FIELD DEVICE

Abstract

A field device having a safe interface is based on two voltage regulators designed to set electrical current between corresponding contacts of the interface. The field device tests via which of the contacts the field device is connected with a superordinate unit and an automatic configuration of the interface can be performed for the appropriate transmission standard. Because the contacting to the superordinated unit is checked repetitively by means of two electrical current regulators it is assured that the field device can determine and automatically react to a change of the contacting at the interface even during measurement operation. This makes the interface safe and thereby increases the safety of the process plant, in which the field device is applied.

Claims

1-10. (canceled)

11. A field device for measuring a measured variable, comprising: a sensor designed to measure the measured variable; an interface having at least four electrical contacts; a first electrical current regulator designed to set a first electrical current between a first contact of the at least four electrical contacts and a second contact of the at least four electrical contacts when the field device is contacted via the interface such that a first voltage source is connected across the first and the second contacts; a second electrical current regulator designed to set a second electrical current between the first contact and a third contact of the at least four electrical contacts when the field device is contacted via the interface such that a second electrical voltage source is connected across the first and the third contacts and to generate a second signal; and a control unit designed to: transmit the measured value according to a predefined digital standard via a fourth contact of the at least four electrical contacts when the second electrical current is settable between the first contact and the third contact, and control the first electrical current regulator such that the electrical current level of the first electrical current corresponds to the measured value according to a predefined electrical current signal standard when the second electrical current regulator generates the second signal.

12. The field device as claimed in claim 11, wherein the first electrical current regulator is designed to generate a first signal when the field device is contacted in such a manner that no electrical voltage source is connected across the first contact and the second contact.

13. The field device as claimed in claim 12, wherein, depending on contacting of the interface, the first voltage source or the second voltage source supplies the first electrical current regulator, the second electrical current regulator, and/or the control unit with power.

14. The field device as claimed in claim 13, wherein the first electrical current regulator comprises a controllable operational amplifier for controlling the electrical current level of the first electrical current, and wherein the control unit is designed to detect the control signal of the operational amplifier as the first signal when the operational amplifier is working in saturation.

15. The field device as claimed in claim 11, wherein an TO-Link standard is implemented in the control unit as a digital standard for transmitting the measured value via the fourth contact.

16. The field device as claimed in claim 11, wherein a 4-20 mA standard is implemented in the control unit as a standard for electrical current signal-based transmitting of the measured value via the first contact and the second contact.

17. The field device as claimed in claim 11, wherein the interface is designed as an M12 plug-in connection.

18. A method for transmitting a measured value of a field device, comprising: providing the field device, including: a sensor designed to measure the measured variable; an interface having at least four electrical contacts; a first electrical current regulator designed to set a first electrical current between a first contact of the at least four electrical contacts and a second contact of the at least four electrical contacts when the field device is contacted via the interface such that a first voltage source is connected across the first and the second contacts; a second electrical current regulator designed to set a second electrical current between the first contact and a third contact of the at least four electrical contacts when the field device is contacted via the interface such that a second electrical voltage source is connected across the first and the third contacts and to generate a second signal; and a control unit designed to: transmit the measured value according to a predefined digital standard via a fourth contact of the at least four electrical contacts when the second electrical current is settable between the first contact and the third contact, and control the first electrical current regulator such that the electrical current level of the first electrical current corresponds to the measured value according to a predefined electrical current signal standard when the second electrical current regulator generates the second signal; measuring the measured value, setting the second electrical current between the first contact and the third contact when the field device is contacted via the interface such that a second electrical voltage source is connected across such contacts, and otherwise generating the second signal; transmitting the measured value according to the predefined digital protocol via the fourth contact when the second signal is not generated; setting the first electrical current between the first contact and the second contact when the field device is contacted via the interface such that a first electrical voltage source is connected across such contacts, and otherwise generating the first signal; wherein method steps are cyclically repeated when the first signal is not generated, and wherein, in the other case, measuring the measured value, transmitting the measured value according to the predefined digital protocol via the fourth contact, setting the first electrical current and possible generating of the first signal are repeated.

19. The method as claimed in claim 18, further comprising: controlling the first electrical current regulator such that the electrical current level of the first electrical current corresponds to the measured value according to the predefined electrical current signal standard when the second signal is generated, wherein method steps are cyclically repeated when the first signal is generated, and wherein, in the other case, measuring the measured value and controlling the first electrical current regulator are repeated, such that the electrical current level of the first electrical current corresponds to the measured value according to the predefined electrical current signal standard.

20. The method as claimed in claim 19, wherein the first electrical current between the first contact and the second contact is set a maximum of 300 milliseconds after the second electrical current regulator sets the second electrical current between the first contact and the third contact.

Description

[0034] The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:

[0035] FIG. 1 a field device of the invention shown on a container and connected via an interface to a superordinated unit,

[0036] FIG. 2 an equivalent circuit diagram of the field device, and

[0037] FIG. 3 a flowchart of the method of the invention for operation of the field device.

