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Sensors & Controls > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

What will happen if you use a PIN photodiode in a photoconductive mode?

A

Less sensitive. Generates very low current.

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2
Q

Signals with frequency lower than 100 Hz

A

High-pass

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3
Q

Signals with frequency higher than 10 kHz

A

Low-pass

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4
Q

How to know if strain gauge is compressed vs stretched

A

Increase in resistance = stretched
Decrease in resistance = compressed

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5
Q

Why photodiode is more popular than photoresistor?

A

Linear response.
Identical sensor output regardless of input current (or voltage).

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6
Q

What is the purpose of using an op-amp for the LED circuit in a forward bias?

A

To protect the LED from unnecessary high current.
The output current from the op-amp will be capped.

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7
Q

Voltage Divider Relationship

A

Used for resistors in a series.
Vout = (Vin)(R2/R1+R2)

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8
Q

Current Divider Relationship

A
  • Used for resistors in parallel.
  • I1 = (Iin)(R2/R1+R2)
  • I2 = (Iin)(R1/R1+R2)
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9
Q

What is voltage “droop?”

A

A small decrease in voltage as the load current increases.

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10
Q

How to back calculate size of Resistor in DMM with measured Vout.

A

Rdmm = (R)(Vout/Vin-Vout)

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11
Q

Draw the I-V curve for typical diode as well as Zener diode.

A

Zener diode has less rapid breakdown

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12
Q

How does a voltage regulator (using a Zener diode) work?

A

To maintain a stable output voltage, even when the input voltage or load conditions fluctuate.

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12
Q

Zener Diode equation

A

Ir = (Vin - Vz) / (R)

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13
Q

How is the emitter current controlled by the base current in an NPN transistor?

A

Current flows due to electrons moving from the emitter to the collector, and the transistor is active when the base is positive relative to the emitter.

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14
Q

Why do you need an op-amp to protect your LED and Zener diode? If you are not using an op-amp,
how can you prevent a large amount of current flowing through your LED and Zener diode?

A

For dynamic control and feedback regulation Without one, protect LEDs and Zener diodes using simple series resistors, preventing damage from excessive current.

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15
Q

Why do you need a 1-Ω resistor to measure ILED and Izener, assuming that you only have a voltmeter?

A

Creates a measurable voltage drop proportional to the current flowing through the diode. This allows you to calculate the current with a voltmeter which only measures voltage.

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16
Q

Why is zener diode the most popular to measure temperature?

A

Simplicity, compact size, and stable reference voltage although it may not be as sensitive or accurate as thermocouples or thermistors in measuring temperature over a wide range.

17
Q

In the zener diode temperature sensor circuit shown in Chapter 4, what will happen if a very large
input current (> 1 A) is applied?

A

Can lead to overheating, thermal runaway, component failure, voltage instability, etc.

18
Q

Why does the voltage drop when holding a zener diode with your finger?

A

The heat from the finger increases the diode’s temperature. The Zener voltage drops due to its negative temperature coefficient.

19
Q

What is a Wheatstone Bridge?

A

Electrical circuit used to measure a very small change in resistance, not readily detectable by a typical DMM. Consists of four resistors arranged in a diamond configuration.

20
Q

How does a strain gauge measure strain?

A

Detects changes in its electrical resistance as it deforms in response to applied stress

21
Q

What is a cantilever biosensor?

A

A strain gauge used to monitor biological reactions. When an analyte binds to them, they begin to bend.

22
Q

With the measured Vbd, can you identify whether the strain gauge was compressed or stretched?
The Wheatstone bridge was initially balanced.

A

Yes.
Positive = stretched
Negative = compressed

23
Q

Why does the voltage output of an op-amp saturate?

A

Due to the inherent limitations of the op-amp’s design and the conditions of the circuit

24
Q

Why is the resistor in a photoresistor (= photoconductive cell) S-shaped?

A

Increases the surface area exposed to light

25
Q

Low-Pass Op-Amp

A
  • High frequencies
  • Created by placing Capacitor in parallel with Rf
  • (1) / (2piRfC)
26
Q

High-Pass Op-Amp

A
  • Lower frequencies
  • Created by placing Capacitor in series with Ri and Rf in parallel with capacitor
  • (1) / (2piRiC)
27
Q

Band-Pass Filter

A
  • An electronic filter that allows signals within a certain frequency range.
  • It combines the characteristics of both a low-pass filter and a high-pass filter.
28
Q

High-Pass Filter

A
  • Implemented to allow signals above a certain frequency to pass through
  • Consists of a capacitor in series with the input resistor
29
Q

Low-Pass Filter

A
  • Allows signals below a certain frequency to pass through
  • Consists of a capacitor in parallel with the feedback resistor
30
Q

Units of frequency (f)

A
  • Hz
  • s^-1
31
Q

Compare photovoltaic and photoconductive modes of a photodiode

A

Photovoltaic Mode
- No external bias required
- Generates voltage
- Lower sensitivity
- Slower Response
- Used for low light levels (solar cells)
Photoconductive Mode
- Requires reverse bias
- Generates current
- Higher sensitivity
- Used for high light levels

32
Q

How do solar cells work?

A
  • Sunlight hits the solar cell and generates electron-hole pairs.
  • The electric field at the p-n junction separates the electrons and holes.
  • Electrons flow through the external circuit, generating an electric current.
  • The voltage across the cell combined with the current generates usable power.
33
Q

PIN photodiode takes the advantages of both photovoltaic and photoconductive mode. How does it work?

A

By using a reverse-biased p-i-n junction, where the intrinsic (i) layer increases the depletion region, allowing for higher light absorption, better charge carrier separation, faster response, and greater sensitivity compared to a standard photodiode

34
Q

How do LEDs emit light?

A
  • LED is made from a p-n junction semiconductor. P-type region is rich in holes (positively charged carriers), n-type region is rich in electrons (negatively charged carriers).
  • Voltage is applied in forward bias
  • Electrons and holes combine, dropping to lower energy level
  • Excess energy released in form of a photon
  • Light depends on energy gap
35
Q

What is laser?

A
  • Light Amplification by Stimulated Emission of Radiation
  • Device that generates a concentrated, coherent beam of light through a process called stimulated emission
  • Highly directional, monochromatic (single wavelength), and coherent (all light waves are in phase)
36
Q

How does a laser diode work?

A
  • Has p-n junction like an LED, but it also has layer called the active region.
  • Forward bias similar to LED
  • The active region is placed between two mirrors, creating an optical cavity.
  • The light bounces between the mirrors in the optical cavity, growing in intensity. Small fraction of this light exits through one of the partially reflective mirrors as a laser beam.
37
Q

How to calculate gain for inverting?

A

β = - (Rf / Ri)

38
Q

How to calculate gain for non inverting?

A

β = (Rf / Ri) + 1

39
Q

Inverting vs non inverting setup

A

Inverting = Vin connected to -
Non = Vin connected to +

Sensors & Controls (2 decks)

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