IRIS S550, Applications Manual, Page: 9 / 19

viewing head sight path will greatly improve the
performance, particu larly with regard to discrimi
-
nation between flames. Although saturation is less
likely with the Ge (germanium) IR photo de tector
used for the S550 as compared to prior model
viewing heads using the PbS (lead sulfide) type
photo de tector, the possi bility should not be
ignored. Saturation is more prob able with large
power utility boilers where the burners are very
large and relatively close to one another. If one
cannot look at the flame with the naked eye
without it hurting, then orificing should be used.
This eye test works for incan descent type flames
such as oil and coal but will not be valid for
natural gas flames.
Orificing may help improve the discrimi nation
charac ter istics for the UV detector as well as the
IR. The UV tube in the S550 is not likely to
saturate; how ever, orificing will usually improve
the discrimi nation ratio for large size burners.
An orificing disc is simply a metal disc with a
circular hole in the cen ter which is placed directly
in front of the lens. Four orificing discs are
available with cen ter hole diameters of 3/8, 1/4,
3/16 and 1/8 inch. These discs are installed with
retaining rings in the flange at the edge of the 1/2
inch NPT female pipe thread for the purge air. An
internal type retaining ring is first installed by
positioning a ring in the machined groove inside
flange opening from the housing side. The
orificing disc is then inserted. Use a second
retaining ring to hold it in place so that it is
sandwiched tightly between the two retaining
rings.
Usually an orificing disc with a larger diameter
hole is tried first. There will be a reduction in the
signal level so if the associated S550 and signal
processor has been previ ously calibrated it will be
necessary to calibrate the processor again so that
the gain settings will be correct. If the discrimi
-
nation is still not satis factory then try an orificing
disc with a smaller diameter hole.
Generally speaking, orificing should always be
considered when the burner(s) are large (50K lbs
of steam and up), particu larly when the IR
detector is used which would be the case for oil or
pulverized coal.
The following table shows the signal reducing
charac ter istics of the different orificing discs:
Ap er ture
Hole
Fn
(f Stop)
Rela tive light
pass ing power
1" 2 1
3/8" 5.3 1/8
1/4" 8 1/16
3/16" 10.7 1/32
1/8" 16 1/64
DEFAULT SETTINGS FOR THE S550
A new P520 / P522 will send the S550’s default
“Gains” as follow:
UV Gain = 32 (out of 0-99 range)
Fil ter = Fil ter 3 (high pass above 33Hz)
IR Gain = 451 (out of 0- 699 range)
These are nominal settings that should allow for
initial sightings and adjust ments. Both UV and
IR sensors are active in the default mode. They
are the same settings that will be active in an S550
when used with an older version of the P520/P522
or with an M502 signal processor. If the settings
for the S550 have been changed from the default
settings the operator may reset the “Gain” to the
factory default from the P520 / P522 control
panel. (See
Return to Default Settings
on Page 12.)
WHERE S550 SETTINGS ARE STORED
Settings for the S550s are stored in EEPROM in
the particular P520/P522 which made the adjust
-
ments. On subse quent power-up cycles the
P520/P522 will send out the settings again to the
S550 viewing head. In fact, if one S550 is
exchanged with another one, the P520/P522
cannot tell one S550 from another and will send
out the same settings. This simplifies field
replace ments; all S550’s are made to very close
PAGE 9
IRIS MODEL S550 APPLICATION MANUAL