IPF Study

• IPF (Instrumented Protection Functions) are functions which comprises of

· One or more initiators

· A logic solver or an Instrumented Protection System. Some refer it to as PLC

· One or more final elements

With the purpose to prevent and mitigate hazardous situations

• IPF Study is a study which consists of

1. SIL Classification (Proceed with all)

2. IPF Verification

3. IPF Implementation

4. IPF Review – Every 5 years

• SIL Classification

· Most time consuming

· Classifying consequence of IPF failure upon demand (Dangerous Failure)

· Classifying consequence of IPF initiated without demand (Safe Failure/ Spurious Trip/ Nuisance Trip)

· Classifying demand rate. Demand rate is a scenario that causes demand for an IPF

· To assign SIL

· No calculation – just assign SIL. In verification will only be calculation

· SIL Requirements

o 0 no IPF required – In PPTSB 90% was SIL 0

o a1 – Pre-alarm is adequate

o a2 – Triggers a switch action (interlock from DCS) + pre-alarm. Can integrate with control function

o 1 – Triggers switch action + pre-alarm.

§ Final Element can be control valve if fail safe

o 2 – Trigger switch action + pre alarm

§ Final element can be control valve in 1oo2

§ Share initiator with control transmitter in 1oo2

o 3 – Trigger switch action + pre-alarm

§ Share initiator with control transmitter in 2oo3

o 4 – Shall be avoided, very low PFD, more economical to redesign

· PFD

o Sil 1 : 1/10

o Sil 2 : 1/100

o Sil 3: 1/1000

o Sil 4 : 1/10000

• SIL Verification

· To verify the installation at site. Look for common installations. Audit like

· Calculate the PFD (Probability of Failure Upon Demand)

· To obtain as low as SIL requirement

· Is calculated by obtaining

· HWFT (Hardware fault tolerance)

· DCF(Diagnostic Coverage Factor)

· Safe Failure Fraction (SFF)

· Number of safe failures vs number of total failures

· Proof Test Coverage Factor

· How much unsafe failures one covers during testing

· Test and repair durations

· Mission Time

· The time between test intervals

· Mission – The mission is referred to the mission the IPF is taking during it’s operation

· The smaller the mission time, the lower the PFD

·

·

· 2 Layers of verification

· Architectural Constraint. Consists of the following :-

· Hardware Fault Tolerance (HWFT)

· Is the tolerable number of dangerous failures in the IPF

· For 2oo3, HWFT = 3-2 = 1.

· For 1oo3, HWFT = 3-1 = 2

· For 2oo2, HWFT = 2-2 = 0

· Safe Failure Fraction (SFF)

· Any hardware can be

· Working Normally

· Safe Failure

· Dangerous Failure (Already failed but not known)

· SFF is the ratio of safe failures to the total number of possible failures (Safe + Dangerous)

· Provided by manufacturer

· Type of Instruments

· Type A – All failure modes and effect known. Well documented.

· Type B – Complicated Instruments

Type A Instrument Used

Type B Instrument Used

Safety Integrity Levels (SIL)

· Safety Integrity Levels (SILs) are a safety-measurement standard defined by IEC in IEC61508 to quantify the chance of dangerous failures in electrical or electronic safety devices, that is, the probability of the device to fail in performing its Safety function.

· Four SIL levels are possible, with SIL4 being the most dependable and SIL1 being the least. Each are based on it’s corresponding PFD (Probability of Failure Upon Demand) – Which is the probability that an instrument will not respond to a demand. It usually works on frequency of demand

· TÜVs (Technischer Überwachungsverein) are German organizations that aim to protect humans and the environment against hazards coming from factories and mechanisms of all kinds. As an independent consultant, it examines monitoring-needy plants, motor vehicles, energy installations and devices. The many subsidiaries of the TÜVs can also appear as project developers for energy and traffic concepts, problem solutions in the area of environmental protection and certification bodies

Lightning

• Lightning is the transient passage of electrons between a cloud to

· Surface of earth, 50% of all lightning are cloud to surface

· Another cloud

· Air

• There are also ground to cloud strikes but these are very rare
• Lightning are formed when the atmosphere has high variation in pressure and temperature. Large particles will move down and small particlaes will move up. This causes and imbalance of charge as large particles are more negative. This creates a large potential difference which if large enough will cause all the negative charges to move down to the surface of the earth

• Lightning causes damage to equipment in 3 different ways

· Direct lightning strike

· Carried lightning strike -lightning is carried by cable to an equipment

· Induced lightning strike – lightning induces electromagnetic field which creates surge currents. Magnetic fields can also induce

• Interesting Facts on Lightning

· 99 % of strikes are of intensity exceeding 3000A, 50 % of strikes exceed intensity of 28000A and 1% of strikes exceed around 200,000A

· The duration of stroke are typically 100 microseconds while in exceptional cases it may exceed 1 second. The voltage present on a charged cell will be in the magnitude of 100MV

· The high current flashes start first from tall structures.

