|
|
| Home |
| CS |
| Sites |
| ABdA |
| Help |
|
|
WEEK 11: PROCESS RESPONSE / CHARACTERISTICS Sections: Definitions | Time Constant Delay | Transfer Lag | Transport Lag | Relation Definition. Process response is the reaction of the process itself to the final correcting device signal. Process Characteristics is the certain amount of time to fully respond to a change in input. Sections: Definitions | Time Constant Delay | Transfer Lag | Transport Lag | Relation Definition. Also known as the Process Reaction Delay [PRD], the duration of time delay between the application of the corrective action and the appearance of the final result of that correctibe action. Virtually, all industrial processes show this type of reaction. Many are in seconds, some in few minutes, while occasionally a few exhibit time constant delay in a matter of hou or more. Factors Affecting TCD/PRD. Relevant Quantity can be in the following forms: Relevant Potential can be in the following forms: 2. Resistance. A certain potential difference necessary to cause a certain rate of flow. Potential Difference can be in the following forms: Rate of Flow can be in the following forms: The larger the thermal resistance, the larger is the time constant and the more time is necessary to reach a final steadt temperature. Also, the larger the thermal capacitance, the larger is the time constant. Thermal Time Constant depends on the thermal resistance and thermal capacitance of the system/proces. Sections: Definitions | Time Constant Delay | Transfer Lag | Transport Lag | Relation Definition. Also known as the two-capacity process delay. It is the delay caused by the measured process variable, e.g., temperature, pressure, etc., to initially respond very strongly to a corrective action. A typical example is the reheating of a billet, shown in the diagram, below. As compared to a one-capacity process, particularly showing the Time Constant Delay curve, the Transfer Lag curve usually lies below the TCD curve. Additional capacities would be detrimental to the delay. Sections: Definitions | Time Constant Delay | Transfer Lag | Transport Lag | Relation Definition. Also known as the Distance-Velocity Lag, the delay is associated with the controlled medium moving from one physical location to another. This is the most difficult process response to be studied. The response is felt in the controlled variable for a certain period. The controller signals the corrective device after some time. Thereby, there exist the so called dead time, the amount of time the correcting device changes remain undetected. The slower the speed of movement, the worse is the Transportation Lag. The farther the distance between two points, the worse the Transportation Lag. As compared to TCD, the Transportation Lag curve usually lags behind it by the amount of the dead time of the system. Dead time can be increased aside from Transportation Lag, e.g., gear back lash. |
