ANALOG INTERFACE UNIT

Abstract: The present invention relates to a device for adaptation of analog input signals (AI) or output signals (AO) and which, per se, exhibits the functions selection between utilization as analog input or output unit, selection between function as current or voltage input unit, in the latter case with an optional voltage range, as well as selection between function as current or voltage output unit. In addition, the device is provided with overcurrent protection and overvoltage protection as well as circuits for supervision of current and voltage values at the output. The latter supervision is realized by feeding back the current and voltage values and comparing them with expected values. The protection function of the device allows unlimited faulty connection under current and voltage conditions within the field of application. All of these enumerated functions are accommodated within one and the same electronic unit, which is achieved by a far-reaching integration of the components used in few integrated circuits. The selection of function mode is achieved by a simple programming.

Description: Analog interface unit TECHNICAL FIELD The present invention relates to a device for adaptation of signals in an electrical system in which members in the form of sensors, actuators, transducers or similar members are fed with analog output signals from the device or in which these members feed the device with analog input signals . BACKGROUND ART In connection with communication between electrical units, for example when electrical members of various types commu- nicate with an electronic unit for conveying information to or collecting information from these members, demands for signal adaptation between the electrical units will imme¬ diately arise. To carry out this signal adaptation, an input or output unit can be connected nearest the electrical member, which input or output unit is intended to see to the need of signals of the connected member or the electronic unit with respect to current and voltage level as well as signal type. Both analog and digital signal types occur. In this description only adaptation when using analog signal types is described. In modularized building systems, special input and output units occur, in this case analog I/O units, AI/AO, which take care of the above-mentioned signal adaptation. Such building systems are utilized, for example, within car electronics and industrial process adaptation systems. To cover as many of the signal types occurring as possible, the AI/AO units are designed with a plurality of different functions for adaptation to various demands . The relevant functions of a AI/AO unit are primarily its use as AI unit or AO unit as well as the selection of current and voltage ranges for input and output, respectively, overcurrent protection, overvoltage protection, constituting protection functions, as well as current and voltage supervision in case of AO function. All of the above functions are each currently applied in known technique within the field. To be able to satisfy different requirements for fields of applications for AI/AO units, such units have been designed in a number of diffe¬ rent variants corresponding to different specifications of requirements. This causes problems in the design and in- stallation of electronics systems according to the above, since each individual AI/AO unit must be specified. A requirement for realization of one single type of AI/AO unit will naturally arise, which, per se, comprises all of the above desirable functions. Modularized AI/AO units already exist on the market, which units integrate several of the above-mentioned functions in one and the same module, however, not all of those enumera¬ ted above at the same time. In the following description, a AI/AO module will be described which claims to have all of the above-mentioned functions available and integrated in one and the same module . SUMMARY OF THE INVENTION The present invention comprises a device for adaptation of analog input signals or output signals and which, per se, exhibits the following functions: selection between utili¬ zing the device as analog input or output unit, selection between function as current or voltage input unit, in the latter case with an optional voltage range, as well as selection between function as current or voltage output unit. In addition, the device is provided with overcurrent protection and overvoltage protection as well as circuits for supervision of current and voltage values at the output. The latter supervision is realized by feeding back current and voltage values and comparing them with expected values. The protection function of the device permits unlimited faulty connection under current and voltage conditions within the field of application. All of these enumerated functions are accomodated within one and the same electronic unit, which is achieved by a far-reaching integration of the components used in few integrated circuits. The selection of function mode is obtained by a simple programming. The device described constitutes part of a complete AI/AO interface, that is, the part between connection to an external sensor/actuator and an A/D and D/A convertor, respectively. Such an interface may comprise also A/D and D/A convertors, respectively, depending on the field of use. An interface of the kind mentioned may be used, for example, in a process computer system. In this case a device accor¬ ding to the description is used for analog signal adaptation in an analog interface unit between A/D and D/A units, respectively, in the interface and transducers or the like in a supervised process. The principal characteristics of the AI/AO unit according to the invention can be summarized as follows: - the same device can be used as either analog input unit or analog output unit, - the same device can be used for all feasible voltages within the field of application, - the device has different types of protection and supervision functions, and - the function mode is selected by an operative setting which programs the device with respect to functions. When using the device as an analog output unit, the following functions are possible to use separately: - analog voltage output, and - analog current output. When using the device as an AI unit, different analog input signal modes are defined: - different regions for analog voltage supply, and - analog current supply. The interface unit comprises control circuits and circuits for protection functions as well as circuits for the above- mentioned supervisions. These circuits are integrated on one, two or few integrated circuits of the application specified integrated circuits type, so-called ASIC circuits, or similar circuits. In this way, all the components can be integrated in ASIC circuits without free components having to be utilized in the AI/AO unit in most applications. The unit can be programmed for its functions from a super- ordinate electronic unit by select signals and threshold values for voltages and currents setting the AI/AO unit to act in accordance with the intended function. An AI/AO unit according to the invention considerably faci¬ litates, for example, design, installation and service of electronic systems in which analog interface units are uti¬ lized. One single type of I/O units fulfils the requirements for most of the cases of analog signal adaptation occurring. This means, for example, that during installation in a process control system, it is not necessary to know in advance the distribution between AI channels and AO channels or the voltage levels thereof, which entails great savings and a gain in time. In addition, the protection functions applied to the unit have an economic importance in so far as the programmability extends the mean service life of indi- vidual AI or AO units since different forms of operations thereof become superfluous . An application of an analog interface unit according to the invention, miniaturized and integrated in the described manner, constitutes its use in a process control system. The far-reaching integration of the interface unit makes possible the production of single-channel analog interface units housed in small modules. These analog interface modules make it possible to distribute interface units closer to external electrical members in a process, whereby communication between the interface module and a supervision unit, for example a computer, takes place via a databus . Modules of the kind mentioned may be mounted on standard mounting rails, where communication by means of the super¬ vision unit takes place via conducting paths located in or on the surface of the mounting rail. In such an application, the use of prior art multi-channel process adaptation circuit boards collected in centrally located cubicles will become superfluous. The miniatyrization of the AI/AO unit also creates a possibility of locating this unit closer to sensors or actuators or even inside these. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a system diagram of an AI/AO unit according to the present description. Figure 2 illustrates how an interface unit according to the invention may be realized on two ASIC circuits to compose an AI/AO interface. Figures 3a and 3b illustrate the connection of external means to an AI/AO interface which accomodates an interface unit according to the invention. Figure 4 shows a diagram of the function of the AI/AO unit in case of voltage input in a lower voltage range . Figure 5 describes the function of the AI/AO unit in case of voltage input in a higher voltage range. Figure 6 shows the function of the AI/AO unit in case of analog current input . Figure 7 shows the function of the AI/AO unit in case of analog voltage output . Figure 8 shows the function of the AI/AO unit in case of analog current output . Figure 9 shows a complete block diagram of the AI/AO unit where the unit is realized in two IC circuits with an A/D and/or D/A convertor integrated in one of these circuits. Figure 10 shows the configuration of a protective circuit called VDDp ro t/ and Figure 11 describes the configuration of a protective circuit called I/Op ro tection• DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a preferred embodiment of an AI/AO unit with characteristics according to the appended claims will be described in the following with reference to the accom¬ panying figures. As will be clear from Figure 1, the AI/AO unit is realized in a far-reaching integrated embodiment. The AI/AO unit is designed as at least one ASIC circuit, on which all the components and functional blocks shown in the figure have been integrated. The AI/AO unit has