Estimating temperature
A method of estimating a temperature of a material being heated is described. The method may comprise supplying electrical power to a heating element in dependence on a measured temperature, calculating a rate at which the amount of electrical power supplied changes over time, comparing the calculated rate with a plurality of known values in order to determine the value of a parameter relating to thermal properties of the material being heated, and calculating an estimated temperature based on the determined value of said parameter. In some embodiments, the method may further comprise detecting a drop in temperature of the material being heated, by detecting a change in the calculated rate at which the amount of electrical power supplied changes over time.
1. A method of estimating a temperature of a material in a container being heated by a heating element, the method comprising:
sensing a temperature proximate the heating element;
controlling a varying supply of electrical power to the heating element to maintain a predetermined dependence of the electrical power supplied on the sensed temperature;
calculating a rate at which the supplied electrical power varies with time;
determining a thermal inertia parameter value for the material being heated by comparing the calculated rate of variation supplied power with a plurality of known rates for maintaining said predetermined dependence on the sensed temperature, said known rates corresponding with respective known thermal inertia parameter values; and
estimating the temperature of the material being heated based on data including the determined thermal inertia parameter value.
2. The method of claim 1 , where the varying supply of electrical power to the heating element is controlled by repeatedly switching the supplied electrical power on and off to maintain said predetermined dependence on the sensed temperature.
3. The method of claim 2 comprising applying a moving-average filter to power data representing the varying supply of electrical power and calculating an average rate at which said supply of electrical power varies with time.
4. The method of claim 1 where the estimated temperature is calculated based on the equation:
T
=
T
f
+
(
T
0
-
T
f
)
*
exp
(
-
t
B
)
where T is the estimated temperature, T 0 is a starting temperature, T f is a preset temperature, t is an elapsed time since the start of heating, and B is the thermal inertia parameter value determined for the material being heated.
5. The method of claim 1 where the sensed temperature is representative of a temperature of at least one of:
the heating element; and
an interface layer located between the heating element and the container.
6. The method of claim 1 where the varying supplying of electrical power to the heating element is controlled to maintain a value of the sensed temperature within a predetermined temperature range.
7. The method of claim 1 including detecting a temperature drop of the material being heated by detecting a change in the calculated rate at which the supplied electrical power varies with time.
8. The method of claim 7 including re-estimating the temperature of the material being heated, after detecting the temperature drop, based on data representing the variation of the supplied electrical power before and after the temperature drop.
9. Apparatus for estimating a temperature of a material in a container being heated, the apparatus comprising:
a heating element arranged for heating the container;
a power supply adapted to controllably supply electrical power to the heating element;
a temperature sensor disposed to sense a temperature proximate the heating element; and
a control unit adapted to:
receive the sensed temperature;
control the supply of power from the power supply to provide a varying supply of electrical power to the heating element to maintain a predetermined dependence of the power supplied on the sensed temperature;
calculate a rate at which the supplied electrical power varies with time;
determine a thermal inertia parameter value for the material being heated by comparing the calculated rate of variation of the supplied power with a plurality of known rates for maintaining said predetermined dependence on the sensed temperature, said known rates corresponding with respective known thermal inertia parameter values; and
estimate the temperature of the material being heated based on data including the determined thermal parameter value.
10. The apparatus of claim 9 comprising a switching unit coupling the power supply to the heating element, said switching unit being switchable between an ON state in which electrical power is supplied to the heating element and an OFF state in which electrical power is not supplied to the heating element, where the control unit is adapted to repeatedly switch the switching unit between the ON and OFF states to maintain said predetermined dependence on the sensed temperature.
11. The apparatus of claim 10 where the control unit is adapted to apply a moving-average filter to power data representing the varying supply of electrical power and to calculate an average rate at which said supply of electrical power varies with time.
12. The apparatus of claim 9 where the temperature sensor is disposed in proximity to the heating element to sense a temperature of at least one of:
the heating element; and
an interface layer located between the heating element and the container.
13. The apparatus of claim 9 where the control unit is adapted to control the varying supply of electrical power to the heating element to maintain a value of the sensed temperature within a predetermined temperature range.
14. The apparatus of claim 9 where the control unit is adapted to detect a temperature drop of the material being heated by detecting a change in the calculated rate at which the supplied electrical power varies with time.
15. The apparatus of claim 14 where the control unit is adapted to re-estimate the temperature of the material being heated, after detecting the temperature drop, based on data representing the variation of the supplied electrical power before and after the temperature drop.