Athens Programme 2008. 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
Metrology of Electrical Quantities
Laboratory of Legal Metrology
Department of Measurements
Faculty of Electrical Engineering
Czech Technical University in Prague
Prof. Ing. Jaroslav Bohacek, DrSc.
Phone +420 22435 2220
E-mail [email protected]
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.
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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Metrology is the science of measurement.
Metrology covers three main activities:
Metrology is considered in three categories with different levels of complexity and accuracy:
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.
Athens 2006See you in Prague!
IC1 = IC2 = IC3 = I
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.
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:
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,
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.
is an apparatus based on counterbalancing the attractive force between electrodes of a capacitor.
Ns = 1000 turns
ns = 11 turns
in steps of
Np 2000 turns,
steps of 10-4 turnsDC comparator potentiometer
1000 turnsRealization of the equivalentof fractional turns
TE2RMS/DC thermocouple comparator
TE2Automatic RMS/DC thermocouple comparator
to relay R refrigerator
to relay R
Rs2RMS/DC thermistor comparator
T2Improved RMS/DC thermistor comparator
fixed coilsElectrodynamic method of measurement of AC power
ic1=i1 + I1
ic2=i2 - I2
moving coilElectrodynamic method of measurement of AC power