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Unit 7: Control systems (HL)

Syllabus

7.1.1 Discuss a range of 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.

7.1.6 Discuss the social impacts and ethical considerations associated with the use of embedded systems.

7.1.7 Compare a centrally controlled system with a distributed system.

7.1.8 Outline the role of autonomous agents acting within a larger system.

Introducing control systems

A control system is a device, or set of devices, that manages, commands, directs or regulates the behaviour of other devices or systems. Industrial control systems are used in industrial production for controlling equipment or machines. (Wikipedia)

Some examples of control systems include:

Microprocessors

What use does a microprocessor have in control systems?

Sensor input

What role do sensors or transducers have in control systems?

Sensors can be broadly categorised into two types: active and passive.

Generally, active sensors require an external power supply to operate, called an excitation signal which is used by the sensor to produce the output signal. Active sensors are self-generating devices because their own properties change in response to an external effect producing for example, an output voltage of 1 to 10v DC or an output current such as 4 to 20mA DC. Active sensors can also produce signal amplification.

A good example of an active sensor is an LVDT sensor or a strain gauge. Strain gauges are pressure-sensitive resistive bridge networks that are external biased (excitation signal) in such a way as to produce an output voltage in proportion to the amount of force and/or strain being applied to the sensor.

Unlike an active sensor, a passive sensor does not need any additional power source or excitation voltage. Instead a passive sensor generates an output signal in response to some external stimulus. For example, a thermocouple which generates its own voltage output when exposed to heat. Then passive sensors are direct sensors which change their physical properties, such as resistance, capacitance or inductance etc.

There are an enormous variety of sensors easily available for hobbyist projects. Check adafruit.com for an indication.

Sensors can also be categorised into analogue or digital. Analogue sensors produce a voltage or signal output response which is proportional to the change in the quantity that they are measuring (the stimulus). Digital Sensors produce a discrete output representing a binary number or digit such as a logic level “0” or a logic level “1”.

Common sensors and transducers by environment they detect are:

Source: https://www.electronics-tutorials.ws/io/io_1.html

Digital v Analogue input

What input devices would be best suited for…?

Brainstorm other familiar situations where there could be a computer with an input device. What input devices would be best suited for that situation?

Transducer (outputs)

Open and closed loop systems

There is commonly a cyclic relationship between a sensor, the processor and an output transducer. This can be either an open-loop or a closed-loop depending on the circumstance. The difference between the two is the role that feedback plays within the system. If the output has a direct bearing on future inputs, then it is said to be a closed loop system.

What other examples could we illustrate with?

Social impacts and ethical considerations

Control systems, commonly also referred to as embedded systems, come with a range of social and ethical issues.

Some examples:

Central vs distributed control

Control systems deployed in industry may be either centrally controlled or use a distributed system of control.

In a centrally controlled system, all sensors and transducers run cabling (or wireless signal) over a network back to a central control system; where as in the distributed model control is more locallised. Each method comes with it’s own advantages and disadvantages.

Autonomous agents acting within a larger system

An autonomous agent is an intelligent agent operating on an owner’s behalf but without any interference of that ownership entity. (Wikipedia, 2017)

The defining metaphor of an autonomous agent is the thinking machine.

They are (usually) designed in interact with their environment:

It has been suggested agenthood of a computer system is restricted to the following (Woolridge et al 1995):

From Federico Gobbo, 2013

Example: Self driving cars. When not everything is within the systems control.

Activity

The best way of learning about how different sensors and transducers interact is through hands on experience. Using a Raspberry Pi or Arduino, experiment with different inputs and outputs.

Experiment and gain practical hands-on experience from a programmers perspective of:

If time allows, experiment with creating a simple closed loop feedback system. Options include:

Past paper questions

Ask me for access.