Capacitive level sensing
Concept of capacitance - A capacitor is formed by two electrodes electrically insulated from each other the electrodes themselves must be conductive and typically made from metal.They can be any shape the two parallel plates are easiest to visualize.The capacitors have the ability to store energy in an electric field between its electrodes caused when a voltage or potential is applied to the circuit.The property of capacitance relates the amount of energy stored in this field to the applied potential .By placing non conductive material between the electrodes the ability for the capacitor to store energy increases and so the capacitance increases .This material between the electrodes referred to as the dielectric. They key property of dielectric material is known variously as dielectric constant or relative permittivity . This property is the amount of charge the material can still define relative to a vacuum and other gases such as fuel vapors have values similar to a vacuum .
Sensing Liquid Level
As a dielectric is introduced between the electrodes of the capacitor and capacitance changes progressively and the liquid level can be determined .
To measure variations in capacitance electric energy flowing in to and out of the electrodes
is the measured as the circuit potential is varied.A regular flow of energy is established by connecting the electrodes to an alternating current measurement circuit .The more energy flow in to the electrodes the greater the capacitance meaning more dielectric between the electrodes.
For sensor calibration reference measurement its empty and full tank condition must be taken
.Generally we need to know the dielectric constants of the liquid being measured to calibrate the sensor at its full condition.
Liquids level measurement
Powered and granular solids
Liquid metals at very high temperature
Liquefied gases at very low temperature
Very high pressure industrial processes
Advantages of capacitance level measurement
Contains no moving parts
Good range of measurement
Simple to use
Easy to clean
High temperature and high pressure application
Not suitable for low dielectrcic material