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TEMPERATURE CONTROL USING ANALOG PID CONTROLLER

Project report submitted in partial fulfillment of the requirements

For the award of the degree of

BACHELOR OF TECHNOLOGY

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

By

P.BHARGAVA (08241A0261)

B.PRASANNA KUMAR (08241A0283)

J.RAMESH BABU (08241A0290

S.VENKATESH (08241A02B3)

Under the guidance of

Ms. K. Sireesha

Assistant Professor

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Department of Electrical and Electronics Engineering

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING & TECHNOLOGY,

BACHUPALLY, HYDERABAD-72

2012

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GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND TECHNOLOGY

Hyderabad, Andhra Pradesh.

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

C E R T I F I C A T E

This is to certify that the project report entitled TEMPERATURE CONTROL USING ANALOG PID CONTROLLER that is being submitted by

P.BHARGAVA, B.PRASANNA KUMAR , J.RAMESH BABU, S.VENKATESH in partial fulfillment for the

award of the Degree of Bachelor of Technology in Electrical and Electronics

Engineering to the Jawaharlal Nehru Technological University is a record of bonafide work carried out by him under my guidance and supervision. The results embodied in this project report have not

been submitted to any other University or Institute for the award of any Post graduation degree.

Prof P.M.Sharma Ms. K.Sireesha Dr. S.N.Saxena

HOD, EEE Assistant Professor, EEE Dept. Professor, Coordinator,

GRIET, Hyderabad GRIET, Hyderabad EEE Dept.

(Internal Guide) G.R.I.E.T, Hyderabad

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ACKNOWLEDGEMENT

This is to place on record my appreciation and deep gratitude to the persons without whose

support this project would never seen the light of day.

We wish to express my propound sense of gratitude to Mr. P. S. Raju, Director, G.R.I.E.T for his

guidance, encouragement, and for all facilities to complete this project.

We have immense pleasure in expressing my thanks and deep sense of gratitude to my guide

Ms K.Sireesha, Asst. Professor, Department of Electrical Engineering, G.R.I.E.T for his guidance

throughout this project.

We are also thankful to Mr.Chakravarthi, Assoc. Professor, Department of Electrical Engineering,

G.R.I.E.T who help.ed us a large wit his excellent guidance.

We also express our sincere thanks to Prof.P.M.Sharma, Head of the Department, G.R.I.E.T for

extending his help.

We express our gratitude to Dr. S.N. Saxena, Professor, Department of Electrical and

Electronics Engineering, Coordinator, Project Review Committee, G.R.I.E.T for his valuable

recommendations and for accepting this project report.

Finally we express our sincere gratitude to all the members of faculty and my friends who

contributed their valuable advice and helped to complete the project successfully.

P.BHARGAVA (08241A0261)

B.PRASANNA KUMAR (08241A0283)

J.RAMESH BABU (08241A0290)

S.VENKATESH (08241A02B3)

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ABSTRACT

The objective of our project is maintaining the temperature constant in a particular area

using analog PID controller. The motivation for doing this project is the fact that

temperature control has become an integral part of any control system operating in a

temperature sensitive environment Whatever the process or the parameter (temp, flow,

speed, ..) the principles of control are similar. Input and output signals are specified in this

project are analog. Control of a process is achieved by means of a closed loop circuit. One

of the primary purposes of using feedback in control system is to reduce the sensitivity of

the system to parameter variations.The project deals with a simple aspect of giving

information about the controlling of temperature in a furnace. In this project we are

developing a system, which can control temperature of a furnace automatically. The furnace

temperature is compared with the value set by the user and if the temperature goes beyond

the Preset temperature then heater will get off and if temperature goes below the set value

then heater gets on.In this project we tried to control the temperature of surrounding area of

the bulb.Initially the input voltage of the system for a particular temperature at bulb is noted

and it is taken as reference or set point and that temperature is maintained constant using

analog pid controller with the help of heat sensor LM35 whose output is fed back to the

input as feed back.

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CONTENTS

Chapter

No.

Name Of The Chapter

Page No.

