19. A d/p cell used to measure liquid level has a "suppressed zero." This means: (A) The transmitter is located above the 0% liquid level mark (B) The transmitter uses filter circuits to suppress noise to a zero level (C) The liquid is less dense than water (D) The transmitter is located below the 0% liquid level mark (E) The elevation of the vessel is below sea level 20. A guided-wave radar transmitter is able to measure liquid interface levels based on differences of between the two liquids. (A) lonization potential (B) Density (C) Speed of light (D) Temperature (E) Dielectric constant 21. What is the procedure and preparation to be done before carrying any work in instrument, like ESD Pressure Transmitter?