INDEX

PRESSURE MEASUREMENT Q&A
LEVEL MEASUREMENT Q&A
FLOW MEASUREMENT Q&A
TEMPERATURE MEASUREMENT Q&A
FIRE AND GAS SYSREM Q&A

1. P R E S S U R E.

PRESSURE CONVERSIONS :

1psi =	27.74 " H2O
1 Kg/cm2 =	14.223 psi
1 Bar =	14.504 psi
1 Kpa =	0.145 psi
1 Kg/cm2 =	10.000mm of H20
1 Bar =	1.0197 Kg/cm2
1 Kg/cm2 =	0.98 Bar
1 Torr =	1 mm of Hg.

Pressure: It is defined as Force per unit Area. P = F/A

Units : bar, Pascal, kg / cm², lb / in².

Que. : What is absolute pressure ?

Ans. : Absolute pressure is the total pressure present in the system

Abs. pressure = Gauge pressure + Atm. pressure.

Que. : What is absolute zero pressure ?

Ans. : Absolute zero = 760 mm Hg Vacuum.

Que. : What is the maximum Vacuum ?

Ans. : The maximum Vacuum = 760 mm Hg.

Que. : What is Vacuum ?

Ans. : Any pressure below atmospheric pressure is vacuum.

Atm = 760 mm 0 Vacuum Zero Gauge

_______________________________

' _______ Max. Vacuum 760 mm HG

Zero Absolute.

Que. : What are the primary elements for measuring pressure ?

Ans. : The primary elements used for measuring pressure are :

1. Bourdon tube.

2. Diaphragm.

3. Capsule.

4. Bellows.

5. Pressure Springs.

The above are known as elastic deformation pressure elements.

Type of Bourdon tubes.

1. ' C ' type.

2. Spiral.

3. Helix.

Diaphragm : The diaphragm is best suited for low pressure measurement.

Capsules : Two circular diaphragms are welded together to form a pressure capsule.

Material Used : phosphor bronze, Ni-spanc stainless steel.

Bellows : Bellows is a one - piece, collapsible, seamless metallic unit with deep folds formed from very tin walled tubing.

Material used : Brass, phosphor bronze, stainless steel. Used for high pressure.

PRESSURE SPRINGS : Pressure springs of helical or spiral shape used for measuring high pressures.

Que. : What is the principle of a pressure gauge ?

Ans. : Pressure works on Hooks law.

Principle : "Measuring the stores in an elastic medium"

Que. : Draw and explain a pressure gauge ? What is the used of a Hair spring ?

Ans. : The parts of a pressure gauge are :

1. 'C' type Bourdon tube.

2. Connecting link.

3. Sector gear.

4. Pinion gear.

5. Hair Spring.

6. Pointer.

7. Dial.

Uses of Hair Spring : Hair spring serves two purposes name

1. To eliminate any play into linkages.

2. It serves as a controlling torque.

Que. : How will you calibrate an absolute pressure transmitter vacuum manometer Range 0-400mm abs. ?

Ans. : The procedure for calibration is as follows :

1. Connect air supply to the transmitter.

2. Connect a test gauge of 0-1.4 Kg/cm2 to the output.

3. Connect Vacuum pump with tee off to the manometer.

4. Apply 760 mm Vacuum ( or nearest ) and adjust zero.

5. Apply 360 mm Vacuum adjust span. ( 760 - 360 = 400 mm abs. )

Que. : You are given a mercury manometer range 0 -760 mm ? A vacuum gauge reads 60 mm vacuum. The test manometer reads 50 vacuum ? Which of the two in correct.

Ans. : The transmitter is correct because 760 - 50 = 710 mm abs.

1.what are the application advantages of a dead weight tester and a gauge comparator?

Dead weight tester: Generally it is used for calibrating a test gauge. It works on the hydraulic principle, where a test gauge is compared with the standard dead weights.

Calibration procedure is laborious.

Gauge comparator: It is used for calibrating a pressure gauge against a test gauge. Calibration procedure is simple and quicker.

2.How would you select a pressure gauge for a process?

While selecting a pressure gauge for a process, consider the following points:

_ Characteristic of the process (corrosive or non-corrosive)

_ Operating pressure

_ Maximum process pressure

_ The gauge range should be a minimum of twice the process operating pressure.

3. Write the types of Bourdon tubes? Explain the purpose of different Bourdon tubes.

The following are the commonly used Bourdon tubes used in industries:

· Spiral –Low range 10 –100kpa

· C type –Medium range 100 – 5000kpa

· Helical – High range 5000 – 20000kpa

(refer to the manufacturers manuals for correct parameters)

4.What is function of a hair –spring in a pressure gauge?

Hair – spring in a pressure gage eliminates the Hysterisis (backlash/angularity) error caused in the quadrant (gear and pinion mechanism) and the weight of the pointer.

5.Name a few pressure switch manufacturing companies.

Barksdale, United electric, CCS…etc.

6.What is the output of a pressure switch?

Output of an electric switch is a contact- open or close.

Out put of a pneumatic switch is a port operation- open or close, vent

7.How would you select a pressure switch for 500kpa Hi operatin?

The following points are to be considered wile selecting a pressure switch for any process operation:

· The process operating pressure

· The maximum process pressure

· The process pipeline vibration

· The maximum working pressure of the pressure switch should be times greater then the maximum operating pressure

· The micro switch contact rating

· Process connection

· Local or remote mounting

· …etc.

8.Expain the contact selection on high and low pressure alarm switches? And explain why?

On a high pressure switch, the wiring is terminated on the “common” and the “normally close” contact terminals.

On a low pressure switch, the wiring is terminated on the “common” and the “normally open” contact terminals.

This type of contact termination is done to achieve a close contact from the switch during a normal (healthy) process condition which is a fail safe method.

9.What is to be done, if a transmitter gives a maximum output , where the transmitter range (jumper) is already in maximum selection?

Replace the capsule (sensor) for a higher range in the transmitter.

10.Explain how to carryout a field zero check on a pressure transmitter?

· If the transmitter signal is used for controlling, then put the controller on manual.

· Connect a digital multimeter in the current range in series with the transmitter output.

· Isolate the process valve

· Isolate the instrument isolation valve.

· Open the equalising valve

· Open the bleed valve and de-pressurise the transmitter.

· Check for 4.00mA output signal, if not, adjust the zero screw.

11.What-test equipment is required to calibrate a pressure transmitter in the field?

If it is a low range transmitter, then precision pneumatic test equipment like “wallace and tiernier” and pneumatic pump (or air supply) may be used.