1

2

3

4

INTRODUCTION

PID CONTROLLER THEORY

2.1 P - Characteristics

2.2 I - Characteristics

2.3 D - Characteristics

2.4 PID - Characteristics

2.5 Importance Of Temperature Control

2.6 Advantage Of PID Controller For Temperature

Control

CONTROL LOOP BASICS

PROJECT OVERVIEW

4.1 Op Amp IC741

4.1.1 Description

4.2 Temperature Sensor LM35

4.2.1 Description

9

11

12

14

16

18

20

21

23

26

28

29

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5

6

4.3 Relay RAS0510

4.3.1 Description

4.4 Bridge Rectifier BR 68

4.4.1 Description

4.5 Voltage Regulators 7915 7815 7015

4.5.1 Description

PHYSICALLY IMPLEMENTING OF PID CONTROLLER

5.1 Ideal versus Standard PID Form

5.2 Loop Tuning

5.2.1 Stability

5.2.2 Optimum Behaviour

5.2.3 Manual Tuning

DESCRIPTION OF PROJECT KIT

6.1 Design Of Panel Board

6.2 Panel Board Circuit

6.3 Working Of The Panel

6.3.1 Power Circuit

6.3.2 PID Circuit

6.3.3 Sensor Circuit

30

31

33

34

36

37

40

41

45

46

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7

8

9

CONCLUSION

FUTURE SCOPE OF PID CONTROLLER

8.1 Improvements

8.1.1 Feed Fprward

8.1.2 Other Improvements

BIBILOGRAPHY

9.1 APPENDIX

9.1.1 Appendix A

9.1.2 Appendix B

9.1.3 Appendix C

9.1.4 Appendix D

9.1.5 Appendix - E

48

50

51

52

54

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CHAPTER 1

INTRODUCTION

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The PID controller is the most common form of feedback. It was an essential

element of early governors and it became the standard tool when process control emerged in the

1940s. In process control today, more than 95% of the control loops are of PID type, most loops

are actually PI control. PID controllers are today found in all areas where control is used. The

controllers come in many different forms. There are standalone systems in boxes for one or a few

loops, which are manufactured by the hundred thousands yearly. PID control is an important

ingredient of a distributed control system. The controllers are also embedded in many special

purpose control systems. PID control is often combined with logic, sequential functions,

selectors, and simple function blocks to build the complicated automation systems used for

energy production, transportation, and manufacturing. Many sophisticated control strategies,

such as model predictive control, are also organized hierarchically. PID control is used at the

lowest level; the multivariable controller gives the set points to the controllers at the lower level.

The PID controller can thus be said to be the bread and butter t of control engineering. It is an important component in every control engineers tool box. PID controllers have survived many changes in technology, from mechanics and pneumatics to microprocessors

via electronic tubes, transistors, integrated circuits. The microprocessor has had a dramatic

influence on the PID controller. Practically all PID controllers made today are based on

microprocessors. This has given opportunities to provide additional features like automatic

tuning, gain scheduling, and continuous adaptation. To accurately control process temperature

without extensive operator involvement, a temperature control system relies upon a controller,

which accepts a temperature sensor such as a thermocouple or RTD as input. It compares the

actual temperature to the desired control temperature, or set point, and provides an output to a

control element. The controller is one part of the entire control system, and the whole system

should be analyzed in selecting the proper controller.

The following items should be considered when selecting a controller:

1. Type of input sensor (thermocouple, RTD) and temperature range 2. Type of output required (electromechanical relay, SSR, analog output) 3. Control algorithm needed (on/off, proportional, PID) 4. Number and type of outputs (heat, cool, alarm, limit)

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CHAPTER 2

PID CONTROLLER THEORY

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2.1 P CHARACTERISTICS (Proportional term)

The proportional term produces an output value that is proportional to the current error

value. The proportional response can be adjusted by multiplying the error by a constant Kp,

called the proportional gain.

The proportional term is given by:

Proportional - To handle the immediate error, the error is multiplied by a constant P (for "proportional"), and added to the controlled quantity. P is only valid in the band over which a

controller's output is proportional to the error of the system. For example, for a heater, a

controller with a proportional band of 10 C and a set point of 20 C would have an output of

100% at 10 C, 50% at 15 C and 10% at 19 C. Note that when the error is zero, a proportional

controller's output is zero

A high proportional gain results in a large change in the output for a given change in the error.

If the proportional gain is too high, the system can become unstable (see the section on loop

tuning). In contrast, a small gain results in a small output response to a large input error, and a

less responsive or less sensitive controller. If the proportional gain is too low, the control action

may be too small when responding to system disturbances. Tuning theory and industrial practice

indicate that the proportional term should contribute the bulk of the output change.

