1 the distributed measurement systems: a new challenge for the metrologists by alessandro ferrero...
TRANSCRIPT
11
The Distributed Measurement The Distributed Measurement Systems: a New ChallengeSystems: a New Challenge
for the Metrologistsfor the Metrologists
byby
Alessandro FerreroAlessandro Ferrero and Roberto Ottoboni and Roberto OttoboniPolitecnico di Milano – Dipartimento di ElettrotecnicaPolitecnico di Milano – Dipartimento di Elettrotecnica
Milano - ItalyMilano - Italy
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 22
OverviewOverview
IntroductionIntroductionEvolution of the Measurement InstrumentsEvolution of the Measurement Instruments
DSP-based architecturesDSP-based architecturesVirtual Instruments (VI)Virtual Instruments (VI)Distributed Measurement Systems (DMS)Distributed Measurement Systems (DMS)
Metrology issuesMetrology issues
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 33
Signal processing & MeasurementSignal processing & Measurement
Signal processing is the basis of the Signal processing is the basis of the measurement activitymeasurement activity
Any evolution in signal processing Any evolution in signal processing techniques has a direct impact on techniques has a direct impact on measurement systemsmeasurement systems
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 44
Digital Signal ProcessingDigital Signal Processing
Analog signals can be converted into a Analog signals can be converted into a sequence of digital samplessequence of digital samplesThe sampling theorem provides the conditions The sampling theorem provides the conditions
for preserving the information associated with for preserving the information associated with the original analog signalthe original analog signal
The modern instruments are based on The modern instruments are based on DSP techniquesDSP techniques
They have benefited of the recent, They have benefited of the recent, impressive evolution of the DSP impressive evolution of the DSP techniques and devicestechniques and devices
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 55
The first revolution:The first revolution:DSP-based instrumentsDSP-based instruments
T&C ADC Mem Comp
Field
Input signalsMeas.
Ana
log
proc
essi
ng
Digital processing
From: A measurement, an instrument
To: A measurement, an algorithm
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 66
The second revolution:The second revolution:Virtual InstrumentsVirtual Instruments
T&C ADC Mem Comp
Field
Input signalsMeas.Interf.
An interface is added to:An interface is added to:Provide an instrument-like, user-friendly Front Provide an instrument-like, user-friendly Front
PanelPanelProvide a graphic programming interfaceProvide a graphic programming interface
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 77
The third revolution:The third revolution:Distributed Measurement InstrumentsDistributed Measurement Instruments
T&C ADC Mem Comp
Interf.
Net Int.
Field
World
Input signals
An interface to an An interface to an interconnection interconnection network is addednetwork is added
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 88
The new paradigmThe new paradigm
The desired measurement result is The desired measurement result is provided by a network of cooperating provided by a network of cooperating instruments that share their resourcesinstruments that share their resources
The desired measurement result is The desired measurement result is provided by a network of provided by a network of cooperatingcooperating instruments that instruments that shareshare their resources their resources
Internet/Intranet
Field
Field
Field
ADC
ADCADC
Measurement unit 1
Measurement unit jMeasurement unit N
Supervising unit
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 99
Better performance …Better performance …
……more problems!more problems!The different units share resources and The different units share resources and
datadatacollected under different conditionscollected under different conditionsacquired by different hardware systemsacquired by different hardware systems
The evaluation of the measurement The evaluation of the measurement uncertainty becomes a problem.uncertainty becomes a problem.
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1010
The most mischievous problemThe most mischievous problem
The lack of time synchronization between The lack of time synchronization between the sampling devices of the different units.the sampling devices of the different units.
When measured data are shared across a When measured data are shared across a public-domain network (Internet), the public-domain network (Internet), the transmission time becomes largely transmission time becomes largely unpredictable.unpredictable.
The risk is that the different units start The risk is that the different units start working on different timelines.working on different timelines.
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1111
The lack of synchronizationThe lack of synchronization
The same event is seen at different time The same event is seen at different time instants by the different unitsinstants by the different units
Different delays are introducedDifferent delays are introducedTheir estimation may be cumbersomeTheir estimation may be cumbersome
The consequent uncertainty estimation uselessThe consequent uncertainty estimation useless
Unit 1Unit 1
Event at time Event at time tt11
Unit 2Unit 2
Event at time Event at time tt22
t
t
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1212
The solutionThe solution
Clock synchronizationClock synchronizationA unique timeline is defined for all unitsA unique timeline is defined for all unitsA timestamp can be associated to each A timestamp can be associated to each
transmitted datatransmitted dataMeasurement uncertainty is not related to Measurement uncertainty is not related to
the transmission delay, but to the the transmission delay, but to the residual residual synchronization errorsynchronization error..
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1313
Clock synchronizationClock synchronizationHow accurate?How accurate?As always, it depends on the As always, it depends on the target target
uncertaintyuncertainty..The case of the identification of the origin The case of the identification of the origin
of transient disturbances in the electric of transient disturbances in the electric system.system.
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1414
Measuring unit 1
Measuring unit 2
t0t1t2
t If If tt22 - - tt11 > 0, > 0,
then the disturbance’s origin is upstream then the disturbance’s origin is upstream the measuring unit 1the measuring unit 1
The synchronization uncertainty must be The synchronization uncertainty must be significantly lower than significantly lower than tt22 - - tt11
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1515
Clock synchronizationClock synchronizationHow accurate?How accurate?As always, it depends on the As always, it depends on the target target
uncertaintyuncertainty..The case of the identification of the origin The case of the identification of the origin
of transient disturbances in the electric of transient disturbances in the electric system.system.A GPS synchronization is requiredA GPS synchronization is required
50 ns with respect to UTC50 ns with respect to UTCThe case of the identification of harmonic The case of the identification of harmonic
disturbancesdisturbances
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1616
Each measurement unit measures suitable Each measurement unit measures suitable power quality indices power quality indices averagedaveraged over a over a given intervalgiven interval
The synchronization uncertainty must be The synchronization uncertainty must be significantly lower than the duration of the significantly lower than the duration of the averaging intervalaveraging interval
Load1
Load 2
Load j
Load N
Feeder
Measuring units
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1717
Clock synchronizationClock synchronizationHow accurate?How accurate?As always, it depends on the As always, it depends on the target target
uncertaintyuncertainty..The case of the identification of the origin The case of the identification of the origin
of transient disturbances in the electric of transient disturbances in the electric system.system.A GPS synchronization is requiredA GPS synchronization is required
50 ns with respect to UTC50 ns with respect to UTCThe case of the identification of harmonic The case of the identification of harmonic
disturbancesdisturbancesA NTP synchronization is sufficient (A NTP synchronization is sufficient (10 ms)10 ms)
Politecnico di Milano
INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008INGRID 2008 – Lacco Ameno – Ischia – ITALY – April 9-11, 2008 1818
ConclusionsConclusionsDMS benefit of the evolution of the DMS benefit of the evolution of the
interconnection of the computing systems.interconnection of the computing systems.They are the natural evolution of the They are the natural evolution of the
remote measurement systemsremote measurement systemsThey are a promising tool for the solution They are a promising tool for the solution
of very complex measurement tasksof very complex measurement tasksThe present new problems in metrologyThe present new problems in metrology If disregarded they may lead to largely If disregarded they may lead to largely
incorrect resultsincorrect results