29 • Chapter 3: Operation GX-3R Pro Operator’s Manual
Performing a Demand Zero
Perform a demand zero before using the GX-3R Pro. A demand zero operation sets the
combustible gas, H
2
S, CO, and super toxic channels to zero and the OXY channel to 20.9%.
If the instrument has a CO
2
sensor installed and if CO2AIR SETTING is set to ON in User
Mode, the CO
2
channel gets set to 400 ppm (0.04% volume). If CO2AIR SETTING is set to
OFF in User Mode, the CO
2
channel is not adjusted during the demand zero.
1. Find a fresh-air environment. This is an environment free of toxic or combustible gases and of
normal oxygen content (20.9%).
2. Turn on the unit as described above in Turning On the GX-3R Pro.
3. Press and hold AIR. The LCD prompts you to continue holding AIR and the buzzer pulses
while you hold the button (if KEY TONE is set to ON in User Mode).
4. Continue to hold AIR until the LCD prompts you to release it. The GX-3R Pro sets the fresh
air readings for all channels. Start up is complete and the unit is now ready for monitoring.
5. If Password Protection is turned On (factory setting is Off) using the SDM-3R PC program,
a user-set password is required to perform a demand zero. When the password screen appears,
adjust each digit with the AIR button and press and release the POWER MODE button to
move on to the next digit. Once the password is entered, the instrument performs the demand
zero.
Turning Off the GX-3R Pro
1. Press and hold POWER MODE.
2. TURN OFF appears on the display and the buzzer pulses for about five seconds (if KEY
TONE is set to ON in User Mode).
3. Release the button when TURN OFF disappears from the display.
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