Ion Science MVI - Manual (Page 7)

MVI MANUAL Ion Science Ltd
Page 7 of 23
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Introduction
The Mercury Vapour Indicator (MVI) is primarily used to monitor environments where Mercury or any of the
Mercury compounds are produced, processed or stored and applications where Mercury vapours may pose
a health hazard to personnel.
Units of measurement used for detecting Mercury vapour are micrograms/cubic metre expressed as µg/m
3
.
The MVI has two manually switched ranges of measurement:
0-200 µg/m
3
with a resolution of 0.1 µg/m
3
0-2000 µg/m
3
with a resolution of 1 µg/m
3
Principle of Operation
A sample of the immediate atmosphere under investigation is drawn by the pump into a glass sampling cell
where a Ultra-Violet light source is absorbed by the sample. Photodiode detectors are used to measure the
intensity of radiation passing through the sample chamber. The optical system is designed specifically to
detect Mercury in the Ultra-Violet region of 254 nm.
The presence of Mercury vapour will reduce the radiation energy reaching the photodiode detector in
proportion to the vapour concentration. This change is then converted into an electrical signal and
conditioned to provide a linear reading on the front LCD as µg/m
3
.
An audible alarm is fitted which gives warnings when preset conditions are achieved.