• The damage lightning does are as follows

· For human , massive current flow causes disturbances in the human electrochemical system, nerve damage. The heat generated from lightning burning can turn sweat instantaneously to steam. These steam is known to blow of people’s boots, shoes and clothing.

· For Electronics, it can cause vaporization of PCBs, transistors and fuses due to the heat it generates when arcing through high resistance insulation.

· For other equipments, it can create sparks and if there is combustible gasses nearby, it will cause fire

• It is experienced several times that lightning can travel in long distance electrical cables

Lightning Protection System

• Lightning strikes equipment by the following
  • Direct strike – There is no way to minimize damage dobe by a direct strike. One can only divert the strike to somewhere else
  • Direct Energization – Lightning strikes on a cable/piping/tracks which there are equipment connected at it’s ends. Even when the lightning reaches the ground, it can still travel through underground cables and pipes.
  • Induced / Near Field Coupling(EMP) –Electric fields are developed adjacent of the strike path due to the tremendous negative potential. The electric field may rise up to 8000 V/m within a 1 mile distance. Voltage may not be enough to cause major arcing but enough to vaporize PCB, Transistor and fuses.
  • Ground Potential Raise – When lightning strikes on the ground, it causes a ground potential gradient. This will cause some small surges. Example : A 100MV lightning strike at 30,000A can cause a ground potential of Rise of 75000V
• Lightning damages electronics/instruments by the following
  • Memory discharge – Data loss, software corruption
  • Degradation – Degradation of electronic components due to transient currents
  • Damage by heat – High current flowing can create heat
• Although lightning is devastative, 95% of electronics fail due to degradation of equipment are not from lightning, but from transients currents, which occur momentarily from
  • Collapsing magnetic field in inductors
  • Charging and discharging of capacitors
• The most important thing that needs to be done to avoid lightning strike is to ensure that all critical equipments potential rise together and no potential difference is created. Totally eliminating lightning is not possible. When there is a potential difference, this will cause arcing which is a source of ignition and extreme heat. It is important that all metallic equipments are connected together with the earthing grid
• A lightning protection system is a system which protects a structure from lightning strikes either by safely conducting the strike to ground or preventing the structure from being struck.
• The main components of a lightning protection systems are
  • Air termination / electrode / lightning rod
  • Down conducter – to conduct lightning for the air termination
  • Earthing / grounding system – to dissipate the charge to earth
  • Bonds and clamps – to connect all the systems together
  • Surge arrestors
• The down conductor must be put around a building, distanced
  • 10m apart for tall buildings (>20m)
  • 20m apart for short buildings (<20m)
• Grounding System
  • All plants have a single earthing grid buried inside the soil of the earth. In between these earthing grids, an electrode will be plunged to the ground. The earth electrode is a galvanized steel pipe. The rod’s are >9m
• Surge Arrestors
  • A SPD (Surge protection device) or lightning arrestor is a device which limits the current going through the line by channeling the excessive current to ground. Lightning arrestors must be installed at every line
  • The most effective protection is combination of SPD (surge protection device) at both ends, together with a low impedance grounding system
    • SPD shall be before the barrier
    • Instrument – SPD – Cable – SPD – Barrier - DCS
    • SPD is not used in off shore since there is no lightning in off shore platform
• Instrument Earth and Electrical Earth is connected by a High frequency choke
  • Lightning is a very high frequency voltage
  • The choke is actually a HF inductor which give low impedance at high frequency
  • This allows IE and PE to be equalized during lightning
  • The choke shall be protected by a 100v surge protector put in parallel with the choke.
    • The surge arrestor is normally a GDT type
    • At high voltage, it will give low impedance
    • During lightning, the surge arrestor will have low impedance and hence allows current to flow through it
    • This reduces the current flowing through the choke hence protecting it from damage
• Types of SPD
  • GDT (Gas discharge Tube)
    • Has a gas which becomes highly conductive at high voltage
    • Diverts the charge to ground
  • Zener Diode (Most Commonly used for instrument)
    • Zener diodes allow current to flow in the opposite direction at larger than the zener voltage
    • When high voltage occurs during lightning, the zener diode (arranged upside down) will flow through to ground
  • Metal Oxide Varistor (MOV)
    • At high voltage, it has low resistance but at low voltage has high resistance
    • When high voltage occurs during lightning, the MOV will have low resistance and route all the current through it to ground

