Critical liquid-level warning circuit

Claim 2

A critical liquid-level warning circuit for association with a liquid-level indicating circuit coupled to a DC source of electrical energy through a switch, said indicating circuit including a sensing device which provides a voltage which varies between upper and lower voltage limits as a function of a liquid level sensed by said sensing device, said critical liquid-level warning circuit comprising: an operational amplifier having inverting and non-inverting inputs and having an output, said sensing device being coupled to one of said amplifier inputs to supply said sensing device voltage thereto; means for providing a critical reference voltage to the other of said inputs to said operational amplifier; an electrically actuable warning device; a first transistor having a control electrode and having an output circuit, said first transistor output circuit being connected in series with said warning device and said first transistor control electrode being connected to the output of said operational amplifier; a capacitor coupled to said output circuit of said first transistor, said capacitor being connected to accumulate a potential difference across it when said first transistor is in a conductive state corresponding to actuation of said warning device; a second transistor having a control electrode and an output circuit, said second transistor output circuit being coupled to said control electrode of said first transistor; and a resistor and a capacitor connected in series, said seriesconnected resistor and capacitor being connected across said source of electrical energy when said switch is in a closed condition and the junction formed between said resistor and said capacitor being coupled to said control electrode of said second transistor.

Claim 3

A critical liquid-level warning circuit in accordance with claim 1 wherein said indicating circuit further includes a second switch coupled to said sensing device, said second switch having a condition wherein said sensing device voltage reaches one of said voltage limits, and wherein said warning circuit further includes a second capacitor coupled to the output of said first transistor, said second capacitor accumulating a potential difference across it when said first transistor is conductive and said warning device is actuated, and solid-state switching means coupled to said second capacitor, coupled to said indicating circuit at a location between said sensing device and said second switch and coupled to said junction formed between said series-connected resistor and first-mentioned capacitor, for maintaining said first transistor output circuit in a conductive state when said second switch is in said condition wherein said sensing device voltage reaches one of said voltage limits.

Claim 4

A critical liquid-level warning circuit for association with a liquid-level indicating circuit coupled to a DC source of electrical energy through a switch, said indicating circuit including a sensing device which Provides a voltage which varies between upper and lower voltage limits as a function of a liquid-level sensed by said sensing device and a second switch coupled to said sensing device, said second switch having a condition wherein said sensing device voltage reaches one of said voltage limits, 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 above or below a predetermined critical level; an electrically actuable warning device; second circuit means for actuating said warning device when said first circuit means electrical signal is in one of said two conditions and for preventing actuation of said warning device when said first circuit means electrical signal is in the other of said two conditions, said second circuit means being coupled to said first circuit means; third circuit means, coupled to said second circuit means, for actuating said warning device for a predetermined time subsequent to the closure of said switch coupling said DC source of electrical energy to said indicating circuit; and fourth circuit means for causing said warning device to retain the state of warning attained by it immediately prior to said second switch being placed in said condition wherein said sensing device voltage reaches said one of said voltage limits.

Claim 5

A critical liquid-level warning circuit for association with a liquid-level indicating circuit coupled to a DC source of electrical energy through a switch, said indicating circuit including a sensing device which Provides a voltage which varies between upper and lower voltage limits as a function of a liquid-level sensed by said sensing device and a second switch coupled to said sensing device, said second switch having a condition wherein said sensing device voltage reaches one of said voltage limits, 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 above or below a predetermined critical level; an electrically actuable warning device; second circuit means for actuating said warning device when said first circuit means electrical signal is in one of said two conditions and for preventing actuation of said warning device when said first circuit means electrical signal is in the other of said two conditions, said second circuit means being coupled to said first circuit means; third circuit means, coupled to said second circuit means, for actuating said warning device for a predetermined time subsequent to the closure of said switch coupling said DC source of electrical energy to said indicating circuit; and fourth circuit means for causing said warning device to retain the state of warning attained by it immediately prior to said second switch being placed in said condition wherein said sensing device voltage reaches said one of said voltage limits.

