Yokogawa Single Channel Oxygen Analyzer System ZR22/ZR402 - Manual (Page 124)

IM 11M13A01-02E 8-7
8. Detailed Data Setting
8.3 Setting Oxygen Concentration Alarms
The analyzer enables the setting of four alarms — high-high, high, low, and low-low
alarms — depending upon the oxygen concentration. The following section sets out the
alarm operations and setting procedures.
8.3.1 Alarm Values
(1) High-high and high alarm values
If high-high and high alarm values are set to ON, then alarms occur if measured valves
exceed the alarm set values. The oxygen alarm set values can be set in the range 0 to
100% O
2
.
(2) Low and low-low alarm values
If low-low and low alarm values ore set, then alarms occur if measured values fall
below the alarm set values. The oxygen alarm set values can be set in the range 0 to
100% O
2
.
8.3.2 Alarm Output Actions
If the measured values of the oxygen concentration fluctuate between normal (steady-
state) values and alarm setting, there may be a lot of alarm-output issuing and canceling.
To avoid this, set the alarm delay and hysteresis for alarm canceling under the alarm
output conditions, as Figure 8.4 shows. When the delay time is set, an alarm will not be
issued so quickly even the measured value differs from the steady-state and enters the
alarm setpoint range. If the measured value remains within the alarm setpoint range for a
certain period of time (for the preset delay time), an alarm will result. On the other hand,
there will be a similar delay each time the measured value returns to the steady state
from the alarm setpoint range (canceling the alarm status). If hysteresis is set, alarms
will be canceled when the measured value is less than or greater than the preset hyster-
esis values. If both the delay time and hysteresis are set, an alarm will be issued if the
measured value is in the alarm setpoint range and the delay time has elapsed. When the
alarm is reset (canceled), it is required that the measured value be beyond the preset
hysteresis value and that the preset delay time has elapsed. Refer to Figure 8.4 for any
further alarm output actions. The delayed time and hysteresis settings are common to all
alarm points.
Delay time:
5 seconds
7.5%
High-limit alarm setpoint
5.5%
Oxygen concentration
Alarm output ON
OFF
Hysteresis
2.0%
A B C D
Alarm range
Delay time:
5 seconds Delay time:
5 seconds
F8.4E.EPS
Figure 8.4 Alarm Output Action