TM 5-6640-212-14
(6) Alarm Reset Switch. The alarm reset switch is
b. Initial Startup Adjustments.
a momentary contact pushbutton switch located on the
(1) Measure and adjust the detector voltage at the
cabinet door. Depressing the switch deactivates the
remote detector head, and adjust the volt control in the
holding circuits of the alarm and warning relays if a safe
corresponding module.
gas condition has been restored at the remote detector.
(2) Measure the detector voltage at the cabinet as
If a safe condition does not exist, the unit cannot be
follows:
reset.
(a) With instrument power on, connect the high-
(7 Indicator Meter. The indicator meter shows the
resistance, direct-current voltmeter leads to the detector
concentration of combustible gas at the detection point.
voltage test points on the printed circuit board (terminals
(8) Terminals. Terminals are accessible when the
B). Observe the polarity.
front panel is open and the printed circuit card is
(b) Record the voltmeter reading. The reading
removed. Terminals are provided for incoming power,
recorded is the detector voltage without resistance due to
remote detector leads, alarm and failure devices, and for
detector lead length.
This procedure provides a
external warning devices and recorder, if desired.
convenient means of checking the detector voltage at
d. The alarm system detector consists of the body,
any time without disassembling the remote detector.
detector element, and shield assembly. The body
(3) Expose the detector to a sample of combustible
houses the detector element and holds the shield in
gas. See that the meter reads up-scale and that the
place. The element is a replaceable gas sensing unit
alarms come on at the desired levels.
that plugs directly into the body when the shield is
(4) If the warn and alarm set points need to be
removed. The shield assembly consists of a shield and
adjusted, proceed as follows:
a flashback screen, which prevents ignition of
(a) Make sure that the detector is in a
combustible gases. The detector, which is explosion
combustible gas-free environment.
proof, is located in an area where flammable gas or
(b) Remove the warn and alarm relays (first and
vapor may be released. In the semitrailer, one is located
last relays) from the printed circuit board.
on the floor of the front compartment where the vacuum
(c) Turn the warn and alarm adjusters fully
pump and exhaust units are, and another on the floor
counterclockwise. Both the warn and alarm lights should
under the oxidation stability bath by the rear partition in
come on.
the laboratory compartment (fig. 2-17).
(d) Turn the zero adjuster on the control module
printed circuit board until the meter reads approximately
2 percent below the desired warn setting.
2-22. Placing the Alarm System in Operation.
(e) Turn the warn adjuster slowly clockwise until
the warn light goes off.
a. Initial Startup Procedures.
(f) Turn the zero adjuster slowly clockwise and
(1) Turn on the power (the pilot light should come
see that the warn light comes on at the desired level.
on). A 45-second delay disables the alarm circuits to
(There is a 2-second delay on warn and alarm
permit instrument warmup. Allow the system to stabilize
indication).
for 5 minutes.
(g) Repeat the above three steps for the alarm
(2) Make sure that the remote detector is in a
set point.
combustible gas-free area. The area surrounding the
(5) The instrument may now be placed in
detector can be checked by using a portable combustible
operation.
gas indicator.
c. Inspections.
(3) Zero the indicating meter; use a small
(1) Daily.
screwdriver to turn the zero adjuster on the printed circuit
(a) Inspect the instrument and pilot lights to see
board. Turning the adjuster clockwise increases the
that they show normal operation.
reading.
(b) Check the meter readings and investigate any
(4) Depress the warn/test button, and verify an up-
abnormal deviations from zero.
scale meter reading. The warn and alarm lights should
come on. A 2-second delay on the alarm indication is
provided.
2-33
