MAINTENANCE
7-9
7.4 Turning on the UV Lamp
The UV lamp is made of a glass envelope and a UV
window (salt crystal) on one end of the envelope. The
inside of the lamp is filled with low pressure gases. To turn
on the lamp, a high voltage electric field is applied from
the outside of the glass envelope. The molecules inside the
lamp are ionized and produce a glow discharge that
generates the UV light. The MiniRAE 2000 has a built-in
sensing mechanism to monitor the status of the UV lamp
and display a “Lamp” error message if it is not on.
If the UV lamp has not been used for a long period of time
(> 1 month), it may become slightly harder to turn on. If
such a condition occurs, the “Lamp” message will appear
in the monitor display during the power on sequence. This
phenomenon is more significant in 0.25” UV lamps used in
ToxiRAE and MultiRAE Plus products, because of the
relatively small lamp size. To solve this problem, simply
turn on and off the monitor a few times and the lamp
should turn on. Gently shaking the monitor will also help
to initiate the glow discharge process. After the UV lamp
is turned on for the first time, it should be easier to turn on
the UV lamp next time.
It is possible that the UV lamp is actually on when the
lamp error message appears. This is because when the
lamp becomes old, the internal threshold level to detect
lamp failure may have shifted and cause a false alarm. To
eliminate such possibility, simply check to see the UV
lamp is actually on. This can be done easily by removing
the sensor cap and observing the glow light of the UV
lamp in a dark place. The user can also feed the monitor
with calibration gas and observe if the sensor reading
