IRIS P520, Applications Manual

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IRIS MODEL P520 APPLICATION MANUAL
Page 19
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 set up 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 13.
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 dis-
crimination problem in multiburner applications.
Note: The 55x-series viewing heads can-
not 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 igniter, 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 signal 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 REAR PCB).
Note that both the SIG and SIG GND circuits are
switched. However, this can cause a lockout condi-
tion if the transfer of the viewing heads is done dur-
ing the dark period. This problem can be avoided
by changing channels when switching heads (i.e.,
by wiring the two terminal blocks V.H. SEL and
CHAN SEL together in parallel). This will inform
the P520 that the viewing heads are being transferred,
and the pulses counted during the dark period will
be ignored.
& 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
FIGURE 13 - CUTOFF FREQUENCIES