OMG200N1.23
G200 Analyser Range
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30
©
Copyright 2010 Geotechnical Instruments (UK) Limited
stores an average N
2
O reading every 15 minutes. This is used to calculate and display a
long term eight hour TWA (time weighted average) reading which is the operator’s
personal exposure level to N
2
O over their working day (often called OEL - occupational
exposure limit). The TWA calculation used by the instrument is that described by the
Health and Safety Executive EH20/2002 Occupational Exposure Limits 2002, where the
TWA is represented mathematically by the following equation: (C1T1 + C2T2...CnTn /
8hrs). In this mode the instrument will alarm when the operator has exceeded the
recommended TWA limit (the OEL for N
2
O = 100ppm). This operating mode incorporates a
confidence chirp which sounds every 30 seconds to give the operator confidence that the
monitor is still operating correctly. There is also an option which allows the operator to set
an additional alarm for the actual N
2
O level, i.e. greater than 300ppm.
It is possible using Analyser Data Manager to change the OEL level for the TWA limit
(default 100ppm). We would also recommend that the operator changes the ‘Site’ and
‘ID’ fields to ‘Site’ and ‘Name’ using the ‘Configuration’ tab.
Once IDs have been selected and accepted, readings commence immediately and are
monitored continuously. To stop monitoring the operator selects the soft-key ‘Person’,
enters the stop code 5709 and presses the ‘Enter’ key. Readings are automatically stored.
Area:
‘Area’ enables the operator to monitor in area or room mode. This mode automatically
stores a rolling average N
2
O reading every ‘n’ minutes. This calculates the average using
a different method, i.e. a rolling average over the elapsed period which is identified by
lowercase ‘twa’ on the user screen. The alternate ‘twa’ is represented mathematically by
the following equation : (C1 + C2...Cn / elapsed time in hrs). This mode would typically be
used to monitor a ventilation system in an operating theatre or similar where N
2
O is used
throughout the day with different people coming and going. Primarily for room or area
monitoring, this mode is intended to give the operator a little more flexibility and can be
user modified to suit the application. The monitoring interval and duration can be
adjusted by the operator. There are alarm options which allow the operator to set
an alarm for the average and actual N
2
O levels, i.e. greater than 300ppm.
As with previous modes it is possible using Analyser Data Manager to change the ‘Site’ and
‘ID’ fields to ‘Site’ and ‘Room or Area’ using the ‘Configuration’ tab.
Once IDs have been selected and accepted, readings commence immediately and are
monitored continuously. To stop monitoring the operator selects the soft-key ‘Area’,
enters the stop code 5709 and presses the ‘Enter’ key. Readings are automatically stored.
Leak Detection:
‘Leak’ enables the operator to monitor the instrument in leak detection mode. This extends
the range of the N
2
O sensor up to 10,000ppm and speeds up the response time to enable
it to indicate the current level of N
2
O. This allows the instrument to work as an effective
leak monitor. The operator gets audio and visual feedback in addition to the displayed
value to help with this. The back-light changes from green-thru-yellow to red as the gas
concentration increases. And the instrument’s beeper also increases in frequency and tone
to further help bring attention to any gas detected. There are no additional user alarms or
setting for this mode. It is not possible to store data whilst in this mode.
The operator starts and stops monitoring by selecting the soft-key ‘Leak’.
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Note:
When monitoring gases using any of the above methods the ‘Mute’ key may
be activated to eliminate the instrument monitoring sound.
