1. Sensors Transducers Presentation

Sensors-transducers

Presented by: I&C Technician

Introduction to process Introduction to process measurementmeasurement

• The purpose of measurement• Kinds of signals• Remote vs local display• Error in measurement system• Calibration• Calibration laboratory• Field calibration

Function of sensorFunction of sensor

1. An instrument must sense the process to be measured. part of the instrument must stretch bend, or change position or characteristics when affected by process.

2. The instrument must convert this response into an electrical or pneumatic signals.

CONTROL LOOPCONTROL LOOP

transmitter

Function of transducerFunction of transducer

• The process sensing element is usually a bellow, a diaphragm or a bourden tube.

• The primary conversion element converts the mechanical action of a process sensing element to an electrical signal, usually an electrical resistance or a voltage.

• The secondary conversion element is usually an electronic circuit that produces a standard signal according to the need of the control system.

Sensors transducersSensors transducers

• Pressure sensors.• Flow sensors.• Thermometers.• Liquid level sensors.• Vibration and speed sensors.• Proximity and displacement sensors.• Fire, Flame and smoke detectors.• Analyzers.

Transducer principleTransducer principle1. Capacitive. 2. Inductive.3. Piezoelectric.4. Resistive.5. Potentiometer.6. Strain gage.7. Photoconductive.8. Thermoelectric.

PRESSURE

PRESSURE SENSOR

PRESSURE TRANSDUCER

STRAIN GAUGE

DIAPHRAGM

BELLOWS

MAGNETIC

BOURDEN TUBE

INDUCTIVE

POTENTIOMETRIC

CAPACITVE

PIEZOELECTRIC

PHOTOELECTRIC

Bourdon tubesBourdon tubes

bellowsbellows

diaphragmdiaphragm

Strain gaugeStrain gauge

Capacitive Capacitive

potentiometerpotentiometer

piezoelectricpiezoelectric

inductiveinductive

Working on transmitterWorking on transmitter

• A measurement device is made up of two parts• Primary element• Transmitter

• Converts signal (Transducer)• Transmits signal

flow metersflow meters

• Flow is the motion of fluid.• Flow rate is the time rate of motion fluid.• Total flow is the rate integrated over a specific

time interval.• Flow meter is a flow rate transducer.• Laminar flow.• Turbulent flow.• Reynolds no.

Units of measurementUnits of measurement

• Cubic foot/minuet.• Gallon/minuet.• Liter/sec.

FLOW

DIFFERENCIAL PRESSURE MECHANICAL FLOWMETER ELECTRONIC FLOWMETER

POSITIVE DISPLACEMENT VORTEX FLOWMETER

ULTRASONIC FLOWMETER

MEGNATIC FLOWMETERTURBINE FLOWMETER

ROTARY FLOWMETER

PRIMARY ELEMENT

Common Devices To Measure Flow

• Orifice plate

• Veturi tube

• Flow nozzle

Types and use of orifice plate

1. Concentric

opening in center. It is for normal use.

2. Eccentric Opening slightly off

center. Used for the fluid or gas

which has solid particles.

Types and use of orifice plate

3 . Segmental

semi circular in shape. It is for used for slurries.

Venturi TubeVenturi Tube

Flow NozzleFlow Nozzle

Variable area instrumentsVariable area instruments

Rota meterRota meter

Positive displacement Positive displacement flow metersflow meters

• Trap a known volume of fluid and allow it to pass from meter inlet to outlet.

• Total flow measurement.

• They have accurate,precise,and have a wide flow range.

• They are expensive and object to corrosion.

• They are used for water meters and gasoline pumps.

PD flow meters typesPD flow meters types

• Piston flow meter• Notating-disc flow meter• Lobed impeller and oval flow meter• Rotary vane meter• Turbine flow meter

Nutating and rotary-vane flow Nutating and rotary-vane flow metermeter

Piston type flow meterPiston type flow meter

Lobed impeller and oval flow Lobed impeller and oval flow metermeter

Turbine flow meterTurbine flow meter

Magnetic flow meterMagnetic flow meter

Vortex flow meterVortex flow meter

Ultrasonic flow meterUltrasonic flow meter

temperature

Bimetallic and liquid filled system

Resistance temperature detector

thermister

thermocouple

Temperature

Hotness or Coldness of a Substance

Temperature Units

– Celsius °C

– Fahrenheit °F

– Kelvin °K

Temperature Measuring Instruments

Located at Distance

Thermometers

Pyrometer

Instrument Inserted or Attached

Basic Types Of Thermometers

Bimetallic

– From –75 °C to 540 °C

Liquid In Glass

– From -120 °C to 320 °C

Filled System

– From -273 °C to -185 °C

– From 650 °C to 760 °C

Metals expand on heating and contract on cooling.

Each metal has a coefficient of thermal expansion

Bimetallic strip bends toward metal of lower rate of

thermal expansion, on heating.

