Transfer Lag Research

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Instrumentation Test #3 Take-Home Essay Questions Question #1: The time is takes for a process variable to arrive at the set point is called transfer lag. Draw and Explain in detail with an example of a process taken into an account for a small capacity process, a moderate capacity, and a large capacity. As explained above, a Transfer Lag is the time is takes for a process variable to arrive at the set point. This lag is caused by many variables such as capacitance, mass, and dead time in the control system. I will outline an example using three different capacities, but with static process, and flow rate. The point of this example is to showcase the difference in transfer lag between capacities of small, moderate and large containers. The small capacity will be a 500mL can of soup (Fig. 1.1), the moderate capacity will be a 50L kid’s pool (Fig 1.2), and the large process will be an Olympic-sized pool, set at 2.5 million Liters (Fig 1.3). The process in question is simply water, flowing out from a tap at approximately 12L/min. Fig. 1.1 Fig. 1.2 Fig. 1.3 As you can see, we have each capacity at a 30% Set Point. The flow is the same for each at 12L/min, and the process is water for each. The Transfer Lag comes in when we want to increase our Set Point from 30% to 50%. In the can, this change will not be as instant as turning ON an incandescent bulb, it will take some time before it reaches this point, and thus Transfer Lag is apparent. Now, we use different capacities to showcase the positive correlation between capacity and transfer lag, if flow and process are kept static. Example, as we increase the capacity from a 500mL can to a 50L kiddy pool, our transfer lag will increase linearly with it (Fig 2.1). Figure 2... ... middle of paper ... ...tart to be less than ON or OFF (0 or 100%), but our measured water level change will have an 0-100% range. In sum, we can see that if you would like to have the controller output to have a smaller range, the proportional band would need to be more than 100%, anything less would render a 0-100%, or ON-OFF range. If the proportional band is set too narrow, the final control element will often act as an On-Off controller, rather than the throttling type of controller, if it is set too high, the controller will not respond to small disturbances in the process variable, and the process will not be controlled at setpoint. Proportional plus integral (reset) control. The integral is a time averaging process of the offset compared with the set point. Draw and explain in detail with an example where this would be used and the advantages of having this in the process system.

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