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Plot of PV vs time, for three values of Kp (Ki and Kd held constant)

Because a non-zero error is required to drive the controller, a pure proportional controller

generally operates with a steady-state error, referred to as droop. Droop is proportional to the

process gain and inversely proportional to proportional gain. Droop may be mitigated by adding

a compensating bias term to the set point or output, or corrected by adding an integral term

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2.2 I CHARACTERISTICS ( Integral term)

Integral - To learn from the past, the error is integrated (added up) over a period of time, and

then multiplied by a constant I (making an average), and added to the controlled quantity. A

simple proportional system either oscillates, moving back and forth around the set point because

there's nothing to remove the error when it overshoots, or oscillates and/or stabilizes at a too low

or too high value. By adding a proportion of the average error to the process input, the average

difference between the process output and the set point is continually reduced. Therefore,

eventually, a well-tuned PID loop's process output will settle down at the set point. As an

example, a system that has a tendency for a lower value (heater in a cold

environment), a simple proportional system would oscillate and/or stabilize at a too low value

because when zero error is reached P is also zero thereby halting the system until it again is too

low.

The integral term accelerates the movement of the process towards setpoint and eliminates the

residual steady-state error that occurs with a pure proportional controller. However, since the

integral term responds to accumulated errors from the past, it can cause the present value

to overshoot the set point value

Integrator Circuit

If a capacitor is used as the feedback element in the inverting amplifier, shown in figure 21, the

result is an integrator. An intuitive grasp of the integrator action may be obtained from the

statement under the section, Current Output, that current through the feedback loop charges the capacitor and is stored there as a voltage from the output to ground. This is a voltage input

current integrator.

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Plot of PV vs time, for three values of Ki (Kp and Kd held constant)

The contribution from the integral term is proportional to both the magnitude of the error

and the duration of the error. The integral in a PID controller is the sum of the instantaneous

error over time and gives the accumulated offset that should have been corrected previously. The

accumulated error is then multiplied by the integral gain ( ) and added to the controller output.

The integral term is given by:

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2.3 D CHARACTERISTICS (Derivative Term)

Derivative - To handle the future, the first derivative (the slope of the error) over time is

calculated, and multiplied by another constant D, and also added to the controlled quantity. The

derivative term controls the response to a change in the system. The larger the derivative term,

the more rapidly the controller responds to changes in the process's output. Its D term is the

reason a PID loop is also sometimes called a "predictive controller." The D term is reduced when

trying to dampen a controller's response to short term changes. Practical controllers for slow

processes can even do without D term. More technically, a PID loop can be characterized as a

filter applied to a complex frequency-domain system. This is useful in

order to calculate whether it will actually reach a stable value. If the values are chosen

incorrectly, the controlled process input can oscillate, and the process output may never stay at

the set point.

The derivative term slows the rate of change of the controller output. Derivative control

is used to reduce the magnitude of the overshoot produced by the integral component and

improve the combined controller-process stability. However, the derivative term slows

the transient response of the controller. Also, differentiation of a signal amplifies noise and thus

this term in the controller is highly sensitive to noise in the error term, and can cause a process to

become unstable if the noise and the derivative gain are sufficiently large. Hence an

approximation to a differentiator with a limited bandwidth is more commonly used. Such a

circuit is known as a phase-lead compensator.

Differentiator Circuit

Using a capacitor as the input element to the inverting amplifier, figure 22, yields a

differentiator circuit. Consideration of the device in figure 23 will give a feeling for the

differentiator circuit. Since the inverting input is at ground potential:

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Plot of PV vs time, for three values of Kd (Kp and Ki held constant)

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The derivative of the process error is calculated by determining the slope of the error over

time and multiplying this rate of change by the derivative gain . The magnitude of the

contribution of the derivative term to the overall control action is termed the derivative gain,

.

The derivative term is given by.

2.4 PID CHARACTERISTIC (PID Term)

A proportionalintegralderivative controller (PID controller) is a generic control

loop feedback mechanism (controller) widely used in industrial control systems a PID is the

most commonly used feedback controller. A PID controller calculates an "error" value as the

difference between a measured process variable and a desired set point. The controller attempts

to minimize the error by adjusting the process control inputs.

The PID control scheme is named after its three correcting terms, whose sum constitutes the

manipulated variable (MV). The proportional, integral, and derivative terms are summed to

calculate the output of the PID controller. Defining as the controller output, the final form

of the PID algorithm is:

where

Kp: Proportional gain, a tuning parameter

Ki: Integral gain, a tuning parameter

Kd: Derivative gain, a tuning parameter

: Error

t: Time or instantaneous time (the present)

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The PID loop adds positive corrections, removing error from the process's controllable

variable (its input). Differing terms are used in the process control industry: The "process

variable" is also called the "process's input" or "controller's output." The process's output is also

called the "measurement" or "controller's input." This "up a bit, down a bit" movement of the

process's input variable is how the PID loop automatically finds the correct level of input for the

process. "Turning the control knob" reduces error, adjusting the process's input to keep the

process's measured output at the set point. The error is found by subtracting the measured

quantity from the set point. "PID" is named after its three correcting calculations, whose sum

constitutes the output of the PID controller.

