slides-02

MEASUREMENT SYSTEMS

AND THEIR PRINCPLES

Ideal current source: A souce that has infinite output resistance and supply infinite current.

Ideal voltage source: A souce that has zero output impedance and supply infinite current.

Ideal ammeter: A meter that has zero input

resistance and has no voltage drop accross it.

Ideal Voltmeter: A meter that has infinite input resistance and draws no current.

Measuring with ideal instruments 2 1 2 1 2 1

//

R

R

R

R

R

R

R

_eq

+

=

=

s m

V

V =

No measurement error

Effect of source and meter impedances s eq out eq m

V

R

Z

R

V

_' '

−

=

Ω = = R k R 1 2 1 Ω = M1 in Z Ω = 50 out Z

V

V

₌

9

.

09

_{measurement error= 9.1%}

Keithley Model 2400-C General-Purpose SourceMeter (200V and 1A, 20W)

GPIB interface Boards

Front view Rear view

Keithley Model 2010 7-1/2-Digit, Low-Noise, Autoranging DMM

Digital Multimeters

Oscilloscopes

Analog Oscilloscope

s oc

V

R

R

R

V

2 1 2

+

=

2 1 2 1

R

R

R

R

R

_TH

+

=

Thevenin’s Therem:

Given a pairs of terminals in

a linear electrical network, the network may be

replaced by an ideal voltage source V

_OC

in

series with a resistance R

_TH.

V

_OC

is equal to the

open circuit voltage accross terminals, and R

_TH

is the equivalent resistance accross the

terminals when independent voltage sources

are replaced by open circuits.

Norton Equivalent:

Linear network is replaced by

an ideal current source I

_SC

and the Thevenin

Resistance R

_TH

in parallel with this source. I

_SC

is

found by calculating the current that would flow

through the terminals if they were shorted

Norton

equivalent

circuit

Thevenin

equivalent

circuit

IMPEDANCE MATCHING

s i L L L V R R R V + =

(

)

2 2 2 S i L L L L L V R R R R V P + = = 0 = L L dR dP i L

R

R =

IMPEDANCE MATCHING

ELECTRICAL INTERFACE

dt

dB

A

V

_noise

=

V

_measured

=

V

_actual

+

V

_noise

Static Characteristics of Instruments

• Accuracy: Precision/Repeatibilty/Reproducibility Tolerance Range or Span Bias Linearity Sensitivity of Measurement Sensitivity to Disturbance Hyteresis Dead Space Treshold Resolution