Projekt „ESSNBS“ DAAD

Niš, November 4th – 7th, 2012 - 1 -

Single point calibration applied on multivibrator-based signal conditioning circuits for passive

modulating sensors

M. Sc. Zivko KokolanskiPh.D. Student

kokolanski@feit.ukim.edu.mk

Niš, November 4th – 7th, 2012 - 2 -

OUTLINE

• Introduction to signal conditioning• Multivibrator in monostable and astable

configuration• Measurement uncertainty• Single point calibration• Systematic errors• Transfer characteristic• Temperature variation test• Conclusions

Niš, November 4th – 7th, 2012 - 3 -

SIGNAL CONDITIONING

A/D

Sensor Oscillator

mC

Programmable measurement system with A/D converter

Programmable measurement system with oscillator

• Simple, low cost• Direct digital interface • Wider dynamic range• Lower electromagnetic interference

mC

Rela

xati

on

osc

illato

r

Cref,Rref

Sensor

Direct Sensor-to-microcontroller interface

ADVANTAGES:

Programmable signal cond.

circ.Sensor

mC

Niš, November 4th – 7th, 2012 - 4 -

MULTIVIBRATOR

Basic representation of a multivibrator in

monostable (a) and astable (b) configuration

Niš, November 4th – 7th, 2012 - 5 -

MEASUREMENT UNCERTAINTY

• Two effects are dominant: quantization and trigger uncertain.

6)( 0Tzu

)()()( 22 zuxuyu

2

22

2

22)(

B

nB

A

nA

t

V

ex

t

V

exxu

)(2)(2)(2)(22

yuzuxuyu monmonmonast

Niš, November 4th – 7th, 2012 - 6 -

MONOSTABLE MULTIVIBRATOR (555) FAMILY

cc

th

V

VRCT 1ln kRT ???k

Niš, November 4th – 7th, 2012 - 7 -

MONOSTABLE MULTIVIBRATOR WITH SINGLE POINT CALIBRATION

cc

thc

cc

thx

c

x

V

VCR

V

VCR

T

T

1ln

1ln

cc

xx R

T

TR

Niš, November 4th – 7th, 2012 - 8 -

SYSTEMATIC ERRORS

11

1*

1

1

edson

xxdsonx

RR

RkRRR

Offset Gain Nonlinearity

cRc

x

RR

R no

e

s

n

dson

1

1

1

211

121

1

For DRx<1/2LSB

The condition limits the measurement range

Niš, November 4th – 7th, 2012 - 9 -

TRANSFER CHARACTERISTIC

• Realization with DAQ card USB6218

• 20 MHz timebase• ENOB = 14.2 bits (0.1 )• Measurement range

1000 to 3000 • Maximal relative error of

the approximated transfer characteristic was 0.11%

Niš, November 4th – 7th, 2012 - 10 -

TEMPERATURE VARIATION TEST

• Rapid temperature rise increased Tx and Tc for 2%• Rx decreased 0.2%• Single point calibration reduce the temperature effects nearly 10 times

Niš, November 4th – 7th, 2012 - 11 -

CONCLUSIONS

• The performances of the multivibrator as a sensor signal conditioner are limited by temperature, aging and other effects

• The single point calibration improves the stability of the measurements and performs temperature compensation

• The input resistances and leakage currents introduce gain, offset and nonlinearity errors and limit the measurement range

• The experimental results show that a resolution better than 0.1W in the measurement range from 1000 W to 3000 W with maximal relative error of 0.11% is achivable

THANK YOU!