Grounding / Earthing

• Earthing is the conduction of fault electricity current to earth.
• Earth is used because it is the most reliable low impedance path of the fault current
• The purpose of equipment earthing is
  • In electrical circuits it is used as a current sink since it has the ability to absorb a high amount of current without changing it’s potential. Though this is rare
  • For electrical supply, it is used as a common neutral reference. The grounding is done at a distribution sub station. As a normal user, we will see this as neutral terminal in our 3 pin socket
  • For lightning protection i.e. to ensure safe route of lightning and transient current to ground so that it will not effect other equipments
  • For EM reduction i.e. to sink electrical noise in signal transmission cables (such as telephone, microphone and etc)
• Every plant will have a plant earth ring. This will be one of the first things people will do during construction of a plant. The earth ring are made of conductors sized at 70mm².
• Instruments are connected to the plant earth ring via a earthing cable. The size of the earthing cable for instruments are recommended at 25mm².
• The earthing resistance of any earth electrode or ground rod is made up of:
  • Resistance of the (metal) electrode – This is usually neglected
  • Contact resistance between the electrode and the soil – This is usually neglected
  • Soil resistivity
    • The temperature effect on soil resistivity is negative but is negligible for temperatures above freezing point.
• In the plant we also have an instrument earth
• Instrument earth is used to quickly discharge noise from screen wire cables to the ground. The screen cable are usually grounded at the control room and should be left hanging on the field side
• These noise are normally from electromagnetic coupling between wires. As wires are typically bundled close to each other, current flowing through them will create electromagnetic field. These electro magnetic field can cause current in other wires
• It is a common practice to have instrument earth totally isolated from the electrical system earthing grid. This is because if there is stray currents in the earthing grid, this may induce interference current in the instrument signal
• The earthing system for instrument earth shall be as clean as possible. Therefore, it is important to put the instrument earth as far as possible from other earthing points. >5m should be okay
• The earth resistance for instrument earth is very low typically <2 ohms. This is typically achieved by having an array of parallel electrodes planted. The electrodes will be connected by cable. Typically for instrument earth, there will be up to 10 earth electrodes
• Should instrument and electrical earth be connected?
• Latest technology has promoted EMC certified devices where they are more susceptive to signal noises. With the use of EMC certified devices, we do not need screen cables anymore
• Normally in a plant, instrument and electrical earth are connected by an inductor and surge clamper.
  • The inductor is used to filter out high frequency noise from the earth grounding system

Electro Magnetic Interference

• Electro magnetic Interference (EMI) is unwanted disturbance that affects electrical circuit due to electromagnetic conduction or electro magnetic radiation
• Electromagnetic Compatibility (EMC)
  • Is a study branch in electrical engineering to try an ensure equipments are protected from EMI (electro magnetic interference)
  • The word EMC is commonly referred on a 2004 directive by the European parliament that:-
    • States the requirements of certified equipments do not emits electromagnetic signals that disturb other signals such as radio and television
    • States the requirements and governs the immunity of certified equipments to radio emissions
  • Manufacturers will usually seek EMC testing to ensure that they’re products are EMC certified

Wirings / Cables

• Cable Glands

· Cable will be terminated by a cable gland before going into a junction box/equipment. The purpose of the cable gland is

· to grip the cable so that it hangs on to the equipment

· to void water ingress into the junction box

· To ensure hazardous are protection

The usual cable entry used is M20 type. The M’s range from M16 to M175 (smaller to larger cables). The complete M20 annotation is usually described as ‘M20x15’. 15 here means 15 mm length of the thread. M20 usually has a hexagon ring to ensure better gripping

• Cable Gloves
  • After the cable gland, the cable will usually be covered by a cable glove. This is for cosmetics and also to avoid direct hit of rain on the cable gland.

