Instrumented Protection Functions

IPF Study

· 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

1. SIL Classification (Proceed with all)

2. IPF Verification

3. IPF Implementation

4. IPF Review – Every 5 years

· 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


o Sil 1 : 1/10

o Sil 2 : 1/100

o Sil 3: 1/1000

o Sil 4 : 1/10000

· 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






< 60%




60% - 90%




90% - 99%




> 99%




Type A Instrument Used






< 60%




60% - 90%




90% - 99%




> 99%




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



· 4

· 10-5 to 10-4

· 3

· 10-4 to 10-3

· 2

· 10-3 to 10-2

· 1

· 10-2 to 10-1

· 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 and grounding


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

· Another cloud

· Air


· 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

· 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.

· 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

Lightning Protection System

SPD Type




Can be used for AC


Provides hardest clamping

Cannot be used for AC


Can be Used for AC

Grounding / Earthing

Electro Magnetic Interference

Wiring and Cabling

Wirings / Cables

· 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 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

· 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

· 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

· 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

· Cat 5 Cables

· Color Coding


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

· 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


Wireless Transmission

· 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

· 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)

· 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

· 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

· 0 – 4KHz : Telephone audio inside cables

· 25KHz – 1MHz : Broadband Internet

· 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

· 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

Instrument Intrinsic Safety

Instrument Safety

IP First number - Protection against solid objects

0 No protection.
1 Protected against solid objects up to 50mm, e.g. accidental touch by hands.
2 Protected against solid objects up to 12mm, e.g. fingers.
3 Protected against solid objects over 2.5mm (tools and wires).
4 Protected against solid objects over 1mm (tools, wire, and small wires).
5 Protected against dust limited ingress (no harmful deposit).
6 Totally protected against dust.

IP Second number - Protection against liquids

0 No protection.
1 Protection against vertically falling drops of water e.g. condensation.
2 Protection against direct sprays of water up to 15o from the vertical.
3 Protected against direct sprays of water up to 60o from the vertical.
4 Protection against water sprayed from all directions o limited ingress permitted.
5 Protected against low pressure jets of water from all directions o limited ingress.
6 Protected against low pressure jets of water, e.g. for use on ship decks - limited ingress permitted.
7 Protected against the effect of immersion

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

0 No protection.
1 Protects against impact of 0.225 joule (e.g. 150g weight falling from 15cm height).
2 Protected against impact of 0.375 joule (e.g. 250g weight falling from 15cm height).
3 Protected against impact of 0.5 joule (e.g. 250g weight falling from 20cm height).
4 Protected against impact of 2.0 joule (e.g. 500g weight falling from 40cm height).
5 Protected
Substance LEL UEL
Acetone 3% 13%
Acetylene 2.5% 82%
Benzene 1.2% 7.8%
Butane 1.8% 8.4%
Ethanol 3% 19%
Ethylbenzene 1.0% 7.1%
Ethylene 2.7% 36%
Diethyl ether 1.9% 36%
Diesel fuel 0.6% 7.5%
Gasoline 1.4% 7.6%
Hexane 1.1% 7.5%
Heptane 1.05% 6.7%
Hydrogen 4% 75%
Hydrogen sulfide 4.3% 46%
Kerosene 0.6% 4.9%
Methane 4.4% 17%
Octane 1% 7%
Pentane 1.5% 7.8%
Propane 2.1% 9.5%
Propylene 2.0% 11.1%
Styrene 1.1% 6.1%
Toluene 1.2% 7.1%
Xylene 1.0% 7.0%



Equipment Protection

· 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

· 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