ass1 review of sensor technology for engineering measurements (1)

8/13/2019 Ass1 Review of Sensor Technology for Engineering Measurements (1)

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ExperimentalMethods

NG0H203

Review of Sensor Technology for

Engineering Measurements

Temperature Sensors

Lecturer: Mrs Rhian Kerton

Name: Adrian Secan

Enrolment Number: 12032239


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I . SummaryAs a result of this report I can say that different sensors are required for different

types of applications or experiments.

Liquid in glass thermometer is good in applications where the accuracy of thethermometer is not that important and only few measurements are needed.

Thermocouple sensor is the most used sensor in the industry with applications

worldwide because it has a medium price and can provide an acceptable accuracy.

The platinum resistance thermometer is an expensive thermometer which can beused in most of the industrial applications but because of the high price it should be used

only in some specific environments where the thermocouple sensor is not good.

Radiation sensors are the most expensive thermometers available on the market

and they are usually used just in some fields of the industr or experiments because of the

price. It is used just in some circumstances when a platinum resistance thermometer is

not suitable for that measurement. The main reason why this sensor is choose is that itcan measure temperature from distance without being affected of environmental factors

as vibration and shock.

I I . Table of contentsI. Summary----------------------------------------------------------------- i

1) Introduction------------------------------------------------------------- 1

2) Procedure---------------------------------------------------------------- 12.1. Platinum resistance thermometry---------------------------1

2.2. Liquid in glass thermometry-------------------------------- 32.3. Thermocouple thermometry---------------------------------5

2.4. Radiation thermometry-------------------------------------- 6

3) Conclusion-------------------------------------------------------------- 7

3) Symbols------------------------------------------------------------------8

4) References---------------------------------------------------------------8


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1)IntroductionThe construction and application of temperature sensors may vary from the aim of

use. The subject of the report is review of temperature sensors. The purpose is finding the

advantageously type of sensor for different aims of use and ranges of temperature

measurement.This report analyses different types of sensors from different points of view:

Construction material.

The range of the temperature which can be measured.

Durability.

2)ProcedureIn the report 4 sensors are analysed and they are:1st. Platinum resistance thermometry.

2nd. Liquid in glass thermometry.

3rd. Thermocouple thermometry.

4th. Radiation thermometry.

2.1. Platinum resistance thermometry

Platinum resistance thermometry (PRTs) is an exceptional temperature sensor. It

can measure temperature in the range -259C to 960 C. It can be use many times andstill provide a good resistance bridge.

The market has a generous offer of PRT from small ones, standard PRT (SPRT) to

big industrial ones which are specific just for several ranges of temperature.

The simplest platinum resistance thermometry is a coil of wire mounted in an

insulating support which is made out of steel for range between -200C and 250C,glass for -200C and 450C,quartz for -200 and 960C(see Fig,1) . In the construction

process of the resistance thermometer the essential objective is to be sure that the metal

is in touch whit the temperature and it is unresponsive to other environmental factors

like: humidity, pressure, vibration and corrosive chemicals. The PRT becomes instablewhen is exposed to mechanical shock and thermal expansion. The errors caused by

mechanical shock and thermal expansion may be split in to four groups: thermal contact

errors, sensor errors, signal transmission error and signal processing error. All the errors

may be established with simple tests. It is easy to separate the parts in a PRT and

identify the cause of the error. The clarity of operation allowed platinum resistance

thermometry to become such an accurate and reliable thermometer. (J.V.Nicholas,

1994)

The three main factors consult before choosing a PRT are;a. Accuracy

A calibrated PRT have accuracy between 1C and 1 mK depending onthe price and range of temperature to be measured.


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b. Temperature range

The temperature range to be measure is ~ -200 C to ~ 950 C

c. Environment

The major problems are shocks and vibration.

Fig.1

The accuracy and range that can be achieved with fullz support, partial support and

standard PRT:

Fig.2


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The resistance of nickel, copper and platinum as a function of temperature.

Fig.3

Examples of industrial platinum resistance thermometer elements.

1. A thick film element.

2. A PRT designed for printed circuit mounting.

3, 4. Glass PRT.

5, 6. Ceramic PRT. (J.V.Nicholas, 1994, pp.153-98)

2.2. Liquid in glass thermometry

The first form of thermometer was liquid in glass thermometer and it was used

for at least two hundred years as most accurate thermometer, until new types of

thermometer were developed. This thermometer was very important and helps a lot inthe development of temperature measurement. It can measure temperature in the range

of -190 Cto 600 Cbut for a high precision thermometer the right one is platinum

resistance thermometer which gives superior performance and is accessible withmodern resistancebridge. The cheapest temperature sensor on the market is a liquid in

glass thermometry. It is still used in many specified tests where only few temperaturemeasurements are required and because of the low price. (J.V.Nicholas, 1994)


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The thermometer has four fundamental parts (see Fig4) :

Bulb

-a container which hold the liquid

and is made of a very thin glass

Stem-a capillarity tube made of glass

Liquid(see table 1)-most of the time mercury or an organic

liquid

Markings

-most of the time printed on the steam.

Liquid Expansion

Rate(

)

Temperature

range

Mercury 0.000 16 -35 to 510 C

Ethanol 0.001 04 -80 to 60 C

Pentane 0.001 45 -200 to 30C

Toluene 0.001 03 -80 to 100 C

Table.1

Working range of some thermometric

liquids.

Fig.4Liquid in glass thermometer,

main parts.

