1.Explain the Difference between Digital & Analog Sensors ?

The term "analog sensor" refers to various sensors that create a continuous
analog output signal. The analog sensors give a continuous output signal
proportional to the measurement. Digital sensors, unlike analog sensors,
produce discrete values (0 and 1). In digital communication, discrete values are
referred to as digital or binary signals .
Analogue sensors give signals whose size is proportional to the size of the
variable being monitored. e.g. a thermocouple ,a RTD, strain gauge etc. Digital
sensors can give either discrete signals or pulses. Devices which give discrete
signals (either a “voltage” or “no voltage” condition). Devices which give pulses
can be considered to be essentially discrete devices which gives a sequence of
on-off signals.

2 List Digital and Analog Sensors?

“DIGITAL” SENSORS
• Digital sensors interface directly with the process equipment
translate physical process variables into convenient Electrical signals or
Pneumatic pressure, digital in nature.
• The following sensors are digital sensors
1. Pressure switches
2. Temperature switches or Thermostats
3. Flow switches
4. Proximity switches
5. Tacho switches
“ANALOGUE” SENSORS
• Analog sensors convert continuously varying signals
convenient Electrical signals
1. Pressure transmitters
2. Temperature transmitters
3. Tacho-generators
4. Load cells
5. Flow transmitters
6. Velocity transmitters
3. Explain Difference between Open Loop and Close Loop systems ?
A system in which the output is dependent on input but controlling action is
totally independent of the output is called an Open-loop system.
It is also referred to as a non-feedback system, which is a type of continuous
control system in which the output has no influence or effect on the control
action of the input signal. These are the systems in which the control action is
independent of output. Example: Traffic signals, bread toaster, ordinary
washing machine, and systems having no sensor

A system in which the controlling action is dependent on the output is called

a Closed-loop system.
4. With the help of diagram explain close Loop Control System ?

5. With the Help of Diagram explain any Closed Loop Control system on
ships?
6. What is ON/OFF Control System ?
On-Off Controller Definition: An on-off controller is defined as a control system
that fully opens or closes the control element when the process variable
crosses a preset level.
Working Principle: The on-off controller works by fully opening or closing the
output value, causing the process variable to change direction and cycle
continuously.
Example of Application: A typical example is the cooling fan control in
transformers, which activates based on temperature levels.
7. What is PID Controller ? Explain working with help of drawing?
A PID controller continuously calculates an error value e(t) as the difference
between a desired setpoint (SP) and a measured process variable (PV) and
applies a correction based on proportional, integral, and derivative terms
(denoted P, I, and D respectively), hence the name.
A PID (Proportional Integral Derivative) controller consists of three components
that are adjusted based on the difference between a set point (SP) and a
measured process variable (PV).
e(t)=SP−PVe(t)=SP−PV
The output of a PID controller (u(t)) is calculated using the sum of the
Proportional, Integral, and Derivative terms where KP, KI, and KD are constants
that can be adjusted to fine-tune the performance of the controller.
8. Explain what is Proportional ,Integral and Derivative Control ?

Proportional term: take the error and multiply it by a constant Kp

Integral term: take the cumulative total error and multiply it by a constant Ki
Derivative term: take the rate of change in error and multiply it by a constant
Kd
Finally, it adds all three of the above values together to produce the final
output u for that cycle
u(t) is the drive coming from the Controller, into the Process, at time t
e(t) = ysp(t) - y(t) is the difference between the setpoint and measured process
variable at time t
Kp, Ki, Kd are the respective P, I, and D constants
9. What is PID Tuning ?
The process of setting the optimal gains for P, I and D to get an ideal response
from a control system is called tuning.
PID tuning is a systematic process aimed at finding the optimal values for the
proportional, integral, and derivative parameters of a PID controller tuning. The
objective is to fine-tune these parameters to achieve the desired control
system performance, including fast response, minimal overshoot, and robust
stability. The process of PID tuning typically involves several steps.
10. Explain Manual Tuning of PID Controller ?
Start with Kp, Ki, and Kd at 0.
Increase Kp until steady-state error is very low.
Increase Ki until steady-state error is removed entirely.
Increase Kd until oscillations are removed.
11. What is Automatic Tuning of PID Controllers ?
Automated PID tuning, as the name suggests, is a process where the tuning of
the PID controller parameters is done automatically using software algorithms.
These methods are more precise and less labour-intensive than manual tuning
and are preferred when a mathematical model of the system is available or can
be derived.
12. Explain working principle of RTD ,Thermistor, Thermocouple ?
RTD (Resistance Temperature Detector) is a temperature sensor
whose resistance changes as its temperature changes, with resistance
increasing as the sensor’s temperature rises. RTDs are typically made from pure
platinum, which provides high accuracy, stability, and repeatability across a
wide temperature range. The Platinum 100 RTD, often known as the Pt-100
RTD, is the most widely used element in the industry. At the 0° C (32° F), the
RTD has a resistance of 100 ohms.
Thermister :
The thermistor works on the simple principle of change in resistance due to a
change in temperature. NTC stands for Negative Temperature coefficient. They
are ceramic semiconductors that have a high Negative Temperature Coefficient
of resistance. The resistance of an NTC will decrease with increasing
temperature in a non-linear manner. A PTC thermistor works a little differently.
When temperature increases, the resistance increases, and when temperature
decreases, resistance decreases. This type of thermistor is generally used as a
fuse.
Thermocouple
The thermocouple working principle is based on the Seeback Effect. This effect states that when a
closed circuit is formed by jointing two dissimilar metals at two junctions, and junctions are
maintained at different temperatures then an electromotive force (e.m.f.) is induced in this closed
circuit. The amount of induced e.m.f. is different for different metal combinations and is proportional
to the temperature difference of the junctions. This is the basic thermocouple working principle.

