Measuring device, measuring probe, and method of operating the measuring device

The measuring device has at least one measuring probe, e.g., a physical or electrochemical measuring probe, which is equipped with one or more memory units and which is connected through a cable, e.g., a coaxial cable, to a transmitter which includes a processor. The measuring probe has a ground wire and is connected to the memory unit through a first signal wire, wherein under the control of the processor in accordance with a transmission protocol, the first signal wire and a connecting cable serve for the unidirectional transmission of the analog or digital measuring signal of the measuring probe as well as the preferably bidirectional transmission between the measuring probe and the transmitter of digital operating data which are read from or to be written into the memory unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to EP Application 06101681.2 filed in European Patent Office on 14 Feb. 2006, the entire contents of which are hereby incorporated by reference in their entireties.

FIELD

A measuring system is disclosed with at least one measuring probe. A physical or electrochemical measuring probe can be used for the measuring device. A method of operating the measuring device is also disclosed.

BACKGROUND INFORMATION

The control of industrial processes, for example in the chemical and pharmaceutical industry, in the textile industry, in the food- and beverage industry, in the processing of paper and cellulose or in the water purification and waste water treatment is based on the measurement of process parameters which are determined with suitable measuring probes or sensors.

According to reference [1], “Process Measurement Solutions Catalog 2005/06”, Mettler-Toledo GmbH, CH-8902 Urdorf, Switzerland, pages 8 and 9, a complete measuring system consists of a housing, a measuring probe, a cable and a measurement converter (also called a transmitter). By means of the housing, the measuring probe is brought into contact with the process that is to be measured or monitored, for example by immersing the probe in the process material and holding it there. The measuring probe serves to measure specific properties of the process. Through a cable which in the case of reference [1], page 8, has five leads the measuring signals are sent to the transmitter which, in turn, communicates with a process control system and converts the measuring signals into readable data. The measuring probes are selected depending on what properties of the process material need to be measured.

An important factor for a problem-free process control is the condition of the measuring probes, whose properties will normally change over a longer operating time period.

A method disclosed in reference [3], EP 1 550 861 A1, serves to determine the condition of measuring probes which are integrated in a system with one or more stages and which are cleaned from time to time in state-of-the-art CIP- or SIP processes, i.e., without uninstalling the probe. According to this method, the temperature of the measuring probe or of the medium surrounding the measuring probe is measured by means of a sensor that is located inside or outside the measuring probe, and the condition of the measuring probe is determined from the time profile of the measurements of the temperature and in some cases of the process-related value (for example pH) that has been recorded during the operation of the measuring probe.

According to reference [4], WO 92/21962, the hydrogen ion concentration in liquids, i.e. the pH value, is often measured with glass electrodes. Preferably the condition of the glass electrodes is continuously monitored, as the measuring accuracy could become compromised for example if the ion-sensitive membrane is damaged, the diaphragm is contaminated, and if an electric connection inside the electrode is interrupted and/or short-circuited.

According to reference [4], a square pulse that is variable in amplitude and duration is applied with a high impedance to the measuring probe which contains a glass electrode as measuring electrode and also contains a reference electrode; the voltage across the measuring probe which has been changed by the probe impedance is measured and the measured values are compared to a reference value for a new measuring probe that has been determined by experiment or calculation. The square pulses in this arrangement are delivered by an analog output terminal of a processor and sent to the measuring probe by way of a separate conducting lead.

In the method described in reference [5], EP 0 419 769 A2, the monitoring is performed by means of symmetrical bipolar current pulses which are produced by a control unit. The duration of the current pulse periods is freely selectable and can be set to different lengths depending on the accuracy desired for checking the probe. This method requires a comparatively complex circuit, in particular two control leads which, for the purpose of generating symmetrical bipolar current pulses, allow switching between a positive voltage source and a negative voltage source, or switching from the measuring phase in which the pH value is measured to the checking phase in which the electrodes are checked.

