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102 Electricity/Medical Instrumentation 1 Fall 2013 > CVT 102 Exam #2 Pulses PP and Filters PP > Flashcards

CVT 102 Exam #2 Pulses PP and Filters PP Flashcards

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USMLE® Step 1 flashcards
1
Q

Define “pulse” (in our context).

A

Square wave. A sudden, Brief increase or decrease in a current flow

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2
Q

What is an ideal square wave?

A

The ideal square wave shows amplitude increasing immediately to maximum, staying for a given length of time at maximum amplitude, then decreasing immediately to minimum amplitude.

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3
Q

What do we call the distortion that causes the amplitude to bounce up and down at the top and bottom of a square wave?

A

Ringing- the amplitude continues to bounce up and down

It is a distortion

Like the ringing of a
bell, the oscillations
you hear after the strike.

Notice that the frequency stays
the same. The amplitude is what
changes.

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4
Q

What is distortion?

A

refers to any kind of deformation of a waveform when compared to the original waveform.

Distortion is unwanted in the input and processing stages of the instrumentation chain.

The shape of the wave isn’t what it should be idealy

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5
Q

What is clipping?

A

is one form of distortion that occurs when a deviceis overdriven.

It clips off the top of the waveform

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6
Q

What causes it clipping?

A

This happens when there is increased voltage or current beyond the output capability of the device.

The excess signal
(beyond the capability of the device)
is simply cut off, resulting in a
distorted signal.

(sometimes musicians want clipping to happen but not in the medical business)

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7
Q

What is damping?

A

is another form of distortion. It is a reduction of amplitude (i.e., reduction of energy).

The signal attenuates
(a reduction in amplitude and intensity)
but does not lose other wave characteristics.
Damping can quickly bring a signal to “0” amplitude

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8
Q

Is it ever desirable?

A

yes

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9
Q

What is attenuation?

A

Loss of energy

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10
Q

What are overdamping and underdamping?

A
  • Overdamping occurs when there is excessive restraining of vibratory motion. Overdamping is like an automatic door closer pulling a door closed too slowly
  • Underdamping will close the door very quickly, but causes oscillation of the signal around zero, before stabilizing at a zero amplitude
  • Serious underdamping can lead to ringing: signal continues to oscillate—more noise.
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11
Q

Critical damping?

A

Just the right amount. Strike a balance between over-damping and

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12
Q

What is overshoot?

A

-Overshoot (underdamping) adds unwanted signal to the real information.

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13
Q

What is Undershoot?

A

overdamping

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14
Q

What is a wave (in our context)?

A

-A repeating change of amplitude
- a periodic fluctuation in a current or voltage
Virtually an infinite variety / configurations of types of waves
-Singular polarity (DC) or Bipolar (AC)

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15
Q

Are they only AC?

A

No, DC can create a current too. But it will be one direction from the baseline.

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16
Q

DC waves

A
  • Have only positive polarity

Can have multiple shapes

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17
Q

AC waves

A
  • AC waves
    Have positive/negative polarity
    Can have multiple shapes (square, sine, triangle)
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18
Q

What are common shapes of waveforms?

A

Square wave, sine wave, triangle wave, and a variation of the triangle might be a saw tooth wave

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19
Q

What can happen when two or more waves interact?

A

Interfere with each other.
Can be constructive meaning the net amplitude is increased of the summing of two waves

Or can be destructive meaning the net amplitude is decreased.

Two slightly out-of-phase waves;
the sum may increase amplitude in some places, decrease in other places.

180° out of phase.
The sum of the waves
at each moment = zero
(principle of phase cancellation)

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20
Q

What is phase (with respect to waves)?

A

Two slightly out-of-phase waves;

the sum may increase amplitude in some places, decrease in other places.

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21
Q

What is out of phase?

In phase vs. out of phase?

A

180° out of phase.
The sum of the waves
at each moment = zero
(principle of phase cancellation)

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22
Q

How are signals carried by waves?