[0038] For providing a general understanding of the invention, FIG. 1 shows schematically a container 3, in which a medium 2, such as, for example, chemicals, grain, cement, water, liquefied gas or a bulk good is located. In order to determine a measured variable relevant for the process installation, thus a measured variable such as the temperature, the pressure or a fill level, there is mounted laterally on the container 3 a field device 1 of the invention. For transmitting the corresponding measured value to, or for the exchange of other measuring device-specific data with, a superordinated unit 4, the field device 1 includes a suitable interface 11. The superordinated unit 4 can be, for example, a process control station for monitoring the process plant.

[0039] An established analog standard for transmitting the measured value in the field of process automation is the 4-20 mA standard. In such case, the value of a first direct current a.sub.1 changes linearly with the measured value. This means that an electrical current level of 4 mA corresponds to 0% of the measured value, while 20 mA is equivalent to 100% of the measured value. In the case of a fill level measurement, for example, 4 mA corresponds, thus, to a completely empty container 3. 12 mA corresponds to a 50% filled container 3. And a completely filled container 3 is represented by a 20 mA electrical current level of the signal. Accordingly, the interface 11 of the field device 1 requires for implementing the 4-20 mA standard at least two electrical contacts 111, 112, such as shown in FIG. 2. The first electrical current a.sub.1 of the 4-20 mA signal is set, in such case, by a first electrical current regulator 12 of the field device 1. For control of the first electrical current a.sub.1 in the simplest case, the first electrical current regulator 12 can operate based on an operational amplifier, which is connected, for example, as a voltage current converter. The first electrical current regulator 12 is, in turn, controlled by a control unit 14, such as, for example, a microcontroller, by means of a corresponding control signal. In such case, the control unit 14 obtains the measured value from a sensor 10, which is designed appropriately for measuring a measured variable.

[0040] In the case of the embodiment of the field device 1 shown in FIG. 2, both the control unit 14 as well as also the first electrical current regulator 12 are supplied with the required power via the interface 11 from the superordinated unit 4. In the circuit diagram of FIG. 2 this power supply is provided via the first contact 111 and the second contact 112 of the interface 11 by a first voltage source Q.sub.1. Analogously thereto, also the sensor 10 can, depending on functional principle, be supplied with power from the same source (not explicitly shown in FIG. 2).

[0041] Advantageous in the 4-20 mA standard is that an interrupted line between field device 1 and superordinated unit 4 is easily recognizable as a disturbance, since the first electrical current a.sub.1 is, in such case, completely interrupted. Disadvantageous in such standard, however, is the relatively high electrical current consumption and the only conditionally present opportunity to transmit, supplementally to the measured value, additional data or parameters. Therefore, the measured value transmission in modern process plants occurs increasingly purely on a digital basis.

[0042] In order to be able to be applied variably in different fields of use, the interface 11 of the field device 1 is designed flexibly, so that the measured value can be transmitted according to the 4-20 mA, analog standard, or along with other data, also using digitally based transmission standards. Digital standards for this include, for example, “10-Link” according to the IEC standard 61131-9, “PROFIBUS”, “HART”, “wireless HART” and “Ethernet”. Accordingly, the interface 11 of the field device 1 includes, such as shown in FIG. 2, besides the two contacts 111, 112 for the 4-20 mA-based measured value transmission, two other contacts 113, 114. Since the IO-Link standard requires three contacts 111, 113, 114, it is, in such case, correspondingly an option that the control unit 14 transmits the measured value or other parameters by means of this standard via the fourth contact 114, wherein, in such case, the third contact 113 of the interface 11 serves as ground potential. In contrast with the illustration, the control unit 14 can use for generating the corresponding signal a separate IO-Link module, which is activated only in the case of configuration of the interface 11 for IO-Link based transmission. In the case of this configuration of the interface 11, the control unit 14 can be supplied with power from the superordinated unit 4 via the first contact 111. In the equivalent circuit diagram shown in FIG. 2, such is provided, in turn, by a second voltage source Q.sub.2 connected between the first contact 111 and the third contact 113. The interface 11 can be designed, for example, in the form of an M12-plug connection or a comparable plug connection-type having at least four contacts.

[0043] In the case of start-up on the container 3, the field device 1 must be configured for the at least two potentially possible standards the interface 11 is to use. Moreover, the corresponding contacts 111-114 of the interface 11 must be correctly contacted. If such does not happen, then such can in the worst case lead to the fact that the incorrect wiring, or the incorrect configuration, is not detected by the superordinated unit 4 and the transmitted signals are interpreted rather as a measured value not correctly reflecting the actual measured value.

