Flame sense circuit with variable bias
AssigneeHoneywell International Inc.
InventorsJan Vorlicek, Jiri Kastan
Life of this patent
Estimating the term…
Abstract
A system for changing a bias level of a flame sensing circuit to identify leakage in the flame sensing circuit. The bias level may be varied in the positive or negative axis and the flame current may be noted to identify leakage. The bias level may be changed by a microcontroller. The bias level may be changed using an operational amplifier configuration which is used as a signal conditioner for interfacing the flame signal to the microcontroller.
Claims20
A method for determining a condition of a flame sense signal comprising:
- detecting a high impedance flame signal from one or more devices selected from a group comprising a flame sensor and a flame amplifier;
- buffering the high impedance flame signal to decouple the high impedance or low current flame signal from a biasing circuit;
- biasing a buffered flame signal at a first voltage from a microcontroller;
- measuring the buffered flame signal biased at the first voltage;
- biasing the buffered flame signal at a second voltage from the microcontroller;
- measuring the buffered flame signal biased at the second voltage;
- and
- comparing a measured buffered flame signal biased at the first voltage with a measured buffered flame signal biased at the second voltage;
- and
- wherein high impedance means an impedance greater than 200K ohms;
- and
- wherein low current means a current lower than 50 micro-Amperes.
A flame sense circuit comprising:
- a capacitor having a first terminal for connection to a flame amplifier;
- a first amplifier having an input connected to the first terminal of the capacitor;
- and
- a second amplifier having input connected to an output of the first amplifier, having an output connectable to an input terminal of a microcontroller, and having a second input connectable to a first output terminal of the microcontroller;
- and
- wherein the first terminal of the capacitor is connectable to a second output terminal of the microcontroller, or to a switching element controlled by the microcontroller.
A system for determining a quality of a flame sensing signal, comprising:
- a capacitor connectable to a flame amplifier or flame sensor;
- an interface circuit having an input connected to the capacitor;
- and
- a microcontroller having an input connected to an output of the interface circuit, a first output connected to the interface circuit, and a second output connected to the capacitor;
- and
- wherein:
- the interface circuit provides a connection between the capacitor and the microcontroller that compensates for a difference of an impedance at the capacitor and the impedance at the input of the microcontroller;
- the first output from the microcontroller provides a voltage to the interface circuit for biasing a flame detection signal to the input of the microcontroller;
- and
- the second output from the microcontroller provides a drive signal that recharges the capacitor having at least some discharge caused by an occurrence of the flame detection signal at the capacitor.
Dependencies are inferred from the claim text.