B1

Intrinsic Safety Exi:Origins

PrinciplesApparatus

Applications

Intrinsic safety

Gary Friend

Sales Director

B2Explosions

B3

Mine Signalling Systemcirca 1910

BREAK FLASH

BARE WIRES

BELLBATTERY

WINCH OPERATOR

Origins of Intrinsic Safety B4

Hazardouslocation

Air(Oxygen)Gas

Source ofIgnition

SparkHeat

Fire triangle

B5

1. Limit Current

2. Limit Voltage

3. Limit Stored Electrical Energy

Three Principles of Ex i Design B6

Open Circuit Voltage

ShortCircuitCurrent

VOC

ISC

Output characteristic

of simple resistivesource

I

Ignitionoccurs

Energy

Power

Ignitionoccurs

VIs/c

R

Ignition does not

occur

The Load line

LIMITEDPOWER

LIMITED

ENERGY

Voltage and Current Characteristics

B7

HazardousArea

Apparatus

UncertifiedSafe AreaApparatus

Hazardous Area Safe Area

CertifiedSafe AreaApparatus

HazardousArea

Apparatus

CertifiedInterface

Intrinsically safe systems B8

A system, comprising apparatus and interconnecting wiring, in which any spark or thermal effect in any part of the system intended for use in hazardous areas is incapable of causing ignition.

Intrinsically Safe System

Definition

B9

Probability of

Gas/Air Mixture

being present

Probability of

Source of

Ignition

X =Acceptable

Risk

Reasoning: Higher probability of the gas/air mixture being present requires a lower probability of having a source of ignition and vice versa.

Hence, different Ex protection types are only permitted in specific levels of risk owing to their level of reliability.

Why Area Classify? B10

Hazardous places are classified in terms of zones on the basis of the frequency & duration of the occurrence of an explosive atmosphere

Zone 0 : an explosive atmosphere in the form of gas, vapour, or mist is present continuously, for long periods or frequently

Zone 1 : an explosive atmosphere in the form of gas, vapour, or mist is likely to occur in normal operation occasionally

Zone 2 : an explosive atmosphere in the form of gas, vapour, or mist is not likely to occur in normal operation, but if it does occur, will persist for a short period only

Area Classification - gas, vapour & mist

B11

Liquid

surface

Zone 0

Zone 1

Zone 2

typically 3m from

vent openings

typically 3m above the roof

typically 3m

horizontally

from tank

sump

Area Classification Example

Bund wall

B12

"Faults" are those in componentsupon which safety of the

installation depends.

Ex iaIntrinsically safe

with two faults

Zones 0, 1 and 2

Intrinsic safety levels of protection

Ex ibIntrinsically safe

with one fault

Ex icIntrinsically safe

in normal operation

Zone 2

Zones 1 and 2

Note.Intrinsic safety is the only protection concept that considers failure of the

field wiring.

B13Gas Group / T rating B14

Hazardous Area Apparatus:

Certified: Complex energy-storinge.g instruments

or

Uncertified: "Simple Apparatus"

SafetyCertificate

SANS/IEC 60079-11

Clause 5.7

Hazardous Area “Apparatus”

B15

Examples:

Simple Apparatus

What is considered Simple Apparatus?

Passive components e.g. switches, junction boxes, potentiometers and simple semiconductor devices

Sources of stored energy within well defined parameters

Sources of generated energy which do not exceed 1.5V, 0.1A or 25mW

IEC 60079-11, Clause 5.7 says:-

“Devices need not be certified or marked”

B16Combustible dusts and powders

B17

Zone 20 : an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, for long periods or frequently

Zone 21 : an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally

Zone 22 : an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation, but if it does occur, will persist for a short period only

Notes: Layers,deposits and heaps of combustibledust must be considered as a source that can form

an explosive atmosphere

Area Classification - Dusts B18

Area classification of dusts and powders must be treated differently from gases and vapours:

Dusts don’t disperse with time

Ventilation can convert layers into clouds

Other considerations

Resistivity - low resistivity powders e.g. metals are more hazardous and require additional measures to be applied to equipmentCloud concentration, particle size, moistureLayer thickness

