Operation
How the Detector Senses the Target Gas
Ambient air surrounding the detector housing diffuses inside the housing where it comes into
contact with the sensor. Although the detector’s circuitry dissipates very little power, a small
amount of heat is produced inside the housing. This heat causes air to rise up through the
bottom vents, past the sensor(s), and out the upper vents on either side of the unit. Any target
gas present in this air causes a response from the sensor. If the detector is located properly,
the sensor will respond to the average amount of the target gas present in the area. For help
in properly locating the detector, please read the mounting guidelines on page 14. This
detector monitors the actual concentration of the target gas exposed to the sensor. This actual
value may be different than the time-weighted-average values displayed by many personal gas
monitors. Please take this difference into account when comparing the response of the two
units. A new target gas reading is taken and displayed every 5 seconds per sensor installed.
How the Detector Controls the Ventilation Equipment
Upon sensing target gas, the detector has three threshold levels that it uses to control external
ventilation and alarm equipment.
Low Alert
Once the concentration of target gas has exceeded the threshold set by the user, the delay
countdown timer, also set by the user, begins. During this time, the appropriate LED will blink
short-on-long-off. If the concentration is still above the threshold after this delay, the Low Alert
relay will close and the corresponding LED on the front panel will flash slowly. Any equipment
connected to the Low Alert relay will be energized at this time.
After the target gas concentration drops below the threshold, the delay countdown timer will
initiate again. If the concentration is still below the threshold after this delay, the Low Alert
relay will open and the corresponding LED on the front panel will stop blinking. Any equipment
connected to the Low Alert relay will be de-energized at this time.
High Alert
If the target gas concentration continues to rise above a second, factory-set threshold, the
High Alert relay will close and the corresponding LED on the front panel will flash quickly. The
Low Alert relay will remain closed if the jumpers on JP5 and JP10 are set to the “50/100”
position; otherwise, the Low Alert relay will open upon the High Alert relay closing. Should the
IOM01
Rev 1.0 – December 22, 2020 23
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