This set of Biomedical Instrumentation Multiple Choice Questions & Answers (MCQs) focuses on “Telemedicine System”.
1. _______________ will reject any common mode signal that appears simultaneously at both amplifier input terminal.
a) ac coupled amplifiers
b) dc amplifiers
c) carrier amplifiers
d) differential amplifiers
Explanation: Most of the amplifiers used for measuring bioelectric signals are of the differential type. A differential amplifier is one which will reject any common mode signal that appears simultaneously at both amplifier input terminals and amplifies only the voltage difference that appears across its input terminals. AC amplifiers have a limited frequency response and are, therefore, used only for special medical applications such as electrocardiograph machine.
2. The amplifier from the following that has a limited frequency response is _________
a) dc amplifiers
b) differential amplifier
c) ac coupled amplifiers
d) carrier amplifiers
Explanation: AC amplifiers have a limited frequency response and are, therefore, used only for special medical applications such as electrocardiograph machine. For electrocardiograms, an ac amplifier with sensitivity, giving 0.5 mV/cm, and frequency response up to 1 kHz and an input impedance of 2 to 5 MW is used. For such applications as retinography, EEG and EMG, more sensitive ac amplifiers are required, giving a chart sensitivity of say 50 mV/cm with a high input impedance of over 10 MW.
3. Which of the following amplifiers are used with transducers which require an external source of excitation?
a) ac coupled amplifiers
b) dc amplifiers
c) carrier amplifiers
d) differential amplifier
Explanation: Carrier amplifiers are used with transducers which require an external source of excitation. They essentially contain a carrier oscillator, a bridge balance and calibration circuit, a high gain ac amplifier, a phase-sensitive detector and a dc output amplifier. They are characterized by high gain, negligible drift, extremely low noise and the ability to operate with resistive, inductive or capacitive type transducers.
4. Which feedback system is employed in DC amplifiers?
a) Can be any positive or negative doesn’t matter
c) Depends on the application
Explanation: DC amplifiers are generally of the negative feedback type. They are not practical for very low level applications because of dc drift and poor common-mode rejection capabilities. They are used for medium gain applications down to about 1 mV signal levels for full scale.
5. Digital filters are not sensitive to temperature as compared with analog filters.
Explanation: It is True. Digital filters are insensitive to temperature as compared with analog filters. They are also insensitive to ageing, voltage drift and external interference as compared to analog filters. Their response is completely reproducible and predictable, and software simulations can exactly reflect product performance.
6. The number of amplifiers incorporated in the module of a Chopper stabilized dc amplifiers are ___________
Explanation: Chopper stabilized dc amplifiers are used for low level but preferably wideband applications such as oscilloscopes, tape recorders and light beam oscilloscope recorders. This includes an ac amplifier for signals above about 20 Hz, a dc chopper input amplifier for signals from about 20 Hz down to dc plus wideband feedback stabilized dc amplifier. These are complex amplifiers having three amplifiers incorporated in the module.
7. _____________ is employed with resistive transducers which require an external source of excitation.
a) differential amplifier
b) dc bridge amplifier
c) carrier amplifier
d) ac coupled amplifier
Explanation: Essentially, the amplifier comprises a stable dc excitation source, a bridge balance and calibration unit, a high gain differential dc amplifier and a dc output amplifier. DC bridge amplifiers are employed with resistive transducers which require an external source of excitation. They can be used as conventional dc high gain amplifiers and offer operating simplicity and high-frequency response.
8. Which of the following IC is a variable negative voltage regulator?
Explanation: LM337 is a variable negative voltage regulator IC. It is capable of drawing current up to 1.5A and voltage range from (-1.25V) – (-30V) ideally. LM317 is a variable positive voltage regulator IC. 7905 and 7912 are fixed voltage regulator IC that give output voltage as -5V and -12V respectively.
9. Chopper input dc amplifiers are preferred for high level inputs to instrumentation systems because of their high sensitivity, negligible drift and excellent common mode rejection capability.
Explanation: It is False. Chopper input dc amplifiers are preferred for low level inputs to instrumentation systems because of their high sensitivity, negligible drift and excellent common mode rejection capability. Their high frequency response is limited to about one half of the input chopper frequency.
10. The amplifier configuration must contain _____________ to achieve the low frequency response for medical applications?
a) higher resistance
b) lower resistance
c) lower capacitance
d) higher capacitance
Explanation: To achieve the low frequency response required for medical applications, the amplifier must have large values of coupling capacitance. The response should be down to less than one hertz which is a very frequent requirement. In all RC-coupled amplifiers, low frequency response is limited by the reluctance of the coupling capacitors.
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