Carbon Monoxide Alarm User Manual

Page 22
Chapter 4 Setting alarm levels
PhD
2
alarms are user adjustable and may be set
anywhere within the range of the sensor channel. When
an alarm set point is exceeded a loud audible alarm
sounds, and an individual bright red LED alarm light for
each affected sensor blinks.
PhD
2
alarms are normally self-resetting, that is, as soon
as readings drop below the alarm set point, the alarm
ceases. It is possible, if desired, to set PhD
2
alarms so
that they "latch." In the latched condition, once an alarm
occurs both visual and audible alarms continue to sound
even after the atmospheric hazard has cleared. The
instrument must be manually reset by pressing the
MODE button. Pressing the MODE button silences the
alarms and restores normal operation.
Procedures for latching PhD
2
alarms are given in
Section 5.3.7.
4.1 Alarm adjustment sequence
It is necessary to be in the "Alarm Adjust" mode before it
is possible to change alarm settings. Once in this mode,
it is possible to adjust any of the oxygen, LEL, or toxic
gas alarm set points.
In many cases it is possible to comply with OSHA
guidelines while using higher alarm points than those
used by Biosystems. It is important to note that the
default alarm point settings used in the PhD
2
design are
very conservative in order to provide maximum worker
safety. PhD
2
default alarm setting are listed in
Section 4 of Appendix B.
To enter the alarm adjust mode , it is necessary to do the
following.
(1) Turn the instrument on and remove it from its vinyl
carrying case.
(2) Remove the keypad cover exposing the four mini-
push-buttons.
(3) Verify that the instrument is in the Technician
operating mode. Switch modes (if necessary) by
simultaneously holding down the "+" and"-" keys.
Each time that the operating mode is changed, the
meter screen will briefly indicate the current
operating mode.
(4) Turn the instrument off by pressing the MODE button
for three full seconds until the "release button"
message appears in the screen.
(5) With the unit turned off, press and hold down the
"Alarm" button.
(6) While holding down the "Alarm" button, press the
MODE button to turn the PhD
2
back on. The "Alarm
Adjust" message will appear briefly on the screen.
This message is followed by a screen showing the
first alarm point to be adjusted.
(7) Pressing the alarm button again will advance the
display to the next available alarm adjustment option.
Pressing the MODE button at any time cancels the
alarm adjustment mode, and returns the instrument
to the gas reading screen.
(8) When the desired alarm adjust option has been
reached, the "+" and "-" keys are used to raise or
lower the alarm set point.
(9) When all alarm adjustments have been completed,
press and hold the "Alarm" button down until an
information screen indicates that alarm adjustment is
complete.
The instrument will automatically return to normal
operation.
4.2 Restoring the factory default
alarm settings
PhD
2
alarm settings are set at the factory in the most
conservative way possible. (See Appendix B) It is
possible to restore these default settings at any time by
doing the following.
(1) Turn the instrument on and make sure it is in the
Technician Mode. (See Section 2.2.4.)
(2) Press the "Alarm" button on the instrument keypad.
The display will briefly show the following screen.
(3) This screen will be followed by several more showing
the specific default alarm settings for each type of
sensor installed. These screens will be shown in
continuous rotation. In the case of a PhD
2
with
combustible, oxygen, carbon monoxide, and
hydrogen sulfide sensors installed, the following
sequence of screens would be shown.
Oxygen and combustible gas:
Toxic gas ceilings:
Toxic 1 STEL and TWA: