Analytical Industries GPR-35 Oxygen Analyzer - Manual (Page 16)

Advanced Instruments Inc.
16
Alarms
The alarm comparator section of the electronics consists of an IC (integrated circuit) with internal references. The comparator
compares the oxygen signal with the internal reference point. Two alarm points are set at 20.0% oxygen CAUTION (or optional
HIGH O2 setpoint) alarm and 19.5% oxygen DANGER (or optional LOW 02 setpoint) alarm in compliance with OSHA
specifications.
Danger: To avoid the possibility of electric shock exercise extreme caution when connecting the external power cables to the
alarm relay terminal block illustrated below. The user supplied external cables should:
1. Never be connected to their power source during installation or service.
2. Never have their ends stripped more than 1/4”
3. Always be fully inserted into the Alarm Relay Contact Terminal Block and the screws tightened securely.
When the relay contacts are switched by the comparator, the normally open (NO) contact is turned into normally closed (NC)
and vice versa. When the oxygen level goes beyond the CAUTION alarm set point, the comparator triggers the alarm and the
corresponding red LED on the front panel and switches the relay contacts. When the oxygen concentration falls below the
DANGER alarm set point, the comparator turns on the corresponding red LED on the front panel and switches the contacts of
the second relay. The red LED indicator alarms and relays remain energized until the oxygen level rises above the alarm set
points.
The alarm comparators have a 2% of full scale (0.4% O2) hysteresis to prevent chattering of the alarm relays. Once the 20.0%
CAUTION alarm is activated, the audio alarm and relay will not deactivate until the oxygen level reaches 20.4%.
Alarm Bypass
An alarm bypass toggle switch is mounted on the main circuit board. By placing the switch knob to the OFF position will
deactivate the relays but the red LED indicators will continue to operate until the oxygen concentration exceeds the alarm set
point and the 2% hysteresis described above. The alarm bypass feature is useful in preventing false alarms when changing or
replacing the oxygen sensor.
Caution: Again, we recommend the user exercise extreme caution not only in using this feature but granting access to it.