Question 5 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is D ### Explanation of Why Option D is Correct **D) Continuous-level detectors produce an analog signal proportional to the liquid level in the tank.** Continuous-level liquid level detectors (such as guided wave radar, hydrostatic pressure sensors, or ultrasonic sensors) are designed to provide real-time, instantaneous measurements across the entire range of the tank. 1. **Analog Signal:** Historically and commonly, these industrial sensors output a standard continuous electrical signal (e.g., 4–20 mA current loop or 0–10 V voltage). This output is an **analog signal** because it can take on any value within a specified continuous range, directly mirroring the continuous physical process (the liquid level). While modern systems often convert this analog signal to digital later (e.g., HART, Foundation Fieldbus), the primary signal generated by the sensing element for industrial control is fundamentally analog. 2. **Proportional:** The signal output (current or voltage) is designed to scale directly and positively with the measured level. For example, if a 4-20 mA sensor is used: * 4 mA represents the lowest level (e.g., 0% or empty). * 20 mA represents the highest level (e.g., 100% or full). * 12 mA represents the 50% level. Therefore, the output signal is directly **proportional** to the liquid level in the tank. --- ### Explanation of Why Other Options are Incorrect **A) Continuous-level detectors produce a digital signal inversely proportional to the liquid level in the tank.** * **Incorrect (Signal Type):** While modern industrial communication often utilizes digital protocols (like HART), the primary measurement signal is inherently analog (4-20 mA) before digitization. * **Incorrect (Proportionality):** The signal is almost universally set up to be *directly* proportional, not *inversely* proportional. An inverse signal (where 4 mA is full and 20 mA is empty) is possible but highly non-standard and rarely used for general level measurement. **B) Continuous-level detectors produce a digital signal proportional to the liquid level in the tank.** * **Incorrect (Signal Type):** As noted above, the standard output for continuous measurement sensors in industrial settings is the analog 4-20 mA loop, making the primary signal analog, even if digital communication is layered on top. **C) Continuous-level detectors produce an analog signal inversely proportional to the liquid level in the tank.** * **Incorrect (Proportionality):** The signal is designed to be **directly proportional** to the level. An inverse signal (where a high level results in a low mA output) would violate standard industrial scaling conventions, which mandate that 20 mA represents the maximum measured value (100%).