Experiment no 11

LEVEL CONTROL MODULE

PID Controller

Evaluation Table:

Organization and Analysis of

Components / Conclusion Total
Content Results
Weightage (3) (10)
(3) (4)

Obtained marks

Objective:
 To verify the effects of the gain of the loop on the dynamic response of
the system.
 To represent the dynamic response curve of the system.
Apparatus:

Figure 1 Level Process Rig

List of Equipment:
● Digital Multimeter
● Set of Leads
● Level Process Rig

Working Principle:

A proportional controller adjusts the output in direct proportion to the error, while a
proportional-integral (PI) controller also considers the accumulated error over time to eliminate
steady-state error. A proportional-derivative (PD) controller, on the other hand, responds to the
rate of change of the error to minimize overshoot and oscillations. By varying the gain of each
type of controller, the system's response to changes in the input signal can be monitored and
dynamic response of the system can be represented via curves.

Theoretical Background:

Introduction

The concept of level measurement is integral to countless applications across industries, serving
as a cornerstone for maintaining operational efficiency, safety, and environmental integrity.
Whether it's managing fluid levels in storage tanks, controlling processes in chemical plants, or
monitoring water levels in environmental conservation, accurate level measurements are the
heartbeat of many critical systems. In this comprehensive theoretical background, we will
embark on a journey through the realm of level measurement, explore the significance of level
transducers, delve into the intricacies of various level sensors, uncover the inner workings of
float switches and LVDTs, and underscore the vital role of calibration in achieving precision and
reliability.

What is Level?

At its core, liquid level refers to the height or depth of a liquid substance in a container, relative
to a reference point. It's a universal metric used in a wide range of industries, from ensuring
consistent fuel levels in vehicles to maintaining the correct fluid levels in medical devices.
Understanding and accurately quantifying liquid level are fundamental to optimizing processes
and ensuring the quality and safety of operations.

Level Controllers:

A level controller, also known as a level control system or level control device, is an automated
system or instrument used to maintain and regulate the liquid level within a tank, reservoir, or
other container. It is designed to monitor the liquid level and take corrective actions to ensure
that the level remains within a desired or specified range.

Importance of Level Control:

The importance of level controllers lies in their ability to provie precise and consistent control
over liquid levels in various industrial, commercial, and residential applications. Here's a closer
look at the importance of level controllers:

● Safety: Level controllers help prevent overflows and underflows, which can lead to
hazardous conditions, damage to equipment, and safety risks. For example, in chemical
processing, maintaining the right liquid level is crucial to prevent spills of potentially
dangerous substances.
● Process Efficiency: Proper level control is essential for optimizing the use of resources
such as raw materials, energy, and labor. It ensures that processes operate at their
designed capacities, reducing waste and increasing operational efficiency.
● Quality Assurance: In manufacturing and production, precise level control is critical for
maintaining the quality and consistency of products. This is particularly important in
industries such as food and pharmaceuticals, where product quality and safety are
paramount.
● Equipment Protection: Level controllers help protect equipment such as pumps, motors,
and heating elements by preventing them from running dry or being damaged due to
excessive liquid levels. This extends the lifespan of the equipment and reduces
maintenance costs.
 ● Environmental Compliance: Many industries are subject to environmental regulations
that require them to control liquid levels to prevent spills and contamination. Compliance
with these regulations is essential to avoid legal and financial consequences.
● Cost Savings: Proper level control can lead to significant cost savings by reducing the
consumption of resources, minimizing waste, and optimizing energy usage. It helps
organizations operate more efficiently and sustainably.
● Process Consistency: Maintaining consistent liquid levels ensures that processes run
predictably and reliably. This is particularly important in continuous manufacturing and
chemical processes, where variations in level can lead to product defects or process
disruptions.
● Energy Efficiency: Level controllers can contribute to energy efficiency by optimizing
the operation of pumps and valves. They can reduce unnecessary energy consumption
and associated costs.
● Productivity: In agriculture, irrigation systems with effective level controllers can
enhance crop yields by providing the right amount of water when needed, leading to
increased agricultural productivity.
● Convenience: In everyday life, level controllers are used in applications such as
maintaining water levels in household appliances (e.g., washing machines and
dishwashers) and ensuring consistent water levels in swimming pools and hot tubs,
enhancing convenience and comfort.

