lecture 3 in the name of allah - ali...

Lecture 3

Dr. Ali Karimpour Feb 2018

Instrumentation

In The Name of Allah

Dr. Ali Karimpour

Associate Professor

Ferdowsi University of Mashhad

Lecture 3


2

Temperature measurement

Topics to be covered include:

v Resistive Thermometers

v Thermistor Thermometers

v Thermocouple Thermometers

v Semiconductor Junction Thermometers

v Bimaterials Thermometers (Bimetal)

v Pyroelectric(Infrared) Thermometers

v Fiber-Optic Thermometers

v …….

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3

Resistive Thermometers

v PTC

Positive Temperature Coefficient.

v NTC

Negative Temperature Coefficient.

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4


Sensitivity is defined as the amount of resistance change of the sensor

per degree of temperature change.

Nickel is very good for sensitivity.

However, have a limited temperature

range,

Copper has a very linear resistance-to-

temperature relationship. However,

copper oxidizes at moderate

temperatures and cannot be used above

150°C.

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5


Platinum is the best metal for RTD

elements.

• It follows a very linear resistance-

to-temperature relationship.

• It follows its resistance-to-

temperature relationship in a highly

repeatable manner over its

temperature range.

• It has the widest temperature range

among the metals used to make RTDs.

• Platinum is not the most sensitive metal; however, it is the metal

that offers the best long-term stability.

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6


Wire-wound RTD.

Thin film RTD.

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7


Industrial Platinum Resistance Thermometers (IPRTs) are designed to

withstand industrial environments and are almost as durable as

thermocouples.

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8

Linearity (least square method)

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9


Calibration

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02010 TTTTTTRR

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10


Calibration

Exercise 3-1: Resistance of an RTD at 60°C is 106Ω. The resistance

Variation with time is:

a) Derive a first order model for system and find FSO%(Suppose

113.6 is full scale).

b) Derive a second order model for system and find FSO %(Suppose

113.6 is full scale).

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11


PTC100.

• It is often from platinum.

• Its resistance at 0°C is 100 Ω.

• Its sensitivity is 0.00385

Example 3-1: What is the resistive

of PTC100 at 300°C ?

215.5 Ω.

Platinum RTD usually used in -200°C800°C

Nickel RTD usually used in -100°C260°C

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12

Thermistor Thermometers

A thermistor is a thermally sensitive resistor whose primary function is to

exhibit a change in electric resistance with a change in body temperature.

Unlike a wire-wound or metal film resistance temperature detector

(RTD), a thermistor is a ceramic semiconductor.

Thermistors have a large temperature coefficient compare to RTD but

it is nonlinear.

Thermistors usually used in -90°C130°C

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13


Calibration

)(1010

TTRR

RTD

Thermistor

)11

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0

0TT

eRR

10R

dT

dR

1

0

dTR

dRIts sensitivity is 0.00385

RTdT

dR2

0

2

0

TRdT

dR Its sensitivity is -0.045

Calibration

T: Degrees Kelvin

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Calibration

Calibration curve of Thermistor by

Steinhart-Hart equation:

3)(lnln1

RCRBAT

T: Degrees Kelvin

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15


Calibration

Exercise 3-2: TR91 Series 10KΩ@25°C Thermistor calibration table

is:

a) Derive β for TR91 and find maximum error in ohms.

LSM. use and ofln derive :Hint)

11(

0

0TT

eRR

b) Derive A, B and C for Steinhart-Hart equation of TR91 and find

maximum error in ohms.

LSM. use :Hint

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16

RTD and Thermistor Thermometers

Suitable circuits to convert R V

Voltage divider. Voltage divider with follower.

DD

SEN

OUTV

RR

RV

1

1

Advantages:

• Simplicity

• Detection of open sensor (failure)

Disadvantages:

• Poor noise rejection

• Voltage is non-linear function of resistance

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17



Voltage divider by current source.

SENSENOUTIRV

Advantages:

• Linearity of resistance to voltage conversion.

• Robust in noise.

Disadvantages:

• Cost.

Two

wireFour

wire

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18



Wheatstone bridge

Two

wire

Three

wire

Two

wire

s

RTD

OU

RR

R

RR

RU

3

3

21

2

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19


RTDs and Thermistors self heating

The ability of the sensor to dissipate heat is defined by its dissipation

factor, δ, which has units of mW/°C.

The definition for δ is the amount of power that it takes to the

raise the body temperature of the sensing element 1°C.

Example 3-2: An RTD with R=500Ω at 20°C and sensitivity

coefficient 0.005 1/°C with dissipation factor δ=30 mw /°C let

R1=R2=500 Ω. Derive R3 for balance of bridge in 0°C. Us=10V

R3=450 Ω. In the case of no dissipation.

R3=454 Ω. By considering of dissipation.

