초록 ▼

A linear compensated capacitive fluid-level sensing device includes three capacitors. A measurement capacitor is positionable during use to receive a fluid. A compensation capacitor is submerged in the fluid so that the fluid fills the space between the electrodes. An offset capacitor has a capacita

A linear compensated capacitive fluid-level sensing device includes three capacitors. A measurement capacitor is positionable during use to receive a fluid. A compensation capacitor is submerged in the fluid so that the fluid fills the space between the electrodes. An offset capacitor has a capacitance equivalent to the capacitance of the measurement capacitor when only air exists between the measurement electrodes. Charge applied to each of the three capacitors is discharged to an associated differential amplifier through a respective switch when the capacitors are disconnected from a charging voltage supply. The offset amplifier generates an inverted output current that is applied to the discharge currents of the measurement and compensation amplifiers. The compensation amplifier output gates a frequency-controlled oscillator that in turn controls the switches.

대표청구항 ▼

A dielectric-compensated device for sensing capacitively the quantity of a material present, comprising: (a) measurement capacitor means having a pair of measurement electrodes spaced apart and positionable to receive said material between said measurement electrodes during use, said measurement cap

A dielectric-compensated device for sensing capacitively the quantity of a material present, comprising: (a) measurement capacitor means having a pair of measurement electrodes spaced apart and positionable to receive said material between said measurement electrodes during use, said measurement capacitor means having a capacitance determined by the quantity and dielectric constant of said material between said measurement electrodes; (b) a voltage supply; (c) measurement switch means responsive to a switch signal for cyclically coupling said measurement capacitor means to said voltage supply and decoupling said measurement capacitor means from said voltage supply, said measurement electrodes charging to a level representative of the capacitance of said measurement capacitor means when said measurement switch means couples said voltage supply to said measurement capacitor means; (d) measurement circuit means coupled to said measurement switch means for discharging said measurement capacitor means when said measurement switch means is decoupled from said voltage supply, the discharge of the measurement capacitor means being representative of the capacitance of said measurement capacitance means, said measurement circuit means further generating an output signal representative of the discharge of said measurement capacitance means, and therefore the quantity of said material between said measurement electrodes; (e) compensation capacitor means having a pair of compensation electrodes and a predetermined amount of said material constantly between said compensation electrodes during use, said compensation capacitor means having a capacitance determined by the amount and dielectric constant of said material between said compensation electrodes; (f) compensation switch means responsive to the switch signal for cyclically coupling said compensation capacitor means to said voltage supply and decoupling said compensation capacitor means from said voltage supply, said compensation electrodes charging to a level representative of the capacitance of said compensation capacitor means when said compensation switch means couples said voltage supply to said compensation capacitor means; (g) compensation circuit means coupled to said compensation switch means for discharging said compensation capacitor means when said compensation switch means is decoupled from said voltage supply, the discharge of the compensation capacitor means being representative of the capacitance of said compensation capacitor means, said compensation circuit means further generating a compensation signal representative of the discharge of said compensation capacitance means, whereby the compensation signal changes according to a change in the dielectric constant of said material; and (h) generating means responsive to the compensation signal for generating the switch signal with a frequency representative of the compensation signal, said frequency affecting said output signal representative of the quantity of said material present so as to compensate for changes in the dielectric constant of said material.