IRIS Multiburner Requirements, Multiple Viewing Heads, IRIS MODEL P522 APPLICATION MANUAL

IRIS MODEL P522 APPLICATION MANUAL

The effectiveness of the sighting will depend upon both the type of viewing head as well as the fuel. UV flame detection works fine on natural gas, but will cause problems with fuels that either block or absorb the UV signal.

For example: in a pulverized coal burner, there can be unburned fuel at the burner nozzle, creating a “skirt” that blocks the UV radiation coming from the flame. Heavy oil burners can also cause prob- lems with UV-type flame detection, par- ticularly if the fuel has a high sulfur con- tent, which will absorb the UV radiation.

UV, which doesn’t have one) be switched to a higher position. This reduces the low-frequency flicker reaching the detector so that the set points can be adjusted to affect flame discrimination. The four cutoff frequencies are outlined in Figure 8.

A higher filter position creates a narrower bandwidth, causing an overall reduction in the flame signal; how- ever, the ratio of flame ON to flame OFF may be im- proved by properly setting this four-position filter. Note the readings on the four-digit display when mak- ing these adjustments. The four-digit number is an absolute indication of signal strength, and is not af- fected by changing the gain of the analog output.

MULTIBURNER REQUIREMENTS

Multiburner installations require discrimination. This means that, in spite of the brightness of other flames in the furnace, the flame relay must respond only to the presence or absence of the flame pro- duced by the burner that it is monitoring. Not every viewing head can be positioned so that its line of sight does not intercept flames from other burners – a situation that occurs in multi-level, opposed fired furnaces where the burners face each other.

In such cases, the sighting angle is setup as described above, with the viewing head sighting along the flame directly into the flame root. If an opposing or adjacent burner flame falls within the line of sight of the viewing head, it may be effectively tuned out by setting the FLAME OFF set point high enough to ignore this background. If discrimination cannot be achieved by doing this, it is recommended that the filter switch in the viewing head (except the S506

S511 &	S512	S550 &	s552
LL	36Hz	1	16Hz
L	71Hz	2	24Hz
M	105Hz	3	33Hz
H	186Hz	4	52Hz
		5	75Hz
		6	100Hz
		7	155Hz
		8	215Hz

FIGURE 8 - CUTOFF FREQUENCIES

MULTIPLE VIEWING HEADS

This system can accommodate the parallel operation of two viewing heads with one signal processor. The flame signals will be additive, possibly requiring a lower sensitivity setting. A word of caution about this type of operation: the unwanted background with the burner flame out will also be additive, possibly causing a discrimination problem in multiburner applications.

Note: The S5xx-series viewing heads cannot be wired in parallel.

Another variation is to switch the flame signal ON and OFF from each viewing head.

For example: one viewing head can be used for the igniter, and the other for the main burner. While proving flame from the ig- niter, the main burner signal circuit can be opened, leaving only the igniter viewing head signal to be read. And, when proving flame from the main burner, the igniter sig- nal circuit can be broken.

We recommend that only the flame signal from each viewing head be switched, leaving the other connec- tions to the viewing head intact (the one exception would be the S506 UV head). Both the flame signal and shutter drive circuits should be switched so that when the head is not being used, the shutter is not switched on and off. This was done in the design of the rear mother board (see section WIRING AND INSTALLATION).

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