Engineering Science Flashcards
What are the 2 types of electronic control?
- closed loop
- open loop
Description of open loop control:
Everything is manual.
eg. a tap - you have to turn it on and off.
Description of closed loop manual control:
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.
Description of closed loop automatic control:
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.
In transistor questions always remember to subtract what from the base voltage?
saturation voltage
- 0.7v bipolar transistor
- 1.4v MOSFET
What is group air?
This is when a pneumatic circuit is split into sections which can be isolated with an additional 5/2 valve.
What is an energy audit diagram?
A universal systems diagram with values instead eg. input = 36W power, output = 24W power, 67% efficieny
In a voltage divider Vout is the same as V1 or V2?
V2
If the LDR is at the top of the voltage divider it detects
light. At bottom it detects dark.
3 advantages of electronic control of pneumatic systems:
- electronic signals are faster
- signals travel further than pneumatic ones
- electronic components are smaller
3 types of coupling:
- flange (2 plates bolted together)
- muff ( casing over 2 shafts)
- universal joint
What are bush bearings?
A surface made of a soft material to reduce friction and wear.
2 types of clutch are:
- friction clutch
- dog clutch
Example of class 1 lever:
see-saw or crowbar
Example of class 2 lever:
wheel-barrow
Example of class 3 lever:
tweezers
efficiency of a mechanism =
Mechanical Advantage (MA) =
Velocity Ratio (VR) =
MA / VR x 100%
load / effort
d of effort / d of load or input speed / output speed
What is torque?
Amount of turning cause by a force.
Difference between torque and a moment:
Torque is a moving force, a moment is a static force.
How to solve a uniformly distributed load question:
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
What property of materials does Young’s Modulus determine?
Stiffness, greater the modulus the greater the stiffness. Stiffness is resistance to buckling under compression.
Factors affecting a factor of safety:
- max. load
- type of load
- reliability of material
- consequences of failure
Current gain of a Darlington pair:
hfe total = hfe1 x hfe2
If current or voltage is too large for a transistor then the transistor can be used to drive a
relay.
A MOSFET is a transconductance amplifier which means:
As gate voltage increases, drain current increases.
Transconductance (gm) of a MOSFET is measured in
AV-1 (amps per volt to the power of -1)
To amplify current what component is used?
Transistors (MOSFET and BJT).
To amplify voltage what component is used?
Operational amplifier (op - amp).
An op - am is a differential amplifier, what does this mean?
It amplifies the difference between two input voltages.
What is open loop mode?
When there is no connection between the output and input of an op - amp.
What is the gain of an op - amp in open loop mode?
Very high, usually around 100,000.
Av (voltage gain) =
V out / V in
no units since it is a ratio
What is the maximum output voltage an op - amp can supply?
85% of the supply voltage. This is when it is said to be saturated.
What is Ao?
Open loop gain.
How is the gain of an op-amp reduced?
Connecting the output to the inverting input via a feedback resistor.
What are the 6 different ways to connect an op-amp?
- inverting amplifier
- non-inverting amplifier
- summing amplifier
- voltage follower
- comparator
- difference amplifier
Inverting Amplifier:
Av =
-Rf / R1
gain is inverted / negative
In terms of op-amps what are each of these:
Rf -
Av -
Ao -
R1 -
Rf - feedback resistance
Av - voltage gain
Ao - open loop gain
R1 - input resistor
Non-Inverting Amplifier:
Av =
1 + Rf / R1
no inversion, gain is positive
What is the gain of a voltage follower op-amp?
- (Output voltage = input voltage)
How is the gain of a voltage follower op-amp achieved?
Connecting the output directly to the inverting input.
In an op-amp symbol which input has the + sign and which input has the - sign?
+ is the non-inverting input
- is the inverting input (above the + in the symbol)
What are voltage followers used for?
- 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
What does a summing amplifier do?
Many inputs are connected to inverting input, the op-amp amplifies each in isolation then sums the outputs.
What type of op-amp is it:
- Any no. of inputs can be added
- Rf affects the gain of every input
Summing amplifier.
What is a duty cycle?
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.
What does pwm stand for?
Pulse width modulation.
What is pwm?
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.
What is the main benefit of pwm?
It maintains a high torque and means lightbulbs are less likely to overheat etc.
What does a comparator op-amp do?
Compares the 2 inputs and gives an output only if there’s a difference between the inputs.
What mode is a comparator op-amp in?
Open loop mode, there is no way of controlling the magnitude of the output voltage.
The output signal from a comparator op-amp can either be fully negative or fully positive, what is this known as?
Two state control.
Comparator op-amp:
- Av =
- If V2 > V1, Vout =
- If V2 < V1, Vout =
- Ao
- output
- output
What circuits are comparator op-amps useful for?
Control circuits where the output is simply on or off.
In a comparator op-amp what is the inverting input voltage also called?
Reference voltage.
What does a difference amplifier op-amp do?
It will give an output if there is a difference between its 2 inputs. The output is the difference multiplied by the gain.
A difference amplifier will give an output if there is a difference between its 2 inputs, what is this also known as?
Differential mode.
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?
Proportional control.
Difference amplifier:
- Av =
- Vout =
- When inputs are equal, Vout =
- Rf / R1
- Rf / R1 x (V2 - V1)
- 0v
What are difference amplifiers commonly used for?
When the output must be carefully controlled.
