CBET Basic 5 — Questions and Answers
Question 1: What is the purpose of the line isolation monitor (LIM) in an isolated power system?
- Maintain balanced phase voltages on the distribution panel
- Detect and alarm when the impedance to ground falls below a safe threshold (Correct answer)
- Regulate current to connected medical devices
- Measure total harmonic distortion on the isolated bus
Correct answer: Detect and alarm when the impedance to ground falls below a safe threshold
The LIM continuously monitors the impedance between the isolated power conductors and ground, alarming when a fault path to ground is detected before a hazard occurs.
Question 2: Which sterilization method uses ethylene oxide (EtO) gas?
- Autoclave steam sterilization
- Dry heat sterilization
- Low-temperature chemical gas sterilization (Correct answer)
- UV radiation sterilization
Correct answer: Low-temperature chemical gas sterilization
Ethylene oxide (EtO) is a low-temperature gas sterilization method suitable for heat-sensitive or moisture-sensitive medical devices.
Question 3: What does the term 'resolution' mean in the context of an analog-to-digital converter (ADC)?
- The maximum input voltage the ADC can process
- The number of discrete output values the ADC can represent, determined by its bit depth (Correct answer)
- The sampling rate in samples per second
- The time required to complete one conversion cycle
Correct answer: The number of discrete output values the ADC can represent, determined by its bit depth
ADC resolution is defined by the number of bits: an n-bit ADC can represent 2ⁿ discrete values, determining the smallest detectable signal change.
Question 4: According to the Nyquist theorem, what minimum sampling rate is required to faithfully reconstruct a 1,000 Hz signal?
- 500 Hz
- 1,000 Hz
- 2,000 Hz (Correct answer)
- 4,000 Hz
Correct answer: 2,000 Hz
The Nyquist theorem requires a sampling rate of at least twice the highest frequency component, so a 1,000 Hz signal requires at least 2,000 samples per second.
Question 5: Which type of memory retains its contents without power in embedded biomedical systems?
- SRAM (Static RAM)
- DRAM (Dynamic RAM)
- Flash (EEPROM) (Correct answer)
- Cache memory
Correct answer: Flash (EEPROM)
Flash memory and EEPROM are non-volatile, retaining stored data when power is removed, making them suitable for firmware and calibration data storage.
Question 6: What is the primary safety risk of macroshock in a medical setting?
- Tissue burns at the point of electrode contact only
- Ventricular fibrillation from current passing through the chest (Correct answer)
- Auditory damage from electromagnetic interference
- Disruption of pacemaker telemetry signals
Correct answer: Ventricular fibrillation from current passing through the chest
Macroshock occurs when sufficient current (typically >100 mA) passes through the body, with the primary lethal risk being ventricular fibrillation.
Question 7: In ultrasound imaging, what physical property of tissue determines the acoustic impedance?
- Temperature and viscosity
- Density and speed of sound in the tissue (Correct answer)
- Elasticity and attenuation coefficient only
- Water content and electrical conductivity
Correct answer: Density and speed of sound in the tissue
Acoustic impedance (Z = ρ × c) is determined by tissue density (ρ) and the speed of sound (c) through that tissue.
CBET Basic 5
What is the purpose of the line isolation monitor (LIM) in an isolated power system?