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S5 Engineering Science > Engineering Science > Flashcards

Engineering Science Flashcards

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1
Q

What are the 2 types of electronic control?

A
  • closed loop

- open loop

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2
Q

Description of open loop control:

A

Everything is manual.

eg. a tap - you have to turn it on and off.

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3
Q

Description of closed loop manual control:

A

It will carry out an operation but you have to adjust it to your preferred settings.
eg. shower - turn it out and adjust temperature to your preference, then turn it off when finished.

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4
Q

Description of closed loop automatic control:

A

Set it to do something and it will constantly adjust to carry it out.
eg. fridge - set the temperature and it keeps it the same.

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5
Q

In transistor questions always remember to subtract what from the base voltage?

A

saturation voltage

  • 0.7v bipolar transistor
  • 1.4v MOSFET
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6
Q

What is group air?

A

This is when a pneumatic circuit is split into sections which can be isolated with an additional 5/2 valve.

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7
Q

What is an energy audit diagram?

A

A universal systems diagram with values instead eg. input = 36W power, output = 24W power, 67% efficieny

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8
Q

In a voltage divider Vout is the same as V1 or V2?

A

V2

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9
Q

If the LDR is at the top of the voltage divider it detects

A

light. At bottom it detects dark.

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10
Q

3 advantages of electronic control of pneumatic systems:

A
  • electronic signals are faster
  • signals travel further than pneumatic ones
  • electronic components are smaller
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11
Q

3 types of coupling:

A
  • flange (2 plates bolted together)
  • muff ( casing over 2 shafts)
  • universal joint
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12
Q

What are bush bearings?

A

A surface made of a soft material to reduce friction and wear.

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13
Q

2 types of clutch are:

A
  • friction clutch

- dog clutch

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14
Q

Example of class 1 lever:

A

see-saw or crowbar

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15
Q

Example of class 2 lever:

A

wheel-barrow

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16
Q

Example of class 3 lever:

A

tweezers

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17
Q

efficiency of a mechanism =

Mechanical Advantage (MA) =

Velocity Ratio (VR) =

A

MA / VR x 100%

load / effort

d of effort / d of load or input speed / output speed

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18
Q

What is torque?

A

Amount of turning cause by a force.

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19
Q

Difference between torque and a moment:

A

Torque is a moving force, a moment is a static force.

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20
Q

How to solve a uniformly distributed load question:

A

Take the force and concentrate it over the centre of the area it covers eg.
2kN/m over 2m from pivot = 4kN at 1m from pivot

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21
Q

What property of materials does Young’s Modulus determine?

A

Stiffness, greater the modulus the greater the stiffness. Stiffness is resistance to buckling under compression.

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22
Q

Factors affecting a factor of safety:

A
  • max. load
  • type of load
  • reliability of material
  • consequences of failure
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23
Q

Current gain of a Darlington pair:

A

hfe total = hfe1 x hfe2

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24
Q

If current or voltage is too large for a transistor then the transistor can be used to drive a

A

relay.

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25
Q

A MOSFET is a transconductance amplifier which means:

A

As gate voltage increases, drain current increases.

26
Q

Transconductance (gm) of a MOSFET is measured in

A

AV-1 (amps per volt to the power of -1)

27
Q

To amplify current what component is used?

A

Transistors (MOSFET and BJT).

28
Q

To amplify voltage what component is used?

A

Operational amplifier (op - amp).

29
Q

An op - am is a differential amplifier, what does this mean?

A

It amplifies the difference between two input voltages.

30
Q

What is open loop mode?

A

When there is no connection between the output and input of an op - amp.

31
Q

What is the gain of an op - amp in open loop mode?

A

Very high, usually around 100,000.

32
Q

Av (voltage gain) =

A

V out / V in

no units since it is a ratio

33
Q

What is the maximum output voltage an op - amp can supply?

A

85% of the supply voltage. This is when it is said to be saturated.

34
Q

What is Ao?

A

Open loop gain.

35
Q

How is the gain of an op-amp reduced?

A

Connecting the output to the inverting input via a feedback resistor.

36
Q

What are the 6 different ways to connect an op-amp?

A
  • inverting amplifier
  • non-inverting amplifier
  • summing amplifier
  • voltage follower
  • comparator
  • difference amplifier
37
Q

Inverting Amplifier:

Av =

A

-Rf / R1

gain is inverted / negative

38
Q

In terms of op-amps what are each of these:

Rf -
Av -
Ao -
R1 -

A

Rf - feedback resistance
Av - voltage gain
Ao - open loop gain
R1 - input resistor

39
Q

Non-Inverting Amplifier:

Av =

A

1 + Rf / R1

no inversion, gain is positive

40
Q

What is the gain of a voltage follower op-amp?

A
  1. (Output voltage = input voltage)
41
Q

How is the gain of a voltage follower op-amp achieved?

A

Connecting the output directly to the inverting input.

42
Q

In an op-amp symbol which input has the + sign and which input has the - sign?

A

+ is the non-inverting input

- is the inverting input (above the + in the symbol)

43
Q

What are voltage followers used for?

A
  • Often used to section circuits to improve safety and reliability
  • high input resistance and low output resistance so used to match sources that can only produce a low current to a load with a low resistance
44
Q

What does a summing amplifier do?

A

Many inputs are connected to inverting input, the op-amp amplifies each in isolation then sums the outputs.

45
Q

What type of op-amp is it:

  • Any no. of inputs can be added
  • Rf affects the gain of every input
A

Summing amplifier.

46
Q

What is a duty cycle?

A

The ratio of how long the output signal is on with how long it is off, eg. 75% duty means the output is high for 75% of the time.

47
Q

What does pwm stand for?

A

Pulse width modulation.

48
Q

What is pwm?

A

When the output is pulsed to control eg. the speed of a motor or brightness of a light. Controls it by frequency rather than voltage magnitude.

49
Q

What is the main benefit of pwm?

A

It maintains a high torque and means lightbulbs are less likely to overheat etc.

50
Q

What does a comparator op-amp do?

A

Compares the 2 inputs and gives an output only if there’s a difference between the inputs.

51
Q

What mode is a comparator op-amp in?

A

Open loop mode, there is no way of controlling the magnitude of the output voltage.

52
Q

The output signal from a comparator op-amp can either be fully negative or fully positive, what is this known as?

A

Two state control.

53
Q

Comparator op-amp:

  • Av =
  • If V2 > V1, Vout =
  • If V2 < V1, Vout =
A
  • Ao
    • output
    • output
54
Q

What circuits are comparator op-amps useful for?

A

Control circuits where the output is simply on or off.

55
Q

In a comparator op-amp what is the inverting input voltage also called?

A

Reference voltage.

56
Q

What does a difference amplifier op-amp do?

A

It will give an output if there is a difference between its 2 inputs. The output is the difference multiplied by the gain.

57
Q

A difference amplifier will give an output if there is a difference between its 2 inputs, what is this also known as?

A

Differential mode.

58
Q

A differential amplifier will produce a large output if there’s a large difference between its inputs and a small output if the difference is small. What is this known as?

A

Proportional control.

59
Q

Difference amplifier:

  • Av =
  • Vout =
  • When inputs are equal, Vout =
A
  • Rf / R1
  • Rf / R1 x (V2 - V1)
  • 0v
60
Q

What are difference amplifiers commonly used for?

A

When the output must be carefully controlled.

S5 Engineering Science (1 decks)

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