• Cable routes
  • Electrical and Instrument cables shall be 3m apart with exception of crossing. As long as the instrument cable is crossing perpendicularly with electrical cables, this shall have no effect. When crossing it should be at least >0.3m apart
  • Instrument cables should not be routed through severe EMI areas
  • If possible, cables should be routed though areas that are protected by lightning strikes
  • Cables should be routed near earthed steel structures and piping to reduce EMI
  • Transmission from field junction box to MDF must go underground in a multicore cable to prevent damage from fire or mechanical forces and also to prevent theft.

• Cable Properties

· Cable thickness

· Cable thickness will determine the maximum cable carrying capacity.

· When one says cable thickness, it means the inner core NOT including the insulation.

· Cable thickness is usually measured in mm2 and will range between 0.005 to 100 mm2

· Sometimes cable thickness is measured in mm and this will range between 0.08 to 11 mm (you can calculate the area by using [PI*(D/2)^2]

· Field Instrument Signal wires

· use copper type wires which are usually around 1.13 mm

· The minimum cable diameter should be 1.13mm for single pair wires and 0.8mm for multicore wires (PTS)

· When specifying cable thickness, one will use standard. The most common standards used are

· American Wire Gauge (AWG)

· Standard Wire Gauge (SWG)

· Cable Capacitance

·

· Cable Insulation

· Cable insulation will determine the maximum voltage carrying capacity

· Screened or Unscreened

· Also called metal sheet. This is to remove noise and is made up of aluminum

· Metal sheet layer must be provided for small voltage signals to remove noise (Note that this wire must be grounded to instrument earth at the MDF). It is usually made of aluminum. TSometimes the metal screen will be also traced by a thin copper wire. This is to ensure continuity of the metal screen since usually, when the wires are bent, the aluminum sheath may tear apart. This wire is also called a drain wire

· Individual or overall screen

· Signal cables require screen while power cables do not

· The metal screen maybe available on every pair of cables. Even in a 10P-multicore cable, each pair will have a metal screen.

· Some multicore cable provide an single overall screen wire and do not have single wires on each pair

· Paired or Unpaired

· Some cables are paired while some aren’t.

· When they are paired, it is common to have individual screen for each pairs

· Inner layer insulating Material

· Typically polyethylene is used

· Outer layer insulating material

· Typically PVC is used because it is fire proof

· Underground Cable Protection

· Underground cabling must be provided with a special layer called AL/HDPE/PA (aluminium with high density polyethylene with polyamide (nylon) layer) to prevent moisture, chemical fumes or termite attacks. The AL (aluminum) layer also acts as a metal screen, hence no MS is required when AL/HDPE/PA is used

· Mechanical Protection

· Some cables will have an armour Layer

· It can either be steel wired armour or steel wire braiding

· To prevent mechanical forces, the use of steel wire armored or steel wire braiding is required (Note that this wire must be grounded to safety earth and the JB). Steel wire braiding is like a net style interface. This wire can also act as a metal screen. In this case the wire is grounded to the clean earth at the MDF. However some protective is installed at the cable gland of the JB so that the braided steels do not touch the gland since this gland is grounded to safety earth

· Fire Protection

· Fire resistant cables have a special layer before the SWA called ‘MICA’ a silica based material having high fire resistance.

· Fire retardant cables will have a high oxygen index. Oxygen index refers to how much oxygen is required to burn the cables. Normal cables will have oxygen index of 23% while fire retardant cables will have o2 index of 30%

· Thermocouple Cables

· If for thermocouple we require type K (Chromel Alumel) connections, which are red(+ve) and yellow(-ve) of color

• Cable Construction Guide:-

· As a general guideline, instrument cables must have the following construction:-

· The conductor (Usually Copper Type)

· Insulator for conductor (Usually Poly Ethlyene)

· A Bedding Layer (To avoid direct contact of armour layer on screen) This layer provides insulation on the effect circulating ground currents (Since electrical earth is grounded in many places, current will flow in the ground wire due to ground potential difference)

· Cables shall be specified with low smoke and zero halogen. Halogen is very toxic to the body

• PTS outlines a signal level class level from 1 to 5. Level 1 is for computer us signals, thermocouples and analyzers. Instrument 4-20mA signals are Level 2. Level 4 and 5 are for power cables.
• KR2 Project instrument wire specs which are available in the market are of the following

