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Simulation of On-Off Control with Hysterisis

Description| How it works



On Off controllers (also known as bang-bang controllers) are simple examples of feedback controllers. The are commonly encountered in thermostats, used to control temperature in many electrical devices. This app simulates an on off controller with hysteresis used to control a first order process with delay process. Many heating and cooling processes can be modelled as a first order process with time delay.

Bang Bang control

Download

.xls file (115 KB) or .zip file (31 KB)

How to use

The process parameters are keyed into the cells C6 through C8. For the controller, only has the hysteresis parameter to be set. This parameter represents the percentage by which the process value has to move before the controller changes state. For instance, hysteresis of 10% means that the process value must move over 10% of its range over the setpoint before the controller turns off.

Obviously, controllers with high hysteresis values are not desirable, higher hysteresis means that the process value will swing through a larger range. The following screenshots illustrate this, they show behaviour of controllers with different hysteresis controlling the same process. Note that the variation in the process value is larger when the controller has larger hysteresis.

Bang Bang Control

On Off Control

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