| Date | May 2018 | Marks available | 3 | Reference code | 18M.1.HL.TZ0.14 |
| Level | HL | Paper | 1 | Time zone | no time zone |
| Command term | Explain | Question number | 14 | Adapted from | N/A |
Question
A number of devices in and around the home can be operated by control systems.
A home owner wishes to install automatic lights to illuminate a water fountain in her garden. These lights will automatically turn on at sunset and turn off at sunrise.
Describe two hardware components that would be an essential part of this control system.
Explain the concept of feedback, with respect to computer control systems in general.
The home owner has also installed a control system that waters the flowerbeds in the garden. This system aims to maintain the water content of the flowerbeds between a minimum and a maximum value. However, the system is only activated when the light intensity is below a certain level.
Outline the algorithm involved in controlling the watering system described above.
Markscheme
Award [1] for identifying the hardware component and [1] for describing its purpose within the control system.
Mark as [2] and [2].
Sensor;
To detect the presence/absence of the light;
Microprocessor;
To carry out any processing;
Output transducer / Actuator / Activator;
To turn the lights on or off;
The output value is (continuously) compared to the desired value;
To produce an error value/difference between observed and measured;
The controller uses the error value/difference between observed and measured;
To determine the new input to the system;
Award [5 max] for the following:
[1] the system is turned on (when the light intensity is below a given value);
[1] for light loop/while input light intensity is below the given value the system continues being on;
[1] for comparison and activating watering / checking the water content of the flower beds and turning on water if the water content is not in a given range;
[1] for water loop / watering until maximum value;
[1] for turning off water when the water content of the flower beds is filled to maximum;
[1] for turning off system when the light intensity increases the given value;
Note: Candidates are not requested to construct an algorithm in pseudocode.
Example answer:
