Measuring Fluctuating Temperature Water Level Using Density

SOR from Instrument Specialties

A thermal power plant needed to measure the liquid level in a water storage tank, but due to mounting restrictions and space limitations, they are unable to use traditional liquid level sensing products.

Another approach for indirectly measuring level of water in a storage tank is by using a differential pressure transmitter to measure pressure, and then calculating liquid level through calculating the density. However, the density of water changes with temperature; when temperature increases the water expands in volume and vice versa. This causes the water level to rise without varying the amount of pressure being applied to the transmitter’s sensors. If only a pressure measuring device is used, the system will lack the temperature data required for correctly adjusting the density calculations. Temperature compensation is needed to accurately determine the level of water within the process.


An SOR 815DT Smart Differential Transmitter combined with an SOR 1400 Series Temperature Transmitter Assembly gave the plant personnel all the necessary information they required to calculate the density, and therefore, indirectly measure the water level. With the SOR 815DT’s compact design, it was able to be installed into confined areas where other instruments would be too large.

Both transmitters constantly measure the temperature and pressure and the process data is relayed to a digital control system. The temperature transmitter data is used to compensate the level readings accordingly. The combination of transmitters provides the digital control system with the process parameters needed for precisely calculating the density and thus, it is able to accurately determine the water level within the storage tank.

For more information regarding any level, pressure, temperature, or flow requirement, contact Instrument Specialties, Inc. by calling 407-324-7800 or visiting