Claim 6

A critical liquid-level warning circuit for association with a gauge circuit for a motor vehicle, said motor vehicle having a DC source of electrical energy and an ignition switch, said gauge circuit including a sensing device which provides a voltage which varies between upper and lower voltage limits as a function of the level of a liquid located within said motor vehicle, said liquid level being sensed by said sensing device, said critical liquid-level warning circuit comprising: a first circuit comprising an operational amplifier having a non-inverting input, an inverting input, and an output, said operational amplifier having one of its inputs coupled to said sensing device to receive said sensing device voltage; a voltage supply lead connected through said ignition switch to one terminal of said source of electrical energy; a potentiometer connected between said voltage supply lead and the other terminal of said source of electrical energy, said potentiometer having an arm establishing a critical voltage level, said potentiometer arm being connected to the other of said inputs to said operational amplifier; a solid-state switching device having an output circuit and a control electrode, said control electrode being connected to the output of said operational amplifier; a warning device connected in series with said output circuit of said solid-state switching device, said series-connected warning device and solid-state switching device output circuit being connected between said voltage supply lead and said other terminal of said source of electrical energy; and a warning device prove-out circuit, said prove-out circuit including a second solid-state switching device having an output circuit and a control electrode, said second solid-state switching device output circuit being coupled between said voltage supply lead and said control electrode of said first-mentioned solid-state switching device, a resistor having one of its leads coupled to said voltage supply lead, a capacitor having one of its leads coupled to the other lead of said resistor to form a junction between said capacitor and said resistor, said capacitor having its other lead connected to said other terminal of said source of electrical energy, and said second solid-state switching device having its control electrode connected to the junction formed between said resistor and said capacitor.

Claim 7

A critical liquid-level warning circuit for association with a gauge circuit for a motor vehicle, said motor vehicle having a DC source of electrical energy and an ignition switch, said gauge circuit including a sensing device which provides a voltage which varies between upper and lower voltage limits as a function of the level of a liquid located within said motor vehicle, said liquid level being sensed by said sensing device, said critical liquid-level warning circuit comprising: a first circuit comprising an operational amplifier having a non-inverting input, an inverting input, and an output, said operational amplifier having one of its inputs coupled to said sensing device to receive said sensing device voltage; a voltage supply lead connected through said ignition switch to one terminal of said source of electrical energy; a potentiometer connected between said voltage supply lead and the other terminal of said source of electrical energy, said potentiometer having an arm establishing a critical voltage level, said potentiometer arm being connected to the other of said inputs to said operational amplifier; a solid-state switching device having an output circuit and a control electrode, said control electrode being connected to the output of said operational amplifier; a warning device connected in series with said output circuit of said solid-state switching device, said series-connected warning device and solid-state switching device output circuit being connected between said voltage supply lead and said other terminal of said source of electrical energy; and a warning device prove-out circuit, said prove-out circuit including a second solid-state switching device having an output circuit and a control electrode, said second solid-state switching device output circuit being coupled between said voltage supply lead and said control electrode of said first-mentioned solid-state switching device, a resistor having one of its leads coupled to said voltage supply lead, a capacitor having one of its leads coupled to the other lead of said resistor to form a junction between said capacitor and said resistor, said capacitor having its other lead connected to said other terminal of said source of electrical energy, and said second solid-state switching device having its control electrode connected to the junction formed between said resistor and said capacitor.

Claim 8

A critical liquid-level warning circuit in accordance with claim 4 wherein said motor vehicle gauge circuit further inCludes a second switch coupled to said sensing device, said second switch having a condition wherein said sensing device voltage reaches one of said voltage limits, and wherein said warning circuit further includes a circuit comprising a third solid-state switching device having an output circuit coupled to said junction formed between said resistor and said capacitor and having a control electrode, a fourth solid-state switching device having an output circuit coupled between said voltage supply lead and said control electrode of said third solid-state switching device, said fourth solid-state switching device having a control electrode coupled to said gauge circuit at a point between said sensing device and said second switch, a fifth solid-state switching device having an output circuit connected in series with the output circuit of said third solid-state switching device and having a control electrode, and a capacitor for accumulating a potential difference across it when said warning device is actuated, said capacitor being coupled to said output circuit of said first-mentioned transistor and to said control electrode of said fifth solid-state switching device, said fifth solid-state switching device controlling the actuation of said warning device when said second switch is in its condition wherein said sensing device voltage reaches one of said voltage limits.