If it is a high range transmitter, then a hydraulic pump and a test gauge is to be used.

12.What are pressure measuring/feeding test equipment?

The following are a few commonly used test equipment to measure and feed pressure: Tradinco, Wallance & tiernier, Ralston, Gauge comparator, Dead weight tester…etc.

1.what are the difference between a dead weight tester and a gauge comparator ?

Dead weight tester is used for calibrating a test gauge. It works on the hydraulic principle, where as test gauge is compared with the standard dead weights n dead weight tester.

Gauge comparator: It is used for calibrating a pressure gauge against a test gauge. Calibration procedure is simple and quicker.

2.How would you select a pressure gauge for a process?

While selecting a pressure gauge for a process, consider the following points:

#Characteristic of the process (corrosive or non-corrosive)

#Operating pressure

#Maximum process pressure

#The gauge range should be a minimum of twice the process operating pressure.

3. Write the types of Bourdon tubes? Explain the purpose of different Bourdon tubes.

The following are the commonly used Bourdon tubes used in industries:

#Spiral –Low range 10 –100kpa

#C type –Medium range 100 – 5000kpa

#Helical – High range 5000 – 20000kpa

4.What is function of a hair–spring in a pressure gauge?

Hair–spring in a pressure gauge eliminates the Hysterisis (backlash/angularity) error caused in the quadrant (gear and pinion mechanism) and the weight of the pointer.

5.Name a few pressure switch manufacturing companies.

Barksdale, United electricals, don foss, CCS…etc.

6.What is the output of a pressure switch?

Output of an electric switch is a contact- open or close.

Out put of a pneumatic switch is a port operation- open or close, vent

7.How would you select a pressure switch for 500kpa Hi operatin?

The following points are to be considered wile selecting a pressure switch for any process operation:

#The process operating pressure

#The maximum process pressure

#The process pipeline vibration

#The maximum working pressure of the pressure switch should be 2 times greater then the maximum operating pressure

#The micro switch contact rating

#Process connection

#Local or remote mounting

8.Expain the contact selection on high and low pressure alarm switches? And explain why?

On a high pressure switch, the wiring is terminated on the “common” and the “normally close” contact terminals.

On a low pressure switch, the wiring is terminated on the “common” and the “normally open” contact terminals.

This type of contact termination is done to achieve a close contact from the switch during a normal (healthy) process condition which is a fail safe method.

9.What is to be done, if a transmitter gives a maximum output , where the transmitter range (jumper) is already in maximum selection?

Replace the capsule (sensor) for a higher range in the transmitter.

10.Explain how to carryout a field zero check on a pressure transmitter?

1.If the transmitter signal is used for controlling, then put the controller on manual.

2.Connect a digital multimeter in the current range in series with the transmitter output.

3.Isolate the process valve

4.Isolate the instrument isolation valve.

5.Open the equalising valve

6.Open the bleed valve and de-pressurise the transmitter.

7.Check for 4.00mA output signal, if not, adjust the zero screw.

11.What-test equipment is required to calibrate a pressure transmitter in the field?

If it is a low range transmitter, then precision pneumatic test equipment like “wallace and tiernier” and pneumatic pump (or air supply) may be used.

If it is a high range transmitter, then a hydraulic pump and a test gauge is to be used.

12.What are pressure measuring/feeding test equipment?

The following are a few commonly used test equipment to measure and feed pressure: Tradinco, Wallance & tiernier, Ralston, Gauge comparator, Dead weight tester…etc.

2. L E V E L

Level: The height of the water column, liquid and powder etc., at the desired measurement of height between minimum level points to maximum level point is called level. The measurement principle is, head pressure method.

Units: Meters, mm, cm, percentage.

Que. : Explain the different methods of level measurement in brief ?

Ans. : There are two ways of measuring level :

( 1 ) Direct & ( 2 ) Indirect.

( 1 ) DIRECT LEVEL MEASUREMENT :

1. BOB AND TOP :

2. SIGHT GLASS : This consists of a graduated glass tube mounted on the side of the vessel. As the level of the liquid in the vessel change, so does the level of the liquid in the glass tube.

( 2 ) INDIRECT LIQUID LEVELMEASUREMENT :

1. PRESSURE GAUGE : This is the simplest method, for pressure gauge is located at the zero level of the liquid in the vessel. Any rise in level causes an increase of pressure which can be measured by a gauge.

2. PURGE SYSTEM : In this method a pipe is installed vertically with the open and at zero level. The other end of the pipe is connected to a regulated air r supply and to a pressure gauge. To make a level measurement the air supply is adjusted so that pressure is slightly higher than the pressure due to height of the liquid. This is accomplished by regulating the air pressure until bubbles cab be seen slowly leaving the open end of the pipe.

The method above are suitable for open tank applications. when a liquid is in a pressure vessel, the liquid column pressure can't be used unless the vessel pressure is balanced out. This is done through the use of different pressure meters.

DIFF.PRESSURE METHOD : Connection are made at the vessel top and bottom, and to the two columns of the D.P. meter. The top connection is made to the L.P. column of the transmitter and the bottom to H.P. column of the transmitter. The difference in pressure in the vessel is balanced out, since it is fed to both the column of the meter. The difference in pressure deducted by the meter will be due only to the changing, level of the liquid.

DISPLACER TYPE LEVEL MEASUREMENT :

The leveltrol is one of the most common instruments used measuring level in closed tanks. This instrument works of Archimedes principle. The displacer in immersed in the liquid due to which there is loss of weight depending on the specified gravity of the liquid. This displacer hangs freely on a knife transmitted to the pneumatic or electronic counterpart at the other end.

Que. : Explain how you will measure level with a different pressure transmitter.

Ans. : The bottom connection of the vessel is connected to high pressure side of the transmitter.

Different Pressure = H X D

This difference pressure is applied to H.P. side of the transmitted and calibrated.

Que. : How is D.P. transmitter applied to a close tank ?

Ans. : In close tank the bottom of the tank is connected to the high pressure side of the transmitter and top of the tank in connected to L.P. side of the transmitter. In this way the vessel pressure is balanced.

Que. : How is D.P. transmitter applied to an open tank ?

Ans. : On an open tank level measurement the L.P. side is vented to atmosphere. Whatever pressure acts is on the H.P. side which is a measure of level.

Que. : What is purge level system ?

Ans. : This method is also known as bubbler method of level measurement. A pipe is installed vertically with its open end at the zero level. The other end of the pipe is connected to a regulated air supply and to a pressure gauge or to ^P transmitter. To make a level measurement the air supply is adjusted so that pressure is slightly higher than the pressure due to the height of the liquid. This is accomplished by regulating the air pressure until bubbles can be seen slowly leaving the open end of the pipe. The gage then measures the air pressure needed to over come the pressure of the liquid.

