Servomex SERVOTOUGH LaserExact 2950, Operator'S Manual

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SERVOTOUGH LaserExact Monitor, Operator Manual 02950001A_1
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HAPTER
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1.4 Instrument description
The SERVOTOUGH LaserExact Monitor consists of 3 modules:
•
Cabinet
•
LaserExact cell (under an optional protective cover)
•
Laser beam alignment chamber (under an optional protective cover)
The cabinet is connected to the laser beam alignment chamber, which couples the
laser beam into the LaserExact cell. After multiple passes through the cell, the beam
exits back into the alignment chamber and is coupled onto the detector.
The transmitter inside the cabinet contains a temperature stabilised diode laser with
collimating optics. The laser is tuned to a specific wavelength and frequency and is
modulated to enable gas detection. The wavelength is unique for each gas to be
measured and is within the range from 0.7 to 2.4
µ
m (700 and 2400 nm). By varying
the DC supply current the laser wavelength is scanned over the absorption line of the
gas.
The transmitter is located within the cabinet enclosure and also contains the main
electronics board and the display. Communication with the electronics is provided
through an RS-232 connection to a PC, enabling service and calibration of the
instrument. In addition, communication via an Ethernet connector is possible.
The receiver inside the cabinet contains a detector connected to the receiver
electronics with a short cable. The detected signal is amplified and transmitted back
to the transmitter unit through electrical cables.
The laser beam alignment chamber contains two adjustable mirrors. The first mirror
controls the coupling of the beam into the cell and is adjusted to obtain the correct
angle of incidence; the second mirror controls the coupling of the beam onto the
detector and is adjusted to focus the beam on the detector centre.
The LaserExact cell with volume 0.875 litres (875 ml) is made of electro-polished
stainless steel. Two cell mirrors are mounted inside the cell volume, one at each end
of the cell. In the cell mirror next to the alignment chamber there is a slit, through
which the laser beam enters and leaves the cell volume. A wedged sapphire window
separates the cell from the alignment chamber.
A block diagram of the instrument electronics is shown in Figure 1-2. The transmitter
electronics takes care of all calculations and monitoring operations. Three relays are
integrated in the auxiliary electronics board. The integrated relays are warning, error
and gas alarm relays. The operator can set the gas alarm relay in the software. The
integrated relay functions are further explained in Section 6.8.