A method disclosed in reference [6], EP 0 497 994 A1 relates to the checking of a pH-measuring probe which contains an auxiliary electrode in addition to the glass electrode and the reference electrode. Furthermore, there are two processing devices which are supplied, respectively, by a first and a second generator with an AC test voltage. The first generator in this arrangement operates with a frequency that is an integer multiple of the frequency of the second generator. This allows a separate monitoring of the glass electrode and the reference electrode. In the first case, the property being checked is the resistance of the chain formed of the glass electrode and the auxiliary electrode, while in the second case the resistance of the chain formed of the reference electrode and the auxiliary electrode is being checked. With the selected ratio between the frequencies produced by the generators, a sufficiently accurate differentiation is possible between the output signals in the two processing devices, as in each case one of the output signals is suppressed by the phase-sensitive rectification in the processing device of the other of the two electrodes. The processing devices are therefore no longer directly seeing the difference between the potentials of the glass electrode and the auxiliary electrode. Rather, they detect a difference between the potentials of the glass electrode and the auxiliary electrode or between the potentials of the reference electrode and the auxiliary electrode. As both of the differences in the potentials are referenced to the same potential of the auxiliary electrode, the potential difference between the glass electrode and the reference electrode can be determined with a differential amplifier. In this measuring circuit arrangement, the measuring probe therefore needs to be supplied with the AC test voltages of two different generators. These AC test voltages, in turn, are used for the subsequent phase-coherent processing of the signals and therefore have to be transferred through appropriate conductor leads which normally run from the processing unit to the measuring probe.

However, using additional conducting leads for transferring signals makes the design commensurately more expensive. Furthermore, in systems that are already installed, the required wiring does not exist and can hardly be retrofitted, or only at very high cost and by interrupting the operation of the equipment. This is also a disadvantage because with the trend towards miniaturization and the possibilities that it offers for a decentralized arrangement of intelligent components, the need for transmitting additional signals will rather increase, and more highly developed measuring probes designed for decentralized installation will therefore have only limited use in existing systems.

As was described above, in larger plants as for example breweries a large number of measuring probes are used. Thus, the way in which the installed measuring probes are administrated by the user is of high importance.

SUMMARY

An improved measuring device with at least one measuring probe and a method for operating the at least one measuring probe, as well as a suitable measuring probe, are disclosed.

In a measuring device measuring probes can be advantageously integrated. This means that when a new or previously used measuring probe is installed, the measuring process should register the measuring probe and should possibly be able to make required adaptations in the measuring probe and/or in the measuring process.

The monitoring of the measuring probes is to be further simplified and improved, taking into account extraneous influences and/or inherent properties of the measuring probe or changes of such properties.

An advantageous way of controlling the measuring probes can be realized with the exemplary embodiments.

Furthermore, the operation and administration of the measuring probes of the measuring system is to be simplified.

Accordingly, the infrastructure can be simplified for the transmission of signals which is provided in the measuring device or measuring system.

In exemplary embodiments, the measuring device should in addition remain compatible with conventional measuring probes.

Solutions to meet the foregoing objectives are offered by an exemplary measuring device, specifically a measuring system with at least one measuring probe, e.g., a physical or electrochemical measuring probe, by a measuring probe for use in the system, and by a method for operating the measuring device as disclosed.

The measuring device has at least one measuring probe equipped with at least one or with several memory units, by means of which process variables of a process material can be measured, for example electrical conductivity, dissolved oxygen, pH value, CO2value and/or turbidity. The measuring probe is connected through a cable, e.g., a coaxial cable, to a transmitter which includes a processor and can have several measuring probes-connected to it. The memory unit can be an overwritable solid-state memory, for example an EEPROM of the type Dallas Semiconductor DS 2433.

An exemplary measuring probe has a ground wire and is connected to the memory unit by a first signal wire. Under the control of the processor in accordance with a transmission protocol, the first signal wire and a corresponding signal wire of a connecting cable provide the communication between the measuring probe and the transmitter for the unidirectional transmission of the analog or digital measuring signal of the measuring probe as well as for the preferably bidirectional transmission of digital operating data that are to be read from or written into the memory unit. Thus, the analog or digital measuring signal as well as operating data can be transmitted through the signal wire and the ground connection of the measuring probe and through the signal wire and the ground connection of the cable that is connected to the measuring probe.

