Honeywell 7800 Series Manual page 26

RM7840E,G,L,M
CHECKOUT
Flame
Detector
Flame Rod
Photocell
C7012A,C
C7012E,F
C7015A
C7027A
C7035A
C7044A
C7076A,D
a
This minimum or stronger signal should be obtained easily 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 amplifier is an AMPLI-CHECK™ type.
Measure the flame signal at the appropriate times defined
in the following checkout tests. Read the flame signal in volts
dc at the flame amplifier test jacks + and -(Com).
1. Use a 20 kohm/volt meter with a 0 to 10 Vdc capability.
2. Set the 20 kohm/volt meter to the 0 to 10 Vdc range.
3. Insert the positive (red) probe into the + jack of the
flame amplifier. Insert the negative (black) probe into the -
(Com) jack of the flame amplifier (see Fig. 23).
4. Allow a few seconds for the meter reading to stabilize.
5. If using AMPLI-CHECK™ or shutter check amplifi-
ers, read the average stable voltage, disregarding the peaks
caused by the self-checking operation.
6. The meter reading must be as specified in Table 6 after
all tests are completed and all adjustments made.
As an option, the flame signal can be checked by using the
optional Keyboard Display Module.
If the signal is unstable or less than the minimum accept-
able voltage, check the flame detector installation and cir-
cuitry.
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 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.
3. For a flame rod, make sure:
• There is enough ground area.
• The flame rod is properly located in the flame.
• The temperature at the flame rod insulator is no
greater than 500° F (260° C).
4. For all optical detectors, clean the detector viewing
TABLE 5—FLAME SIGNAL.
Flame Signal
Amplifier
c
R7847A,B
b
R7847C
c
R7848A,B
c
R7849A,B
R7886A
window and inside of the sight pipe as applicable.
detector. If it exceeds the detector maximum rated tempera-
ture:
flame.
26
Minimum
Acceptable
Steady dc
a
Voltage
1.25 Vdc
5. With the burner running, check the temperature at the
• Add a heat block to stop conducted heat 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 that the detector is properly sighting the
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.
1. Open the master switch.
2. Make sure that the manual main fuel shut off valve(s)
is closed. Open the manual pilot shutoff valve. If the pilot
takeoff is downstream from the manual main fuel shutoff
valve(s), just very slightly open the manual main valve to
supply pilot gas flow. Make sure the main fuel is shut off just
upstream from the burner inlet, or disconnect power from the
automatic main fuel valve(s).
3. Close the master switch and start the system with a call
for heat by raising the set point of the operating controller, see
Fig. 17, 18, 19, 20 or RM7840 Sequence of Operation. The
Maximum
Expected
dc Voltage
5.0 Vdc at Keyboard
Display Module
OR
5.0 Vdc at a
20 kohm/volt meter