The PID controller calculation (algorithm) involves three separate constant parameters, and

is accordingly sometimes called three-term control: the proportional,

the integral and derivative values, denoted P, I, and D. Heuristically, these values can be

interpreted in terms of time: P depends on the present error, Ion the accumulation of past errors,

and D is a prediction of future errors, based on current rate of change. The weighted sum of these

three actions is used to adjust the process via a control element such as the position of a control

valve, or the power supplied to a heating element.

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Some applications may require using only one or two actions to provide the appropriate

system control. This is achieved by setting the other parameters to zero. A PID controller will be

called a PI, PD, P or I controller in the absence of the respective control actions. PI controllers

are fairly common, since derivative action is sensitive to measurement noise, whereas the

absence of an integral term may prevent the system from reaching its target value due to the

control action.

2.5 IMPORTANCE OF TEMPERATURE CONTROL

Temperature control is so important because it not only keeps all substances and food items at set

temperatures but it also means that the business is operating completely legally, and its

surprising how temperature can have so much of an effect when it comes to the law.

Manual temperature control is often used, but now theres an even easier way of achieving the

same results wireless temperature monitoring. This is a lot more convenient and hassle-free

than more conventional methods, so businesses should always consider investing in a wireless

system (such as that provided by Kelsius) for complete peace of mind.

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2.6 ADVANTAGE OF PID CONTROLLER FOR TEMPERATURE

The different cases are discussed below:

The P controller shows a relatively high maximum overshoot , a long settling

time as well as a steady-state error .

The I controller has a higher maximum overshoot than the P controller due to the slowly

starting I behaviour, but no steady-state error.

The PI controller fuses the properties of the P and I controllers. It shows a maximum

overshoot and settling time similar to the P controller but no steady-state error.

The real PD controller to with has a smaller maximum overshoot due to the

'faster' D action compared with the controller types mentioned under a) to c). Also in this

case a steady-state error is visible, which is smaller than in the case of the P controller.

This is because the PD controller generally is tuned to have a larger gain due to the

positive phase shift of the D action. For the results shown in Figure the gain for the P

controller is and for the PD controller . The plant has a gain

of .

The PID controller to with fuses the properties of a PI and PD controller. It

shows a smaller maximum overshoot than the PD controller and has no steady state error

due to the I action.

The qualitative concepts of this example are also relevant to other type of plants with delayed

proportional behaviour. This discussion has given some first insights into the static and dynamic

behaviour of control loops.

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Figure Behaviour of the normalised controlled variable for step

disturbance at the input to the plant ; for different

types of controllers

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CHAPTER 3

CONTROL LOOP BASICS

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A familiar example of a control loop is the action taken when adjusting hot and cold

faucets (valves) to maintain the water at a desired temperature. This typically involves the

mixing of two process streams, the hot and cold water. The person touches the water to sense or

measure its temperature. Based on this feedback they perform a control action to adjust the hot

and cold water valves until the process temperature stabilizes at the desired value.

The sensed water temperature is the process variable or process value (PV). The desired

temperature is called the set point (SP). The input to the process (the water valve position) is

called the manipulated variable (MV). The difference between the temperature measurement and

the set point is the error (e) and quantifies whether the water is too hot or too cold and by how

much.

After measuring the temperature (PV), and then calculating the error, the controller decides when

to change the tap position (MV) and by how much. When the controller first turns the valve on, it

may turn the hot valve only slightly if warm water is desired, or it may open the valve all the

way if very hot water is desired. This is an example of a simple proportional control. In the event

that hot water does not arrive quickly, the controller may try to speed-up the process by opening

up the hot water valve more-and-more as time goes by. This is an example of an integral control

Making a change that is too large when the error is small is equivalent to a high gain controller

and will lead to overshoot. If the controller were to repeatedly make changes that were too large

and repeatedly overshoot the target, the output would oscillate around the set point in either a

constant, growing, or decaying sinusoid. If the oscillations increase with time then the system is

unstable, whereas if they decrease the system is stable. If the oscillations remain at a constant

magnitude the system is marginally stable.

In the interest of achieving a gradual convergence at the desired temperature (SP), the controller

may wish to damp the anticipated future oscillations. So in order to compensate for this effect,

the controller may elect to temper its adjustments. This can be thought of as a derivative control

method.

