US 8,008,604 B2Granted

Low profile heater

AssigneeHonor Tone, Ltd.

InventorHim Chung Tsang

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Abstract

A portable, low profile electric radiant heater has an elongated heating element. A plurality of thermistors are disposed proximate to and along the length of the elongated heating element, spaced at substantially equal intervals. A microcontroller switches a reference resistor in series with a charging capacitor to determine a reference timer value. The microcontroller switches banks of multiple thermistors in series with the charging capacitor to determine associated timer values. The microcontroller calculates thermistor resistance values using the reference timer, reference resistor, and thermistor timer values. A lookup table is employed to determine a temperature value associated with the thermistor resistance value. This serves as the sensed temperature of the associated bank of thermistors. A plurality of tip-over switches are provided. One tip-over switch is disposed between the microcontroller and the heating element. Another tip-over switch is disposed between the microcontroller and the banks of temperature sensing thermistors.

A method of sensing an overheating condition in a portable electric heater having a heating element, a reference resistor having a known resistance of R_Reference, a plurality of thermistors organized into at least a first bank of multiple thermistors and a second bank of multiple thermistors and disposed proximate the heating element in substantially evenly spaced intervals, and a capacitor, the method comprising the steps of:

placing the reference resistor in series with the capacitor to form a first RC timing circuit;
determining an amount of time TIMER_Reference that it takes for a point between the reference resistor and the capacitor to reach a predetermined threshold voltage;
switching, via a first control signal output from a microcontroller, only the first bank of multiple thermistors in series with the capacitor to form a second RC timing circuit;
determining an amount of time TIMER_BANK#1 that it takes for a point between the first bank of multiple thermistors and the capacitor to reach a predetermined threshold voltage;
determining a resistance value R_BANK#1 corresponding to the first bank of multiple thermistors using the equation:
R_Referemce
TIMER_Reference
=
R_Bank
⁢
⁢
#1
TIMER_Bank
⁢
⁢
#1
;
performing a table lookup of a first temperature value corresponding to R_BANK#1;
determining if the first temperature value is indicative of an overheating condition;
switching, via a second control signal output from the microcontroller, only the second bank of multiple thermistors in series with the capacitor to form a third RC timing circuit;
determining an amount of time TIMER_BANK#2 that it takes for a point between the second bank of multiple thermistors and the capacitor to reach a predetermined threshold voltage;
determining a resistance value R_BANK#2 corresponding to the second bank of multiple thermistors using the equation:
R_Referemce
TIMER_Reference
=
R_Bank
⁢
#2
TIMER_Bank
⁢
#2
;
performing a table lookup of a second temperature value corresponding to R_BANK#2;
and
determining if the second temperature value is indicative of an overheating condition.

32 more elements

Abstract

Claims7