This document presents information on on-off controllers. It discusses that on-off controllers have only two output states - fully on or fully off. When the process variable exceeds the setpoint, the controller output switches fully on, and when it falls below the setpoint, the output switches fully off. This causes oscillations in the process variable. The document describes examples of on-off control schemes for fans, water heaters and water level. It also lists advantages like low cost and quick response, and disadvantages like inability to control systems with delays and lack of accuracy.

1. TECHNOINDIA, SALTLAKE
DEPARTMENT OF ELECTRICAL ENGINEERING
CONTROL SYSTEM-I [EE-503]
SUBMITTED BY:
 SAYAN SARKAR (ROLL: 13001616049)
 PRATYAY NAYAK (ROLL:13001616078)

2. PRESENTATION
ON
ON-OFF
CONTROLLER

3. CONTENT
 Introduction
 Industrial automatic controller
 What is on of controller
 Theory of on-off controller
 Differential gap
 Example
Fan controlling scheme
water heater controller
water level controller
 Advantages of on-off controller
 Disadvantages of on-off controller
 Conclusion

4. The automatic controller determines the value of controlled
variable,compare the actual value to desired value(reference
input),determines the deviation and produces a control signal that
will reduce the deviation to zero or to a smallest possible
value.The method by which the automatic controller produces the
controll signal is called mode of controll or controll action.
The controll action may operate through either mechanical,
hydraulic,pneumatic or electromechanical means i.e.,controllers
can be electrical,hydraulic,pneumatic,electromechanical or
electronic types.

5. Industrial Automatic Controller
The controller consists of an error detector and amplifier.The measuring
element is a device which converts the output variable to another suitable
variables such as displacement, pressure or electrical signals, which can be
used for comparing the output to the reference input signal.

6. WHAT IS ON-OFF CONTROLLER
 On-Off control is the simplest form of feedback
control.
 Sometimes, the control element has only two
positions either it is fully closed or fully open. This
control element does not operate at any intermediate
position, i.e. partly open or partly closed position.
Transmitts only two output signal-ON(100%) &
OFF(0%).
 The control system made for controlling such
elements is known as on off controller. In this
control system, when process variable changes and
crosses certain preset level, the output valve of the
system is suddenly fully opened and gives 100 %
output.
 ON-OFF controller is also known as Bang-Bang
controller or 2 Step controller.
Symbol of
On-Off
controller

7. In this type of control the output of the controller is quickly changed to either a
maximum or minimum value depending upon whether the controlled variable is greater
or less than the set point or in other words depends upon the actuating error signal. The
minimum value is usually zero.
m=Output of the controller
M1=Maximum value of output of the controller
M2=Minimum value of output of the controller
e=Actuating error signal or deviation.
The equations for two-position control will be
m=M1 when e>0
m=M2 when e<0
In ON-OFF controller there is an overlap as the error increases through zero or
decreases through zero. The overlap creates a span of error. During this span of error,
there is no change in the controller output. This span of error is known as Dead
Zone or Dead Band.

8. • Till the error changes by de there is no change in the
controller output. Similarly while decreasing the error must
decrease beyond de below 0 to change the controller output.
Hence, during 2de there is no change in the controller
output. This zone is known as Differential Gap.
• The differential gap can also be defined as the range through
which the actuating error signal must move before the
switching occurs.
• In this type of controller, the control variable
always oscillates with a frequency which increase
with decreasing width of the dead zone(differential
gap). The decrease in dead zone, the number of
ON-OFF switching of controller increases, hence
therefore the useful life of component decreases.
Hence dead band should be designed to prevent the
oscillations in ON-OFF controllers.

9. FAN CONTROLLING SCHEME
A very common example of on-off control theory is fan controlling scheme of transformer
cooling system. When transformer runs with such a load, the temperature of the electrical
power transformer rises beyond the preset value at which the cooling fans start rotating
with their full capacity. As the cooling fans run, the forced air (output of the cooling
system) decreases the temperature of the transformer. When the temperature (process
variable) comes down below a preset value, the control switch off fans trip and fans stop
supplying forced air to the transformer. After that, as there is no cooling effect of fans, the
temperature of the transformer again starts rising due to load. Again when during rising,
the temperature crosses the preset value, the fans again start rotating to cool down the
transformer. Theoretically, we assume that there is no lag in the control equipment. That
means, there is no time day for on and off operation of control equipment.witch of fans trip
and fans stop supplying forced air to the transformer.

10. WATER HEATER
• Water Heater Controller, a system that enables remote
and convenient control of water heater via smart phone
or web enabled device.
• It control steam or heating materials in water tank to
maintain required temperature.

11. WATER LEVEL CONTROLLER
A water level controller is a device that manages water levels
on a variety of systems such as water tanks, pumps and
swimming pools. The basic function of a water level
controller is to regulate water flow and optimize system
performance.

12. Advantages of On-Off
Controller
• It is most easiest and intuitive method to implement.
• It is a basic method and very simple.
• Low initial cost.
• Plain structure.
• Quick response.
• No tuning required for start-up.

13. Disadvantages of On-Off
Controller
• It is unable to controll moving processes with time delays.
• It is not accurate enough.
• It does not have enough quality.
• PID controllers should be used for reducing the fluctuation
produced by On-Off controller but parameter’s setting for PID
controllers is difficult.
• Accepts only binary input.
• More energy is used by valves.

14. CONCLUSION
Summing up, we can say that the on-off temperature control in the tank of
a bioreactor is a good case study in explaining the basic terms of process control with
minimal usage of mathematics. It is a simple example of a relay-type control in which
the CV assumes only two discrete values. A system of the on-off control can be applied
in a situation when: a periodical fluctuation in the PV is acceptable and oscillations vary
within reasonable limits, acceptable in a particular case. This fluctuation results from
periodical step changes in values of the CV. This is acceptable when the object of
control
is to exhibit a ‘smoothing’action, i.e. when it is to be characterised by a slow response
to the step changes of the CV. Such requirements are easily fulfilled in the case of tem-
perature control of thermal objects or in the control of the level of liquid or pressure in
containers where the PV values can only change slowly. The advantage of the relay in
the control system is the ease of switching over of actuators of high electric power at
low
power used for the control itself.

15. THANK
YOU