Flame Detection by Flame Rectification 

Our flame igniter systems feature a dual purpose electrode. During the spark phase, a spark is produced between the electrode and burner head, which ignites the air and fuel gas mixture. When the spark phase is complete, usually about 4 seconds after initiation, the same electrode is used to prove the presence of a flame by the principle of flame rectification.

The diagram above shows the tip of a torch and the spark-gap between the electrode and burner head.

The electrode is positioned within the flame and is much smaller than the burner head, which is connected to earth. Given these two conditions, when an alternating current is applied between the electrode and burner head, the flame will conduct and rectify the current, resulting in a pulsating direct current. 

If the control unit detects a pulsating direct current, then it knows that a flame is present. 

If the control unit detects an alternating current, then it knows that no flame is present and it shuts down. This would only happen if there is an electrical short in the circuit.

If no current is detected, or the current falls below a specified level, then the control unit knows that there is no flame or the flame is of poor quality and it shuts down.

By connecting an ammeter to the control unit (see instructions), this current can be measured. A current of between 10 and 25 microamps is to be expected, depending on the system type.

A bad or erratic reading signifies a problem such as:

• Incorrect electrode position
• Dirty or oxidized electrode or burner head
• Bad electrical connection
• Moisture in the system

Connecting an oscilloscope to the control unit will give a waveform similar to that shown below.