If a controller starts from a stable state at zero error (PV = SP), then further changes by the

controller will be in response to changes in other measured or unmeasured inputs to the process

that impact on the process, and hence on the PV. Variables that impact on the process other than

the MV are known as disturbances. Generally controllers are used to reject disturbances and/or

implement set point changes. Changes in feed water temperature constitute a disturbance to the

faucet temperature control process.

In theory, a controller can be used to control any process which has a measurable output (PV), a

known ideal value for that output (SP) and an input to the process (MV) that will affect the

relevant PV. Controllers are used in industry to regulate temperature, pressure, flow rate

,chemical composition, speed and practically every other variable for which a measurement

exists

Consider a typical process control system. For a particular example let us look at an open tank,

which supplies a process, say, a pump, at its output. The tank will require a supply to maintain its

level (and therefore the pumps positive suction head) at a fixed predetermined point. This

predetermined level is referred to as the set point (SP) and it is also the controlled quantity of the

system. Clearly whilst the inflow and outflow are in mass balance, the level will remain constant.

Any difference in the relative flows will cause the level to vary. How can we effectively control

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this system to a constant level? We must first identify our variables. Obviously there could be a

number of variables in any system, the two in which we are most interested are: The controlled

variable - in our example this will be level. The manipulated variable . the inflow or outflow

from the system. If we look more closely at our sample system (Figure 1), assuming the level is

at the set point, the inflow to the system and outflow are

balanced. Obviously no control action is required whilst this status quo exists. Control action is

only necessary when a difference or error exists between the set point and the measured level.

Depending on whether this error is a positive or negative quantity, the appropriate control

correction will be made in an attempt to restore the process to the set point. Henceforth, the error

will always take the form of:

Error = Set point . Measured Quantity

OR

e = SP - M

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CHAPTER 4

PROJECT OVERVIEW

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List of Components used in the project (Panel Board)

Op Amp IC741

Temperature Sensor LM35

Relays RAS0510

Bridge Rectifier BR 68

Voltage Regulators 7915 7815 7015

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4.1 Op Amp IC741

DECRIPTION

An operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltage amplifier with

a differential input and, usually, a single-ended output. An op-amp produces an output voltage

that is typically hundreds of thousands times larger than the voltage difference between its input

terminals.

Operational amplifiers had their origins in analog computers where they were used in many

linear, non-linear and frequency-dependent circuits. Characteristics of a circuit using an op-amp

are set by external components with little dependence on temperature changes or manufacturing

variations in the op-amp itself, which makes op-amps popular building blocks for circuit design.

Op-amps are among the most widely used electronic devices today, being used in a vast array of

consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in

moderate production volume; however some integrated or hybrid operational amplifiers with

special performance specifications may cost over $100 US in small quantities.[citation needed]

Op-

amps may be packaged as components, or used as elements of more complex integrated circuits.

The op-amp is one type of differential amplifier. Other types of differential amplifier include

the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation

amplifier (usually built from three op-amps), the isolation amplifier (similar to the

instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an

ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and

a resistive feedback network) .

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4.2 Temperature Sensor LM35

Description

An analog temperature sensor is pretty easy to explain, its a chip that tells you what the ambient

temperature is!

These sensors use a solid-state technique to determine the temperature. That is to say, they dont

use mercury (like old thermometers), bi metallic strips (like in some home thermometers or

stoves), nor do they use thermistors (temperature sensitive resistors). Instead, they use the fact as

temperature increases, the voltage across a diode increases at a known rate. (Technically, this is

actually the voltage drop between the base and emitter - the V be - of a transistor. By precisely

amplifying the voltage change, it is easy to generate an analog signal that is directly proportional

to temperature. There have been some improvements on the technique but, essentially that is how

temperature is measured.

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Because these sensors have no moving parts, they are precise, never wear out, don't need

calibration, work under many environmental conditions, and are constant between sensors and

readings. Moreover they are very inexpensive and quite easy to use

These stats are for the temperature sensor in the Ad a fruit shop, the Analog Devices TMP36 (-40

to 150C). Its very similar to the LM35/TMP35 (celsius output) and LM34/TMP34 (farenheit

output). The reason we went with the '36 instead of the '35 or '34 is that this sensor has a very

wide range and doensn't require a negative voltage to read sub-zero temperatures. Otherwise, the

functionality is basically the same.

