Microprocessors and Input in Control Systems

7.1.2 Outline the uses of microprocessors and sensor input in control systems.
7.1.3 Evaluate different input devices for the collection of data in specified situations.
7.1.4 Explain the relationship between a sensor, the processor and an output transducer.
7.1.5 Describe the role of feedback in a control system.

IB Subtopic

A microprocessor is a small processor that contains most or all of a central processing unit (CPU) functions on a single chip or unit. These processors are can process information in the CPU through registers, but usually require a small operating system and have limited primary and secondary memory.

There are various types of microprocessors:

General Purpose: microprocessors that can handle a variety of tasks. Examples of these include laptop CPU’s, desktop CPUs, Raspberry Pi, Arduino, and micro:bit.

Embedded controller or microcontroller: Many systems contain specialized cpu’s that perform specific operations. Automatic doors, heating systems, taxi meters, and elevators all use microcontrollers that contain embedded RAM and ROM. The microprocessor for a heating system most likely will not work inside a washing machine system.

Graphics processing unit (GPU): a GPU is specialized microprocessors that include hardware to allow for faster handling of graphics related mathematics such as matrix multiplication and vector arithmetic. GPU must calculate and render polygons and pixels on a screen at high speeds.

Sensors

Sensors are a device that detects or measures a physical property so that a control system records, indicates, or otherwise responds to it.

In order for any of these microprocessors to perform any processing, they must receive some input. These inputs will come from sensors that will provide them with readings of physical measurements like speed, temperature, humidity, and pressure and turn them into digital signals that a computer can use. This conversion will happen through analog-to-digital converters(ADC).

There are a few qualities that all sensors must meet, regardless of the measurements they are meant to make:

Accuracy: must make measurements that are accurate in analog and digital representations.
Range: must measure an acceptable range of the physical quantity.
Resolution: must measure in acceptable increments, such as 0.1C or 0.01m/s
Focus: should not be influenced by other physical conditions. A temperature sensor should not be influenced by the movement of objects around the room.
Side-effects: should not create physical conditions that will affect its measurements. A temperature sensor should not create heat that will affect its own measurement.

Types of Sensors

Sound: Detect sound waves

Motion: Detect moving objects

Vibration: Detect vibrations/movement

Optical/Image
Active Pixel Sensor: Cameras
Infrared: Can be used to detect movement

Pressure: Usually used in touch screens and computer peripherals.

Temperature: Measures temperature

Proximity: Gives a reading of how close an object is.

Transduction

Sensors need to create electrical signals that computers understand. Those electrical signals are created by the transducer, which takes a physical input and converts it into a representation that the computer can understand. This process is called transduction.

You’ll often find that control systems use an input, process that information and then perform an action. The part of the system that performs the action is called an actuator. This actuator will usually take some input, like an electric signal and translate it into physical motion through the use of a digital-to-analog converter(DAC). Actuators are also considered transducers since they convert one form of energy to another.

If we take a microphone system as an example, we see that the actuator is the speaker, which received electrical signals and creates a physical representation as sound waves.

Feedback

Feedback is an important part of control systems. When a process indicates an actuator that an action must be taken, that action will have a side effect on the physical world. The system should have a sensor that will be ready to pick up that feedback and let the system know to act appropriately. In the example of a cleaning robot vacuum, the actuators move the robot until it hits something, the sensors then let the system know that a bump happened and the actuators will then be asked to move in a different direction.

Open Loops

Systems like microwaves or toaster don’t usually use a feedback system. This is called an open-loop system. You press the button, the system processes the level of heat you want and the output is the heat itself. Once the timer goes off, the system goes off.

Closed Loops

Some systems use closed loops. This means that the output directly affects the input sensors. The system stop when the feedback decides it has reached a specific level. The feedback system can also serve to regulate the system and maintain stability.