This paper describes the development of a
microinstrumentation system in silicon containing all the
components of the data acquisition system, such as sensors,
signal-conditioning circuits, analog-digital converter, interface
circuits, sensor bus interface, and an embedded
microcontroller (MCU). The microinstrumentation system is
to be fabricated using the Multi-Chip-Module (MCM)
technology based on a chip-level infrastructure. A standard
silicon platform is the floorplan for individual smart sensor die
attachment and an on-chip local sensor bus interface, testing
facilities, optional compatible sensors (such as thermal
sensors). The microinstrumentation system is controlled by a
MCU with several modes of low-power operation (inclusive
stand-by mode). As the intended application requires a huge
amount of data-processing, a RISC-type MCU architecture is
to be used. The MCU communicates with the front-end sensors
via a two-line (clock and data lines) intramodule sensor bus
(Integrated Smart Sensor bus). The sensor scan rate is
adaptive and can be event triggered. This upgraded version of
the ISS bus allows: service and interrupt request from the
sensors, test and calibration facilities. However, the additional
functionality requires a third line. The MCU also controls the
power consumption and the thermal budget of all system. This
paper also presents three applications for the
microinstrumentation system: condition monitoring of
machines, an inertial navigation system and a miniature
spectrometer.STW - Project DEL55.3733.
TUDelft.
Junta Nacional de Investigação Científica e Tecnológica - Praxis XXI-BD/5181/95

Bartek, M.

Correia, J. H.

Cretu, E.

Wolffenbuttel, R. F.

