US 3,938,117 A · Critical liquid-level warning circuit

Abstract

A critical liquid-level warning circuit for association with a liquid-level indicating circuit, the indicating circuit including a sensing device that provides a voltage which varies between upper and lower voltage limits as a function of the level of a liquid. The warning circuit is particularly suitable for use in indicating a low fuel level in the fuel tank of a vehicle and, in the preferred embodiment, includes a first operational amplifier responsive to the sensing device voltage and a second operational amplifier that controls the actuation of a warning device. A delay circuit is interposed between the first and second operational amplifiers. The output of the first operational amplifier changes from one condition to another condition upon occurrence of a critical liquid level. The delay circuit provides a voltage which varies in magnitude as a function of time elapsed subsequent to the change in condition of the output of the first operational amplifier. This variable voltage controls the second operational amplifier. Preferably, the second operational amplifier circuit includes means for delaying the de-actuation of the warning device, thereby, to prevent intermittent warning device operation.

Claims11

Dependent claims

A critical liquid-level warning circuit for association with a liquid-level indicating circuit, said indicating circuit including a sensing device which provides a voltage that varies between lower and upper voltage limits as a function of a liquid level sensed by said sensing device, said critical liquid-level warning circuit comprising:

first circuit means, supplied with said sensing device voltage, for generating an electrical signal having one of two conditions depending upon whether said sensing device voltage is below or above a predetermined critical level;
an electrically actuable warning device;
second circuit means for controlling the actuation of said warning device, said second circuit means having an output coupled to said warning device and having an input responsive to a predetermined voltage level to cause said output to actuate said warning device;
and
a delay circuit, coupled to the output of said first circuit means and to the input of said second circuit means, said delay circuit producing a voltage signal which varies in magnitude as a function of time elapsed subsequent to the change of said electrical signal generated by said first circuit means from one of said two conditions to the other of said two conditions, said second circuit means actuating said warning device when said variable voltage signal reaches a predetermined level.

2 more elements

first circuit means for generating a first reference voltage signal;
an amplifier having a first input coupled to said first circuit means to couple said first reference voltage signal to said first input of said first amplifier, said amplifier having a second input adapted to be supplied with said sensing device voltage, said first amplifier having an output voltage which changes from a first condition to a second condition when the polarity of said sensing device voltage, with respect to said first reference voltage signal, changes;
a time delay circuit including a resistor and a capacitor, said capacitor being charged through said resistor when the output of said first amplifier changes from said first condition to said second condition;
means for generating a second reference voltage signal;
a second amplifier having a first input to be supplied with said second reference voltage signal and having a second input coupled to said time delay circuit, said second amplifier having an output which changes from a first condition to a second condition when the voltage across said capacitor in said time delay circuit reaches a predetermined level;
and
a warning device, said warning device being actuated when said second amplifier output changes from its first condition to its second condition.

4 more elements

Dependencies are inferred from the claim text.

Critical liquid-level warning circuit

Life of this patent

Critical liquid-level warning circuit

Life of this patent

Abstract

Claims11