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Zorluk: OrtaMultimeter: Voltage and Current Measurement

A technician intending to measure the current drawn by an energized direct-current (DC) motor accidentally places the multimeter test leads in parallel across the motor terminals while the meter is configured in the 10 A10\text{ A} DCA mode. What is the most likely result of this setup?

  1. A
    The meter acts as a high-impedance load and safely displays the voltage drop across the motor.
  2. B
    The meter creates an open circuit that immediately cuts all electrical power to the motor without harming the meter.
  3. A massive short-circuit current flows through the meter's low internal resistance, blowing the meter's internal protective fuse.Cevap
  4. D
    The meter's internal circuit breaker trips and automatically resets as soon as the test leads are removed.

Cevap

A massive short-circuit current flows through the meter's low internal resistance, blowing the meter's internal protective fuse.
When configured to measure current, a digital multimeter inserts a very low-resistance shunt into the circuit so that it can measure current without adding series resistance. If an ammeter is connected in parallel directly across an energized load or voltage source, this low resistance creates a direct short circuit across the supply. The resulting high current will immediately melt the meter's internal protective fuse to safeguard the meter circuitry and the user.

Adım Adım Çözüm

1
Analyze the internal electrical characteristics of a multimeter configured for current measurement (ammeter mode).
An ammeter is designed with an extremely low internal shunt resistance (near 0 Ω0\ \Omega) so that it does not drop significant voltage when inserted in series with a circuit.
Understanding meter impedance is essential to predicting circuit behavior during hookup.
2
Evaluate the circuit configuration when connecting low resistance in parallel across an energized load.
Connecting near-zero resistance across the voltage source creates a short circuit, causing a severe current spike through the meter according to Ohm's Law (I=VRI = \frac{V}{R}).
Determines the electrical pathway taken by the source current.
3
Identify the protective response of standard digital multimeters to overcurrent in the current jacks.
The current exceeds the current rating of the meter input channel, causing the fast-acting internal ceramic/glass fuse to open and protect the meter movement/electronics.
Explains the physical outcome of the incorrect connection.

Anahtar Kavram

Multimeter internal resistance differences between voltage (high impedance in parallel) and current (low shunt resistance in series) modes, and the resulting fuse protection mechanisms.
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Multimeter: Voltage and Current Measurement

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