Home / Industry Articles / Submersible Level Transmitters The Mercoid® Division of Dwyer Instruments, Inc. offers four series of submersible level transmitters with different features suitable for different applications: the FBLT, PBLT, MBLT, and SBLT. Submersible Level Transmitters are pressure transmitters manufactured to read hydro-static pressure from inside the fluid. These transmitters are submersed into the fluid that they are measuring and will give an output proportional of the fluid level above the sensor location. Hydrostatic pressure is the pressure created by the hydrostatic force per unit area at the base of a column of liquid. This can also be called the pressure head or head pressure and is often referred to as the height of the fluid, such as inches of water column, inches of mercury, or feet of water. The measurement is dependent on the liquid density and independent of the shape of the container. This is based on the property that pressure is equal to density times the height of the liquid. Since these instruments are measuring the hydro-static pressure they must compensate for the atmospheric pressure that acts on the fluid surface. Variations of barometric pressure with weather changes will affect the accuracy of readings. Atmospheric pressure is the pressure due to the force per unit area created by weight of the gases in the atmosphere above that surface where it is being measured. Atmospheric pressure decreases as elevation increases as there is less mass of gases above the point being measured. For this reason all Mercoid® Submersible Level Transmitters include a vent tube that allows for atmospheric pressure compensation. Standard, Mercoid® installs a maintenance vent filter to protect the sensor from water and debris. The Model A-297 Desiccant Vent Filter is also available as an accessory to remove humidity from the air entering the vent tube. When purchasing a Submersible Level Transmitter, the range must be specified at the time of ordering. The range can be ordered in psi, ft of water column, or meters of water column. If the fluid being monitored is not water based, a specific gravity correction may be programmed into the receiving or controlling device connected to the transmitter.