Adjustments And Checkout - Honeywell 7800 Series Manual

CR7890B 7800 SERIES INTEGRATED BURNER CONTROL
not met, a hold condition is initiated and is displayed on the
optional KDM for at least five seconds. When the tolerances
are met, the INITIATE sequence restarts. If the condition is not
corrected and the hold condition exists for four minutes, the
CR7890 locks out. Causes for hold conditions in the INITIATE
sequence:
a. AC line dropout detection.
b. AC line noise that can prevent a sufficient reading
of the line voltage inputs.
c. Brownouts caused by a low line voltage.
Standby
The CR7890 is ready to start an operating sequence when the
operating control input (terminal 1) recognizes a call for heat.
The burner switch, limits, operating limit control and all
microcomputer monitored circuits must be in the correct state
for the CR7890 to continue into the Safe Start Check.
Normal Start-Up Safe Start Check
The CR7890 verifies that a flame or flame simulating condition
does not exist and proceeds into the Ignition Trial. If a flame or
flame simulating condition is present, the CR7890 remains in
the STANDBY period.
Ignition Trials
1. Pilot Flame Establishing Period (PFEP):
a. The pilot valve and ignition transformer, outputs 8
and 4, are energized. The CR7890 is an intermittent
pilot valve device.
b. Flame must be proven by the end of the ten-second
PFEP or a safety shutdown occurs.
c. Once flame is proven, the ignition, output 4 is
de-energized and the main valve, output 2, is
energized.
Run
The CR7890 is now in RUN and remains in RUN until the
controller input, terminal 1, opens, indicating that the demand
is satisfied or a limit has opened. if flame signal is lost during
RUN, the CR7890 goes to a Safety Shutdown state, which
de-energizes the pilot valve, output 8 and main valve, output 2
are de-energized and alarm, output 3 is energized, along with
the red LED. A code 22 will flash on the Power LED.

ADJUSTMENTS AND CHECKOUT

Burner Lightoff
For initial burner lightoff, consult the burner manufacturer
instructions or the flame safeguard control instructions.
Adjust CR7890 Sighting
With the CR7890 installed and the burner running, adjust the
sighting position for optimum flame signal.
Measure the flame signal with a volt/ohmmeter.
It is suggested that a volt/ohmmeter with a minimum
sensitivity of one megohm/volt and a zero to five or ten Vdc
scale be used for flame signal measurements.
65-0259—1
1. Remove the four black faceplate screws (Fig. 5) from
the faceplate.
2. Remove the faceplate.
3. Measure the flame signal as illustrated in Fig. 8. Be
careful to make the proper connections of positive (red)
meter lead to positive (+) control jack and negative
(black) meter lead to negative (-) or (-Com).
Fig. 8. Measuring the CR7890 flame signal voltage (with
4. Measure the voltage flame signal, CR7890 (with
nameplate removed).
5. Move the device and sight pipe around to sight the
flame from various positions and angles. Try to get a
maximum reading on the meter that is above the
minimum acceptable voltage of 2.0 Vdc. The maximum
reading is 5.0 Vdc.
6. Measure the flame signal for the pilot alone, the main
burner flame alone, and both together (unless
monitoring only the pilot flame when using an
intermittent pilot, or only the main burner flame when
using direct spark ignition).
7. Measure the flame signal at low and high firing rates
and while modulating in between (as applicable). With
the CR7890 in its final position, all required flame
signals must be steady (or stable) and greater than 2.0
Vdc. If you cannot obtain the proper signal, refer to the
Troubleshooting section.
8. Replace the faceplate and secure with the screws
removed in step 1.
9. Tighten the screws to ensure that the foam gasket is
fully compressed. Avoid cracking the faceplate by
overtightening the screws.
Pilot Turndown Test
When the CR7890 is used to prove a pilot flame before the
main fuel valve(s) can be opened, perform a Pilot Turndown
Test before welding the sight pipe into position. Follow the
procedures in the flame safeguard control instructions and in
the burner manufacturer instructions.
12
the cover removed).