Annunciators

AnnunciatorsElectronic SensorsAnti surge & Speed Controller

Presentation ByPC SharmaAnnunciatorsProcess Safety Time

Layer of protectionCommunity ResponsePlant Response Relief Devices Safety valves,PLC Emergency Shutdown SystemDCS Basic Control SystemProcess Alarm SystemLayer of protectionDCS (Basic Process Control System)The plant control system is the foundation of safe operation. Its correct design and function is necessary, to operate the plant safely when in normal mode. Alarms (Pre Alarm System)These alarms provide early warning of any unsafe condition that requires immediate action.

Layer of protectionPLC System Emergency Shutdown SystemIt is automatic protection systems that where the operators cannot be relied upon any more (e.g. because of the level of risk or required fast reaction time). Relief devices Rupture disc, Safety valves or flares. It is physical means used to prevent damage to equipment or danger to life.

Layer of protectionPlant response This is a mitigation layer and not a prevention layer. This involves a plan of action where the disaster has happened already. Community response This layer plays a role when plant response methods have been exhausted (fire brigade, evacuation). The role of programmable electronic devices is in alarm annunciators to handle critical alarms.AlarmAn alarm is a signal that is annunciated to the operator usually by an audible sound, a visual flashing indication and the presence of a message or other identifier.An alarm indicates a problem requiring operator attention Alarm initiated by a process measurement passing a defined alarm setting as it approaches an undesirable or potentially unsafe value.

Good AlarmRelevantalarms must have operational significance.Uniquethere should be no redundant alarms.Timelyalarms must provide sufficient time for operator intervention.Prioritizedalarm priority should clearly rank alarms according to risk and intervention time.Understandablealarm messages must be clear.Alarm SystemAlarm systems notify an operator of an occurrence of abnormality in the process that requires action.Primary purpose of an alarm system is to alert an operator, It provide information in the form of visual display with an audible warning (buzzer, siren)or an alarm log.Alarm SystemAlarm points monitored are to be less often in hundreds and not infrequently more than a thousand. Every alarm should have a defined responseAdequate time for the operator to carry out his defined response. This implies that: the alarm should occur early enough to allow the operator to correct the faultthe alarm rate should not exceed that which the operator is capable of handling Alarm system

Alarm SystemAlarm system or Annunciator is a device that receives the alarm input, a sequence of actions is necessary in order to return the process to normal conditionAcknowledge activating a pushbutton to stop indicating the alarm as a new alarm (also referred to as accept)Reset activating a pushbutton in order to return the annunciator device to a normal state. This is possible after the removal of abnormal.AnnunciatorsIn modern technology, these requirements, can be implemented in either a dedicated device i.e. alarm annunciator or in DCS (PC) software and displayed on computer screens.

Alarm systemCONFIDENTIALALARM STATUS

Alarm listed in Process Alarm viewAlarm displayed in System Message Banner16When an alarm occurs, the alarm is indicated on the faceplate, tuning view, System Message Banner and is also listed in the Process Alarm View. It indicates a color change and an audible buzzer sound.CONFIDENTIALTAG MARK COLORALARM STATUS

