FLAME SCANNER VIEWING HEAD FOR FLAME MONITOR
MODELS S506, S509, S511 AND S512

The S506 uses a specially designed UV tube that has excellent quenching characteristics and, with the unique electronics circuitry used in the S506, results in a wide linear range. This characteristic is extremely important for being able to discriminate between burners in difficult application such as low Nox gas burners.

In general, the S506 will work very well on natural gas flames. It will respond to oil flame but with a lower signal level. The sighting should be parallel to the axis of the burner and aimed at the root of the flame. Photographs of gas and oil flames using visual and UV-sensitive film show clearly that the UV zone is much smaller than the visible zone, and the highest UV intensity occurs near the root of the flame. In addition, the zone of higher UV intensity does not overlap the same zones of adjacent or opposing burners so that, with proper sighting, discrimination is predictable.

The S506 employs self-checking which is implemented by using a shutter that blocks the flame light path every second for 200 milliseconds. Each time the shutter closes the flame signal drops out resulting in a chopped flame signal. This chopped flame signal is fed to unique patented circuitry in a signal processor which monitors this (chopped) signal in a fail-safe manner.

The signal from the two detectors are amplified separately then combined into one signal which is transmitted to the signal processor. The signal from these detectors is a flicker signal. All flames pulsate creating a flicker component which is what the S509 detects. The flicker frequencies emitted from flames range 0-2000Hz. The S509 responds to only the higher frequencies while rejecting the lower frequencies which are part of the general furnace or background flames.

The Si element responds to only incandescent or visible (to the naked eye) flames and will not pick up luminescent flame such as natural gas. The PbS element, on the other hand, will respond to all types of flames including natural gas. For this reason, if one is using the S509 for natural gas it is recommended that Si channel be turned off. This can easily be done by turning the Si pot (potentiometer) on the viewing head full counter-clockwise.

The Si element is a photodiode that is operated in the photovoltaic mode. (The diode generates current when exposed to light or radiation). The sensitivity range of this element is quite large so some means to prevent saturation in the first stage of amplification is required. (The PbS element has a rather limited dynamic range exhibiting not more than 15:1 ratio from dark to a bright signal). In order to prevent saturation an AGC (automatic gain control) circuit is used so that the DC component or "brightness" signal doesn't saturate causing a loss of the AC component or flicker signal.

The S509 employs electronics self-checking which is implemented by using an electronic switch that disconnects the photo detectors every second for 200 milliseconds. The resulting chopped signal is fed to the signal processor which monitors the signal in a fail-safe manner.

The S511 is a bonafide infrared flame detector that detects all flame and is particularly useful for application where the combustion process might be considered inconsistent or unstable such as those found in the process industries. For example, the S511 works well on lime kilns because the AGC creates a more uniform flame signal throughout the different combustion stages. It also works well on sour gas (sulfur recovery) application principally because of the AGC action.

The signal from the detector is a flicker signal. All flames pulsate creating a flicker component which is what the S511 detects. The flicker frequencies emitted from flames range 0-2000Hz. The S511 responds to only the higher frequencies while rejecting the lower frequencies which are part of the general furnace or background flames.

The Ge element is a photodiode that is operated in the photovoltaic mode. (The diode generates current when exposed to light or radiation). The sensitivity range of this element is quite large so some means to prevent saturation in the first stage of amplification is required. (The PbS element has a rather limited dynamic range exhibiting not more than 15:1 ratio from dark to a bright signal). In order to prevent saturation an AGC (automatic gain control) circuit is used so that the DC component or "brightness" signal doesn't saturate causing a loss of the AC component or flicker signal.

The S511 employs electronics self-checking which is implemented by using an electronic switch that disconnects the photo detectors every second for 200 milliseconds. The resulting chopped signal is fed to the signal processor which monitors the signal in a fail-safe manner.

The signal from the detector is a flicker signal. All flames pulsate creating a flicker component which is what the S511 detects. The flicker frequencies emitted from flames range 0-2000Hz. The S512 responds to only the higher frequencies while rejecting the lower frequencies which are part of the general furnace or background flames.

The S512 with its PbS photo detector has a linear response from low to medium brightness flames, that is, no distortion of flame signal occurs with regard to any amplifier saturation or AGC action (compression), However, saturation will occur with the PbS element on bright flame. This condition can easily be rectified by using orificing (placing disk with small aperture in front of lens to reduce the amount of light or radiation).

The S512 employs electronics self-checking which is implemented by using an electronic switch that disconnects the photo detectors every second for 200 milliseconds. The resulting chopped signal is fed to the signal processor which monitors the signal in a fail-safe manner.

The S512 is a bonafide infrared flame monitor (not to confused with the Si detector which are really visible light detectors). The S512 is particularly useful for multi-burner oil and coal fired boilers where discrimination is paramount consideration.

* Flaming background such as wood waste, black liquor etc.

1. Depending on background fuel.
2. Not so good if background fuel is wood waste grate fired.