In a thermostat control system for a home heating system

Which of the following statements are true? (a) Feedback and feedforward control both require a measured variable. (b) The process variable to be controlled is measured in feedback control. (c) Feedforward control can be perfect in the theoretical sense that the controller can take action via the manipulated variable even while the controlled variable remains equal to its desired value. (d) Feedforward control can provide perfect control; that is, the output can be kept at its desired value, even with an imperfect process model. (e) Feedback control will always take action regardless of the accuracy of any process model that was used to design it and the source of a disturbance.

Consider a home heating system consisting of a natural gas-fired furnace and a thermostat. In this case the process consists of the interior space to be heated. The thermostat contains both the measuring element and the controller. The furnace is either on (heating) or off. Draw a schematic diagram for this control system. On your diagram, identify the controlled variables, manipulated variables, and disturbance variables. Be sure to include several possible sources of disturbances that can affect room temperature.

In addition to a thermostatically operated home heating system, identify two other feedback control systems that can be found in most residences. Describe briefly how each of them works; include sensor, actuator, and controller information.

Does a typical microwave oven utilize feedback control to set cooking temperature or to determine if the food is "cooked"? If not, what mechanism is used? Can you think of any disadvantages to this approach, for example, in thawing and cooking foods?

Driving an automobile safely requires a large amount of individual skill. Even if not generally recognized, the driver needs an intuitive ability to utilize feedforward and feedback control methods. (a) In the process of steering a car, the objective is to keep the vehicle generally centered in the proper traffic lane. Thus, the controlled variable is some measure of that distance. If so, how is feedback control used to accomplish this objective? Identify the sensor(s), the actuator, how the appropriate control action is determined, and some likely disturbances. (b) The process of braking/accelerating an auto is highly complex, requiring the skillful use of both feedback and feedforward mechanisms to drive safely. For feedback control, the driver normally uses distance to the vehicle ahead as the measured variable. The "set point" then is often recommended to be some distance related to speed, for example, one car length separation for each 10 mph. If this assertion is correct, how does feedforward control come into the accelerating/braking process when one is attempting to drive in traffic at a constant speed? In other words, what other information-in addition to distance separating the two vehicles, which obviously should never equal zero-does the driver utilize to avoid colliding with the car ahead?

The distillation column shown in the drawing is used to distill a binary mixture. Symbols x, y, and z denote mole fractions of the more volatile component, while B, D, R, and F represent molar flow rates. It is desired to control distillate composition y despite disturbances in feed flow rate F. All flow rates can be measured and manipulated with the exception of F, which can only be measured. A composition analyzer provides measurements of y. (a) Propose a feedback control method and sketch the schematic diagram. (b) Suggest a feedforward control method and sketch the schematic diagram.

Two flow control loops are shown in the drawing. Indicate whether each system is either a feedback or a feedforward control system. Justify your answer. It can be assumed that the distance between the flow transmitter (FT) and the control valve is quite small in each system.

I. M. Appelpolscher, supervisor of the process control group of the Ideal Gas Company, has installed a 25 X 40 X 5-ft swimming pool in his backyard. The pool contains level and temperature sensors used with feedback controllers to maintain the pool level and temperature at desired values. Appelpolscher is satisfied with the level control system, but he feels that the addition of one or more feedforward controllers would help maintain the pool temperature more nearly constant. As a new member of the process control group, you have been selected to check Appelpolscher's mathematical analysis and to give your advice. The following information may or may not be pertinent to your analysis: (i) Appelpolscher is particular about cleanliness and thus has a high-capacity pump that continually recirculates the water through an activated charcoal filter. (ii) The pool is equipped with a natural gas-fired heater that adds heat to the pool at a rate Q(t) that is directly proportional to the output signal from the controller p(t) (iii) There is a leak in the pool, which Appelpolscher has determined is constant equal to F (volumetric flow rate). The liquidlevel control system adds water from the city supply system to maintain the level in the pool exactly at the specified level. The temperature of the water in the city system is T w, a variable. (iv) A significant amount of heat is lost by conduction to the surrounding ground, which has a constant, year-round temperature T 0 . Experimental tests by Appelpolscher showed that essentially all of the temperature drop between the pool and the ground occurred across the homogeneous layer of gravel that surrounded his pool. The gravel thickness is Lh, and the overall thermal conductivity is k 0 . (v) The main challenge to Appelpolscher's modeling ability was the heat loss term accounting for convection, conduction, radiation, and evaporation to the atmosphere. He determined that the heat losses per unit area of open water could be represented by where Tp = temperature of pool Ta = temperature of the air, a variable U = overall heat transfer coefficient Appelpolscher's detailed model included radiation losses and heat generation due to added chemicals, but he determined that these terms were negligible. (a) Draw a schematic diagram for the pool and all control equipment. Show all inputs and outputs, including all disturbance variables. (b) What additional variable(s) would have to be measured to add feedforward control to the existing pool temperature feedback controller? (c) Write a steady-state energy balance. How can you determine which of the disturbance variables you listed in part (a) are most/least likely to be important? (d) What recommendations concerning the prospects of adding feedforward control would you make to Appelpolscher?

In a thermostat control system for a home heating system (a) Identify the manipulated variable (b) Identify the controlled variable (c) How is a valve involved in the control system? What does it manipulate? (d) Name one important disturbance (it must change with respect to time).

Identify and describe three automatic control systems in a modern automobile (besides cruise control).

In Figure 1.2 (h), identify the controlled, manipulated, and disturbance variables (there may be more than one of each type). How does the length of time for the dialysis treatment affect the waste concentration?

For the steam-heated tank shown below, identify manipulated, controlled, and disturbance variables. What disturbances are measured for feedforward control? How would the control system react to an increase in feed temperature in order to keep the tank temperature at its setpoint?