Interview Questions on Gas detection system
https://instrumentationtools.blogspot.com/2015/05/interview-questions-on-gas-detection-system.html
1.What is a ‘combustible gas mixture’?
Combustible
gas mixture is the proper ration of fuel and air within the ignition limits.
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| Gas detection system |
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:
General
monitor
Seiger
monitor
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
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.
