What type of device is used to alert abnormal levels or positions in systems such as water storage tanks?

• A. Alarm
• B. Supervisory
• C. Indicator
• D. Control

Answer: (B)

Supervisory signals are used to indicate that a monitored condition is out of its normal or safe range and requires operator attention, without automatically changing the process. For a water storage tank, when the water level falls outside the set range or a valve position is not as commanded, a supervisory alert communicates that something needs checking, guiding a human to intervene. This differs from an alarm, which typically triggers a loud warning for immediate danger; an indicator merely displays status locally; and a control actively changes the process (such as starting/stopping pumps or moving valves). The supervisory type is the best fit for signaling an abnormal level or position that needs attention without forcing an automatic action.