Basics_of_Instrumentation_Fire_Gas.doc

AREA CLASSIFICATIONGAS:ZONE 0 :- Flammable atmosphere present continuously 1000hrs/annum.ZONE 1:- Flammable atmosphere present intermittently 101000 Hrs / annumZONE 2:- Flammable atmosphere present abnormally 10 hrs/annumCERTIFICATION CODECertified to the CENELEC standardEExiaT4IICTemperature ClassificationApparatus group (gas group)Protection concept (IS)Explosion protectedGROUP II ELECTRICAL APPARATUS for gas atmospheresCategory 1GCodePermitted zone012Oil immersionoProtection by gas exclusion - transformersPressurizedpProtection by gas exclusion analyzersPowder filledqProtection by gas exclusion weighing machinesFlame proofdPrevention of propagation of internal explosion dc motorsIncreased SafetyePrevention by design induction motorsIntrinsic Safety iaiaLow energy. Safe with two faults-level measurementIntrinsic safety ibibLow energy. Safe with one fault - displaysIntrinsically Safe device Exi:An Intrinsically safe device is on that is inherently incapable of producing energy levels sufficient to ignite a flammable gas.As an example, Hydrogen requires 20 Micro-joules of energy for ignition. The intrinsically safe device is incapable of generating 20 micro-joules of energy.Intrinsically safe devices can be certified of Exia or Exib. The difference between the two is “ia” is safe even with two faults in the device, while ib is safe with one fault.An Explosion Proof equipment (Exd) also known as Flame proof equipment is one in which if an explosion takes place inside the equipment (say a junction box) the hot gas that comes out of the enclosure gets sufficiently cooled by the time the flue gas reaches the atmosphere so that the hot gas (flue gas) is incapable of igniting the flammable gas in the atmosphere. Oil Immersion Exo The sparking contacts are immersed in Oil so that gas cannot be present near the sparking contacts, not so much used in instrumentation.Pressurization Technique Exp: This system of protection is used typically in large volume equipment, control rooms located in hazardous areas. The equipment / the room is kept under pressure so that the room is at a higher pressure (by a few inches of water) so that hazardous gas cannot enter the room or the equipment from outside since inside pressure is more than the outside. The air to pressurize is usually taken not from near the gas atmosphere. Further a pressure switch senses the room pressure and in case the pressure drops will give an alarm in the CCR besides tripping the power for equipment in the room. Powdered filled Exq: Not so much used in instrumentation, the principle is the same as Oil immersion.Increased Safety Exe: Typical examples is Exe junction boxes we normally encounter. The safety is built in the inherent design and manufacture.ONLY INTRINSICALLY SAFE DEVICES Exia can be used in Zone 0. No Electrical / electronic instruments can be used in Zone 0 except Exia. Please see the table above for details of which type of protection can be used for the different zones.All other techniques including Exib can be used in Zone 1 and Zone 2.INGRESS PROTECTION (IP) CODESThe IP code consists of 2 digits XY. The first numeral X stands for protection against solid bodies and the second numeral Y stands for protection against liquid bodies.This IP code is intended for electronic enclosures, junction boxes, panels and so on.Example: IP65 stands for equipment is dust-tight and protected against water jets.8 INDEFINITE IMMERSIONNO PROTECTIONOBJECTS GREATER THAN 50 mmOBJECTS GREATER THAN 12 mmOBJECTS GREATER THAN 2.5 mmOBJECTS GREATER THAN 1.0 mmDUST- TIGHTDUST PROTECTED015432061234567 SPLASHED WATERVERTICALLY DRIPPING WATER NO PROTECTIONANGLED DRIPPING WATER-75 0 TO 90 0 SPRAYED WATER WATER JETS HEAVY SEAS EFFECTS OF IMMERSIONCalibration of various field instruments.Different Type of Transmitters:Pressure transmitters, Temperature transmitters, Differential pressure transmitters, Level Transmitters and so on. The ISA letter that denotes a Transmitter is “T” so that TT stands for Temperature Transmitter and so on.The output of an Electronic transmitter is 4-20mA for 0 100% measurement.0%4 mA25%8 mA50%12 mA75%16 mA100%20 mASo mA Reading = (%age reading X 16) + 4So 10% of