Table 8-Flame Signal; Fig. 29-Flame Signal Measurement - Honeywell 7800 Series Manual

RM7838B
CHECKOUT
Flame
Detector
Flame Rode
Photocell
C7012A,C
C7012E,F
C7015A
C7027A
C7035A
C7044A
C7076A,D
a
This minimum or a stronger signal should easily be obtained if the detector is correctly installed and positioned to properly
sense the flame. This voltage must be obtained before completing checkout.
b
The flame signal amplifier circuitry is tested one-half second every five seconds during burner operation and shuts down the
burner if the amplifier fails (all installations).
c
The flame amplifiers are AMPLI-CHECK™ type.
Fig. 29—Flame signal measurement.
NEGATIVE (-)
METER LEAD
If the signal is unstable or less than the minimum accept-
able voltage, check flame detector installation and circuitry.
1. Check the supply voltages at terminals 4 (L1) and
L2 (N). Make sure the master switch is closed, connections
are correct, and the power supply is of the correct voltage,
frequency and is sinusoidal.
2. Check the flame detector wiring for defects including:
• Incorrect connections.
• Wrong type of wire.
• Deteriorated wire.
• Open circuits.
• Short circuits.
• Leakage paths caused by moisture, soot or accu-
mulated dirt.
65-0120—1
TABLE 8—FLAME SIGNAL.
Flame Signal Minimum Acceptable
Amplifier Steady dc Voltage
c
R7847A,B
b
R7847C
c
R7848A,B
c
R7849A,B
R7886A
POSITIVE (+)
METER LEAD
ONE
MEGOHM/VOLT
METER
M7382
a
1.25 Vdc 5.0 Vdc at the Keyboard Display Module or
5.0 Vdc at a 20 kohm/voltmeter
3. Clean the detector viewing window and inside of the
sight pipe as applicable.
4. With the burner running, check the temperature at de-
tector. If it exceeds the detector maximum rated temperature:
• Add a heat block to stop conductive heat from
traveling up the sight pipe.
• Add a shield or screen to reflect radiated heat.
• Add cooling (refer to sight pipe ventilation in the
detector Instructions).
6. Make sure that the flame adjustment is not too lean.
7. Make sure the detector is properly sighting the flame.
8. If necessary, resight or reposition the detector.
INITIAL LIGHTOFF CHECK FOR PROVED PILOT
Perform this check on all installations that use a pilot. It
should immediately follow the preliminary inspection.
NOTE: Low fuel pressure limits, if used, could be open. If so,
bypass them with jumpers during this check. These steps
may require two people, one to open the manual valves
and one to watch the ignition.
1. Open the master switch.
2. Make sure that manual main fuel shutoff valve(s) is
closed. Open the manual pilot shutoff valve. If the pilot
takeoff is downstream from the manual main fuel shutoff
valve(s), very slightly open the manual main valve to supply
pilot gas flow. Make sure the main fuel is shut off just up-
stream from the burner inlet, or disconnect power from the
automatic main fuel valve(s).
3. Close the master switch and the Burner Control to start
the system; see Figs. 21 and 22, RM7838B Sequence. Note
the Alarm will sound until flame has been detected. The
program sequence will start when the Recirculating Fan Air-
flow Switch closes and applies power to terminal 6 through
the Stop Switch and any limits.
36
Maximum Expected
dc Voltage