Maintenance and Troubleshooting | 6-15
Loss of AC power to the furnace
Verify the correct line voltage at L1 and L2 of the sensor board.
With line voltage present, check the voltage at terminals R and S on the
sensor board. (The voltage at terminals R and S will be either on or pulsat-
ing on and off.) If voltage is present and the system is not heating, discon-
nect power and check the furnace resistance. If no voltage is present at
terminals R and S on the sensor board, check for the DC furnace drive
signal at terminals 3 (+) and 4 (-) at the sensor board. The furnace drive is
a 15 VDC pulse train and depending on the duty cycle of the pulse train,
the measured voltage will be between 4 and 15 VDC. If this furnace signal
is present, LED DS1 is on, and you have no voltage at terminals R and S,
replace the sensor board.
If the furnace drive signal is not present, check the interconnecting wir-
ing. If the interconnecting wiring is correct, check across FURNACE and
15V COM on the control unit wiring card for the furnace drive signal. If
the signal is not present, check fuse F1 on the wiring card. If this fuse is
OK replace the control unit power supply/keypad module. If this fuse in
not OK, replace the fuse (1/4 amp, 125 volts). Check the interconnecting
wiring for short circuits before reapplying power to the control unit.
Process Pressure Checks
To check that you have entered the process correctly, select the Process
Pressure menu option from the Setup Key. Also ensure that the calibration
process pressure equals normal operating process pressure.
Cell Checks
If the cell fails when you first begin to use the analyzer, it is likely that
there is a leak in the sensor plumbing or an improper calibration gas
setup, and there is not a problem with the cell itself.
If the analyzer has been operating for some time and you feel the oxygen
reading is inaccurate, first check by running a known calibration gas to
verify the analyzer’s response. If the analyzer responds to the calibra-
tion gas correctly, it indicates either leaking or plugged plumbing on the
sample gas line.
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