This has several advantages. For example, the cost and complexity of the installation are reduced since, instead of a multi-wire cable, only one cable can be used, e.g., a coaxial cable which contains the signal wire and, if the ground connection is not realized in another way, the ground wire. The term “wire” as used here encompasses physical electrical connections of any kind, besides wires in the actual sense of the word. Furthermore, installed measuring probes can be centrally controlled by the transmitter or, for example, by the lead computer. Every measuring probe can have its own globally unique identification code, which can have product properties assigned to it. Segments of e.g. a 64-bit code can serve to register for example the type of the probe (for example pH probe) and its serial number. With the identification code, the administration of all measuring probes of a system therefore becomes a simple task. The lead computer can for example access a database in which all data for the type of probe in question are registered. For example all performance characteristics, configuration data and operating parameters or operating programs can be registered, which can be updated by the manufacturer in periodic intervals. As a possible option, although with a higher cost, the storage of the foregoing data can be decentralized in the one or more memory units of the measuring probes.

In an exemplary embodiment, the first signal wire is connected to the reference electrode and a second signal wire is connected to the measuring electrode, or the first signal wire is connected to the measuring electrode and the second signal wire to the reference electrode of a measuring probe that serves for pH measurements, wherein the signals of the measuring electrode and of the reference electrode can in some cases be transmitted as analog signals through an impedance converter to the transmitter, where they may be processed by means of a differential amplifier. This kind of an arrangement allows the analog measuring signals to be processed in the transmitter, with only one additional signal wire being required in this case. In other words, with two signal wires it is possible to transmit two analog measuring signals as well as digital operating data.

This exemplary embodiment of the device can be realized by means of a coaxial coupler which has three contact elements which are concentric to each other and configured in the shape of rings, sleeves, cylinders, bushings, discs and/or pistons separated from each other by insulating layers and which can be connected to the cable through a further, corresponding coaxial coupler in such a way that the first signal wire connects to the core conductor, the second signal wire connects to the inner screen conductor, and the ground wire connects to the outer screen conductor of the coaxial cable which is connected to the transmitter.

With this exemplary embodiment, a known coaxial coupler of the type which has until now been used in measuring probes can be expanded in the sense that instead of only one contact connection for a screen conductor, two separate contact connections for screen conductors become available. The original contact connection for the screen conductor is in this case split in such a way into two separate contact segments that the resultant three-pole coaxial coupler of the measuring probe can be connected to a conventional two-pole coaxial coupler of a cable that is connected to the transmitter. When connected to the conventional two-pole coaxial coupler, the two screen conductor connections of the three-pole coaxial coupler are short-circuited, so that the memory unit of the measuring probe which is connected to these short-circuited contacts is not tied into the measuring device. New measuring probes are therefore compatible with existing systems and can be put into service already before the system itself is expanded.

In a further exemplary embodiment, the measuring probe is equipped with a processor which may be connected to the first signal wire through a parallel/serial converter component (for example Dallas Semiconductor type DS 2408) and may integrally include the at least one memory unit. The processor in this case has the capability for processing the measuring signals that were collected by means of the measuring probe and digitized and, if applicable, for writing corresponding digital data into, or reading such data out of, the at least one memory unit, and/or for configuring and/or controlling the measuring probe in accordance with the operating data provided by the transmitter.

These measures make it possible to control essential parts of the measuring and diagnostic processes within the measuring probe itself, whereby the centralized systems are relieved and the capacity and flexibility of the process system are significantly increased. For example, the physical structure and the centrally controlled administration and maintenance are simplified. By controlling the setting of operating parameters, it is possible to adapt and optimize the measuring probes when process conditions change. Particularly advantageous is the capability for using controllable measuring probes which are configured to meet requirements, To name an example, a controllable voltage generator (e.g. Dallas Semiconductor type DS 2890) is used in the measuring probe, which allows a selectable setting of a polarization voltage for example for oxygen-measuring electrodes.

