Calibrating a System with Two Detectors per CD800/830 Control Unit. (continued)
Turn screw adjustment of ZERO potentiometer R24 on control module printed circuit board to set
meter indicator to zero on meter scale.
If meter indicator cannot be set to zero, disconnect detector 2 at the control module and install a set
of 15-ohm resistors across DET 2 A-C-R terminals. If meter indicator can not be adjusted to zero
with one operating detector, probably the response characteristics of the paired sensor elements are
too dissimiliar while both are operating. (One element may have been long in use and the other
If necessary, replace old sensor element, reconnect detector 2 to control module, and adjust ZERO
potentiometer R24 to set meter indicator to zero on meter scale.
After meter indicator has been set to zero, calibrate paired detectors to co-ordinate meter indicator
percent L. E. L. deflection range with detector response to gas as follows:
Apply sample gas of known concentration from J-W gas calibration cylinder or Professional
Calibration Kit 51-7070 to one detector. Second detector must be simultaneously sampling zero
Turn adjustment screw of GAIN potentiometer R10 on control module circuit board until meter
reading matches percent L. E. L. concentration of gas specified on sample gas cylinder label or
produced by Professional Calibration Kit 51-7070.
Remove sample gas from first detector. Confirm that meter returns to zero in response to fresh air.
Expose second detector to sample gas. Compare meter reading with first reading taken. Do not
readjust GAIN control R10. If readings differ more than 10 percent of the L. E. L. reading, replace
sensor element in detector with lowest reading and repeat ZERO and GAIN adjustment procedures,
following steps 1 and 2 above.