three connections at its output. These are ground GND, input and output signal connection I/O for connection to external means as well as a connection for an external voltage source VDD. The associated process equip- ment is always connected between terminal I/O and terminal GND in all modes, that is, voltage output, current output, voltage input and current input . As shown in Figure 2, the AI/AO unit may be designed as two integrated circuits ICl, IC2, and these may also comprise AD and DA convertors, which in the following description is assumed and illustrated as an example. The two integrated circuits ICl, IC2 together form a complete AI/AO interface. Both circuits ICl IC2 are designed as ASIC circuits, which gives the AI/AO interface very small dimensions. To achieve an interface of the kind mentioned it is, of course, not necessary to integrate the different functional blocks in the manner shown in this description. Functional blocks which are described as belonging to the first integrated circuit ICl in this description may alternatively be inte¬ grated in the second integrated circuit IC2. Further, it is possible to integrate all the circuits included in the AI/AO interface in one single ASIC circuit if this is desirable. The task of the AI/AO unit according to the invention is to function as a signal adaptation unit between AD and DA convertors and externally connected means. In addition, the AI/AO unit has the function of protecting the internal circuits from overload if a faulty voltage or current source has been connected to the input/output terminals I/O, VDD of the AI/AO unit. In analog input mode AI, the AI/AO unit is supplied with power by way of internal circuits . On the other hand, an external voltage source Vext supplies the AI/AO unit with power by way of the VDD output in analog output mode. All forms of communication with the AI/AO unit from/to a computer or some other electrical member for supervision, measurement, control etc. are carried out via the input of the AI/AO unit. At this input, in Figure 1, a digital-to- analog convertor DA is illustrated, which feeds the AI/AO unit with analog signals. In a similar way, also an analog- to-digital convertor AD is shown at the input, which conver- tor receives analog signals from the AI/AO unit. Both of these convertors AD, DA may constitute an integral part of the AI/AO unit . For selection of the mode of operation and the function mode of the AI/AO unit, a connection for mode selection MODE is also arranged at the input of the AI/AO unit. This mode selection connection MODE is, in the AI/AO unit, connected to three electronic switches SI, S2, S3. Depending on the selection of function mode, these switches are set in different positions, such that the shown functional blocks are utilized in different ways. The different function modes will be described in the following with reference to the accompanying figures . For the description of the modes of operation of the different function modes, only the functional blocks which are relevant for the respective function mode have been illu¬ strated in the figures. The determining selection for deter¬ mination of the mode of operation of the AI/AO unit is if this is to operate as an AI or an AO unit. This selection as well as the selection of the different function modes is carried out by an operative setting of the AI/AO unit, which entails a programming of the mode of operation of the AI/AO unit. The device, that is the AI/AO unit, will first be described in its application as an AI unit. In this appli¬ cation the unit can be operated in different modes depending on externally optional settings. In the embodiment described the different modes are: a) operating range for input voltages for externally connected members ~Vχ < Vin < Vi b) operating range for input voltages for externally connected members -V2 < Vin <V2 c) operating range for input currents for externally connected members -Ii < Iin < Iχ In a preferred embodiment, Vi amounts to 1.2 V, V2 to 12 V and Iχ to 22 mA. The AI/AO unit in the AI mode according to the invention operates as shown in Figure 3a. The figure shows that an externally connected electrical member, as a transducer, is connected between the I/O connection and ground. The ground terminal on the AI unit may be grounded. The VDD terminal is not utilized in the AI mode. When the AI unit operates in a function mode according to a, the electronic switches S1-S3 are set such that the unit utilizes the function according to Figure . A signal vol- tage with an absolute amount of the voltage Ua, which in the embodiment is smaller than Vi, is fed in via the output I/O and further into an analog-to-digital convertor AD in the first integrated circuit ICl. A resistor Rs is necessary for protecting functional blocks in the first integrated circuit ICl from overcurrents . The second integrated circuit IC2 with blocks for protection functions are not utilized in this mode if the resistor Rs is assumed to be located out¬ side the AI/AO unit. This resistor may possibly be integra¬ ted in some of the integrated circuits ICl, IC2 of the AI/AO unit, as previously exemplified. With the AI/AO unit operating in function mode b, still as AI unit, the mode of operation is as shown in Figure 5. An analog signal voltage with an absolute value of the voltage Ub, which