· 1Pair/2P/3P/1Triad/2T/3T - 1.13mm PEI-MS -SWA-PVCS

· 1Pair/2P/1T/2T/3T – 1.13mm PEI-MS-AL/HDPE-SWA-HDPE/NC (for underground)

· 5P/10P/20P/10T/15T – 0.8mm PEI-MS-AL/HDPE-SWA-HDPE/NC (for underground)

· 1P/2P – 4.0mm2 PEI-MS-AL/HDPE-SWA-PVCS (for instrument power cables)

· 1P/5P/10P – 4.0mm2 PEI-MS-AL/HDPE-SWA-HDPE/NC (for instrument power cables)

· 1P/2P – 1.13mm PEI-MS-PVCS (internal cabinet wiring or installations with conduit)

· 10P/20P – 0.8mm PEI-MS-PVCS (internal cabinet wiring or installations with conduit)

· Fibre Optic Cables – FO-AL/HDPE-SWA-PVCS/NC (for underground)

· Cable Costs bought from vendor (who already marked up the price) in general are more or less the following

· 1P – RM40/m

· 10P – RM120/m

· Fibre Optics

• Multi Mode

· Cheaper, more commonly used

· Has a larger diameter core

· 100 MBit/s for 2KM, 1000 MBit/s for 500m, 10GBit/s for 300m

· Multiple Data, Have 2 different wavelengths

• Single Mode – Only 1 wavelength

· Cat 5 Cables

• In the US the quality of cables to carry out signal is defined by CatX. Cat5 cable is currently the recognized cable for broad band transmission. Cat5e cable is the cable being recommended by IEEE and many equipment manufacturers. In the Europe they are rated in class, Class D being simlar to cat5 cables
• CAT5 is an Ethernet cable standard defined by the Electronic Industries Association and Telecommunications Industry Association (commonly known as EIA/TIA). CAT5 is the 5^th generation of twisted pair Ethernet cabling and the most popular of all twisted pair cables in use today. It has 4 twisted pairs of copper wire terminated on an RJ45 connector. Cat-5e (CAT 5 enhanced) cabling supports frequencies up to 100 Mhz and speeds up to 1000 Mbps.

· Color Coding

• The purpose of cable color coding is to know

·

Junction Box

· Cable entries shall be from the bottom. This is to prevent water ingress. If there is not enough space at the bottom, installation can be from the side. The cables however ned to be slanted to the bottom to allow water to flow downwards

· Ex junction boxes have a groove to allow heat to dissipate through. This will allow heat to go out of the junction box. CAUTION, it is wrong to tape the junction box as it will seal this groove. Experience has shown that when this groove is sealed, we may get melted termination blocks

·

Wired Signal transmission

• Signal transmission in wires are exposed to the following 3 types of noise

· Magnetically induced noise.

· This is caused due to flux produced at the flowing current. When another wire is nearby, it will cause a flux cutting and induce voltage.

· Using a twisted pair wire will cancel out this induction

· Static noise.

· This is caused since two wires are close by, the wires create and imaginary capacitance between. The capacitance causes a build up of charge.

· By having a metal screen wire, this charge can be dissipated to clean earth (instrument earth)

· Common mode noise.

· This is the noise caused from the current created by different electrical grounding points

·

• The electromagnetic spectrum are as follows:-

Wireless Transmission

• Wireless transmission is performed by a medium called the electromagnetic spectrum. Currently only the radio and microwave frequencies are used for this communication
• The electromagnetic spectrum are as follows:-

· 1 to 30 to 300Hz

· Extremely Low Radio Frequency (ELF) and Super low frequency (SLF)

· Used for Communication with submarines – This is a one way communication

· Waves are produces by mounting 2 large antennas apart

· Extremely slow communication, Few characters per minutes

· 300-3KHz – Ultra Low Radio Frequency (ULF) – Used for communication in mines

· 3 - 30KHz

· Very Low Radio Frequency (VLF)

· Can penetrate up to 40m deep under water

· Used for communication with satellites on the surface

· Used in electromagnetic geophysical surveys (detecting gold, minerals)

· 30 – 300KHz

· Low Radio frequency (LF)

· Used for navigation, radio clocks

· In some countries used for AM modulation

· 300 – 3000KHz

· Medium Radio Frequency (MF)

· Used for AM Broadcasting

· 3 - 30MHz

· High Radio Frequency (HF)