B19

Dust flammability

About 70% of dusts occurring in industry are flammable

Ignition energy

Dusts and powders typically require higher spark energy levels for

ignition (1000 times greater than vapours)More likely mechanism is hot surface ignition

Ignition temperatureWhereas the majority of flammable gases have ignition temperatures

above 350°C, some dusts ignite at 150 - 200°C

Ingress protection alone is not enough

Ingress protection alone for equipment is not enough: must protect against ignition by raised temperatures of enclosures

Combustible dusts and powders B20

Intrinsic SafetyInterfaces:

BASIC PRINCIPLES of

Barriers & Isolators

Intrinsic SafetyInterfaces:

BASIC PRINCIPLES of

Barriers & Isolators

Safe Area

B21

Output Input

Maximum

output

current

cannot

exceed

VZ/CLR

(Hazardous area)(Safe area)

Vinput

Maximum

output

voltage

cannot

exceed VZ

FUSE

Fuse protects Zener diodefrom becoming overstressed.Current Limiting

Resistor

R

Voltage-clampingZener diode VZ

Voltage and current limiting network B22

Vz

Assessment of Component Failure Risk:

Component: Failure modes SAFE?

Open Circuit: Short Circuit:

Fuse Yes Unlikely YES

Resistor Considered Not considered YES

Diode Yes YES

Diode Yes NO**

** Yes: because triplicated such that 2 may fail

Fuse

Safe area connection

Hazardous area

connection

If components fail, safety must be assured.

Basic shunt-diode safety barrier

B23

Barriers must be encapsulated orfuses prevented from replacement.

Connection to a high integrity, low resistance earth point

Fuse must be capable of breakingUmax (usually 250Vrms) by design.

Two diodes are permitted for ‘ ia’if additional testing is done.

Vz

Fuse

Worst case fault source250V RMS with a shortcircuit current capabilityof 1500A.

The BARRIER B24

Typical for 28V, 300ΩΩΩΩ barrier

The “Safety Description”:

Highest o/c Voltage = VZ: 28V

Lowest source resistance R: 300ΩΩΩΩ

Highest s/c Current =VZ/R: 93mA

When Vin is GREATER than Vz

End-to-End Resistance

When Vin isLESS than Vz

Operational Characteristics:

End-to-end resistance: 340ΩΩΩΩ

VWORKING: Voltage input applied when

leakage current =< 10µA: 25.5V

VMAX : Highest continuous voltage input

without blowing fuse: 26.6V

Vout VinVz

Fuse

Safety & Operational characteristics

B25

Positive Negative

ACunpolarised

+VE -VE

~

V+

-V

+

-

V

Single channel Zener barriers B26

Multi-channel barriers almost always have the same polarity, though not necessarily the same voltage

simpler installation, saving space and cost

HazardousArea

Apparatus

neitherline

earthed

Two positive channels shown

Two channel zener barrier

B27

PSU

ELECT.

ISDevice

Structural Bond

Intrinsically Safe Earth

Instrument DistributionEarth500V

Isolation!

Worst CaseInternal Fault!

Internal Fault B28

Certifiedtransformer

Certifiedcomponent

Energy-limiting

Safe areaconnection

Hazardousareaconnection

Power

Safe

ty S

eg

reg

ati

on

Safearea

circuit

Hazardousarea

circuit

Galvanic Isolation

B29Applications of IS interfaces

The Application of Ex i Instrument Loops Considering a System

Use of Barriers and Isolators Comparison of their use

To demonstrate Safety Compatibility

and

Operational Compatibility

Basis of Comparison Simple Apparatus (Contact or Status Inputs)

and

Certified Apparatus (4/20mA Transmitters)

B30

4-20mATransmitters

CertifiedApparatus

Analogue Input

B31Transmitter parameters

SAFETY What does the Certificate state?

Certification codeeg EEx ia IIC T4Transmitter "entity" parameters typically are quoted e.g. Ui < 30V Ii < 100 mA Pi < 1.3 W Li < 10µH Ci < 20nF Must be MATCHED to Interface…… follows

OPERATION Will it work?

