BTC Biomedical Instrumentation & Electrical Fundamentals 2 — Questions and Answers
Question 1: A pressure transducer in a patient monitoring system converts mechanical pressure into which type of output signal?
- Optical pulses
- An electrical signal proportional to pressure (Correct answer)
- Digital binary codes directly
- Magnetic flux changes
Correct answer: An electrical signal proportional to pressure
A pressure transducer is an electrochemical sensor that produces an electrical signal (typically voltage or current) directly proportional to the applied mechanical pressure.
Question 2: In biomedical signal conditioning, which circuit stage is primarily responsible for removing unwanted frequency components from a physiological signal before digitization?
- Amplifier stage
- Filter stage (Correct answer)
- Sample-and-hold stage
- Digital-to-analog converter
Correct answer: Filter stage
The filter stage selectively passes desired signal frequencies while attenuating unwanted noise and interference before the signal reaches the analog-to-digital converter.
Question 3: Common Mode Rejection Ratio (CMRR) is a critical specification for biomedical amplifiers because it describes the amplifier's ability to:
- Increase the frequency bandwidth of the signal
- Reject noise signals common to both inputs (Correct answer)
- Convert analog signals to digital values
- Match the impedance between stages
Correct answer: Reject noise signals common to both inputs
A high CMRR means the amplifier rejects interference (such as 60 Hz noise) that appears equally on both differential inputs, preserving the small physiological signal of interest.
Question 4: An isolation transformer used in patient-care areas provides electrical isolation primarily to:
- Step down voltage to safe low levels
- Prevent patient electrical shock by eliminating a direct ground reference (Correct answer)
- Increase current capacity for medical equipment
- Regulate output voltage automatically
Correct answer: Prevent patient electrical shock by eliminating a direct ground reference
Isolation transformers break the direct electrical connection to ground, preventing a completed shock circuit if a patient or caregiver contacts a live conductor.
Question 5: A biomedical technician needs to pass ECG signals (0.05–150 Hz) while blocking both very low-frequency baseline wander and high-frequency EMG noise. Which filter type should be used?
- High-pass filter
- Low-pass filter
- Band-pass filter (Correct answer)
- Notch filter
Correct answer: Band-pass filter
A band-pass filter passes only frequencies within a defined range (e.g., 0.05–150 Hz for ECG), blocking both below-band drift and above-band noise simultaneously.
Question 6: A 12-bit analog-to-digital converter (ADC) sampling a 0–5 V signal provides how many discrete output levels?
- 256
- 1,024
- 4,096 (Correct answer)
- 65,536
Correct answer: 4,096
A 12-bit ADC produces 2^12 = 4,096 discrete quantization levels, providing a resolution of approximately 1.22 mV per step over a 0–5 V range.
Question 7: Electromagnetic interference (EMI) from nearby surgical electrosurgical units most commonly causes which artifact in patient monitors?
- Baseline flatline on ECG
- High-frequency noise obscuring the waveform (Correct answer)
- Inverted QRS complexes
- Slowed heart rate display
Correct answer: High-frequency noise obscuring the waveform
Electrosurgical units generate high-frequency RF energy that couples into patient leads and monitoring circuitry, producing characteristic high-frequency noise that obscures physiological waveforms.
BTC Biomedical Instrumentation & Electrical Fundamentals 2
A pressure transducer in a patient monitoring system converts mechanical pressure into which type of output signal?