· Ionosphere can reflect these frequencies – Due to this HF has a very long distance. This phenomena is called skywave. Skywave is however effected by a lot of whether factors

· Used by amateur radios (private radios) since they would enjoy the long transmission

· 30 – 300MHz

· Very High Frequency (VHF)

· FM Radio transmission

· Previously used for black and white Television Broadcast. Could not be used for colour TV due to limited bandwidth

· 300MHz – 3GHz

· Ultra High Frequency (UHF)

· 450MHz is used for ATUR communication

· 900 – 1800MHz is used for Cellular Communication

· 900 Mhz band is used for Celcom and Maxis communication

· 1800 Mhz is used for adam.timecel and digi

· Wireless transmitters use 902 – 928 MHz Signal

· 470 – 800 MHz is used for color TV channels

· 2.4GHz Wifi Communication

· 2.45 GHz is used for microwave oven and blue tooth

· 3 – 30GHz

· Super High Frequency (SHF), popularly called the Microwave

· Used for WiMax

· Used for radar, as most objects reflect microwave signals

· Blue tooth use

• As seen above, most signals are segregated by frequency. A recent technology, CDMA (Code Division Multiple Access) now allows signal to be segregated by code. CDMA is used for frequencies constructed from the band between
• ISM (Industrial, scientific and medical) Band is a defined by ITU-R for the use of Industrial, Scientific and medical purposes which is free. All communication equipment must accept any interference from ISM equipment

· 6765-6795 kHz (centre frequency 6780 kHz)

· 13553-13567 kHz (centre frequency 13560 kHz)

· 26957-27283 kHz (centre frequency 27120 kHz)

· 40.66-40.70 MHz (centre frequency 40.68 MHz)

· 433.05-434.79 MHz (centre frequency 433.92 MHz) in Region 1

· Walkie Talkie

· 902-928 MHz (centre frequency 915 MHz) in Region 2

· Wireless Transmitters

· Cordless Phones

· 2400-2500 MHz (centre frequency 2450 MHz)

· 5725-5875 MHz (centre frequency 5800 MHz)

· 24-24.25 GHz (centre frequency 24.125 GHz)

· 61-61.5 GHz (centre frequency 61.25 GHz)

· 122-123 GHz (centre frequency 122.5 GHz)

· 244-246 GHz (centre frequency 245 GHz)

• Wireless signals are created by an Antenna which generates a radiating EM field
• The government body which dictates frequency usage in Malaysia is the MCMC (Malaysian Communication and Multimedia Commission). We pay them yearly
• About Handphones

· HP use a network called the cellular network. The cellular network is made out of cellular towers, normally known as cell sites. The most popular cellular network standard use is GSM(Global System for Mobile Communication)

· GSM operates in 2 frequency bands 900Mhz and 1800Mhz

· The first generation of HP, called 1G, uses analogues signals for communication.

· The second generation 2G, uses digital signals for communication. Voice signal is sent in a digital signal of around 10Kbits/s

· The third generation of mobile phones is 3G. This was enabled by packet switching technology which provides a higher bandwidth. Can go upto 1MBit/S

· The fourth generation of mobile phones is 4G. 4G is still conceptual, but the enabling technology would be the removal of all circuit switch communication into a fully IP based packet switched integrated system. It will also combine with Wifi and Wimax infrastructure. Can go up to 100Mbit/S

• LOS issue can be as follows

· Size :- Obstruction which effects the signal must e larger than then the wave length

· Material :- If an obstruction is a good conductor, it will reflect the signal which is not good. However if the obstruction is a good insulator, the signal will pass thorugh. The degree to which a material is a good conductor or insulator also depends on the wavelength. The higher the wave length, the better the signal may pass through the object

• The current most popular technology for wireless transmission is the Motorola canopy
• The general frequency are as follows

· 0 – 4KHz : Telephone audio inside cables

· 25KHz – 1MHz : Broadband Internet

• Comparison between 900Mhz and 2.4GHz

· 900Mhz more range

· 900 Mhz has more interference from pager and mobile communication

· 900 Mhz can reach without LOS

· 900 Mhz has lower power consumption

• Range of wireless transmission is limited by the following factors

· The type of signal in use (i.e. the underlying technology), similarly to the fact that AM radio waves reach further than FM radio waves

