Input circuit that can be made redundant, input circuit unit having at least one input circuit, and method for operating the input circuit unit

Abstract

A method and input circuit unit having a first input circuit and a redundant second input circuit, wherein each input circuit includes an input for feeding a measurement current that can be obtained from a signaling device and that can be switched over and operated in such an input circuit unit, where the measurement current causes a voltage drop across a measurement resistor that can be evaluated as a measured value, where a parallel connection of the first and second input circuits causes division of the measurement current among the first and second input circuits, and where at least one input circuit include a device for compensating the decreased voltage drop across the measurement resistor resulting from the division of the measurement current.

Claims

1. A switchable input circuit placeable into a redundant state, the switchable input circuit being operable in accordance with a respective operating mode as a binary input circuit or as a current input circuit, the switchable input circuit comprising: an input for receiving a measurement current obtained from a signaling device; an input resistor and a measurement resistor, each of which being connected to between the input and ground, said measurement current providing a voltage drop across the measurement resistor; a measurement system configured to evaluate the voltage drop as a measured value; a switch coupled in parallel to the input resistor and directly coupled to the measurement system, said switch being activatable electronically as a function of the operating mode of the input circuit, and in a closed state said switch bridging the input resistor; wherein a cross coupling operably to provide detection of a further input circuit which is placeable into a redundant state as a redundant input circuit; and means for compensating for a reduced voltage drop, said means for compensating for a reduced voltage drop being activated as a result of a detected redundant input circuit which occurs due to a division of the measuring current among the input circuit and the redundant input circuit.

2. The switchable input circuit that can be made redundant as claimed in claim 1, wherein the electronically activatable switch comprises a plurality of transistors combined to form a Darlington circuit.

3. An input circuit unit with a part circuit comprising the input circuit as claimed in claim 1, and a further part circuit comprising the redundant input circuit as claimed in claim 1, which is combinable with the input circuit, comprising a second input circuit; wherein a parallel connection of the input circuit and the second input circuit causes division of a measurement current among the input circuit and the second input circuit; and wherein at least one of the (i) the input circuit and the second input circuit includes means for compensating for a reduced voltage drop across the measurement resistor resulting because of the division of the measuring current.

4. The input circuit unit as claimed in claim 3, wherein means for compensating for the reduced voltage drop across the measurement resistor resulting because of the division of the measuring current comprises a microcontroller; and wherein a multiplication of the measured value by a predetermined or predeterminable factor performed by the microcontroller.

5. A method for operating a switchable input circuit unit; the method comprising: detecting a parallel connection of the switchable input circuit unit and a second input circuit unit via a switch coupled in parallel to an input resistor and directly coupled to a measurement system of the switchable input circuit, said switch being activatable electronically as a function of an operating mode of the switchable input circuit unit, and in a closed state said switch bridging the input resistor; and compensating for division of a measuring current among the switchable input circuit unit and the second input circuit unit; wherein a parallel connection of the switchable input circuit unit and the second input circuit unit are recognized automatically and as a result of such an automatic recognition; and wherein said compensation for the division of the measurement current comprises multiplication of a measured value able to be obtained as a result of the voltage drop across the measurement resistor by a predetermined or predeterminable factor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the invention is explained below on the basis of the drawings. Objects or elements corresponding to one another are provided in all figures with the same reference characters, in which:

(2) FIG. 1 shows a circuit unit for processing input signals with two redundant part circuits;

(3) FIG. 2 shows a specific form of embodiment of a part circuit; and

(4) FIG. 3 is a flowchart of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(5) FIG. 1 shows a schematic diagram of a circuit unit for redundant signal detection, i.e., to detect input signals. The circuit unit functions accordingly as input circuit unit 10. The input circuit unit 10 comprises a first part circuit 12, which can be used for redundant signal detection, together with an identical or at least functionally-equivalent, complementary second part circuit 14. The part circuit or each part circuit 12, 14 of the input circuit unit 10 functions within the input circuit unit 10 as input circuit 12, 14, so that the designations input circuit 12, input circuit 14 and part circuit 12, 14 have the same meaning.

