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Electronics Engineering QUESTION #11733
Question 1
A clamp meter is used to measure DC current in a cable. The reading is unstable and drifts. The most likely cause is:
  • AC interference from adjacent cables inducing error in the Hall-effect sensor
  • The cable insulation thickness exceeds the clamp jaw capacity
  • The DC range requires the meter to be zeroed (nulled) before measurement
  • Both A and C✔️
Correct Answer Explanation
DC clamp meters use a Hall-effect sensor which is sensitive to ambient magnetic fields. (A) AC stray fields from neighbouring cables cause induced errors; (C) DC Hall sensors have an inherent offset that drifts with temperature — the meter must be zeroed with no current flowing before measurement. Both are valid and common causes of unstable DC clamp readings.