TM 5-6640-212-14
(d) Record meter responses to each detector to
4. Note reading on module indicating meter after
aid in evaluating future performances of the detectors.
45 seconds. Reading should approximate percent LEL
value for same liquid at temperature of 70 degrees F
(8) Calibrating a System for Volatile Hydrocarbons
listed in table 4-2. (Heat or cool vaporizing jug to
With Flash Points Below 70 Degrees F. The following
thermometer reading 70 degrees for testing.)
materials are required to calibrate a detector/module
5. Adjust GAIN potentiometer R10 on control
system for response to volatile liquid vapors:
module circuit board to move meter indicator to read on
Graduated pipette, 01- ml (icc).
scale at approximate table 4-2 value.
One-gallon jug with cap
Piece of aluminum foil
NOTE
Thermometer Sample of volatile liquid
The percent LEL reading for
(a) Calibrate detector/module system for response
compounds other than those listed in
to volatile liquid vapors as follows. Before exposing
table 4-2 may be calculated by using
detector to sample mixture, con-firm that meter reads
the following formula:
zero with detector sampling fresh air. Adjust ZERO
Reading = Specific Gravity x 11,200
control R24 of CD800/830 Systems, or Channel 1 Z1
Divided by Molecular Weight x LEL.
(R9) and Channel 2 Z2 (R13) of CD802/832 Systems, if
Example: n-Pentane molecular weight
necessary.
= 72.15
1. Using pipette, drop 0.2 cc of liquid from which
Specific Gravity - 0.634
vapors are to be detected in a one-gallon jug. Place
Reading: 0.634 x 11,200 Divided by
aluminum foil on jug to aid in mixing vapor in air.
72.15x 1.5 = 66% LEL.
2. Cap jug and agitate until liquid has completely
b. Adjustments. With percent LEL meter response
evaporated and vapor has diffused.
properly adjusted for the specific detector element type
NOTE
and kind of combustible gas monitored, adjust warning,
Toluene, hexane, and xylene may
alarm, test, and recording circuits to operate at the
take up to half an hour to evaporate
desired voltage levels in accordance with the following
and diffuse.
procedures.
3. Remove cap and place mouth of jug over
(1) Warning Circuit Adjustment. Adjust warning circuit
detector. Invert jug if position of detector permits, since
to operate at the voltage level representing a specified
vapors of all flammable liquids are heavier that air.
percent LEL gas-air mixture as follows:
Table 4-2. Percent LEL Reading With 0.2 cc
Vaporized Volatile Liquid in One Gallon of Air
Material
Percent LEL at 70 Degrees F
Acetone
58
Allyl Alcohol
66
Ethyl Alcohol
59
Methyl Alcohol
41
Ethyl Ether
57
Methyl Ethyl Ketone
69
Methyl Isobutyl Ketone
63
n- Heptane
70
n-Hexane
78
n-Pentane
66
Toluene
88
Xylene
91
4-9
