53. Ultraviolet (UV) Scanner
With a 20,000 ohms/volt test meter set on the low VDC scale and plugged into the test jacks on
control (Fig. 29) (top jack - and bottom jack + ) the flame relay will pull in at approximately 3VDC NOTE
IF THE METER READS BACKWARDS, REVERSE THE JACKS Now, start the heater.
To assure sufficient margin of signal to hold In during random momentary downware fluctuations of the
signal, it is desirable to obtain an average of 3 50 DC or more A good reading will be from 3.5VDC to
Allow the flame program control to program normally and observe a signal on the volt- meter. If the
signal Is below 3.5 volts, this is indicative of either A) a dirty or otherwise obscured viewing window on
the U V. cell or B) a faulty cell A smoky fire will also reduce detection.
If the readings are normal as indicated In "3" above, further check the U V. cell by shutting down the fuel
supply. Within two (2) seconds of burner flameout, the meter will read "0" and the burner will go into
alarm requiring a manual reset Refer to Fig 29 to restart and recycle
If the U V cell does not check out as described in the above, refer to Fig. 38 for removal and/or
Removal Refer to Fig. 38 and remove the U.V cell and electron tube.
Turn nut on U V cell counterclockwise and remove from 112" NPT pipe attached to burner body
Disconnect electrical connections & remove from control.
Replace in reverse order.
Cleaning and Inspection.
Clean all parts with a cloth dampened with an approved cleaning solvent and dry thoroughly. The
viewing window in particular should be clean and free of obstruction.
Inspect the U.V. cell and electron tube for defects and damage Inspect for a bent or misaligned viewing
Inspect mounting hardware for cracks, breaks, and damaged threads. Replace any defective parts.
Installation. Refer to Fig. 38 and Install the U.V. cell and electron tube.