Principle of a digital frequency counter: Frequency is measured by enabling a counter for a precisely known sampling (gate) time and counting how many input pulses occur during that interval.

Introduction / Context:
Digital frequency counters fundamentally convert an analog phenomenon (a repeating waveform) into a digital count by time-gating pulses. By knowing the gate time exactly, the count maps directly to frequency, enabling accurate and stable measurement across a wide range.

Given Data / Assumptions:

• Input is periodic with countable edges.
• A precise reference timebase defines the sampling (gate) interval.
• A digital counter tallies edges within the gate time.

Concept / Approach:
If N pulses are counted during gate time T, then the displayed frequency is f ≈ N / T. Longer T improves resolution (more counts per measurement); shorter T improves update rate. Reciprocal techniques can measure period instead, but the stated approach is the classic method used in many counters.

Step-by-Step Solution:
Stabilize a reference clock → derive precise gate time T.Pulse-shape the input to valid logic levels.Enable the counter for interval T; count rising (or falling) edges → N.Compute/display frequency: f = N / T.

Verification / Alternative check:
Cross-check by measuring period with a time-interval counter: period P → frequency f = 1 / P. Both methods converge when the reference is accurate and jitter is controlled.

Why Other Options Are Wrong:
“Incorrect” contradicts the established method. 50% duty cycle is unnecessary; only stable edges are needed. Dual counters help with continuous display but are not required. Reciprocal counters are an alternative method, not a refutation.

Common Pitfalls:
Too short a gate time yields poor resolution; noisy inputs cause double counts; improper trigger level causes missed edges.

Final Answer:
Correct