13 List the difference between RTD, Thermistor, Thermocouples ?

RTD Thermistor Thermocouple

Temp Range -260 – 850 Deg C -80 - 150 Deg C -270 - 1800 Deg C
Lineraity Best Poor Moderate
Stability Best Moderate Poor
Power Yes Yes Not Required
Material Metal Semiconductor Metal
Applications Air/Oil/Water
Bearing/Exhaust Winding Temp Exhaust Gas
Fire Heat Sensor
Overload
14. Draw and Explain working of RTD measuring exhaust gas Temperature of
Incinerator on ships ?
A loop transmitter measures a process variable, and regulates the loop current
between 0.004 and 0.02 A, (4 mA…20 mA), by varying the opposition to current
flow of the loop.
In the example below a loop transmitter measures a temperature sensor. The
transmitter is programmed to regulate loop current flow between 4…20 mA as
temperature changes from 0…100°C.

15. With the help of diagram explain three wire RTD ?

16. What is See Beck effect ?
The Seebeck effect can be explained by the behavior of electrons in conductors
and semiconductors. Electrons are negatively charged particles that move
freely in these materials. When a conductor or a semiconductor is heated, its
electrons gain more kinetic energy and tend to move faster. This causes them
to diffuse from the hot region to the cold region, creating an electric current.

17. What is cold Junction Compensation in Thermocouple ?

Cold Junction Compensation is usually done automatically by the measuring
instrument. The instrument measures the temperature at the cold junction and
adds it back to the equation.
1000 (hot junction) - 100 (cold junction) = 900 deg. F + 100 deg. F (cold junction
temp) = 1000 deg F.
This way the instrument indicates the actual temperature of the hot junction .

18. List various pressure sensing devices ?

Common Pressure Detectors
Bourdon and Helical Pressure Sensors
Bellows
Diaphragms
Capsules
Differential Pressure Transmitters
Pressure Transmitter

19. Explain working Differential Pressure Transmitter ?

The transmitter consists of two pressure sensing diaphragms, one on each side
of the differential pressure being measured. These diaphragms are typically
made of a flexible material, such as stainless steel or silicon, and are separated
by a small gap. The diaphragms are designed to deform in response to changes
in pressure, causing a change in the capacitance between them.
The capacitance is the ability of the diaphragms to store electrical charge, and
it is directly proportional to the distance between the diaphragms. As the
pressure difference across the diaphragms changes, the diaphragms move,
altering the distance between them and thus changing the capacitance.

The capacitance change is then converted into an electrical signal by a sensing

circuit within the transmitter. This signal is typically proportional to the
differential pressure being measured and can be further processed and
displayed by a control system or a human operator.

20 What is Hydrostatic pressure ?

21. What is LVDT ?
LVDT is used in those applications where displacement ranging from fraction of
a mm to few cm. As a primary transducer, it converts the mechanical
displacement into electrical signal.
the primary is connected to an AC source so alternating current and voltages
are produced in the secondary of the LVDT. The output in secondary S1 is
e1 and in the secondary S2 is e2. So the differential output is,

The amount of change in voltage either negative or positive is proportional to

the amount of movement of core and indicates amount of linear motion.The
output voltage of an LVDT is linear function of core displacement .

22. What is the working principle of Srain Guage ? Explain any one application
of Strain Guage ?
The amount of increase in resistance is proportional to the force that produced
the change in length and area. The output of the strain gauge is a change in
resistance that can be measured by the input circuit of an amplifier.
The strain gauge is a device that can be affixed to the surface of an object to
detect the force applied to the object. One form of the strain gauge is a metal
wire of very small diameter that is attached to the surface of a device being
monitored .
Hull Stress Monitoring System :- Application of Starin Guage
The StressAlert is a hull stress monitoring system that allows the ship’s Master
to obtain both advance warning of structural deterioration in service and up-
to-date stress information, allowing the vessel to be used to its maximum safe
efficiency. Correct use of StressAlert will reduce the risk of overstressing and
hence out-of-service time.
The basic StressAlert system monitors stress at four locations, using specialist
deck mounted Long Baseline Strain Gauges (LBSGs). These, together with a
bow slam accelerometer are monitored by a system that computes the
stresses and bending moments experienced by the ship and displays the
results graphically on a colour monitor.