The architecture of the digitally operating modules of the measuring device can be chosen selectively. For example, a single-wire bus architecture is used consistently inside the measuring electrode as well as between the measuring electrode and the transmitter. In this arrangement, the master processor, which can be located in the transmitter, can control the slave processor which can be arranged in the measuring probe. The master processor can be able to access all other digital single-wire modules, each of which can have a globally unique address, and e.g., to read data from the at least one memory unit. The probe processor in this exemplary arrangement can process data, for example status data of the measuring probe, and can store them in the memory unit which is typically interrogated in a cycle by the lead computer or the transmitter. If the master processor is connected through a parallel/serial converter component to the probe processor, the latter with at least one memory unit can be imbedded in a largely autonomous multi-bit environment. For this exemplary case, only the master processor and the slave- or probe processor would communicate with each other.

The communication through the single-wire bus can be according to a known data transmission protocol, e.g., of a kind that is described in reference [7], U.S. Pat. No. 5,809,518.

In a further exemplary embodiment, the measuring electrode and the reference electrode of the pH-measuring probe are each connected to separate input terminals of a multiplexer by way of respective impedance converters. As an alternative, the measuring electrode and the reference electrode of the pH-measuring probe are each connected to separate input terminals of a multiplexer by way of respective impedance converters, where in addition the output terminals of the impedance converters are also connected to the input terminals of a differential amplifier whose output, in turn, is connected to a further input of the multiplexer. From the measuring signals of the measuring electrode and the reference electrode, the differential amplifier forms a measuring signal that corresponds to the measured process variable, specifically to the pH value. The latter measuring signal, after it has bee digitized, can be transmitted through the single-wire bus to the transmitter. If the design concept does not include an analog differential amplifier, the difference is determined digitally in the processor that is arranged inside the measuring probe. In both cases (i.e., with or without differential amplifier), the measuring signals of the measuring electrode and the reference electrode can be evaluated separately in order to examine the condition of the measuring probe.

To perform this function, the processor of the measuring probe or a frequency generator controlled by the processor produces test signals such as square-wave signals of a first frequency or of first and second frequencies and delivers the test signals to the measuring electrode and/or to the reference electrode, and the resultant time profiles of the voltage at each of the electrodes is evaluated by means of the processor of the measuring probe in order to obtain status data of the measuring probe and in certain cases to store the data in the memory unit.

In yet a further exemplary embodiment, a temperature sensor in the measuring probe is connected to a further input of the multiplexer in order to determine temperature data of the measuring probe or of the medium surrounding the measuring probe and, by means of the processor of the measuring probe, to store the data in certain cases in the memory unit or to directly evaluate them, in order to determine load exposures or the condition of the measuring probe and/or to determine the magnitude of corrections to be applied to the measuring signals. Notably, contaminations can occur on measuring probes which are used for the monitoring of chemical or microbiological processes, whereby errors can be introduced in the result of the measurement. Contaminations will therefore have to be removed not only in the system of conduit pipes but also on the measuring probes in order to simultaneously ensure correct measurement results and the absolutely sanitary condition of the system. Because of the large number of measuring probes being used, they are normally not uninstalled for cleaning but are cleaned or sterilized in a CIP- or SIP procedure (where CIP stands for “Cleaning In Place” and SIP for “Sterilizing In Place”).

An exemplary way to determine the resultant load exposures of the measuring probes is to compare the temperature with at least one threshold value and, after the threshold has been exceeded:a) to register a corresponding load exposure,b) to determine the cumulative sum of all load exposures and/orc) to determine the cumulative sum of all load exposures and, through a comparison with a permissible maximum value for the cumulative load exposure, to calculate a permissible remaining load exposure or remaining operating life.

For example, after a load exposure has been found, the registered remaining operating life of the measuring probe is commensurately reduced. The permissible remaining load exposure or remaining operating life is for example represented as the remaining permissible number of CIP- or SIP processes.

Status data and/or load exposure data can be transmitted directly, but can be stored in the memory unit and requested by the transmitter or the lead computer. If a malfunction of the measuring probe is detected, it can be signaled without delay. For example, a status interrogation occurs in short time cycle intervals to check for the presence of malfunction signals (for example whether an error bit has been set).

The operating data which can be transmitted from the measuring probe to the transmitter and in certain cases forwarded to the lead processor therefore can include identification data, characteristic data, configuration data, status data of the measuring probe, test data determined, e.g., during operation of the measuring probe, and/or load exposure data.

