Device and method for controlling the temperature of a thin film resistive heater

• US 6,303,911 B1
• Filed: 01/12/2000
• Issued: 10/16/2001
• Est. Priority Date: 01/12/2000
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Welch, Ronald F. Jr.
• Primary Examiner(s): Hoang, Tu Ba
• Application Number:
  US09/481,785
• Time in Patent Office: 643 Days
• Field of Search: 219/482-485, 219/488, 219/490, 219/494, 219/497
• US Class Current: 219/497
• CPC Class Codes: G02F 1/133382 Heating or cooling of liquid crystal cells other than for activation, e.g. circuits or arrangements for temperature control, stabilisation or uniform distribution over the cell
• CPC Class Codes: G05D 23/2401 using a heating element as a sensing element

Abstract

A circuit for controlling the temperature of a thin film conductive heater includes a control circuit for applying a voltage to the heater. The control circuit regulates the temperature of the heater element by using a modeling technique which assumes that the thin film coating functions as a single electrical resistor.

Claims

1. A circuit for controlling the temperature of a heater containing a thin film conductive coating, said circuit comprising:

a control circuit for applying a voltage to said heater and said control circuit including;

a power supply for applying a voltage to said heater;

a resistor that is connected in series with said power supply and said heater;

a voltage measuring device which measures voltage drops occurring across said resistor; and

a temperature control circuit which monitors said voltage measuring device and said power supply to regulate the temperature of said heater by using a modeling technique which assumes that said thin film coating functions as a single resistor.

2. The circuit of claim 1, wherein said temperature control circuit regulates the temperature of said heater by:

(i) calculating the resistance of said thin film coating and,

(ii) calculating the temperature of said thin film coating based on the calculated resistance.

3. The circuit of claim 2, wherein said resistance R₂ of said thin film coating is calculated by using the equation R₂=R₁(V_SUPP/V−

1), where R₁ is the resistance value of said resistor, V₁ is a value based on a voltage drop across said resistor, and V_SUPP is a known value.

4. The circuit of claim 3 wherein said temperature T₂ of said thin film coating is calculated by using the equation T₂=T₀+(R₂−

R₀)/a, where T₀ is a reference temperature of the thin film conductive coating, and “

a”

is a constant unique to the material of the coating.

5. A method for calculating the temperature of a heater containing a thin film resistive coating, said method comprising the steps of:

(i) calculating a resistance R₂ of said thin film coating by using the equation R₂=R₁ (V_SUPP/V₁−

1), wherein V_SUPP represents a voltage applied to said heater, R₁ represents a resistance value of a resistor connected in series to said heater, and V₁ represents a voltage drop across resistor R₁; and

(ii) calculating a temperature of said thin film coating based on the resistance calculated in step (i).

6. The method of claim 5, wherein said temperature of said thin film coating is calculated by using the equation T₂=T₀+(R₂−

R₀)/a, wherein T₀ represents a reference temperature of said thin film coating at a known resistance, R₀ represents a resistance of said thin film coating, at a known temperature, and the coefficient “

a”

represents a constant that is unique to said thin film coating.

7. A circuit for controlling the temperature of a glass substrate thin film resistive heater in a liquid crystal display, said circuit comprising:

a power supply for applying a voltage to a thin film resistive coating on said glass substrate;

a resistor connected in series with said power supply and said thin film resistive coating;

a voltmeter connected across said resistor for measuring the voltage drop thereacross; and

a temperature control circuit responsive to said voltmeter and connected to said power supply to regulate the temperature of said resistive coating on said glass substrate.

8. A method for controlling the temperature of a glass substrate heater in a liquid crystal display, the glass substrate heater being connected to a power supply, said method comprising the steps of:

calculating the voltage drop across a resistor in series with the glass substrate heater and the power supply; and

controlling the current supplied by the power supply to the glass substrate heater in response to the calculated voltage drop to control the temperature of the glass substrate heater.