in the embodiment is smaller than V2, is fed in via the output I/O. A precision voltage divider with the resistors Rdl and Rd2 are used to reduce the voltage applied to the AD convertor in the first integrated circuit ICl to an absolute value corresponding to the voltage amount Ua, as mentioned above. The resistors are protected to withstand stresses in, for example, industrial environments with vol¬ tage transients by connecting high-voltage capacitors Cl, C2 in parallel with the respective resistors Rdl, Rd2. Varistors may replace the capacitors if desired. The second integrated circuit IC2 is not utilized in this mode either. The resistors Rdl, Rd2 and the capacitors Cl, C2 are assumed to be located outside the AI/AO unit, but may also be integrated therein. The capacitors Cl, C2 may be omitted in most of the applications where a transient protective device is considered superfluous. For the third alternative function mode for the AI/AO unit operating as an AI unit, the mode of operation is illu¬ strated in Figure 6. In this mode, the AI/AO unit operates as an AI unit for signals with current intensities with an absolute value up to Ii in the embodiment . The fed-in analog signal is supplied via the output I/O to a functional block I/Oprotec t ion accomodated in the second integrated circuit IC2. This functional block I/Op rot ection is adapted to function as protection against overcurrents . The fed-in current signal is forwarded to a shunt resistor Rshunt, across which a voltage with an absolute value smaller than the value Ua is generated. The generated voltage signal across the shunt resistor Rshunt is fed to a differential amplifier DIFFAMP, which may be located in the second integrated circuit IC2 or the first integrated circuit ICl. The output signal from the differential amplifier is then forwarded to a analog-to-digital convertor AD in the first integrated circuit ICl. The shunt resistor Rshunt is suitably integrated in the second integrated circuit IC2 or, alternatively, in the first integrated circuit ICl. As men¬ tioned, protection against overcurrents must be provided. The shunt resistor Rshunt is thereby protected against over¬ voltage by the functional block I/Op ro tection disconnecting the I/O connection when an overvoltage is detected at the I/O output, for example at voltages with absolute values exceeding Vι+, where the voltage Vχ+ somewhat exceeds the above-mentioned value Vi . By external programming of the AI/AO unit, such that the three switches S1-S3 therein are reset, the AI/AO unit may be caused to operate as an analog output unit, that is, as a pure AO unit . This AO unit may thus operate in two different function modes . These function modes are in the embodiment shown d) analog voltage output with voltage V-OUT within the range 0 V < V-OUT < V3, and e) analog current output with current I-OUT within the range 0 mA < I-OUT < I 2 In a preferred embodiment of the device, the value V3 amounts to 10 V, whereas the current I 2 may reach the value 20 mA. An AI/AO interface with an AO unit according to the inven¬ tion operates as shown in Figure 3b. The figure shows that an externally connected electrical member, for example a transducer, is connected between the I/O connection and ground. The ground terminal on the AI unit may be grounded. An external voltage source Vext is connected between the VDD terminal and ground for power supply of the AI/AO unit . In the mode analog voltage output according to d and illus- trated in Figure 7, a digital signal is supplied to a digital-to-analog convertor DA, located in the first inte¬ grated circuit ICl, from where the signal is forwarded in analog form to an operational amplifier operating as a vol¬ tage amplifier VA. The voltage amplifier VA is supplied with power by an external voltage source Vext, as mentioned above. The analog signal is forwarded to a protective cir¬ cuit I/Opro t ectionr from the output of which the signal feeds the output I/O of the AO unit. The previously utilized vol- tage divider with the resistors Rdl and Rd2, together with the parallel capacitances Cl, C2 thereof, is connected between the mentioned output I/O of the AO unit and ground. From this voltage divider a voltage feedback takes place to the voltage amplifier VA. The digital-to-analog convertor DA generates a voltage within the interval 0V to V_/n . This voltage is amplified n times in the voltage amplifier VA. The voltage amplification n amounts to, for example, 10. The protective circuit I/Op rot ection protects the output on the voltage amplifier VA against overvoltages . The AO unit is closed when the voltage Vi/o at the output I/O exceeds Vχ+ volt. This is achieved by comparing voltage V-IN supplied to the voltage amplifier VA with the feedback voltage thereto. The protective circuit I/Op ro tection anσ - the voltage ampli- fier VA are integrated in the second integrated circuit IC2. The protective circuit I/Op ro tec t ion is supplied with voltage from the first integrated circuit ICl . In the second alternative output mode e with current output shown in Figure 8, a digital voltage signal is supplied to a digital-to-analog convertor DA, located in the first integrated circuit ICl, from where the signal is forwarded in analog form as input signal V-IN to a voltage/current convertor VCC, from where an analog current signal