How it works...
Petrotag utilizes Hydrostatic Tank Gauge (HTG) principles with some key modifications in order to provide accurate liquid level measurements.
The system uses a series of tubes that enter into a tank through a 3 inch diameter entry. The tubes are connected to a set of “plates” on our probe. These tubes are used to pressurize each of the plates on the probe by supplying a flow of Nitrogen to each plate.

These pressures are then digitized and mathematical
calculations are preformed upon the pressures in order to determine liquid densities and in turn the liquid levels.
As long as two or more of the plates on the probe are covered the Petrotag system will be capable of determining the density of the product in the tank and therefore determining an accurate liquid level. In the event that only a single plate is covered by liquid the system will use its last know density values to perform liquid level calculations thereby eliminating the need for two or more plates to be covered at all times.
The diagram below illustrates the ideal conditions for the Petrotag Crude Oil measurement system

For optimal performance of the system, when installed intoa tank containing two different liquids, the liquids should be in such a way that initially the top most liquid is contained between any two sequential plates (Y and X in figure 1) and the second liquid should be contained between any two
other sequential plates (B and A in figure 1). This is usually accomplished by ensuring that at least two probe plates are located below the heating tube in a standard oil field tank and that at least two plates are located above the heating tube. This setup allows the system to accurately determine
the densities of the two different liquids and therefore determine the interface point between the two fluids.

After the system is in operation this condition may be changed because the Petrotag system will keep running averages of the densities of the fluids it can therefore still determine the interface point of the two liquids even if either one of the liquids is not contained between two plates.
Understandably the above mentioned condition can not always be met during the startup of a tank due to unknown water and oil quantities being produced from the well and as such estimate densities can be entered into the system.
As the system operates its running averages of the densities will become more accurate from the initial estimates and therefore produce more accurate results.

The system communicates using the MODBUS ASCII protocol, currently over RS-232, and supplies the user with two values. These values indicate the height of the top liquid (Hoil in fig. 1) and the height of the bottom liquid (Hw in fig. 1), both results are reported in millimeters from the