Athens Programme2008 Athens Programme2008 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 firstname.lastname@example.org http://measure.feld.cvut.cz/...
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.
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.
Laboratory visits Course objectives Lectures What is metrology? Previous intro Laboratory demonstrations Please, select some topic above to continue
Laboratory demonstrations • Thompson-Lampard's capacitance standard • Frequency performance of resistance standards • Calibration of capacitance boxes
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.
Lectures • 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
Lectures • Lecture 2 • Voltage and current inductive ratio devices and optimization of their metrological parameters.
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
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)
What is Metrology? Metrology is the science of measurement.
What is Metrology? Metrology covers three main activities: • The definitionof internationally accepted units of measurement, e.g. the metre. • The realizationof units of measurement by scientificmethods, e.g. the realizationof a metre through the use of lasers. • The establishment of traceabilitychains 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.
What is Metrology? Metrology is considered in three categories with different levels of complexity and accuracy: • Scientific metrologydeals with the organisation and development of measurementstandards and with their maintenance (highest level). • Industrial metrologyhas to ensure the adequate functioning of measurementinstruments used in industry as well as in production and testing processes. • Legal metrologyis concerned with measurements where these influence thetransparency of economic transactions, health and safety.
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.
Laboratory visits: • Czech Metrology Institue • www.cmi.cz • Calibration of digital multimeters • Quantum Hall effect based calibrations of resistance standards
Laboratory of Legal Metrology, CTU Prague Athens 2006 See you in Prague!
C1 C2 IC1 = IC2 = IC3 = I C3 Current balance IC1 enters C1 at the bottom and leaves it at the top, IC2 enters C2 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.
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.
Current balance operation A separate moving experiment makes it possible to avoid the troublesome calculation of f from the dimensions of the coils: Coil C3, which is threaded by the magnetic flux produced by the current I flowing in C1 and C2, is moved with a constant velocity v in the vertical direction, a voltage u(t) being induced in it:
Current balance operation If a voltage drop U = R I isproduced 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,
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.
Voltage balance is an apparatus based on counterbalancing the attractive force between electrodes of a capacitor.
Is Ip Constant current PS Slave PS R Ux, Ue Ns ns Np PD Ns = 1000 turns OSC ns = 11 turns in steps of 10-4 turns Np 2000 turns, steps of 10-4 turns DC comparator potentiometer
SPS Is ... 500 50 Ω Ω 5.625 Ω 1turn/step R 1000 turns Realization of the equivalentof fractional turns
Primary voltage standard system with closed-cycle refrigerator
Primary voltage standard system with closed-cycle refrigerator • 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
1 2 S1 S2 Rs1 Rs2 Ux Ur TE1 R TE2 RMS/DC thermocouple comparator
Ux Ur Rs1 Rs2 TE1 TE2 Automatic RMS/DC thermocouple comparator
to relay R drives A R R to relay R drives A Thermocouple protection
Ua R1 R2 Ur A Rs1 T1 T2 Ux Rs2 RMS/DC thermistor comparator
Ua R1 R3 R2 Ur A1 A2 Rs1 Rs2 Ux R4 T1 T2 Improved RMS/DC thermistor comparator
moving coil ic1 ic1 ic2 fixed coils Electrodynamic method of measurement of AC power ic1=i1 + I1 ic2=i2 - I2
Uout Ur I1 I2 Control circuit R R ic1 ic2 electrodynamometer R R uI uU i2 i1 A2 A1 fixed coils moving coil Electrodynamic method of measurement of AC power i1
uU Uout R R R R A4 A2 A1 R R R R uI A3 Thermal wattmeter