Fault-tolerant multi-point flame sense circuit
First Claim
1. A fault-tolerant multi-point flame sense circuit, comprising:
- an electronically controllable switch having a control input, an RC network having a first node coupled to the control input of the switch and a second node coupled to ground; and
a plurality of flame sense electrode channels, each flame sense electrode channel having a separate capacitive coupling to a line voltage input and a separate resistive coupling to the first node of the RC network.
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Accused Products
Abstract
A fault-tolerant multi-point flame sense circuit utilizes a single electronic switch to signal the presence or absence of flame to an electronic controller. Multiple flame sense electrodes may be input to this circuit. By configuring these electrodes in accordance with the present invention, cross-contamination of a single failed flame sense electrode will not affect the other flame sense electrodes'"'"' ability to sense a flame at their associated burner. The circuit provides inputs for a number of flame sense electrodes via input channels that are capacitively coupled to the line voltage and resistively coupled to an RC network that controls the state of an electronic switch. When a flame is present at any one of the electrodes, the resulting unbalance current flow through the RC network turns the switch off to indicate the presence of flame. This operation is not affected by a short on any other electrode in the circuit.
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Citations
13 Claims
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1. A fault-tolerant multi-point flame sense circuit, comprising:
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an electronically controllable switch having a control input, an RC network having a first node coupled to the control input of the switch and a second node coupled to ground; and
a plurality of flame sense electrode channels, each flame sense electrode channel having a separate capacitive coupling to a line voltage input and a separate resistive coupling to the first node of the RC network. - View Dependent Claims (2)
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3. A fault-tolerant multi-point flame sense circuit, comprising:
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an electronically controllable switch having a control input, an RC network having a first node coupled to the control input of the switch and a second node coupled to ground;
a plurality of flame sense electrode channels, each flame sense electrode channel having a separate capacitive coupling to a line voltage input and a separate resistive coupling to the first node of the RC network;
wherein each flame sense electrode channel further includes a current limiting resistor coupling a flame sense electrode to a junction between the capacitive coupling to the line voltage input and the resistive coupling to the first node of the RC network; and
wherein the flame sense electrode channels are balanced with one another such that current flow between the line voltage input and the ground during both positive and negative half cycles of an external line voltage applied thereto is equal when no flame is present at any of the flame sense electrodes, and wherein the electronically controllable switch remains in a quiescent state when no flame is present at any of the flame sense electrodes. - View Dependent Claims (4, 5)
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6. A fault-tolerant multi-point flame sense circuit, comprising:
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an electronically controllable switch having a control input, an RC network having a first node coupled to the control input of the switch and a second node coupled to ground; and
a plurality of flame sense electrode channels, each flame sense electrode channel having a separate capacitive coupling to a line voltage input and a separate resistive coupling to the first node of the RC network;
wherein each flame sense electrode channel further includes a current limiting resistor coupling a flame sense electrode to a junction between the capacitive coupling to the line voltage input and the resistive coupling to the first node of the RC network; and
wherein the flame sense electrode channels are balanced with one another such that current flow between the line voltage input and the ground during negative half cycles of an external line voltage applied thereto is equal when flame is present at any of the flame sense electrodes resulting in a negative charge developing across the RC network, and wherein the electronically controllable switch changes from a quiescent state when flame is present at any of the flame sense electrodes.
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7. A fault-tolerant multi-point flame sense circuit, comprising:
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a line voltage input adapted to receive AC line voltage from an external source;
an electronically controllable switch;
a switch control circuit coupled to the electronically controllable switch;
a plurality of parallel flame sense channels, each flame sense channel being coupled between the switch control circuit and the line voltage input. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A flame sense circuit, comprising a first flame sense electrode coupled through a first resistor to a first node coupling a first capacitor and a second resistor, the first capacitor being coupled to a line voltage input and the second resistor being coupled to a flame sense input node, the flame sense input node being coupled to a third resistor that is coupled to a gate of a junction field effect transistor, a drain of which is coupled through a resistor to a control voltage input and a source of which is coupled to ground, the flame sense input node further being coupled to a fourth resistor and to a second capacitor, both of which are also coupled to ground, and a second flame sense electrode coupled through a sixth resistor to a second node coupling a third capacitor and a seventh resistor, the third capacitor being coupled to the line voltage input and the seventh resistor being couple to the flame sense input node.
Specification