Operating data transmitted to the measuring probe can include updated configuration data and/or control data by means of which the measuring probe can be configured and/or controlled.

As mentioned above, the disclosure is not limited in its application to certain measuring probes but can be used for any measuring probes with one or more electrodes such as measuring and reference electrodes or measuring sensors.

Furthermore, the measuring probes or measuring sensors can be used to advantage not only in industrial plants but also in the measuring laboratory.

DETAILED DESCRIPTION

FIG. 1illustrates a system with a material-holding portion8consisting of a container81filled with a process material6, which may be connected by means of a connecting conduit pipe82to a system unit of a next-following process stage. The properties of the process material6are measured by means of exemplary measuring probes1a,1b,1c, which are connected through single-wire and dual-wire signal conductors2a,2b,2c—i.e. cables with one or two signal wires or electrical connections for signals and with a ground wire or ground connection—to a transmitter3aor3bwhich serves for example as a processing unit, a measurement converter, or in the simplest case as a relay station which exchanges data with the lead computer300by way of a segment coupler30.

In a schematic illustration,FIG. 2shows the principal structure of an exemplary pH-measuring probe which is configured as a single-rod measuring chain with a measuring electrode in the form of a glass electrode, with a reference electrode, and in certain cases also an auxiliary electrode18. In the measuring probe1, the glass electrode which includes a conductor element16and the reference electrode which includes a reference element15are built together in a unitary form of construction. In a first chamber inside an interior tube11which is joined to a thin-walled glass hemisphere or glass membrane111, the conductor element16is immersed in a solution of a defined pH value, or an interior buffer solution14, which establishes the conductive connection between the inside of the glass membrane111and the conductor element16. Inside an exterior tube12, the reference element15is immersed in an electrolyte, or an exterior buffer solution13, which slowly diffuses through a porous separating wall or diaphragm121into the process medium6. The voltage potential which is present at the conductor element16during the measurement (seeFIG. 7, signal source SQ1G) and the voltage potential which is present at the reference element15during the measurement (seeFIG. 7, signal source SQ1R) are transmitted through impedance converters and the two signal wires21,22of the cable2to the transmitter3. The measuring probe further has a memory unit MEM which is connected to the transmitter through one of the signal wires21.

In this exemplary configuration of the measuring probe, there is further a temperature-measuring sensor17arranged in the interior buffer space, which in further exemplary embodiments of the measuring probe1allows temperature-related influence factors to be automatically compensated and temperature cycles to be registered.

FIG. 3shows the measuring device ofFIG. 2in an exemplary embodiment with a pH-measuring probe1which contains a glass electrode and a reference electrode where the respective voltages uGand uRappear as soon as the measuring probe1is immersed in the process medium or the material that is the subject of a measurement. The material6being measured and the glass membrane111together constitute the voltage source SQ1whose internal resistance is determined primarily by the high resistance RGof the glass membrane111. The voltages uGand uRare transmitted through the signal wires21,22of the cable2to the input terminals of a differential amplifier DV which is part of the transmitter3and whose output is connected by way of an analog/digital converter A/D to a processor MPT. Included in the measuring probe1, which is further connected to the transmitter3through a ground wire23, is a memory unit MEM (for example an EEPROM of the type Dallas Semiconductor DS 2433) which in this embodiment is connected to the processor MPTin the transmitter3by way of the second signal wire22′,22which serves as data bus. The processor MPTin this arrangement functions as bus master with the ability to access and to exchange data with the memory unit MEM which has a unique address. After the symbolically indicated switch S1has been closed by the processor MPTby means of a control signal delivered through a control output terminal CL, a data transmission can take place through the second signal wire22′,22between the data port “I/O” and the memory unit MEM in the measuring probe1. The switch S1remains open, on the other hand, during the transmission of analog signals.

The transmission protocol provides for a sequential data transmission to take place after the circuit is initialized. While the processor MPTis active as bus master, it can address each of the components served by the signal wire22′,22or data bus22′,22and send data to, and/or receive data from, the component being addressed. For example a ROM component allows only the reading of data, an EEPROM allows data to be written into it and to be subsequently read back, a controllable voltage source POT (seeFIG. 7) can receive control signals in order to set a voltage potential. In addition, there can be controllable switches for example to turn sensors or electrodes on and off or to switch over from one to another.

