Name two common sensor types used for temperature measurement in DDC and one key characteristic.

• A. Thermocouples and RTDs; thermocouples have a wide temperature range and RTDs offer high accuracy.
• B. Thermistors and RTDs; thermistors have a wide temperature range.
• C. Thermocouples and thermistors; thermocouples have a wide temp range.
• D. Bimetal strips and RTDs; RTDs have good stability.

Answer: (A)

Two common temperature sensors used in direct digital control are thermocouples and RTDs. Thermocouples generate a tiny voltage that changes with temperature, which lets them measure over a very wide temperature range, making them versatile for processes that get very hot or very cold. RTDs rely on the resistance of a metal changing with temperature, and they provide high accuracy and stable, repeatable readings, which is valuable for precise control and consistent performance over time. In DDC, you’ll typically match these with appropriate signal conditioning: thermocouples need cold-junction compensation to account for the reference temperature at the connection point, while RTDs require a known excitation current and careful resistance measurement to convert to temperature.

The given choice captures the practical pairing: a wide-range capability from thermocouples and high accuracy from RTDs. The other options mix sensor types that are less common in standard DDC practice or assign characteristics that don’t align as well with how these sensors perform in control systems.