초록 ▼

A carrier frequency based system employs a capacitive probe which is located at a predetermined desired fluid detection level in a fluid containing vessel. The probe forms one plate of a capacitor where the other plate is formed by the fluid in which the probe is immersed. A carrier frequency is inj

A carrier frequency based system employs a capacitive probe which is located at a predetermined desired fluid detection level in a fluid containing vessel. The probe forms one plate of a capacitor where the other plate is formed by the fluid in which the probe is immersed. A carrier frequency is injected into the fluid by means of a suitable oscillator and at a frequency which is close to the system resonant frequency. When the probe is immersed in fluid, the probe will receive a predetermined carrier frequency of an amplitude determined by the system. The output of the probe is coupled to suitable sensing circuits which monitor the amplitude of the signal frequency coupled to the probe. When the fluid level recedes and therefore a portion of the probe or the total probe is out of fluid, the capacitance of the system changes. A different signal from the injected carrier frequency is now applied to the probe indicating to the sensing circuit that the probe is not immersed and therefore indicating an alarm condition. The output of the sensing circuit is monitored by control circuitry which can operate an alarm indicating to the user that the probe is not fluid immersed and that preventive measures should be taken. The fluid sensing probe utilizing the carrier injected frequency can discriminate between fluid and foam, “probe fouling”and probe shorting and is relatively fail proof.

대표청구항 ▼

A liquid level detection apparatus for monitoring the level of a fluid volume in a storage tank or vessel, comprising: a capacitive probe positioned at a given level in said vessel indicative of a desired fluid level at which said probe is immersed in said fluid volume at said level; means for injec

A liquid level detection apparatus for monitoring the level of a fluid volume in a storage tank or vessel, comprising: a capacitive probe positioned at a given level in said vessel indicative of a desired fluid level at which said probe is immersed in said fluid volume at said level; means for injecting a carrier frequency signal into said fluid volume as contained in said vessel to cause said carrier frequency signal to propagate through said fluid volume to said probe; circuit means coupled to said probe for monitoring the presence of said carrier signal and responsive to the amplitude of said signal to provide a control signal when said amplitude is below a given value.