On off controller

This is a presentation of a topic of control system engineering

1. TECHNO INDIA, 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. INTRODUCTION

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. Theory of ON-OFF Controller 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. Differential Gap 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.

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