Universidade do Minho: RepositoriUM

A Microinstrumentation System for Industrial ApplicationsJ. Higino Correia*, E. Cretu, M. Bartek and R. F. WolffenbuttelDelft University of Technology, Dept. of Electrical EngineeringLab. for Electronic Instrumentation, 2628 CD Delft, The Netherlands*University of Minho, Dept. Industrial Electronics4800 Guimarães, Portugal (presently Ph.D. student at DUT) Abstract – This paper describes the development of amicroinstrumentation system in silicon containing all thecomponents of the data acquisition system, such as sensors,signal-conditioning circuits, analog-digital converter, interfacecircuits, sensor bus interface, and an embeddedmicrocontroller (MCU). The microinstrumentation system isto be fabricated using the Multi-Chip-Module (MCM)technology based on a chip-level infrastructure. A standardsilicon platform is the floorplan for individual smart sensor dieattachment and an on-chip local sensor bus interface, testingfacilities, optional compatible sensors (such as thermalsensors). The microinstrumentation system is controlled by aMCU with several modes of low-power operation (inclusivestand-by mode). As the intended application requires a hugeamount of data-processing, a RISC-type MCU architecture isto be used. The MCU communicates with the front-end sensorsvia a two-line (clock and data lines) intramodule sensor bus(Integrated Smart Sensor bus). The sensor scan rate isadaptive and can be event triggered. This upgraded version ofthe ISS bus allows: service and interrupt request from thesensors, test and calibration facilities. However, the additionalfunctionality requires a third line. The MCU also controls thepower consumption and the thermal budget of all system. Thispaper also presents three applications for themicroinstrumentation system: condition monitoring ofmachines, an inertial navigation system and a miniaturespectrometer.I. INTRODUCTIONThe development of integrated smart microsystemsmerging sensors, microactuators, low-power signal-processing circuits, microcontrollers and interface for theexternal world using wireless or hardwired link (e.g. RS-232, RS-485) promises to have a significant impact in manyinnovative products, enabling application in such diverseareas as industrial process automation and automotivesystems [1].The microinstrumentation system is built around anembedded MCU (see Fig.1) having on-chip memory,timers, serial communications facilities, low-power modes,and when required incorporates an A/D converter.A microinstrumentation system, as shown in Fig.2,includes all features of a complex measurement system onthe smallest possible material carrier; a silicon chip. Thesystem is composed of an universal platform which is to bepopulated with the required sensors, microactuators and amicrocontroller using MCM (Multi Chip Module)techniques, to solve a particular measurement problem.The sensors are scanned periodically by the MCU (basedon the variation in the parameters measured), or preferablyby the use of interrupt and service requests in order todecrease the power consumption. The digital compensationof the data is strongly sensor dependent and is chosen tominimize power consumption, processing time, and MCUmemory code. To control power consumption betweensensor scans when the MCU goes into a sleep mode, thepower is removed from all idle devices and only the sensorswith permission for Service request and Interrupt request areable to wake the system from its sleep mode.The temperature sensor has priority to interrupt thesystem when the temperature reaches a threshold.The sensor bus used is an enhanced version of theIntegrated Smart Sensor bus (developed in the Laboratory ofElectronic and Instrumentation of Delft University ofTechnology) [2]. This bus is a serial sensor bus for usage insmall data-acquisition and control systems, aiming at anefficient and low-cost interconnection of sensors, actuatorsand bus masters. II. INTERNAL BUS INTERFACE Besides the simplicity, this bus interface has twoconvenient features which makes it very suitable for anintegrated instrumentation system, composed from severalheterogeneous subsystems. Firstly, analog data can betransferred over the bus. Data generated by a sensor withlimited signal processing capability usually comes in thisform, so this requirement is necessary, but not present in theusual standard interfaces, which are designated tointerconnect only digital subsystems (their degree ofabstraction is too high).Secondly, the use of the Manchester encoding scheme fortransmission of the data at the logical level adds furtherflexibility. In such a scheme, the clock is embedded into thedata allowing four logical level instead of having two (seeFig.3). The physical structure (physical layer) of the classicISS bus consists of two wires, a data line and a clock line,both open drain driven. Beside these two communicationlines, the subsystems have two other common power supplywires, one for the positive supply and the other for theground. The data line allows half-duplex communicationbetween the modules connected to the bus [3].In order to increase the flexibility, in the enhanced ISSbus a second data line was added, to be used for duplextransmission, like for instance in the case of an on-line sen-sor calibration or testing procedure. But this supplementaryline will be used only in this case of a duplex communica-tion, all the rest of the protocol makes use of only the clockand primary data line. Fig.4 shows the block diagram of theintegrated smart sensor bus interface developed with thethree lines (Clock, Data and Calibration).Fig. 1. Block diagram of the microinstrumentation system Fig. 2. The microinstrumentation systemTelemetryMCUBusInterface Interface SensorBusInterface Interface SensorBusInterface Interface SensorBusInterface Interface SensorEPROMRAM SCITimers A/DCrystalI/O PortPressureSensorWired I/OPortDriverRS-232RS-485TemperatureSensor SensorCoriolisAccelerationGyroscopeInput rotationrateΩAccelerationFig. 