Lecture 3


RTD in a process

گیج های دما

گیج های مخزن آبفشار

RTD

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21

RTD in a process

RTDدما مربوط به شیربرای اندازه گیری دمای آب خروجی

Lecture 3


ADAM-4561ماژول ADAM-4024ماژول

سطح بهمانند آنچه در ست کنترل فلو و کار رفته است

را داراست 6RTDاین ماژول قابلیت خواندن ADAM-4015ماژول

RTD and data acquisition module

Lecture 3


RTD and data acquisition module

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24

Thermocouple Thermometers

The Seebeck effect is the conversion of temperature differences

directly into electricity

(Thomas Johann Seebeck 1821)

For example, the Seebeck coefficients

of Cu is 1.5 μV/K, and of Al −1.5 μV/K.

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The Peltier effect is the presence of heating or cooling at an electrified

junction of two different conductors(Jean Charles Athanase Peltier

1834.)

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The Seebeck effect:

How to use?

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Seebeck Coefficients for Some Metals

and Alloys, Compared to Platinum.

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Properties of several different thermocouple types

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Thermocouples are not linear enough so we need

lookup table.

31


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Thermocouples measures the difference temperature

so we need to know readout temperature:

External ice-point reference junction:

Thermocouple refrigeration method:

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Using two ovens to simulate ice-point reference:

Using a thermometer to sense the temperature:

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The sensitivity of RTD is very small.

The thermistor’s output is quite nonlinear.

Resistive, thermistor and thermocouple thermometer

The RTD and thermistor’s

output is …...

The thermocouple output is a very

small signal that is nonlinear

with temperature.

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36

Semiconductor Junction Thermometers

A silicon temperature sensor 730 mV at –40°C and 300 mV at 150°C

The narrowly specified Vbe ranges between 580 mV till 620 mV at 25°C.

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Linearity error (in mV) vs. temperature for a silicon temperature

sensor

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LM335 provides 10 mV/°K (A Zener diode)

LM34 provides 10 mV/°F

AD592 provides 0.001 mA /°K

Or LM335 provides 2.73+10 mV/°C .

Output:

+10 mV/°C .

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LM34 provides 10 mV/°F

5 °F 50 mV

300 °F 3.00 V

-50 °F ??

-50 °F -500 mV

300 °F 3.00 V

Sensors are not near to source??

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Sensors are not near to source??

We use two wires not three!

We transmit current instead of voltage!

IQ is 70 μA

But sensor is not grounded!

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Now it is grounded.

Note 1: Temperature coefficient of the 499-Ω resistor must be as low

as possible.Note 2: The output voltage must be taken differentially between +V

and signal returned from the sensor.

AD592 provides 0.001 mA /°K

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AD592 provides

0.001 mA /°K

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16-bit sigma-delta ADC converts the low-level thermocouple voltage into a 16-bit

serial digital output.

From: https://www.maximintegrated.com/en/app-notes/index.mvp/id/4026

Electronic reference compensation.

MAX6610: Determines

the cold-junction temperature

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Thermocouple ThermometersFrom: https://www.maximintegrated.com/en/app-notes/index.mvp/id/4026


Sweeping the cold junction from -40°C to +85°C in an oven and keeping the hot

junction at +100°C in a separate oven.

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MX7705 Functional Diagram

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Application of MX7705.

• Flow and Gas Meters

• Industrial Instruments

• Medical Instrumentation

• Pressure Transducers

• RTD Measurements

• Strain-Gauge Measurements

• Thermocouple Measurements

• Weigh Scales

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48


Unlike a local temperature-sensing IC, an external diode-connected NPN transistor to

measure the cold-junction temperature.

From: https://www.maximintegrated.com/en/app-notes/index.mvp/id/4026


MAX 6002: Provides a stable 2.5V

reference voltage for the ADC

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Sweeping the cold junction from -40°C to +85°C in an oven and keeping the hot

junction at +100°C in a separate oven.

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The temperature-sensing diode in the IC is used as a sensing for the

ambient temperature.


Sweeping the cold junction

from 0°C to +85°C in an

oven and keeping the hot

junction at +100°C in a

separate oven.

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52

Most available thermometers

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Bimaterials Thermometers (Bimetal)

Bimetallic thermometers make use

of change of volume with temperature.

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54

Pyroelectric(Infrared) Thermometers

An infrared (IR) thermometer is a noncontact radiant energy detector.

IR thermometers capture the invisible infrared energy that is naturally

emitted from all objects warmer than absolute zero (0 K).

IR thermometers are ideal for moving targets such as glass, plastic, and

steel. They do not interfere with the process.

The TC or RTD will not respond to these temperature changes

quickly enough to permit close control.

The IR thermometer will instantly measure the actual product

temperature, not the environment surrounding the product.

IR thermometer is not measuring temperature but radiated energy.

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55

Moving electric charge ≈ Variable electric field

(all atoms are made of electriccharges)

And again, when the magnetic field changes, it results

in a coupled with it variable electric field, and so on.


Variable electric field Alternating magnetic field

Thus, a moving particle becomes a source of

electromagnetic field that propagates outwardly

with the speed of light and is called thermal radiation.

Different T Different movement Different radiation

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56

Pyroelectric (Infrared) Thermometers

valueemissivityis:

Power of electromagnetic radiation per unit of wavelength

Planck’s law:

Power of electromagnetic radiation per unit of wavelength

Wien’s law:

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valueEmissivity

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valueEmissivity

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Distance does not affect the measurement. Models are available that

can measure from 0.3 to 91 m.

However, the farther away from the target the sensor is, the larger the

spot.

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The infrared thermometer must be carefully aimed to avoid focusing on

reflected solar radiation.

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Kelvin.in T ... 4TAbo

Planck’s law or Wien’s law:

Total radiated power limited within a particular bandwidth

Practically, when the range between λ1 and λ2 embrace well over 50%

of the total radiated power

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64


Infrared spectrum for

practical measurement

• Wavelength bands centered on 0.65 and 2.6 µm are used for metals and can see

through quartz windows.

• The 3.4µm band (±0.05µm) and the 7.9-µm band(±0.15 µm) are used to measure

thin plastic films.

• The 5µm band (±0.2µm) is used to measure glass windows and containers

• The 8- to 14µm wavelength is probably most commonly used for low temperature

applications for textiles, paper, and food. It also is a very common wavelength for

portable infrared thermometers.

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65

Portable Thermometer

THERMOMETER, 3 in 1 Model : TM-2000

Infrared thermometer + Pt 100 ohm + Type K, J, R, E, T, intelligent.

With laser target guide for IR measurement

• IR range : -20 to 400 C

• Type K, J, R, E, T : -100 to 1700 C maximum

• PT100 : -200 to 850 C

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66



Infrared Thermometer

Resolution: 1 C / 1 F

Range: -20 to 400 C / -4 to 752 F

Accuracy: max±(3% of reading), ±(3 C / 5 F)(accuracy test under 300 C)

Emissivity value set by 0.95, which will cover 90% of application

Setting range of emissivity 0.2 to 1.0

Measurement Wave length region 6 to 12 micrometer.

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67



Thermocouple Thermometer

Type K

Resolution: 0.1 C / 0.1 F

Range -100 to -50.1 with ±(0.2%+1 C ) accuracy

Range -50 to 1300 C with ±(0.2%+0.5 C ) accuracy

Accuracy just for metering.

Linearity correction (Calibration curve in CPU)

And other types information( J, T, E and R)

Thermocouple Probe model TP-01

Range: -40 to 250 C / -40 to 482 F

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68



Platinum Pt 100 ohm

Resolution: 0.1 C / 0.1 F

Range: -200 to 850 C / -328 to 1562 F

Accuracy: ±(0.2% + 0.5 C) / ±(0.2% + 1 F) (for metering)

Pt 100 probe input, cooperate with an 0.00385 alpha coefficient,

meet DIN IEC 751

4 wires Pt 100 ohm probe (model: PT-100) optional

PT-100 ohm Probe model TP-100

Range: -50 to 400 C / -58 to 752 F

Accuracy: ±(0.002T + 0.15) C

Linearity correction (Calibration curve in CPU)

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Laser Target Guide

Emissivity Adjustment

Offset Value Adjustment

LCD Back-Light

RS232 Serial Interface

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Fiber-Optic Thermometers

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72

Some more thermometers

Temperature sensing by expansion

Temperature sensing by displacement

Temperature sensing

by pressure.

Lecture 3


System Design

73

Two-point control: (also called on–off control)

is the simplest type of closed-loop control strategy.

Inverting Amplifier

PVSPSPPVerror VVVR

RV

R

RV )(

2

3

2

3

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74

System Design

Hysteresis circuit

Lecture 3


75

System Design

Exercise 3-3: Consider following TR91 Series 10KΩ@25°C Thermistor

calibration table.

Design a circuit that turn on the fan of a car at 95°C and turn it off at

85°C.

Lecture 3


References

v Industrial Control Electronics J.M. Jacob, Prentice-Hall,

1989

v مبانی اندازه گیری در سیستمهای ابزار دقیق، حمید رضا تقی راد و سید

1392علی سالمتی، انتشارات دانشگاه صنعتی خواجه نصیرالدین طوسی،

v Principles and Practice of Automatic Process Control,

Third edition, C. A. Smith, A. Corripio, Wiley 2006

v Instrument Control Engineers' Handbook Fourth

Edition, Béla G. Lipták, editor-in-chief. CRC Press 2003

76

Lecture 3


Some Useful websites for the course

77

v http://saba.kntu.ac.ir/eecd/ecourses/instrumentation.htm

v http://profsite.um.ac.ir/~shoraka/Instrumentation.htm

v http://karimpor.profcms.um.ac.ir/index.php/courses/10328

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