the transmitter value is = (10/100) X 16 + 4 = 0.1X 16 + 4 = 5.6So 25% of the transmitter value is = (25/100) X 16 + 4 = 0.25X 16 + 4 = 8In case the Full scale is = 20 Bar and the reading of the transmitter is 1.5 BarThen 1.5 Bar forms 1.5 / 20 (Reading / Full scale reading) = 0.08 or 8%So the reading of the transmitter is 0.08 X 16 + 4 = 1.28 + 4 = 5.28 OR GENERALLY Reading = 4 + (Instrument Reading X 16) Instrument SpanTransmitter output for a Reading of 3 Bar for a full scale reading 50 BarmA Reading of the transmitter = 4 + (3 X 16) = 4 + 0.06 X 16 = 4.96 50Pt100 stands for Platinum Resistance whose Resistance at 0 deg C is 100 Ohms. Its resistance at 100 deg C is 138.5 Ohms. Pt10 stands for Platinum Resistance whose Resistance at 0 deg C is 10 OhmsAuto motor start stop circuitACRONYM / ABBREVIATIONS:ACAlternating CurrentAFCApproved for ConstructionANSIAmerican National Standard InstitutionAPIAmerican petroleum InstituteDCSDistributed Control systemHIPPSHigh Integrity Pressure Protection SystemHVACHeating Ventilation and Air-ConditioningISAInstrument Society of AmericaISOInternational Standards InstitutionLSZHLow Smoke Zero halogen (Normally used for cable specifications) particularly for cables used in confined rooms so that toxic fumes will not be released from the cable in case of fire. Chlorine, Bromine, Fluorine and Iodine belong to the Halogen family.NACENational Association of Corrosion EngineersPVCPolyvinyl ChlorideP&IDPiping and Instrumentation DiagramPIDProportional Integral Derivative (control)PLCProgrammable Logic ControllerPsigPounds Per Square Inch GaugePsiaPounds Per Square Inch AbsoluteSILSafety Integrity LevelSWASteel Wire ArmourSSStainless SteelTMRTriple Modular Redundancy (Triconex and HIMA PLCs employ in their control schematics)XLPECross-Linked Polyethylene (used in cable specifications)Basic information on control valvesAND GATE The Out put is a “One” when Input A AND Input B are ONE.I/PO/PABC000100010111OR GATEThe Out put is a “One” when Input A OR Input B is ONE.I/PO/PABC000101011111NOT (INVERSION) (If A is ONE then B is Zero and If B is ONE then A is Zero)AB1001N AND (Output of AND is inverted i.e. NOT AND)I/PO/PABC001101011110NOR (Output of OR is inverted i.e. NOT OR)I/PO/PABC001100010110XORI/PO/PABC000(Please note when I/Ps are different O/P = 1)101011110X NOR (Output is Inverted XOR i.e. NOT XOR)I/PO/PABC001100010111Accuracy in any loop is the sum of the accuracies of all the instruments in that loop.Example:If there is a transmitter whose accuracy is + 0.1% (FSD) and a recorder with an accuracy of + 0.5% the total accuracy of the loop = + 0.6% ( cumulative accuracy of all the instruments in the loop)RESISTORS IN SERIESRESISTORS IN PARALLELCAPACITORS IN SERIESCAPACITORS IN PARALLELVARIOUS FIRE AND GAS DEVICES AND SYSTEMS:Various Types of Fire, Gas Detectors and Fire Fighting Systems: A. Combustible Gas DetectorsB. Flame DetectorsC. Low Temperature DetectorsD. Open Path Gas DetectorsE. Smoke DetectorsF. H2S Gas DetectorsG. Pull Handle / Call PointsH. Fire Control Panels & CO2 panelsI. Heat DetectorsJ. SO2 Gas DetectorsK. Fire and Gas Safety Logic and Monitoring SystemL. Deluge Skid Inst. SystemsM. High Expansion Inst. SystemsN. Dry chemical powder instrumentsO. Rim Seal Agent InstrumentsP. CO2 System InstrumentsQ. Water Monitor TowerR. ITM ProgramsFIELD DEVICES:1. SMOKE DETECTORS:IONIZATION TYPEOPTICAL TYPEIonization Type Smoke Detectors: Referring to the adjacent diagram Electrode A is treated with a Very level of Radiation material and a potential is applied between Electrodes A and B. On account of Radiation the air between the Electrodes A and B is ionized and ionization current flows between the Electrodes. In the presence of smoke Between the electrodes the ionization current varies (due to the smoke particles) and thus the smoke is sensed. The Output from the electrodes is fed to an Electronics amplifier and a schmmit Trigger which will give an ON / OFF output for the Presence / Absence of smoke.The smoke Detector is tested periodically (once in 6 months or as the case may be depending on the policy of the organization) by an Aerosol spray from a smoke canister. (NOT BY CREATING A SMOKE)The Optical type of smoke detector is based