A
  • Amplitude Modulation (AM)
    Vary the amplitude of the signal; constant frequency
    Differing amplitude sequence creates signal
    Subject to noise due to lowering of amplitude
  • Frequency Modulation (FM)
    Vary the frequency of the signal; constant amplitude
    Differing frequency sequence creates signal
    Less noise due to constant amplitude of wave
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23
Q

What is modulation?

A

-varying a periodic waveform
(such as a tone) in order to use that signal
to convey a message.

e.g., radio:
AM (amplitude modulation)
or
FM (frequency modulation)

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24
Q

How is AM different from FM?

A
  • Amplitude Modulation (AM)
    Vary the amplitude of the signal; constant frequency
  • Frequency Modulation (FM)
    Vary the frequency of the signal; constant amplitude
    which makes it clearer
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25
Q

Signals

A 
A periodic waveform
Conveys information (in a common format)
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26
Q

periodic:

A

occurring at regular intervals

period, represented by “P” sec/cycle

27
Q

What is noise (in our context)?

A
  • ALL electronic circuits and therefore devices, generate small, random electrical waves.

When unwanted, they are called noise.

An unwanted signal characteristic of all electronic circuits.

28
Q

Are we ever free of it?

A

no

29
Q

Is it AC or DC signals that tend to drift away from the 0 baseline?

A

DC tends to drift overtime
which is why we need a wheatstone bridge
(AC tends to be self centering)

DC signals often have a tendency to drift away from the proper zero baseline (possibly due to thermal noise).

A “balance” control might be used to return the baseline to the proper level.

30
Q

What is a Wheatstone bridge?

A

a

31
Q

What is S/N?

A

signal to noise ratio

how stong is the signal to the noise

32
Q

What is the most common form of noise we encounter in the cardiovascular biz?

A

60 Htz interferences

33
Q

Describe two causes

A

Poor electrode placement, poor design, restless patient, shivering patient, movement.

34
Q

How do we combat this noise?

A

filters

35
Q

What are the four basic components of the instrumentation chain?

A
  1. Detect & Acquire the Biological Signal
  2. Amplify, Filter & Process The Signal
  3. Display the Signal
  4. Store The Signal
36
Q

What is a detector?

A

Detectors, in general, respond to physical or physiologic change (Frequency) in the body, in some way or another.

37
Q

Signal Detectors:

A

Components (transducers) which convert the original biological signal to some other form of energy, usually electrical
• The first stage in the instrument chain
• Must be fairly sensitive
• Subject to detecting discrete signals plus noise

38
Q

What is a transducer?

A

a device that converts one type of energy to another, for measurement or information transfer.

All medical transducers do one basic task:
Change a physical property to electrical energy

39
Q

What is a signal conditioner?

A

Amplifiers Alter the level of energy of the signal
• Filters Alter the frequency content of the signal
• Signal Processors Derive (new) information from the signal Noise is actually removed in this step

40
Q

What is gain/sensitivity?

A
  • gain means increasing an amplitude of a signal.
  • sensitivity is the same thing. If you make an instument more sensative, it will increase the amplitude.
  • Used to increase the electrical voltage or current (energy) of the initial signal
41
Q

What ratio describes amplification of a signal?

A

output/input=

a dimensionless ratio called SENSITIVITY or GAIN for eventual use by an output device

42
Q

What is a deciBel?

A 
A decibel (dB) is logarithmic, and therefore, a non-linear value. 
An important reference value is a change of -3 dB in a signal’s: 
Power (watts) OR Voltage (v) or Current (amps).
43
Q

How many kinds are there?

A

2 kinds of dB

44
Q

Which kind of dB is for which parameters?

A

A reduction of 3 decibels in voltage or current represents a reduction to 70.7% of the original signal value.
A reduction of 3 decibels in power represents a reduction to 50% of the original signal value.

45
Q

(Power vs. volts/current) 3 dB is a reduction of what percent for each?