3. Manchester encoding systemFig. 4. Block diagram of the enhanced ISS bus interfaceClock Data“1” “0” “Error” “Idle” “Bus Free”ISS Busline driverline receiverClkclock bufferManchesterDecoderAddress RegisterConfiguration registerAddress+ConfigurationControlSensororSmart DataCal_lineManchesterEncodingDigital InputBitstream, Analog, PWM, Frequency,......InputProgrammable IntegratorService and InterruptRequest ControlInterrupt RequestService RequestSensorSensor ISS Bus InterfaceIII. REQUEST PROTOCOL in a 1.6 µm CMOS process. A photograph of the chipIn the case of the embedded systems, particularly forinstrumentation systems, one would like to also exist somefacilities for the sensor modules to announce the controllerwhen they have available data [3], or more generally, whensome particular event happened. In the developed interfacethis flexibility is obtained by adding an interrupt request anda service request protocol.An interrupt request message, if it is not disabled by theconfiguration used for that particular module, could be sentover the bus in any moment, even if the controller was in themiddle of another conversation. A service request instead isallowed only if the bus is in idle state, that is, no othercommunication takes place in that moment. Nevertheless,the treatments of both interrupt and service requests by thecontroller are unified in a single mechanism, since bothrepresent the same abstraction: a request message from aslave module. Except for the request messages, all the othermessages are initiated by the controller and are frameoriented.The length of the frame is variable, depending on itssignificance. The bus interface functions have been realised(1.5x0.7 mm2) is shown in Fig.5.IV. EXPERIMENTAL RESULTSA typical addressing sequence transmitted serially overthe data bus has been recorded and is shown in Fig.6. Theframe transmitted was composed by start bit, 4 bits for thesensor address more 4 bits related with sensor internalconfiguration. The chip has a power consumption of 500µW(5V@100kHz) and 2mW (5V@4MHz). A network withthree bus interfaces was implemented and the request blockwas successfully tested. Fig.7 shows a service request froma sensor. When clock and data lines are idle (in high levelwithout transfer of data) the sensor demands a servicerequest by putting down the data line, and in reply the masterissues a request for the address sensor (the master is notobligate to answer to this request and if an interrupt requesthappens it has high priority). The procedure for the interruptrequest is done when the sensor puts down the Clock lineand the master that controls the line will proceed in the sameway like service request.Fig. 5. A microphotograph of the bus interfaceFig. 6. The oscilloscope traces of the clock and data lines.Fig. 7. A service request from a sensorThe features of the microinstrumentation bus interfaceare:- Simplicity of structure; only two communication wiresare used in the minimum configuration.- Reliable data transfer by using the Manchester encodingwith error detection schemes.- Flexibility of signal type, as synchronous andasynchronous transmission of digital data is possible in combination with semi-digital signals, such asbitstreams, or even analog signals.- Flexibility of signal handling based on a maskableinterrupt mechanism.- Sensor self-test capability over the bus using separatedirectional data lines.- To be used as a separate die in microsystems and alsosuitable for on-chip integration with sensors.V. PACKAGINGThe microinstrumentation system is basically composedof a chip organized as a platform that contains allinfrastructural functions. Sensor dies and microcontrollerare bonded on top. This type of two-level integrated devicecomplicates packaging. The packaging plays a fundamental role in the operationand performance of a component and in this case is criticalbecause one has sensors combined with electronics. A goodpackage must comply with a large variety of requirements:electrical, mechanical and thermal properties, low cost.Mounting the dies directly on the substrate offers asubstantial benefit when performance or density is a majorissue [4]. The main advantages of the active Multi-Chip-Module(a-MCM) approach over conventional MCM are theincreased packaging density and performance. The MCMtechnology can also reduce power consumption, since largeoutput drivers become superfluous, due to reduced loadcapacitance of the output pads. Its main disadvantage is theeconomics, because this technology requires someadvanced manufacturing steps that make the processexpensive. The cooling of a package depends upon thethermal conduction of the packaging material. Since packaging approaches that feature a low thermaldie-to-ambient resistance are very expensive, limitingpower dissipation of the circuits is an economic necessity.VI. APPLICATIONS The microinstrumentation system has many industrialapplications. Three applications, condition monitoring