Liquid level in a storage tank can be controlled by measuring pressure at two measurement points, for example, one point above the fluid and another near the bottom of the tank. The fluid level can be calculated utilizing differential pressure and fluid density data. As temperature increases, the fluid density decreases and the level rises without an accompanying increase in differential pressure which leads to an inaccurate level measurement and possibly overflow of the tank.
FIG. 1 illustrates a prior art tank overflow protection system 100 that includes a remote seal transmitter 110 connected to a storage tank 150 for measuring liquid level within the tank 150. The remote seal transmitter 110 generally includes a pair of seals 120 and 130 attached to the storage tank 150. The pair of seals 120 and 130 can be attached to the remote seal transmitter 110 by fluid-filled capillaries 140 to measure differential pressure. The variable H1 shown in FIG. 1 represents fluid level at time T1 and the variable H2 represents fluid level at a time T2. The remote seal transmitter 110 with the fluid filled capillaries 140 is capable of only measuring the differential pressure. The fluid height change due to density change and level change due to temperature is undetectable with the prior art system 100 shown in FIG. 1.
Based on the foregoing, it is believed that a need exists for an improved tank overflow protection apparatus and/or method. A need also exists for an improved pressure transmitter for measuring process temperature and pressure at two measurement points with respect to, for example, a fluid storage tank, as described in greater detailed herein.