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Medical Instrumentation > Sensors > Flashcards

Sensors Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the purpose of a pre-amplifier?

A

Conditions the electrical signal for transmission to the acquisition system

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2
Q

What is the sensitivity of a sensor?

A

The transfer function (dy/dx)

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3
Q

What is the resolution of a sensor?

A

The smallest change of input that can be reliably detected (determined by noise)

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4
Q

What is the difference between range and dynamic range?

A

Range is two numbers, while dynamic range is the difference between the max.and min. numbers

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5
Q

What is hysteresis?

A

When the value of a parameter changes depending on the direction of change

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6
Q

What is characteristic error?

A

When there is a difference between the ideal and real transfer function e.g. d.c. offset, non-linearities

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7
Q

What is dynamic error?

A

Error due to transient behaviour, i.e. slow responses

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8
Q

What are four examples of light sensors and what electrical property do they transmit?

A

Photodiode (V)
Photodiode PMT (I)
Photoresistor (R)
Charge-coupled device (Q)

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9
Q

What are three examples of temperature sensors and what electrical property do they transmit?

A

Thermocouple (V)
IR thermocouple (I)
Positive/negative temperature coefficient materials (R)

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10
Q

What are two examples of force sensors and what electrical property do they transmit?

A 
Piezoelectric (V, Q)
Strain gauge (R)
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11
Q

What is the difference between accuracy and precision?

A

Accuracy is the closeness to the true value

Precision is the closeness of multiple observations

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12
Q

What is the difference between repeatability and reproducability?

A

Repeatability is the closeness of multiple observations over a short time interval
Reproducability is the closeness of multiple observations over a long time interval or with different operators/instruments/location

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13
Q

What is bias error?

A

The difference between true value and measurement average

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14
Q

What is the sensitivity error?

A

The difference between max. and min. sensitivity at a given sensor output

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15
Q

What is the purpose of calibration?

A

To eliminate or reduce bias in the measurement system

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16
Q

What are the three levels of standard in instrument calibration?

A

Primary standard - doesn’t need calibration
Secondary standard - calibrated against primary
Working standard - calibrated against secondary

17
Q

What circuit is analogous to an angular potentiometer?

A

A voltage divider

18
Q

What are the characteristics of PT100?

A

A platinum thermistor which has 100ohm resistance at O degrees
Low sensitivity, high reproducability
Stable calibration
Linear

19
Q

What is n and p doping?

A

n - addition of electrons

p - addition of holes

20
Q

Name 4 common semi-conductor materials

A

Silicon
Phosphorus
Arsenic
Boron

21
Q

What are the semiconductor properties of silicon?

A

High temperature dependence
High sensitivity, low reproducability
Non-linearity

22
Q

What does NTC stand for?

A

Negative temperature coefficient

23
Q

Give two exapmles of materials with -ve alpha values

A

Graphite and silicon

24
Q

How do photodiodes generate a current proportional to incident light?

A

Incident photons create electron-hole pairs in spatial charge region of semiconductor

25
Q

Is photodiode performance linear?

A

Yes, over a wide range

26
Q

How to photodiodes behave at different frequencies of light?

A

UV - photodiode too opaque, so photons absorbed at surface
Visible Light - Response
Near IR - Peak response
IR - Photons do not have enough energy to generate electron-hole pairs

27
Q

What is the difference between a metal and a silicon strain gauge?

A

Silicon gauge factor 100x that of metal

28
Q

How can temperature sensitivity of a strain gauge be compensated for?

A
  • Use a dummy gauge not exposed to strain
  • Use low thermal expansion coefficient material
  • Use low thermal resistivity dependent materials
  • Use bridge configuration
29
Q

How can a wheatstone bridge be configured to compensate for temperature crosstalk?

A

Replace R3 with a strain gauge which doesn’t experience the strain, but does experience the temperature

30
Q

How can a wheatstone bridge be modified to detect bending?

A

Replace R2 with a strain gauge

As R4 is extended R2 compresses, so bridge is unbalanced

31
Q

How can a wheatstone bridge be modified to detect extension and compression?

A

Replace R1 with a strain gauge

As R4 is extended, R1 is also extended and so the bridge is unbalanced

Medical Instrumentation (5 decks)

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