Temperature-controlled laboratory beaker comprising a heating element and temperature sensor bonded to the outer surface of the beaker by a silicone-rubber molding

• US 5,271,085 A
• Filed: 02/20/1992
• Issued: 12/14/1993
• Est. Priority Date: 02/20/1992
• Status: Expired due to Fees

• Current Assignee: Rodolfo A. Carballo
• Original Assignee: Rodolfo A. Carballo
• Inventors: Carballo, Rodolfo A.
• Primary Examiner(s): Bartis, Anthony
• Application Number:
  US07/838,034
• Time in Patent Office: 663 Days
• Field of Search: 392/444, 392/458, 392/459, 392/480, 219/436, 219/438, 219/441, 219/442, 219/535, 219/543, 219/549
• US Class Current: 392/444
• CPC Class Codes: G05D 23/24 the sensing element having a resistance varying with temperature, e.g. a thermistor
• CPC Class Codes: H05B 2203/017 Manufacturing methods or apparatus for heaters
• CPC Class Codes: H05B 2203/021 Heaters specially adapted for heating liquids
• CPC Class Codes: H05B 3/36 heating conductor embedded in insulating material

Abstract

A temperature-controlled laboratory heating apparatus consisting of a flexible electrical heater wrapped around the exterior surface of a conventional glass or metal beaker and permanently encased within a rubber molding forming an insulating ring around it. The heater is electrically connected to a power source through an integrated-circuit temperature control panel. A thermistor is mounted against the outside surface of the beaker within the rubber molding and is connected to the control panel to regulate the flow of current through the electrical heater to reach and maintain the temperature set by the user. In one embodiment of the invention, the current through the heater is automatically regulated to optimize the time required to heat the liquid in the beaker to the desired temperature and to then deliver trickle currents, as needed, to minimize fluctuations from the set-point.

Claims

1. An apparatus for heating a liquid to a set-point temperature and for automatically maintaining that temperature, comprising:

(a) a beaker made of thermally conductive material;

(b) an electric heater wrapped around and affixed to the outside wall of said beaker;

(c) electrical means for energizing said electric heater;

(d) temperature sensing means in contact with and thermally coupled to the outer surface of said beaker for developing a signal corresponding to the temperature of the beaker;

(e) electronic means connected to said temperature sensing means for receiving a signal therefrom indicative of the temperature of the beaker and including means for comparing the signal so received to a set-point temperature corresponding to a temperature chosen by a user and for activating said electrical means for energizing said electric heater when the temperature corresponding to the signal is below the set-point temperature; and

(f) a molding bonded to the outer surface of said beaker and formed around said electric heater and said temperature sensing means, wherein said molding completely covers the electric heater and the temperature sensing means and permanently bonds the heater and the temperature sensing means to the outer surface of the beaker;

wherein said electronic means for comparing the signal developed by said temperature sensing means to a set-point temperature and for activating said electrical means for energizing said electric heater consists of an integrated circuit comparator connected to said temperature sensing means, to a rheostat for adjusting the set-point temperature, and to a triac device serving as a switch in said electrical means for controlling the current flow through said electric heater.

2. The apparatus described in claim 1, wherein said temperature sensing means consists of a thermistor.

3. The apparatus described in claim 1, wherein said heater consists of a flexible electrical heater permanently attached to the exterior wall near the bottom of said beaker and the heater'"'"'s height is chosen to approximately match the expected level of the liquid in the beaker during use.

4. The apparatus described in claim 1, wherein said molding consists of silicone rubber.

5. A method of manufacturing an apparatus for heating a liquid to a set-point temperature and for automatically maintaining that temperature, comprising the following steps:

(a) providing a beaker made of thermally conductive material;

(b) wrapping an electric heater around the outside wall of said beaker;

(c) providing a thermistor thermally coupled to and in contact with the outer surface of said beaker for developing a signal corresponding to the temperature of the liquid in the beaker;

(d) forming a molding around and completely enclosing said electric heater and said thermistor;

(e) providing a source of electric energy connected to said electric heater; and

(f) providing electronic means for comparing the signal developed by said thermistor to a set-point temperature corresponding to a temperature chosen by a user and for energizing said electric heater in response to a temperature corresponding to the signal being below the set-point temperature;

wherein said electronic means consists of an integrated circuit comparator connected to said thermistor and to a rheostat for adjusting the set-point temperature, and actuating a triac device serving as a switch for controlling the current flow through said electric heater;

wherein said heater consists of a flexible electrical heater permanently attached to the exterior wall near the bottom of said beaker and the heater'"'"'s height is chosen to approximately match the expected level of the liquid in the beaker during use; and

wherein said molding consists of silicone rubber.

6. The method described in claim 5, wherein said step of forming a molding around said electric heater and said temperature sensing means is accomplished by providing a donut-shaped mold clamped around the beaker with a cavity surrounding the heater and temperature sensing means, by filling the cavity with liquid silicone rubber, and by letting it cure at 120°

F. for approximately 30 minutes.

7. The method described in claim 5, wherein said step of forming a molding around said electric heater and said temperature sensing means is accomplished by providing a donut-shaped mold clamped around the beaker with a cavity surrounding the heater and temperature sensing means, by filling the cavity with solid silicone rubber, and by fluidizing it by the pressure to which it is subjected when the mold is clamped around it, and by allowing it to cure for at least eight hours at room temperature.