[0044] According to the invention, the field device 1 includes, consequently, additionally, a second electrical current regulator 13, which is arranged between the first contact 111 and the third contact 113 of the interface 11. In this way, it is possible to set a second electrical current a.sub.2 between the first contact 111 and the third contact 113 when the field device 1 is contacted via the interface 11 such that the superordinated unit 4, and the second electrical voltage source Q.sub.2, is connected across such contacts 111, 113. In such case, the second electrical current a.sub.2 reaches as electrical current level a lower value, for example, 200 μA. When it is possible to set the second electrical current a.sub.2 by means of the second electrical current regulator 13, then the field device 1 is, as a result, then so configured that it transmits the measured value, or other parameters, via the fourth contact 114 by means of the predefined digital protocol, such as the IO-Link.

[0045] In the case, in which the second electrical current a.sub.2 between the first contact 111 and the third contact 113 can be set by means of the second electrical current regulator 13, nevertheless also the first electrical current regulator 12 is activated, in order, for the sake of safety, to check, whether the superordinated unit 4, thus the first electrical voltage source Q.sub.1, is connected across the first contact 111 for the power supply and the second contact 112 for the grounding of the first electrical current signal a.sub.1. The operation of the first electrical current regulator 12 can occur, in such case, very near in time, for example, 300 ms, after the second electrical current regulator 13 sets the second electrical current a.sub.2 between the first contact 111 and the third contact 113. For just checking whether a first electrical current a.sub.1 can be set between the first contact 111 and the third contact 113, its electrical current level does not have to correspond to the measured value according to the 4-20 mA standard. Instead, a significantly lower electrical current level, for example, again, 200 μA can be used.

[0046] If the testing shows that the first electrical current a.sub.1 is not settable by means of the first electrical current regulator 12, then this is interpreted as confirmation that the three contacts 111, 113, 114 are still connected with the superordinated unit 4 for digital data transmission. Accordingly, the digital data transmission via the fourth contact 114 remains active. The first electrical current regulator 12 signals the control unit 14 by means of a corresponding first signal s.sub.f1 that the first electrical current a.sub.1 is not settable. When the first electrical current regulator 12 is based on an operational amplifier, the control unit 14 can, for example, detect the control signal of the operational amplifier as first signal s.sub.f1, in case the operational amplifier is operating in saturation, thus, when it is attempted to set the first electrical current a.sub.1 to no avail.

[0047] When the testing by means of the first electrical current regulator 12 shows that the first electrical current a.sub.1 cannot be set and, thus, the measured value cannot be transmitted as analog data via the contacts 111, 112, the first electrical current regulator 12 can, in such case, be deactivated. FIG. 3 shows these method steps schematically.

[0048] While these above mentioned method steps are cyclically repeated, as long as the second voltage source Q.sub.2 is connected across the first contact 111 and the third contact 113, or as long as the first electrical current a.sub.1 is not settable, the control unit 14 of the field device 1 can detect a change in the situation as soon as it happens.

[0049] If the control unit 14 detects due to a missing first signal s.sub.f1 of the first electrical current regulator 12 that now the first electrical current a.sub.1 between the first contact 111 and the second contact 112 can be set, then the control unit 14 deduces therefrom that the field device 1 is henceforth so to be configured that the measured value is now to be transmitted via these contacts 111, 112 by analog measured value transmission. For checking this, the second electrical current regulator 13 is (or remains) activated, in order to verify that indeed no second electrical current a.sub.2 can now be set between the first contact 111 and the third contact 113. In the case of corresponding verification, thus when the second electrical current regulator 13 transmits a corresponding signal s.sub.f2 to the control unit 14, the control unit 14 controls the first electrical current regulator 12 such that the first electrical current a.sub.1 corresponds to the measured value measured by the sensor according to the 4-20 mA standard.

[0050] The method of the invention is shown in summary in FIG. 3. Advantageous here is that the two electrical current regulators 12, 13 virtually redundantly check via which of the contacts 111-114 the field device 1 is contacted with the superordinated unit 4, such that the corresponding transmission standard can be set. By the cyclic repetition of the method steps, it is assured that the field device 1 determines a change of the contacting even during measurement operation and can automatically react, without requiring that the configuration of the field device 1 must be manually changed. This supplementally increases the safety of the total process plant.

LIST OF REFERENCE CHARACTERS

[0051] 1 field device [0052] 2 fill substance [0053] 3 container [0054] 4 superordinated unit [0055] 10 sensor [0056] 11 interface [0057] 12 first electrical current regulator [0058] 13 second electrical current regulator [0059] 14 control unit [0060] 111 first contact [0061] 112 second contact [0062] 113 third contact [0063] 114 fourth contact [0064] 141 electrical current measuring device [0065] a.sub.1 first electrical current [0066] a.sub.2 second electrical current [0067] Q.sub.1 first voltage source [0068] Q.sub.2 second voltage source [0069] s.sub.f1 first signal [0070] s.sub.f2 second signal