Temperature control system for electric fluid heater

Claim 2

In combination: a container defining a chamber for heating conductive liquid contained therein by passing electric current through the liquid, said container having spaced apart electrodes positioned within said chamber for interconnecting said electrodes with a source of electric power, electronic power control means for interconnecting said electrodes with a source of electric power, said power control means being responsive to application of a predetermined control signal thereto for controlling the electric power applied to said electrodes in accordance with an electrical characteristic of the control signal; a temperature sensor thermally connected to the liquid in said container, electronic control circuit means connected to said temperature sensor and said power control means, said control circuit means normally generating the predetermined control signal, said control circuit means being responsive to the temperature sensor for altering the electrical characteristic of the control signal whenever the temperature of the liquid varies from a preset value, said control circuit means including means for sensing the current flowing through the electrodes and a power limiting circuit responsive to the sensed current for generating a power detection signal whose magnitude represents the power being drawn by said electrodes, said control circuit means being reponsive to said power detection signal exceeding a preset value for altering the control signal to decrease the power applied to said electrodes.

Claim 3

The combination defined by claim 1 in which said power control means controls the electric power applied to said electrodes by alternately blocking and passing current from the source of electric power to said electrodes, said power control means controlling the relative durations of blockage and passage of current in accordance with the electric characteristic of the control signal.

Claim 4

The combination defined by claim 1 in which said power limiting circuit produces a current signal representative of current being drawn through said electrodes and quasi-integrates said current signal to generate said power detection signal.

Claim 5

The combination defined by claim 1 in which said control circuit means further includes a peak current circuit responsive to the sensed current for producing an inhibit signal of substantial duration whenever the current flowing through said electrodes exceeds a predetermined value, said control circuit means being responsive to said inhibit signal for inhibiting generation of said control signal during the duration of said inhibit signal.

Claim 6

The combination defined by claim 1 in which said electronic control circuit means includes a capacitor, means for cyclically charging said capacitor at a variable charging rate representative of deviation of the temperature of the liquid from the preset value, and means responsive in each charging cycle to the charge in said capacitor for generating the predetermined control signal.

Claim 7

The combination defined by claim 5 in which said electronic control circuit means is responsive to said power detection signal for reducing the charginG rate of said capacitor.

Claim 8

The combination defined by claim 5 in which said electronic control circuit means further includes means responsive to the sensed current for inhibiting charging of said capacitor for a substantial period of time whenever the current applied to said electrodes exceeds a predetermined value.

Claim 9

In combination: a container adapted to be connected between a source of water and a receiver of liquid, said container being composed of electrically conductive metal and enclosing a liquid heating chamber for receiving liquid to be heated, said container having spaced apart electrically conductive electrodes positioned within said chamber adapted to be connected to a source of electric power for passing electric current through liquid within said heating chamber, said container having a liquid input tube established therein for connecting said chamber with the source of liquid and for limiting leakage current from said electrodes to the source of liquid, said container further including a liquid output tube established therein for connecting said chamber with the receiver of liquid and for limiting leakage current flow from said electrodes to the receiver, said chamber having an electrically continuous layer of electrically insulating material covering the surfaces of said chamber and extending into said tubes and covering the inner surfaces of said input and output tubes for predetermined distances therelong to thereby direct leakage current from said electrodes through liquid confined in said input and output tubes, electronic power control means for interconnecting said electrodes with a source of electric power, said power control means being responsive to application of a predetermined control signal thereto for controlling the electric power applied to said electrodes in accordance with an electrical characteristic of the control signal, a temperature sensor thermally connected to the liquid in said container, electronic control circuit means connected to said temperature sensor and said power control means, said control circuit means normally generating the predetermined control signal, said control circuit means being responsive to the temperature sensor for altering the electrical characteristic of the control signal whenever the temperature of the liquid varies from a preset value, said control circuit means including means for sensing the current flow through the electrodes and a power limiting circuit responsive to the sensed current for generating a power detection signal whose magnitude represents the power being drawn by said electrodes, said control circuit means being responsive to said power detection signal exceeding a preset value for altering the control signal to decrease the power applied to said electrodes.

Claim 10

In combination: a container adapted to be connected between a source of water and a receiver of liquid, said container being composed of electrically conductive metal and enclosing a liquid heating chamber for receiving liquid to be heated, said container having spaced apart electrically conductive electrodes positioned within said chamber adapted to be connected to a source of electric power for passing electric current through liquid within said heating chamber, said container having a liquid input tube established therein for connecting said chamber with the source of liquid and for limiting leakage current from said electrodes to the source of liquid, said container further including a liquid output tube established therein for connecting said chamber with the receiver of liquid and for limiting leakage current flow from said electrodes to the receiver, said chamber having an electrically continuous layer of electrically insulating material covering the surfaces of said chamber and extending into said tubes and covering the inner surfaces of said input and output tubes for predetermined distances therelong to thereby direct leakage current from said electrodes through liquid confined in said input and output tubes, electronic power control means for interconnecting said electrodes with a source of electric power, said power control means being responsive to application of a predetermined control signal thereto for controlling the electric power applied to said electrodes in accordance with an electrical characteristic of the control signal, a temperature sensor thermally connected to the liquid in said container, electronic control circuit means connected to said temperature sensor and said power control means, said control circuit means normally generating the predetermined control signal, said control circuit means being responsive to the temperature sensor for altering the electrical characteristic of the control signal whenever the temperature of the liquid varies from a preset value, said control circuit means including means for sensing the current flow through the electrodes and a power limiting circuit responsive to the sensed current for generating a power detection signal whose magnitude represents the power being drawn by said electrodes, said control circuit means being responsive to said power detection signal exceeding a preset value for altering the control signal to decrease the power applied to said electrodes.