Accurate level measurement serves as the linchpin in numerous applications. It's the guardian of
chemical processes, preventing dangerous overflows; it's the steward of environmental
preservation, ensuring proper water management; it's the protector of health, guaranteeing
accurate medication dosages and patient care.

What is a Control System?

A control system is an integrated set of components or devices that work together to maintain or
modify the behaviour of a system or process. Control systems are designed to achieve specific
objectives by continuously adjusting the system's inputs or outputs based on feedback
information. These systems are indispensable in industries ranging from manufacturing and
transportation to healthcare and aerospace.

Importance of Control

Control systems serve several critical purposes:

● Stability: Control systems help maintain system stability, ensuring that processes operate
within acceptable bounds, preventing instability or catastrophic failures.
● Precision: They enable precise regulation of processes, leading to higher product quality
and consistency.
● Efficiency: Control systems optimize resource usage, leading to energy savings and cost
reduction.
● Safety: They enhance safety by monitoring and responding to unsafe conditions,
reducing risks to personnel and equipment.

Types of Control Systems

Control systems can be categorized into several types based on their characteristics and control
strategies:

Open-Loop Control Systems

Open-loop control systems, also known as non-feedback or feedforward control systems, are a
fundamental type of control system. Open-loop control systems provide a constant input to the
system without considering the actual system output. These systems are simple but lack the
ability to respond to changes or disturbances in the system.. In open-loop control, the control
action is determined solely by the input command or setpoint, without considering the actual
system output or the system's response to the control action. This control strategy relies on the
assumption that the relationship between the input and the desired output is well-defined and
predictable.
 Figure 2 Open Loop Control System

Closed-Loop (Feedback) Control Systems

Closed-loop control systems, also known as feedback control systems, incorporate a feedback
loop that continuously compares the system's output to a reference value (setpoint). Based on this
comparison, a controller adjusts the system's inputs to maintain the output close to the desired
setpoint. Closed-loop systems are widely used for their ability to handle disturbances and
maintain system stability.

Figure 3 Closed Loop Control System

Proportional-Integral-Derivative (PID) Control

PID control is a common control strategy used in closed-loop systems. It combines proportional,
integral, and derivative control actions to achieve precise and stable control. The proportional
term corrects the current error, the integral term eliminates past errors, and the derivative term
anticipates future errors, resulting in a well-balanced control response. In PID control, the three
control actions work together to provide precise and stable control in a wide range of
applications.

Proportional Control (P-Controller)

Introduction

Proportional Control, often abbreviated as P-Controller, is a fundamental building block of

control systems engineering. It forms the basis for more complex control strategies and is
essential in the regulation of various processes.

Operating Principle

The P-Controller operates on the principle of adjusting the control input in direct proportion to
the current error, which is the deviation between the desired setpoint and the actual process
variable. The control action (u) at any given time 't' is calculated using the proportional gain
(Kp):

u(t)=Kp∗e(t)

Where:

u(t) is the control action at time 't'.

Kp is the proportional gain, a constant that governs the controller's sensitivity to the error.

e(t) is the error at time 't'.

Advantages

 Simplicity: P-Controllers are straightforward to understand and implement. They serve

as a foundation for control system design.
 Quick Response: P-Controllers are highly responsive to changes in the error, making
them suitable for systems requiring rapid adjustments.

Limitations
  Steady-State Error: P-Controllers cannot entirely eliminate steady-state errors, resulting
in a residual error even after system stabilization.
 Potential for Oscillations: High proportional gain (Kp) values can lead to oscillations
and instability, necessitating careful tuning.

Proportional Integral Control (PI-Controller)

Introduction

The Proportional Integral Controller, or PI-Controller, builds upon the P-Controller's framework
by incorporating an integral action. The goal is to eliminate the steady-state errors that persist in
P-Controllers.

Operating Principle

In a PI-Controller, the control action (u) at any time 't' is a combination of proportional and
integral actions:

u(t)=Kp∗e(t)+Ki∗∫e(τ)dτ

Where:

u(t) is the control action at time 't'.

Kp is the proportional gain.