ofmachines, an inertial navigation system and a miniaturespectrometer will be discussed here.A. Condition monitoring of machinesCondition monitoring of machines and major mechanicalstructures has become increasingly important for the earlydetection of upcoming failures, so when the machine ofstructure is not yet damaged or before any personal hazardsmay arise. Especially, the monitoring of the vibrationspectrum of such a machine is an important parameter topredict failure. Another obvious parameter that affectslifetime is the operating temperature. A conditionmonitoring system based on the micro-instrumentationcluster on silicon with an array of accelerometers for thedetection of the vibration spectrum in three dimensions plusa thermal sensor would be a promising solution for thisapplication.Ch1Ch2B. An inertial navigation systemGyroscope devices [5,6] for measuring angular rotationor rotation rate have been the subject of extensive research.The development of low-cost miniature siliconmicromachined gyroscope is important for someapplications like: automotive industry (traction controlsystems and ride stabilization systems), consumerelectronics (video camera stabilization and model aircraftstabilization), computer industry (inertial mouse), roboticsand military applications. The fabrication of gyroscopes in silicon using resonatingmicrostructures is one of the most demandingmicromachining tasks, which leaves little margin fortechnological compromises that might be needed toestablish fabrication compatibility between sensorprocessing and micro-electronic fabrication in case of on-chip integration [7]. Generally, the requirements for thesesensors are: a resolution between 0.2 deg/sec to 2 deg/sec, afull-scale of 100 deg/sec and a response bandwidth of100Hz. This application requires three accelerometers andthree gyroscopes for measuring of linear and angularacceleration in three dimensions from which the actualposition can be calculated. Moreover, a significant amountof data processing is required to derive position information.Therefore, the use of a microcontroller based on RISCarchitecture (with math libraries for calculus in cache) andlow-power  is of huge advantage.C. Miniature spectrometerAn array of tunable Fabry-Perot resonance cavities for thespectral analysis of visible and near-infrared radiation isanother application where the data-processing requirementswill match the capabilities offered by themicroinstrumentation platform infrastructure [8,9]. Theminiature spectrometer is based on a Fabry-Perotinterferometer (optical element consisting of two partiallyreflecting low-loss parallel mirrors separated by a gap). Thespace that is enclosed between the two mirrors is an opticalresonance cavity and, when it equals multiples of a halfwavelength of the incident light, series of sharp resonanttransmission peaks result (caused by multiple reflections ofthe light in the cavity). Small changes in the cavitydimensions can produce large changes in transmission [10]. The resolving power of the device is strongly dependenton the reflectance of the two mirrors and the parallelismbetween them. VII. CONCLUSIONS The concept of microsystems provides an opportunity tosolve many measurement problems using a system of thesmallest dimensions. The main advantages of themicroinstrumentation system are:- universal applicable platform- solving measurement problems on system level- smallest carrier- adaptable to different applications by populating withsensors or/and software- the low unit-costs in mass productionThe disadvantages are the large die area and the 2-leveldie assembly, that complicates and increases the cost of thepackage of  the whole microsystem.VIII. ACKNOWLEDGMENTSThis work is supported in part by STW (project DEL55.3733), TUDelft and JNICT- Portugal (Program PraxisXXI-BD/5181/95).IX. REFERENCES[1] A. Mason, N. Yazdi, K. Najafi, K. Wise,”A low-powerwireless micro-instrumentation system for environmental monitoring”, Proc. Transducers ‘95 pp. 107-110.[2] J.H.Huijsing, F. Riedijk, G. v. Horn, “Developments inintegrated smart sensors”, Proc. Transducers ‘93, pp.320-326.[3] J. Bryzek, “Introduction to IEEE-P1451 the emerginghardware independent communication standard forsmart transducers”, Proc. Eurosensors X - 1996Belgium, pp. 853-876.[4] J. Rabaey, Digital integrated circuits: a designperspective, Prentice-Hall, 1996.[5] M.Putty, K. Najafi, A Micromachined Vibrating RingGyroscope, Solid-State Sensor and Actuator WorkshopHilton Head, South Carolina, 1994, pp. 213-220.[6] M. Hashimoto, M. Esashi, Silicon resonant angular ratesensor using electromagnetic excitation and capacitivedetection, J. Micromech. Microeng. 5, 1995, pp. 219-225.[7] R. F. Wolffenbuttel, Silicon sensors and circuits: on-chip compatibility, Chapman-Hall, 1996.[8] J. H. Jerman, D. J. Clift, S. R. Mallinson, “A miniatureFabry-Perot interferometer with a corrugated silicondiaphragm support”, Sensors and Actuators A, vol.43,1994, pp.17-23.[9] M. C. Wu, L. Y. Lin, K. S. J. Pister , “Micromachinedfree-space integrated micro-optics”, Sensors andActuators A, vol. 50, 1995, pp.141-146. [10] Y. Kim, D. P. Neikirk, “Micromachined Fabry-Perotcavity pressure transducer”, IEEE Photon. Technol.Lett., vol. 7, 1995, pp.382-384.

A microinstrumenation system for industrial applications

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A microinstrumenation system for industrial applications

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