on the principle that when smoke passes through a source of Light (LED) and a photodiode / photocell the current through the Photocell / Photodiode varies. The arrangement is a source of light (say LED) is mounted in front of a Photodiode or a Photocell or may be a photo-resistor, under “No Smoke” condition the light falls on the photocell and a quiescent current flows in the circuit. When smoke passes through (between) the Light and the photocell the current in the circuit varies sensing the smoke. The signal is further processed (amplified and fed to a schimmt trigger) and a switch action is generated for the presence or absence of smoke.The smoke Detector is tested periodically (once in 6 months or as the case may be depending on the policy of the organization) by an Aerosol spray from a smoke canister.(NOT BY CREATING A SMOKE)Usually one smoke detector will be located for each 3 Square meters of area. There is a NFPA (National Fire Protection Agency / Association, USA) regulation for the number of detectors for a given area.Normally a number of smoke detectors will be associated with one zone. Due to atmospheric humidity many times smoke detectors may give rise to false alarms. As a result whenever there is a trip connected with smoke detectors it will never be based on one smoke detector sensing the smoke. Normally a given area will be divided into two zones and when one smoke detector from each zone in the same area simultaneously sense smoke then only the control action will be initiated. Consequently while testing the smoke detectors ensure that the smoke detector under test is (alarm acknowledged) reset before testing another smoke detector in the same area (look at the cause & Effect Sheet). Each F & G system has a “Zone Module” to which the field devices are connected. Each Zone module gives an output depending on the alarm generated by the field devices. Each zone module has the following indications:1. Power On Indication2. smoke / Fire Alarm indication3. Card / Device Inhibit indicationEach zone module has the following controls:1. Alarm Accept / Acknowledge2. Alarm Reset3. Output Action InhibitNormally there will be a facilities module in the Panel (may be in each row) to which all the Alarms and control actions are wired in the row.The power to the field devices is usually provided from the zone module. So, whenever a field device is to be replaced, if we pull out the zone module the power to the field will be last. However before pulling out the module check the cause & effect sheet.HSSD / VESDA:High Sensitivity Smoke Detection system / Very Early Smoke Detection Apparatus works similar to Optical smoke detector except that a high sensitive detection system (LASER) is used for detection. Further an Aspirator / pump is installed in the detection system that sucks the air sample and the same is passed through the detection system. This arrangement combined with the high sensitive detection system gives a high sensitive detection / Very Early Detection of smoke.The principle difference between a normal smoke detector and HSSD / VESDA is that in the latter the smoke is detected very early even when the smoke is in incipient stage (beginning to from) so that corrective action can be taken at a very early stage of smoke.THERE IS NO FIRE WITHOUT SMOKE. So the objective is to tackle the situation before it can get out control! The smoke is detected very early before it is too late.There is a special test jig for testing the VESDA. A wire provided by the manufacturer is connected to a transformer (provided by the manufacturer) and the transformer is powered. The wire is located where the air will be sucked by the pump, this will be sensed by the VESDA and alarm is generated in the device.HEAT DETECTORS ( BI-METALLIC SWITCHES)Heat Detectors are used mainly in kitchens and turbine compartments. Those used in turbine compartments are color coded for various temperatures (at which the detector gives alarm/trip signal)These are Bi-Metallic Switches and function based on temperature rise in the surrounding. They are preferred to smoke detectors in Kitchen as Kitchens produce smoke during cooking and used in Turbine compartments since the ambient temperature in