CBET Electronics and Electrical Safety 5 — Questions and Answers
Question 1: When testing electrical safety with a safety analyzer, the 'patient lead to ground' leakage test measures current flowing from:
- The power cord ground pin to chassis
- Applied parts to the equipment ground (Correct answer)
- The chassis to the neutral conductor
- The power line to the chassis
Correct answer: Applied parts to the equipment ground
Patient lead-to-ground leakage measures current that could flow through a patient from applied parts to ground, reflecting direct patient risk.
Question 2: What is the function of a decoupling capacitor placed near an IC power pin?
- Increase power supply output voltage
- Filter high-frequency noise on the supply rail (Correct answer)
- Provide gain to the digital signal
- Convert AC to DC for the IC
Correct answer: Filter high-frequency noise on the supply rail
Decoupling capacitors suppress high-frequency transients and noise on the supply voltage rail, stabilizing IC operation.
Question 3: An op-amp configured with the non-inverting input connected to a voltage divider and output fed back to the inverting input is functioning as a:
- Comparator
- Differentiator
- Voltage follower (buffer) (Correct answer)
- Voltage regulator
Correct answer: Voltage follower (buffer)
When the output feeds directly back to the inverting input with no other feedback components, the op-amp becomes a unity-gain voltage follower.
Question 4: Which condition does a Line Isolation Monitor (LIM) detect in an isolated power system?
- Overvoltage on the supply line
- First fault to ground in the isolated circuit (Correct answer)
- Excessive current draw by connected equipment
- Reverse polarity wiring
Correct answer: First fault to ground in the isolated circuit
A LIM continuously monitors the impedance from the isolated conductors to ground and alarms when the first fault reduces isolation below safe limits.
Question 5: In a full-wave bridge rectifier with four diodes, the output ripple frequency relative to the AC input frequency is:
- Equal (1×)
- Half (0.5×)
- Double (2×) (Correct answer)
- Four times (4×)
Correct answer: Double (2×)
A full-wave bridge rectifier conducts on both half-cycles, producing two output pulses per input cycle, doubling the ripple frequency.
Question 6: According to electrical safety standards, the ground wire in a medical device power cord must be:
- The same gauge as the hot conductor (Correct answer)
- A larger gauge than the hot and neutral conductors
- Optional if a double-insulated design is used
- Connected to the chassis only, not the plug ground pin
Correct answer: The same gauge as the hot conductor
The equipment ground conductor must be at least the same gauge as the current-carrying conductors to safely carry fault current.
Question 7: Thermal runaway in a bipolar junction transistor (BJT) is caused by:
- Excessive base current limiting resistance
- Positive feedback between temperature rise and collector current increase (Correct answer)
- Breakdown of the emitter-base junction at low voltages
- Capacitive coupling between collector and base
Correct answer: Positive feedback between temperature rise and collector current increase
As a BJT heats up, leakage current increases, raising collector current which generates more heat, creating a destructive positive feedback loop.
CBET Electronics and Electrical Safety 5
When testing electrical safety with a safety analyzer, the 'patient lead to ground' leakage test measures current flowing from: