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PnIC Experiment 2-Level Measurement

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ABSTRACT
The level measurement and calibration experiment were conducted to fulfil the
objective which to analyse the relationship between the levels and their differential
percentage by using pressure device. The experiment was dividing into 4 part with variable
for open and closed tank by using heater or not. The general setup procedure being
followed, and the experiment was using sight glass device to record the actual level. All four
experiment showed the actual value LG is lower than actual value LI. The difference
between the LG and LI values are very small. It is important for the values to be as close to
the suggested value to reduce the occurrence of error while carrying out a reaction. There
are several recommendations for this experiment in term of safety. The preparation to
analyse the equipment and understanding the usage of every valve before its running are
compulsory. Level measurement and calibration is essential in process industry as it is very
important to keep track of the amount of substances or reactants in a reactor. This is
because malfunction in the level measurement might cause unfortunate accidents as some
substance that are being handled might be very harmful and needs a special care.
Figure 1: the sight glass device used in level
measurement and calibration experiment.
OBJECTIVES
The level measurement and calibration experiment objectives are:
•
To carry out the level measurement and calibration experiment systematically.
•
To study the level measurement using Pressure device
•
To investigate the relationship between level and their differential percentages.
INTRODUCTION AND THEORY
Level measurement is the measure of solid height or fluid within a tank or vessel.
These measurements are important to run a plant and required by many industrial process.
Some instruments that are used in the process are displacement type, level gauges, float
type, echo type, hydrostatic pressure measurement and displacement type. The use of level
measurement is to monitor, control process or operation and carry out some analysis to
prove the accuracy of theories (Ghosh, 2012). Level measurement can be divided into two
types of level measurement comparison. The first one is contact and the second one is noncontact shown in figure 1.
The objective of this experiment is to identify the important component for level
measurement in the instrumentation, to carry out the start-up procedure systematically, to
study the level measurement using related device. This is done by comparing between
different level measurements from 700 mm down to 300 mm and to study the level
measurements in open and closed tank, to investigate the relationship between level and
their differential percentage.
Calibration very important in this experiment. It is a measurement that consist of two
parts, a correction. This is to adjust the measured parameter to the normal value and the
second part is to measure on how wrong the correction could be. (Bently, 1998). It is very
crucial because for example it the measurement was too high, pumping of material will
occurs some difficulty and might even damage due to overflows and dangerously high
pressure. Through the experiment the process involve was measuring different levels of
water with or without the function of heater within closed or open tank. The variable that
include in this experiment is suggested level (mm), actual level LG (mm) that can be
obtained by the sight glass and actual level from the level indicator at the front panel (LI).
The formula used to measure level of 700 mm to 300 mm is
Deviation = [LG –LI] mm
The machine contains several components that its used in order to aid the flow of the
process. One of them is valve for example top vent, by pass valve, drain valve, pump
discharge valve. The function of this device is to maintain direct control of moving fluid and
gas by open and closed the device. Secondly is overflow valve. Since in industry of
plumbing, pipe and electricity it has been issue on safety device that’s pressure building up
and by the help of sensor it can alert the operator regarding the issue. Same goes to the
valve that’s function by sensing the pressure up pipe.
METHODOLOGY
The experiment was run by 4 major different set up. Firstly, Tank T1 as OPEN Tank,
Heater OFF, secondly, Tank T1 as CLOSED Tank, Heater OFF next, Tank T1 as OPEN
Tank, Heater ON and lastly, Tank T1 as CLOSED Tank, Heater ON. The plant started up
procedure was run by filled the water in Tank T2 up to its overflow level. At the same time,
the drain valve needs to fully close. At the front panel, the heater and pump were off. Then,
the main power supply located at the front panel was switched on. The pump suction valve
and all pump discharge valves were fully open. The pump by-pass valve (BV) was opened
one turn before starting the pump. After pump start-up, the BV was fully closed. First
experiment for tank T1, the top vent and overflow manual valves were fully opened. Then the
pump was started by pressing the green pushbutton at the front panel. The flowrate was
adjusted by using Variable Area Flowmeter (FI) to about 2.5m3/hr. The manual discharge
gate valve at tank T1 was closed and the pump was stopped. The bottom globe valve of tank
T1 was opened to allow the water in tank T1 to flow into tank T2 until the level at LG reads
about 700mm. Then, the bottom globe valve was closed. The reading was recorded 2 set in
the Table 1. The measurement level was continued from 600 mm until 300 mm. These
procedures basically are same for second experiment. The different just at the beginning
which for Tank T1 as CLOSED Tank, Heater OFF, fully CLOSE the vent, overflow, bottom
gate valve and globe valves of tank T1. For third and fourth experiment, the heater was
switched on and the procedures were repeated for T1 opened and closed tank respectively.
After all the experiments were done, the shutdown procedure was run by switched off the
heater. The overflow manual valve and the top vent valve of tank T1 were fully opened. The
water in tank T1 was drained out by opening the manual discharge valve i.e. the gate valve.
After that, fully close both the gate valve and globe valve. The water in tank T2 was drained
out by opening its manual drain valve. Lastly, the main power supply was switched off.
DISCUSSIONS
The title of this experiment is level measurement and calibration. In this experiment,
we measured the level in an open and closed tank with heat on and heat off. Level
measurement is important in the process control industry as the need to measure the level of
a process material in a container.
Level measurement can be a determining factor in both profit margins and safety. For
each section of the experiment, two sets of readings were taken and then the average was
calculated. This is done to obtain a more precise value. For the open tank with heater off
situation, as we can see from the bar graph plotted the level gauge (LG) and the level
indicator (LI) is reducing as suggested level set is reducing. This shows that the level
measurement of the tank is effective. For the second case, which is the closed tank with
heater on the LG and LI value is decreasing with the reduce in the suggested level of liquid
in the tank.
For the third case, close tank with heater on the LG and LI value is subsequently
decreasing with the suggested value as well. Lastly for the fourth scenario where it’s an
open tank with heater off the LG and LI is also decreasing with suggested value. For all
these values, the difference between the LG and LI values are very small. It is important for
the values to be as close to the suggested value to reduce the occurrence of error while
carrying out a reaction.
Level measurement and calibration is essential in process industry as it is very
important to keep track of the amount of substances or reactants in a reactor. This is
because malfunction in the level measurement might cause unfortunate accidents as some
substance that are being handled might be very harmful and needs a special care.
CONCLUSIONS AND RECOMMENDATIONS
This level measurement and calibration experiment involved four sections, which the
level was measured in an open and closed tank with heat on and heat off. For each section,
two sets of reading were taken to obtain a precise value and the average was calculated.
For first section, tank T1 was opened and heater off, the bar graph plotted shows the level
gauge (LG) and the level indicator (LI) is reducing as suggested level set is reducing. Next,
for the closed tank and heater on, the value is decreases as the suggested level of the liquid
was reduced. When the tank was closed with the heater on, the result shows that the value
of both LG and LI is decreasing as the suggested value reduced. For the last section, where
the tank was opened with heater off, value of LG and LI also decreases as well as
suggested level. To conclude, the difference between all the LG and LI values are very small
and it is very important for the values to be as closed to the suggested value to avoid any
errors.
There are a few precautions should be taken to obtain more precise results. The first
one is, to make the experiment run smoothly, the level of the water in tank T2 should be
maintained to avoid the shutting off the heaters and the pump. Next, when taking the reading
for the level indicator (LI), it is needed to make sure that students wait for the reading to be
constant before noting down the value. In addition, it is compulsory to know which valve
needed to be open or close so that there are no errors occur. Lastly, before starting the
experiment, make sure all the equipment, switches, valves that will be used are working
properly to avoid any interruption during the experiment.
TUTORIAL
1. Level is measured in many of the processes in the industry. List and explain the most
common reasons for measuring level.
a. To keep track the liquid level. The most common device that is use for monitoring
the level measurement is float level switch. This device is operated using buoyancy
principle and it is float and contain powerful and permanent magnets. When put in
vertically it provide the accuracy and reading of the level measurement and all the
level point are being monitored.
b. To monitor and control the level of measurement for example rotary level indicator
that are used for particulate materials such as powder, plastic, wood dust, cement
and sand. It is located at above the material or to the side to measure high or low
level control.
c. For ultrasonic level measurement. In this measurement unit, it consists of
piezoelectric crystal stored in the transducer. The function of transducer is to convert
electrical sign to sound energy. It is use for measure a hot, boiling and corrosive
liquid. The range frequency that is use normally 40-200 KHz.
2. Name the two methods of level measurement used in the experiment.
a. Direct method which is not required compensation for changes level causes by
temperature change.
b. Indirect method the compensate due to sensitive on specific gravity and
temperature.
3. How the depth of a liquid does correspond to changes in liquid pressure? Can a pressure
transmitter be used to measure level?
All things on Earth include water have gravity which mean the body and things are
pulled down by the force. The pressure of water is the effect of weight at the water
the upside push downward on water below. For example, as we go deeper into the
sea there is a lot water exists above, therefor a higher weight pushing down. As for
the result, the deeper the water, the higher the pressure will be.
Pressure transmitter can be used to measure level because the function of this
device is to measure the pressure inside the machinery. One of the functions is to
give a warning before a catastrophe happen.
4. The differential pressure transmitter is used to measure level in an open tank or closed
tank system. Discuss how this is done.
The differential pressure is the differential between high pressure and low pressure.
The high pressure for open tank was used a atmospheric pressure meanwhile,
closed tank was used gas pressure inside the tank because the tank was fully
closed.
5. Discuss briefly the possible errors affecting the accuracy in pressure / level measurement
as observed in the experiment.
The first one is when taking the result. The student does not focus on the task given
for example taking the reading of measurement and actual level. This may affect the
result of the experiment. Secondly, before the experiment the student also need to
familiar with valve, pump and all machine part because if not, a few miss step and
wrong open and closed valve might occur.
6. What are the main objectives of a wet lag calibration?
Throughout the process of using differential pressure transmitter, the fluid can
evaporate and condensed. The main objective of the wet leg measurement is to
measure the level of the phase in gas or liquid. So, the condensate fluid does not
affect the reading by giving the false indication.
REFERENCES
Bently, E. R. (1998). Handbook of Temperature Measurement Volume 3. The Theory and
Practice of Thermoelectric Thermometry. Springer, Singapore. Pp 115.
Chetpattananondh K., Tapoanai T., Phukpattaranont P., Jindapetch N. (2014). A selfcalibration water level measurement using an interdigital capacitive sensor. Sensors and
Actuators: Physical (Volume 209) 175-182.
Ghosh, A. K. (2012). Introduction To Measurements And Instrumentation, fourth ed. PHI
Learning Private Limited, New Delhi. Pp 1.
Lansey K.E., El-Shorbagy W., Ahmed I., Araujo J., Haan C.T. (2001). Calibration
Assessment and Data Collection for Water Distribution Networks. Vol.127, Issue 4.
Visual
Encyclopedia
of
Chemical
Engineering.
Level
Measurement.
http://encyclopedia.che.engin.umich.edu/Pages/ProcessParameters/LevelMeasurement/Lev
elMeasurement.html (accessed 6 August 2018)
Sciencing. Why does water pressure increase with depth. https://sciencing.com/waterpressure-increase-depth-6556057.html (accessed 6 August 2018)
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