4.3 Relays RAS0510

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Description

A relay is an electrically operated switch. Many relays use an electromagnet to operate a

switching mechanism mechanically, but other operating principles are also used. Relays are used

where it is necessary to control a circuit by a low-power signal (with complete electrical isolation

between control and controlled circuits), or where several circuits must be controlled by one

signal. The first relays were used in long distance telegraph circuits, repeating the signal coming

in from one circuit and re-transmitting it to another. Relays were used extensively in telephone

exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric motor or

other loads is called a contactor. Solid-state relays control power circuits with no moving parts,

instead using a semiconductor device to perform switching. Relays with calibrated operating

characteristics and sometimes multiple operating coils are used to protect electrical circuits from

overload or faults; in modern electric power systems these functions are performed by digital

instruments still called "protective relays" .

4.4 Bridge Rectifier BR 68

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FEATURES

Low cost

This series in UL recognized under component

index, file number E127707

High forward surge current capacity

Ideal for printed circuit board

High isolation voltage from case to leads

High temperature soldering guaranteed:

260OC / 10 seconds, at 5 lbs. (2.3kg) tension.

MECHANICAL DATA

Technology: Cell with vacuum soldered

Case: Molded plastic body

Terminal: Lead solderable per MIL-STD-202E

method 208C

Polarity: Polarity symbols marked on case

Mounting: Thru hole for #10 screw, 5 in-lbs torque max.

Weight: 0.13 ounce, 3.66 gram

MAXIMUM RATINGS AND ELECTRICAL CHARACTERISTICS

Ratings at 25OC ambient temperature unless otherwise specified

Single Phase, half wave, 60Hz, resistive or inductive load

For capacitive load derate current by 20%

4.5 Voltage Regulators 7915 7815 7015

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Description

A voltage regulator is an electrical regulator designed to automatically maintain a

constantvoltage level. A voltage regulator may be a simple "feed-forward" design or may

include negative feedback control loops. It may use an electromechanical mechanism, or

electronic components. Depending on the design, it may be used to regulate one or

more AC or DC voltages.

Electronic voltage regulators are found in devices such as computer power supplies where they

stabilize the DC voltages used by the processor and other elements. In automobile alternators and

central power station generator plants, voltage regulators control the output of the plant. In

anelectric power distribution system, voltage regulators may be installed at a substation or along

distribution lines so that all customers receive steady voltage independent of how much power is

drawn from the line.

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CHAPTER 5

PHYSICALLY IMPLEMENTING OF PID CONTROLLER

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In the early history of automatic process control the PID controller was implemented as a

mechanical device. These mechanical controllers used a lever, spring and a mass and were often

energized by compressed air. These pneumatic controllers were once the industry standard.

Electronic analog controllers can be made from a solid-state or tube amplifier, a capacitor and

a resistance. Electronic analog PID control loops were often found within more complex

electronic systems, for example, the head positioning of a disk drive, the power conditioning of a

power supply, or even the movement-detection circuit of a modern seismometer. Nowadays,

electronic controllers have largely been replaced by digital controllers implemented

with microcontrollers or FPGAs.

Most modern PID controllers in industry are implemented in programmable logic

controllers (PLCs) or as a panel-mounted digital controller. Software implementations have the

advantages that they are relatively cheap and are flexible with respect to the implementation of

the PID algorithm. Variable voltages may be applied by the time proportioning form of Pulse-

width modulation (PWM) a cycle time is fixed, and variation is achieved by varying the

proportion of the time during this cycle that the controller outputs +1 (or 1) instead of 0. On a

digital system the possible proportions are discrete

e.g., increments of .1 second within a 2 second cycle time yields 20 possible steps: percentage

increments of 5% so there is a discretization error, but for high enough time resolution this

yields satisfactory performance

5.1 Ideal versus Standard PID Form

The form of the PID controller most often encountered in industry, and the one most relevant to

tuning algorithms is the standard form. In this form the Kp gain is applied to the Iout,

and Dout terms, yielding:

Where

Ti is the integral time

Td is the derivative time

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In this standard form, the parameters have a clear physical meaning. In particular, the

inner summation produces a new single error value which is compensated for future and past

errors. The addition of the proportional and derivative components effectively predicts the error

value at Td seconds (or samples) in the future, assuming that the loop control remains unchanged.

The integral component adjusts the error value to compensate for the sum of all past errors, with

the intention of completely eliminating them in Ti seconds (or samples). The resulting

compensated single error value is scaled by the single gain .

In the ideal parallel form, shown in the controller theory section the gain parameters are

related to the parameters of the standard form through and This parallel form, where the

parameters are treated as simple gains, is the most general and flexible form. However, it is also

the form where the parameters have the least physical interpretation and is generally reserved for

theoretical treatment of the PID controller. The standard form, despite being slightly more

complex mathematically, is more common in industry.

