Interview Questions on Flow Measurement
https://instrumentationtools.blogspot.com/2015/05/interview-questions-on-flow-measurement.html
1.What is ‘volumetric’ and
‘rate of flow’? Write their measuring units in metric.
Volumetric Flow: The total amount of fluid passed through a process line. Generally
it is measured on counters. The measuring unit is cubic meter, Barrels…etc.
Rate of flow: The amount of fluid moving through a process line per period of
time. Generally it is measured on indicators, recorders. The measuring uit is
cubic meter per day, barrels per day…etc.
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| Interview Questions on Flow Measurement |
2.What are the types of
flow; measuring instruments used in industries?
Orifice plate and a DP transmitter,
Daniel orifice and DP transmitter, Rotameter, Dall Tube, Venturi Tube, PD
meters…etc.
3.What are the types of
flow measurements commonly used in DPU-A?
Orifice plate and a DP transmitter,
Daniel Orifice and a DP Transmitter, Rotameter, PD meters.
4.What is ‘Burnollious
Theorem’? What does it explain?
It explains that when there is a
restriction line a fluid flow line a ‘DP’ (differential pressure) is created.
The DP is maximum at the veena contract point. The flow measured in the flow
line is proportional to the square root of the DP measured where ‘K’ is a
constant.
Q=
k 6(sq root of (DP))
5.What is the function of
an orifice plate in flow measurement?
An orifice plate creates a differential
pressure in a flow line. The DP created is use for measuring the flow through
the process line.
6. How much maximum and minimum
orifice ‘d’ (orifice diameter) id permitted in a pipeline?
0.25
D<d<0.75 D
‘d’ – the Orifice diameter should be
in-between 0.25 and 0.75 of the pipeline ‘D’ diameter.
7.What is the difference
between an orifice plate used in oil and gas flow measurement?
The orifice plate used in a gas line
will be having a smal drain whole at the bottom of the orifice plate.
8.Draw a simple sketch of an
orifice plate showing it’s upstream, downstream and the shamper edge.
9.How to identify a newly
installed orifice plate upstream in a pipeline?
The upstream can be identified by the
orifice plate’s Tag number markings. Tag numbers are always marked on the
upstream of the orifice plate.
10.How much upstream and downstream straight length run is essential
for an orifice plate flow measurement?
An upstream of 28D and a down steam of
minimum 7D is essential for an accurate orifice plate flow measuring system
(where D= pipe line diameter). Greater the upstream and downstream length,
lesser the flow turbulence and grater the accuracy in the flow measurement.
11.What type of orifice tapping is commonly used in P.D.O.?
PDO in general, is using the ‘Flange Tapping’.
The upstream and downstream orifice tapping are taken from the flanges.
12.Why and when is flow measured on a square root scale?
Flow is measured on a square root scale
only when the measurement is done through an orifice plate and a DP
transmitter. The flow measured through the orifice plate is always proportional
to the square root of the DP across the orifice plate.
Q = k 6 sq root of DP
Q
= Flow
K
= Constant
DP
= Differential Pressure
13.What is a ‘flow factor’?
A ‘flow factor’ is to multiply the flow
transmitter signal measured on a 0-10 square root or 0-100 linear scale to get
the flow calculated by flow metering. This is used due to the standardization
of the transmitters signals, to 20-100 kPa or 4-20mA.
14.What are the important parameters considered in deriving a flow
factor?
The following points are considered for
flow calculation and in deriving the flow factor:
D = pipe diameter,
Small d = orifice diameter
Service = gas or liquid
PI = operating pressure
DP
= Transmitter differential pressure
T =operating temperature
Small p= density or molecular weight
Small v= viscosity
Q= expected total flow
15.Explain the installation of a DP flow transmitter on a gas and
liquid pipeline?
Gas line: the transmitter is installed
above the orifice plate to prevent the condensation of gas in the signal line
and in the HP & LP chambers.
