7
Hydrogen Sulfide Detection - Models RGC-301/311 and RGA-411/412
The electrochemical cell used to detect CO also responds quantitatively to hydrogen
sulfide (H
2
S). The response to 1 ppm H
2
S is registered as 4 on the PPM CO display. This ratio
holds for all values of H
2
S up to about 100 ppm H
2
S. Thus, 10 ppm H
2
S will register as 40 on
the PPM CO display. Since these detectors monitor ambient levels of hydrogen sulfide, as well
as CO and they will alarm if the H
2
S concentration rises above one quarter of the limit set for the
CO alarm.
If an atmosphere contains both CO and H
2
S, the response of the detector is additive. If a
reading for CO only is needed or desired, the flue gas probe and its attached filter can be used for
sampling ambient air. The filter removes H
2
S and the reading then corresponds to the CO
concentration.
WARNING:
A detector will not respond to H
2
S when the sampled gas is drawn through
the flue gas probe and filter.
Hydrogen Sulfide Detection in Ambient Air - Models RGA-611/612
Connect the standard probe to the dust and water block filter and set the selector switch to
"PPM H
2
S". After warm-up, the display shows the ambient concentration of H
2
S in PPM.
If an atmosphere contains both CO and H
2
S the detector will selectively display the
concentration of CO on the PPM CO scale and the concentration of H
2
S on the PPM H
2
S scale.
The CO sensor in these detectors has an internal H
2
S filter, which results in CO selectively.
WARNING:
A detector will not respond to H
2
S when the sampled gas is drawn through
the flue gas probe and filter.
C. Alarms
A detector alerts the user acoustically, with a sound alarm or beeper, and visually by
"flashing" the symbol(s) for the detected gas(es) whose concentration exceeds preset limits.
Visual alarms are displayed in-between readings for the particular display in use. For example, if
the display is showing readings for natural gas (selector switch at "% GAS") and the
concentration of CO rises above its alarm limit, the display will flash
"CO",
approximately every
two seconds, in-between displays of the concentration of natural gas. If the concentration of
natural gas also rises above its alarm limit, the display will show a reading, then
"GAS",
then a
reading, then
"CO"
, and so on. Simultaneously, the sound alarm will be on.
Visual alarm symbols are
"GAS"
for natural gas,
"CO"
for carbon monoxide.
"LoO2"
for
low oxygen,
"HiO2"
for high oxygen, and
“H2S”
for hydrogen sulfide (models 611/612 only).
Factory set alarm limits are 1.0% methane (20% LEL), 200 ppm CO, and 19.5% for
low and 23.0% for high oxygen, and 10 ppm for H
2
S.