/\ P = H X D

USE : On for corrosive liquids where the transmitter cannot be directly connected to process eg... Acids, Some organic liquids.

Que. : Explain the working of a leveltrol.

Ans. : The leveltrol is used for measuring level 0 liquids in a closed vessel.

PRINCIPLE. : It works on Archimedes principle "The loss in weight of a body immersed in a liquid is equal to amount of liquid displaced by the body". The leveltrol basically consists of the following :

DISPLACER : It is consists of a cylindrical shape pipe sealed and filled inside with sand or some weight. The purpose of this is to convert change in level to primary motion. The variation in buoyancy resulting from a change in liquid level varies the net weight of the displacer increasing or decreasing the load on the torque arm. This change is directly proportional to change in level and specific gravity of the liquid.

RELAY : Amplifies pressure variations at the nozzles.

REVERSING ARC : It is used for the following purposes.

1. Motion take of from Torque tube.

2. Means of reverse control action.

3. Adjustment for specific gravity.

PROPERTIONAL UNIT. : Converts primary motion to a proportional output air pressure.

CONTROL SETTING UNIT : Provides a motions of varying the set point.

Que. : Explain the working an electronic leveltrol.

Ans. : The variation in buoyancy resulting from a change in liquid level, varies the net weight of the displacer increasing or decreasing the load on the torque arm. This change is directly proportional to the change in level and specific gravity of the liquid. The resulting torque tube movement varies the angular motion of the rotor in the RVDT (Rotary Variable Differential. Transformer) providing a voltage change proportional to the rotor displacement, which is converted and amplified to a D.C. current.

Que. : How will you reverse an action of the leveltrol.?

Ans. : The reversing are serves as motion take off arm from the torque tube. It is provided with a slot on each side of the center so that link can be connected either for reverse or direct action.

Que. : What is interface level ? How do you calculate it ?

Ans. : When a vessel is filled with two liquids of two different specific gravities the level measurement refers to as interface level.

DP = H ( D - d )

On a level set the difference of two specific gravities.

Que. : How will you calibrate a leveltrol in the field ?

Ans. : 1. First close both the primary isolation valves and drain the liquid inside the chamber.

2. Adjust the zero to get 0% output.

3. Connect a transparent PVC tube to the drain point as shown in hook up.

4. Fill it to the center of the top flange.

5. Adjust the specific gravity or span adjustment ( Electronic Level ).

6. Fill it up to 50 %, check linearity.

5. To check linearity apply average of the two weights.

Que. : What will happen if the displacer has fallen down while in line ?

Ans. : The output will be minimum. ( wrong )

The output will be maximum (100 %) true.

Que. : What will happen if the displacer has a hole in it while in line ?

Ans. : The output will be maximum.

Que. : What is the used of Suppression and elevation ?

Ans. : Suppression and elevation are used on Level applications where (1) transmitters are not mounted on some level (2) Wet leg. i.e. condensable vapors are present.

Que. : What are the limitations of leveltrol ?

Ans. : The limitations of a level control that it cannot be used for lengths more than 72".

Que. : How will you commission D.P. transmitter in field in pressurized vessel.

Ans. : 1. Close both the isolation valves, Vent the H.P. side.

2. Fill it with the sealing liquid.

3. Open the L.P. side vent valve.

4. Adjust zero with suppression spring.

5. Close the L.P. side vent valve.

6. Open both the isolation valves.

Que. : How will you check zero of a level D.P. transmitter while is line ?

Ans. : 1. Close both the isolation valves.

2. Open the vent valve on L.P. leg and H.P. leg drain.

3. Check and adjust zero if necessary.

Que. : Explain the working of an Enraf level gauge ?

Ans. : The Enraf level precise level gauges are based on servo powered null balance technique. A displacer serves as continuos level sensing element.

Principle :

A displacer A with a relative density higher than that of a product to be measured, is suspended from a stainless steal wire B tat is attached to a measuring drum. A two phase servo motor controlled by a capacitive balance system winds unwinds the measuring wire until the tension on the weight springs is in balance with the wt. of the displace part immersed in the liquid. The sensing system in principle measures the two capacitance formed by the moving central sensing rod E provided with two capacitor plates and the si plates. In balance position the capacitance are of equip value. A level variation will cause a difference in buoyancy of the displacer. The center sensing rod will move in to direction of one of the side capacitor plates. This causes difference in value of this capacitance. By an electrolyte rotation of the servo motors the can driven transmitter continuously change the voltage pattern to remote indicate of which the receiver motor drives a counter indicating low variation.

h= height of the liquid column

2.What are the simple methods for measuring level?

Gauge glass, Pressure Gauge – scale graduated in % of level, Rope and weight , Dip Tape…etc

3.How to convert a pressure gauge into a level gauge?

Calculate the static head in kpa using the formula “pgh”. Select a pressure gauge and calibrate it for the calculated static head. Graduate the pressure gauge scale in terms of %of level.

4.What is the density of crude oil?

The density of crude oil is approximately 0.8.

5.What is an “interface dip tape”? Where it used?

Interface dip tape is an instrument used for measuring the total and the interface liquid level in vessel.

For example: It is used in oil storage tanks to measure the total liquid level and water level.

6.Explain how a Leveltrol works? Name the parts of a pneumatic Leveltrol.

A Leveltrol in and instrument used for measuring the liquid level between two known points. The Leveltrol works on the buoyancy principal. Leveltrol has a float, which submerses proportionately with liquid level raise in the float chamber. The amount of submersion of the displacer depends on the liquid density, which produces a torque. The amount of torque produced in measured in terms of % of level.

Parts of Leveltrol:

Float chamber, Float, Torque lever, Knife edge, Feedback Bellows, Air Relay, Restriction, Flapper, Nozzle, Feedback link, Density range, Action change lever, HP and LP flange,

7.What is a static head level transmitter?

A static head level transmitter is used for measuring the total liquid level in the tank.

8.What are the application limits of a Leveltrol and a static head level transmitter?

A Leveltrol can measure only for a short and fixed height of level. A Leveltrol has a high gain output. In can be used for liquid level as well for the interface level measurement.

Static head transmitter is used for measuring the total liquid level in the tank. The transmitter output is linear.

9.What is the operating principle of a Magnetrol level switch?

The Magnetrol level switch works on the principle of Buoyancy force.

10.What are the points to consider while selecting a level switch for a particular process?

While selecting a level switch, the following points are to be considered:

· The characteristic of process (corrosive or non – corrosive)

· The process pressure

· The liquid density

· The flange ratings

· Proof pressure of the switch

· The micro switch contact rating

11.What type of level measuring instrument is suitable for closed tank?

If the level measurement is required for a fixed and small height, a Leveltrol is more suitable.

If it is for a total height, then either a static head or a differential pressure transmitter with its HP leg connected to the bottom of the liquid level and the LP leg connected to the top of the tank to gas phase.

12.What is Zero suppression and Zero elevation in level measurement?

Zero suppression: when a static head transmitter is installed below the zero liquid level, the transmitter gets a +ve error in the level measurement. This error is corrected by a zero suppression kit.

Zero elevation: when a static head transmitter is installed above the zero liquid level, the transmitter gets a –ve error in the level measurement. The error is corrected by a zero elevation kit.

13.What is an interface in level measurement?

An interface is the separation point between the two de-missible liquids levels In a vessel. This condition arises when the liquid does not mix due to its chemical composition and difference in their density.

14.How to calibrate a leveltrol for an interface level measurement?

Fill the leveltrol chamber 100% with the lower density liquid and adjust its zero for 4.00mA output.

Drain the liquid and fill the leveltrol chamber 100% with the higher density liquid and adjust its span for 20.00 mA output.

The transmitter on line measures the percentage of higher density liquid in the lower density liquid at a known height.

15.How to calibrate a static head level transmitter for an interface measurement?

Static head level transmitter is not commonly used for measuring the interface level. But the following procedure may be used for calibrating it to measure the interface level in a tank.

Fill the vessel 100% with the lower density liquid and adjusts its zero for 4.00 mA output. Drain the liquid and fill with the vessel 100% with the higher density liquid and adjust its span for 20.00mA output. 100% transmitter level is to be continuously maintained.

The transmitter on line measures the percentage of higher density liquid in the lower density liquid in a know height.

16.Why is a leveltrol more suitable tan a static head level transmitter on a separator?

Leveltrol is more accurate in measuring the small height of liquid level. The process pressure change does not affect the leveltrols performance. Leveltrol offers a high gain output verses the change in the liquid level.

17.Why is static head level transmitter more suitable than a leveltrol on a surge tank?

A leveltrol has a limitation in measuring the maximum height of liquid. Considering huge of the surge tank, a static head level transmitter is more suitable.

18. Why is a gap controller often used in controlling a level in a high pressure vessel?

Gap controllers output changes from minimum to maximum and visa versa when the process measurement deviates the setpoint by the set gap. Hence the final control element i.e. control valve acts like an on-off valve. This helps in minimizing the trim erosion due to a high DP across the control valve while partially open.

19. How to use a DP (differential pressure) transmitter for level measurement?

A differential pressure transmitter gives a linear output for the differential pressure measured across its HP and LP chambers.

Connect the transmitter’s HP leg to the bottom of the tank and its LP leg to the top of the tank. The transmitter will read the liquid level accurately irrespective of the change in process pressure above the liquid surface.

Indirect level measurement:

(A) Pressure gauge:

This is the simplest method, for pressure gauge is located at the zero level of the liquid in the vessel. Any rise in level causes an increase of pressure which can be measured by a gauge.

(b) Purge system:

In this method a pipe is installed vertically with the open and at zero level. The other end of the pipe is connected to a regulated air r supply and to a pressure gauge. To make a level measurement the air supply is adjusted so that pressure is slightly higher than the pressure due to height of the liquid. This is accomplished by regulating the air pressure until bubbles cab be seen slowly leaving the open end of the pipe.

The air pressure to the bubbler pipe is minutely in Excess of the liquid pressure in the vessel, so that Air pressure indicated is a measure of the level in The tank.

The method above is suitable for open tank applications. When a liquid is in a pressure vessel, the liquid column pressure can't be used unless the vessel pressure is balanced out. This is done through the use of different pressure meters.

Connections are made at the vessel top and bottom, and to the two columns of the D.P. meter. The top connection is made to the L.P. column of the transmitter and the bottom to H.P. column of the transmitter. The difference in pressure in the vessel is balanced out, since it is fed to both the column of the meter. The difference in pressure deducted by the meter will be due only to the changing, level of the liquid.

(d) Displacer type level measurement:

30. Explain how you will measure level with a different pressure transmitter.

The bottom connection of the vessel is connected to high pressure side of the transmitter.

Different Pressure = H X D

This difference pressure is applied to H.P. side of the transmitted and calibrated.

31. How is D.P. transmitter applied to a close tank?

In close tank the bottom of the tank is connected to the high pressure side of the transmitter and top of the tank in connected to L.P. side of the transmitter. In this way the vessel pressure is balanced.

32. How is D.P. transmitter applied to an open tank?

On an open tank level measurement the L.P. side is vented to atmosphere. Whatever pressure acts is on the H.P. side which is a measure of level.

SPAN = (X) (Sp. Graf)
ZERO SUPPRESSION = (Y) (Sp.Grav)

33. How is D.P transmitter applied to a close tank & open tank with Dry leg?

Span = (X) (GL₎

H_W at minimum level = ( Z ) ( G_S ) + ( Y ) ( G_L )

H_W at maximum level = ( Z ) ( G_S ) + ( X + Y ) ( G_L )

Where:

G_L= Specific gravity of tank liquid.

G_{S =} Specific gravity of seal liquid.

H_W = Equivalent head of water.

X, Y & Z are shown in fig (1.1)

Example:

Open tank with X = 300 inches

Y = 50 inches

Z = 10 inches

G_L = 0.8

G_S = 0.9

Span = (300) (0.8) = 240 inches

H_W at minimum level = ( 10 ) ( 0.9 ) + ( 50 ) ( 0.8 ) = 49 inches

H_W at maximum level = (10 ) ( 0.9 ) + ( 50 + 300 ) ( 0.8 ) = 289 inches

Calibrated range = 49 to 289 inches head of water

2.3 DEFINITION OF INSTRUMENT RANGE AND SPAN

Legend:

Range Defined in IEC 60902 as follows: The region of values between the lower and upper limits of the quantity under consideration.
It is expressed by stating the lower and upper limits (e.g. minus 1 to 10 bars (ga)).

Span Defined in IEC 60902 as follows: The algebraic difference between the upper and lower limit values of a given range.
It is expressed as a figure and unit of measurement (e.g. 8 bars).

LRL Lower Range Limit; the lowest quantity that a device is designed to measure.

URL Upper Range Limit; the highest quantity that a device is designed to measure.