23 Explain working of Magnetic Flow meters ?

Magnetic flow meters or, “mag meters”, use the principal of Faraday’s law of
electromagnetic induction to calculate the fluid flow rate. Faraday’s law states
that a voltage will be induced when a conductor moves through a magnetic
field. For this case, the liquid fluid serves as the conductor and the magnetic
field is applied to the metering pipe. This will create a potential difference that
is monitored by electrodes that are aligned perpendicular to the flow. The
potential difference, or voltage produced, is directly proportional to the
velocity, which then allows us to find the flow rate.
24. Explain working of Ultrasonic Flow meter ?
Doppler flow meters use the principal that sound waves will be returned to a
transmitter at an altered frequency if reflectors in the liquid are in motion. This
frequency shift is in direct proportion to the velocity of the liquid. It is precisely
measured by the instrument to calculate the flow rate.

25. Explain how Flow measure with Differential Pressure Transmitter ?

Differential pressure flow meters operate by introducing a restriction in the
cross-sectional area of a flowing fluid. Restricting the flow area causes a
pressure drop across the constriction; this pressure drop is cause by a change
in the fluids velocity. The operating principal is based on the Bernoulli equation
and the continuity equation of fluid flow, combining these equations you can
find the relationship between the flow rate and pressure drop.
The square root extractor is an electronic (or pneumatic) device that takes
the square root of the signal from the flow transmitter and outputs a
corresponding linear flow signal. The square root extractor is actually a kind of
signal conditioner. So that we can have indicators, recorders and controllers
that actually register linearly with the flow velocity, we must mathematically
“condition” or “characterize” the pressure signal detected by the differential
pressure transmitter to corresponding flow rate
The flow rate “Q” of a fluid through an orifice plate increase in proportion to
the square root of the pressure difference on each side multiplied by the K
factor.
26. Explain Level measurement using Air Purge system ?
For small air flow rate, about one bubble per second, a pressure equal to that
in the dip tube will be applied to the indicator as shown in figure below. This
simple bubbler device is an arrangement that is similar to the well known
pneumercator used for determining depths of water and oil in tanks. Air supply
to the open ended pipe in the tank will have a pressure which is directly
proportional to the depth of liquid in the tank.
27. Explain Radar Tank Level Measurement on ships ?
The level of the liquid (or solid) is measured by radar signals transmitted from
the antenna at the tank top. After the radar signal is reflected by the liquid
surface the echo is picked up by the antenna. As the signal is varying in
frequency the echo has a slightly different frequency compared to the signal
transmitted at that moment. The difference in frequency is proportional to the
distance to the liquid, and can be accurately calculated. This method is called
FMCW (Frequency Modulated Continuous Wave) and is used in all high
performance radar gauges.

28. With help drawing explain Capacitance Tank Level Measurement ?

Capacitance Level Measurement
If the area (A) of and the distance (D) between the plates of a capacitor remain
constant, capacitance will vary only as a function of the dielectric constant of
the substance filling the gap between the plates. If a change in level causes a
change in the total dielectric of the capacitance system, because the lower part
of area (A) is exposed to a liquid (dielectric l) while the upper part is in contact
with a vapor (dielectric v, which is close to 1.0), the capacitance measurement
will be proportional to level.

29. Draw and explain Voltage divider Circuit with Resistance ?

Voltage Divider Rule

 The voltage division rule states that: The voltage divided between two
series resistors, are in direct proportion to their resistance
 Which means your circuit can have more than 2 resistors!
Applications
Potentiometers
The most common voltage divider circuit is the one involving a
potentiometer, which is a variable resistor. A potentiometer's
schematic diagram is shown below:

30 Draw and explain Voltage Divider Circuit using Capacitance ?

Capacitive Voltage Divider circuits produce voltage drops

across capacitors connected in series to a common AC supply.
Generally capacitive voltage dividers are used to “step-down”
very high voltages to provide a low voltage output signal which
can then be used for protection or metering.
Unlike resistive voltage divider circuits which operate on both AC
and DC supplies, voltage division using capacitors is only possible
with a sinusoidal AC supply. This is because the voltage division
between series connected capacitors is calculated using the
reactance of the capacitors, XC which is dependent on the
frequency of the AC supply. When using pure capacitors the sum
of all the series voltage drops equals the source voltage, the
same as for series resistances. While the amount of voltage drop
across each capacitors is proportional to its reactance, it is
inversely proportional to its capacitance.
As a result, the smaller 10uF capacitor has more reactance
(318.3Ω) so therefore a greater voltage drop of 69 volts compared
to the larger 22uF capacitor which has a reactance of 144.7Ω and
a voltage drop of 31 volts respectively.