Ki is the integral gain, a constant controlling the controller's sensitivity to the cumulative error.

e(t) is the error at time 't'.

∫e(τ) dτ signifies the integral of the error over time, indicating the accumulation of past errors.

Advantages

 Steady-State Error Elimination: The integral action ensures that steady-state errors are
driven to zero, enhancing system accuracy.
  Improved Stability: PI-Controllers offer superior stability when compared to P-I
Controllers.

Limitations

 Slower Response: The integral action may slow the response time in certain systems,
which can be undesirable in applications requiring rapid adjustments.
 Potential for Oscillations: High integral gain (Ki) values can lead to oscillatory
behavior, necessitating precise tuning.

Proportional Derivative Control (PD-Controller)

Introduction

The Proportional Derivative Controller, or PD-Controller, enhances control by introducing a

derivative action, which considers the rate of change of the error. This action can improve the
transient response of a system.

Operating Principle

In a PD-Controller, the control action (u) at any time 't' combines both proportional and
derivative actions:

u(t)=Kp∗e(t)+Kd∗ dt de(t)

Where:

u(t) is the control action at time 't'.

Kp is the proportional gain.

Kd is the derivative gain, a constant that controls the sensitivity to the rate of change of the error.

e(t) is the error at time 't'.

{de(t)}{dt} represents the rate of change of the error with respect to time.
Advantages

 Improved Transient Response: The derivative action helps reduce overshoot and
enhance the system's transient response, making it valuable in applications where
overshoot minimization is critical.
 Damping Oscillations: PD-Controllers can be used to dampen oscillations in a system,
improving overall stability.

Limitations

 Amplification of Noise: PD-Controllers may amplify high-frequency noise, requiring

additional filtering in some cases.
 Ineffectiveness for Steady-State Error: PD-Controllers alone cannot eliminate
steadystate errors, and they are often used in combination with PI-Controllers or PID-
Controllers for this purpose.

All this is summarized below

Control Action Description

Proportional control, often referred to as P-control, adjusts the system's input in direct
proportion to the current error, which is the difference between the desired setpoint and
the actual system output. The control output is calculated as Pout=Kp⋅e(t), where Kp is the
Proportional Control
proportional gain, and e(t) is the error at time t. This control action corrects the current
error but does not consider past or future errors, potentially leading to oscillations and
steady-state errors.

Integral control, also known as I-control, addresses steady-state errors by accumulating

the past errors over time. It continuously adjusts the system input based on the integral
(sum) of all previous errors. The control output is given by Iout=Ki⋅∫e(t)dt, where Ki is the
Integral Control
integral gain and ∫e(t)dt represents the integral of the error with respect to time. Integral
control eliminates steady-state errors and provides improved system stability. However, it
can lead to control windup if not implemented properly.
 Derivative control, or D-control, anticipates future errors by considering the rate of change
(derivative) of the error. It adjusts the system input based on the rate of change of the error
with respect to time. The control output is determined as Dout=Kd⋅dtde(t), where Kd is the
Derivative Control
derivative gain, and dtde(t) represents the time derivative of the error. Derivative control
helps dampen oscillations and improve system response. However, it can amplify noise if
the error signal is noisy.

Gain in Control Systems

Gain, in the context of control systems, refers to a numerical value that multiplies the error signal
to determine the control action. It plays a pivotal role in influencing the dynamic response and
performance of the controlled system.

Types of Gain

Proportional Gain (Kp)

Proportional gain, often denoted as Kp, determines the strength of the proportional control action
in a system. It represents the proportionality between the error and the control action. Higher Kp
values result in a stronger response to errors, leading to faster system adjustments.

Integral Gain (Ki)

Integral gain, represented as Ki, contributes to eliminating steady-state errors in a control system.
It accumulates the past error values and produces a control action based on the integral of error
over time. A higher Ki value increases the system's ability to drive the error to zero over time,
enhancing steady-state accuracy.

Derivative Gain (Kd)

Derivative gain, known as Kd, introduces a damping effect to the control system. It takes into
account the rate of change of the error, mitigating overshoot and oscillations. Higher Kd values
lead to stronger damping and can result in a quicker response with reduced oscillations.

