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Athens Programme 2008

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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 bohacek@fel.cvut.cz

http://measure.feld.cvut.cz/...

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.

Laboratory

visits

Course

objectives

Lectures

What is

metrology?

Previous

intro

Laboratory

demonstrations

Please, select some topic above to continue

- Thompson-Lampard's capacitance standard
- Frequency performance of resistance standards
- Calibration of capacitance boxes

- 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.

- 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

- Lecture 2

- Voltage and current inductive ratio devices and optimization of their metrological parameters.

- 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

- 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)

Metrology is the science of measurement.

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.

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.

- Czech Metrology Institue

- www.cmi.cz

- Calibration of digital multimeters

Laboratory of Legal Metrology, CTU Prague

Athens 2006

TOPIC 3

C1

C2

IC1 = IC2 = IC3 = I

C3

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.

- 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.

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.

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

SPS

Is

...

500

50

Ω

Ω

5.625 Ω

1turn/step

R

1000 turns

- 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

Ux

Ur

Rs1

Rs2

TE1

TE2

to relay R

drives

A

R

R

to relay R

drives

A

Ua

R1

R2

Ur

A

Rs1

T1

T2

Ux

Rs2

Ua

R1

R3

R2

Ur

A1

A2

Rs1

Rs2

Ux

R4

T1

T2

moving

coil

ic1

ic1

ic2

fixed coils

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

i1

uU

Uout

R

R

R

R

A4

A2

A1

R

R

R

R

uI

A3