Instrument range the region in which the instrument is designed to operate. It is a physical capability of the device. The region limits are expressed by stating the LRL and URL.

Instrument minimum span the minimum distance between the URV and LRV for which the instrument is designed. It is a physical limitation of the device.

Instrument maximum span The maximum distance between the URV and LRV for which the instrument is designed. It is a physical limitation of the device.

LRV Lower Range Value; the lowest quantity that a device is adjusted to measure.

URV Upper Range Value; the highest quantity that a device is adjusted to measure.

Adjusted range The measurement region. It is expressed by stating the LRV and URV.

Adjusted span The distance between the URV and LRV.

Example: A differential pressure transmitter is used to measure the level in a vessel, using a wet reference leg. 0% level corresponds with a differential pressure of -800 mbar and 100% level with - 100 mbar. The catalogue of the selected transmitter lists -1800/+1800 mbar for LRL/URL respectively and span limits of 300 to 1800 mbar, so:

Instrument range	=	-1800 to +1800 mbar
Instrument minimum/maximum span	=	300 / 1800 mbar respectively;
LRV / URV	=	-800 / -100 mbar respectively;
Adjusted range	=	-800 to -100 mbar.
Adjusted span	=	700 mbar.

NOTE: ‘Adjusted’ range and ‘adjusted’ span are frequently referred to as ‘calibrated’ range and ‘calibrated’ span. This term is however only correct, if a calibration facility is used to set the LRV and URV. For ‘intelligent’ measuring devices, the supplier is usually calibrating the device at the LRL/URL and the user is setting the required LRV and URV by remote communication.

2.4 SELECTION OF RANGES

The accuracy (2.8) and adjusted range of an instrument should be selected to cover the operating window (2.1), which includes applicable abnormal operation and alternative operating modes. Unless otherwise stated, the normal design value should lie between 50% and 75% of the adjusted range

NOTE: For certain applications it might not be possible to combine all normal and abnormal operating conditions in one measurement at the required accuracy. In such cases, a case-by-case analysis should disclose whether additional instruments are required or the accuracy requirements and/or operating window may be relaxed. It might be acceptable to present measured values during some of the abnormal operating cases at a lower accuracy or it might be justifiable for the measurement not to produce a sensible signal under some of the abnormal process conditions during start-up, commissioning, regeneration, emergency conditions and the like.

IPF transmitters should have the same instrument range, adjusted range and accuracy as corresponding process transmitters in order to facilitate measurement comparison. For details and exceptions, see DEP 32.80.10.10‑Gen. Trip settings should lie between 10% and 90% of the adjusted range.

The LRV should be selected so that the displayed result represents the zero or sub-zero value of the process variable (e.g. 0-150 tons/day, 0-100% level, 0-10 bar (ga), -1/+3 bar (ga), 0‑500 °C, -50/+50 °C etc.). Elevated zero’s (100-300 tons/day, 100-200 °C) should be avoided.

Close tank with wet leg:

Span = (X) (GL₎

H_W at minimum level = ( Y ) ( G_L) – ( d )( G_S)

H_W at maximum level = ( X + Y ) ( G_L) – ( d ) ( G_S)

Where: G_L = Specific gravity of tank liquid

G_S = Specific gravity of tank liquid

H_W= Equivalent head of water

X, Y and Z are shown in fig.

Example :

X = 300 inches

Y = 50 inches

d = 500 inches

G_L = 0.8

G_S = 0.9

Span = ( 300 ) ( 0.8 ) = 240 inches

H_W minimum level = ( 50 ) ( 0.8 ) - ( 500 ) ( 0.9 ) = - 410 inches

H_W maximum level = ( 300 + 50 ) ( 0.8 ) – ( 500 ) ( 0.9 ) = - 170 inches

Calibrated range = - 410 to –170 inches head of water.

( minus sings indicate that the higher pressure is applied to the low pressure side of the transmitter )

34. What is purge level system?

This method is also known as bubbler method of level measurement. A pipe is installed vertically with its open end at the zero level. The other end of the pipe is connected to a regulated air supply and to a pressure gauge or to ^P transmitter. To make a level measurement the air supply is adjusted so that pressure is slightly higher than the pressure due to the height of the liquid. This is accomplished by regulating the air pressure until bubbles can be seen slowly leaving the open end of the pipe. The gage then measures the air pressure needed to over come the pressure of the liquid.

/\ P = H X D

USE: On for corrosive liquids where the transmitter cannot be directly connected to process eg... Acids, Some organic liquids.

35. Explain the working of a leveltrol.

The leveltrol is used for measuring level of liquids in a closed vessel.

1. PRINCIPLE. : It works on Archimedes principle "The loss in weight of a body immersed in a liquid is equal to amount of liquid displaced by the body". The leveltrol basically consists of the following :

2. DISPLACER: It is consists of a cylindrical shape pipe sealed and filled inside with sand or some weight. The purpose of this is to convert change in level to primary motion. The variation in buoyancy resulting from a change in liquid level varies the net weight of the displacer increasing or decreasing the load on the torque arm. This change is directly proportional to change in level and specific gravity of the liquid.

3. RELAY: Amplifies pressure variations at the nozzles.

4. REVERSING ARC: It is used for the following purposes.

· Motions take of from Torque tube.

· Means of reverse control action.

· Adjustment for specific gravity.

5. PROPERTIONAL UNIT. : Converts primary motion to a proportional output air pressure.

6. CONTROL SETTING UNIT: Provides motions of varying the set point.

36. Explain the working an electronic leveltrol.

The variation in buoyancy resulting from a change in liquid level, varies the net weight of the displacer increasing or decreasing the load on the torque arm. This change is directly proportional to the change in level and specific gravity of the liquid. The resulting torque tube movement varies the angular motion of the rotor in the RVDT (Rotary Variable Differential. Transformer) providing a voltage change proportional to the rotor displacement, which is converted and amplified to a D.C. current.

37. How will you reverse an action of the leveltrol?

The reversing are serves as motion take off arm from the torque tube. It is provided with a slot on each side of the center so that link can be connected either for reverse or direct action.

38. What is interface level? How do you calculate it?

When a vessel is filled with two liquids of two different specific gravities the level measurement refers to as interface level.

DP = H (D - d)

On a level set the difference of two specific gravities.

39. How will you calibrate a leveltrol in the field?

Calculation # 1 If the calibrating liquid is water: Process Liquid Density / 1* Displacer height = mm of H2O.

Calculation # 2 If the calibrating liquid is other liquid: Process Liquid Density / Calibrating liquid density * Displacer height = mm of H2O. (Calibrating liquid height in mm).

