Instrumental final

Question 1

Time-Domain signals

Answer 1

Information encoded as the time relationship of signal fluctuations (frequency, period, pulse, width)

Question 2

Digital signals

Answer 2

Each piece of data represents a bit (binary digit) of information

Question 3

What does noise limit?

Answer 3

The detectability of every instrumental method

Question 4

What is signal to noise equal to?

Answer 4

mean of the signal measurements over the standard deviation of numerous measurements of the signal strength

Question 5

What does the signal to noise ratio have to be for it to be a readable signal?

Answer 5

3 times

Question 6

What are sources of chemical noise?

Answer 6

Temperature, pressure, humidity, vibrations

Question 7

What are fluctuations?

Answer 7

Uncontrolled variables

Question 8

What is instrumental noise?

Answer 8

Noise from instrumental components such as source, detector, electronic components

Question 9

What are types of instrumental noise?

Answer 9

Thermal or Johnson, shot, flicker or 1/f, environmental

Question 10

What is thermal noise?

Answer 10

Thermal motion of electrons or other carriers in resistors, capacitors, detectors, and electrochemical cells. The agitation of charge carriers is random and can produce inhomogeneities setting up voltage fluctuations as noise.

Question 11

Does there have to be a current to have thermal noise?

Answer 11

No, it can be present without current

Question 12

How can you decrease thermal noise?

Answer 12

Decrease temperature, lower electrical resistance, narrow the bandwidth

Question 13

What is the adverse effect of narrowing the bandwidth?

Answer 13

It affects the rise time of the instrument, making it slower to respond to signal change

Question 14

What is rise time?

Answer 14

Response time in seconds to changes in input. It’s measured as the time required for the output to increase from 10 to 90 percent of its final value.

Question 15

What is shot noise?

Answer 15

Movement of electrons across a junction which produces random currents

Question 16

What is flicker or 1/f noise?

Answer 16

Any noise that is inversely proportional to the frequency of the signal

Question 17

When is flicker noise usually significant?

Answer 17

At low frequency (under 100 Hz)

Question 18

What does flicker noise depend on?

Answer 18

Types of materials use and the shapes of devices

Question 19

What are examples of flicker noise?

Answer 19

long-term drift in DC amplifiers, light sources, voltmeters

Question 20

What is environmental noise?

Answer 20

The composite of many noise sources in the surroundings

Question 21

What is the type of noise in IR equipment detectors?

Answer 21

Johnson/thermal noise

Question 22

What is source flicker noise?

Answer 22

Slow drift in radiant output

Question 23

How do you minimize source flicker noise?

Answer 23

Good voltage power supplies or a split beam arrangement

Question 24

What are methods used to improve signal to noise from hardware?

Answer 24

Grounding and shielding, difference and instrumentation amplifiers, analog filtering, modulation, signal chopping, lock-in amplifiers

Question 25

What is shielding?

Answer 25

Surrounding the electronics with a conducting material connected to earth ground

Question 26

What is the effectiveness of the shield dependent on?

Answer 26

thickness, conductivity, and continuity

Question 27

What does analog filtering-RC filtering do?

Answer 27

Uses low-pass analog filters to remove high frequency components of the signal such as thermal and shot noise. High pass filters used for high frequency signals to reduce drift and flicker noise

Question 28

What is modulation?

Answer 28

Convert low frequencies or DC signals from detector to high frequency AC

Question 29

What devices cause modulation?

Answer 29

Choppers, lock-in amplifiers, etc

Question 30

What are software methods to improve signal to noise?

Answer 30

Ensemble averaging, boxcar averaging, digital filtering, correlation methods

Question 31

What is ensemble averaging?

Answer 31

Adding spectra together. Each data set is stored and summed point by point for averaging

Question 32

What is important with ensemble averaging?

Answer 32

Must be sampled at twice the frequency or higher than the highest frequency component of the waveform

Question 33

What instruments can use ensemble averaging?

Answer 33

NMR and FTIR

Question 34

What does boxcar averaging do?

Answer 34

Helps smooth peaks and enhance signal to noise in the waveform by averaging 2-50 adjacent points to generate the final point

Question 35

In what situations is boxcar averaging a bad technique?

Answer 35

Complex signals or signals that change rapidly with time

Question 36

What are types of digital filtering?

Answer 36

fourier transformation, least squares polynomial smoothing, and correlation