IRIS P522 Selecting the Pipe, Determining Sight Pipe Size Mounting Hole, Mounting of Sight Pipe

IRIS MODEL P522 APPLICATION MANUAL

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.

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).

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