EP2335025B1 - Process automation field device - Google Patents

Process automation field device Download PDF

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Publication number
EP2335025B1
EP2335025B1 EP09783147.3A EP09783147A EP2335025B1 EP 2335025 B1 EP2335025 B1 EP 2335025B1 EP 09783147 A EP09783147 A EP 09783147A EP 2335025 B1 EP2335025 B1 EP 2335025B1
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EP
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Prior art keywords
current sink
field device
current
controllable current
controllable
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EP09783147.3A
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German (de)
French (fr)
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EP2335025A1 (en
Inventor
Jürgen Meier
Martin Lange
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Endress and Hauser SE and Co KG
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Endress and Hauser SE and Co KG
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
    • G08C19/00—Electric signal transmission systems
    • G08C19/02—Electric signal transmission systems in which the signal transmitted is magnitude of current or voltage

Definitions

  • the invention relates to a field device of process automation technology, with at least one interface for outputting a current signal, with at least one default unit, which specifies at least one value, from which the current signal to be output via the interface is dependent.
  • measuring devices which output signals and in particular measured values as 4 ... 20 mA signals.
  • EP 1 158 274 A1 controlled current sources of two-wire measuring instruments which generate as measuring signal between 4 mA and 20 mA lying output current and which are controlled by a control signal generated by means of a physical-electrical sensor element shown.
  • the two conductors are used both for the power supply, for which a DC voltage source is to be applied to the two conductors from outside, and for the transmission of the measuring signal.
  • the task of in the EP 1 158 274 A1 specified invention is to provide improved controlled power sources of two-wire gauges, which is required for the start when switching the DC voltage source, compared to the normal operation higher energy demand is provided, so that the controlled current source starts to work automatically.
  • error signal is output, which is usually outside the actual signal range between 4 and 20 mA.
  • the error signal is thus either below 4 mA or above 20 mA.
  • the object of the invention is therefore to propose a field device which permits a check of the error signaling without this resulting in an impairment, in particular of the units connected downstream of the field device.
  • the object is achieved by the invention in that at least one first controllable current sink and a second controllable
  • the field device is in particular a 4 ... 20 mA signal field device.
  • An embodiment provides that the field device signals the presence of a fault of the field device by an error signal via the interface, wherein the error signal is within an error signal interval.
  • the error signal interval is in particular between 0 mA and 4 mA or 3.6 mA, if the interface is a 4 ... 20 mA interface.
  • An embodiment includes that the error signal has a current intensity below a predetermined value, in particular less than 3.6 mA.
  • An embodiment includes that at least one control unit is provided, and that the control unit is configured such that the control unit sets the first controllable current sink and the second controllable current sink respectively to a predeterminable current intensity starting from the default unit.
  • control unit is configured such that the control unit starting from the default unit, the first controllable current sink and the second controllable current sink such controls that the signal present at the interface varies within a predefinable interval.
  • An embodiment includes that the first controllable current sink consists of at least a first current sink, a first regulator, a first resistor and a first measuring resistor, wherein the first measuring resistor is connected in series with the first current sink and is provided for tapping a first measuring voltage.
  • the second controllable current sink at least consists of a second current sink, a second regulator, a second resistor and a second measuring resistor, wherein the second measuring resistor is connected in series with the second current sink and is provided for tapping a second measuring voltage.
  • An embodiment includes that a capacitor and a diode are incorporated in the first controllable current sink and / or in the second controllable current sink.
  • An embodiment provides that a first switch and a first bridging resistor are provided parallel to the first current sink and to the first measuring resistor.
  • An embodiment includes that a second switch and a second bridging resistor are provided parallel to the second current sink and the second measuring resistor.
  • control unit has at least two microprocessors which essentially independently of one another control the first controllable current sink and the second controllable current sink.
  • an inventive field device 10 is shown. This is, for example, a measuring device for determining and / or monitoring a process variable.
  • the process variable is, for example, level, density, viscosity, flow, pH or temperature.
  • the field device 10 has an interface 11, via which, for example, the measured values are output as 4... 20 mA signals. In the event that there is an error of the field device 10, a signal is output, whose current is outside this range reserved for normal use. In one embodiment, the "fault current" is below 3.6 mA.
  • the circuit shown here allows the test of whether this fault current can be generated without the error signal coming directly to the interface 11.
  • two controllable current sinks 1, 2 are connected in series.
  • a part of the first controllable current sink 1 is a current sink I1.
  • This is an electronic load whose load current is electronically adjustable.
  • An example is a field effect transistor (FET).
  • the first controllable current sink 1 comprises the first regulator RE1, the first measuring resistor R1 and the first resistor R5.
  • the controller RE1 is an operational amplifier, of which an input to the control unit 13 or specifically with the first microprocessor M1 of the control unit 13 and another input with the first resistor R5 or with the voltage drop across the first measuring resistor R1 to which is connected by an operational amplifier and whose output causes the adjustment of the current intensity of the first current sink I1.
  • the input of the regulator RE1 not connected to the control unit 13 is connected to a contact point of the interface 11 via the first resistor R5. This contact point is also connected to ground.
  • the first measuring resistor R1 also allows the tapping of a first measuring voltage U1.
  • the first current sink I1 is connected to the other contact point of the interface 11 and to ground.
  • a zener diode Vz and, in parallel thereto, a capacitor C are also provided between the first current sink I1 and ground.
  • the second controllable current sink 2 is constructed analogously to the first 1. It consists of the second current sink I2, the second regulator RE2, the second resistor R6 and the second measuring resistor R2. In this case, the first current sink I1 and the second current sink I2 are connected in series.
  • the second controller RE2 is controlled here via the second microprocessor M2 of the control unit 13.
  • the two microprocessors M1, M2 operate independently of each other and also independently of one another via the regulators RE1, RE2, the current strengths of the two current sinks I1, I2.
  • the respective nominal value for the current at the interface is specified by the default unit 12. This is in particular the evaluation unit of the sensor component of the field device 10.
  • the current at the interface is thus set such that it corresponds, for example, to a determined measured value for a process variable or that it represents, for example, the reaching of a limit value.
  • the current signal is varied within a predetermined interval, i. it fidgets around the setpoint of the default unit 12 and thus is a life signal for the field device 10. For example, assume a set point of 19 mA, which alternates between two current values, i. For example, an output signal of 19 mA ⁇ 0.25 mA results. This alternation thus means for the receiving unit 15 that the field device 10 is still alive.
  • the following components are provided in the circuit according to the invention:
  • the first controllable current sink 1 has a first measuring resistor R1, connected in series with the first current sink I1, via which a first measuring voltage U1 is tapped. Parallel to the first current sink I1 and the first measuring resistor R1, a first switch S1 and a first bypass resistor R3 are provided.
  • a second measuring resistor R2 for a second measuring voltage U2, a second switch S2 and a second bridging resistor R4 are provided at the second controllable current sink 2.
  • the two controllable current sinks 1, 2 are "decoupled” from one another and allow regulation substantially independently of one another.
  • the time sequences and the occurring currents are shown. Shown are from top to bottom: the output current at the interface 11, the current at the first measuring resistor R1, the current at the first bridging resistor R3, the Current at the second measuring resistor R2 and the current flow at the second bridging resistor R4.
  • switches S1 and S2 are open.
  • the control of the switches takes place, for example, via the control unit 13, or individually via the provided microprocessors M1 and M2, which are associated with the first controllable current sink I1 and the second controllable current sink I2.
  • the first current sink I1 is set to 19.25 mA and the second current sink I2 to 18.75 mA.
  • the output current at the interface 11 is determined by the second current sink I2.
  • the flowing current is measured via the two measuring resistors R1 and R2 and converted in each case via an operational amplifier in a voltage proportional to the current U1 or U2 and the microprocessors M1 and M2 supplied for control (these compounds are not shown here for clarity).
  • test I1 in the Fig. 2 the test of the first current sink I1 (test I1 in the Fig. 2 ):
  • the switch S1 is closed.
  • the current of 18.75 mA is split across branch I1 and R1 and branch R3 and S1. Essentially the same current flows in both branches when the resistors R1 and R3 are of equal size and the resistance of the switch S1 and the internal resistance of I1 are very small.
  • the voltage drop across the measuring resistor R1 voltage U1 is measured and compared with a reference value. Then, the default value of the current for the first current sink I1 from the first microprocessor M1 and the first controller RE1 from the above set 19.25 mA to a test value less than 18.75 mA, z. B. set to 3 mA.
  • the first regulator RE1 sets the first current sink I1 so that the voltage across the resistor R5, which is measured via the first measuring resistor R1, the setpoint input from the first microprocessor M1, i. equal to 3 mA, corresponds.
  • I1 flows 3 mA.
  • the remaining current of 18.75 mA - 3 mA flows through the parallel branch of the resistor R3 and the switch S1.
  • currents between 0 mA and a value Itestmax1 at the first current sink I1 are adjustable.
  • the value Itestmax1 is dependent on the ratio between the resistors R3 and R1.
  • the default value for the first current sink I1 via the first microprocessor M1 and the first regulator RE1 of 3 mA is set to a value greater than 19.25 mA.
  • the partial current 18.75 / 2 mA flows again via the first current sink I1 and the first measuring resistor R1.
  • This partial current can be measured as voltage U1 and compared with a reference value.
  • the partial current Itotal - 3 mA flows through the resistor R3 and the switch S1. To the terminals and thus to the outside flow constantly 18.75 mA. Subsequently, the switch S1 is opened. The current is still held by the second current sink I2 to 18.75 mA.
  • the default value for the second current sink I2 is set to 19.25 mA via the second microprocessor M2 and the second regulator RE2. Since the first current sink was set to a current greater than 19.25, the second current sink I2 determines the output current at the interface, which is thus 19.25 mA. The output signal therefore varies between the two values 18.75 mA and 19.25 mA. Thus, the field device 10 shows that it is still alive.
  • the default value for the first current sink I1 is reduced from the value greater than 19.25 mA to 18.75 mA.
  • the first current sink I1 determines the current to the outside (18.75 mA).
  • the voltage measurements at R1 and R2 give the correct current value in the fault-free case. If the value is correct, the switch S1 has opened and the first current sink I1 is in order.
  • the second switch S2 is closed.
  • the current of currently 18.75 mA is split across branch I2 and R2 and branch R4 and S2.
  • approximately the same current flows when the resistors R2 and R4 are the same size and the resistance of the switch S2 and the internal resistance of the second current sink I2 are very small.
  • the voltage U2 is measured and compared with a reference value.
  • the default value of the second current sink I2 via the microprocessor M2 and the second regulator RE2 of 19.25 mA to a value less than 18.75 mA, z. B. set to 3 mA.
  • the second regulator RE2 sets the second current sink I2 so that the voltage across the resistor R6, which is measured via the second measuring resistor R2, the setpoint input from the second microprocessor M2, ie equal to 3 mA corresponds.
  • I2 3 mA flows.
  • the remaining current of 18.75 mA-3 mA flows via the parallel branch of the resistor R4 and the switch S2.
  • test currents between 0 mA and a value Itestmax2 at the second current sink I2 are adjustable.
  • the value Itestmax2 is dependent on the ratio between the resistors R4 and R2.
  • the partial current 18.75 / 2 mA which can be measured via the voltage U2 and is comparable to a reference value, flows again via the second current sink I2 and the measuring resistor R2.
  • the partial current I total flows less 3 mA via the bridging resistor R4 and the switch S2.
  • the interface 11 is constant at a current signal of 18.75 mA.
  • the switch S2 is opened, wherein the current is still held by the first current sink I1 to 18.75 mA.
  • the default value for the first current sink I1 is set to 19.25 mA via the first microprocessor M1 and the first regulator RE1.
  • the first current sink I1 sets the current at the interface 11 to 19.25 mA.
  • the default value for the current value of the second current sink I2 is reduced from the value greater than 19.25 mA to 18.75 mA, so that the second current sink I2 determines the current via the interface 11 to the outside.
  • the voltages U1 and U2 are measured to monitor the presence of the respective required current. Do the voltages U1 and U2 the reference values, so the switch S2 has opened and the second current sink I2 is OK.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Tests Of Electronic Circuits (AREA)
  • Measurement Of Current Or Voltage (AREA)
  • Arrangements For Transmission Of Measured Signals (AREA)
  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)