Bimetallic Thermometers

– Spiral – Helix, Multiple Helix

Office and Home Use

Bimetallic Thermometers (Cont.)

Industrial Use


Advantages :

Inexpensive, Rugged and Easy to Read

Reasonably Accurate, Handle Carefully

Best for Local Use


RTDsSome Metal’s Resistance Increase on Increase of Temperature Metals Used in RTD Must Be

Pure

Uniform Quality

Stable With Given Temperature Rage

Able to Reproduce Resistance Temp. Reading

Temperature, °C

Metal Resistance

0 Platinum Copper Nickel

100 100 100


175 186 250


250 275 485

RTDs

RTD act just like a variable resistor Used in resistance bridge circuit Output voltage resistance of RTD Heating or cooling cause bridge unbalance Lead wire error 250 ft copper wire has 1 ohm resistance. If resistance 139 ohm temp. will be 100°C exclude 2

ohm then R=137 which show 94.4 °C error 5.1 %

RTDs

Compensating Lead Error

– Use of Third Wire, RTD Wire Should Be Opposite Arm

– Error With 2 Lead Wires 4°C, With Three Lead 0.1 °C and by Fourth Wire Error 0.03°C

RTDs

–Construction of RTD

RTDs

–Measuring Surface Temperature RTDS

–Protecting Well for RTDs

RTDs

Advantages of RTD– Extremely accurate – Measure temperature within 0.15 °C– Fast in response and small in size

Disadvantages of RTD– Expansive and complex– Require bridge circuit, power supply, meter

RTDs

Thermistors

Special Type Of Resistors

High temp. resistance coefficient

Negative as well as positive Temperature Coefficient

Resistance Increases Temp. Decreases

Advantages

– Three & four wire bridge circuit not required

– Two lead wire provide sufficient accuracy

– Less expansive and less complicated

Disadvantages

– Lack RTD accuracy.

Thermocouple Two Different Metals or Alloy

– Two Junction

• Reference Junction ( to be at constant temperature)

– Measuring Junction

• Heating measuring junction produce voltage across MJ

& reference junction

Thermocouple

Extension Wires Thermocouple wires Same as thermocouple ( iron constantan, copper constantan Other material for platinum thermocouple Copper or copper alloy

• Construction of Thermocouple

Thermocouple

Advantages

– In Expansive, Rugged, Accurate

– Do not use bridge circuit

– Wide temperature range –273 to 2800 oC

Disadvantages

– Low voltage.

– Reference junction kept to be constant

Thermocouple

Level

Pressure head instruments

Electrical instruments

Differential pressure

displacer

Sight glass

vibration

ultrasonic

Float switches

Definition of Some Points

Datum point: A fixed reference point from which level is measured

Buoyancy: Upward force exerted by liquid on an object submerged & floating in it

Buoyant force: Net upward force exerted by liquid on submerged or floating object equal the weight of the displaced liquid.

Displacer: A nearly stationary object whose purpose is to displace liquid, used for liquid measurement.

Level Measurement by Float A float, cable, sliding pointer arrangement. A fixed scale is mounted on the exterior of the tank A cable connects the float with the pointer through two pullies. Pointer move up and down and also serve as counter weight. Float type level indicators are installed on the open tanks and the

tank of the atmospheric pressure.

Float-based level switchFloat-based level switch

Level Measurement by Displacer

Displacer do not ride on the surface of the liquid but they are design to submerge as the level rises.

Displacer mechanism transfer the slight mechanical motions due to loss of weight which can be used in instruments to indicate level.

Torque Tube DisplacersTorque Tube Displacers

The most common type of displacer mechanism is a torque tube displacer.

Torque tubes are useful when level measurement is needed on the liquid under pressure.

As the liquid level changes, the buoyant force moves the displacer slightly and twist the torque tube.

The motion of the torque tube makes the pointer move to indicate the liquid level on the scale.

Displacement levelDisplacement level

Level Measurement Using Differential Pressure Instruments

Differential pressure measurement is suited to level measurement in closed vessels

When liquid level is measured in an open tank, piping from the lower end of the tank is connected to the high pressure side of the transmitter and the low pressure side is vented.

When liquid level is measured in a closed tank the effect of tank pressure is compensated by connecting a line from the top of the tank to the low pressure side of the differential.

The pressure due to the height of the liquid is a measure of its

level.

Hydrostatic tank gaugingHydrostatic tank gauging

Differential pressure cell Differential pressure cell designdesign

Ultrasonic level Ultrasonic level

analyzers

Hydrazine monitor

Sodium monitor

Dissolve oxygen monitor

Flue gas oxygen monitor

Silica monitor

Conductivity monitor

Ph monitor

hydrazinehydrazine

Main component

sensor

Sample and solution flow

Calibration sequence

Sodium Sodium • Reagent solution• Standard solution• Etch solution

Dissolved Oxygen SensorDissolved Oxygen Sensor• Oxygen molecules diffuse

through the membrane based on the partial pressure of oxygen.

• ORP Reaction– Oxygen is reduced to

hydroxide ions (OH-) at the gold cathode.

– Silver is oxidized to silver bromide (M-4) or silver chloride (M-4HD) at the silver anode

• The current flow is directly proportional to the concentration of Dissolved Oxygen in solution

Calibration Calibration • Zero calibration• Air calibration

Silica monitoringSilica monitoring

Sample and solution flow

Calibration and Calibration and maintenancemaintenance

• Reagent solution• Standard solution

Flue gas oxygen monitor

installation

Main probe component

Cell and tube assemblyCell and tube assembly

Diffuser and detectorDiffuser and detector

Inner probe assemblyInner probe assembly

Calibration setupCalibration setup

CONDUCTIVITY ANALYZERSCONDUCTIVITY ANALYZERS

Measuring principleMeasuring principle

Conductance is a measure ability of electric circuit to pass current.

Na+

Cl-

G = 1/R(siemense)

Variables affecting conductivityVariables affecting conductivity

• Temperature• Concentration• contamination

Conductivity probesConductivity probes• Electrode type• Inductive type

Na+

Cl-

Typical Conductivity ValuesTypical Conductivity Values

0.055

0.5

1

50

50,000

355,000

0 1 100 10,000 1,000,000

Ultra Pure Water

Distilled Water

Boiler Feed Water

Mains Water Supply

Sea Water

10% NaOH

CONDUCTIVITY IN HUB PLANT

CONDENSER/EXTRACTION PUMPS

STATOR COOLING WATER

BOILER FEED WATER

Calibration

Zero standard solution

Span standard solution

Grab sample

Conductivity ranges vs. resistance input

Decade boxDecade box

PH monitorPH monitor

pH TheorypH Theory• pH is a Unit of Measurement

– pH = Power of Hydrogen (H+)– Defined as the Negative Logarithm of

Hydrogen Ion Activity• pH = log (1/H+)

• Used for Determining the Acidity or Alkalinity of an Aqueous Solution– Practical pH Scale for Industrial

Instrumentation• 0 - 14 pH

pH Sensor ComponentspH Sensor Components• pH Measuring Electrode

– Purpose is to Develop a Millivolt Potential Directly Proportional to the Free Hydrogen Ion Concentration in an Aqueous Solution

• Reference Cell– Purpose is to Maintain a

Constant Reference Potential Regardless of pH Change or Other Ionic Activity in the Solution

• Reference Cell Liquid Junction– Purpose is to Maintain

Electrical Contact Between the Reference Electrode and the Measuring Electrode by way of the Solution

Ag/AgCl Element

pH Measuring Electrode Reference Cell

pH Sensitive Glass Liquid Junction

KCl Gel

KCl Buffered to 7 pH

pH is a Potentiometric pH is a Potentiometric MeasurementMeasurement

• The Measuring System consists of a pH Measuring Electrode and Reference Electrode

• The Potential Difference Between the Two Electrodes is a Function of the pH Value of the Measured Solution

• The Solution Must Be Conductive and is Part of the Electrical Circuit

pH Measuring Electrode Reference Electrode

Ion ConcentrationIon Concentration

pH Hydrogen Ion (H+) Hydroxyl Ion (OH-)Acid 0 1 0.00000000000001

1 0.1 0.00000000000012 0.01 0.0000000000013 0.001 0.000000000014 0.0001 0.00000000015 0.00001 0.0000000016 0.000001 0.00000001

Neutral 7 0.0000001 0.00000018 0.00000001 0.0000019 0.000000001 0.00001

10 0.0000000001 0.000111 0.00000000001 0.00112 0.000000000001 0.0113 0.0000000000001 0.1

Alkaline 14 0.00000000000001 1

Typical pH ValuesTypical pH Values

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0

4.9 % H2SO4

Lemons

Oranges

Tomatoes

Beer

Milk

Pure Water

Blood

Crackers

4.0% NaOH

pH

Ph measurement in hub plant

Boiler feed water

Waist water treatment

calibration

Standard buffers Grab sample

Fire and smoke detectors

Ionization sensors

Infrared and ultraviolet sensors

Thermal sensors

Photo sensors

Flam detector

heat generated

Ionization

radiation

Fire and smoke detectors

Ionization sensors

Infrared and ultraviolet sensors

Thermal sensors

Photo sensors

Flam detector

heat generated

Ionization

radiation

Proximity and displacement sensors

Digital output and encoders

Ultrasonic sensors

Capacitive sensors

Optical sensors

Mechanical limit switches

LVDT sensors

Magnetic sensors

Inductive sensors

Documents

1. Sensors Transducers Presentation