The Keller Castello level meter is a flexible, modular tank contents measurement system for liquids in ventilated or pressurized tanks. The Castello offers a user-friendly way to represent the pressure measurement at the bottom of a tank as the quantity of remaining liquid. At the push of a button, the micro-controller performs the calculations using the information of the tank shape and dimensions and displays the remaining tank content quantity on the clearly legible 5-digit LED display in the desired unit (liters, gallons, etc.).
The Castello is a complete level measurement system that consists of an electronics enclosure and a pressure transmitter. The transmitter can be either a submersible level transmitter (Series 26Q) or threaded pressure transmitter (Series 23Q) in two different ranges, one for 5 meter tank level and one for 10 meter tank level. The 5 meter system comes standard with 10 meters of cable and the 10 meter system comes standard with 15 meters cable.
The Castello housing integrates an air pressure sensor, ranged between 0.8 bar and 1.2 bar absolute. The sensors to measure the hydrostatic pressure at the bottom of the tank are calibrated from 0.8 to 1.8 bar absolute for tanks up to 5 meters in height, and 0.8 to 2.3 bar absolute for tanks up to 10 meters in height. The pressure difference, calculated by the micro-controller, is the relative hydro-static pressure. The exclusive use of absolute pressure sensors in the Castello system eliminates the use of capillary vented cables with all the problems associated with a gauge pressure measurement.
The Castello has an overall system accuracy of 2 mbar which is achieved using a computerized calibration and compensation procedure for the pressure sensors. The coefficients for this calculation are stored in EEPROMs in the sensors. These are retrieved by the microprocessor at each measurement and employed within the equations to calculate the pressure values. The Castello housing and hydrostatic sensor can be interchanged at will.
The Castello is configured using a PC and the easy-to-use software so that the filling level, which determines the pressure, can be converted into an appropriate filling quantity. First the tank shape is selected, then the tank dimensions and the specific gravity of the liquid are entered. The program covers the most common tank shapes, but also enables any shape by entering the parameters into a specified table.
The power supply to the system (8 to 28 V) can be provided externally or internally using a 9 V battery. The display is obtained by pressing the button on the front, and the value appears for a configurable duration. The Castello has two switch outputs with configurable functionality and threshold values. An external power supply must be provided if the switch outputs are used.