· The transmitter's rated power

Wireless Transmitters

• Wireless transmitter work in the ISM band of 902-928Mhz. Development is currently being done for 2.4GHz which has less interference and higher band width
• Data rate is 4.8 kbps, 19.2 kbps and 76.8 kbps
• Has CRC check to ensure data accuracy
• Wiring cost saving of RM40 per meter
• The waves sent are omni directional in comparison with Motorola canopy which is angles at +45 vertical and +30 horizontal
• Range is about 600m but varies accordingly

Instrument Safety

• Intrinsically Safe is the state of a device, instrument or component that will not produce any spark or thermal effects under any conditions that are normal or abnormal that will ignite a specified gas mixture. Electrical and thermal energy limits are at levels incapable of causing ignition. It is common practice to use external barriers with intrinsically safe installations
• Ingress Protection (IP) is derived from the IEC 60529 classification standard defining the state of an enclosure. IP has 3 digits, though 2 digit notation is the most commonly seen. The first digit is about solid contact, either 0(total contact, anything can get through) to 6 (not even dust can get through). Usually, 6 is used for process plants instruments since we do not want any dust to enter the electronic boards. The second digit is for protection against water ingress valued from 0 to 8. Usually 6 is used. In our plant, most of the instruments are IP65

IP First number - Protection against solid objects

IP Second number - Protection against liquids

IP Third number - Protection against mechanical impacts (commonly omitted)

• Fuel can ignite when the concentration of combustibles in air is between LEL(Lower Explosive Limit) and UEL(Upper Explosive Limit). This is because a correct Air to Fuel Ratio is required for a combustion.

• An LEL meter detects the concentration of all combustible gases and translates it into percentage of an LEL limit. Typically, LEL meters are calibrated to Methane(CH4). Methane LEL limit is used as a reference for all other gasses. Most plants will set %LEL limit at 10% for hot works. This means that since methane LEL is 4.4%, if the gas detected is methane, the LEL limit will be 0.44%. From the view of an LEL meter, it will give 10%. 10% LEL is used as a safe level so that whatever the gas is, it is always safe to work since the LEL is still far away.

Equipment Protection

• Area in a plant is usually divided into

· Classes or Zone

· Zone is used for Europe

· Zone 0 = Flammable material always present

· Zone 1 = Intermittent available and for long hours (>10 hours)

· Zone 2 = Not always available and for short durations only (<10 hours)

· Class is used in US

· Rosemount transmitters use

· Gas group

· Refers to a group of gas which has similar propertie as the group gas. The main property is the ignition energy

· Group I = Methane

· Group IIA = Propane

· Group IIB = Ethylene

· Group IIC = Hydrogen

· Temperature Classes

· Each gas has an auto ignition temperature

· An area can be classified from T1 and T6. T1 has the highest auto ignition temperature hence it is safest.

· An equipment can be certified as T1 to T6. This is the worst case temperature the equipment can get hot

• Typically, for zone 1 it shall be 3m away from zone 0,
• Ex is a certification chop for explosive protection equipment, i.e. equipments that protect explosion from happening such as JB and instrument enclosures. It is stated on the requirements from ATEX directive. In Europe, every Ex marked equipment shall have a CE mark
• CE is also a mark like Ex. It was introduced by the European commission. With the CE sign, the product complies to the safety standards to be sold in Europe.
• Protection types

· Ex ‘d’ = Flame proof – Not designed to be gas tight, energy is released through flame path, Large design to prevent explosion.

· Ex ‘o’ = oil immersion – used for transformers, Zone 1 and 2

· Ex ‘p’ = Pressurized – used for analyzers, Zone 1 and 2 – Equipment needs to be powered off if the enclosure is opened. This is why purging is ‘’not usually recommended

· Ex ‘q’ = Powder field – weighing machines, Zone 1 and 2

· Ex ‘ma’ = encapsulation – Zone 1 and 2

· Ex ‘d’ = Flame proof , explosion is confined within box– DC motors, Zone 1 and 2

· Ex ‘e’ = Increased safety, it is not possible for explosion to happen. The box is designed in such a way to prevent

· Connections oversized

· Terminations more robust

– Induction motors, instrument JB, Zone 1 and 2

· Ex ‘ia’ = instrinsic safety – if 1 component fails, IS can still retain - Zone 0,1,2

· Ex ‘ib’ = intrinsically safe, Zone 1 and 2 only

• For zone 0