IRIS MODEL P522 APPLICATION MANUAL
Page 15
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 P522 that the viewing heads are being transferred,
and the pulses counted during the dark period will
be ignored.
DETERMINING SIGHT PIPE SIZE
In order to determine the proper sight pipe, it is im-
portant to understand how the viewing head “views”
the flame. The viewing head employs a plano-con-
vex lens in front of the photodetector that focuses
the flame radiation on the surface of the detector.
The active photodetector element is quite small, and
its diameter and the focal length of the lens deter-
mines the angle of view. For the S509 viewing head,
this angle of view is about 2.8 degrees. For the S512,
the angle is slightly less.
To understand what this means, imagine a circular
target of flame radiation, one inch in diameter, 24
inches away from the lens: this is the maximum field
of view the detector sees. In other words, a one-inch
diameter sight pipe two feet long will allow maxi-
mum signal to be detected. A two-inch diameter
sight pipe four feet long presents the same target.
Actually, a one-inch target three feet away causes
an immeasurable signal attenuation, so you can use
a two-inch diameter pipe up to six feet long, with no
signal attenuation.
The angle of view for the S511 viewing head is 1.1
degrees. This translates into a one-inch, circular tar-
get 52 inches away from the lens. In other words, a
one-inch diameter sight pipe four feet long (or, a two-
inch diameter sight pipe eight feet long) will allow
maximum signal to be detected.
For a detailed explanation of how the angle of view
is derived, refer to section ANGLE OF VIEW OF
VIEWING HEAD.
If a long sight pipe is required, then we recommend
that a swivel mount be used to overcome any optical
misalignment that might be present (see Figure 20).
In this way, the flame signal can be optimized by
adjusting the viewing head to the target at the end of
the pipe.
SELECTING THE PIPE
We recommend a black iron pipe to provide reliable
flame sensing. The viewing head is tapped for a one-
inch national pipe thread (NPT) threaded pipe. Any
diameter sighting-pipe larger than one inch will require
a reducer coupling or swivel mount (see Figure 20).
MOUNTING HOLE
Cut a hole for the sight pipe in the burner front
windbox at the selected location. The hole should
be large enough in diameter to allow adjustment of
the sighting angle. If register vanes interfere with
the desired line of sight, trim the interfering vanes to
ensure an unobstructed view of the flame.
MOUNTING OF SIGHT PIPE
After cutting the pipe to the desired length, thread
one end of the pipe to fit the viewing head flange or
required coupling (see Figure 20). Insert the other
end of the pipe into the mounting hole, align the pipe
to the desired sighting angle, and tack weld it in place
to allow further sighting adjustments. Make sure
the tack weld will support the weight of the detector
when it is installed. Once the final position has been
determined, weld the sight pipe in place.
INSTALLING THE VIEWING HEAD
The viewing-head flange screws directly onto a one-
inch NPT threaded pipe (see Figure 20). Use a cres-
cent wrench to tighten the flange onto the sight pipe.
PURGE AIR
Use a flexible air supply line, allowing reposition-
ing of the sight pipe until the permanent detector
position has been verified. A continuous flow of air
must be maintained in order to keep the head cool
and the sight pipe clean. We recommend that at least
three CFM at approximately eight inches of water
column above windbox pressure be provided for each
viewing head. The air supply must be clean, free
from oil and water, and preferably cool.
