Placing the Alarm System in Operation.

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