DESCRIPTION

(3) An aspect of the invention is provides a protective circuit arrangement for redundantly supplied field devices, which arrangement protects itself from overloading.

(4) An aspect of the invention proceeds from a device for intrinsically safe redundant current supply of field devices with a common current-limiting resistor in the mesh of the field device.

(5) According to an aspect of the invention, a current sensor is provided in the mesh of the field device, the output signal of which sensor is connected to a controllable voltage source in the two redundant current supply units.

(6) The mesh current, acquired using the current sensor, of the field circuit is identical to the total current of the partial currents supplied by the redundant current supplies, independently of the individual current strengths thereof.

(7) As soon as the mesh current of the field circuit reaches the permissible limit value, the controllable voltage sources in the two redundant current supply units respectively limit the individual output current of the respective current supply unit, by reducing the voltage drop across the current-limiting resistor. In this case, the power loss is divided among the current-limiting resistor and the controllable voltage sources in the two redundant current supply units. Accordingly, a design which can be housed in a miniaturized housing is permissible for the current-limiting resistor.

(8) The location of the current sensor in the current loop can advantageously be freely selected.

(9) In an advantageous development of the invention, the current sensor is designed in analogous input assemblies to acquire the measured value transferred by the field device as imprinted current. As a result, separate means for acquiring the measured value received and transferred by the field device can be dispensed with.

(10) In a development of the invention, the current sensor is embodied as a diode in the forward direction. The forward voltage of the diode is therefore a measure for the mesh current of the field circuit. The forward voltage of the diode reduces the voltage drop across the current-limiting resistor and discharges same when the permissible limit value of the mesh current of the field circuit is reached.

(11) In an alternative development of the invention, the current sensor is embodied as a resistor. In this case, the sensor resistor forms a resistor network with the current-limiting resistor, which resistor network can be used for other functions. The sum of the current-limiting resistor and the sensor resistor limits the current. The power loss is divided between the sensor resistor, the current-limiting resistor and the controllable voltage sources in the two redundant current supply units.

(12) The invention is explained in more detail below on the basis of an exemplary embodiment. The single figure illustrates a device for intrinsically safe redundant current supply of field devices 3 which consists of at least two identical current supply units 11 and 12 and a connection circuit 2.

(13) Each current supply unit 11 and 12 has a controllable voltage source 111 and 121. The current supply units 11 and 12 are connected on the output side to the connection circuit 2 and are electrically connected in parallel.

(14) The connection circuit 2 has the current-limiting resistor 21, a current sensor 22 and connection means for the connection of a field device 3. The current sensor 22 of the connection circuit 2 is connected to the controllable voltage sources 111 and 121 of each current supply unit 11 and 12.

(15) Each controllable voltage source 111 and 121 has a measuring amplifier, in which the measured value of the current sensor 22 is compared with a reference value. In the case of a positive control deviation, when the measured current value is greater than the reference value, the controllable voltage source 111 and 121 reduces its output voltage and hence the loop current.

(16) In the case of a negative control deviation, when the measured current value is less than the reference value, the controllable voltage sources 111 and 121 output a preset operating voltage. Such a function is achieved using a degenerative operational amplifier with a diode in the feedback branch to the reference voltage.

(17) The voltage drop across the diode is negligible in terms of energy in the normal operating state since this reduces the inevitable voltage drop across the current-limiting resistor 21.

(18) In an advantageous configuration of the invention, the connection circuit 2 is designed as configuration-determining plug unit according to DE 101 35 980 C1, which allows both singular and redundant supply of the same field device 3.

(19) Further embodiments may use other suitable current sensors.

(20) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.

(21) The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B, and C” should be interpreted as one or more of a group of elements consisting of A, B, and C, and should not be interpreted as requiring at least one of each of the listed elements A, B, and C, regardless of whether A, B, and C are related as categories or otherwise. Moreover, the recitation of “A, B, and/or C” or “at least one of A, B, or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B, and C.

LIST OF REFERENCE SIGNS

(22) 11, 12 current supply unit

(23) 111, 121 voltage source

(24) 2 connection circuit

(25) 21 current-limiting resistor

(26) 22 current sensor

(27) 3 field device