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Sensors Flashcards

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1
Q

Temperature

A

measures temperature of the surroundings by sending signals; these signals will change as the temperature changes

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2
Q

Moisture

A

measures water levels in, for example, soil (it is based on the electrical resistance of the sample being monitored)

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3
Q

Humidity

A

this is slightly different to moisture; this measures the amount of water vapour in, for example, a sample of air (based on the fact that the conductivity of air will change depending on the amount of water present)

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4
Q

Light

A

these use photoelectric cells that produce an output (in the form of an electric current) depending on the brightness of the light

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5
Q

Infrared

A

these use an invisible beam of infrared radiation picked up by a detector; if the beam is broken, then there will be a change in the amount of infrared radiation reaching the detector (sensor)

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6
Q

Infrared passive

A

these sensors measure the heat radiation given off by an object, for example, the temperature of an intruder or the temperature in a fridge

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7
Q

Pressure

A

a pressure sensor is a transducer and generates different electric currents depending on the pressure applied

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8
Q

Sound

A

these are basically microphones that convert detected sound into electric signals/pulses

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9
Q

Gas

A

most common ones are oxygen or carbon dioxide sensors; they use various methods to detect the gas being monitored and produce outputs that vary with the oxygen or carbon dioxide levels present

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10
Q

Ph

A

these measure acidity through changes in voltages in, for example, soil

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11
Q

Magnetic field

A

these sensors measure changes in magnetic fields – the signal output will depend on how the magnetic field changes

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12
Q

Accelerometer

A

these are sensors that measure acceleration and motion of an application, i.e. the change in velocity (a piezoelectric cell is used whose output varies according to the change in velocity)

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13
Q

Proximity

A

these sensors detect the presence of a nearby object

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14
Q

Flow rate

A

these sensors measure the flow rate of a moving liquid or gas and produce an output based on the amount of liquid or gas passing over the sensor

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15
Q

Level

A

these sensors use ultrasonics (to detect changing liquid levels in, for example, a tank) or capacitance/ conductivity (to measure static levels (for example, height of water in a river) – note, level sensors can also be optical or mechanical in nature

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16
Q

Examples of monitoring

A

» Monitoringofapatientinahospitalforvitalsignssuchasheartrate,temperature, etc.
» Monitoring of intruders in a burglar alarm system
» Checking the temperature levels in a car engine
» Monitoring pollution levels in a river.

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17
Q

Examples of control

A

» Turning street lights on at night and turning them off again during daylight
» Controlling the temperature in a central heating/air conditioning system
» Chemical process control (for example, maintaining temperature and pH of
process)

» Operating anti-lock brakes on a car when necessary » Controlling the environment in a green house.

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18
Q

Monitoring applications

A

the system is activated by keying in a password on a keypad
» the infrared sensor will pick up the movement of an intruder in the building
» the acoustic sensor will pick up sounds such as footsteps or breaking glass
» the pressure sensor will pick up the weight of an intruder coming through a
door or through a window
» the sensor data is passed through an ADC if it is in an analogue form …
» … to produce digital data
» the computer/microprocessor will sample the digital data coming from these
sensors at a given frequency (e.g. every 5seconds) …
» … the data is compared with the stored values by the computer/microprocessor
» if any of the incoming data values are outside the acceptable range, then the
computer sends a signal …
» … to a siren to sound the alarm, or
» … to a light to start flashing
» a DAC is used if the devices need analogue values to operate them
» the alarm continues to sound/lights continue to flash until the system is re-
set with a password.

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19
Q

Monitoring of patients in a hospital

A

» A number of sensors are attached to the patient …
» … these measure vital signs such as: temperature, heart rate, breathing rate, etc.
» these sensors are all attached to a computer system
» the sensors constantly send data back to the computer system
» the computer samples the data at frequent intervals
» the range of acceptable values for each parameter is keyed into the computer
» the computer compares the values from the sensors with those values keyed in
» if anything is out of the acceptable range, a signal is sent by the computer …
» … to sound an alarm
» if data from the sensors is within range, the values are shown in either
graphical form on a screen and/or a digital read out
» monitoring continues until the sensors are disconnected from the patient.

