ABA Electrical Systems & Wiring 2 — Questions and Answers
Question 1: What is the primary purpose of electrical grounding in an audiology test booth?
- To increase signal amplification
- To reduce electrical noise and protect patients from shock (Correct answer)
- To improve transducer frequency response
- To calibrate audiometer output levels
Correct answer: To reduce electrical noise and protect patients from shock
Grounding provides a low-resistance path for fault current and minimizes electrical noise that can contaminate audiological measurements.
Question 2: Which type of shielding is most effective at blocking low-frequency magnetic interference in audiological equipment?
- Copper foil shielding
- Aluminum mesh shielding
- High-permeability mu-metal shielding (Correct answer)
- Silver-coated polymer shielding
Correct answer: High-permeability mu-metal shielding
Mu-metal, a high-permeability nickel-iron alloy, is the most effective material for shielding low-frequency magnetic fields.
Question 3: A ground loop in an audiology suite is MOST likely to produce which artifact?
- High-frequency white noise
- 60 Hz hum in recordings (Correct answer)
- DC offset in ABR waveforms
- Intermittent signal clipping
Correct answer: 60 Hz hum in recordings
Ground loops create a current path between two grounded points at different potentials, inducing 60 Hz AC line-frequency hum.
Question 4: What is the recommended maximum skin-electrode impedance for reliable ABR recording?
- Less than 50 kΩ
- Less than 5 kΩ (Correct answer)
- Less than 500 Ω
- Less than 50 Ω
Correct answer: Less than 5 kΩ
Electrode impedance below 5 kΩ (and ideally balanced between electrodes) ensures adequate signal quality and common-mode rejection for ABR.
Question 5: In a differential amplifier used in evoked potential recording, common-mode rejection ratio (CMRR) is important because it:
- Amplifies the neural signal symmetrically
- Cancels electrical noise present on both inputs equally (Correct answer)
- Increases the bandwidth of the recording system
- Reduces the need for electrode preparation
Correct answer: Cancels electrical noise present on both inputs equally
High CMRR allows the differential amplifier to reject interference signals (like 60 Hz) that appear identically on both inputs while preserving the neural signal.
Question 6: Which wiring configuration BEST reduces electromagnetic interference pickup in long electrode lead cables?
- Parallel unshielded wires
- Twisted-pair shielded cables (Correct answer)
- Coaxial cable with braided shield only
- Flat ribbon cable
Correct answer: Twisted-pair shielded cables
Twisted-pair shielded cables cancel magnetically induced EMI through opposing loop areas in adjacent twists while the shield blocks electric field interference.
Question 7: An isolation transformer in an audiology suite primarily serves to:
- Step up voltage for high-power transducers
- Galvanically isolate equipment from mains ground to reduce leakage current (Correct answer)
- Filter high-frequency RF interference from power lines
- Regulate voltage against building fluctuations
Correct answer: Galvanically isolate equipment from mains ground to reduce leakage current
An isolation transformer breaks the direct conductive path from mains to equipment ground, significantly reducing potentially hazardous leakage current to patients.
ABA Electrical Systems & Wiring 2
What is the primary purpose of electrical grounding in an audiology test booth?