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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Athens Programme 2008 Metrology of Electrical Quantities Laboratory of Legal Metrology Department of Measurements Faculty of Electrical Engineering Czech Technical University in Prague Responsible professor: Prof. Ing. Jaroslav Bohacek, DrSc. Phone +420 22435 2220 E-mail bohacek@fel.cvut.cz http://measure.feld.cvut.cz/...

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 William Thomson, Lord Kelvin I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it … … but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind.

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Brian W. Petley Far from being a dull area of science, high-precision measurements are an increasingly exciting area in which to work, for they push theory and experiment to the very limits of which they are capable… If we recall that the rich oil deposits under the North Sea remained unknown until the advent of the very precise geophysical measurements, or that the spin of the electron was inferred from precise spectroscopic measurements, we see more clearly the class of discoveries which can come from precise measurement.

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Course objectives Lectures Previous intro Laboratory demonstrations Laboratory visits What is What is metrology? metrology? Please, select some topic above to continue

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8Laboratory demonstrations 1.Thompson-Lampard's capacitance standard 2.Frequency performance of resistance standards 3.Calibration of capacitance boxes

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Course objectives: to present an overview of modern and perspective methods for precision measurements of electrical quantities, to demonstrate various techniques used in calibrations of electrical measurement instruments and standards.

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8Lectures Lecture 1 Introduction Measurement units and measurement standards Quantum standards of voltage and resistance Thompson-Lampard's capacitance standard Equivalent circuits of standard resistors, capacitors and inductors Resistors with calculable frequency performance Transfer standards

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Lectures Lecture 2 Voltage and current inductive ratio devices and optimization of their metrological parameters.

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Lectures Lecture 3 Methods for precision measurement of dc current and dc voltage Modern potentiometers Measurement of voltage, power and energy in audiofrequency range Sample lecture

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Lectures Lecture 4 Bridges for dc and ac measurements of resistance Transformer and current-comparator-based capacitance bridges Metrological applications of the quantum Hall effect (QHE)

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8What is Metrology? Metrology is the science of measurement.

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 What is Metrology? Metrology covers three main activities: 1.The definition of internationally accepted units of measurement, e.g. the metre. 2.The realization of units of measurement by scientific methods, e.g. the realization of a metre through the use of lasers. 3.The establishment of traceability chains by determining and documenting the value and accuracy of a measurement and disseminating that knowledge, e.g. the documented relationship between the micrometer screw in a precision engineering workshop and a primary laboratory for optical length metrology.

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 1. Scientific metrology deals with the organisation and development of measurement standards and with their maintenance (highest level). 2. Industrial metrology has to ensure the adequate functioning of measurement instruments used in industry as well as in production and testing processes. 3. Legal metrology is concerned with measurements where these influence the transparency of economic transactions, health and safety. What is Metrology? Metrology is considered in three categories with different levels of complexity and accuracy:

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Systematic measurement with known degrees of uncertainty is one of the foundations of industrial quality control and, generally speaking, in most modern industries the costs bound up in taking measurements constitute 10 -15% of production costs.

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8Laboratory visits: Czech Metrology Institue Calibration of digital multimeters Quantum Hall effect based calibrations of resistance standards www.cmi.cz

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Laboratory of Legal Metrology, CTU in PragueAthens 200 8 Laboratory of Legal Metrology, CTU PragueAthens 2006 See you in Prague!

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TOPIC 3

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Current balance C1C1 C2C2 C3C3 I C1 = I C2 = I C3 = I I C1 enters C 1 at the bottom and leaves it at the top, I C2 enters C 2 at the top and leaves it at the bottom. Electromagnetic forces on the suspended coil, produced by these two currents, are of the same sense.

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Current balance

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Current balance operation The mass of the suspended coil plus the vertical electromagnetic force exerted on it are counterbalanced by means of a mass m on the left scale pan. After reversing the current in the suspended coil, the change m of this mass, necessary to offset the change F of the acting electromagnetic force, is determined.

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Current balance operation A separate moving experiment makes it possible to avoid the troublesome calculation of f from the dimensions of the coils: Coil C 3, which is threaded by the magnetic flux produced by the current I flowing in C 1 and C 2, is moved with a constant velocity v in the vertical direction, a voltage u(t) being induced in it:

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Current balance operation If a voltage drop U = R I is produced by the current I on a known resistance R and if a velocity v is choosen for which in the moment of passage of the scale beam through its equilibrium position,

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Electronic kilogram In case that quantum standards of voltage and resistance are used to measure the current I flowing in the coils in course of the weighing experiment, a current balance with a known value of f can be used to produce known values of electromagnetic force and to monitor variations of masses which are used to counterbalance it.

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Voltage balance is an apparatus based on counterbalancing the attractive force between electrodes of a capacitor.

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DC comparator potentiometer Constant current PS Slave PS IsIs IpIp RUx,UeUx,Ue NsNs nsns NpNp PD OSC N s = 1000 turns n s = 11 turns in steps of 10 -4 turns N p 2000 turns, steps of 10 -4 turns

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Realization of the equivalent of fractional turns 50 Ω SPS IsIs 500 Ω R 1turn / step 5.625 Ω 1000 turns...

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Primary voltage standard system with closed-cycle refrigerator

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100 nV calibration accuracy -11 V to 11 V range available from 10-V system typically 1 hour stability time at 10 V for 10-V system automatic voltage calibration in minutes automatic calibration of DVMs complete system diagnostics

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RMS/DC thermocouple comparator S1S1 S2S2 UxUx UrUr TE 1 TE 2 12 R R s1 R s2

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Automatic RMS/DC thermocouple comparator UxUx UrUr R s1 R s2 TE 1 TE 2

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Thermocouple protection R R A A to relay R drives to relay R drives

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RMS/DC thermistor comparator UrUr R2R2 UaUa UxUx A R s1 Rs2Rs2 R1R1 T1T2

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Improved RMS/DC thermistor comparator UaUa UxUx R1R1 R3R3 R2R2 Rs1Rs1 Rs2Rs2 R4R4 A1 A2 UrUr T1 T2

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Electrodynamic method of measurement of AC power fixed coils moving coil i c1 i c2 i c1 = i 1 + I 1 i c2 = i 2 - I 2

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Electrodynamic method of measurement of AC power i1i1 moving coil Control circuit electrodynamometer fixed coils UrUr U out uUuU uIuI R R R R A2 A1 I1I1 I2I2 i2i2 i c1 i c2 i1i1

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Thermal wattmeter R R R R R R R R A1 A2 A3 A4 U out uUuU uIuI

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