Abstract

A field device of process automation technology having an interface for output of an electrical current signal and a specifying unit, which provides a value, on which depends an electrical current signal to be output via the interface. A first controllable electrical current sink and a second controllable electrical current sink are provided. The first controllable electrical current sink and the second controllable electrical current sink are settable to predeterminable electrical current levels, and that the first controllable electrical current sink and the second controllable electrical current sink are connected with the interface in such a manner that the electrical current signal which at the interface essentially depends on the lower of the predeterminable electrical current levels, to which the first controllable electrical current sink and the second controllable electrical current sink are set.

Description

Die Erfindung bezieht sich auf ein Feldgerät der Prozessautomatisierungstechnik, mit mindestens einer Schnittstelle zur Ausgabe eines Stromsignals, mit mindestens einer Vorgabeeinheit, welche zumindest einen Wert vorgibt, von welchem das über die Schnittstelle auszugebende Stromsignal abhängig ist.The invention relates to a field device of process automation technology, with at least one interface for outputting a current signal, with at least one default unit, which specifies at least one value, from which the current signal to be output via the interface is dependent.

Im Stand der Technik sind Feldgeräte, insbesondere Messgeräte bekannt, welche Signale und insbesondere Messwerte als 4...20 mA-Signale ausgeben. Beispielsweise sind in der EP 1 158 274 A1 gesteuerte Stromquellen von Zwei-Leiter-Messgeräten, die als Messsignal einen zwischen 4 mA und 20 mA liegenden Ausgangsstrom erzeugen und die von einem mittels eines physikalisch-elektrischen Sensorelements erzeugten Steuersignal gesteuert sind, dargestellt. Bei diesen Zwei-Leiter-Messgeräten werden die beiden Leiter sowohl für die Energiespeisung, wozu an die zwei Leiter von außen eine Gleichspannungsquelle anzulegen ist, als auch für die Übertragung des Messsignales benutzt. Die Aufgabe der in der EP 1 158 274 A1 angegebenen Erfindung ist es, verbesserte gesteuerte Stromquellen von Zwei-Leiter-Messgeräten anzugeben, wobei der für den Start beim Einschalten der Gleichspannungsquelle benötigte , gegenüber dem Normalbetrieb höhere Energiebedarf zur Verfügung gestellt wird, so dass die gesteuerte Stromquelle automatisch zu arbeiten beginnt.In the prior art field devices, in particular measuring devices are known, which output signals and in particular measured values as 4 ... 20 mA signals. For example, in the EP 1 158 274 A1 controlled current sources of two-wire measuring instruments, which generate as measuring signal between 4 mA and 20 mA lying output current and which are controlled by a control signal generated by means of a physical-electrical sensor element shown. In these two-wire measuring devices, the two conductors are used both for the power supply, for which a DC voltage source is to be applied to the two conductors from outside, and for the transmission of the measuring signal. The task of in the EP 1 158 274 A1 specified invention is to provide improved controlled power sources of two-wire gauges, which is required for the start when switching the DC voltage source, compared to the normal operation higher energy demand is provided, so that the controlled current source starts to work automatically.

