Zero Suppression refers to which mounting condition?

• A. When a transmitter is mounted above the top of a tank.
• B. When a transmitter is mounted inside the tank.
• C. When a transmitter is mounted below the bottom of the tank.
• D. When a transmitter is mounted outside the tank.

Answer: (C)

Zero suppression is achieved when the transmitter’s zero point is set by its mounting position so that zero level truly means no liquid above the sensor. Placing the transmitter below the bottom of the tank accomplishes this because the sensed pressure is only the hydrostatic head of the liquid above the sensor. When the tank is empty, there’s no liquid above, so the pressure at the sensor is zero, giving a true zero output. If the sensor were mounted above the bottom or inside the tank, air pockets, vapor pressure, or head effects could create a nonzero reading even with no liquid above, requiring offset corrections. Mounting below the bottom thus provides a clean, true zero for level measurement.