TM 5-6640-212-14
(d) Close regulator valve on cylinder and
NOTE
remove sample cup from detector. (Meter reading
Both detectors must be sampling
should return to zero).
Disassemble sampling kit
zero
combustible
gas
before
components and replace in kit. Store sample gas
adjusting indicating meter to zero.
cylinder in cool area when not in use.
(d) For access to control unit screw adjustments in
(e) After 24 hours of operation, confirm that meter
many rack and cabinet installations, remove circuit
reading indicates zero in absence of combustible gas. If
board, plug circuit card extender 0023-4023 into
necessary, readjust reading to zero (as in step (4) (a).
connector strip at rear, and plug circuit board into card
Repeat readjustment, if necessary, after one week.
extender. Use of the card ex-tender during circuit
(6) Calibrating a System With Two Detectors Per
adjustment prevents remote alarms from operating.
Control Unit. The following special tools are required to
(e) Turn screw adjustment of ZERO potentiometer
calibrate a paired detector system.
R24 on control module printed circuit board to set meter
(a) Portable Combustible Gas Indicator; 2 Gas
indicator to zero on meter scale. (t) If meter indicator
Calibration Kits (0023-7260) (1 if fresh air is assured at
cannot be set to zero, disconnect detector 2 at the
both detectors).
control module and in-stall a set of 15-ohm resistors
(b) Two Sample Cups (fig. 4-4).
across DET 2 A-C-R terminals. If meter indicator cannot
(c) Two Gas Calibration Cylinders: Either 100%
be adjusted to zero with one operating detector, probably
Nitrogen (0023-4003) or Zero-Gas/Dry-air (0023-4004) if
the response characteristics of the paired sensor
combustible-gas-free air does not exist at both detectors
elements are too dissimilar while both are operating.
(one or none required if one or both detectors are in
(One element may have been long in use and the other
fresh air.)
new.)
(d) Gas Calibration Cylinder containing sample
(g) If necessary, replace old sensor element,
gas similar to that expected at detector locations.
reconnect detector 2 to control module, and adjust ZERO
potentiometer R24 to set meter indicator to zero on
(e) 0-10 Volt Range DC Voltmeter With + or - 2%
meter scale.
Accuracy in 5-6 Volt Range.
(7) After meter indicator has been set to zero,
(f) Test Socket Adapter 0023-4027 ig) Circuit
calibrate paired detectors to coordinate meter indicator
Card Extender 0023-4023 (except for CD800P models
percent LEL deflection range with detector response to
with built-in extension feature).
gas as follows:
(6) Calibrate a paired-detector alarm system for
(a) Apply sample gas of known concentration from
zero meter indication in gas free air as follows:
gas calibration cylinder to one detector. Second detector
(a) Read supply voltage at both detectors (using
must be simultaneously sampling zero combustible gas
test socket adapter and voltmeter).
(fig. 4-6).
(b) If supply voltages are not within + or - 0.15
(b) Turn adjustment screw of GAIN potentiometer
VDC at both detectors, correct faulty circuit conditions
R10 on control module circuit board until meter reading
(poor connections, leakage, open or short circuits,
matches percent LEL concentration of gas specified on
unbalanced resistances in supply lines due to wrong
sample gas cylinder label.
choice of wire gauges for length of run). Remove test
(c) Remove sample gas from first detector.
socket adapter(s) and reinstall sensor elements in
Confirm that meter returns to zero in response to fresh
detectors socket(s). (c) Using portable combustible gas
air. Expose second detector to sample gas. Compare
indicator, test surrounding air at both detectors. If
meter reading with first reading taken. Do not readjust
combustible gases are present at one or both detectors,
GAIN control R10. If readings differ more than + or -
use gas calibration kit(s), sample cup(s), and 100%
10% of the LEL reading, replace sensor element in
Nitrogen or Zero- Gas/Dry-Air cylinder to supply
detector with lowest reading and repeat ZERO and GAIN
combustible-gas-free air. (See instructions Al paragraph
adjustment procedures, following steps (a) and (b)
above.
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