Full-flow opacimeter. The only general precautions to be observed in steady-speed and free-acceleration tests are the following:
3.1. Joints in the connecting pipes between the exhaust pipe and the opacimeter shall not allow air to enter from outside.
3.2. The pipes connecting with the opacimeter shall be as short as possible, as in the case of sampling opacimeters. The pipe system shall be inclined upwards from the exhaust pipe to the opacimeter, and sharp bends where soot might accumulate shall be avoided. A bypass valve may be provided upstream of the opacimeter to isolate it from the exhaust-gas flow when no measurement is being made.
3.3. A cooling system may also be required upstream of the opacimeter.