Turbine compartments are very high and smoke detectors cannot function at theses high temperatures.The Heat Detectors used in Kitchen are usually Rate of Rise detectors and operate at about 85 deg. C (my figure may not be accurate). The Heat Detectors used in the kitchen very similar to conventional smoke detectors except that there is no opening for the passage for smoke (as it functions based on heat and not on smoke).The Heat Detectors employed in Turbine enclosures carry a color code, to specify the temperature at which the detectors change state (change of state of switch). Currently I do not have the information on the color code corresponding to the temperature at which the detector changes state. The Heat detector for each area in the turbine is selected based on the ambient temperature in which the detector is to be installed. As for example close to the Burner compartment the heat detector selected may be as high as one to operate at 350 deg C (as for example) and the near auxiliary compartment may operate at 120 deg C (as for example).While replacing the detector, if the color is not clear in the detector refer to the drawing to find out the temperature class of the detector to be mounted.The Heat Detector is tested using a Hot Air Blower which can generate sufficient heat for the detector to change state.The number of Heat Detectors may also be connected to each zone just like smoke detectors and all the precautions and explanations provided above regarding the zone modules apply for heat detectors as well.The power to the field devices is usually provided from the zone module. So, whenever a field device is to be replaced, if we pull out the zone module the power to the field will be last. However before pulling out the module check the cause & effect sheet.MANUAL ALARM CONTACTS / BREAK GLASSManual Alarm Contact or Break Glass is a device that is intended to manually generate an alarm in case of an emergency. Usually this device will be located at the Exit / Entrance of a room, so that in case of an emergency in the room those who run out of the room can initiate the alarm at the exit. The Break Glass basically consists of a Spring operated Push Button switch (N/O or N/C) kept pushed under pressure by a glass. The glass is mounted on a bezel and screwed to the cabinet. Whenever someone breaks the glass with a hammer tied to the cabinet the switch pops out resulting in a change of state for the switch which is used for the Fire alarm. In order to test the device we need to loosen the screws of the glass so that the switch pops out giving the alarm. Once the device is tested the glass may be screwed back in place and the alarm accepted and reset in the zone module.Usually a MAC / break glass will not be associated with any trip but alarm only, however it is always good to see the cause & effect sheet prior to working on any device.FLAME DETECTORSThere is light emanating out of any fire and the frequency spectrum of the fire ranges from Ultra-violet to Infra-red. The Flame Detector contains a Photo-tube / Geiger Muller Tube and when the light falls on the Detector the Tube gives an output that is a function of the UV-IR coming out of the fire.These devices operate using dual detectors in a single unit, UV and I/R are continuously monitored and both detectors have to respond to initiate an alarm condition.The Photo-tube / Geiger Muller Tube may require high voltage for the tube to perform, normally 24 VDC supplied to the Flame Detector. There may be an inverter inside the Flame detector to produce high voltage required for the Photo-tube / Geiger Muller Tube.An UV/IR Torch is used to test the Flame detectors. CAUTION DO NOT SEE THE LIGHT COMING OUT OF THE UV-IR TORCH AS THE UV IS DANGEROUS TO THE EYES.Each flame Detector has a cone of Vision usually 90 deg.Each flame detector will be associated with one zone assigned to one zone module.The power to the field devices is usually provided from the zone module. So, whenever a field device is to be replaced, if we pull out the zone module the power to the field will be last. However before pulling out the module check the cause & effect sheet.A flame Detector (Detronics) has an “Optical Integrity Ring” known as Oi.