The voltage uBSwhich is required for the operation of the memory unit MEM and in certain cases further components is drained parasitically from the data bus22,22′ by means of a diode D1which charges a capacitor C1as soon as a logic voltage is present on the data bus which is introduced from a voltage source UBby way of a resistor R1and the closed switch S1.

The two signal wires21′,22′ running inside the measuring probe1as well as the ground wire23′ are connected to the contacts210,220,230of a three-pole coaxial coupler20M which are separated from each other by insulating layers240,250. The coaxial coupler20M can be connected by way of a matching coaxial coupler20F (seeFIG. 5) to the coaxial cable2in such a way that the first signal wire21′ is connected to the core conductor21, the second signal wire is connected to the inner screen conductor22, and the ground wire23′ is connected to the outer screen conductor23of the coaxial cable2. The two outer contacts220,230of the coaxial coupler20M are divided into segments that lie in the same plane and are separated from each other by the insulating layer250, so that they can connect to the corresponding contacts of the further coaxial coupler20F when the two coaxial couplers20M,20F are plugged into each other. The two coaxial couplers20M,20F thus provide a reliable three-pole connection.

However, in many known systems, the connections between the measuring probe l′ and the transmitter3are only of the two-pole kind with corresponding two-pole coaxial couplers20KF,20KM as shown inFIG. 4.

The exemplary three-pole coaxial coupler20M, which is shown inFIGS. 3 and 5, can now be mechanically and electrically connected to the three-pole coaxial coupler20F ofFIG. 5as well as to a two-pole coaxial coupler20KF (which is shown inFIG. 4), where in the latter case the two screen-conductor contacts220and230of the three-pole coaxial coupler20M lie against the screen conductor contact223of the two-pole coaxial coupler20KF and are thereby electrically connected to each other. Using the three-pole coaxial coupler20M and the two-pole coaxial coupler20KF, an exemplary measuring probe1can therefore be connected to a conventional transmitter that is not equipped for the transmission of digital data to the measuring probe1. The memory unit MEM will in this case not be used.

This makes it possible for the manufacturer to produce only one kind of measuring probe which can be used universally for measuring devices and systems of the known type as well as the exemplary disclosed embodiments. The user gains the advantage of being able to purchase and use the exemplary measuring probes in an existing system already before it has been upgraded to work.

FIG. 6shows an exemplary measuring device with an exemplary measuring probe1, where the measuring probe contains a processor MPSwhich has a memory unit MEM and is connected through a single-wire signal conductor21and the ground connection23of a cable2to a transmitter3. Arranged in the transmitter ′3is the processor MPTwhich functions as bus master with the capability to exchange data with the slave- or probe processor MPSthrough the single-wire conductor21which serves as data bus.

The probe processor MPSis operable to receive the sequential transmission of the measuring signals uG′, uR′, uG′−uR, and uTRwhich are produced by the measuring probe1and arrive at the probe processor MPSby way of a multiplexer MUX (which is controlled by the probe processor) and an immediately following analog/digital converter A/D. Of course, the multiplexer MUX, the analog/digital converter A/D and the probe processor MPScan also be integrated in a housing.

The glass electrode and the reference electrode of the measuring probe1which serves to measure pH are connected through respective impedance converters OVG, OVRto the first and second input terminals P1and P2of the multiplexer MUX. The outputs of the impedance converters OVG, OVRin addition can be connected to the input terminals of a differential amplifier OVDwhose output, in turn, is connected to the third input terminal P3of the multiplexer MUX. The fourth input terminal P4of the multiplexer MUX receives the signal UTRof a temperature sensor (for example of the type PT100).

The digitized differential signal uG′−uR′or, alternatively, the difference calculated by the probe processor MPSbetween the signals uG′and uR′after they have been digitized corresponds to the pH value of the process medium6. Without further processing or after applying a correction if necessary, the probe processor MPScan send the digital difference value to the transmitter3and/or store it in the memory unit MEM which in this′ exemplary embodiment is integrated in the probe processor MPS.

