Definition
A voltmeter with very high internal electrical resistance, designed to draw almost no current from the circuit it is measuring. This allows it to read voltage accurately in sensitive electronic circuits without disturbing their operation.
Plain English
A voltage-measuring instrument that takes its reading without pulling enough electricity from the circuit to change what it is measuring.
Context Anchor
Seen in aircraft electrical troubleshooting, especially when checking sensors, electronic controls, and avionics circuits.
Derivation
Impedance comes from the Latin impedire, meaning 'to hinder' or 'hold back.' A high-impedance meter strongly holds back the flow of current through itself, so it doesn't drain the circuit it's testing.
Why Pilots Care
Allows accurate voltage checks on sensitive aircraft circuits without altering the reading or risking damage to electronic components.
Analogy
It is like checking something with a very light touch. The meter observes the voltage without pushing or pulling enough electricity to change what is happening.
Intuition Check
High-impedance does not mean the voltmeter reads higher voltage. It means the meter resists drawing current from the circuit, so the voltage reading is less likely to be disturbed.
Example Sentence 1
The avionics technician used a high-impedance voltmeter to check the signal voltage on the autopilot circuit board.
Example Sentence 2
During an avionics inspection, a high-impedance voltmeter was used to measure the output of the voltage regulator without loading the circuit.