(6) In an input circuit unit 10 with two such part circuits 12, 14, to make a distinction, a first part circuit/input circuit 12 is referred to below as the master circuit 12 (or master 12 for short) and a second complementary part circuit/input circuit 14 is accordingly referred to as the slave circuit 14 (or slave 14 for short). The input circuit unit 10 comprising one part circuit 12, 14 or both part circuits 12, 14, to distinguish it from the or from each part circuit/input circuit 12, 14 that it contains, is thus referred to below as the overall circuit 10.

(7) The slave circuit 14 is optional within the overall circuit 10 and both the first part circuit 12 and also the second part circuit 14 can assume the functionality of the master circuit 12. With part circuits 12, 14 that are modular, plug-in or able to be releasably connected to the overall circuit 10 in any other suitable manner, the functionality of one of the two part circuits 12, 14, as master 12 or slave 14, is produced by the circumstances as to which of the two part circuits 12, 14 has first become active in the overall circuit 10.

(8) In a manner known per se, a signal source referred to below as a signaling device 16, is connected to the input circuit unit 10 and thus to at least one part circuit 12, 14 included therein. Such a signaling device or any other measurement transducer usually involves a signal source located in a technical process to be controlled or monitored, such as a power station, i.e., an analog or digital sensor basically known per se. By means of such a signaling device 16 (and in practice with a plurality of such signaling devices 16), the state of the respective technical process is detected in a manner known per se.

(9) In the schematic depicted in FIG. 1, it can be seen that the signaling device 16 is connected to the input 18 of the first part circuit 12 and to the input 20 of the second part circuit 14. This can be achieved by corresponding attachment of the or of each signal line 22 coming from the signaling device 16 or via a bridge 24 within the overall circuit 10.

(10) With a signal from the signaling device 16, a measurement current I.sub.M flows into the respective part circuit 12, 14. By means of a switching element included in the part circuit 12, 14 and referred to below for short as switch S.sub.1, the function of the respective input 18, 20 as a binary input or as an analog input for current signals can be set. The switch S.sub.1 is able to be activated by a control device, such as a microcontroller 26 and a control current able to be output by the controller, included in the part circuit 12, 14. For the measurement, the part circuit 12, 14 includes a voltage divider with an input resistor R.sub.E and a measurement resistor R.sub.M, connected to ground and thus functioning as a pull-down resistor. Here, the switch S.sub.1 is connected in parallel to the input resistor R.sub.E.

(11) For operation as a current input, the switch S.sub.1 is closed. This leads to the input 18, 20 of the part circuit 12, 14 being low-resistance. For operation of the part circuit 12, 14 as current input, a measurement current I.sub.M is detected in the usual value range, such as 0 to 20 mA or 4 to 20 mA. In the other cases, i.e., when the part circuit 12, 14 is functioning as a binary input or as an analog voltage input, the switch S.sub.1 is open.

(12) To obtain the voltage drop across the measurement resistor R.sub.M referred to below, a measured value U.sub.M is detected, for example, by a measurement system 28 comprising a multiplexer, a measurement amplifier and an analog-to-digital converter (ADC) and is read in by the microcontroller 26 and evaluated as the respective input signal. If the part circuit 12, 14 is operated as binary input, a digitized signal output by the measurement system 28 is evaluated by the microcontroller 26 in relation to a predetermined or predeterminable upper and/or lower threshold value and, if the threshold value is exceeded or not reached, then a logical high or logical low signal is created.

(13) The master property is assigned via a cross coupling 30 to the respective redundancy partner, i.e., from the first part circuit 12 to the second part circuit 14 and vice versa. By means of the cross coupling 30, it is also recognizable for a part circuit 12, 14 whether a further part circuit 12, 14 is present as a redundancy partner. If a redundancy partner is present, the measurement current I.sub.M is divided up and a small extent flows via the input 20 of the slave circuit 14. On the part of the master circuit 12, this is able to be corrected computationally and, in the presently described embodiment, a correction is provided in the form of a multiplication by a fixed factor. The microcontroller 26 is considered as a way to provide such a correction, and for correction the microcontroller 26 accordingly causes the read-in input signal to be multiplied by the respective correction factor. If a redundancy partner is not plugged in, the measurement current I.sub.M flows entirely in the master 12 and accordingly no correction is necessary.

(14) When inputs 18, 20 functioning as current input are made redundant, only the switch S.sub.1 of the part circuit 12 functioning as the master 12 is closed. Here, significant proportion of the measurement current I.sub.M flows across the measurement resistor R.sub.M of the master circuit 12 and creates the voltage drop U.sub.M. When inputs 18, 20 functioning as binary input (voltage input) are made redundant, both switches S.sub.1, i.e., the switch S.sub.1 of the part circuit functioning as the master 12 and the switch S.sub.1 of the part circuit 14 functioning as the slave 14 are open.

(15) FIG. 2 shows a schematic of a particular embodiment as a realization of one of the part circuits 12, 14 or two redundant part circuits 12, 14. The switch S.sub.1 (FIG. 1) is realized in this embodiment in the form of two transistors T.sub.1, T.sub.2 in a Darlington circuit. The switch S.sub.1 or each of the switch elements/transistors T.sub.1, T.sub.2 functioning as switch S.sub.1 is activated via a control signal (U.sub.St) output by the microcontroller 26. Specifically, when the switch S.sub.1 is realized in the form of two transistors T.sub.1, T.sub.2 combined into a Darlington circuit or a Darlington transistor, only a negligibly small falsification of the measurement current I.sub.M is produced by the electronic activation of the switch S.sub.1.

(16) In the embodiment shown in FIG. 2, the control signal U.sub.St generated by the microcontroller is given to a series transistor T.sub.3 functioning as an inverting stage.

(17) The series transistor T.sub.3 is connected between ground and, via a pull-up resistor (R.sub.P), an operating potential. The Darlington circuit is supplied with power from the operating voltage potential. For a control signal U.sub.St from the microcontroller 26 with a HIGH level the series transistor T.sub.3 becomes conductive and the switch S.sub.1 is open. For a control signal U.sub.St from the microcontroller 26 with a LOW level the series transistor T.sub.3 is open and the Darlington circuit is connected to the operating voltage potential, so that the switch S.sub.1 closes and the input resistor R.sub.E is short circuited. The series resistor R.sub.V is high-resistance, so that only a low control current flows, which only increases the measurement current I.sub.M insignificantly.

(18) Individual advantages of the switchable input circuit unit 10 described here lie in the fact that a single connecting terminal is sufficient as an input 18, 20, because when the circuit is made redundant the measurement current I.sub.M can be conveyed via a bridge 24 (see FIG. 1) within the circuit to the slave circuit 14. The measurement current I.sub.M, in redundant operation, but just as much in individual operation as well, is tapped off within the circuit to ground and thus does not require any further measures within the input circuit unit 10 or the respective part circuit 12, 14. The respective input type, i.e., binary, current analog or voltage analog is able to be selected by the microcontroller 26 via software or predetermined or predeterminable parameters. The switchover is performed electronically via the microcontroller 26. Even with the input type current analog making the circuit redundant is possible by direct parallel connection of two parallel part circuits 12, 14. External additional measures, such as bridge settings within the input circuit unit 10, are not necessary. Binary values can also be measured as an analog voltage. The state is determined via a predetermined or predeterminable comparison threshold. Overload protection of the input circuit unit 10 can be achieved by a clocked opening and closing of the switch S.sub.1 of the part circuit or of each part circuit 12, 14.

(19) A part circuit 12, 14 of the type described here is also able to be operated autonomously as input circuit 12, 14, i.e., as an input circuit 12, 14 able to be switched over by a corresponding activation of the electronically controllable switch S.sub.1 contained therein. Depending on the switch position of the switch S1, an analog current measurement or an analog or digital voltage measurement is performed via the input circuit 12, 14.

(20) FIG. 3 is a flowchart of a method for operating an input circuit unit (10). The method comprises detecting a parallel connection of the first and the second input circuit (12, 14), as indicated in step 310. Next, a compensation of the division of a measuring current (I.sub.M) among first and the second input circuits (12, 14) is performed, as indicated in step 320.

(21) While there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.