5.2 Loop Tuning

Tuning a control loop is the adjustment of its control parameters (proportional band/gain,

integral gain/reset, derivative gain/rate) to the optimum values for the desired control response.

Stability (bounded oscillation) is a basic requirement, but beyond that, different systems have

different behavior, different applications have different requirements, and requirements may

conflict with one another.

A PID controller needs to be tuned (PID gains set to appropriate values for your specific

system) to function properly. The performance of your control system is defined by a set of

measurements made when applying a specific input step function as the set point command

variable (going from 0 to 100% of the output value instantaneously) and then measuring the

response of the process variable. These measurements are shown in the graph of a systems

response to a step input below

When tuning your controller, you may desire an over-damped, critically damped, or under-

damped system. In most robotics applications overshoot is unacceptable and may cause damage

to the system. Most robotics systems are over-damped so that they never overshoot their setpoint.

The goal of tuning such systems, then, is decreasing the rise-time and steady-state error to

achieve the best possible performance

PID tuning is a difficult problem, even though there are only three parameters and in

principle is simple to describe, because it must satisfy complex criteria within the limitations of

PID control. There are accordingly various methods for loop tuning, and more sophisticated

techniques are the subject of patents; this section describes some traditional manual methods for

loop tuning.

Designing and tuning a PID controller appears to be conceptually intuitive, but can be hard

in practice, if multiple (and often conflicting) objectives such as short transient and high stability

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are to be achieved. Usually, initial designs need to be adjusted repeatedly through computer

simulations until the closed-loop system performs or compromises as desired.

Some processes have a degree of non-linearity and so parameters that work well at full-load

conditions don't work when the process is starting up from no-load; this can be corrected by gain

scheduling (using different parameters in different operating regions). PID controllers often

provide acceptable control using default tunings, but performance can generally be improved by

careful tuning, and performance may be unacceptable with poor tuning.

5.2.1 Stability

If the PID controller parameters (the gains of the proportional, integral and derivative terms)

are chosen incorrectly, the controlled process input can be unstable, i.e., its output diverges, with

or without oscillation, and is limited only by saturation or mechanical breakage. Instability is

caused by excess gain, particularly in the presence of significant lag.

Generally, stabilization of response is required and the process must not oscillate for any

combination of process conditions and set points, though sometimes marginal stability (bounded

oscillation) is acceptable or desired

5.2.2 Optimum Behaviour

The optimum behavior on a process change or set point change varies depending on the

application.

Two basic requirements are regulation (disturbance rejection staying at a given set point)

and command tracking (implementing set point changes) these refer to how well the

controlled variable tracks the desired value. Specific criteria for command tracking include rise

time and settling time. Some processes must not allow an overshoot of the process variable

beyond the set point if, for example, this would be unsafe. Other processes must minimize the

energy expended in reaching a new set point

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5.2.3 Manual Tuning

If the system must remain online, one tuning method is to first Ki set Ki and Kd values to

zero. Increase the Kp until the output of the loop oscillates, then the Kp should be set to

approximately half of that value for a "quarter amplitude decay" type response. Then

increase until Ki any offset is corrected in sufficient time for the process. However, too

much Ki will cause instability. Finally, increase Kd, if required, until the loop is acceptably quick

to reach its reference after a load disturbance. However, too much Kd will cause excessive

response and overshoot. A fast PID loop tuning usually overshoots slightly to reach the set point

more quickly; however, some systems cannot accept overshoot, in which case an over-

damped closed-loop system is required, which will require a Kp setting significantly less than

half that of the Kp setting causing oscillation

Effects of increasing a parameter independently

Parameter Rise time Overshoot Settling time Steady-state error Stability

Decrease Increase Small change Decrease Degrade

Decrease[4]

Increase Increase Decrease

significantly Degrade

Minor

decrease

Minor

decrease

Minor

decrease No effect in theory

Improve

if small

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CHAPTER 6

DESCRIPTION OF PROJECT KIT

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6.1 Design Of Panel Board

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6.2 Panel Board Circuit

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6.3 Working Of The Panel

6.3.1 Power Circuit

It consists of Transformer, bridge rectifier ,Voltage regulators namely 7815 and 7915 followed

by filter circuit. The transformer used is 230/36 volts. Bridge rectifier used is BR68 .The AC

supply voltage of 230 is fed to the transformer which whose out put is 36V AC. This 36V is fed

to the BR68 rectifier which converts the voltage from AC to DC. This voltage obtained is filtered

using capacitors. The Output from the filter is fed to the regulators 7915 and7815 whose output

is +15 Volts and -15Volts respectively. This is used as +Vcc and Vee for an Operational

amplifiers used in the circuit.

