Operation
N
2
O Portable Monitor
8
Instruction 3015-4787
3.4 Time Weighted Average (TWA) Operation
3.4.1 Overview
In addition to displaying the current N
2
O level, the monitor can also calculate and display a
T
ime
W
eighted
A
verage ppm value. This value is available in two formats (8 Hour or Continuous). This provides
users with the most appropriate data on their average ppm N
2
O exposure in the working environment.
TWA operation is selected by using the
2ndUNIT
function
(
page 13).
The two TWA formats are identified by the appearance of either “TWA” or ‘twa” in the upper-right corner
of the
Data Display
screen.
•
TWA
(upper case letters) is calculated over an 8-hour period. This format is designed to show the
user’s average ppm N
2
O exposure level during a typical work day. After 8 hours has expired, an
asterisk (*) will be displayed but the TWA will continue to be updated.
•
twa
(lower case letters) is continuously calculated over the operating time of the monitor. This
mode is useful for monitoring an area for a few minutes or more and is the preferred mode of
operation for checking operating room atmospheres.
3.4.2 Starting a New or Continuing TWA/twa
When the monitor is turned ON the following message appears if the monitor is set up to display
TWA/twa.
Press either . . .
•
ENTER
to start a new TWA/twa
•
ESC
to continue with the current TWA/twa.
Tip:
If NO button is pressed within 60 seconds the monitor automatically continues
with the current TWA/twa.
Note:
During the time the monitor is OFF, the gas measurement is assumed to be zero
and will be factored into the TWA/twa calculation.
After selecting whether to start or continue a TWA/twa, the next screen shows the current elapsed
TWA/twa time.
Where: xx is the accumulated time used by the monitor in calculating the TWA/twa.
PURGE 00TWA
100ppm N2O
PURGE 00twa
100ppm N2O
PRESS ENTER FOR
NEW TWA/twa
ELAPSED TWA TIME
IS xx MINUTES