Transmitters require Minimum “Lift-off” supply voltage (order of 12V at 20 mA) Load (conditioning) resistor; Most safe area equipment uses 250ΩΩΩΩ

Passage of SMART Communications (HART, etc)

B32

CC < 0.063 µF

LC < 4.20 mH

L/RC < 55 µH/ΩΩΩΩ

System

EEx ia IIC T4

Cable Parameters

Verification of safety compatibility

Transmitter

EEx ia IIC T4

Ui < 30 VIi < 100 mAPi < 1.3W

Ci < 20 nFLi < 10µH

[EEx ia] IIC

For MTL7787+Cable parameters are quoted forIIC unless otherwise stated

Interface

Uo < 28 VIo < 93 mAPo < 0.65 W

Co < 0.083 µFLo < 4.2 mHL/R < 55 µH/ΩΩΩΩ

MTL7728+

B33Transmitters with 2-channel barriers

Many systems use bulk power supplies Signals often referenced to a common 0V connection

One-channel barriers cannot be used with bulk supplies

2-channel barriers are necessarySO....…

The combination of two channels has to be shown to be safe in the particular hazard intended:

Two-channel barriers are normally certified as one unit

B34

333ΩΩΩΩ max

Hazardous area Safe area

IS Earth

4-20 mA

24V+

0 Volts

250ΩΩΩΩConditioningresistor

1-5V

Tx: Diode Return Barrier (MTL7787+)

B35Operational compatibility (MTL7787+)

Loop voltage drops at 20mA are:

Barrier (6.7+0.5+0.9) = 8.1 Transmitter = 12.0Instrument = 5.0

Total = 25.1V

Nom. working voltage = 26.6 V (for 10µA leakage)

Overall loop supply limits:-High Limit:- 25.1 to 26.6V OK to use 26.6V max because

leakage in the outgoing leg does not go through the loadLow Limit:- Transmitter will not calibrate at Full Scale!And .. Communications lost when tx saturates!

Leakage on the return leg is insignificant: 7.2V max at 20mA

B36Diode return barrier for 2-wire Tx

Two channel barrier permits “common-ed” power supply (-ve) and input

circuits

3 Schottky diodes have about 0.9 V forward volt-drop, so overall return channel

drop at 20mA is 1.4V

Return channel blocking diodes prevent fault current into the hazardous area The Safety Description is the same as for a 28V 300R 93mA barrier

The return channel 28V rating removes its vulnerability to being damaged by

accidental connection reversal (an advantage over earlier two-channel types,

such as MTL 788)

Loop supply voltage range is 25.1 to 26.6 volts for 12 volts transmitter and lines Supply below Loop Minimum will prevent transmitter operation at full-scale!

Supply channel leakage for above 26.6V (VWORKING) does not add inaccuracy to

loop Care with operation above 27.2 (VMAX) will stress fuse and cause premature failure

B37

Load(600ΩΩΩΩ)

4-20 mA 16.5V

300ΩΩΩΩ

28V

Isolation

Hazardous area Safe area

Isolator for 2-wire transmitters

24VdcSupply

4-20 mAPowered fromHazardousArea

Non-Energy Storing

Input Terminals

HHC

B38Isolator specification

Things to remember Choosing an Isolator

Isolators are designed to suit a particular applicationCheck compatibility for SafetyCheck compatibility for Operation

Other IssuesRequires power supply. Cannot loop power!Heat generationSmart Transmitters

Isolator model specifications vary typically greater than 15V at 20mA Safe Area load resistance can be up to 800 ohms! DC transfer accuracy better than 10µµµµA throughout 4/20mA

range Industry standard Safety Descriptions used: 28V, 300R, 93mA

B39Summary of key points Barriers / Isolators

Transmitters Is there a floating power supply?

Single-channel barrier may be OK

Establish input circuit of instrument

Will the transmitter have sufficient voltage at 20mA?

Establish safety compatibility of transmitter and IS interface -

Comparison of safety parametersConsult System CertificateProduce ‘DSD’ Descriptive Systems Document according to IEC/SANS 60079-25

B40

Barriers IsolatorsSimple and reliable

Extremely accurate in manyapplications

High integrity bond required

Predictable response to earth faults

Inexpensive

Applications are defined in terms of voltage and resistance

Encapsulated design necessary

Tight power supply limits(except 'protected’/fused barriers)

Easier to fault-find (earth reference)

Fairly complex, statisticallylower MTBF than barrier

Flexibility in bonding practice

Flexible response to earth faults

Active devices: power and heat

Generally more expensive

'Application-specific', defined interms of function

Replaceable supply fuse common

Wide power supply tolerance

Comparison of Barriers & Isolators

B41

Exd ExiMechanical protection

No live working without gas clearance certificate

Expensive cabling (e.g. armoured), enclosures and cable glands

Suitable for high power–110/220 Vac(pumps, motors etc.) and higher power solenoids.