Wenn ein Fehler im Feldgerät vorliegt, so wird ein sog. Fehlersignal ausgegeben, welches üblicherweise außerhalb des eigentlichen Signalbereichs zwischen 4 und 20 mA liegt. Das Fehlersignal liegt somit entweder unterhalb von 4 mA oder oberhalb von 20 mA.If there is an error in the field device, a so-called error signal is output, which is usually outside the actual signal range between 4 and 20 mA. The error signal is thus either below 4 mA or above 20 mA.

Im Rahmen des Konzepts der Selbstüberprüfung der Feldgeräte ist es dabei auch erforderlich, dass das Gerät dazu in der Lage sein sollte, einen solchen Fehlerstrom zu signalisieren. Dabei besteht jedoch die Problematik darin, dass dieses Fehlersignal selbst nicht an den Ausgang des Gerätes gelangen sollte, da es sich nur um einen Test und nicht um das Vorliegen eines solchen Fehlers handelt. Als einfache Lösung werden daher in Testzeiträumen von den Feldgeräten entsprechende Fehlersignale absichtlich erzeugt. In diesen Zeiträumen ist daher jedoch ein normaler Prozessbetrieb nicht möglich.As part of the concept of self-checking the field devices, it is also necessary that the device should be able to signal such a fault current. However, the problem is that This error signal itself should not get to the output of the device, since it is only a test and not the presence of such an error. As a simple solution, error signals corresponding to the field devices are therefore intentionally generated in test periods. In these periods, however, a normal process operation is therefore not possible.

Die Aufgabe der Erfindung besteht daher darin, ein Feldgerät vorzuschlagen, welches eine Überprüfung der Fehlersignalisierung erlaubt, ohne dass dies zu einer Beeinträchtigung, insbesondere der dem Feldgerät nachgeschalteten Einheiten kommt.The object of the invention is therefore to propose a field device which permits a check of the error signaling without this resulting in an impairment, in particular of the units connected downstream of the field device.

Die Aufgabe löst die Erfindung dadurch, dass mindestens eine erste steuerbare Stromsenke und eine zweite steuerbareThe object is achieved by the invention in that at least one first controllable current sink and a second controllable

Stromsenke vorgesehen sind, dass die erste steuerbare Stromsenke und die zweite steuerbare Stromsenke derartig ausgestaltet sind, dass die erste steuerbare Stromsenke und die zweite steuerbare Stromsenke jeweils auf eine vorgebbare Stromstärke einstellbar sind, dass die erste steuerbare Stromsenke und die zweite steuerbare Stromsenke in Reihe geschaltet sind, und dass die erste steuerbare Stromsenke und die zweite steuerbare Stromsenke derartig mit der Schnittstelle verbunden sind, dass das Stromsignal, welches an der Schnittstelle anliegt, im Wesentlichen von der niedrigeren Stromstärke der vorgebbaren Stromstärken, auf welche die erste steuerbare Stromsenke und die zweite steuerbare Stromsenke eingestellt sind, abhängig ist. Bei dem Feldgerät handelt es sich insbesondere um ein 4... 20 mA-Signal-Feldgerät.Current sink are provided, that the first controllable current sink and the second controllable current sink are configured such that the first controllable current sink and the second controllable current sink are each adjustable to a predetermined current, that the first controllable current sink and the second controllable current sink are connected in series in that the first controllable current sink and the second controllable current sink are connected to the interface in such a way that the current signal which is present at the interface essentially depends on the lower current intensity of the specifiable current intensities to which the first controllable current sink and the second controllable current sink are dependent on. The field device is in particular a 4 ... 20 mA signal field device.

Eine Ausgestaltung sieht vor, dass das Feldgerät das Vorliegen eines Fehlers des Feldgerätes durch ein Fehlersignal über die Schnittstelle signalisiert, wobei das Fehlersignal innerhalb eines Fehlersignalintervalls liegt. Das Fehlersignalintervall liegt dabei insbesondere zwischen 0 mA und 4 mA bzw. 3.6 mA, wenn es sich bei der Schnittstelle um eine 4...20 mA-Schnittstelle handelt.An embodiment provides that the field device signals the presence of a fault of the field device by an error signal via the interface, wherein the error signal is within an error signal interval. The error signal interval is in particular between 0 mA and 4 mA or 3.6 mA, if the interface is a 4 ... 20 mA interface.

Eine Ausgestaltung beinhaltet, dass das Fehlersignal eine Stromstärke unterhalb eines vorgegebenen Wertes, insbesondere kleiner 3,6 mA, aufweist.An embodiment includes that the error signal has a current intensity below a predetermined value, in particular less than 3.6 mA.

Eine Ausgestaltung beinhaltet, dass mindestens eine Steuereinheit vorgesehen ist, und dass die Steuereinheit derartig ausgestaltet ist, dass die Steuereinheit ausgehend von der Vorgabeeinheit die erste steuerbare Stromsenke und die zweite steuerbare Stromsenke jeweils auf eine vorgebbare Stromstärke einstellt.An embodiment includes that at least one control unit is provided, and that the control unit is configured such that the control unit sets the first controllable current sink and the second controllable current sink respectively to a predeterminable current intensity starting from the default unit.

Eine Ausgestaltung sieht vor, dass die Steuereinheit derartig ausgestaltet ist, dass die Steuereinheit ausgehend von der Vorgabeeinheit die erste steuerbare Stromsenke und die zweite steuerbare Stromsenke derartig steuert, dass das an der Schnittstelle anliegende Signal in einem vorgebbaren Intervall variiert.An embodiment provides that the control unit is configured such that the control unit starting from the default unit, the first controllable current sink and the second controllable current sink such controls that the signal present at the interface varies within a predefinable interval.

Eine Ausgestaltung beinhaltet, dass die erste steuerbare Stromsenke mindestens aus einer ersten Stromsenke, einem ersten Regler, einem ersten Widerstand und einem ersten Messwiderstand besteht, wobei der erste Messwiderstand in Reihe zur ersten Stromsenke geschaltet ist und zum Abgreifen einer ersten Messspannung vorgesehen ist.An embodiment includes that the first controllable current sink consists of at least a first current sink, a first regulator, a first resistor and a first measuring resistor, wherein the first measuring resistor is connected in series with the first current sink and is provided for tapping a first measuring voltage.