I-OUT is applied to the protective circuit I/Op ro tec t ion• From this protective circuit the current signal I-OUT is then fed over the output I/O of the AI/AO unit. The digital voltage signal is converted to a current signal with a current intensity within the interval 0 mA - I 2 mA. In the embodiment, the output is disconnected if the voltage at the output exceeds V 2 + . Also in function mode e the voltage amplifier VA is fed with power from an external voltage source Vext . Voltage/current convertor VCC and protective circuit VA are integrated in one of the ASIC circuits ICl, IC2 which build up the AI/AO unit. Figure 9 illustrates a more detailed circuit diagram of the configuration and function of an AI/AO unit according to the description of the embodiment. It is of importance that as many functions as possible are integrated in one and the same electronic chip, but there is nothing preventing cer¬ tain parts, for example one or more of the discrete compo- nents for any function, from being positioned outside the chip. In the following, the function of some of the above- mentioned functional blocks will be described in greater detail. These may, of course, be realized in different ways. Only one solution to a realization of the respective function will be given here. In the AO mode the voltage amplifier VA and the voltage/current convertor VCC are supplied with power by means of an external voltage source Vext via a connection for an external voltage source VDD. This connection VDD is to be disconnected when or if the voltage at this connection VDD exceeds a proposed value 32 V. This can be achieved in the following ways: 1) The voltage divider Rd3, Rd4 is used to sense the VDD voltage and delivers the signal VDD-V which is related to the VDD voltage. 2) When an overvoltage detector VDDI in the first integrated circuit ICl detects an overvoltage via the signal VDD-V, a signal VDD-OFF is activated. 3) The voltage of the signal VDD-OFF is converted to a required voltage in a level shifter LS . 4) A second protective circuit VDDp rot disconnects the connection for the external voltage source VDD if the input signal VDD-OFF is activated. The second protective circuit VDDp ro t withstands an alter¬ nating voltage of at least 250 V at the connection for the external voltage source VDD. This second protective circuit VDDp r o t a Y b e realized in a plurality of ways. Figure 10 shows an embodiment of this circuit. An external voltage is applied to the connection VDD, is brought over the diode Dl to a MOSFET transistor Ml to the output VDD-INT, which supplies the above-mentioned circuits with their require¬ ments of external voltage. The signal VDD-V which is taken out from the voltage divider Rd3, Rd4 is used, as mentioned, for sensing the supplied voltage at the output VDD of the AI/AO unit. A second MOSFET transistor M2 switches off the first MOSFET transistor Ml when the above-mentioned signal VDD-OFF is activated, the signal being supplied to the gate of the second MOSFET transistor M2 thus closing or opening this . A voltage convertor VC converts the voltage obtained from the second protective circuit VDDp rot to the necessary vol¬ tages before these are forwarded to the circuits which are supplied with power from the external voltage source. The voltage amplifier block VA consists of an operational amplifier. The voltage Vχ/_ a the output of the AI/AO unit is fed back for the purpose of supervision via the voltage divider Rdl/Rd2. The electronic switch SI and the protective circuit I/Opro t ection are included in the feedback loop which extends from the output of the voltage amplifier Va and back to the input thereof. A voltage supervision block OVS controls analog output values . In the mode with voltage output the actual output voltage Vj/o is compared with the output voltage V-IN from the digital-to-analog convertor DA. If the difference exceeds 0.1 V, the signal AO-error is activated. The block OVS is supplied with power by means of the external voltage source Vext via the VDD terminal. The protective circuit I/Op ro tection has an internal confi¬ guration as shown in Figure 11. This circuit is to dis- ' connect the I/O terminal when the output voltage from a multiplexor MUX located in the first integrated circuit ICl exceeds Vχ+. This can be achieved with the following preferred configuration 1) When a second voltage supervision block I/O-A in the first integrated circuit ICl senses an overvoltage via the input signal I/O-V, the signal I/O-OFF is activated. 2) The voltage of the signal IO-OFF is transmitted to a necessary voltage in the level shifter LS. 3) The protective circuit I/Op rote c t ion disconnects the I/O connection when the input I/O-OFF is activated. The protective circuit I/Op rot ec t ion withstands at least 250 V alternating current through a suitable selection of components. In addition, the circuit is internally supplied with power. The protective circuit I/Op rotect ion includes, as shown in Figure 11, two MOSFET transistors M3 and M . MOSFET M4 carries current in a direction from the terminal I/O to the terminal I/O-INT, whereas MOSFET M3 carries current in the opposite direction. This is due to the fact that the protec¬ tion against overload must be bidirectional, since both positive and negative currents occur in the analog current input mode. The