Measurement and Instrumentation Flashcards

Which transducer converts displacement into a proportional electrical voltage using magnetic coupling?

Answer: LVDT

The Linear Variable Differential Transformer (LVDT) produces an AC output voltage proportional to the core's displacement from its null position.

In a Wheatstone bridge, balance is achieved when:

Answer: P/Q = R/S

Bridge balance requires P/Q = R/S (or equivalently P×S = Q×R), producing zero galvanometer deflection.

A thermocouple generates an EMF based on the:

Answer: Seebeck effect

The Seebeck effect causes a voltage to develop at the junction of two dissimilar metals when a temperature difference exists.

Which of the following instruments is used to measure power in a three-phase, three-wire unbalanced load using only two wattmeters?

Answer: Two-wattmeter method

The two-wattmeter method correctly measures total three-phase power in any three-wire system regardless of load balance.

Creep in an energy meter refers to:

Answer: Continuous rotation of the disc with no load applied

Creep is the slow continuous rotation of the energy meter disc when voltage is applied but no load current flows, causing measurement error.

The gauge factor (GF) of a strain gauge is defined as:

Answer: ΔR/R divided by strain (ε)

Gauge factor GF = (ΔR/R)/ε represents the fractional change in resistance per unit strain, typically 2–2.5 for metallic gauges.

An oscilloscope probe with a 10× attenuation factor is used. The screen displays 3 V. The actual signal voltage is:

Answer: 30 V

A 10× probe attenuates the signal by 10 before it reaches the oscilloscope, so the actual voltage is 3 V × 10 = 30 V.