Eine Ausgestaltung sieht vor, dass die zweite steuerbare Stromsenke mindestens aus einer zweiten Stromsenke, einem zweiten Regler, einem zweiten Widerstand und einem zweiten Messwiderstand besteht, wobei der zweite Messwiderstand in Reihe zur zweiten Stromsenke geschaltet ist und zum Abgreifen einer zweiten Messspannung vorgesehen ist.An embodiment provides that the second controllable current sink at least consists of a second current sink, a second regulator, a second resistor and a second measuring resistor, wherein the second measuring resistor is connected in series with the second current sink and is provided for tapping a second measuring voltage.

Eine Ausgestaltung beinhaltet, dass ein Kondensator und eine Diode in die erste steuerbare Stromsenke und/oder in die zweite steuerbare Stromsenke eingebaut sind.An embodiment includes that a capacitor and a diode are incorporated in the first controllable current sink and / or in the second controllable current sink.

Eine Ausgestaltung sieht vor, dass parallel zur ersten Stromsenke und zum ersten Messwiderstand ein erster Schalter und ein erster Überbrückungswiderstand vorgesehen sind.An embodiment provides that a first switch and a first bridging resistor are provided parallel to the first current sink and to the first measuring resistor.

Eine Ausgestaltung beinhaltet, dass parallel zur zweiten Stromsenke und zum zweiten Messwiderstand ein zweiter Schalter und ein zweiter Überbrückungswiderstand vorgesehen sind.An embodiment includes that a second switch and a second bridging resistor are provided parallel to the second current sink and the second measuring resistor.

Eine Ausgestaltung sieht vor, dass die Steuereinheit mindestens zwei Mikroprozessoren aufweist, welche im Wesentlichen unabhängig voneinander die erste steuerbare Stromsenke und die zweite steuerbare Stromsenke steuern.An embodiment provides that the control unit has at least two microprocessors which essentially independently of one another control the first controllable current sink and the second controllable current sink.

Die Erfindung wird anhand der nachfolgenden Zeichnungen näher erläutert. Es zeigt:

  • Fig. 1: eine Darstellung einer schematischen Beschaltung eines erfindungsgemäßen Feldgerätes, und
  • Fig. 2: eine Darstellung des zeitlichen Verhaltens einiger Ströme während eines Tests mit dem erfindungsgemäßen Feldgerät der Figur 1.
The invention will be explained in more detail with reference to the following drawings. It shows:
  • Fig. 1 : An illustration of a schematic wiring of a field device according to the invention, and
  • Fig. 2 FIG. 2: a representation of the temporal behavior of some currents during a test with the field device according to the invention FIG. 1 ,

In der Fig. 1 ist ein erfindungsgemäßes Feldgerät 10 dargestellt. Dabei handelt es sich beispielsweise um ein Messgerät zur Bestimmung und/oder Überwachung einer Prozessgröße. Die Prozessgröße ist beispielsweise Füllstand, Dichte, Viskosität, Durchfluss, pH-Wert oder Temperatur.In the Fig. 1 an inventive field device 10 is shown. This is, for example, a measuring device for determining and / or monitoring a process variable. The process variable is, for example, level, density, viscosity, flow, pH or temperature.

Das Feldgerät 10 verfügt über eine Schnittstelle 11, über welche beispielsweise die Messwerte als 4...20 mA-Signale ausgegeben werden. In dem Fall, dass ein Fehler des Feldgerätes 10 vorliegt, wird ein Signal ausgegeben, dessen Stromstärke außerhalb dieses für die normale Anwendung reservierten Bereichs liegt. In einer Ausgestaltung liegt der "Fehlerstrom" unterhalb von 3,6 mA.The field device 10 has an interface 11, via which, for example, the measured values are output as 4... 20 mA signals. In the event that there is an error of the field device 10, a signal is output, whose current is outside this range reserved for normal use. In one embodiment, the "fault current" is below 3.6 mA.

Die hier gezeigte Schaltung erlaubt den Test, ob dieser Fehlerstrom erzeugt werden kann, ohne dass das Fehlersignal direkt an die Schnittstelle 11 gelangt. In dem Feldgerät 10 sind zwei steuerbare Stromsenken 1, 2 in Reihe geschaltet.The circuit shown here allows the test of whether this fault current can be generated without the error signal coming directly to the interface 11. In the field device 10, two controllable current sinks 1, 2 are connected in series.

Ein Teil der ersten steuerbaren Stromsenke 1 ist eine Stromsenke I1. Dies ist eine elektronische Last, deren Laststrom elektronisch regelbar ist. Als Beispiel sind ein Feldeffekttransistor (FET) zu nennen. Weiterhin umfasst die erste steuerbare Stromsenke 1 den ersten Regler RE1, den ersten Messwiderstand R1 und den ersten Widerstand R5. Bei dem Regler RE1 handelt es sich um einen Operationsverstärker, von dem ein Eingang mit der Steuereinheit 13 bzw. speziell mit dem ersten Mikroprozessor M1 der Steuereinheit 13 und ein andere Eingang mit dem ersten Widerstand R5 bzw. mit dem Spannungsabfall über den ersten Messwiderstand R1 mit dem durch einen Operationsverstärker verbunden ist und dessen Ausgang die Einstellung der Stromstärke der ersten Stromsenke I1 bewirkt. Der nicht mit der Steuereinheit 13 verbundene Eingang des Reglers RE1 ist über den ersten Widerstand R5 mit einer Kontaktstelle der Schnittstelle 11 verbunden. Diese Kontaktstelle ist ebenfalls mit Masse verbunden. Der erste Messwiderstand R1 erlaubt auch den Abgriff einer ersten Messspannung U1.A part of the first controllable current sink 1 is a current sink I1. This is an electronic load whose load current is electronically adjustable. An example is a field effect transistor (FET). Furthermore, the first controllable current sink 1 comprises the first regulator RE1, the first measuring resistor R1 and the first resistor R5. The controller RE1 is an operational amplifier, of which an input to the control unit 13 or specifically with the first microprocessor M1 of the control unit 13 and another input with the first resistor R5 or with the voltage drop across the first measuring resistor R1 to which is connected by an operational amplifier and whose output causes the adjustment of the current intensity of the first current sink I1. The input of the regulator RE1 not connected to the control unit 13 is connected to a contact point of the interface 11 via the first resistor R5. This contact point is also connected to ground. The first measuring resistor R1 also allows the tapping of a first measuring voltage U1.

Die erste Stromsenke I1 ist mit der anderen Kontaktstelle der Schnittstelle 11 und mit Masse verbunden. In diesem Bereich der Schaltung sind auch zwischen der ersten Stromsenke I1 und Masse noch eine Zenerdiode Vz und parallel dazu ein Kondensator C vorgesehen. Überdies besteht auch eine Verbindung zwischen den beiden in Reihe geschalteten Stromsenken I1 und I2 und dem zweiten Mikroprozessor M2 der Steuereinheit 13.The first current sink I1 is connected to the other contact point of the interface 11 and to ground. In this area of the circuit, a zener diode Vz and, in parallel thereto, a capacitor C are also provided between the first current sink I1 and ground. Moreover, there is also a connection between the two series-connected current sinks I1 and I2 and the second microprocessor M2 of the control unit 13.

Die zweite steuerbare Stromsenke 2 ist analog der ersten 1 aufgebaut. Sie besteht aus der zweiten Stromsenke I2, dem zweiten Regler RE2, dem zweiten Widerstand R6 und dem zweiten Messwiderstand R2. Dabei sind die erste Stromsenke I1 und die zweite Stromsenke I2 in Reihe geschaltet. Der zweite Regler RE2 wird hier über den zweiten Mikroprozessor M2 der Steuereinheit 13 gesteuert. Die beiden Mikroprozessoren M1, M2 arbeiten unabhängig voneinander und stellen auch unabhängig voneinander über die Regler RE1, RE2 die Stromstärken der beiden Stromsenken I1, I2 ein. Der jeweilige Sollwert für den Strom an der Schnittstelle wird von der Vorgabeeinheit 12 vorgegeben. Dabei handelt es sich insbesondere um die Auswerteeinheit der Sensorikkomponente des Feldgerätes 10. Der Strom an der Schnittstelle wird somit derartig eingestellt, dass er beispielsweise einem ermittelten Messwert für eine Prozessgröße entspricht oder dass er beispielsweise das Erreichen eines Grenzwertes repräsentiert.The second controllable current sink 2 is constructed analogously to the first 1. It consists of the second current sink I2, the second regulator RE2, the second resistor R6 and the second measuring resistor R2. In this case, the first current sink I1 and the second current sink I2 are connected in series. The second controller RE2 is controlled here via the second microprocessor M2 of the control unit 13. The two microprocessors M1, M2 operate independently of each other and also independently of one another via the regulators RE1, RE2, the current strengths of the two current sinks I1, I2. The respective nominal value for the current at the interface is specified by the default unit 12. This is in particular the evaluation unit of the sensor component of the field device 10. The current at the interface is thus set such that it corresponds, for example, to a determined measured value for a process variable or that it represents, for example, the reaching of a limit value.

Um der hier stilisiert dargestellten Empfangseinheit 15 des an der Schnittstelle 11 anliegenden Signals mitzuteilen, dass das Feldgerät 11 noch lebt, wird das Stromsignal innerhalb eines vorgegebenen Intervalls variiert, d.h. es zappelt um den Sollwert der Vorgabeeinheit 12 und ist somit ein Lebenssignal für das Feldgerät 10. Als Beispiel sei ein Sollwert von 19 mA angenommen, welches zwischen zwei Stromwerten abwechselt, d.h. es ergibt sich beispielsweise ein Ausgangssignal 19 mA ± 0,25 mA. Dieses Alternieren bedeutet damit für die Empfangseinheit 15, dass das Feldgerät 10 noch lebt.In order to inform the receiving unit 15, shown stylized here, of the signal present at the interface 11 that the field device 11 is still alive, the current signal is varied within a predetermined interval, i. it fidgets around the setpoint of the default unit 12 and thus is a life signal for the field device 10. For example, assume a set point of 19 mA, which alternates between two current values, i. For example, an output signal of 19 mA ± 0.25 mA results. This alternation thus means for the receiving unit 15 that the field device 10 is still alive.

Werden bei der ersten Stromsenke I1 und der zweiten Stromsenke I2 unterschiedliche Stromstärken eingestellt, so liegt jeweils der niedrigere Stromwert an der Schnittstelle 11 an.If different current intensities are set in the first current sink I1 and the second current sink I2, then in each case the lower current value is applied to the interface 11.

Für den Test, ob das Fehlersignal (hier ein Strom kleiner 3,6 mA) erzeugt werden kann, sind in der erfindungsgemäßen Schaltung noch folgende Komponenten vorgesehen:For the test, whether the error signal (in this case a current less than 3.6 mA) can be generated, the following components are provided in the circuit according to the invention:

Die erste steuerbare Stromsenke 1 verfügt über einen in Reihe zur ersten Stromsenke I1 geschalteten ersten Messwiderstand R1, über den eine erste Messspannung U1 abgegriffen wird. Parallel zur ersten Stromsenke I1 und zum ersten Messwiderstand R1 sind ein erster Schalter S1 und ein erster Überbrückungswiderstand R3 vorgesehen.The first controllable current sink 1 has a first measuring resistor R1, connected in series with the first current sink I1, via which a first measuring voltage U1 is tapped. Parallel to the first current sink I1 and the first measuring resistor R1, a first switch S1 and a first bypass resistor R3 are provided.

Analog sind ein zweiter Messwiderstand R2 für eine zweite Messspannung U2, ein zweiter Schalter S2 und ein zweiter Überbrückungswiderstand R4 bei der zweiten steuerbaren Stromsenke 2 vorgesehen.Analogously, a second measuring resistor R2 for a second measuring voltage U2, a second switch S2 and a second bridging resistor R4 are provided at the second controllable current sink 2.

Wie zu sehen, sind die beiden steuerbaren Stromsenken 1, 2 voneinander "entkoppelt" und erlauben eine Regelung im Wesentlichen unabhängig voneinander.As can be seen, the two controllable current sinks 1, 2 are "decoupled" from one another and allow regulation substantially independently of one another.

Für das Funktionieren der Schaltung sind in der Fig. 2 die zeitlichen Abläufe bzw. die auftretenden Ströme dargestellt. Dargestellt sind von oben nach unten: der Ausgangsstrom an der Schnittstelle 11, der Strom am ersten Messwiderstand R1, der Strom am ersten Überbrückungswiderstand R3, der Strom am zweiten Messwiderstand R2 und der Stromverlauf am zweiten Überbrückungswiderstand R4.For the functioning of the circuit are in the Fig. 2 the time sequences and the occurring currents are shown. Shown are from top to bottom: the output current at the interface 11, the current at the first measuring resistor R1, the current at the first bridging resistor R3, the Current at the second measuring resistor R2 and the current flow at the second bridging resistor R4.

Für den Normalbetrieb sind die Schalter S1 und S2 offen. Die Steuerung der Schalter erfolgt dabei beispielsweise über die Steuereinheit 13, bzw. einzeln über die vorgesehenen Mikroprozessoren M1 und M2, die der ersten steuerbaren Stromsenke I1 bzw. der zweiten steuerbaren Stromsenke I2 zugeordnet sind.For normal operation, the switches S1 and S2 are open. The control of the switches takes place, for example, via the control unit 13, or individually via the provided microprocessors M1 and M2, which are associated with the first controllable current sink I1 and the second controllable current sink I2.

Zum Zeitpunkt t1 sei die erste Stromsenke I1 auf 19,25 mA und die zweite Stromsenke I2 auf 18,75 mA eingestellt. Der Ausgangsstrom an der Schnittstelle 11 wird von der zweiten Stromsenke I2 bestimmt. Der fließende Strom wird über die beiden Messwiderstände R1 und R2 gemessen und über jeweils einen Operationsverstärker in eine dem Strom proportionale Spannung U1 bzw. U2 umgewandelt und den Mikroprozessoren M1 und M2 zur Kontrolle zugeführt (diese Verbindungen sind für die Übersichtlichkeit hier nicht dargestellt).At time t1, the first current sink I1 is set to 19.25 mA and the second current sink I2 to 18.75 mA. The output current at the interface 11 is determined by the second current sink I2. The flowing current is measured via the two measuring resistors R1 and R2 and converted in each case via an operational amplifier in a voltage proportional to the current U1 or U2 and the microprocessors M1 and M2 supplied for control (these compounds are not shown here for clarity).

