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.
