Fluid level detector using thermoresistive sensor
First Claim
1. A fluid level detector for being immersed in a fluid and thereby determining the fluid level, comprising:
- a) a substrate formed of a heat-insulative material;
b) at least one thermoresistive sensor element located on the substrate to form a, having a resistivity that changes substantially linearly in response to temperature change;
c) a current source, connected to the sensor element, for producing a current Through the sensor element for a predetermined time period to thereby heat the sensor element during the predetermined time period, the current source producing a voltage across the sensor element at least during the predetermined time period;
d) means for measuring the voltage across the sensor element during the predetermined time period and for determining a voltage slope that varies relative to the amount of the sensor element that is immersed in the fluid;
and means for monitoring the voltage across the sensor element subsequent to the predetermined time period for determining a stable condition of the sensor element.
1 Assignment
0 Petitions
Accused Products
Abstract
A fluid level detector according to the invention comprises a substrate formed of a heat-insulative material and one or more thermoresistive sensor elements located on the substrate that is adapted to be immersed in a fluid. A current source is connected to the sensor element for producing a current through the sensor element during a predetermined time period. The current heats the sensor element and causes a change in voltage across the sensor element at least during the time period. The amount of change in voltage during the time period is reflective of the fluid level, since the fluid serves as a heat sink for the sensor element. The voltage is measured across the sensor element and a voltage slope is determined. The determined voltage slope is indicative of fluid level.
-
Citations
16 Claims
-
1. A fluid level detector for being immersed in a fluid and thereby determining the fluid level, comprising:
-
a) a substrate formed of a heat-insulative material; b) at least one thermoresistive sensor element located on the substrate to form a, having a resistivity that changes substantially linearly in response to temperature change; c) a current source, connected to the sensor element, for producing a current Through the sensor element for a predetermined time period to thereby heat the sensor element during the predetermined time period, the current source producing a voltage across the sensor element at least during the predetermined time period; d) means for measuring the voltage across the sensor element during the predetermined time period and for determining a voltage slope that varies relative to the amount of the sensor element that is immersed in the fluid; and means for monitoring the voltage across the sensor element subsequent to the predetermined time period for determining a stable condition of the sensor element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 15, 16)
-
-
12. A method of determining fluid level in a container, comprising:
-
a) providing a substrate formed of a heat-insulative material; b) locating a thermoresistive sensor element on the substrate; c) heating the sensor element for a predetermined time period by applying a relatively high electric current to the sensor element; d) measuring a change in voltage of the sensor element during the time period; e) determining a voltage slope based on the measured change in the sensor element; f) indicating fluid level based on the determined slope; g) monitoring the voltage of the sensor element after the predetermined time period by applying a relatively low electric current to the sensor element to thereby detect a stable condition of the sensor element; and h) repeating steps c) to f) once the stable condition has been detected. - View Dependent Claims (13, 14)
-
Specification