HW #32004200456

Lim Myeong Jun

Resistive sensor Capacitive sensor Inductive sensor LVDT Problem solution Piezoelectric sensor Electromagnetic spectrum Radiation thermometer

∵ ρ : Specific resistance

1. Strain gage : Changes in L & ρ2. Force sensing resistor : Changes in

A3. Thermister : Changes in

temperature4. Potentiometer : Changes in Length

R

F

RCeramic

NTC thermister(Negative temperature coefficient)

PTC thermister(Positive temperature coefficient)

R

E [ v ]

R s

+ Vout- Vo, Vs, F, T : Non linear

E [ v ]

RR s

-

+

A )

B )

C )

Bridge circuit

D )

Linearization

Rp

Rs

Rs

Rp

R

Linear range

x

A

εRMost capacitive sensor is based on changes in x.

Capacitive sensor

Inductive sensor

1.Self Inductance 2.Mutual Inductance3.Difference

Inductance

LVDT(Linear Variable Differential Transformer)a

b

c

d

e

fx=0

x=-D

x=D

Primary coil

x= δ

x=-δ

Mutual Inductance Sensor

Magnetic core

+Vo-

Line is Vs and dot is Vo at magnetic core

When core is x=0

When core is x=+δ

When core is x=- δ

Vertical displacement

Given by Vs(t) = sin(2π*1000t) [V] (f = 1000Hz, T = 1ms)

180º Phase change

x=0

x=-D

x=D

D=20mm, 2D=40mm

Method 1: Rectifier + LPF

Full wave

rectifier

LPF

t

V(t)

Method 2: Phase-Sensitive demodulation

Vo(t)

x(t)·Vo²(t)

x(t) = sin(2π· 1000t)

LPF(Low Pass Filter)

V(t)

t

V(t)

In phase-sensitive demodulation

Vo(t)

Vm(t)

x(t) = sin(2π· 1000t)

LPF(Low Pass Filter)

V(t)

formula

x

q : Charge , x : Deflection

That means piezoelectric sensor has no DC response.

Fig. piezoelectric sensor

Ri(t)

Vs(t) = R*i(t)

i=0

i=0

+

IA

-

Vo(t)

1)

2)

i(t), Current flow

-

IA

+

Vo(t)

R

C

0V

Change Amplifier

f

|H|

k/c

fc

= 1/2πRC

If you plan to use the piezoelectric sensor, for measuring pulse, the lowest frequency of pulse, signal is assumed to be 0.1Hz