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6.3.2 PID Circuit

This circuit consists of op amps, voltage regulators, Potentiometers, Diode and Relay. The

Voltage regulator is used to give an input to the op amp. The op amp is use to design the

proportional ,integral and derivative analog controller.. The input to the op amp consist of two

voltages . one is the variable voltage fed from the sensor as feedback and other is the fixed value

taken as reference. The difference between these two inputs is taken as error. The error is fed to

proportional ,integral and derivative block. Where the error is multiplied with proportional gain

in P block and error is multiplied after integrating in I block and the error is multiplied after

differentiating in D block. The output of these three blocks or circuits is added up using a

summer circuit. The output of the summer circuit is fed to the diode IN4007 .The diode is

connected in series with the relay. The output terminals of the relay is connected to the bulb.

6.3.3 Sensor Circuit

The sensor used is LM35 which is a heat sensor consisting of three terminals such as input

output and ground respectively .this sensor is output is amplified using op amp and the output is

fed as feed back to the input terminal of op amp which is compared with the reference value and

the error is calculated.

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CHAPTER 7

CONCLUSION

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Now a days temperature control has become an integral part of any control system operating in a

temperature sensitive environment. Input and output signals are specified in this project is

analog. Control of a process is achieved by means of a closed loop circuit. One of the primary

purposes of using feedback in control system is to reduce the sensitivity of the system to

parameter variations.The project deals with a simple aspect of giving information about the

controlling of temperature in a furnace. In this project we have developed a system which

controls the temperature of a furnace. Here we used a bulb in the place of a heater or furnace and

tried to control the temperature of the surroundings of the bulb using heat sensor LM35 . The

output of the sensor is fed back as input to the system as feed back. Here we used analog PID

controller to control the temperature.The gains are to be tuned manually.But use the softwares

(like labview) apt control is possible.

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CHAPTER 8

FUTURE SCOPE OF PID CONTROLLER

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8.1 Improvements

8.1.1 Feed-forward

The control system performance can be improved by combining the feedback (or closed-loop)

control of a PID controller with feed-forward (or open-loop) control. Knowledge about the

system (such as the desired acceleration and inertia) can be fed forward and combined with the

PID output to improve the overall system performance. The feed-forward value alone can often

provide the major portion of the controller output. The PID controller can be used primarily to

respond to whatever difference or error remains between the setpoint (SP) and the actual value of

the process variable (PV). Since the feed-forward output is not affected by the process feedback,

it can never cause the control system to oscillate, thus improving the system response and

stability.

For example, in most motion control systems, in order to accelerate a mechanical load under

control, more force or torque is required from the prime mover, motor, or actuator. If a velocity

loop PID controller is being used to control the speed of the load and command the force or

torque being applied by the prime mover, then it is beneficial to take the instantaneous

acceleration desired for the load, scale that value appropriately and add it to the output of the PID

velocity loop controller. This means that whenever the load is being accelerated or decelerated, a

proportional amount of force is commanded from the prime mover regardless of the feedback

value. The PID loop in this situation uses the feedback information to change the combined

output to reduce the remaining difference between the process setpoint and the feedback value.

Working together, the combined open-loop feed-forward controller and closed-loop PID

controller can provide a more responsive, stable and reliable control system.

8.1.2 Other improvements

In addition to feed-forward, PID controllers are often enhanced through methods such as

PID gain scheduling (changing parameters in different operating conditions), fuzzy

logic or computational verb logic. Further practical application issues can arise from

instrumentation connected to the controller. A high enough sampling rate, measurement

precision, and measurement accuracy are required to achieve adequate control performance.

Another new method for improvement of PID controller is to increase the degree of freedom by

using fractional order. The order of the integrator and differentiator add increased flexibility to

the controller.

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CHAPTER 9

BIBILOGRAPHY

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www.wekipedia.com, http://en.wikipedia.org/wiki/PDI

PID controller http://en.wikipedia.org/wiki/PID_control

Texas Instruments, Op Amps and Comparators - Don't Confuse Them, SLOA067, Bruce Carter, 09/06/2001

R. J. Widlar, Super Gain Transistors for ICs, IEEE Journal of Solid-State Circuits

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9.1 Appendixes

9.1.1 Appendix A

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9.1.2 Appendix B

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9.1.3 Appendix C

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9.1.4 Appendix D

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9.1.5 Appendix E

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