Würde über einen Parallelpfad - z.B. seien die beiden Schalter S1, S2 offen, aber niederohmig - ein Strom von z.B. 5 mA fließen, so regelt der Regler, welcher für den fließenden Strom bestimmend ist, trotzdem auf den unteren Wert von 18,75 mA, aber in den Messwiderständen R1 bzw. R2 fließt nur der Differenzstrom von 18,75 mA - 5 mA = 13,75 mA. Somit liegt ein Fehler im Feldgerät 10 vor und die jeweilige Stromsenke I1 bzw. I2 würde den Fehlerstrom kleiner 3,6mA einstellen.Would via a parallel path - e.g. Let the two switches S1, S2 open but low impedance - a current of e.g. 5 mA flow, so regulates the controller, which is determining for the flowing current, still to the lower value of 18.75 mA, but in the measuring resistors R1 and R2, only the differential current of 18.75 mA - 5 mA = 13 flows , 75 mA. Thus, there is a fault in the field device 10 and the respective current sink I1 or I2 would set the fault current less than 3.6mA.

Nun zur Testphase, ob das Feldgerät 10 den Fehlerstrom auch zuverlässig einstellen kann. Der hier gezeigte Ablauf ist dabei rein beispielhaft. Die gestrichelten senkrechten Striche geben immer den Zeitraum an, für welchen jeweils ein Schalter geschlossen ist.Now for the test phase, whether the field device 10 can also reliably set the fault current. The procedure shown here is purely exemplary. The dashed vertical bars always indicate the period for which one switch is closed.

Zunächst der Test der ersten Stromsenke I1 (Test I1 in der Fig. 2):First, the test of the first current sink I1 (test I1 in the Fig. 2 ):

Der Schalter S1 wird geschlossen. Der Strom von 18,75 mA teilt sich über den Zweig I1 und R1 und den Zweig R3 und S1 auf. In beiden Zweigen fließt im Wesentlichen der gleiche Strom, wenn die Widerstände R1 und R3 gleich groß und der Widerstand des Schalters S1 und der Innenwiderstand von I1 sehr klein sind. Die am Messwiderstand R1 abfallende Spannung U1 wird gemessen und mit einem Referenzwert verglichen. Dann wird der Vorgabewert der Stromstärke für die erste Stromsenke I1 vom ersten Mikroprozessor M1 und den ersten Regler RE1 von den oben eingestellten 19,25 mA auf einen Testwert kleiner 18,75 mA, z. B. auf 3 mA gesetzt. Der erste Regler RE1 stellt die erste Stromsenke I1 so ein, dass die Spannung am Widerstand R5, welche über den ersten Messwiderstand R1 gemessen wird, der Sollwertvorgabe vom ersten Mikroprozessor M1, d.h. gleich 3 mA, entspricht. Durch den Zweig R1, I1 fließt damit 3 mA. Der restliche Strom von 18,75 mA - 3 mA fließt über den Parallelzweig aus dem Widerstand R3 und den Schalter S1. Bei dieser Schaltungsanordnung sind Testströme zwischen 0 mA und einem Wert Itestmax1 bei der ersten Stromsenke I1 einstellbar. Der Wert Itestmax1 ist abhängig von dem Verhältnis zwischen den Widerständen R3 und R1. Seien die Werte R3 = 100 Ohm und R1 = 10 Ohm, so kann der Teststrom in I1 zwischen 0 mA und R3 * Igesamt/(R3+R1) = 100 Ohm * 18,75 mA / (100 Ohm + 10 Ohm) =17,05 mA eingestellt werden.The switch S1 is closed. The current of 18.75 mA is split across branch I1 and R1 and branch R3 and S1. Essentially the same current flows in both branches when the resistors R1 and R3 are of equal size and the resistance of the switch S1 and the internal resistance of I1 are very small. The voltage drop across the measuring resistor R1 voltage U1 is measured and compared with a reference value. Then, the default value of the current for the first current sink I1 from the first microprocessor M1 and the first controller RE1 from the above set 19.25 mA to a test value less than 18.75 mA, z. B. set to 3 mA. The first regulator RE1 sets the first current sink I1 so that the voltage across the resistor R5, which is measured via the first measuring resistor R1, the setpoint input from the first microprocessor M1, i. equal to 3 mA, corresponds. Through the branch R1, I1 flows 3 mA. The remaining current of 18.75 mA - 3 mA flows through the parallel branch of the resistor R3 and the switch S1. In this circuit test currents between 0 mA and a value Itestmax1 at the first current sink I1 are adjustable. The value Itestmax1 is dependent on the ratio between the resistors R3 and R1. If the values R3 = 100 ohms and R1 = 10 ohms, the test current in I1 can be between 0 mA and R3 * total / (R3 + R1) = 100 ohms * 18.75 mA / (100 ohms + 10 ohms) = 17 , 05 mA can be set.

Dann wird der Vorgabewert für die erste Stromsenke I1 über den ersten Mikroprozessor M1 und den ersten Regler RE1 von 3 mA auf einen Wert größer 19,25 mA gesetzt. Über die erste Stromsenke I1 und den ersten Messwiderstand R1 fließt wieder der Teilstrom 18,75/2 mA. Dieser Teilstrom kann als Spannung U1 gemessen und mit einem Referenzwert verglichen werden. Mit diesen Spannungsmessungen kann somit das korrekte Schließen des Schalters S1 und die Fähigkeit der ersten Stromsenke 11, einen Strom von 3,0 mA einzustellen, überprüft werden.Then, the default value for the first current sink I1 via the first microprocessor M1 and the first regulator RE1 of 3 mA is set to a value greater than 19.25 mA. The partial current 18.75 / 2 mA flows again via the first current sink I1 and the first measuring resistor R1. This partial current can be measured as voltage U1 and compared with a reference value. Thus, with these voltage measurements, the proper closing of the switch S1 and the ability of the first current sink 11 to set a current of 3.0 mA can be checked.

In der Testzeit fließt der Teilstrom Igesamt - 3 mA über den Widerstand R3 und den Schalter S1. Zu den Klemmen und somit nach außen fließen konstant 18,75 mA. Anschließend wird der Schalter S1 geöffnet. Der Strom wird immer noch von der zweiten Stromsenke I2 auf 18,75 mA gehalten.In the test time, the partial current Itotal - 3 mA flows through the resistor R3 and the switch S1. To the terminals and thus to the outside flow constantly 18.75 mA. Subsequently, the switch S1 is opened. The current is still held by the second current sink I2 to 18.75 mA.

Zum Zeitpunkt t2 wird der Vorgabewert für die zweite Stromsenke I2 über den zweiten Mikroprozessor M2 und den zweiten Regler RE2 auf 19,25 mA gesetzt. Da die erste Stromsenke auf einen Strom größer 19,25 eingestellt wurde, bestimmt die zweite Stromsenke I2 den Ausgangsstrom an der Schnittstelle, welcher somit 19,25 mA beträgt. Das Ausgangssignal variiert daher zwischen den beiden Werten 18,75 mA und 19,25 mA. Somit zeigt das Feldgerät 10, dass es noch lebt.At time t2, the default value for the second current sink I2 is set to 19.25 mA via the second microprocessor M2 and the second regulator RE2. Since the first current sink was set to a current greater than 19.25, the second current sink I2 determines the output current at the interface, which is thus 19.25 mA. The output signal therefore varies between the two values 18.75 mA and 19.25 mA. Thus, the field device 10 shows that it is still alive.

Zum Zeitpunkt t3 wird der Vorgabewert für die erste Stromsenke I1 vom Wert größer 19,25 mA auf 18,75 mA herabgesetzt. Damit bestimmt die erste Stromsenke I1 den Strom nach Außen (18,75 mA). Die Spannungsmessungen an R1 und R2 ergeben im fehlerfreien Fall den jeweils richtigen Stromwert. Stimmt der Wert, so hat der Schalter S1 geöffnet und die erste Stromsenke I1 ist in Ordnung.At time t3, the default value for the first current sink I1 is reduced from the value greater than 19.25 mA to 18.75 mA. Thus, the first current sink I1 determines the current to the outside (18.75 mA). The voltage measurements at R1 and R2 give the correct current value in the fault-free case. If the value is correct, the switch S1 has opened and the first current sink I1 is in order.

Der Test der zweiten Stromsenke I2:The test of the second current sink I2:

Hierfür wird der zweite Schalter S2 geschlossen. Der Strom von momentan 18,75 mA teilt sich über den Zweig I2 und R2 und den Zweig R4 und S2 auf. In beiden Zweigen fließt ungefähr der gleiche Strom, wenn die Widerstände R2 und R4 gleich groß und der Widerstand des Schalters S2 und der Innenwiderstand der zweiten Stromsenke I2 sehr klein sind. Zu diesem Zeitpunkt wird die Spannung U2 gemessen und mit einem Referenzwert verglichen. Anschließend wird der Vorgabewert der zweiten Stromsenke I2 über den Mikroprozessor M2 und den zweiten Regler RE2 von 19,25 mA auf einen Wert kleiner 18,75 mA, z. B. auf 3 mA gesetzt. Der zweite Regler RE2 stellt die zweite Stromsenke I2 so ein, dass die Spannung am Widerstand R6, welche über den zweiten Messwiderstand R2 gemessen wird, der Sollwertvorgabe vom zweiten Mikroprozessor M2, d.h. gleich 3 mA, entspricht. Durch den Zweig R2, I2 fließt damit 3 mA. Der restliche Strom von 18,75 mA-3 mA fließt über den Parallelzweig aus dem Widerstand R4 und den Schalter S2. Bei dieser Schaltungsanordnung sind Testströme zwischen 0 mA und einem Wert Itestmax2 bei der zweiten Stromsenke I2 einstellbar. Der Wert Itestmax2 ist abhängig von dem Verhältnis zwischen den Widerständen R4 und R2. Seien die Werte R4 = 100 Ohm und R2 = 10 Ohm, so kann der Teststrom in I2 zwischen 0 mA und R4 * Igesamt/(R4+R2) = 100 Ohm * 18,75 mA / (100 Ohm + 10 Ohm) =17,05 mA eingestellt werden. Dann wird der Vorgabewert für die zweite Stromsenke I2 von 3 mA auf einen Wert größer 19,25 mA gesetzt. Über die zweite Stromsenke I2 und den Messwiderstand R2 fließt wieder der Teilstrom 18,75/2 mA, welcher über die Spannung U2 messbar und mit einem Referenzwert vergleichbar ist.For this purpose, the second switch S2 is closed. The current of currently 18.75 mA is split across branch I2 and R2 and branch R4 and S2. In both branches approximately the same current flows when the resistors R2 and R4 are the same size and the resistance of the switch S2 and the internal resistance of the second current sink I2 are very small. At this time, the voltage U2 is measured and compared with a reference value. Subsequently, the default value of the second current sink I2 via the microprocessor M2 and the second regulator RE2 of 19.25 mA to a value less than 18.75 mA, z. B. set to 3 mA. The second regulator RE2 sets the second current sink I2 so that the voltage across the resistor R6, which is measured via the second measuring resistor R2, the setpoint input from the second microprocessor M2, ie equal to 3 mA corresponds. Through the branch R2, I2 3 mA flows. The remaining current of 18.75 mA-3 mA flows via the parallel branch of the resistor R4 and the switch S2. In this circuit test currents between 0 mA and a value Itestmax2 at the second current sink I2 are adjustable. The value Itestmax2 is dependent on the ratio between the resistors R4 and R2. If the values R4 = 100 ohms and R2 = 10 ohms, the test current in I2 can be between 0 mA and R4 * total / (R4 + R2) = 100 ohms * 18.75 mA / (100 ohms + 10 ohms) = 17 , 05 mA can be set. Then, the default value for the second current sink I2 of 3 mA is set to a value greater than 19.25 mA. The partial current 18.75 / 2 mA, which can be measured via the voltage U2 and is comparable to a reference value, flows again via the second current sink I2 and the measuring resistor R2.

Mit diesen Spannungsmessungen kann das korrekte Schließen des Schalters S2 und die Fähigkeit der zweiten Stromsenke, einen Strom kleiner 3,6 mA einzustellen, d.h. zu sperren, überprüft werden.With these voltage measurements, the proper closing of the switch S2 and the ability of the second current sink to set a current less than 3.6 mA, i. to be checked.

In der Testzeit fließt der Teilstrom Igesamt abzüglich 3 mA über den Überbrückungswiderstand R4 und den Schalter S2. An der Schnittstelle 11 liegt konstant ein Stromsignal von 18,75 mA an.In the test time, the partial current I total flows less 3 mA via the bridging resistor R4 and the switch S2. At the interface 11 is constant at a current signal of 18.75 mA.

Anschließend wird der Schalter S2 geöffnet, wobei der Strom immer noch von der ersten Stromsenke I1 auf 18,75 mA gehalten wird.Subsequently, the switch S2 is opened, wherein the current is still held by the first current sink I1 to 18.75 mA.

Zum Zeitpunkt t4 wird der Vorgabewert für die erste Stromsenke I1 über den ersten Mikroprozessor M1 und den ersten Regler RE1 auf 19,25 mA gesetzt. Damit stellt die erste Stromsenke I1 den Strom an der Schnittstelle 11 auf 19,25 mA ein.At time t4, the default value for the first current sink I1 is set to 19.25 mA via the first microprocessor M1 and the first regulator RE1. Thus, the first current sink I1 sets the current at the interface 11 to 19.25 mA.

Zum Zeitpunkt t5 wird der Vorgabewert für den Stromwert der zweiten Stromsenke I2 von dem Wert größer 19,25 mA auf 18,75 mA herabgesetzt, so dass die zweite Stromsenke I2 den Strom über die Schnittstelle 11 nach Außen bestimmt. An den beiden Messwiderständen R1 und R2 werden die Spannungen U1 und U2 gemessen, um das Vorliegen des jeweils erforderlichen Stromes zu überwachen. Entsprechen die Spannungen U1 und U2 den Referenzwerten, so hat der Schalter S2 geöffnet und die zweite Stromsenke I2 ist in Ordnung.At time t5, the default value for the current value of the second current sink I2 is reduced from the value greater than 19.25 mA to 18.75 mA, so that the second current sink I2 determines the current via the interface 11 to the outside. At the two measuring resistors R1 and R2, the voltages U1 and U2 are measured to monitor the presence of the respective required current. Do the voltages U1 and U2 the reference values, so the switch S2 has opened and the second current sink I2 is OK.