1. First close both the primary isolation valves and drain the liquid inside the chamber.

2. Adjust the zero to get 0% output.

3. Connect a transparent PVC tube to the drain point as shown in hook up.

4. Fill it to the center of the top flange.

5. Adjust the specific gravity or span adjustment (Electronic Level).

6. Fill it up to 50 %, check linearity.

40. How will you calibrate on interface level control. ?

On an interface leveltrol there are two liquid of two different specific gravities.

1. The level will be zero when it is full of lighter liquid.

Zero % level = H X d.

H = Displacer length

d = Specific gravity of lighter liquid.

2 The level will be 100 % when it is full of heavier liquid.

100 % level = H X D.

D = Specific gravity of heavier liquid.

Calibration with water:

1. Fill H X d level with water adjust zero.

2. Fill H X D level with water adjust Sp. gravity or span.

3. Check linearity.


	Y= L* (DH X + (1- X ) * dl) ------- ------ 100 100

Displacer length: L in mm

Density Low : dl in Kg / 1

Density High : DH in Kg / 1

Alarm / Trip point %: X

HH Trip Point: Y in mm

41. How will you apply wt. lest calibration to a leveltrol.

Wt. test calibration method:

Remove the displacer from the torque arm.
Apply equivalent weight on the torque arm that is equal to the wt. of the displacer. Adjust zero % output.
For Span : V = πr²h

Loss in weight = Wt. of float - wt. of the float immersed in liquid

Loss in weight = [ wt. of float - Vol. x d ]

Span wt. = (wt. of float - Loss in wt.)

r = radius of the displacer.

h = ht. of displacer.

Apply equivalent wt. equal to the (Wt. of float - Loss in weight). Adjust Span to get 100 % out put.
To check linearity apply average of the two weights.

42. What will happen if the displacer has fallen down while in line ?

The output will be maximum.

43. What will happen if the displacer has a hole in it while in line?

The output will be minimum.

44. What is the used of Suppression and elevation?

Suppression and elevation are used on Level applications where (1) transmitters are not mounted on some level (2) Wet leg. I.e. condensable vapors are present.

45. What are the limitations of leveltrol?

The limitations of a level control that it cannot be used for lengths more than 72 inches.

46. How will you commission D.P. transmitter in field in pressurized vessel.

1. Close both the isolation valves, Vent the H.P. side.

2. Fill it with the sealing liquid.

3. Open the L.P. side vent valve.

4. Adjust zero with suppression spring.

5. Close the L.P. side vent valve.

6. Open both the isolation valves.

47. How will you check zero of a level D.P. transmitter while is line?

1. Close both the isolation valves.

2. Open the vent valve on L.P. leg and H.P. leg drain.

3. Check and adjust zero if necessary.

48. Explain the working of an Enraf level gauge?

The Enraf precise level gauge are based on servo powered null-balance technique. A displacer serves as a continuous level sensing element.

Principle:

A displacer with a relative density higher than that of the product to be measured, is suspended from a stainless steel wire B, that is attached to a measuring drum. A two phase servo meter controlled by a capacitive balance system winds or unwinds the measuring wire until the tension in the weighing springs is in balance with the weight of the displacer partly immersed in the liquid. The sensing system in principle measures the two capacitance formed by the moving center sensing rod E provided with two capacitor plates and the side plates. In balance position the capacitances are of equal value. A level variation will a difference in buoyancy of the displacer. The center sensing rod will move in the direction of one of the side capacitor plates. This causes a difference in value of these capacitances. By an electronic circuit this change is detected and integrated. During the rotation of the servo motor the cam driven transmitter continuously change the voltage pattern to a remote indicator of which the receiver motor drives a counter indicating level variation.

1. What is ;’cold junction compensation’?

‘Cold Junction Compensation’ is used in temperature measurement by means of a thermocouple. This compensation is to correct the error caused by the room (ambient) temperature. The mv produced by a thermocouple is proportional to the temperature difference between its ‘hot’ and ‘ Cold’ junction. The cold junction is the ambient temperature (control room). Without ‘cold junction compensation’ the temperature at the hot junction will measure inaccurately.

2. What is an RTD? How does it work?

RDT – Resistance Temperature Detector

RTD is a positive temperature coefficient resistance which provides a linear rise in its resistance verses the rise in temperature.

3. What is the commonly used RTD in P.D.O.?

Pt 100 platinum resistance 100 Ohms

12. What is ‘pt 100’? What is the resistance (in ohms) of a pt100 at 0 Deg C?

Pt 100 Platinum resistance which offers 100 ohms at 0 Deg C.

13. What are the advantages and disadvantages of an RTD over a thermocouple?

RTDs are accurate at a lower range of temperature measurement such as -200 Deg C to +200 Deg C.

RTDs are expensive compared to Thermocouples, also there are limitations in measuring at the higher range of temperature.

14. Why does RTD measurement use 3 wires for a field signal connection?

3 wire system is used in temperature measurement by an RTD to compensate the line resistance. Three wire system provides a Wheatstone Bridge in the measuring instrument.

15. What is a ‘bi metallic’ temperature instrument? How does it work? Give an example?

In a bi metallic temperature instrument, two metals with different temperature coefficient of expansion are attached together. Due to its expansion characteristics the higher coefficient of expansion responds more than the lower one and a twist on the element is formed. This principle is ;used in designing temperature measuring instrument for the lower range.

Other than the filled type instruments, most of the temperature indicators are of the bimetallic types.

16. What is a ‘filled type’ temperature instrument? Give an example?

Principle of change in the liquid expansion with the change in temperature is used in designing the ‘filled type’ temperature measuring instrument.

For example : The glass thermometers, filled type capillary temperature dial indicators and switches.

Filled type temperature measuring instruments are used for lower range temperature measurement.

17.Name the instruments used to measure temperature?

1.precision glass thermometers

2.RTD with a resistance measuring instrument in terms of Deg C or Deg F.

3.Thermocouple with a mv measuring instrument in terms of Deg C or Deg F.

5. FIRE & GAS SYSTEM

Fire detection system

1.What is a ‘fire triangle’?

A fire triangle represents the three elements, which causes a fire in a combustible mixture. The three elements are fuel, air and ignition.

2.What is importance or a ‘hood’ on a gas turbine?

During a gas turbine normal running condition, a hood provides:

· prevention of turbine high dB noise to outside areas

· keeps the gas turbine clean from external dust

· provides a draft for the gas leak to the exhaust through the hood fan

During a gas turbine shutdown condition a hood provides:

· cooling the turbine body by way of the hood fan

· During a fire shutdown it facilitates to put out the fire by confining the fire extinguishers on the gas turbine.

