Detcon IR-700 - Manual (Page 25)

Model IR-700
IR-700 Instruction Manual Rev. 3.1 Page 21 of 40
Set Gas Factor is used to make the appropriate signal sensitivity adjustment when the target gas is different
from the cal gas. This is necessary because the IR sensor has different signal strengths for each combustible
hydrocarbon gas. The Gas Factor value is adjustable from 0.2 to 5.0. It represents the translation between the
target gas and the cal gas when they are different.
To calculate the correct Gas Factor, refer to Table 2 and take the Gas Factor of the target gas and divide by the
Gas Factor of the cal gas. The calculated value is the correct number to enter into the menu as the Gas Factor.
For example, if calibrating with methane when propane is the target gas, the correct Gas Factor to enter would
be 0.63/1.0 = 0.63.
For example, if calibrating with butane when ethane is the target gas, the correct Gas Factor to enter would be
0.38/0.72=0.53.
Table 2 shows the Gas Factors of most combustible hydrocarbon gases that will be measured. Find the gas of
interest for the cal gas and the target gas and follow the above instruction. If there is a mixture of target gases,
use a weighted approach to determine the correct Gas Factor. For example, if the target gas was 50% butane
and 50% pentane and the cal gas was methane, the correct Gas Factor would be calculated and entered as ((0.5
x 0.77) + (0.5 x 0.77)) / 1.0 = 0.77.
Table 2 Gas Factors
Gas Factor Gas Factor Gas Factor
Acetic Acid 2.00 Decane 1.53 Naphthalene
Acetone 1.21 Ethyl Alcohol 0.35 n-Nonane 1.53
Benzene 1.00 Ethane 0.38 n-Octane 1.34
1,3-Butadiene 1.80 Ethyl Benzene 1.07 n-Pentane 0.77
Butane 0.77 Ethylene 2.39 Propane 0.63
Iso-Butane 0.72 n-Heptane 0.98 iso-Propyl Alcohol 0.54
Butene-1 0.67 n-Hexane 1.00 Propylene 0.80
n-Butyl Alcohol 0.63 Dimethyl Ether 0.40 Toluene 1.00
iso-Butyl Alcohol 0.63 Methane 1.00 Vinyl Acetate 1.43
Cyclohexane 0.89 Methanol 0.41 Vinyl Chloride
Cyclopropane 0.45 Methyl Ethyl Ketone 0.77 Xylene 1.00
The menu item appears as: “Set Gas Factor”.
From the Set Gas Factor text scroll, hold the magnet over PGM1 or PGM2 until the “” prompt appears and
continue to hold the magnet in place for an additional 3-4 seconds (until the display starts to scroll “Set
Factor”). The display will then switch to “X.XX“(where X.XX is the current gas factor). Swipe the magnet
momentarily over PGM2 to increase or PGM1 to decrease the gas factor level until the correct value is
displayed. Hold the magnet over PGM1 or PGM2 for 3 seconds to accept the new value. The display will
scroll “Factor Saved”, and revert to “Set Gas Factor” text scroll.
Move to another menu item by executing a momentary hold, or, return to Normal Operation via automatic
timeout of about 15 seconds (the display will scroll “Set Gas Factor” 4 times and then return to Normal
Operation).
3.5.5 Set Serial ID
Detcon Model IR-700 sensors can be polled serially via RS-485 Modbus™ RTU. Refer to Section 4.0 for
details on using the Modbus output feature.