A

A reduction of 3 decibels in voltage or current represents a reduction to 70.7% of the original signal value.

46
Q

What is a filter (in our context)?

A

Filters alter the frequency content of a signal

47
Q

What is the primary difference between the ideal filter and the real-world filter?

A

a

48
Q

Are they always the perfect answer to noise?

A

no

49
Q

What is Fourier analysis?

A

Any “analysis” is a breakdown into component parts.
• Fourier* analysis breaks an electronic signal into component frequencies (X axis) and amplitude of each (Y axis)
• The result: a Bode plot

  • Big spikes may represent artificially amplified frequencies
  • The ECG with 60 Hz noise would show a spike at—yes— 60 Hz.
  • Now the equipment designer can construct a filter to remove the offending frequency.
50
Q

How does it help to choose a useful filter?

A
  • Signal detectors and amplifiers are not perfect devices.
  • Non-signal information enters the instrumentation chain as noise.
  • Filters remove non-signal frequencies from the instrument’s output. This makes it more specific.
  • The ideal filter has absolutes: Definite lines of demarcation where it is effective.
  • Filters must be used judiciously: they can eliminate real information and/or introduce new noise.
51
Q

What are the X and Y axes on a Bode plot?

A

frequencies (X axis) and amplitude of each (Y axis)

• The result: a Bode plot

52
Q

What are the four basic types of ideal filter?

A

high pass
low pass
band pass
band reject or notch

53
Q

Which is the most common in medical instrumentation?

A

low pass

54
Q

Which type is used for ECG recording?

A

low pass

55
Q

Which for spectral Doppler display?

A

high pass

56
Q

What are the three regions of operation in a functional (real-world) filter?

A

Pass Band
-frequencies retain 100% amplitude • Transition

Band (Roll-Off)
-frequencies reduce their amplitudes from 100% to 70.7% (over a range of frequencies). This is where the –3 dB frequency happens: considered to be where the filter becomes functional

Stop Band
-frequencies are essentially eliminated (reduced to non-significant levels) because their amplitudes have been reduced to where they are unable to perform work

57
Q

What determines the actual functional level of a filter?

A

a reduction to 70.7% of the signal’s original current or voltage amplitude.

A filter is said to be “active in the stop band” because the frequencies in this range have essentially no ability to perform effective work

58
Q

Functional cut-off frequency:

A

the point at which the frequency reaches a reduction of 3 dB, a reduction to 70.7% of the signal’s original current or voltage amplitude.

59
Q

Wheatstone bridge: how is it constructed?

A
  • invented by Samuel Christie, made popular by Charles Wheatstone
  • Uses two pairs of resistances, with a connection between the pairs
  • The output is altered by a variable resistance on one side
  • Several uses, including determining unknown resistance
  • Allows balancing —-setting zero baseline
  • There are other kinds of bridge circuit, but this is the famous one

-two resistances are fixed (1&3)
-One resistance is variable and controlled (2)
-One resistance is variable and unknown (x)
(example: thermistor on a Swan-Ganz catheter)
-Known variable resistance is changed until the output is zero volts;
now the system is ready to measure the unknown
-This is what happens when you zero the monitor with the hemodynamic setup

60
Q

Why is it useful in instrumentation?

A
  • Allows balancing —-setting zero baseline

- There are other kinds of bridge circuit, but this is the famous one

61
Q

Band Pass Filter

A

A filter that passes frequencies between two cut-off frequencies, but removes all other frequencies above & below the cut-off frequencies.

62
Q

Band Reject, or Notch Filter

A

A filter that passes frequencies below a cut-off frequency and above a second cut-off frequency but removes all frequencies in-between.

63
Q

High Pass Filter

A

A filter that passes frequencies above a specified cut-off frequency (fco)

64
Q

Low Pass Filter

A

A filter that passes frequencies below a specified cut-off frequency (fco)

• This is the most common type for medical instrumentation.

102 Electricity/Medical Instrumentation 1 Fall 2013 (4 decks)

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