Liquid line: the transmitter is
installed below the orifice plate to prevent the gas trapping in the signal
line and in the HP & LP chambers.
16.What is a ‘zero check’ and ‘static zero check’ on a DP flow
transmitter?
Zero Check: A
procedure for checking the transmitter output is equal to 4.00 mA when its HP
& LP chambers are equalized and are at the atmospheric pressure.
Static Zero Check: A procedure for checking the transmitter output
is equal to 4.00 mA when its HP & LP chambers are equalized and are at the
operating pressure.
17.Why is flow measurement not very accurate?
Flow measurement is less accurate
compared to level, temperature and pressure measurement. This is due to the
consideration of various parameters while measuring a flow. These parameters,
such as the accuracy of the orifice plate diameter, the pipeline diameter their
operating parameters such as temperature and pressure do not remain same in the
process operation as the designed parameters. Generally, an accuracy of 5% is
permitted in a flow measurement.
18.What is the actual flow, if the operating pressure is higher then
the designed pressure?
If the operating pressure is higher than
the desiged pressure the true flow will be higher then the measured pressure. A
simple calculation is as follows.
Q
= Q1* sq root of p1/p2
Q
= True Flow
Q1=
Measured Flow
P1=
Operating pressure
P2=
Designed Pressure
19.What will be the new flow factor if a DP transmitter is re-ranged
from 25 kPa to 50 kPa?
A simple calculation is as follows:
Q1/Q2
= Sq root of DP1/ Sq root of DP2
Q1
= Q2 * Sq root of DP1/ Sq root of DP2
Q1 =
New flow factor, Q2 =Existing flow factor
DP1 =
Transmitter new range, DP2= Transmitter existing range
Q1 = Q2*SQ ROOT OF 50/25
Q1
= 1.41*Q2
The new flow factor will be 1.41 times
higher than the existing flow factor.
20. Why generally is a flow
transmitter installed upstream of a flow control valve?
A
flow transmitter is always installed on the upstream of the flow control valve
in order to maintain the operating pressure across the flow transmitter
sensors. Downstream of the control valve the pressure changes as the control
valve opens or closes.
21. Why is a pressure transmitter
installed upstream of a flow transmitter?
Upstream
of a flow control valve a pressure transmitter is installed to measure the
operating pressure. At times it is used for computing the true flow against the
designed pressure. Downstream of the control valve the pressure changes as the
control valve opens and closes.
22. What is the operating principle of a
turbine meter?
A
magnetic pickup installed above a turbine meter measures the number of magnetic
flux cut by the turbine meter blades and produces pulses proportional to the
volume of liquid flow through the meter.
23. What is the output of a turbine
meter?
The
output of the turbine meter is in pulses. The pulse per the volume of liquid is
constant and distinct for each meter. When a known quantity of liquid flows
through the meter, a known number of pulses are produced.
24. What does a pre-amplifier do on a
turbine meter?
The
magnetic pickup inside the turbine meter produces pulses around 30 mv peak to
peak. A pre-amplifier magnifies the small signal to a 12 V DC
25. What are the advantages and
disadvantages of a turbine meter Vs an orifice plate flow measurement?
Turbine
meter is a good flow measuring unit when the fluid is low clean fluid. The
turbine meter measures the volumetric flow. It is directly installed on the
flow line. Its accuracy in flow measurement is high. Accuracy can be
re-calculated and the ‘k’ factor can be reset periodically.
26.
What is a ‘k’ factor on a turbine meter? Who provides the ‘k’ factor?
Each
turbine meter is specified with a ’k’ factor which represents the number of
pulses produced per a known quantity of liquid.
Example: k = 265 pulsed/gallon
Generally
the ‘k’ factor is provided by the manufacturer.
27.
One cubic meter is equal to how many gallons?
1 Cubic Meter = 264.2 gallons.
28.
Why are counters ( totaliser ) used in flow measurement?
Counters
are used for measuring the ‘volumetric flow’ of the fluid in a pipeline.