The errors which may appear when the thermometer is used are complex and

really hard to define because it is a compact instrument and usually it is impossible to

open it and look for possible causes.

It is very important to be careful before choosing a liquid in glass thermometer

for an experiment because of the errors which may appear, if the experiment doesnt

require highprecision or extreme of the usable range because of its low cost liquid in

glass thermometer is the right one. (J.V.Nicholas, 1994)

The main advantages of this thermometer are:

Fully self-contained.

Chemical inertness.

Low susceptibility to electrical interference.

Low thermal conductivity.

Lower initial cost.

The usage of liquid in glass thermometer needs some special attention because itis fragile:

Do not knock the thermometer; it will cause inevitable changes in the

accuracy of the thermometer.


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In an experiment, the thermometer should stay all the time vertically and

dont rest it on the bulb.

Do not use the thermometer at the maximum or minimum temperature of

its range.

Because it is fragile do not put any pressure on it and avoid vibration.

(J.V.Nicholas, 1994, pp.199-236)

2.3. Thermocouple thermometryThermocouple is the most used thermometer in the world. They are simply build

and very reliable; that recommend them for many industrial application. When high

accuracy is required is recommended another type of sensor.A big manufacture of thermocouple said Once a thermocouple has been used at

a high temperature, however, it is not good practice to use it later at a low

temperature, that means: uses the same thermocouple for high temperature or for low

temperature, do not use it for both.The thermocouple is usually called thermoelectric effect because they include

both electricity and heat. (J.V.Nicholas, 1994)

Fig.5

A basic thermocouple circuit.

The market offers a wide range of thermocouple and they are split in three big

groups:

Rare-metal standard thermocouples.

-This thermocouple is inert chemically.-They are 3 types: B, R and S.

-All of them are build whit platinum and its alloys and whit rhodium.

-The sheaths should be made of high-purity insulators or platinum.

-The major disadvantage of Raremetal standard thermocouple is the highcost.

Base-metal standard thermocouples.

-They are not as good as rare-metal thermocouples.

-They are 5 types: T, J, K, E and N.

-They all oxide easily.-The best usage for them is measure temperature in a fixed location over a

limited temperature range.


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And nonstandard thermocouples.

-They are more than 200 types.

-They were developed to measure temperature in difficult

situation.

-They are used in industries to measure temperature up to 3000C.

The errors in measurement whit a thermocouple thermometer appear usually

because of the interaction whit mechanical and chemical effects. (J.V.Nicholas, 1994,

pp.239-81)

2.4. Radiation thermometry

Radiation thermometry is completely different than others thermometers. The

main advantage is that this thermometer can measure temperature from distance.Anyway some time the measurement from distance cause errors because many gases

are not completely transparent. These thermometers are the most expensive on the

market and before choosing one for an experiment the market should be checked and

see if other type of thermometer is not good enough for the purpose of the experiment.

Radiation thermometer has 3 main futures:

Thermodynamic.

Non-contact thermometer.

It uses the surface of the object as a sensor.

Spectral-band thermometer is the most used radiation thermometer in the world.The Fig.6 explains simply how it operates. (J.V.Nicholas, 1994)

Fig.6Main parts and how a radiation thermometer operates.


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The most common errors which appear when the measurement is not validated

for a spectral-band thermometer fall in to three groups:

Characterisation of the sensor errors: reflections and fluoresce.

Transmission path errors: absorption and size of the object.

Signal processing errors: variation in ambient temperature and

instrumental emissivity.Usually before choosing a radiation thermometer for an experiment the market

should be checked and see if a contact thermometer is not better for the purpose of theexperiment because contact thermometer are more accurate than the radiation ones.

Anyway in some situations the radiation thermometer is required and these situations

are:

A fast feedback is required.

A far away measurement is required.

If the temperature is above 1100 C and the measurement is for a long

period of time. The object to be measured is moving.

The environment is too hostile for a contact thermometer because of

vibration and corrosion. (J.V.Nicholas, 1994, pp.283-325)

3)ConclusionIn conclusion I finished my review about temperature sensors. After I analysedthe four sensors: platinum resistance thermometer, liquid in glass thermometer,

thermocouple thermometer and radiation thermometer; I can affirm that all of themhave some industrial application but this depends on some factors which needs to be

consulted before choosing one of this sensor. The factors are:

Price.

Range of the temperature to be measured.

Environmental factors.

All of these four sensors have a different price from very cheap ones like liquid

in glass whit an organic fluid to very expensive ones like radiation thermometer. Forsimple experiments where just a few measurements are required I recommend a liquid

in glass thermometer because is not very expensive and for general industrial use Irecommend a thermocouple thermometer because of the decent accuracy and long term

use. In some situations where a high accuracy is required or where the environment is

hostile because of vibration or corrosion, I recommend for the first situation a platinum

resistance sensor and for the second one a radiation sensor.


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4)SymbolsPRT - Platinum resistance thermometry

mK - millikelvin

5)ReferenceJ.V.Nicholas, D.R.W., 1994. Traceable Temperatures. Chichester: John

Wiley & Sons Ltd.

Turner, J., March ,2009. Momentum Press,pp.85-107 . New York:

Momentum Press.

Materials, A.S.o.T.a., 1993. Manual on The Use of Thermocouples in

Temperature Measurement. West Conshohocken, PA: MNL 12.

L. Michalski, K.E.a.J.M., 1991. Temperature Measurement. London:

John Wiley & Sons.

ass1 review of sensor technology for engineering measurements (1)

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