Answers to all Activities and Mastery Tests section one > core

Think

Box weights: Pressure detectors under the conveyor belt could detect the weight differences.

b) Ball speed: Timed pulses could measure the ball speeds down the delivery chute. This method would be appropriate as it is a motion sensor and the sensor is not attached to the object.

5.

	Advantages:	Disadvantages:
Contact wand scanners	They are inexpensive and rugged devices.	The wand must make contact with the complete width of the barcode. Curved or hard to reach barcodes are not easy for the wand to read.
Hand-held non-contact active scanners	They can read barcodes from a reasonable distance.	They are expensive and contain moving parts which can be damaged if the scanner is treated roughly.

Remember

1. It is necessary to convert data signals between digital and analogue because the real, physical world around us produces analogue signals while the computerised, information system world uses digital signals. Therefore, to use or record real world data in information systems, the real world’s analogue output must first be converted to the technology world’s digital medium.
2. Signal noise is unwanted extra signals caused by interference. This interference or ‘noise’ can be the result of an electrical power supply, static electricity or a strong magnetic field. It can be removed by signal conditioning which alters data signals to improve their signal quality or adjusts/fine tunes the operation of the output device.
3. The three types of signal damping are: underdamping, critical damping and overdamping. An underdamped system reacts very quickly to a change but takes some time to settle down to a new stable output level. A critically damped system reacts quickly to a change and quickly reaches a new stable output level. An overdamped system reacts very slowly to a change and takes a long time to reach a new stable output level.

Think

4. a) Noise on an analogue data link can affect the signal, making it difficult to distinguish between the signal and the interference. Passing the signal through a signal conditioner will remove unwanted noise and therefore the operation of the receiving device won’t be affected.
b) Noise on a digital data link can be detected far more easily than on an analogue link. Digital systems use error detection and correction methods to detect and remove signal errors, thus enabling easy differentiation between signals and noise.
5. A stable system is more sophisticated than a controlled system and undergoes less fluctuations. Controlled systems may respond so quickly to change that fluctuations are unnecessarily high and occur too frequently.
6. a) Bungee jumping is like underdamping: There is a rapid response to change [upon jumping, the limp cord responds dramatically to the sudden weight by going incredibly taut and elastic]; followed by a reasonable period of instability [a set of decreasingly powerful rebounds then occur]; before things settle down to a stable level [the jumper hangs still waiting to dismount].

b) Getting on a set of bathroom scales is like critical damping: There is a speedy response to change [the sudden weight on the scales gets the device calculating rapidly]; before it quickly reaches a stable position with little or no instability period [the scale races to the approximate weight area before adjusting to the final measure which it holds steady while the person remains].

Activities (p261)

Remember

1. The different types of actuators are: solenoids, DC (Direct Current) motors, AC (Alternating Current) motors, stepping motors, relays and hydraulic pumps.
2. Stepping motors and hydraulic pumps can be used to give precise control movements.
3. Relays are ideal for turning other devices on and off.

Think

4. a) DC motor b) solenoid c) stepping motor d) relay.
5. a) If the stepping motor of a hard disk drive was underdamped, it would continually over-shoot its destination in terms of locating specific data at specific disk locations. This would slow down hard disk access and overwork the stepping motor as it continually moved too far back and forth.

b) If the stepping motor of a hard disk drive was overdamped, the hard disk access would again be slow but the stepping motor wouldn’t be moving continually back and forth, rather very slowly toward the desired destination.

6. A hydraulic pump can quickly apply large forces over a range of distances with good precision. The examples given in this chapter of oil passing through the piston chambers of a robotic arm demonstrate the speed and precision of hydraulic pump devices.

Activities (p264)

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