Level Control Experiment

On/Off Control Answers

Since the valve position swings fully closed and fully shut very frequently, the valve would soon wear out. This is obviously undesirable where valve reliability is important. However, it can be used in situations like domestic water systems (see the hot water tank experiment) where tight control of a temperature is not necessary.
You should have noticed that the valve is either wide open or fully closed. The process is controlled within a band or level range and the width of this band (and how often the valve either opens or closes) is determined by the deadzone. The longer the deadzone, the wider the bandwidth, but the further away the process is allowed to get from the setpoint. Also, the more time there is between the valve swinging position to the opposite state.
Another interesting observation can be seen at long deadzone values. The variation in the level is assymmetric (this is seen by the fact the level is not a "sawtooth" around the setpoint) indicating the this process is in fact non-linear.
It should be noted that this sort of control cannot be used for tight control around a setpoint and is not frequently used in the chemical industry.