3.Why do we use ‘Halon’ as a fire extinguisher in a gas turbine hood?

Halon is stored in liquid form in a cylinder. When it is released in a hood during the occurrence of the fire, it discharges the halon in gas from. Halon does not act or react on electrical components.

4.What is the expansion from of B.C.F?

The expansion form of B.F.C is Bromo chloro floride.

5.In a Ruston gas turbine, why are there two Halon cylinders in each bank? How do they function?

The first bottle is the ‘first shot’ and the second bottle is ‘Extended shot’. The first bottle discharges the Galon into the hood through a 1’’ pipe in approximately 15 seconds, where as the extended bottle discharges the Halon through a ¼’’ pipe for another ½’’hour period to maintain the inert atmosphere.

6.How many UV detectors are installed in Solar, Ruston TB-5000 and Ruston TA-1750 gas turbine hoods?

Solar gas turbine hood: 4 UV detectors

Ruston TA-1750 hood: 4 UV detectors

Ruston TB 5000 hood: 12UV detectors

7.What is voting Logic of UV detectors in Soar and Ruston gas turbines?

There are two voting logics, they are: 1 out of 4 UV s and 2 out of 4 UV s

8.What happens when UV detectors detect a fire?

1out of 4 UV s: creates annunciation, audible alarm on the control panel and siren in the field (refer to the station drawings for the exact function and operations).

2 out of 4 UV s: creates annunciation, audible alarm on the control panel, a siren in the field, shutdown of the turbine and release of the fire extinguisher (refer to the station drawings for the exact function and operations).

9.How much is the time delay between fire sensing by a UV detector and confirming with an alarm?

Generally it is set for 4 secs. The UV detectors initiates a fire alarm only when the UV is detecting the fire continuously for 4 secs (refer to the station drawings for the exact settings parameters).

10.What are the Halon manual release facilities available on a Solar gas turbine?

Auto Halon cylinder can be discharged manually from the fire & gas control panel in the control room. On instiating the manual release:

· The unit shuts down.

· The auto Helon cylinder gets discharged in the hood.

· Auto halon discharge confirmation and the auto Halon cylinder pressure low alarm appears on the control panel.

· Audible alarm in the control room and siren in the field occurs.

Manual Halon cylinder can discharged manually from the field through a pall string. On initiating the manual release:

· The unit shutsdown.

· The manual Halon cylinder gets discharged in the hood.

· Manual Halon discharge confirmation and the manual Halon cylinder pressure low alarm appears on the control panel.

· Audible alarm in the control room and siren in the field occurs.

11.Why are there ‘heat switches’ in side the hood, when there are UV detectors?

Heat switches are a mechanical type and they are considered to be a positive type of fire detection system. The heat switch settings are much higher than the hood temperature.

12.What maybe the reasons if a unit shutdown on false heat detected alarm?

The reason could be:

· Hood ventilation fan has failed or stopped.

· Major hot gas leak inside the hood.

13.What happens when a heat switch actuates?

On detection of heat, the heat switch initiates the following.

Annunciation, audible alarm on the control panel, a siren in the field, shut down of the turbine and release of fire extinguisher (refer to the station drawings for the exact settings parameters).

14.Wxplain the operating principle of a gas monitor?

Gas monitor measures the imbalance in the current loop caused by its active and in-active filaments in the presence of a combustible gas.

15.Explain the calibration procedure of a gas monitor system.

· Gas sensor loop current or voltage at the sensor head is set as per the manufacturer’s recommended value.

· Gas monitor zero is adjusted to the instrument air.

· A test gas with a known quantity of combustion gas (Generally methane 2% by volume) is fed to the sensor and the span is adjusted to read 40% on the monitor scale (refer to the station drawings for the exact settings parameters).

· The calibration procedure is repeated until the zero and span reads correctly.

16.What are the alarm and shut down setting on a gas monitor?

Generally on the gas monitor, the alarm is set at 20%rising and the shut down is set at 60%rising (refer to the station drawing for the exact settings parameters)

17.What has to be done prior to entering a gas turbine hood?

Prior to entering a gas turbine, turn on the ‘ventilation defeat switch’.

18.What is a ventilation defeat switch?

On activating, the ventilation defeat switch inhibits the release of Halon in the auto mode and also the unit shutdown on ‘ventilation failure’.

19.How much is the delay between fire detection and Halon release? Why is the time delay required?

A time delay of 15 secs. Is set between the detection of fire and the initiation of Halon release. This is to achieve effective fire extinguishing by allowing the hood fan to run-down to zero speed and the bleed valves to release the compressed air.

20.What does a hood ventilation fan do when a fire is detected? And why?

On detection of fire, the fire system initiates the hood fan shutdown. This is to minimize the presence of air the hood for releasing the extinguisher.

Gas detection system

1.What is a ‘combustible gas mixture’?

Combustible gas mixture is the proper ration of fuel and air within the ignition limits.

2.Explain the operating principle of a gas detection system.

Gas detection system measures the imbalance in the current loop caused by its active and in-active filaments in the presence of a combustible gas.

3.Why is gas detection as important as fire detection?

Presence of combustible gas Is the first stage of a possible occurrence of a fire.

4.What are the components used in a gas detection loop?

A gas sensor, 3 wire system and a gas monitor.

5.What is a ‘flame arrester’ in a gas sensor? What does it do?

Flame arrester is used on the sensors head. The sensors are continuously powered to burn the combustible gas for measuring. The flame arrester prevents the occurrence of fire outside the sensor.

6.What are the name of the filaments inside the gas sensor?

There are two filaments. They are called ‘active’ and ‘non-active’ filaments.

7.How much approximately is the resistance of a gas sensors filament?

From manufacturer to manufacture the sensor resistance varies. It is approximately 3 ohms on each of the filament (refer to the station drawings for the exact parameters).

8.How to check a gas monitor without test gas?

Some gas monitors are provided with a self test facility to check its alarm and shutdown functions(levels).

9.Why is a three wire system used on the sensors?

The three-wire system is used to compensate the line resistance. The active and non-active filament loop form a whetstone bridge in the gas monitor. The amount of unbalance in the current loop during the occurrence of combustible gas is detected as the percentage of combustible gas.

10.What are the types (manufacturer) of gas monitor systems used in P.D.O.?

The commonly use gas monitor systems are:

1. General monitor

2. Seiger monitor

3. Detection instruments

11.What is test gas used to calibrate a gas monitor?

Methane gas is used for calibrating a gas monitor.

