Applications — where is the dual-slope ADC most widely used? Select the instrument class in which the dual-slope (integrating) analog-to-digital converter is extensively employed due to its noise rejection and accuracy characteristics.

Introduction / Context:
Dual-slope (integrating) ADCs are renowned for excellent rejection of line-frequency interference and for stable, accurate measurements over modest speeds. These traits make them ideal for instrumentation where precision outweighs throughput. Identifying their common application helps match ADC type to system requirements.

Given Data / Assumptions:

• Line-frequency noise (50/60 Hz) is a common contaminant in bench measurements.
• Measurement intervals can be synchronized to reject such interference.
• Throughput needs are low (few readings per second).

Concept / Approach:
In a dual-slope ADC, the input is integrated for a fixed time, then a reference of opposite polarity is integrated until the integrator output returns to zero. The time of the second phase is proportional to the input voltage. Averaging during integration inherently filters noise, especially if the fixed interval equals an integer number of line cycles. Digital voltmeters traditionally adopt this approach to maximize accuracy and noise immunity at low cost.

Step-by-Step Solution:

Verification / Alternative check:
Service manuals and block diagrams of classic bench DVMs show integrating ADCs precisely for their line interference rejection and stable calibration behavior.

Why Other Options Are Wrong:

• Function generators: are signal sources, not precision measurement ADC users.
• Frequency counters: count edges with time bases; ADCs are tangential.
• All of the above: overly broad and incorrect.
• Audio DACs: unrelated; this is about ADCs, not DACs.

Common Pitfalls:

• Confusing “integrating ADC” with digital filtering; the integrator is analog and precedes digitization.

Final Answer:
digital voltmeters