Electronic protection

Live working – no gas clearance certificate required

Only technique that takes cable faults into account.

Requires safety analysis andIS loop approval.

Suitable for 24Vdc low power Instrumentation signals.

Limitations driving higher powersolenoids

Comparison of Exd vs Exi B42BEKA range of displays

B43Intrinsically Safe Foundation Fieldbus - FISCO

FISCO power supply

FIELD

CONTROL ROOM

Intrinsically Safe Field wiring hub

Intrinsically safe FISCO Fieldbus devices

Zone 1

Division 1

24Vdc24Vdc

Fieldbus control system (DCS)

FISCO unit combines

fieldbus power supply, conditioner and IS

barrier

B44Typical FNICO installation

FNICO power supply

Ex n or Intrinsically Safe Field wiring

hub

Non-incendive or Intrinsically safe Fieldbus devices

Division 2

Zone 2

24Vdc24Vdc

FIELD

CONTROL ROOM

Live-workableNon-incendivetrunk and spurs

Live-workableEx nL (Non-incendive)

trunk and spurs

Fieldbus control system (DCS) Also has

repeater function for

multiple

trunks

B45Redundant FISCO – key features

Enhancement of field-proven 912x-IS FISCO power supply

Rugged construction for easy cabinet mounting and resistance to shock and vibration

Redundancy achieved by active/hot standby modeSupply arbitration circuit electronically

transfers field load to standby module, if loss of output of active module is detected

Rapid fail-over occurs according to FOUNDATION FieldbusTM specifications, without risk of losing fieldbus devices from bus

B46

Zone 1 Hazardous Area

Power over ethernet (PoEx) implementation

24V dc

Intrinsically Safe PoEx Ethernet

ConventionalEthernet

IS Powered Ethernet Device

IS Ethernet Isolator with PoEx(Power Sourcing Equipment)

assumes safety description of IS

power supply

IS Power Supply for PoEx

B47

Intrinsically Safe Ethernet

Zone 1

Hazardous Area

Building a system

24V dc

ConventionalEthernet

IS multi-port switch

IS Ethernet Isolator

IS Power Supplies for PoEx

PoEx Ethernet links

IS power for switch

IS powerfor each

PoExsegment

24V dc

B48IS WLAN application

Control Room

IS PCwith WLAN

Mobile Ex videoIS computer

+ barcode scannerIS computerIS computer

Safe AreaZone/Division 2Zone/Division 1

Saves 40% in the cost of WLAN access

point

Reduces the cost of powering the access point by 35 to 75%

Overall saving of over €45K on a typical

application with 20 access points.

Wireless IS Ethernet

B49Intrinsically Safe Serial Devices

Control Room

Intrinsically safe

RS232/RS422/RS485 devices

IS Ethernetto RS232/422/485 converter/gateway

Weighingsystem

DisplayAnalyserPollutionMonitoring

I/O

Open Ethernet connectivity

for Intrinsically Safe serial

devices reduces system integration costs

Safe AreaZone/Division 2Zone/Division 1 or 2

IS Ethernetisolator

IS Ethernetswitch

IS EthernetPower supply

B50Future: Intrinsically Safe Ethernet Devices

Control Room

Intrinsically safe Ethernet devices

Weighingsystem

DisplayAnalyserPollutionMonitoring

ControlValve

I/O

PoExTM provides power and

communications over a single

cableOpen Ethernet connectivity reduces

system integration costs

Camera

Safe AreaZone/Division 2Zone/Division 1 or 2

B51Extronics B52

www.airowireless.com

B53 B54

Gary Friend

Sales Director

gary@extech.co.za

011 791 6000

083 309 8200

Thank you,

any questions?

www.extech.co.za