Ametek Land 4500 MKIII, User Manual

Page: 24 / 128

Opacity and Dust Monitor
User Guide
Model 4500 MkIII
A - 18
A3.12 Installation with a Fail-Safe Shutter (FSS)
The Fail-Safe Shutter provides protection to the optical system in the event
of a short-term purge failure. It opens when power is applied and closes on
loss of power, or if it receives a signal from the AFU. When used with a 4500
MkIII, the shutter closes each time the instrument performs an automatic
zero calibration. This function reduces the risk that the shutter will jam in
the open position and fail to close when needed. The instrument gives an
error message if the shutter does not close and open as expected.
The shutter is not designed to withstand extended exposure to stack
gases, and such exposure will cause permanent damage. Depending on the
temperature and composition of the stack gases, damage will typically occur
after a few days' exposure. After this time, the shutter may seize in the
closed position, though it will continue to protect the instrument.
Each shutter is supplied with a 16 m (50 ft) length of 8.3 mm (0.33 inch)
diameter cable which is used to connect it to the AFU.