Zero Suppression occurs when a transmitter is mounted where?

• A. Below the bottom of the tank
• B. At the top of the tank
• C. In the middle of the tank
• D. Above the top of the tank

Answer: (A)

The idea being tested is how the mounting location affects the sensed zero in a hydrostatic level transmitter. A level transmitter that measures pressure is driven by the hydrostatic head—the vertical height of liquid above its sensing point. If you mount the transmitter below the tank bottom, the sensing point sits in a liquid column that extends outside the tank. Even when the tank level is zero, this extra liquid head above the sensor pushes pressure into the transmitter, so the zero point is offset and the instrument can’t read true zero without calibration. This is what “zero suppression” refers to in this setup—the zero reading is suppressed by the additional head from the liquid column in the mounting leg.

If the transmitter were mounted at the top of the tank, in the middle, or above the tank, there isn’t that extra head of liquid below the sensing point when the tank is empty, so the zero reading would align more closely with true zero (aside from normal atmospheric effects and calibration).