14
monitoring for at least fifteen minutes. Until
the minimum monitoring time has elapsed,
the STEL screen will show an "X" where
the reading should be.
↔
After fifteen minutes have elapsed, the
STEL screen will show the appropriate
numerical value.
↔
Press the MODE button again to display
TWA (Time Weighted Average) exposure
levels. Time Weighted Average or TWA
values are calculated by taking the sum of
exposure to a particular toxic gas in the
current operating session in terms of parts-
per-million-hours and dividing by an eight-
hour period. It is not possible to compute a
toxic gas TWA until the Toxi Plus has been
monitoring for at least one hour. Until the
minimum monitoring time has elapsed, the
TWA screen will show an "X" where the
reading should be.
↔
After an hour has elapsed, the TWA screen
will show the appropriate numerical value.
↔
Pressing the MODE button again to return
current gas readings.
Regardless of operating mode selection,
anytime the Toxi Plus is on, it is
remembering the peak readings of all
gases measured, and is calculating both
long term Time Weighted Averages and
Short Term Exposure Levels (for toxic gas
reading detectors) and will go into alarm
whenever appropriate.
2.2.4 Changing operating modes
It’s possible to change operating modes
while the instrument is in use without
affecting the on-going calculations used to
determine Peak, STEL and TWA alarms.
Simply slide the belt clip at the back of the
instrument out of the way to expose the
four mini-push-buttons. Then
simultaneously press and hold the "+" and
"-" buttons until the word “MODE” is
displayed. Each time the operating mode
is changed the display screen will briefly
indicate which operating mode has been
selected.
Note: Shifting modes or otherwise
reprogramming the instrument should
only be done by employees who are
authorized to do so.
Figure 2.2. Toxi Plus with belt clip
removed exposing the four keypad
push-buttons
2.3
Toxi Plus batteries
The Toxi Plus uses a set of three AAA
disposable alkaline batteries. A fresh set of
batteries should power the instrument for
up to 1,500 hours of operation.
2.3.1 Low battery voltage
alarms
When it is time to replace the batteries a
"
B
" will appear in the lower left hand corner
of the display screen, and the audible
alarm will “beep” once per minute until the
batteries are replaced. Once the “B” is
shown, the user should have approximately
one to two weeks of useful battery life
remaining.
2.3.2 Battery replacement
Toxi Plus batteries should be replaced as
soon as possible after a low battery ("
B
”)
message has been noticed.
Use the following procedure to change the
batteries.
