I.R.I.S. FLAME MONITORING SYSTEM P522 - Manual (Page 14)

IRIS MODEL P522 APPLICATION MANUAL
Page 14
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.
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
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.
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).
FIGURE 8 - CUTOFF FREQUENCIES
& 1 1 5 S 2 1 5 S & 0 5 5 S 2 5 5 s
L L z H 6 3 1 z H 6 1
L z H 1 7 2 z H 4 2
M z H 5 0 1 3 z H 3 3
H z H 6 8 1 4 z H 2 5
5 z H 5 7
6 z H 0 0 1
7 z H 5 5 1
8 z H 5 1 2