Electronics Flashcards
An electronic sensor consists of…
- A sensing device that changes one of its physical properties (resistance)with a change in whatever is to be monitored.
- A processing unit (like electrical circuit) to process the change in physical properties and produce an output voltage.
- An output device to indicate this change and respond to a change in voltage.
What is a piezo-electric transducer?
It is a crystal which consists of positive and negative ions in regular arrangement. It is a crystal that when stressed, a small voltage is produced between its faces.
A LDR is made of a high-resistance semiconductor. If light with high enough freq. falls on it, its photons are absorbed, this releases electrons from the atoms in the semiconductor. So for a LDR, resistance reduces with?
Increasing light intensity. (The change is not linear).
In a NTC thermistor, which is made of a semiconductor, that when temp. rises the number of free electrons increases. What happens when temp. increases?
It’s resistance reduces (it isn’t linear).
Why is a thermistor more useful than a metal wire?
There is a much larger change in resistance with change in temp.
Describe the structure of a metal-wire strain gauge.
A strain gauge consists of a length of very fine wire sealed into a small rectangle of thin plastic. (Such that when the plastic is stretched, the length of the wire increases). (It takes adv. of the change in resistance of a metal wire as its length and cross sectional area change).
Equation to use to measure the change in resistance with length of the wire.
R = pL / A.
Equation for output voltage of a potential divider.
V = R / R+F ×E
E is the e.m.f of the cell &F is resistance of fixed resistor
An operational amplifier has two inputs.. Namely…
Inverting input (V-) & Non-inverting input (V+). The op-amp uses the p.d between the two inputs to produce as large an output voltage as possible.
Formula for open-loop gain of an op-amp.
G₀ = V(out) / (Vplus - Vminus).
Properties of an ideal op-amp.
Infinite BIOS:
•Bandwidth:all freq amplified by the same factor.
•Input impedance :no current leaves or enters either of the inputs.
•Open-look gain:of difference between input voltages is very small then the output is saturated.[same as supply volt].
•Slew rate: No delay between changes in input and consequent changes in output.
For an Op-amp there is zero output impedance, meaning…
The whole output voltage is provided across the output load.
Why is it called open-look gain?
Cuz there is no loop of resistors or other components linking the output back to the input.
The maximum voltage an op-amp can produce is a value close to?
The supply voltage.
Functions of the zero volt line.
- as a reference line for which all input and output voltages are measured.
- connecting this way allows the output voltage to be either +ve or -ve.
If output voltage calculated is more than power supply, then….
The amplifier is said to be saturated, thus making the value of output voltage the same as the value for the power supply.
What is the polarity of the output voltage if Vminus is greater than Vplus?
The output voltage is negative.
In a case where Vminus is equal to the output voltage (feedback loop),If open look gain is infinite and the op-amp is not saturated…what is the relationship between Vplus and Vminus?
They are equal.
Equation for closed-loop voltage.
V out / V in = G₀ / (1-G₀).
Advantages of using negative feedback .
- less distortion (as Vin is the same as Vout , this applies when open-loop voltage is high).
- The bandwidth increases (the range of frequencies for which gain is constant increases).
- Gain is more stable (not affected by changes in temp.)
In the inverting amplifier point P is known as the virtual earth cuz…?
In the order that the op-amp to be unsaturated, the two input voltage must almost be the same. And if open-look gain is high then the voltages have to be very close.
Equation for gain of an inverting amplifier.
G = -R f/ R in.
Equation for gain of a non inverting amp.
G = 1 + (R₁/R₂). (Where R₁ is the one closer to the amp).
Maximum current a op-amp can provide is ?
25mA.