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20
Q

Control applications

A

Control of street lighting
This next sequence shows how a microprocessor is used to control the operation of a street lamp. The lamp is fitted with a light sensor which constantly sends data to the microprocessor. The data value from the sensor changes according to whether it is sunny, cloudy, raining or it is night time (etc.):
» the light sensor sends data to the ADC interface
» this changes the data into digital form and sends it to the microprocessor
» the microprocessor samples the data every minute (or at some other frequency
3.2 Input and output devices
rate)

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21
Q

Anti-lock braking systems (on cars)

A

Anti-lock braking systems (ABS) on cars use magnetic field sensors to stop the wheels locking up on the car if the brakes have been applied too sharply:
» when one of the car wheels rotates too slowly (i.e. it is locking up), a magnetic field sensor sends data to a microprocessor
» the microprocessor checks the rotation speed of the other three wheels
» if they are different (i.e. rotating faster), the microprocessor sends a signal to
the braking system …
» … and the braking pressure to the affected wheel is reduced …
» … the wheel’s rotational speed is then increased to match the other wheels
» the checking of the rotational speed using these magnetic field sensors is
done several times a second …
» … and the braking pressure to all the wheels can be constantly changing to
prevent any of the wheels locking up under heavy braking …
» … this is felt as a ‘judder’ on the brake pedal as the braking system is constantly
switched off and on to equalise the rotational speed of all four wheels
» if one of the wheels is rotating too quickly, braking pressure is increased to
that wheel until it matches the other three.

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22
Q

Central heating systems

A

In this example, a gas supply is used to heat water using a heater. A valve on the gas supply is controlled by a microprocessor and is opened if the heating levels need to be increased. A water pump is used to pump hot water around the central heating system whenever the temperature drops below a pre-set value:

23
Q

Chemical process control

A

A certain chemical process only works if the temperature is above 70°C and
the pH (acidity) level is less than 3.5. Sensors are used as part of the control system. A heater is used to heat the reactor and valves are used to add acid when necessary to maintain the acidity. The following description shows how the sensors and computer are used to control this process:
» temperature and pH sensors read data from the chemical process
» this data is converted to digital using an ADC and is then sent to the computer
» the computer compares the incoming data with pre-set values stored in
memory
» … if the temperature < 70°C, a signal is sent to switch on the heater
» … if the temperature >= 70°C, a signal is sent to switch off the heaters
» … if the pH > 3.5, then a signal is sent to open a valve and acid is added
» … if the pH <= 3.5, then a signal is sent to close this valve
» the computer signals will be changed into analogue signals using a DAC so
that it can control the heaters and valves
» this continues as long as the computer system is activated.

24
Q

Greenhouse environment control

A

Five different sensors could be used here to control the greenhouse environment, namely: humidity, moisture, temperature, pH and light. To simplify this problem the control mechanisms are shown in Figure 3.54

25
Q

Data storage

A

All computers require some form of memory and storage. Memory is usually referred to as the internal devices used to store data that the computer can access directly. This is also known as primary memory. This memory can be the user’s workspace, temporary data or data that is key to running the computer.

26
Q

Storage devices allow users

A

to store applications, data and files. The user’s data is stored permanently and they can change it or read it as they wish. Storage needs to be larger than internal memory since the user may wish to store large files (such as music files or videos). Storage devices can also be removable to allow data, for example, to be transferred between computers. Removable devices allow a user to store important data in a different location in case of data loss.

27
Q

However, all of this removeable storage

A

has become less important with the advent of technology such as ‘data drop’ (which uses Bluetooth) and cloud storage.

28
Q

Memory and storage devices can be split up into two distinct groups:

A

» primary memory
» secondary storage.

29
Q

Primary memory

A

Ram
Rom

30
Q

Internal secondary storage

A

Hard disk drive HDD
solid state drive SSD

31
Q

External secondary storage

A

DVD/CD and DVD-RAM
Blu-ray disc
USB memory stick/ flash memory
Removable hard drive

32
Q

Primary memory

A

Directly addressable by the CPU

Contains RAM, ROM and cache memory

33
Q

Secondary storage

A

Not directly addressable by the CPU

All are non-volatile devices

Can be external or internal to the computer

34
Q

Primary memory i

A

s the part of the computer memory which can be accessed directly from the CPU; this includes random access memory (RAM) and read- only memory (ROM) memory chips. Primary memory allows the CPU to access applications and services temporarily stored in memory locations. The structure of primary memory

35
Q

Random access memory (RAM)

A

All computer systems come with some form of RAM. These memory devices are not really random; this refers to the fact that any memory location in RAM can be accessed independent of which memory location was last used. When you run an application or program, data is retrieved from secondary storage and placed temporarily into RAM. Access time to locate data is much faster in RAM than in secondary or off-line devices.