PV BAR COLOUR

TAG MARK COLOUR

NR

GREEN

GREEN

HH/HI/LL/LO/IOP/OOP

RED

RED

DV+/VEL+/MHI/MLO

YELLOW

YELLOW

CAL

CYAN

GREEN

AOF

NO CHANGE

DARK BLUE

TAGS WITHOUT ALARM

----------

WHITE

17The occurrence of an alarm is indicated on the faceplate or tuning view as a color change. The table lists the color changes on the occurrence of an alarm.CONFIDENTIALPROCESS ALARM STATUSALARM STATUSPROCESS STATUSALARM SETTINGSITEM TO BE SET IN THE TUNNG VIEWPV BAR COLORTAG MARK COLORNRPROCESS NORMAL-----------GREENGREENHHPV VERY HIGHPV > HHHHREDREDHIPV HIGHPV > PHPHREDREDLLPV VERY LOWPV < LLLLREDREDLOPV LOWPV < PLPLREDREDDV+/-DEVIATION ALARMDV> DL; DV = PV-SVDL DEVIATION LIMITYELLOWYELLOWVEL+/-VELOCITY ALARMVEL = PV / TVL VELOCITY LIMITYELLOWYELLOWMHIMV HIGHMV > MHMHYELLOWYELLOWMLOMV LOWMV < MLMLYELLOWYELLOWIOP+/-INPUT OPENINPUT IS OUT OF RANGECHECK RAW VALUE IN TUNING VIEWREDREDOOPOUTPUT OPENOUTPUT LINE IS OPEN----REDRED18The table shows the list of process alarms that an instrument can have. It also indicates the settings required for the alarms and the color change when the alarm occurs. The settings can be done in the tuning view.Electronic SensorsThermocoupleWhen two wires with dissimilar electrical properties are joined at both ends and one junction is made hot and the other cold, a small electric current is produced proportional to the difference in the temperature.

ThermocoupleThermocouples come in several forms. They may be wires insulated from each other with plastic or glass fiber materials.For high temperature work, the wire pairs are put inside a tube with mineral insulation. Type J 0 to 800 C Type K 0 to 1200 CType T -199 to 250C Type E 0 to 600CType R 0 to 1600CResistance temperature detectorElectrical resistance of a conductor change with temperature. If a constant voltage is applied to the conductor then the current flowing through it will change with temperature. The main type of wire used is PLATINUM. A typical operating range is -200 to 400oC.

Strain gauges are small elements that are fixed to a surface that is strained. The change in length of the element produces changes in the electrical resistance. This is processed and converted into a voltage. A typical pressure transducer would contain a metal diaphragm which bends under pressure.Strain Gauge

Strain GaugeCapacitance SensorThe pressure produces a change in the capacitance or inductance of an electronic component in the transducer

Magnetic pickup speed sensorThese use an inductive coil placed near to the rotating body. A small magnet on the body generates a pulse every time it passes the coil.

Speed controllerSpeed Controller

Speed Controller

Speed ControllerA turbine is used to operate a mechanical load at constant speed. The speed controller (governor) senses the shaft speed and manipulates the steam supply valve to keep the speed on set point.Variations in load, caused by either shaft loading or variations in supply header pressure, affect the balance between the energy supplied to the turbine from the steam system and the work removed from the turbines shaft.

Speed controllerIf more energy is available than, the shaft will speed up. The governor will detect this increase in speed and act to reduce the energy supplied to the turbine by closing the supply valve. If the net change in the energy balance were negative, the shaft would slow down and the governor would respond by opening the supply valve.Speed Controller

Antisurge controllerSurgeSurge is defined as self oscillation of pressure and flow , often including a flow reversalEvery centrifugal or axial comp has a characteristics combination of maximum head and minimum flow beyond which it will surge. during surge there is actual reversal of flow accompanied by pressure drop

Surge effectFlow reverses in 20 to 50 milli sec.Surge cycle at a rate of .3 to 3 sec.Comp. VibratesTemperature rises.Whooshing noisetrips may occur

Operating curveQ123.MIN.STABLE FLOW POINTMAX.STABLE COMP. FLOW POINT

ABCDPdQsDevelopment of Surge cycleFlowDischarge pressureBasic anti-surge controlDISCHARGESUCT.ANTISURGE CONTROLLER PROTECT THE COMP AGAINST SURGE BY OPENING RECYCLE VALVE.THIS REDUCES RESISTANCE (BACK PRESS)THIS TAKES THE COMP.AWAY FROM SURGEThanks

System internal

diagnostic time

Fault tolerance time of the process or Process Safety Time (PST)

Fault Tolerance Time

on the corrective action

corrective action

Time for reaction of the Process

Time for

t

Failure Occurrence in the

Process or in the

Safeguarding System

Safe status of the

Process assured

Failure is

Detected