Self-Checking; Adjustment Of Vh Sighting And Gain; Orificing - Honeywell 700 User Manual

HONEYWELL MODEL 700/800 SIGNAL PROCESSOR AND VIEWING HEAD
It may also be desirable to sight the detector at an area
containing fewer masking agents such as near the burner
nozzle or near the entrance of the combustion air. Increasing
the viewing area of the detector by shortening the sight pipe or
by increasing the diameter of the sight pipe can also reduce
the attenuating effects of the masking agents.
In general, the UV viewing heads will work well on natural gas
and light oil flames. The sighting for both oil and gas flames
should be parallel to the axis of the burner and aimed at the
root of the flame, as with the IR detector. (See previous
section, "IR Detector.") The highest UV intensity occurs near
the root of the flame (Fig. 15). In addition, the zone of higher
UV intensity does not overlap the same zones of adjacent or
opposing burner so that, with proper sighting, discrimination
can be achieved.
With low NOx gas burners, the UV radiation is usually much
less in intensity and spread out. Relatively high readings can
be obtained from all over the furnace when many burners are
in service. This is particularly true when flue gas recirculation
is used. There will however, be a relatively stronger signal
near the "root" of the flame and the more intense spot should
be located during the aiming or sighting process. This "root" or
intense spot may be further out than with the standard gas
burner so it is imperative that a swivel mount be used when
making sighting adjustments.
Another factor that needs to be considered when aiming the
viewing head is the load condition of the boiler. The flames
from a burner can be radically different at different loads. This
is one of the reasons for choosing an optimum sighting initially
that will minimize signal swing due to changing loads.

Self-Checking

There is a small processor in both the IR and UV viewing
heads, so it is possible that this processor could fail and
produce erroneous viewing-head pulses. The self-check
circuitry guards against this. There are several tasks that
require intelligent interaction between the viewing heads and
the signal processor. If all of these interactions do not occur
properly, the viewing head will not send pulses back to the
signal processor and the flame relay will open.
Verifying the validity of the gain code received is one of the
tasks performed by the processor in the IR and in the UV
viewing heads. The self-check pulse from the signal
processors is a 100ms-wide, 20V to 24V pulse with two
"notches" or breaks in it. The position of each of the two
notches communicates a gain code of one to nine plus parity
to the viewing head. The viewing head sends back an ID
pulse in the first half of the 100ms self- check time. A viewing
head expects to receive data with a certain parity. If a viewing
head does not receive its correct parity plus the gain code
once per second, it produces no output pulses.
There is also intelligent interaction between the older S706
viewing heads, which did not have the gain-change feature
from the signal processor. The processor in the S706 viewing
head monitors the 100ms width of the self-check pulse
coming from the signal processor. If the pulse is not the
correct width the viewing head produces no output pulses.
Also, if the signal processor receives any pulses back from the
viewing head during the last half of the100ms self-check time,
it assumes that a processor failure has occurred in the viewing
head, opens both relays, and displays "LO" (lockout).
66-2069—01

Adjustment of VH Sighting and Gain

NOTE: Adjustment to the viewing head parameters
cannot be made unless the viewing head is
connected and communicating with the signal
processor.
The viewing head should be properly sighted before the
setpoints are adjusted. Adjustment can be made easier by a
1/2 in. swivel joint, which Honeywell can supply if one is not
available (refer to "Accessories" on page 10).
While the burner is firing, vary the viewing angle while
observing the green LED on the connector at the rear of the
viewing head. Adjust the viewing angle for the maximum pulse
rate, then lock the swivel joint to preserve this mechanical
setting. If the green LED pulse rate is very high or very low,
see the two paragraphs below. The locked mechanical setting
should still be correct when Model 700 viewing heads are
interchanged, because inside each Model 700 viewing head
the optical axis is aligned with the mechanical axis within ±1/4
degree. Also, the reading shouldn't change when a viewing
head is rotated in the mount.
For the above sighting adjustments to work properly, the
flashing rate of the green LED in the connector at the rear of
the viewing head must be reasonable. On the -PF (pipe fitting)
version, there are no LEDs. The installer must observe the
flame signal on the signal processor instead.
A count rate of 16 to 20 is recommended for proper operation.
If the displayed count is above 25, the pulses begin to blur
together, making changes in the pulse rate difficult to observe.
If the count is higher (29 or 30), then the viewing head is
saturated. Saturation indicates that the count could be even
higher, possibly 50 or more, but it is internally clamped. With
count rates at or close to saturation, the installer will not be
able to adjust the viewing head in the swivel mount to
maximize the count rate properly. It should be possible to
sufficiently decrease the count rate to a usable level by
decreasing the gain. See "Manual Setup of Setpoints" on
page 13 of this manual. If the gain is set to 1 and the count is
still 25 or higher, orificing is likely required. See the section on
orificing below.
If the displayed count is less than 8 or 10, it will be difficult to
maximize the count by adjusting the viewing head aim, since
the pulses occur too infrequently. In such a case the gain
should be increased. If the gain is set to a maximum and the
count rate persists below 8 or 10, the system can still be made
to work reliably as long as the count rate drops significantly
when the flame is removed. However, the setup should be
reviewed for proper viewing head aim and sight path to ensure
it is optimized.

Orificing

Orifice disks have been used in applications with older viewing
heads that did not have adjustable gain in order to reduce the
extreme brightness of certain burner flames. The orifice disk
kit is part number M-702-6. Orifice disks come with 3/8, 1/4, 3/
16 and 1/8 inch diameter holes. Contact the factory for
guidance is using orifice disks. The disks are installed with
retaining rings in the flange at the edge of the 1/2 inch NPT
female pipe thread for the process connection. An internal
type retaining ring is first installed by positioning a ring in the
machined groove inside the flange opening from the housing
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