Question

The advantage of using dual slope ADC in a digital voltmeter is that

• A. its conversion time is small
• B. its accuracy is high
• C. it gives output in BCD format
• D. it does not require a comparator

Hint:

Dual Slope ADC $\rightarrow$ Slowest but Most Accurate (used in DVMs).
Flash ADC $\rightarrow$ Fastest but Least Accurate (used in high-speed oscilloscopes).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks about the primary operational advantage of using a dual-slope Integrating Analog-to-Digital Converter (ADC) in a digital voltmeter (DVM).

Step 2: Key Formula or Approach:
Dual-slope ADCs operate by integrating the unknown input voltage for a fixed time $T_1$, and then de-integrating using a known reference voltage until the integrator output returns to zero over a variable time $T_2$.
The conversion equation is:
\[ V_{in} = V_{ref} \left( \frac{T_2}{T_1} \right) \]

Step 3: Detailed Explanation:

• From the conversion equation, the input voltage depends only on the ratio of the times $T_2/T_1$ and the reference voltage $V_{ref}$.

• It is completely independent of the integrator's resistance $R$, capacitance $C$, and the clock frequency $f_{clk}$ because any drift in these parameters affects both integration and de-integration phases proportionally and cancels out.

• This makes the dual-slope ADC exceptionally stable and precise over temperature and aging.

• Furthermore, the integration process averages out high-frequency noise and power line interference ($50\text{ Hz}/60\text{ Hz}$ noise), providing excellent noise rejection.

• While its conversion speed is slow ($2^N$ clock cycles), its high accuracy makes it the ideal choice for digital voltmeters where precision is far more important than speed.

Step 4: Final Answer:
The primary advantage of a dual slope ADC is its high accuracy, which corresponds to Option (B).