36
Q

Features of RAM include:

A

can be written to or read from, and the data can be changed by the user or the computer (i.e. it is a temporary memory)
ROM
SRAM
DRAM
120

            3.3 Data storage
 ▲ Figure 3.61 SRAM » used to store data, files, part of an application or part of the operating system currently in use » it is volatile, which means memory contents are lost when powering off the computer. In general, the larger the size of RAM the faster the computer will operate. In reality, RAM never runs out of memory; it continues to operate but just becomes slower and slower as more data is stored. As RAM becomes ‘full’, the CPU has to continually access the secondary data storage devices to overwrite old data on RAM with new data. By increasing the RAM size, the number of times this has to be done is considerably reduced; thus making the computer operate more quickly.
37
Q

There are currently two types of RAM technology:

A

dynamic RAM (DRAM)
» static RAM (SRAM).

38
Q

Each DRAM chip consists of

A

transistors and capacitors. Each of these parts is tiny since a single RAM chip will contain millions of transistors and capacitors. The function of each part is:
» capacitor – this holds the bits of information (0 or 1)
» transistor – this acts like a switch; it allows the chip control circuitry to read
the capacitor or change the capacitor’s value.

39
Q

Dram This type of RAM

A

refreshed (that is, the capacitor needs to be re-charged every 15 microseconds otherwise it would lose its value). If it wasn’t refreshed, the capacitor’s charge would leak away very quickly leaving every capacitor with the value 0.

40
Q

DRAMs have a number of advantages over SRAMs:

A

» they are much less expensive to manufacture than SRAM » they consume less power than SRAM
» they have a higher memory capacity than SRAM.

41
Q

Static RAM (SRAM)

A

A major difference between SRAM and DRAM is that SRAM doesn’t need to be constantly refreshed.
It makes use of flip flops, which hold each bit of memory.
SRAM is much faster than DRAM when it comes to data access (typically, access time for SRAM is 25nanoseconds and for DRAM is 60nanoseconds).

42
Q

DRAM is the most

A

common type of RAM used in computers, but where absolute speed is essential, for example, in the CPU’s memory cache, SRAM is the preferred technology. Memory cache is a high-speed portion of the memory; it is effective because most programs access the same data or instructions many times. By keeping as much of this information as possible in SRAM, the computer avoids having to access the slower DRAM.

43
Q

Dram and sram

A

consists of a number of transistors and capacitors d
uses flip flops to hold each bit of memory s
needs to be constantly refreshed
doesn’t need to be constantly refreshed
less expensive to manufacture than SRAM
has a faster data access time than DRAM
has a higher memory capacity than SRAM
CPU memory cache makes use of SRAM
main memory is constructed from DRAM
consumes less power than SRAM

44
Q

Read-only memory (ROM)

A

Another form of primary memory is read-only memory (ROM). This is similar to RAM in that it shares some of its properties, but the main difference is that it cannot be changed or written to. ROM chips have the following features:
» they are non-volatile (the contents are not lost after powering off the computer)
» they are permanent memories (the contents cannot be changed or written to
by the user, the computer or any application/program)
» the contents can only be read
» they are often used to store data that the computer needs to access when
powering up for the first time (the basic input/output system (BIOS)); these are known as the start-up instructions (or bootstrap)

45
Q

Here is a summary of the main differences between RAM and ROM:

A

temporary memory device. Ram
permanent memory device. Rom
volatile memory
non-volatile memory device
can be written to and read from
data stored cannot be altered
used to store data, files, programs, part of OS currently in use
always used to store BIOS and other data needed at start up
can be increased in size to improve operational speed of a computer

46
Q

Example of an application
We will now consider an application, other than a computer, where both RAM and ROM chips are used:

A remote-controlled toy car has circuitry which contains both RAM and ROM chips. The remote control is a hand-held device. Explain the function of the RAM and ROM chip in this application.