diodes D4 and D5 block voltages which the MOSFET transistors M3, M4, due to their unipolar design, are unable to block. When the protective circuit I/Op rot ec t ion is switched on, that is, has a low impedance, the signal I/O- OFF is active and therefore the switches Tl and T2 have a high impedance. The control voltage on transistor M3 assumes the value -Vicl, which in turn causes the transistor M3 to conduct. The control voltage on transistor M4 assumes the value +Vicl, which also causes the transistor M4 to conduct. The protective devices is activated and a high impedance imparted thereto because the signal I/O-OFF is activated. In this way, the switches Tl and T2 become conducting and thereby set the control voltages for the MOSFET transistors M3 and M4 at 0 volt. This causes a high impedance to be imparted to these transistors M3, M4, the transistors thus blocking the terminal I/O. The diodes D6-D11 constitute protection against transients in the circuit. A voltage convertor ICIV converts a voltate +V obtained from the first integrated circuit ICl to voltages +Vicl, -Vicl for internal supply of circuits in the AI/AO unit. A mode control unit MC delivers different output signals, AO-V and AO-C, respectively, when the unit is functioning as AO unit for voltage signals and as AO unit for current signals, respectively, as well as AI-V1, A1V10 and AI-C for function modes a, b and c, respectively. When the AI/AO unit functions as AI unit, the output signals mentioned are supplied to a multiplexor MUX for selection of analog input VIN-V1, VIN-V2 or a voltage input from the differential amplifier DIFFAMP, a voltage which is proportional to the current value supplied to the AI unit .

Claims: CLAIMS 1. A device for analog input signal or output signal adaptation comprising the functions analog input unit (AI) , analog output unit (AO) , analog current supply, analog voltage supply as well as protection functions against faulty connection and faulty load, respectively, characterized in that the device accomodates all of said functions in only one integrated unit comprising one or few integrated circuits (ICl, IC2), and that said unit is intended to be programmed for - function as analog input unit (AI) or analog output unit (AO) , and - voltage or current supply. 2. A device for analog input signal or output signal adaptation according to claim 1, characterized in that the device is intended, in case of voltage supply, to be programmed for its voltage interval. 3. A device for analog input signal or output signal adaptation according to claim 1, characterized in that the protection functions of the device realized in two protective circuits (VDDp ro t, I/Oprotection) block external inputs and outputs (VDD, I/O), respectively, in case of impermissible levels of the supplied current or voltage. 4. A device for analog input signal or output signal adaptation according to claim 2 or 3, characterized in that the device comprises at least one ASIC circuit (ICl, IC2) or corresponding circuit, which in integrated circuitry accomodates at least one or all of the functional blocks (VA, VC, VCC, OVS, Mux, S1-S3, VDD Prot , I/0 Pro tection) of the device. 5. A device for analog input signal or output signal adaptation according to claim 4, characterized in that all the circuits belonging to the device are integrated on a common ASIC circuit or similar circuit, or a hybrid circuit. 6. A device for analog input signal or output signal adaptation according to claim 4 or 5, characterized in that the device is intended to be used for signal adaptation in process control systems. 7. A device for analog input signal or output signal adaptation according to claim 6, characterized in that the device is intended to be programmed for its function from a superordinate electronic circuit . 8. A device for analog input signal or output signal adaptation according to claim 7, characterized in that the device is intended to be accomodated in single-channel analog interface units housed in small modules, which modules communicate directly via a databus with a super¬ vision unit, for example a computer. 9. A device for analog input signal or output signal adaptation according to claim 8, characterized in that the modules are adapted to be mounted on mounting rails of standard type for communication with the supervision unit via conducting paths located in or on the surface of the mounting rail. 10. A device for analog input signal or output signal adaptation according to claim 4 or 5, characterized in that the device in the selected function as an AO unit may be programmed for the function mode voltage output or current output and that the device in the selected function as an AI unit may be programmed for the function mode current input or voltage input with a programmable selection of voltage range . 11. A device for analog input signal and output signal adaptation according to claim 1, characterized in that process equipment, excluding voltage supply in output mode, is connected to the I/O unit with the same connection terminal (I/O) both in input and output mode.

Inventors: AARENAES ANDERS, BERGSTROEM JAN OLOF, LILJEGREN LARS, SKARHED OVE, AARENAES, ANDERS, BERGSTROEM, JAN, OLOF, LILJEGREN, LARS, SKARHED, OVE
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1992
Main classification: H02H7
IPC codes: G05B19