Influence of Gain on Dynamic Response

Proportional Gain (Kp)

Higher proportional gain amplifies the control action's response to errors. This leads to a faster
reaction to disturbances and rapid adjustments to reach the setpoint. Lower Kp values result in a
weaker response, potentially causing sluggish or inadequate control, especially in the presence of
disturbances.

Integral Gain (Ki)

A higher integral gain enhances the system's ability to eliminate steadystate errors by gradually
accumulating error over time. However, it can also slow down the system's transient
response.Lower Ki values may result in improved transient response but may not completely
eliminate steady-state errors.

Derivative Gain (Kd)

Increasing the derivative gain introduces stronger damping, reducing overshoot and oscillations.
This results in a faster response with improved stability. Lower Kd values lead to weaker
damping, potentially allowing for more oscillations and overshoot, especially in systems with
high inertia.

Balance and Tuning

The choice of gain values, or gain tuning, is a critical aspect of control system design. Achieving
the desired dynamic response requires a balance between proportional, integral, and derivative
gains. An effective control system often involves trial-and-error tuning to optimize the system's
performance while meeting specific control objectives.

The dynamic response of a system is significantly influenced by the choice of gains. Proper gain
tuning is essential to ensure that the control system responds appropriately to disturbances,
settles quickly, and maintains steady-state accuracy. Balancing these factors is a complex and
iterative process, and it requires an understanding of the system's characteristics and control
objectives.

Procedure:
1. Connect, through leads, bush No.11 of the WATER PUMP DRIVER to bush No.11 and
bush No. 12 to bush No. 12.
2. Connect the bush of SET POINT I to bush No. 10 of the WATER PUMP DRIVER.
3. Press the main switch (ON).
4. Turn OFF the main switch.
5. Bring again the water level in the tank to a value of 6.5cm.
6. Remove the lead from bush No. 10 of the WATER PUMP DRIVER and from the bush of
SET POINT 1 and put the knob to OV.
7. Connect bush No. 1 of the Level Sensor to bush No. I of the relevant interface and bush
No. 2 to bush No. 2.
8. Connect the bush of SET POINT 2 to bush No. 6 of the PID controller and bush No. 5 of
the level interface to hush No. 5 of the ND controller.
9. Insert one terminal of the digital voltmeter, set in dc, in the bush of SET POINT 2 and the
other one in the earth bush.
10. Regulate the voltage on SET POINT 2 at 3V.
11. Move the terminal of the digital voltmeter from the hush of SET POINT 2 to bush No. 5
of the PID controller: the voltage value must be equal to 3V; if the voltage is different,
then check if the water level in the tank is 6.5cm, otherwise calibrate the sensor following
the procedures shown in Worksheet No. 2.
12. Move the terminal of the digital voltmeter to hush X I of the PID controller: the voltage
value must be equal to the difference between the voltage applied to bush No. 6 and that
applied to bush No. 5, which is OV.
13. Connect the bush of SET POINT 1 to hush EXT of the PIP) controller. 14) Insert the
terminal of the digital voltmeter in bush Xl.
14. Regulate the voltage on SET POINT 1 to read on the digital voltmeter a voltage of 2V:
this voltage represents the width of the reference step which corresponds to an increase of
about 3cm of the water level.
15. Momentarily remove the lead from bush EXT of the PID controller. 17) Regulate the
PROPORTIONAL knob at 25%.
16. Connect bush No. 7 of the P1D controller to bush No. 7 and bud) No. 10 to bush No. 10
of the WATER PUMP DRIVER.
 17. Move the terminal of the digital voltmeter to bush No. 5 of the PID controller: write
down in Table 6.1 the voltage value (3V).
18. Insert back the lead in bush EXT of the PIT} controller and at the same time start the
chronometer.
19. Write down in Table 6.1 the voltage value read every 15 seconds until thetransitory is
completed.
20. Repeat the same steps for proportional- Integral and Proportional derivative Controller.

Laboratory Precautions:

● Turn on the main switch after cables have been connected.

● Do not touch the apparatus with wet hands as it might result in electric shock.
● Connect the wires carefully.
● Perform experiment carefully and with responsibility.

Circuit Connections:

Proportional Controller:
Proportional-Integral Controller:

Proportional-Derivative Controller: