Heath Consultants GT Series - Manual (Page 106)

11-2
USER HANDBOOK
Note: A Time Weighted Average (TWA) value is the mean
average gas level over a specific period. The STEL
is 15 minutes and the LTEL is 8 hours. In
accordance with legislation, this requires the time
weighted averages to be averaged over a full
period whether the instrument is ON or OFF. Such
averaging essentially makes the instrument single
user applicable. The option is available to restart
the averaging after each instrument switch-off,
thus allowing for multiple user application.
A TWA alarm is intermittent with the actual gas
reading, therefore it is possible to get a value of
zero (0) and an LTEL or STEL alarm.
All alarms are user configurable to meet the specific needs
of different companies.
Note: The gas alarm levels, instantaneous STEL and LTEL,
are set at the time of instrument manufacture. It is
important that the user ensures that the levels are
in accordance with their company’s alarm levels
and with health and safety legislation. The alarm
levels may be changed, if required, as detailed in
the ‘SET-UP SOFTWARE USER HANDBOOK’.