In dem hier gezeigten Diagramm der Fig. 2 wird das Testen mit dem nächsten Test der ersten Stromsenke I1 weitergeführt.In the diagram shown here Fig. 2 the testing continues with the next test of the first current sink I1.

Durch das zeitabhängige Schalten der Stomsenken I1, I2 mit entsprechender Sollwertvorgabe des jeweiligen Stromwertes wird erreicht, dass durch das Öffnen und Schließen der Schalter S1 und S2 keine ungewollten Stromspitzen auf dem 4...20 mA-Signal an der Schnittstelle 11 erzeugt werden.By the time-dependent switching of the Stomsenken I1, I2 with appropriate setpoint specification of the respective current value is achieved that no unwanted current peaks on the 4 ... 20 mA signal at the interface 11 are generated by the opening and closing of the switches S1 and S2.

Claims (11)

  1. Field device (10) used in process automation engineering, with at least one interface (11) for outputting a current signal, with at least one default unit (12) which specifies at least one value on which the current signal to be output via the interface (11) is dependent,
    characterized in that
    at least a first controllable current sink (1) and a second controllable current sink (2) are provided,
    the first controllable current sink (1) and the second controllable current sink (2) are designed in such a way that
    the first controllable current sink (1) and the second controllable current sink (2) can each be set to a predefinable current strength
    and in that the first controllable current sink (1) and the second controllable current sink (2) are switched in series, and
    in that the first controllable current sink (1) and the second controllable current sink (2) are connected to the interface (11) in such a way that the current signal which is present at the interface (11) depends on the lower current strength of the predefinable current strengths to which the first controllable current sink (1) and the second controllable current sink (2) are set.
  2. Field device (10) as claimed in Claim 1,
    characterized in that
    the field device (10) signals the occurrence of an error in the field device (10) by an error signal via the interface (11), wherein the error signal is within an error signal interval.
  3. Field device (10) as claimed in Claim 2,
    characterized in that
    the error signal has a current strength below a predefined value, especially smaller than 3.6 mA.
  4. Field device (10) as claimed in one of the previous claims,
    characterized in that
    at least one control unit (13) is provided
    and
    in that the control unit (13) is designed in such a way that the control unit (13), on the basis of the default unit (12), sets the first controllable current sink (1) and the second controllable current sink (I2) each to a predefinable current strength.
  5. Field device (10) as claimed in Claim 5,
    characterized in that
    the control unit (13) is designed in such a way that the control unit (13), on the basis of the default unit (12), controls the first controllable current sink (1) and the second controllable current sink (12) in such a way that the signal present at the interface (11) varies at a predefinable interval.
  6. Field device (10) as claimed in one of the previous claims,
    characterized in that
    the first controllable current sink (1) consists at least of a first current sink (11), a first regulator (RE1), a first resistor (R5) and a first measuring resistor (R1),
    wherein the first measuring resistor (R1) is switched in series in relation to the first current sink (I1) and is provided to measure a first measuring voltage (U1).
  7. Field device (10) as claimed in one of the previous claims,
    characterized in that
    the second controllable current sink (2) consists at least of a second current sink (I2), a second regulator (RE2), a second resistor (R6) and a second measuring resistor (R2),
    wherein the second measuring resistor (R2) is switched in series in relation to the second current sink (I2) and is provided to measure a second measuring voltage (U2).
  8. Field device (10) as claimed in one of the previous claims,
    characterized in that
    a capacitor (C) and a diode (VZ) are integrated into the first controllable current sink (1) and/or the second controllable current sink (2).
  9. Field device (10) as claimed in one of the previous claims,
    characterized in that
    a first switch (S1) and a first bridging resistor (R3) are provided in parallel to the first current sink (I1) and to the first measuring resistor (R1).
  10. Field device (10) as claimed in one of the previous claims,
    characterized in that
    a second switch (S2) and a second bridging resistor (R4) are provided in parallel to the second current sink (12) and to the second measuring resistor (R2).
  11. Field device (10) as claimed in one of the previous claims,
    characterized in that
    the control unit (13) has at least two microprocessors (M1, M2) which essentially control the first controllable current sink (I1) and the second controllable current sink (I2) independently of one another.
EP09783147.3A 2008-10-15 2009-09-18 Process automation field device Active EP2335025B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102008042851A DE102008042851A1 (en) 2008-10-15 2008-10-15 Field device of process automation
PCT/EP2009/062088 WO2010043468A1 (en) 2008-10-15 2009-09-18 Process automation field device

Publications (2)

Publication Number Publication Date
EP2335025A1 EP2335025A1 (en) 2011-06-22
EP2335025B1 true EP2335025B1 (en) 2013-11-20

Family

ID=41625126

Family Applications (1)

Application Number Title Priority Date Filing Date
EP09783147.3A Active EP2335025B1 (en) 2008-10-15 2009-09-18 Process automation field device

Country Status (5)

Country Link
US (1) US9230428B2 (en)
EP (1) EP2335025B1 (en)
CN (1) CN102187180B (en)
DE (1) DE102008042851A1 (en)
WO (1) WO2010043468A1 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010039271A1 (en) 2010-08-12 2012-02-16 Endress + Hauser Gmbh + Co. Kg Circuit for controlling and monitoring a signal current and a transmitter with such a circuit

Family Cites Families (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5481200A (en) * 1993-09-15 1996-01-02 Rosemont Inc. Field transmitter built-in test equipment
DE4422867A1 (en) * 1994-06-30 1996-01-04 Itt Ind Gmbh Deutsche Sensor with a programmable switching threshold
US5740241A (en) * 1995-05-12 1998-04-14 Carrier Access Corporation T1 channel bank control process and apparatus
DE29917651U1 (en) * 1999-10-07 2000-11-09 Siemens Ag Transmitter and process control system
US6384582B2 (en) 2000-05-19 2002-05-07 Endress + Hauser Flowtec Ag Controlled current sources of two-wire measuring instruments
EP1158274B1 (en) * 2000-05-19 2009-02-18 Endress + Hauser Flowtec AG Controlled current sources of two-wire measuring apparatuses
US7262628B2 (en) * 2004-07-02 2007-08-28 Primarion, Inc. Digital calibration with lossless current sensing in a multiphase switched power converter
DE10361465A1 (en) * 2003-12-23 2005-08-11 Endress + Hauser Gmbh + Co. Kg Process meter with extended hardware error detection
DE102005001601B4 (en) 2005-01-12 2011-07-28 Endress + Hauser GmbH + Co. KG, 79689 Field device with bus interface
DE102005018398B4 (en) * 2005-04-20 2021-02-04 Endress + Hauser Wetzer Gmbh + Co. Kg Device for outputting an electrical output signal and measuring device with it
DE102006024311A1 (en) 2006-05-24 2007-11-29 Berthold Technologies Gmbh & Co. Kg Circuit for transmitting an analog signal value
US8054071B2 (en) * 2008-03-06 2011-11-08 Allegro Microsystems, Inc. Two-terminal linear sensor

Also Published As

Publication number Publication date
CN102187180B (en) 2014-08-20
DE102008042851A1 (en) 2010-04-22
CN102187180A (en) 2011-09-14
EP2335025A1 (en) 2011-06-22
US20110309813A1 (en) 2011-12-22
US9230428B2 (en) 2016-01-05
WO2010043468A1 (en) 2010-04-22

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