By evaluating the further measuring signals uG′and uR′it is possible to determine,the condition of the measuring probe1. To make this determination, the processor MPSof the measuring probe, the processor MPTof the transmitter, or a frequency generator FG (indicated schematically) controlled by one of the processors produces test signals fG, fRsuch as square-wave signals of a first frequency or of first and second frequencies and delivers the test signals, respectively, to the measuring electrode and to the reference electrode. The resultant time profiles of the voltages uG′, uR′at the electrodes, which depend on the respective internal resistances RGand RRof the electrodes, are evaluated by means of the probe processor MPSin order to obtain status data of the measuring probe1, which can then be stored in the memory unit MEM and/or transmitted immediately to the transmitter. If for example a glass breakage or a strong contamination has occurred, the internal resistances RG, RRand the corresponding profiles of the voltages uG′, uR′change and as a result, an operating irregularity or even a malfunction can be registered and/or reported to the central computer300.

The temperature sensor17which is connected to the multiplexer MUX allows the collection of temperature data of the measuring probe1or of the medium6surrounding the measuring probe1. By means of the probe processor MPS, the data can be stored in the memory unit MEM or evaluated in the probe processor MPSitself in order to determine load exposures or the condition of the measuring probe and/or to determine the magnitude of corrections to be applied to the measuring signals.

By means of the diagnostic capability that is incorporated in the measuring probe1, it is therefore possible to detect and register irregularities and defects as well as aging effects or load exposures of the measuring probe1and, if the situation requires it, to report them immediately.

The measuring and diagnostic functions of the measuring probe1can be performed in a largely autonomous way. The necessity of having to transmit test signals from the transmitter3through separate conductors to, and in some cases back from, the measuring probe1is avoided. The result of this concept is a measuring probe1that is easy to install and offers a wide-ranging functionality.

FIG. 7shows the measuring device ofFIG. 6with a probe processor MPSin which a multiplexer MUX and an analog/digital converter A/D are integrated and which is connected by way of the single-wire signal conductor21to memory units MEM1, MEM2, . . . , to a controllable voltage source POT as well as to the master processor MPTin the transmitter3.

The master processor MPTcan have the ability to communicate with all modules that are served by the single-wire bus21,21′. The operating protocol can include the provision that during a reserved time period the probe processor MPScan function as master processor for the single-wire bus21,21′ either locally in the measuring probe1or globally in the measuring device, for example to store data in, or read data from, the memory units MEM1, MEM2, . . . . The memory units MEM1, MEM2, . . . can thus operate in a time-sharing mode. In the initialization, the probe processor MPScan work as local master processor, so that for example an operating program which is downloadable from the lead computer300and which may have been updated can be transferred by the probe processor MPSfrom the memory unit MEM1into the internal memory MEM. This assures that the installed measuring probes1are always up-to-date with the latest state of the art available from the manufacturer.

FIG. 7further illustrates schematically that in a further exemplary embodiment, a probe processor MPSwith a larger bit format (for example an 8-bit processor) can be connected to the single-wire bus21′,21by way of a parallel/serial converter component (for example of the type Dallas Semiconductor DX 2408), which provides more flexibility in the selection of processors that can be used.

The advantages of an exemplary measuring device become particularly evident in a global view of a complex system (as shown partially inFIG. 1). On the one hand, by using exemplary measuring probes1, the entire infrastructure for the data- and signal transmission is reduced while on the other hand important advantages are gained in the architecture, administration and servicing of the system.

Measuring probes1can be put in place and wired when the system is being installed, and they can subsequently be detected, identified and registered from a central location. Thus, the process control extends not only to the measuring function but also includes the administration of the measuring probes.

By registering the condition of the measuring probe1, one gains an increase in process reliability. On the administrative side, the service activities including the placement of orders and the storage of the minimally required replacement probes can be precisely planned. As the installed measuring probes1can be reconfigured online, and with the possibility of even downloading operating programs online, the system is made highly flexible and easier to adapt to changes in the processes. After a measuring probe1chas been replaced by a measuring probe1c′, a verification test can be performed immediately in the lead computer300. The condition of the measuring probe1c′ can further be indicated on the transmitter3or, for example by means of light-emitting diodes, on the measuring probe1c′ itself.

LITERATURE REFERENCES