12.How much is the gas concentration in the test gas cylinder?

Generally methane 2% by volume is used as a test gas to calibrate a gas monitor.

13.What is the important factor set on a gas monitor loop?

Depending on the manufacturer, either it is the loop current or the voltage at the sensor head which has to be set precisely for better accuracy and sensitivity.

14.why is it that Halon is not released on a high gas shutdown alarm in a gas turbine hood?

Halon (fire extinguishing agent) is not released on detection of combustible gas because the presence of gas is not a fire.

15.Why are there gas sensors on the combustion air intake of Ruston TB-5000gas turbines?

The presence of combustible gas in the air intake may result in the failure of stopping the gas turbine during a shutdown, due to the fuel and air mixture continuously available to the turbine.

Smoke detection system

1.What are the types of ‘smoke detectors’ in use in P.D.O.?

Two types of smoke detectors are used in PDO. They are:

1. Optical type, 2. Radioactive type, 3. Ionisation type.

2.Explain the operating principle of the different types of smoke detectors.

Optical type: when the smoke cuts the optical detection path, and unbalance in the detector current loop raises a smoke alarm. These type detectors are sensitive to larger particles of combustion 0.5 to 10 microns. It is suitable for applications where thermal turbulence can be expected.

Radio active type: when the smoke is detected by the radio active substance, the unbalance in the detector current loop raises a smoke alarm. This type of detectors are sensitive to air movement greater than 5m/sec. It is normally installed with the photoelectric (optical type) type smoke detectors.

3.Why is a smok4e detector as important as a ‘heat switch’ and ‘UV detector’?

Smoke detectors are used in confined areas such as control rooms and electrical switch rooms.

4.Where are smoke detectors generally installed in P.D.O.?

Smoke detectors are used in confined areas such as control rooms and electrical switch rooms.

5.What happens when a smoke detector detects smoke?

When a smoke detector detects smoke, the detector loop current changes. The unbalance in the loop current is detected as smoke.

Once in every 10 secs the L.E.D on each smoke detector blinks as self loop check. On detection of smoke, this L.E.D remains continuous on (bright).

6.name the manufacturers of smoke detection systems.

Name of the smoke detector manufactures are Firecheta, Cloride Gent…etc.

7.why are periodic checks and maintenance required on smoke detection system?

Particularly on the optical type smoke detectors, the collection of dust in the sensor path may result in a false alarm. Also the periodic maintenance ensures the reliability of the detection system.

8.What are the common problems faced when maintaining a smoke detection system?

· False alarm due to accumulation of dust, floor cleaning, water vapour

· Loose connection results in the fluctuation of the detector loop current.

Improper base plug-in connection.

1.What is a ‘combustible gas mixture’?

Combustible gas mixture is the proper ration of fuel and air within the ignition limits.

2.Explain the operating principle of a gas detection system.

Gas detection system measures the imbalance in the current loop caused by its active and in-active filaments in the presence of a combustible gas.

3.Why is gas detection as important as fire detection?

Presence of combustible gas Is the first stage of a possible occurrence of a fire.

4.What are the components used in a gas detection loop?

A gas sensor, 3 wire system and a gas monitor.

5.What is a ‘flame arrester’ in a gas sensor? What does it do?

Flame arrester is used on the sensors head. The sensors are continuously powered to burn the combustible gas for measuring. The flame arrester prevents the occurrence of fire outside the sensor.

6.What are the name of the filaments inside the gas sensor?

There are two filaments. They are called ‘active’ and ‘non-active’ filaments.

7.How much approximately is the resistance of a gas sensors filament?

From manufacturer to manufacture the sensor resistance varies. It is approximately 3 ohms on each of the filament (refer to the station drawings for the exact parameters).

8.How to check a gas monitor without test gas?

Some gas monitors are provided with a self test facility to check its alarm and shutdown functions(levels).

9.Why is a three wire system used on the sensors?

10.What are the types (manufacturer) of gas monitor systems used in P.D.O.?

The commonly use gas monitor systems are:

1. General monitor

2. Seiger monitor

3. Detection instruments

11.What is test gas used to calibrate a gas monitor?

Methane gas is used for calibrating a gas monitor.

12.How much is the gas concentration in the test gas cylinder?

Generally methane 2% by volume is used as a test gas to calibrate a gas monitor.

13.What is the important factor set on a gas monitor loop?

Depending on the manufacturer, either it is the loop current or the voltage at the sensor head which has to be set precisely for better accuracy and sensitivity.

14.why is it that Halon is not released on a high gas shutdown alarm in a gas turbine hood?

Halon (fire extinguishing agent) is not released on detection of combustible gas because the presence of gas is not a fire.

15.Why are there gas sensors on the combustion air intake of Ruston TB-5000gas turbines?

The presence of combustible gas in the air intake may result in the failure of stopping the gas turbine during a shutdown, due to the fuel and air mixture continuously available to the turbine.

16.Explain the calibration procedure of a gas monitor system.

Gas sensor loop current or voltage at the sensor head is set as per the manufacturer’s recommended value.

Gas monitor zero is adjusted to the instrument air.

A test gas with a known quantity of combustion gas (Generally methane 2% by volume) is fed to the sensor and the span is adjusted to read 40% on the monitor scale.The calibration procedure is repeated until the zero and span reads correctly.

17.What are the alarm and shut down setting on a gas monitor?

Generally on the gas monitor, the alarm is set at 20%rising and the shut down is set at 60%rising (refer to the station drawing for the exact settings parameters)

Top Smoke detection system Top

1.What are the types of ‘smoke detectors’ in use in P.D.O.?

Two types of smoke detectors are used in PDO. They are:

1. Optical type, 2. Radioactive type, 3. Ionisation type.

2.Explain the operating principle of the different types of smoke detectors.

3.Why is a smok detector as important as a ‘heat switch’ and ‘UV detector’?

Smoke detectors are used in confined areas such as control rooms and electrical switch rooms.

4.Where are smoke detectors generally installed in P.D.O.?

Smoke detectors are used in confined areas such as control rooms and electrical switch rooms.

6.name the manufacturers of smoke detection systems.

Name of the smoke detector manufactures are Firecheta, Cloride Gent…etc.

7.why are periodic checks and maintenance required on smoke detection system?

Particularly on the optical type smoke detectors, the collection of dust in the sensor path may result in a false alarm. Also the periodic maintenance ensures the reliability of the detection system.

8.What are the common problems faced when maintaining a smoke detection system?

False alarm due to accumulation of dust, floor cleaning, water vapour

Loose connection results in the fluctuation of the detector loop current.

Improper base plug-in connection.