A

ROM
» storing the factory settings such as remote control frequencies
» storing the ‘start-up’ routines when the toy car is first switched on
» storing of the set routines; for example, how the buttons on the hand-held
device control turning left, acceleration, stopping, and so on.
RAM
» the user may wish to program in their own routines; these new instructions would be stored in the RAM chip
» the RAM chip will store the data/instructions received from the remote control unit.

47
Q

Secondary and off-line storage

A

Secondary (and off-line) storage includes storage devices that are not directly addressable by the CPU. They are non-volatile devices that allow data to be stored as long as required by the user. This type of storage can store more data than primary memory, but data access time is considerably longer than with RAM or ROM. All applications, the operating system, device drivers and general files (for example, documents, photos and music) are stored on secondary storage. The following section discusses the various types of secondary storage that can be found on the majority of computers

48
Q

Secondary (and off-line) storage falls into three categories according to the technology used:

A

» magnetic » solid state » optical.

49
Q

Magnetic storage

Hard Disk Drives (HDD)

A

Hard disk drives (HDD) are still one of the most common methods used to store data on a computer.
123

            3 Hardware    track sector ▲ Figure 3.63 Tracks and sectors Data is stored in a digital format on the magnetic surfaces of the disks (or platters, as they are frequently called). The hard disk drive will have a number of platters that can spin at about 7000 times a second. Read-write heads consist of electromagnets that are used to read data from or write data to the platters. Platters can be made from aluminium, glass or a ceramic material. A number of read-write heads can access all of the surfaces of the platters in the disk drive. Normally each platter will have two surfaces which can be used to store data. These read-write heads can move very quickly – typically they can move from the centre of the disk to the edge of the disk (and back again) 50 times a second. Data is stored on the surface in sectors and tracks. A sector on a given track will contain a fixed number of bytes. Unfortunately, hard disk drives have very slow data access when compared to, for example, RAM. Many applications require the read-write heads to constantly look for the correct blocks of data; this means a large number of head movements. The effects of latency then become very significant. Latency is defined as the time it takes for a specific block of data on a data track to rotate around to the read-write head. Users will sometimes notice the effect of latency when they see messages such as ‘Please wait’ or, at its worst, ‘not responding’. When a file or data is stored on a HDD, the required number of sectors needed to store the data will be allocated. However, the sectors allocated may not be adjacent to each   other. Through time, the HDD will undergo numerous deletions and editing which leads to sectors becoming increasingly fragmented resulting in a gradual deterioration of the HDD performance (in other words, it takes longer and longer to access data). Defragmentation software can improve on this situation by ‘tidying up’ the disk sectors. All data in a given sector on a HDD will be read in order (that is, sequentially); however, access to the sector itself will be by a direct read/write head movement.
50
Q

Removable hard disk drives

A

are essentially HDDs external to the computer that can be connected to the computer using one of the USB ports. In this way, they can be used as a back-up device or another way of transferring files between computers.

51
Q

Solid state drives (SSD)

A

Latency is an issue in HDDs as described earlier. Solid state drives (SSD) remove this issue considerably since they have no moving parts and all data is retrieved at the same rate. They don’t rely on magnetic properties; the most common type of solid state storage devices store data by controlling the movement of electrons within NAND or NOR chips. The data is stored as 0s and 1s in millions of tiny transistors (at each junction one transistor is called a floating gate and the other is called a control gate) within the chip. This effectively produces a non- volatile rewritable memory.

52
Q

Floating gate and control gate transistors

A

Floating gate and control gate transistors use CMOS (complementary metal oxide semi-conductor) NAND technology. Flash memories make use of a matrix; at each

53
Q

Memory sticks/flash memories

A

Memory sticks/flash memories (also known as pen drives) use solid state technology.
They usually connect to the computer through the USB port. Their main advantage is that they are very small, lightweight devices, which make them very suitable as a method for transferring files between computers. They can also be used as small back-up devices for music or photo files, for example. Complex or expensive software, such as financial planning software, often uses memory sticks as a dongle. The dongle contains additional files that are needed to run the software. Without this dongle, the software won’t work properly. It therefore prevents illegal or unauthorised use of the software, and also prevents copying of the software since, without the dongle, it is useless.

Computer Science (6 decks)

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